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Operation and diagnostics of wastewater treatment facilities using an expert system Chilibeck, Barry Michael 1990

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OPERATION AND DIAGNOSTICS OF WASTEWATER TREATMENT FACILITIES USING AN EXPERT SYSTEM By BARRY MICHAEL CHILIBECK B.A.Sc, University of B r i t i s h Columbia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CIVIL ENGINEERING ENVIRONMENTAL ENGINEERING GROUP We accept t h i s thesis as conforming to the required standard THE © UNIVERSITY OF A p r i l Barry Michael BRITISH COLUMBIA 1990 Chilibeck, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Civ)t w E M o i ^ f g e i M g , The University of British Columbia Vancouver, Canada Date Ap^U & f 11*1 Q DE-6 (2/88) Abstract This research examines the use of microcomputer-based expert systems as a diagnostic t o o l and an operational a i d of conventional secondary wastewater treatment f a c i l i t i e s . The research has shown that rule-based systems are well suited for the domain of wastewater treatment f a c i l i t i e s operations using observational information. Advances i n expert systems software combined with increased microcomputer processing power have made t h i s development work possible with personal computers. These systems possess the c a p a b i l i t y to provide f u l l y automated diagnostics and process control as well as acting as a teaching and development t o o l f o r operators i n f u l l - s c a l e treatment f a c i l i t i e s . The thes i s describes the techni c a l aspects of wastewater treatment as applied to the development of a fi n i s h e d knowledge base system c a l l e d WASTES (WAStewater Treatment Expert System). The th e s i s also discusses the development of the knowledge bases from t h e i r sources to implementation i n the system. Recommendations and conclusions are also presented along with p o t e n t i a l areas for further research. i i Table of Contents Chapter T i t l e Page Abstract i i Table of Contents i i i L i s t of Tables v L i s t of Figures v i Acknowledgements v i i 1.0 Introduction 1 2.0 Fundamentals of Wastewater Treatment 8 2.1 Wastewater 9 2.2 Wastewater Treatment F a c i l i t i e s 18 2.3 Unit Operations 20 3.0 The Model Wastewater Treatment Plant 29 3.1 Introduction 29 3.2 Layout 29 3.3 Operation 31 3.4 Operational Objectives 32 3.5 Process Operation and Control 33 4.0 The FRO Expert System 59 5.0 Development of WASTES Model 68 5.1 Knowledge Sources 68 5.2 Knowledge Development 69 5.3 Completing the Knowledge Bases 72 5.4 Knowledge Logic Structures 75 6.0 Results 98 7.0 Conclusions 105 8.0 Recommendations 107 i i i 9.0 Endnotes 109 10.0 Appendix 1 - WASTES Knowledge Base F i l e L i s t i n g s 113 11.0 Appendix 2 - Microscopic Examination of Activated Sludge 174 12.0 Appendix 3 - WASTES User Manual 178 13.0 Appendix 4 - WASTES System Diskette 184 i v L i s t of Tables Number T i t l e Page I Summary of Environmental Expert Systems under Development 6 II Toxic Loadings f o r Various Metals on the Activated Sludge Process 16 III Process Control Logic used by WASTES System 73 v L i s t of Figures Number T i t l e Page 1 Typical Flow Variations into a STP 12 2 Typical Solids and BOD Removal i n a Secondary STP 19 3 Schematic of the Activated Sludge Process 24 4 WASTES STP Model fo r Expert System 30 5 Pre and Post D e n i t r i f i c a t i o n Process Layouts 50 6 Microbial D i v e r s i t y with respect to F/M 55 7 Common Activated Sludge Organisms 57 8 Expert System S h e l l Structure 59 9 WASTES System F i l e Structure 61 10 LIFT.KB Logic Structure 79 11 RACKS.KB Logic Structure 80 12 GRIT.KB Logic Structure 82 13 MICRO.KB Logic Structure 84 14 CLAR.KB Logic Structure 86 15 RBC.KB Logic Structure 88 16 FLOAT.KB Logic Structure 90 17 ODOUR.KB Logic Structure 92 18 Aeration System Logic Structure (TREAT.KB) 95 19 Activated Sludge Process Control (TREAT.KB) 96 2 0 Activated Sludge Process Control (TREAT.KB) 97 v i Acknowledgements I would l i k e to thank Dr. B i l l Oldham and the Department of C i v i l Engineering, Environmental Engineering Group at the Univ e r s i t y of B r i t i s h Columbia f o r supporting t h i s research. I would also l i k e to thank Mr. Thomas Froese, who design the FRO s h e l l , for h i s i n i t i a l ideas and hours spent helping review the system and Drs. A.D. Russell and W.F. Caselton f o r permission to use t h i s program. F i n a l l y , t h i s work i s dedicated to my grandfather, Michael Chilibeck, who supported me through a l l my years at the University of B r i t i s h Columbia. v i i Chapter 1.0 Introduction This research represents the applications of expert systems i n the f i e l d of wastewater treatment operations, with respect to diagnosis, problem solution and control of the treatment operations. The objectives of the research were as follows. One, to prove that an expert system can be designed and b u i l t to the demonstration l e v e l . Two, that the domain of knowledge regarding wastewater treatment i s viable for knowledge-based systems. Three, that a functioning expert system i s useful as a diagnostic system. Four, that these systems could be used for t r a i n i n g and for further system development. The research examines current expert system applications, the requirements and c a p a b i l i t i e s of wastewater treatment technology, the treatment model used i n the research and a review of present treatment plant control techniques. The thesis w i l l deal s p e c i f i c a l l y with how the expert system operates and how the knowledge bases were developed, and w i l l present the re s u l t s and conclusions of the research as well as recommendations for future research i n the f i e l d . Although expert systems are a r e l a t i v e l y new a n a l y t i c a l t o o l , t h e i r applications involve both older t r a d i t i o n a l engineering applications and research involving more current technology. Expert systems continue to grow as e x i s t i n g problems and new ideas are developed into applications that continue to forward research i n many diverse f i e l d s . l Expert systems (ES) development can be broken down into two d i s t i n c t areas: the development of expert system s h e l l s and programs, and the development of expert system applications. Development of ES s h e l l s and programs i s well advanced and there are a large number of commercially available s h e l l programs for mini and micro systems l i k e KEE, VP Expert, M.l and Insight 2+. Applications development i s also well established at the u n i v e r s i t y research l e v e l and commercial systems are appearing and being used i n such diverse f i e l d s as f i n a n c i a l planning, database development, medical diagnosis and t r a i n i n g systems. C i v i l engineering has also experienced a f l u r r y of applications development as shown by the most current technical journals. At the Department of C i v i l Engineering, University of B r i t i s h Columbia, expert systems applications are developed or under research i n the following areas: Construction Management Project Scheduling Water Resources Drainage and L i f t Station Design Structural Engineering Program Output Interpreter Transportation Engineering Highway Location System Environmental Engineering Waste Treatment Diagnostics. Environmental engineering has been r e l a t i v e l y slow, i n r e l a t i o n to other f i e l d s of c i v i l engineering, i n developing applications. There are several areas i n the f i e l d , including activated sludge process control and plant diagnostics, that are i d e a l for expert systems. More recently, research i n environmental engineering and expert systems has increased dramatically. 2 There has been a great deal of research regarding the development of control and modeling of the activated sludge treatment process.''" However, most of the modeling and control was based on quantitative numerical results u t i l i z i n g b i o l o g i c a l models and various control strategies. To date there are none of the accurate dynamic process models developed i n the same sense as e l e c t r i c a l , mechanical and chemical engineering due mainly to the v a r i a b i l i t y of the complex b i o l o g i c a l systems examined. Other problems have hampered application of control research to p r a c t i c a l activated sludge process control. Generally, treatment plant control concepts are not taught to c i v i l and environmental engineering students who conduct graduate l e v e l research, those people who are expected to design co n t r o l l a b l e f l e x i b l e treatment plants and often oversee operation of such f a c i l i t i e s . There are several p r a c t i c a l problems as well. There i s a lack of r e l i a b l e on-line instrumentation to monitor process parameters. Also i n many plants there i s a lack of proper process control features such as return piping, valving and pumps. U n t i l recent times, the costs of investment for process control instrumentation, personal computers and plant equipment f l e x i b i l i t y have been overlooked as a necessary piece of the treatment process. However, several factors are pushing for increased investment, i n plant c a p i t a l investment and research, and technological innovation i n the wastewater treatment industry. Across the North American continent there has been an increase i n the l e v e l of treatment required and i n many areas sophisticated treatment 3 systems are becoming e s s e n t i a l . Downstream t e r t i a r y processes are dependent on the e f f e c t i v e operation and control of the b i o l o g i c a l activated sludge process, thus reaffirming i t s importance as a treatment operation. Increased use of b i o l o g i c a l removal of nitrogen and phosphorus to protect receiving waters has emphasized"activated sludge as an important part of the f u l l advanced treatment process. Increasing energy and c a p i t a l costs have forced plants to reduce annual operational costs. Reductions i n s t a f f i n g and plant budgets have led to the use of more e f f i c i e n t and automated operations. Technology and cost-effectiveness have forced innovation i n a f i e l d that has been often viewed as mundane and basic. This technological drive has supported past development and continues to fuel research and development i n the f i e l d . Research i n the control and modeling of activated sludge has led to investigation of t h i s f i e l d with expert systems technology. Much of the d r i v i n g force i s due to the need to f i l l the large gap between research theory and p r a c t i c a l treatment plant applic a t i o n . Investigations using experience as a basis for control began as a novel approach to control l o g i c systems. Beck f i r s t suggested the use of q u a l i t a t i v e rule-based or h e u r i s t i c r e s u l t s as a l o g i c a l method for process control of the activated sludge process.^ 4 He has also stated: An operator has a mental image, or model, of the process dynamic behavior based on empirical experience of that process. At the present time t h i s kind of experience i s probably a more valuable asset ... than the currently available mathematical programs. Tong et a l . published further i n the f i e l d based upon the use of 3 fuzzy l o g i c . In his paper, he set up his input and output variables and related them through l i n g u i s t i c rules i n the form: WHEN "ESS i s small and N H 3 - N i s large" DO "make a small p o s i t i v e change i n the RRSP". This translates into "when the effluent suspended so l i d s (ESS) are low and the eff l u e n t ammonia i s high, make a small increase i n the return sludge rate (RRSP)". The "fuzziness" arises i n terms of how the values of "small", "large" and "small p o s i t i v e change" are interpreted under d i f f e r e n t s i t u a t i o n s . Twenty such rules were developed to consider effluent s o l i d s , BOD and N H 3 , and included process operational parameters l i k e aeration rates, wastage and return rates. Jenkins modified Beck's l i n g u i s t i c rules and used his activated sludge numerical simulation program 4 to control a lab-scale activated sludge process. He held discussions with various plant operators to es t a b l i s h a series of discrete operational conditions with known cause or causes. This was the f i r s t attempt to use actual operator experience to 5 control an activated sludge process by a h e u r i s t i c program. Maeda proposed a knowledge-based system for the wastewater 5 treatment process. He theorized that his production rule-based system could replace e x i s t i n g rules with new rules as information became available to the expert system, thus become a forward chaining system. Johnson set up a rule-based diagnostics system based on operator judgement.** Ortolano and Steinemann have summarized 24 unpublished systems under development, the table 7 below shows the knowledge domains investigated. KNOWLEDGE DOMAIN NUMBER Hazardous Waste Treatment 13 Water Treatment Systems 4 Wastewater Treatment Systems 3 Model Ca l i b r a t i o n and Usage 4 Table I - Summary of Environmental Expert Systems under Development In the wastewater treatment domain, two of the systems deal s p e c i f i c a l l y with diagnostics and control. One i s to a s s i s t operators at f a c i l i t i e s with t r i c k l i n g f i l t e r s to diagnose f a i l u r e s and suggest remedies and the other. Another expert system i s to a s s i s t operators of activated sludge f a c i l i t i e s i n diagnosing problems and improving plant performance. Ortolano and Steinemann also reported two researchers i n the United Kingdom working on activated sludge plants and expert systems development. The f i e l d of expert system applications i n environmental engineering i s growing. New systems are being 6 constantly developed and as research continues increasing numbers of these systems w i l l become available for evaluation and eventually commercial use. 7 Chapter 2.0 Fundamentals of Wastewater Treatment Raw sewage i s approximately 99 percent water. The balance consists of s o l i d s , both organic and inorganic, dissolved and suspended. The goal of municipal wastewater treatment i s to modify, remove and dispose of a portion of that small percentage of impurities to improve, protect and maintain the various aspects of the environment. Such treatment i s accomplished by u t i l i z i n g mechanical, physico-chemical and b i o l o g i c a l processes. Before the e f f l u e n t i s discharged, constituents that could negatively a f f e c t the q u a l i t y of the receiving waters are removed. Federal and p r o v i n c i a l regulations set out e f f l u e n t permits and s o l i d s disposal regulations that determine what may be discharged i n the effluent and what must be removed and disposed of by other means. The amount of treatment required i s usually determined by the need to maintain receiving water qu a l i t y . Present technology i n advanced wastewater treatment can consistently achieve high levels of effluent q u a l i t y , removing a l l impurities to extremely low levels of concentration. The question i s often asked why a l l our sewage i s not treated to such high standards. The answer i s that wastewater treatment i s engineered and b u i l t to f u l f i l l the l o c a l treatment objectives using the best available technology i n a c o s t - e f f e c t i v e manner. This often includes u t i l i z i n g the f u l l p o tential of the treatment process plus the natural assimilative capacity of the receiving waters. 8 2.1 Wastewater In the design and operation of a wastewater treatment plant i t i s important to understand the c h a r a c t e r i s t i c s of the i n f l u e n t wastewater. For the design engineer, t h i s provides information for the s e l e c t i o n and s i z i n g of the process and the proper equipment for the f a c i l i t y . In the operation of a plant, the information on the geographical area of generation and the flows and l e v e l s of constituents before, during, and a f t e r the processes provide the basis for process cont r o l . Detailed monitoring and analysis of common parameters provide information for c o n t r o l l i n g the physical and b i o l o g i c a l processes i n the treatment plant. Wastewater can be characterized i n two ways: by o r i g i n and by i t s chemical, physical and b i o l o g i c a l c h a r a c t e r i s t i c s . C l a s s i f i c a t i o n by o r i g i n generally describes the type of area from which the wastewater was produced. Generally, municipal sewage comprises both domestic and i n d u s t r i a l based wastes. The domestic component of a waste stream refers to sewage generated from r e s i d e n t i a l and commercial areas. It includes kitchen, bathroom and laundry flows. The i n d u s t r i a l component of wastewater i s usually generated by manufacturing processes and possesses the c h a r a c t e r i s t i c s that r e f l e c t the raw materials, processing products and by-products of the p a r t i c u l a r manufacturing or production process. Industrial flows can be the major point source contributors of toxic materials and regulations may require pretreatment of these wastes before 9 disposal into sewer systems to prevent overloading and upset of b i o l o g i c a l treatment processes. Stormwater flows r e s u l t from the interception of run-off from p r e c i p i t a t i o n i n combined and sanitary sewage systems. Stormwater increases the hydraulic flow into the plant and c a r r i e s with i t increased g r i t and debris as well as other contaminants. Combined sewerage systems carry wastewater and c o l l e c t e d stormwater. As a r e s u l t , the stormwater can have a major impact on the hydraulic loading of the treatment plant. Sanitary sewerage systems, by d e f i n i t i o n , carry only wastewater, so the e f f e c t of p r e c i p i t a t i o n i s f e l t only by i n f i l t r a t i o n into the sewer system though the j o i n t s and cracks of the network of piping. The increase i n flow due to stormwater i n f i l t r a t i o n i s small when compared to that which occurs i n a combined sewerage system. Considerably more insight into the q u a l i t y of a wastewater i s achieved when the physical, chemical and b i o l o g i c a l c h a r a c t e r i s t i c s are provided. These c h a r a c t e r i s t i c s w i l l vary over time and i n comparison to wastewaters c o l l e c t e d from other geographical areas. Common physical c h a r a c t e r i s t i c s used to describe wastewater include: temperature, odour, color, flow rate and s o l i d s concentration and type. Temperature a f f e c t s most processes within the treatment plant. Char a c t e r i s t i c s such as raw water , water u t i l i z a t i o n processes, and the amount of i n f i l t r a t i o n are factors that determine raw sewage temperatures. Reduced temperatures decrease the reaction rates i n b i o l o g i c a l and chemical processes and can negatively impact on physical 10 processes l i k e f l o c c u l a t i o n and s e t t l i n g . The microbial growth and use of substrates i n activated sludge treatment are reduced with colder wastewater temperatures which may require changes i n the process to maintain adequate treatment. Reduced temperatures may also require changes i n chemical feed rates and may cause decreased floe s e t t l e a b i l i t y i n secondary c l a r i f i e r s . Odour and color are two subjective parameters that are used for checking the operation of several of the treatment processes. T y p i c a l l y a musty, earthy, but disagreeable odour i s associated with oxygenated raw wastewater while a s t a l e , rotten egg-type odour indicates anaerobic or septic conditions. Fresh wastewater w i l l usually be a pale grey color while septic wastewater i s a dark grey or black. Other colors could indicate i n d u s t r i a l discharges into the sewer system and should be investigated. Flow into a plant w i l l naturally exhibit hourly, d a i l y and seasonal v a r i a t i o n s . The size of the v a r i a t i o n i n flows i s of importance to the design engineer and plant operator because flow rates impact on the mass loading rates of impurities and detention times i n key treatment processes that i n turn e f f e c t the effluent q u a l i t y . Municipal sewage flows generally follow a diurnal pattern with peaks i n the morning and evening hours (Figure 1). There can also d a i l y changes through the week as there i s a flux of population i n or out of the serviced area. Seasonal changes are also apparent i n areas with large t o u r i s t populations and where raw water use patterns change. 11 HOURLY FLOW VARIATION 5.5 , — 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 A.M. P.M. DAILY FLOW VARIATION 4.0 -i 3.5 -SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY Figure 1 - Typical Flow into a STP 12 The operator can make changes i n the plant operation to reduce the e f f e c t s of some variations i n flow. However, i f continuous high treatment e f f i c i e n c y i s required, the effects of variations i n flow can be mitigated with flow equalization using dedicated storage basins, spare c l a r i f i e r s and sewer valving systems. One of the more important sewage qual i t y parameters i s the amount and type of s o l i d s loading. Solids are usually c l a s s i f i e d as f l o a t i n g , s e t t l e a b l e , suspended, c o l l o i d a l and dissolved. Flo a t i n g s o l i d s t y p i c a l l y represent the paper, grease and debris that f l o a t to the surface of the wastewater. Settleable s o l i d s represent the suspended s o l i d s that can be removed by simple quiescent s e t t l i n g . Finer suspended and c o l l o i d a l s o l i d s are much smaller i s s i z e and are removed by physico-chemical coagulation and s e t t l i n g or by b i o l o g i c a l means i n conventional treatment plants. Dissolved s o l i d s are generally i o n i c i n nature, and usually require advanced treatment for highly e f f i c i e n t removal. Suspended sol i d s are commonly used as a measure of the amount of material i n effluent discharged from conventional treatment plants. Different forms of s o l i d s are removed by d i f f e r e n t processes within the treatment plant and are discussed i n more d e t a i l with the s p e c i f i c unit operation. Solids can be composed of both i n e r t matter and organic matter, with the terms fixed and v o l a t i l e s o l i d s being used by operators and design engineers. Fixed s o l i d s are the materials remaining a f t e r f i r i n g the sample at 550°C for 1 hour. V o l a t i l e s o l i d s i s 13 the difference between the t o t a l s o l i d s ( f i r e d at 105°C) and the fixed s o l i d s . The amount of v o l a t i l e s o l i d s generally represents the amount of organic material present i n the sample. The v o l a t i l e s o l i d s test i s used to estimate the amount of organic matter i n raw sewage, and the amount of l i v e organisms i n a b i o l o g i c a l sewage treatment process. The chemical c h a r a c t e r i s t i c s of wastewater are determined by the chemical properties of the organic and inorganic s o l i d s and t h e i r r e l a t i v e concentrations. These so l i d s possess the physical properties described previously. Organic compounds contain carbon i n combination with one or more other elements. The organics associated with wastewater are usually dead animal and plant matter, by-products and waste material. Many by-products r e s u l t from b i o l o g i c a l decomposition of the organic materials before the wastewater enters the treatment plant due to the presence of l i v i n g organisms i n the waste materials discharged. Complex organic materials l i k e phenols found i n sewage are often the r e s u l t of i n d u s t r i a l discharges. Bacteria w i l l naturally degrade most organic chemical constituents thereby consuming oxygen and releasing C 0 2 , H 2 O and other end products. In the environment, t h i s process removes dissolved oxygen from the receiving waters which, i f not replaced by re-oxygenation, reduces the net dissolved oxygen content. Dissolved oxygen or DO depletion reduces stream and marine productivity for f i s h and other valuable species. Removal of 14 organic compounds and the DO demand on receiving waters i s a primary wastewater treatment p r i o r i t y . The common measure of t h i s organic oxygen demand i s done through a analysis which indicates the biochemical oxygen demand over a s p e c i f i c amount of time (usually 5 days), hence the term B O D 5 . Testing for chemical oxygen demand (COD) measures the chemically oxidizable f r a c t i o n of a sample. This measurement includes the BOD or b i o l o g i c a l l y degradable substances as well as the other compounds not r e a d i l y assimilated by b i o l o g i c a l processes. COD measurements may be 20 to 500 percent larger that BOD values from the same sewage due to Q the organic complexity and strength. One benefit of COD tests i s that they can be completed i n less than one hour, while the standard BOD t e s t takes 5 days. In the operation of treatment plants, t h i s information i s required as soon as possible; hence COD tests are usually run and correlated to BOD r e s u l t s as a control t e s t . Complex organic compounds require a long period of time to be b i o l o g i c a l l y decomposed and degraded as the bacteria must produce s p e c i a l i z e d enzymes to reduce them. Hence the type and amounts of organic compounds can a f f e c t the operation of any b i o l o g i c a l process which i s being used to s t a b i l i z e and degrade fin e c o l l o i d a l and dissolved organic compounds. Inorganic compounds i n wastewater consist primarily of g r i t , sand, sediment and other r e l a t i v e l y i n e r t substances. Dissolved inorganic compounds include nutrients l i k e phosphorus and nitrogen essential for the microorganisms metabolism, as well as complexed metals and elemental metal ions, and chemical 15 compounds, such as calcium carbonate that make up the waters hardness. Metal ions, which can act as micronutrients i n low concentrations, are often toxic or i n h i b i t o r y to most b i o l o g i c a l organisms at higher l e v e l s . Many of the heavy metals and complex inorganic compounds are usually a r e s u l t of i n d u s t r i a l discharges as well as surface run-off i n combined sewage systems. Table II i l l u s t r a t e s the forgiving nature of the activated sludge process and the a b i l i t y of the bacteria to accept metal loadings on a continuous and slug-loading basis. MATERIAL CONTINUOUS LOADING (mg/l) SLUG LOADING (mg/l) Cd 1 10 Cr 2 2 Cu 1 1.5 Fe 35 100 Pb 1 -Mn 1 -Hg 0.002 0.5 Ni 1 5 Ag 0.03 0.25 Zn 1 - 5 25 Co > 1 -C=N 1 1 -10 As 0.7 1 Table II - Toxic Loading for Various Metals on the 9 Activated Sludge Process The source of g r i t and sediment i s primarily from washed g r i t from cleaning operations l i k e car washes and r e s i d e n t i a l laundry, urban storm run-off, and erosion within the sewerage system. Sewage contains l i v i n g organisms because i t c a r r i e s the waste products of animals whose guts contain l i v i n g organisms. The 16 most common organisms are bacteria, although protozoa, worms and t h e i r eggs and larvae, and viruses are also present. Receiving waters are often used as recreational areas where there i s human contact with d i l u t e d e f f l u e n t material, and as raw water sources for human consumption and use. Removal of these organisms from wastewater i s esse n t i a l to protect the health of people and animals using the receiving water. In North America, most treated wastewater i s di s i n f e c t e d using c h l o r i n a t i o n , which involves the addition, mixing and prolonged contact of chlorine compounds with the wastewater. This operation k i l l s a high percentage of l i v i n g organisms and produces a residual i n the wastewater with the potential of further d i s i n f e c t i o n . Some species of the b a c t e r i a l population present i n the raw sewage i s cultured and used to remove organic impurities from the sewage i n a b i o l o g i c a l waste treatment process. This i s the basis for b i o l o g i c a l wastewater treatment. Differences i n geography, climate and culture insure that no two municipal wastewaters are exactly the same. Even i n a single f a c i l i t y , i n f l u e n t sewage w i l l exhibit v a r i a t i o n i n flow and composition with time. The inf l u e n t parameters w i l l change as the sewered area grows and develops. This i n f l u e n t v a r i a t i o n challenges the engineer to design a f a c i l i t y useful for a 20 to 25 year design l i f e , and the operator who must treat a continually changing i n f l u e n t to provide a much less variable, treated e f f l u e n t . 17 2.2 Wastewater Treatment F a c i l i t i e s The nomenclature "primary f a c i l i t y " or "a secondary plant" i s often used to describe treatment f a c i l i t i e s . The terms preliminary, primary, secondary and t e r t i a r y or advanced treatment describe the general l e v e l of treatment provided and are generally cumulative. A treatment plant i s i n fact an interconnected s t r i n g of i n d i v i d u a l unit operations and unit processes. These units are physical, chemical or b i o l o g i c a l i n nature, and each removes a portion of the contaminants from the sewage. The combined e f f e c t of these units i s to produce a s a t i s f a c t o r y e f f l u e n t . Figure 2 i l l u s t r a t e s where i n f l u e n t s o l i d s of various forms and BOD are removed with respect to the unit operations. Preliminary treatment usually combines the unit operations of raking and screening, shredding and g r i t removal. Primary treatment includes the unit operations of primary sedimentation or microscreening. Secondary treatment involves b i o l o g i c a l or physico-chemical processes. Physico-chemical treatment uses chemical addition, mixing, c l a r i f i c a t i o n and f i l t e r i n g to remove suspended material and organic contaminants. In t h i s t h e s i s , only b i o l o g i c a l secondary processes w i l l be investigated. Advanced treatment can be used to further reduce the concentrations of constituents removed i n lower lev e l s of treatment or to remove special inorganic or organic materials whose removal i s impossible with normal secondary l e v e l treatment. Due to the wide variety and l e v e l of technical 18 < > o L J c r ci q CD o r--O K c r < LJJ O ^ O U J U J r r < -5 c r < CT >-Ql 1— < U J 1— _ J 1 . 1 < 1 1 1 U J c r 1 1 1 c r Q_ t— o o m o SNINIWGd •a-o-a o < 2 CO z cs: < UJ E J O co v "I ! § t - O O Cij < CO CO o >-< a. t r o < o O CO z o cr U J GL o 3 CO Q u i c n • Q 9 c o O Zi -J 9 CO O O J (71 CO O • U J o >. -7 -7 Q L d O p 0 1 m < CO - J YX O 3 O °2 ZJ O c n o o u . c n CO Q _ l O CO UJ I m < _ U J == U J 33 CO CO u . CO Q o CO o < > O :> U J cr ui Q I O 00 c o Q _ l o CO YX U J -O z t < a i Qi < CC CC UJ O CO CD CD Q Figure 2 - Typical Solids and BOD Removal i n a Secondary STP 19 complexity involved with most t e r t i a r y systems, they are not included i n t h i s thesis; however most are outlined i n common design texts. The only advanced treatment process examined w i l l be that of b i o l o g i c a l nitrogen removal. Examples of advanced unit operations include activated carbon f i l t r a t i o n , ion exchange, reverse osmosis and gas s t r i p p i n g . 2.3 Unit Operations Following i s a short description of the unit operations used i n the development of the thesis. 2.3.1 Raw Sewage Pumping The channel roughness, weirs and constrictions of the various unit operations create a loss of energy i n the open channels and piping of the waste treatment plant. The sum of a l l these head losses under the worst conditions i s the maximum head or l i f t required for the sewage to flow through the plant. Raw sewage i s usually pumped above ground i n order that the plant can be b u i l t without major excavation and with enough head for a l l foreseeable flow conditions. The pumps are design to provide required flow and l i f t , and be rugged and r e l i a b l e . Two of the more common types of raw sewage l i f t pumps used are screw pumps and c e n t r i f u g a l pumps. 2.3.2 Racks and Screening Racks and screens are the simplest form of wastewater treatment. This in-stream unit operation has a dual purpose. Raking and 20 screening removes the large inorganic or organic debris such as rags, paper, wood and p l a s t i c s found i n municipal sewage. Generally there are coarse racks, designed to remove pieces of wood and other large items, and fine screens to remove smaller pieces of p l a s t i c , rags and paper. The water flows through the openings and impinges the debris where i t can be removed manually or by automatic rakes, triggered by head loss through the rack or by timers. The WASTES system i s designed to diagnose two types of racks: fixed racks and moving racks. Fixed racks remain stationary with manual or automatic raking. Moving screens revolve continually to remove debris from the flow and are often cleaned using high pressure water j e t s . 2.3.3 Shredding Shredding i s associated with screening because shredders are often attached to the screens to shred the accumulated material allowing i t to flow through the plant and be removed i n the c l a r i f i e r s . Shredding usually occurs i n treatment f a c i l i t i e s where accumulation and disposal of such debris i s problematic. It i s normally preceded by at least coarse racks. 2.3.4 G r i t Removal G r i t removal r i d s the sewage of g r i t , sand, rocks and other dense materials. There are conventional and aerated g r i t tanks which provide c l a s s i c a l d i screte p a r t i c l e s e t t l i n g conditions or u t i l i z e a cyclonic action to remove the denser materials. The s e t t l e d material i s generally c o l l e c t e d by augers or conveyors 21 for disposal by b u r i a l . 2.3.5 Primary C l a r i f i c a t i o n Primary c l a r i f i c a t i o n removes f l o a t i n g s o l i d s , grease, scum and set t l e a b l e s o l i d s . Primary c l a r i f i e r s are an important part of the treatment process because they are capable of removing 25 to 45 percent of the t o t a l BOD entering the plant, while at the same time providing 50 to 70 percent suspended s o l i d s removal. Removal rates decrease as flow rates through the c l a r i f i e r s and the overflow rates over the tanks weirs increase. Settled s o l i d s are pumped from the bottom of the c l a r i f i e r as a sludge while floatables are skimmed from the surface. As a preliminary step to b i o l o g i c a l treatment, primary c l a r i f i e r s reduce the s o l i d s and BOD loading allowing for smaller design tank volumes and a i r requirements i n the subsequent secondary treatment operation. 2.3.6 Microscreening Microscreening i s a primary unit operation that u t i l i z e s a rotating screen that impinges so l i d s from the wastewater flow and i s then scraped or sprayed to remove the so l i d s from the screen. Microscreens occupy much less area than primary c l a r i f i e r s , providing approximately one half of the capacity to remove suspended so l i d s and BOD.*^ 2.3.7 B i o l o g i c a l Treatment B i o l o g i c a l treatment removes c o l l o i d a l and dissolved organic impurities from wastewater. The three most common forms of 22 b i o l o g i c a l treatment used i n North America are the activated sludge process, rotating b i o l o g i c a l contactors, or t r i c k l i n g f i l t e r s . Each of these i s provided with a following c l a r i f i e r to remove the accumulated b i o l o g i c a l s o l i d s . The operation of the b i o l o g i c a l systems and the secondary c l a r i f i e r s are very c l o s e l y related and thus are treated as a single treatment unit. 2.3.7.1 Activated Sludge The activated sludge system uses recycled heterotrophic bacteria from the secondary c l a r i f i e r to be mixed with the wastewater i n the aeration tanks. The combination i s c a l l e d mixed l i q u o r . The aeration tanks are aptly named because a i r or oxygen must be supplied to provide the aerobic bacteria with 02- The b a c t e r i a l floes f i r s t sorb the substrate i n the f i r s t 15 to 30 minutes of contact with the wastewater then they use enzymes to break down the substrate and transport i t inside the c e l l to metabolize 12 i t . The organic contaminants are e f f e c t i v e l y removed from the wastewater by sorption to the f l o e . After the mixed liq u o r flows out of the aeration tanks, i t enters the secondary c l a r i f i e r s where the floes s e t t l e to the bottom and thicken. The c l a r i f i e d e f f l u e n t i s discharged through the weirs on the c l a r i f i e r surface. The thickened sludge, c a l l e d return sludge, i s pumped to the beginning of the aeration tank where the activated sludge floes are mixed with the in f l u e n t sewage. This process occurs continuously as b a c t e r i a l c e l l s feed, grow, multiply and die. Figure 3 i l l u s t r a t e s a simple activated sludge system. 23 PRELIMINARY TREATED INFLUENT EFFLUENT AERATION TANK MIXED PRIMARY CLARIFIER LIQUOR RETURN SLUDGE t PRIMARY SLUDGE SECONDARY CLARIFIER ? SECONDARY SLUDGE TO WASTE The aeration system i s designed and operated to provide oxygen to the microorganisms, and to adequately mix and suspend the floes and substrate. There are two common aeration systems -compressed a i r and mechanical. A compressed a i r system consists of a i r f i l t e r s , compressors, piping and valving, and submerged d i f f u s e r s . The pressurized a i r i s fed into d i f f u s e r s placed near the bottom of the aeration tanks. Coarse bubble d i f f u s e r s produce large bubbles. Large bubbles r i s e quickly through the mixed liq u o r and provide less surface area which re s u l t s i n slower oxygen transfer with the surrounding bulk l i q u i d . Fine bubble d i f f u s e r s produce clouds of very small bubbles with very high transfer e f f i c i e n c i e s . However, there are several drawbacks of f i n e bubble d i f f u s e r s . One i s the high pressure compressed a i r system necessary to overcome the head losses of the d i f f u s e r s , while another i s the cleaning required to keep the d i f f u s e r heads from constantly clogging with g r i t and debris. Both systems provide mixing by reducing the bulk density of the l i q u i d with the bubbles of a i r compared with that surrounding i t . The second common aeration system uses mechanical aerators. Updraft aerators use a blade or pump system to l i f t the mixed li q u o r out of the tank, thus producing turbulence that increases oxygen transfer into the formed l i q u i d droplets. Downdraft mechanical aerators entrain a i r bubbles producing surface and sub-surface turbulence that aids oxygen transfer. 25 Activated sludge systems can be designed and operated to provide nitrogen and phosphorus removal as well as organic carbon removal and t h i s technology i s regarded as advanced wastewater treatment. The complexity and importance of activated sludge units requires a trained s t a f f , rigorous lab analysis and data c o l l e c t i o n for proper operation and a good q u a l i t y e f f l u e n t . 2.3.7.2 RBCs and T r i c k l i n g F i l t e r s RBCs and t r i c k l i n g f i l t e r s are both aerobic fixed b i o l o g i c a l f i l m system that u t i l i z e bacteria, s i m i l a r to those i n activated sludge, to remove organic substrates from the i n f l u e n t sewage as food for growth and reproduction. Primary end products are CO2 and H 2 O . RBCs are large partially-submerged disks that revolve i n the wastewater, sequentially providing both substrate and oxygen to the attached biomass. As the bacteria reproduce, the f i l m on the disks grows thicker and excess material sloughs o f f due to the hydrodynamic drag forces provided by the r o t a t i o n . These so l i d s are captured i n the secondary c l a r i f i e r and need not be r e c i r c u l a t e d to the front of the RBCs, as i s done i n activated sludge systems. This constant sloughing provides a s e l f -regulating loading control that responds nat u r a l l y to the i n f l u e n t organic loading. As a r e s u l t , there i s very l i t t l e process control required for RBC units. Wastewater flows through a series of these large units for a desired l e v e l of treatment. In t r i c k l i n g f i l t e r s , the rock or p l a s t i c media i s stationary and situated i n large c y l i n d r i c a l tanks. The wastewater i s d i s t r i b u t e d v i a a rotating sprayer at the top and flows downward 26 through the media and attached biomass. Large vents around the circumference provide a i r c i r c u l a t i o n upward through the f i l t e r and oxygen for the biomass. The same growth and sloughing occurs i n t r i c k l i n g f i l t e r systems however the shearing action i s provided by the flowing wastewater. 2.3.7.3 Secondary C l a r i f i c a t i o n Secondary c l a r i f i e r s remove the b i o l o g i c a l s o l i d s and scum from the treated wastewater before i t i s d i s i n f e c t e d and discharged. The c o l l e c t e d sludge i s pumped from the bottom of the c l a r i f i e r to the head of the treatment works or to sludge treatment f a c i l i t i e s . In the activated sludge process, a f t e r the mixed l i q u o r has been aerated, i t passes into the secondary or f i n a l c l a r i f i e r s . These tanks are designed to provide conditions suitable for the s e t t l i n g of the activated sludge f l o e . In the quiescent conditions of the c l a r i f i e r , the floe s e t t l e s downward to form a sludge blanket on the bottom of the c l a r i f i e r . The density of the activated sludge floe i s only s l i g h t l y greater than water so secondary c l a r i f i e r s are susceptible to adverse flows and currents that carry the floe s o l i d s over the e f f l u e n t weirs. As the sludge c o l l e c t s on the c l a r i f i e r bottom, i t compacts under i t s own weight, thickening the mass of b i o l o g i c a l s o l i d s and water. T y p i c a l l y a plow-type scraper i s employed to move the sludge towards the center of the tank where i t i s pumped to the head of aeration tank and mixed with the sewage. 27 The operation of the aeration tank and f i n a l c l a r i f i e r i s i n t r i n s i c with the treated effluent entering the c l a r i f i e r and the s e t t l e d sludge pumped back to the aeration tank to mix with the incoming sewage. A portion of th i s sludge i s removed from the system or wasted to control the process. This l i n k i s why e f f e c t i v e treatment and operation of the activated sludge system depends on both the aeration and c l a r i f i c a t i o n processes and t h e i r operation. With RBCs and t r i c k l i n g f i l t e r s , the sol i d s are usually c o l l e c t e d and pumped out of the c l a r i f i e r s for disposal. Proper operation of secondary c l a r i f i e r s i s key for producing q u a l i t y effluents with low BOD and suspended s o l i d s . Major operational problems include changes i n sludge q u a l i t y and flow conditions due to changes i n influent c h a r a c t e r i s t i c s or a combination of pumping and mechanical problems. 28 C h a p t e r 3 . 0 T h e M o d e l W a s t e w a t e r T r e a t m e n t P l a n t 3 . 1 I n t r o d u c t i o n A c o n v e n t i o n a l a c t i v a t e d s l u d g e t r e a t m e n t f a c i l i t y was c h o s e n a s t h e m o d e l f a c i l i t y f o r t h e e x p e r t s y s t e m . T h e r e w e r e s e v e r a l r e a s o n s f o r c h o o s i n g t h i s t y p e o f t r e a t m e n t f a c i l i t y . F i r s t l y , s e c o n d a r y t r e a t m e n t p l a n t s make up t h e l a r g e s t p r o p o r t i o n o f p l a n t s i n u s e i n N o r t h A m e r i c a . S e c o n d l y , d e v e l o p i n g a s y s t e m f o r u s e i n s e c o n d a r y p l a n t s w o u l d i n v o l v e p r e l i m i n a r y , p r i m a r y a n d s e c o n d a r y t r e a t m e n t o p e r a t i o n s a n d p r o c e s s e s , a n d w o u l d t h e r e f o r e f i n d a w i d e r a n g e o f a p p l i c a b i l i t y . T h i r d l y , t h e b i o l o g i c a l p r o c e s s o f a c t i v a t e d s l u d g e was c h o s e n b e c a u s e i t i s u s e d m o s t f r e q u e n t l y a s t h e s e c o n d a r y t r e a t m e n t p r o c e s s o f c h o i c e i n N o r t h A m e r i c a . T h e a c t i v a t e d s l u d g e p r o c e s s r e q u i r e s s u b s t a n t i a l o p e r a t o r k n o w l e d g e a n d i n p u t f o r p r o c e s s c o n t r o l a s c o m p a r e d t o o t h e r s e c o n d a r y p r o c e s s l i k e RBCs a n d t r i c k l i n g f i l t e r s . T h e t r e a t m e n t p r o c e s s i t s e l f i s a l s o a d a p t i v e t o many o p e r a t o r - c o n t r o l l e d p r o c e s s v a r i a t i o n s t h a t r e s u l t i n d i f f e r e n t o p e r a t i o n a l m o d e s . 3 . 2 L a y o u t T h e l a y o u t o f t h e m o d e l t r e a t m e n t p l a n t i s shown i n F i g u r e 4. I n t h e m o d e l p l a n t , i n f l u e n t p a s s e s t h r o u g h a l i f t pump t o t h e r a c k s , s h r e d d e r s a n d g r i t c h a m b e r s . T h e sewage t h e n e n t e r s t h e p r i m a r y c l a r i f i e r s a n d t h e n t h e a e r a t i o n t a n k s . T h e t r e a t e d sewage f i n a l l y e n t e r s t h e s e c o n d a r y c l a r i f i e r s a n d t h e c l a r i f i e d 29 WASTES S Y S T E M DOMAIN PRIMARY SLUDGE RAW SEWAGE LIFT SCREENING RAW SEWAGE EFFLUENT Figure 4 - WASTES STP model for Expert System 30 e f f l u e n t can be chlorinated and discharged. The primary c l a r i f i e r sludge and part of the secondary c l a r i f i e r sludge i s pumped to the sludge treatment and disposal works. The sludge may undergo a series of separate unit operations before f i n a l d isposal. Sludge treatment works were not included i n the development of the expert system because t h e i r operation, although important, has l i t t l e bearing on the operation of the main l i q u i d treatment process. The ch l o r i n a t i o n system was also omitted because most plants already u t i l i z e automated chlorine dosage regulation and measurement systems. 3.3 Operation To understand what i s involved i n the operations of a secondary wastewater treatment plant we should examine the context and conditions i n which i t functions. Most f a c i l i t i e s are operated by municipalities or regional d i s t r i c t s who employ trained s t a f f d i r e c t l y responsible for d a i l y operations and maintenance. In B r i t i s h Columbia, wastewater treatment plants are operated to provide the e f f l u e n t q u a l i t y set out i n the i n d i v i d u a l f a c i l i t y ' s waste discharge permit provided by the Waste Management Branch of the p r o v i n c i a l Ministry of the Environment. These regulations generally set out effluent concentrations for B O D 5 and suspended s o l i d s and other contaminants. These guidelines are based on the d a i l y volume of sewage treated, d a i l y flow v a r i a t i o n , e f f l u e n t d i l u t i o n , receiving water type and volume. Monitoring of these ef f l u e n t concentrations to check compliance i s a r e s p o n s i b i l i t y of the permit holder. If these permitted levels are exceeded 31 r e g u l a r l y , the offender i s asked to correct the problem, offered assistance and can face potential prosecution. The plant s t a f f monitor the operation variables, e f f l u e n t parameters, and maintain and repair the various unit operations. To insure the f a c i l i t y i s running e f f i c i e n t l y and e f f e c t i v e l y , sampling and lab analysis must be undertaken to provide information to control the process. Staff must integrate a l l plant objectives including effluent q u a l i t y , sludge disposal, plant operations, costs, and budgeting. Often the o r i g i n a l plant design may l i m i t the design l i f e or process f l e x i b i l i t y of the f a c i l i t y . This forces the operator to run his plant i n an overloaded condition and face permit v i o l a t i o n s . Budget r e s t r i c t i o n s may l i m i t s t a f f i n g and operational funds, thus leading to reduced effectiveness of unit operations due to mechanical break downs and lack of maintenance. 3.4 Operational Objectives Generally the activated sludge process (the aeration tanks and f i n a l c l a r i f i e r s ) i s operated to provide the following basic goals: o required BOD removal o minimal loss of suspended s o l i d s into the effluent o n i t r i f i c a t i o n where required o d e n i t r i f i c a t i o n where required. 32 The required removal of BOD w i l l occur i f there i s a s u f f i c i e n t mass of active biomass i n the mixed liq u o r to remove and oxidize the organic compounds in the i n f l u e n t , and i f s u f f i c i e n t oxygen i s provided to the biomass. Most in f l u e n t sewage c h a r a c t e r i s t i c s including flows, BOD loading, and temperature are beyond the control of the operator. Operation of the process can simply be stated as an attempt to s a t i s f y the treatment goals subject to the v a r i a b i l i t y of the inputs and l i m i t a t i o n s of the c o n t r o l l i n g variables. 3.5 Process Operation and Control A basic, well designed treatment plant has four basic process control operational variables which the operator manipulates to meet the treatment objectives: o a i r (oxygen) input o return sludge rate o sludge wastage rate o mixing energy. The following sections w i l l describe how and why the model treatment plant responds to these process controls and what parameters are manipulated and changed i n the system. 3.5.1 Aeration Rates The amount of aeration applied to the aeration tanks i s generally determined by the following: 33 o dissolved oxygen requirements o mixing energy to suspend mixed liquor suspended so l i d s (MLSS) Most activated sludge plants are operated with a dissolved oxygen 13 content (DO) i n the bioreactor ranging from 1 to 2 mg/L. If there i s s u f f i c i e n t biomass i n the aeration tanks, i . e . high enough MLSS, oxygen demand i s proportional to the organic loading. The MLSS, or mixed liquor suspended s o l i d s , i s the l i q u i d mixture of wastewater and activated sludge that flows through the plant. The mass organic loading into the plant generally follows a si m i l a r pattern to that of flow (see F i g . 1). Hence, the oxygen demand w i l l not be uniform but w i l l decrease during the night and increase during the diurnal peaks of the day. It i s essential that the process remain aerobic at a l l times so a minimum DO should be present at a l l points i n the aeration tanks. The presence of a s i g n i f i c a n t DO i n the eff l u e n t of the aeration tanks helps to keep the s e t t l e d sludge i n the c l a r i f i e r s aerobic, which i n turn precludes the onset of anaerobic conditions. If the conditions i n the bottom of the c l a r i f i e r s were to become anaerobic, the f a c u l t a t i v e bacteria would use the n i t r a t e present i n the wastewater and produce N2 gas, and r i s i n g sludge. Conservative operational practice suggests a minimum DO l e v e l at the eff l u e n t end of the aeration 14 basin of 2.0 mg/L. This l e v e l of DO at the ef f l u e n t end of the aeration tanks w i l l maintain aerobic conditions i n the c l a r i f i e r s . Without a functioning control strategy, aeration 34 demands for minimum DO requirements at peak organic loading w i l l lead to elevated DO concentrations and possible overaeration at lower loadings. Overaeration of the biomass wastes power and increases operating costs. The b i o l o g i c a l f l o e i s a c t u a l l y broken apart by the mixing energy. This allows oxygen into the floe's center, and can aid i n the development of robust, healthy activated sludge f l o e s . There are two basic methods for measuring and c o n t r o l l i n g the DO l e v e l i n the aeration tanks: one i f the plant aeration i s manually controlled and the other i f the plant has automatic DO contr o l . Manually c o n t r o l l i n g the DO requires the use of a DO probe, measuring the DO at c r i t i c a l locations, and adjusting the aeration valving or operation of the mechanical aerators to match the oxygen requirements. Automatic control uses permanently i n s t a l l e d probes throughout the aeration tank that automatically adjust the a i r valving along the length of the tank to match the oxygen demand or adjusts mechanical aerators. Automatic c o n t r o l l e r s can eliminate excessive aeration and reduce power costs. Monitoring the DO p r o f i l e along the tank also i d e n t i f i e s shock loads on the biomass and aeration system f a i l u r e s . 3.5.2 Return Sludge Flow (RSF) As i l l u s t r a t e d e a r l i e r , the purpose of the return sludge flow i s to pump the produced mass of activated sludge floes back to the head of the aeration tanks i n order to provide rapid a s s i m i l a t i o n of the organic wastes i n the i n f l u e n t . Maintaining the correct 35 return sludge flow: o maintains an adequate aeration tank MLSS o optimizes the sludge blanket i n the c l a r i f i e r . Optimizing the sludge blanket i n the c l a r i f i e r s accomplishes several things. F i r s t , i t maximizes the amount of activated sludge i n the aeration tanks available for increases BOD loading. Second, i t keeps the return sludge flow as low as possible while at the same time keeping the storage of s o l i d s i n the c l a r i f i e r low enough to minimize the r i s k of loss of s o l i d s into the plant e f f l u e n t due to plant hydraulic overloading or other plant upset condition. Methods that are commonly used to determine the correct return sludge flow include: o c a l c u l a t i o n of a mass balances on the system o measurement of the sludge blanket thickness i n the secondary c l a r i f i e r s . The correct RSF can be calculated using a mass balance approach. This requires the operator to monitor the s o l i d s concentration and flow rate i n the return sludge underflow, i n the c l a r i f i e r and aeration tanks. This method i s can be used but i t has several drawbacks. One, i t requires a l o t of c a l c u l a t i o n and monitoring of s o l i d s concentrations and flows. Second, the concentration i n the various parts of the system can change ra p i d l y and unless the monitoring int e r v a l s are short, large 36 errors can accumulate. C o n t r o l l i n g RSF i s one of the most complex operations i n the activated sludge treatment plant because continuous control i s affected by almost a l l aspects of the treatment plant process; i n f l u e n t flows and BOD loading, c l a r i f i e r design and s o l i d s loading rate, and activated sludge c h a r a c t e r i s t i c s are just three of the major parameters a f f e c t i n g RSF. Increased BOD loading, whether through increased flow or increased i n f l u e n t BOD concentration, into the plant w i l l increase the so l i d s loading on the c l a r i f i e r s through the conversion of BOD to c e l l matter or activated sludge f l o e s . The flow through the system w i l l carry the sol i d s from the aeration tanks into the c l a r i f i e r s . As long as the proper design s o l i d s loading rate on the c l a r i f i e r s and the hydraulic loading on the eff l u e n t weirs are not exceeded, the extra activated sludge w i l l simply c o l l e c t into a sludge blanket i n the bottom of the c l a r i f i e r s . The actual hydraulic retention time (AHRT) i s the retention time of i n the aeration tanks including the RSF. The nominal hydraulic retention time (NHRT) i s the retention time that uses only the influent flowrate and does not include the RSF. Subsequently, increasing the RSF w i l l decrease the AHRT (while the NHRT i n the aeration tanks and overflow rate of the c l a r i f i e r s remain the same) and i t w i l l reduce the sludge blanket thickness; however, i t w i l l , at least i n the short term, increase the s o l i d s loading on the c l a r i f i e r s . This could possibly cause 37 a loading rate above the so l i d s loading capacity and cause a loss of s o l i d s or wash-out into the effluent. Experiments by the USEPA confirm that the MLSS concentration l e v e l s i n the aeration 15 tanks respond poorly to changes i n RSF flows. Large increases i n the RSF produce only minor changes i n the MLSS l e v e l s i n the bioreactor during steady hydraulic conditions. While the effects of RSF may be minor i n a f f e c t i n g the MLSS i n the aeration tanks, decreasing the RSF w i l l increase the AHRT i n the aeration tanks tending to o f f s e t the reduction caused by increased sewage flows. This i n turn w i l l decrease the s o l i d s loading rate on the c l a r i f i e r s . As long as the c l a r i f i e r s have the capacity to store the sol i d s over the hydraulic "event" and the overflow rate on the weirs i s not exceeded, no s o l i d s should be l o s t into the eff l u e n t . After the period of reduced AHRT due to high inflows, the RSF could be increased to remove the sludge blanket and return the so l i d s to the aeration tanks. This transfer of sol i d s from the bioreactor to the c l a r i f i e r s , then back to the bioreactor. The e f f e c t of changing the RSF i s lim i t e d by the sol i d s loading capacity of the c l a r i f i e r s . The c l a r i f i e r s should be operated with a low stored volume of sludge, which can be monitored by measuring the blanket thickness (BLT). Minimizing the BLT i s a method of operation that reduces chances of so l i d s losses. It also ensures that most of the activated sludge solids are kept i n the aeration tanks where they can a c t i v e l y metabolize substrate. However, RSF and s o l i d s loading rate are not the only factor that e f f e c t BLT. The 38 blanket thickness i s also function of the sludge s e t t l e a b i l i t y and the amount of so l i d s i n the combined aeration tank and c l a r i f i e r . The sludge blanket i n the c l a r i f i e r w i l l r i s e as the sludge s e t t l e a b i l i t y decreases. Conversely, the blanket l e v e l w i l l drop i f the s e t t l e a b i l i t y increases. Disregarding the q u a l i t y of sludge i n terms of i t s s e t t l e a b i l i t y can lead to wrong operating decisions. If the s e t t l e a b i l i t y i s poor or slow, increasing the RSF w i l l only make matters worse as the s o l i d s loading on the c l a r i f i e r s i s increased. As referenced e a r l i e r , aeration tank MLSS levels are poorly affected by return sludge rates, but they do respond strongly to wasting rates. Wasting sludge from the system i s the key to c o n t r o l l i n g the en t i r e activated sludge process. Higher s o l i d s production i n the aeration tanks requires more sludge to be pumped from the secondary c l a r i f i e r s to the head of the aeration tanks. It also produces greater s o l i d s loadings on the c l a r i f i e r s . Wholly inadequate RSF rates w i l l cause an increase i n the BLT over a very short time i f the so l i d s loading capacity i s not exceeded. Hobson 1^ also suggests the following operational point concerning RSF control: o adjust RSF 10 to 25 percent per adjustment o large RSF adjustments should be made i n 2 or 3 smaller adjustments, 2 or 3 hours apart. o there i s a minimum RSF below which the sludge may plug return sludge piping. 39 Increases i n BOD loading w i l l also create increased s o l i d s loading, but they w i l l occur over a longer time frame r e s u l t i n g i n a gradual increase i n the BLT v a r i a t i o n over a varying inflow and constant RSF. Waste sludge flow (WSF) happens to be one way the whole activate sludge process i s controlled, so observations concerning blanket changes or s o l i d s loadings on the c l a r i f i e r s could reveal even more important process control information. 3.5.3 Waste Sludge Flow and Process Control The discussion i n t h i s section deals with the general behavior of the activated sludge process to external forces. The e f f e c t s of d i f f e r e n t loadings and plant design and operational factors may produce d i f f e r e n t sludge c h a r a c t e r i s t i c s and plant conditions. Under conditions of constant inflow and BOD loading and no WSF, the mass of b i o l o g i c a l s o l i d s i n the system w i l l increase due to the conversion of the influent organics into more bacteria through growth and reproduction. The MLSS concentration would increase i n the system, and the b i o l o g i c a l s o l i d s would eventually f i l l the c l a r i f i e r s and wash out the e f f l u e n t weirs. At the same time, the sludge might not s e t t l e well i n the c l a r i f i e r and the effluent q u a l i t y would deteriorate. From an operational point of view, the solution i s to remove or waste some of the b i o l o g i c a l s o l i d s or sludge from the system. How much and why i s the basis of activated sludge process c o n t r o l . 40 In general, the activated sludge process responds to and i s regulated by two basic variables: food (organics) and microorganisms (bacteria). The F/M or food-to-microorganism r a t i o plays an important role i n process control because i t a f f e c t s : o effluent q u a l i t y o dissolved oxygen consumption o sludge q u a l i t y and quantity. B a c t e r i a l growth rates are generally proportional to the r e l a t i v e amount of substrate; more food creates a high growth rate i n the organisms, provided that DO, nutrients, or other environmental conditions are not l i m i t i n g . A high F/M produces high r e l a t i v e growth rates and under such conditions, a larger percentage of the BOD removed i s synthesized into new c e l l u l a r material than i s used for energy i n the c e l l s . A low F/M r e s u l t s i n lower growth rates and accordingly more BOD i s used for energy requirements than reproduction. From an operational point of view t h i s i s important because by c o n t r o l l i n g the F/M we can control growth rates and the s e t t l i n g c h a r a c t e r i s t i c s of the activated sludge. A high b i o l o g i c a l s o l i d s growth rate may r e s u l t i n : o incomplete BOD removal. o excess sludge production o cloudy effluent o poor s e t t l i n g sludge. 41 The rates of BOD removal per unit mass of b i o l o g i c a l s o l i d s i s higher, but the high F/M and high growth rate can also r e s u l t i n the formation of large, lacy, low density activated sludge f l o e s . These floes s e t t l e and compact poorly to create a bulking sludge that can b u i l d up and escape out the c l a r i f i e r e f f l u e n t weirs. Pin floes can develop from the poor adsorptive, or floe forming c h a r a c t e r i s t i c s i n the fast-growing bacteria due to a lack of external enzymes which a s s i s t f l o c c u l a t i o n . These pin floes can also develop from shearing of already formed lacy floes which can cloud the effluent and do not s e t t l e out i n the c l a r i f i e r , and r e s u l t i n g i n high effluent suspended s o l i d s . Overall, the high F/M system has high organic loading on the sludge f l o e s , r e s u l t i n g i n a higher growth rate and increased sludge production as the BOD i s converted into more c e l l matter. Savings are r e a l i z e d i n the smaller bioreactor volumes or shorter HRT required for removal of the substrate, but the s e t t l i n g c h a r a c t e r i s t i c s of the sludge could r e s u l t i n having to design the c l a r i f i e r s for a "younger", poorly s e t t l i n g sludge. The amount of sludge produced can be excessive for the sludge handling and disposal unit operations i f they are not designed i n i t i a l l y for t h i s treatment mode. A low F/M means a r e l a t i v e lack of food per unit mass of microorganisms. With the lower growth rate of the organisms, they begin endogenous r e s p i r a t i o n where they begin to use t h e i r own c e l l contents as food. Operating the activated sludge process at a low F/M may r e s u l t i n : 42 o high BOD removal o low net sludge production o cloudy effluent o large aeration requirements. The higher MLSS concentration l e v e l s , along with lower growth and substrate removal rate, require higher tankage volumes for adequate BOD removal (lower BOD removal rate per unit mass). The poorly s e t t l i n g sludge and cloudy effluent can be a t t r i b u t e d to the nature of the b a c t e r i a l floe under low F/M conditions. The lack of food w i l l cause the floe to decrease i n si z e as the c e l l s endogenously respire. The problem with the small floes i s the lack of agglomeration of the smaller discrete p a r t i c l e s that would normally be trapped by larger activated sludge f l o e s . These can cloud the c l a r i f i e r e f fluent and create suspended s o l i d s problems even i f the floes s e t t l e e a s i l y . Very old sludge w i l l also become less dense as the floe decreases i n mass as the bacteria undergo endogenous r e s p i r a t i o n . The r e s u l t i s small l i g h t floes that can r i s e over the effluent weirs. Even with the poor ef f l u e n t s o l i d s conditions, low F/M operation i s often used. One example i s c a l l e d extended aeration. It provides low e f f l u e n t soluble BOD with some loss of r e l a t i v e l y i n e r t suspended s o l i d s combined with low sludge wastage volumes to handle and dispose. Drawbacks of t h i s operating mode are the r e l a t i v e l y large tank volumes and aeration requirements that must be provided to allow operation at a low F/M r a t i o . 43 Besides operating at d i f f e r e n t F/M r a t i o s , the aeration and mixing rates, bioreactor design and return sludge flow can be varied i n order to operate the process i n d i f f e r e n t modes. Two of the most common process configurations for the activated sludge process are complete mix and plug flow. Complete mix activated sludge (CMAS) uses square or rectangular tanks whose entire contents are aerated and mixed so the MLSS has e s s e n t i a l l y a uniform F/M p r o f i l e from i n l e t to outlet. Plug flow tanks are long (L:W generally > 5:1) and have a tapered F/M, high at the i n l e t and low at the outlet. Whereas the completely mixed tank has a uniform MLSS quality, the plug flow system has a varied MLSS that lags the F/M curve. This tapered F/M and MLSS lead to the need for tapered aeration which w i l l provide DO to match the loading and MLSS demand. Another form of the plug flow tank i s the step feed system. In t h i s mode, influent sewage and return sludge are introduced into d i f f e r e n t parts along the plug flow tank. This mode i s p a r t i c u l a r l y r e s i s t a n t to shock loadings. Another configuration, often c a l l e d contact s t a b i l i z a t i o n , has a f i r s t tank where the substrate i s sorbed r a p i d l y by the activated sludge f l o e . The mixed liquor flows into a second tank by re-aerating the activated sludge, o v e r a l l higher plant loadings can 17 be achieved. Co n t r o l l i n g the activated sludge process for organic carbon removal involves maintaining the b i o l o g i c a l F/M r a t i o i n a range of values that provides adequate BOD removal concomitantly with the development of sludge c h a r a c t e r i s t i c s that provide good 44 s e t t l i n g i n the c l a r i f i e r . The F/M i s managed because the increased mass of sol i d s due to growth and reproduction would b u i l d up and decrease the F/M r a t i o from i t s optimum. Wasting sludge i s the method of removing those s o l i d s r e s u l t i n g from growth and maintaining the desired process F/M. S t r i c t F/M control would require keeping the b i o l o g i c a l process at a fixed F/M. As the organic loading increased, a suitable amount of biomass would be introduced to the reactor to keep a constant F/M r a t i o . The extra accumulated so l i d s would subsequently be wasted as the BOD loading dropped. Although t h i s control scheme makes sense, i n p r a c t i c a l applications i n i s very d i f f i c u l t to achieve. This operation would require f a i r l y sophisticated sampling equipment or a rigorous hand sampling program by the operator. V a r i a b i l i t y i n the hydraulic and organic loading would make i t very d i f f i c u l t to maintain one F/M over the course of a day or week as influent conditions change. Problems r e s u l t from attempting to maintain and store viable sludge to release into the aeration tank as loadings increase. The plant F/M i s useful as an occasional check of plant operation but not as a regular control strategy. C o n t r o l l i n g the MLSS maintains the mixed liq u o r i n the aeration tanks at a constant s o l i d s concentration. This technique i s used by operators of small plants because i t i s easy to understand and requires a minimum amount of laboratory work. Large fluctuations i n hydraulic and organic loading make i t d i f f i c u l t to maintain a 45 steady MLSS and attempts at thi s control regime often r e s u l t i n poor q u a l i t y e f f l u e n t . The operator maintains a wasting regime that keeps the MLSS at a l e v e l that appears to provide the best e f f l u e n t and sludge q u a l i t i e s for the current BOD loading into the plant. If the MLSS increases, the operator wastes a b i t more sludge from the system. If the MLSS decreases, wasting i s reduced to bring up the mixed liquor l e v e l s . The major drawback of t h i s process control method i s the i n a b i l i t y to adjust to changing conditions i n the treatment plant. If problems occur there i s a lack of data with which to make r a t i o n a l process adjustments. For example, seasonal variations bring colder i n f l u e n t temperatures that necessitate increasing MLSS concentrations to overcome the reduction i n b i o l o g i c a l a c t i v i t y and thereby to maintain BOD removal. Unless the operator had a seasonal schedule of MLSS le v e l s , t h i s strategy provides no basis from which to determine a solution to t h i s problem. Mean c e l l retention time (MCRT) or so l i d s retention time (SRT) control i s considered one of the best methods of contro l . MCRT or SRT refers to the time i n days an average bacterium or s o l i d s p a r t i c l e resides i n the system before being wasted or l o s t i n the ef f l u e n t . Most process design manuals can t h e o r e t i c a l l y show that MCRT and F/M and MLSS are related through the following equation: i = Y * F/M - kd ... 18 46 where: 6 C = mean c e l l retention time, days F/M = process loading factor, kg BOD/kg MLVSS-day Y = y i e l d c o e f f i c i e n t , kg VSS/kg BOD removed k<-j = b a c t e r i a l decay c o e f f i c i e n t , day~l This equation shows that our three control options are i n fact r e l a t e d to each other. By setting the MCRT, the F/M i s fixed because kd and Y are r e l a t i v e l y constant. A long MCRT equates to a low F/M operation and a short MCRT relates to a high F/M. By f i x i n g the F/M, the biomass growth rate and MLSS responds to the organic loading of the process which i s a function of the flow and i n f l u e n t BOD concentration. Maintaining a given MCRT involves wasting a set percentage of the systems s o l i d s every day. If the c l a r i f i e r s are operated with minimum sludge blankets most of the so l i d s w i l l be i n the aeration tanks and wasting 10% of the aeration tank volume per day w i l l give a 10 day MCRT. The operator can waste sludge by either wasting MLSS from the aeration tanks or wasting some of the return s o l i d s underflow to account for that set percentage of so l i d s i n t o t a l . Wasting from the underflow can often lead to problems. The return s o l i d s concentration must be known to calc u l a t e the amount of return s o l i d s to waste. As the return sludge flow increases the sol i d s concentration w i l l drop as the sludge thins out and the amount of so l i d s a c t u a l l y wasted can vary. In smaller plants, the RSF i s often intermittent; so the RSF concentration w i l l vary with time of operation. Plant flow 47 variations w i l l a f f e c t the soli d s blanket lev e l s and sludge concentrations as increased flows s h i f t s o l i d s into the c l a r i f i e r s . If so l i d s are wasted from a f a i r l y constant RSF and steady blanket height, the so l i d s content should be steady. One benefit to wasting from the c l a r i f i e r underflow i s that the sol i d s content of the waste stream i s higher than the mixed liqu o r concentration so that the volume of sludge wasted would be less than wasting MLSS from the aeration tanks. This point can be very important i f the sludge processing and treatment f a c i l i t i e s have a limited capacity. 19 Hobson's advice for wasting includes : o adjust MCRT by no more than 10% allowing at lea s t 2 MCRTs before adjusting again o MCRT must be increased 20 to 50 percent to allow for adequate removal where mixed liquor temperatures f a l l d r a s t i c a l l y during winter months o t r y to account for a l l s o l i d s including those l o s t i n effluent and stored i n the c l a r i f i e r s when c a l c u l a t i n g wastage. Setting the MCRT w i l l determine the qu a l i t y of sludge i n the activated sludge process i n the plant. Hobson, i n r e l a t i n g operational experiences, noted that, i n general, a f a i r l y f a s t r i s i n g c l a r i f i e r sludge blanket (minutes or hours) i s usually a re s u l t of improper RSF rates while slow increases i n blanket height (days or weeks) i s usually a function of s o l i d s build-up 20 due to i n s u f f i c i e n t wasting. 48 3.5.4 B i o l o g i c a l Nitrogen Removal B i o l o g i c a l nutrient removal i s an advance wastewater treatment that uses variations i n the activated sludge process to remove nitrogen and/or phosphorus from wastewaters. B i o l o g i c a l nitrogen removal uses a combination of n i t r i f i c a t i o n and d e n i t r i f i c a t i o n . N i t r i f y i n g bacteria u t i l i z e the ammonia to produce n i t r i t e s then n i t r a t e s . D e n i t r i f y i n g bacteria then use the n i t r a t e s and produce nitrogen gas which escapes to the atmosphere. N i t r i f i c a t i o n requires aerobic conditions and s u f f i c i e n t MCRT. D e n i t r i f i c a t i o n requires anaerobic or anoxic conditions and a carbon substrate for the heterotrophic bacteria, the BOD i n the raw sewage provides t h i s i n the p r e - d e n i t r i f i c a t i o n process. Advances i n process control and design have led to single sludge systems that u t i l i z e p r e d e n i t r i f i c a t i o n or p o s t d e n i t r i f i c a t i o n or both. In the single sludge system some carbonaceous BOD removal also occurs i n the anoxic reactor, due to the metabolic requirements of the heterotrophic d e n i t r i f i e r s . The lack of BOD may be a l i m i t i n g condition i n the operation of post-d e n i t r i f i c a t i o n reactors and t h i s requires a large tankage volume i n order to give s u f f i c i e n t HRT for endogenous d e n i t r i f i c a t i o n . The use of movable bulkheads and p a r t i t i o n s i n plugflow aeration tanks allows variable tankage volumes to s u i t i n f l u e n t conditions and process function. With any type of b i o l o g i c a l nutrient c o n t r o l , no sludge blanket should be developed i n the secondary c l a r i f i e r s . Figure 5 i l l u s t r a t e s both the pre and post d e n i t r i f i c a t i o n layouts for activated sludge systems. 49 o • f l I— C n CD ui •a 1-1 CD (D a *o o CO rt rj CD 3 I— rt h t-h o 0) rt h" O 3 h O n CD U) ro tr> o> •< o c rt cn PREDENITRIF ICATION INFLUENT ANOXIC AEROBIC CARBON • DENITRIFICATION REMOVAL i AND NITRIFICATION EFFLUENT RETURN SLUDGE FLOW POSTD EN ITRI FICATION INFLUENT AEROBIC CARBON ANOXIC REMOVAL DENITRIFICATION AND NITRIFICATION EFFLUENT RETURN SLUDGE FLOW 3.5.5 Microscopic Observations Controlled operation of the activated sludge process requires knowledge of microbial organisms and t h e i r roles i n the treatment process. Some of the important types and forms of microorganisms include: o heterotrophic bacteria o autotrophic bacteria o protozoa o filamentous organisms. Oxygen i s required to support the aerobic heterotrophic bacteria that u t i l i z e organic carbon compounds, oxi d i z i n g them for energy 21 and c e l l synthesis, releasing CO2 and H 2 O . Oxidation: bacteria COHNS + 0 2 > ENERGY + C0 2 + NH^ + H 20 + others C e l l Synthesis: COHNS + 0„ + ENERGY > CcH_N0o ( c e l l material) Endogenous r e s p i r a t i o n : C 5H 7N0 2 + 50 2 > ENERGY + 5C0 2 + NH^ + 2H20 These bacteria are the most common i n the mixed liq u o r and are responsible for removing the c o l l o i d a l and dissolved BOD materials. When there i s a lack of food, the bacteria can u t i l i z e t h e i r own c e l l mass for endogenous r e s p i r a t i o n . In addition, there may be some autotrophic n i t r i f y i n g bacteria 51 present, which use C0 2 to synthesize c e l l material. They also use ammonia for energy production, with the formation of n i t r i t e s and ni t r a t e s i n a process c a l l e d n i t r i f i c a t i o n . nitrosomonas NH 4 + + 3/202 > N02~ + 2H + + H2<J nitrobacter N02~ + l/30 2 > N03~ NH 4 + + 20 2 > N0 3 + 2H + + H 20 Anoxic conditions i n the mixed liq u o r t r i g g e r some heterotrophic organisms to use compounds other than 02 as t h e i r f i n a l electron acceptors; such organisms are c a l l e d f a c u l t a t i v e aerobes. Some fa c u l t a t i v e aerobic organisms can use ni t r a t e s to produce free N2 gas i n a process c a l l e d d e n i t r i f i c a t i o n , as indicated i n the following. N 0 3 + organic carbon > N 0 2 + C 0 2 + H^O N 0 O + organic carbon > N_ + C 0 O + H_0 + 0 H ~ 2 3 2 g 2 2 6N0-, + 5CH,0H > 3N_ + 5C0_ + 7H_0 + 5C0„ + 60H 3 3 2 g 2 2 2 The organic carbon source required by the heterotrophic bacteria i n the d e n i t r i f y i n g process w i l l most often be a va r i e t y of organics naturally present i n the sewage. 52 B a c t e r i a l floes are small masses of bacteria. Floc-forming bacteria such as Zooqloea ramiqera produce e x t r a c e l l u l a r capsules of slime that enmesh other bacteria, organic and inorganic p a r t i c l e s and form the t y p i c a l activated sludge f l o e s . Under c e r t a i n process conditions, the presence of small, non-settleable b a c t e r i a l floes cause a cloudy effluent from the c l a r i f i e r s . Their numbers are reduced and a clearer effluent r e s u l t s , by agglomeration with other bacteria and by removal through predation. Microscopic animals such as C i l i a t e s and Rotifers are found i n the activated sludge. They graze over the sludge f l o e s , consuming organic matter and free bacterium. Using r o t i f e r s or other advance protozoa as an indicator organisms, the operator can often i d e n t i f y when the plant has experienced a toxic loading. Under normal conditions, r o t i f e r s and c i l i a t e s are a c t i v e l y moving about and feeding. If a slug of toxic material has recently entered the plant, the protozoa w i l l be i n a c t i v e , or worse, apparently absent. Filamentous organisms such as Sphaerrotilus natans form long fibrous strands v i s i b l e under the microscope. In small numbers, they can aid i n forming and enmeshing b a c t e r i a l floes i n the 22 activated sludge process. However, i n excess these filaments create a spongy, poor s e t t l i n g sludge also known as bulking sludge. High powered microbial examination of bulking sludge i s necessary to determine the exact type of filamentous organisms. Their presence does not necessarily cause bulking, nor does i t cause high effluent s o l i d s . However, i t i s generally true that 53 i f t h e i r numbers reach a high enough l e v e l r e l a t i v e to other b a c t e r i a l species i n the mixed liquor, bulking sludge conditions w i l l be experienced. The rel a t i o n s h i p between sludge volume and mass i s measure by the sludge volume index (SVI), which i s the volume occupied by 1 g of activated sludge s o l i d s a f t e r 30 minutes s e t t l i n g i n a 1000 ml graduated cylinder. It i s useful for r e l a t i n g the s e t t l i n g c h a r a c t e r i s t i c s within a given plant. Correlating Sludge Volume Index (SVI) to an observed percentage filaments i n a microscopic f i e l d of view at a c e r t a i n magnification can provide a means for predicting a de t e r i o r a t i o n of s e t t l i n g q u a l i t y of the sludge and operational sludge bulking for a p a r t i c u l a r plant. Eikelboom notes that just a small increase i n the number of filaments can change a good s e t t l i n g 23 sludge into a bulking sludge. There i s a whole ecology of bacteria and microscopic animals and organisms within the process regulated by the presence of two variables: oxygen, substrate (food), and population (microorganisms). The F/M or food-to-microorganism r a t i o plays an important role i n determining the microbial d i v e r s i t y of the plant. Different activated sludge systems operate at d i f f e r e n t F/M r a t i o s or MCRTs. Figure 6 below shows the r e l a t i v e predominance of the type of organisms at various F/Ms or MCRTs as well as the succession of organisms that can generally be 24 expected i n an activated sludge process. The longer MCRTs allow higher l e v e l organisms to p r e v a i l while the shorter MCRTs show a predominance of simple faster reproducing f l a g e l l a t e s and 54 MCRT Figure 6 - Microbial D i v e r s i t y with respect to F/M bacterium. High F/M loadings could be seen microbial by a predominance of large, lacy, dark colored activated sludge floes r e s u l t i n g from rapid growth caused by excess substrate. There would be very few of the slower growing r o t i f e r s or stalked c i l i a t e s while f l a g e l l a t e s and other dispersed organisms would appear. Midrange F/M loadings, as found i n conventional activated sludge plants, would show a f a i r l y diverse range of organisms i n the mixed liquor including b a c t e r i a l f l o e s , stalked and free swimming c i l i a t e s . Figure 7 i l l u s t r a t e s some of the common types of microscopic organisms found i n activated sludge. The b a c t e r i a l floes could be described as f u l l and well developed i n d i c a t i n g balanced floe growth. The unchlorinated e f f l u e n t from the secondary c l a r i f i e r might reveal a few r o t i f e r s and other higher protozoa i n d i c a t i n g a low BOD and good q u a l i t y treatment. Low F/M loadings found i n extended aeration activated sludge systems show small, compact, l i g h t e r b a c t e r i a l f l o e s . The long MCRTs allow the higher order protozoa to predominate with l i t t l e e l s e . In d i f f e r e n t treatment plants there w i l l be a completely d i f f e r e n t ecology, which i s always changing i n response to the plant organic loading. The operator must learn what each organism means i n terms of the plant operations. The succession of free c i l i a t e s , stalked c i l i a t e s and r o t i f e r s can be i d e n t i f i e d with periods of good operation (low e f f l u e n t BOD, good s e t t l i n g sludge) and changes and s h i f t s i n those populations as indicators to operational problems. Only during start-up or plant recovery conditions are amoebic organisms present i n the microscopic 25 examination of mixed liquor. Dispersed bacteria could also be 56 vulgaris ROTIFERS voriceld STALKED •LIATES Figure 7 - Common Activated Sludge Organisms 57 an i n d i c a t i o n of very young sludge present as the plant begins operation. Dispersed bacteria are a natural occurring phenomena i n stable systems as the sludge floes are broken apart and endogenously respire during aeration and differences i n the r e l a t i v e numbers, younger sludge being higher, would d i s t i n g u i s h the two d i f f e r e n t MCRTs. In conjunction with hard process control numbers (MLSS, flows and BOD loadings), the process control of the expert system uses the observational r e s u l t s of the color and condition of the mixed li q u o r and aeration tanks, and i t s microscopic inhabitants. The operational goals of the model secondary treatment plant have been incorporated and developed for use i n the expert system. The expert system attempts to maintain the objectives of BOD removal, minimal effluent suspended s o l i d s losses, and b i o l o g i c a l n i t r i f i c a t i o n and d e n i t r i f i c a t i o n u t i l i z i n g the process control parameters available to the operator. Chapter 6 further explains the exact information that was cataloged, assembled and used i n the system and i t also d e t a i l s the process control l o g i c as i t pertains to the expert system developed. 58 Chapter 4.0 The FRO Expert System The WASTES system u t i l i z e s an expert system s h e l l developed by Thomas Froese, a research engineer at U.B.C. who worked under Drs. A.D. Russell and W.F. Caselton. The system s h e l l i s c a l l e d FRO and i n part i s a chaining, rule-based, goal-driven system that provides the expert system reasoning. An expert system created using FRO i s made up of two basic parts: the inference engine and the knowledge base. The inference engine i s the compiled FRO program and i t provides the reasoning system and user interface. The WASTES system i s the structured knowledge base f i l e that i s compiled by the inference engine and executed. INFERENCE ENGINE USER INTERFACE SHELL KNOWLEDGE BASE EXPERT SYSTEM Figure 8 - Expert System Shell Structure 59 The WASTES system consists of not one, but several problem f i l e s . The core of the system i s the "TREAT.KB" f i l e which contains the basic menu structure, the activated sludge system knowledge and the basic treatment system questions. The other related f i l e s are smaller knowledge bases that are loaded according to the needs of the main knowledge base. This separation of knowledge bases minimizes f i l e loading and boot-up times and f a c i l i t a t e s easier l o g i c development and ed i t i n g . Figure 9 represents how the system i s loaded and maintained with respect to the various knowledge bases. Fro's basic task i s to solve primary goal statements as defined i n the knowledge base. In order to solve the primary goal, the expert system may need to solve other sub-goals and so on. The primary goal i s written i n the TREAT.KB knowledge base as: goal run. rule run i f setup and solve. The goal run i s completed i f both setup and solve are solved or proven. Knowledge i s represented i n the form of propositions that are i n the forms of facts, rules and questions for the purpose of solving the primary goal. These propositions have the form: CONCEPT i s VALUE 60 • 10 DDI minium 274 L O A D E D IN M E M O R Y TREAT. KB KNOWLEDGE BASE RBC.KB KNOWLEDGE BASE FILES ON DISK LIFT.KB KNOWLEDGE BASE RACKS.KB KNOWLEDGE BASE GRIT.KB KNOWLEDGE BASE CLAR.KB KNOWLEDGE BASE MICRO.KB KNOWLEDGE BASE FLOAT. KB KNOWLEDGE BASE ODOUR.KB KNOWLEDGE BASE Figure 9 - WASTES System F i l e Structure 61 Where CONCEPT i s some variable or symbol of i n t e r e s t and VALUE i s a value we assign to that concept. Examples of propositions include: Jack i s boy. 'average plant flow' i s 4.25. Both the CONCEPT and the VALUE can be a s t r i n g or an atom. A s t r i n g must be enclosed inside a pair of d o l l a r signs: $What i s the condition of the primary solids?$ $Aeration Tanks$. Strings take up more memory but can be larger than atoms and are used only for p r i n t statements i n WASTES. An atom can contain only lowercase l e t t e r s and consist of a single s t r i n g of characters or be enclosed i n apostrophes. Atoms are used i n a l l forms of the propositions i n the knowledge base: boy the_white_foam 'screen s o l i d s ' . Atoms using uppercase characters are i d e n t i f i e d as VARIABLES. They are special VALUES i n that t h e i r value i s determined through further inference with rules or question statements. The words and names used i n the propositions have no value but are a r b i t r a r y symbols used by the expert system s h e l l to i n f e r l o g i c to further rules. Assigning variables to atoms allows further f l e x i b i l i t y i n the inference structure by increasing the p o s s i b i l i t y of d i f f e r e n t outcomes based on the user input. It i s important that these propositions be worded accurately and 62 p r e c i s e l y . They must convey the understanding of the knowledge and reasoning c l e a r l y . They must also be singular and independent so that one concept does not represent more than one value. The knowledge lo g i c w i l l be accurate and comprehensible i f i t i s assembled this way. In many occasions the knowledge has more than one attribute per CONCEPT. For example, the color of the dog i s brown relates ATTRIBUTE of the CONCEPT (dog) i s VALUE (brown). The dog can also have a s i z e , shape and name ( a l l with d i f f e r e n t values) but i t i s s t i l l the same dog or CONCEPT. Propositions can not have multiple values but by assigning ATTRIBUTES to CONCEPTS we e f f e c t i v e l y get multiple VALUES. The statement form i s : CONCEPT(ATTR 1, ATTR 2, ...) i s VALUE. Multiple attributes provide increased inference r e s o l u t i o n by better defining the knowledge i n the system. In the knowledge base, propositions are written i n the form of fac t s , rules and question statements. Facts are the most basic form of knowledge storage used by the FRO system consisting of a proposition followed by a period. For example: 'average plant flow' i s '4.25'. 'wastewater temp' i s '10.4'. These facts are stored i n the system database and used to solve r u l e s . Generally they represent knowledge that relates to a l l problems, hence are c a l l e d domain knowledge. The above fact 63 statements are good examples of domain knowledge i n the WASTES system. Rules allow the system to perform reasoning by storing the inference relationship knowledge. Rules are made up from a proposition and a premise, which i t s e l f consists of one or more propositions, i n the form: rule CONCEPT i s VALUE i f PREMISE If the PREMISE i s s a t i s f i e d , the proposition i s stored as a fact i n the system and used to solve higher l e v e l statements. In e f f e c t the PREMISE becomes the new goal of the system as i t attempts to solve that p a r t i c u l a r ru l e . If the PREMISE can not be s a t i s f i e d , the rule neither succeeds or f a i l s and the system looks for other means to solve the higher l e v e l query. The propositions i n the premise may be separated by "and", "or", and the use of parenthesis. The "and" separates the propositions i n the PREMISE into separate goals, each of which must succeed i n order for the rule to succeed. The "or" allows the en t i r e PREMISE to succeed i f any one of the separated propositions are proven. The FRO system places l o g i c a l precedence on "and" over "or". The use of l i n e returns, short rule statements and parenthesis aids debugging and l o g i c viewing when the PREMISE becomes quite complex. For example: rule 'check DO1 i f ('type aer' i s 'diffused a i r ' 64 and 'solve DO diffused' and succeed) or ('type aer* i s 'mechanical' and 'solve DO mechanical' and succeed). Note that the value for the concept 'check DO' i s not present. In these cases, FRO assumes the value ' i s true' and continues attempting to prove that concept. The 'succeed' proposition acknowledges that the premise i s completed and the rule i s proven. Question statements enable the system to intera c t with the user i n order to gain information on the VALUE of a CONCEPT i n a proposition. A question statement i s can be written i n the basic form: CONCEPT ask QUESTION a l t (ALT 1, ALT 2, . . . ) . The concept i s the valueless e n t i t y that can be assigned one of the selected alternatives l i s t e d i n the statement (ALT 1, ALT 2, . . . ) . The QUESTION i s a s t r i n g that i s printed to the screen to which the user responds. Therefore the question statement that looks l i k e : 'ask rotate' ask $What i s the c i r c u l a r sludge c o l l e c t i o n scraper arm doing?$ a l t ('rotating', 'not rotating', 'rotating but e r r a t i c a l l y ' ) . would appear on the screen as: What i s the c i r c u l a r sludge c o l l e c t i o n scraper arm doing? 1. rotating 65 2. not rotating 3. ro t a t i n g but e r r a t i c a l l y >>>> The user could then select the best al t e r n a t i v e that answers the system query and i t would continue by assigning that a l t e r n a t i v e value to the CONCEPT. A second l i s t of alternatives can be placed i n the question statement that are assigned as the values to the concept instead of the l i s t e d a l t e r n a t i v e s . This feature allows for more e x p l i c i t a l t e r n a t i v e description with shorter value statements i n accompanying rules. If no alter n a t i v e s are placed a f t e r the question statement, the system waits for a data entry from the user. This i s used with variables i n the rul e statements. An "explain" feature can also provide additional information by p r i n t i n g a user-supplied s t r i n g to the screen. It can expand on the question posed by the system by supplying a more de t a i l e d description. It can explain how the question statement rel a t e s to the l o g i c of the knowledge base and the development of the rules to support a s p e c i f i c goal. It can also explain what information i t hopes to gain from each of the a l t e r n a t i v e s . Simple yes/no questions can be given the form: CONCEPT ask QUESTION a l t yn. i n which a yes/no corresponds to true/ f a l s e value assigned to the CONCEPT. Complex expert systems can be developed using the fact, r u l e and 66 question statements provided i n the FRO system s h e l l . Fact statements can provide basic domain knowledge avail a b l e to the en t i r e system. Rule statements develop the l o g i c structure and main body of the system. The structuring of question statements and t h e i r alternatives form the basis of the user int e r f a c e and input. Combined with e f f e c t i v e i n t e r a c t i o n through p r i n t i n g strings to the screen, WASTES uses these statements to represent the knowledge domain of wastewater treatment plant operations. 67 Chapter 5.0 Development of WASTES Model Developing the knowledge bases for the WASTES system requires: o knowledge a c q u i s i t i o n and development o l o g i c assembly o t e s t i n g the knowledge bases. 5.1 Knowledge Sources Developing the WASTES knowledge base requires extensive research and a c q u i s i t i o n of operational and process control information from both written and human sources. The written sources of information consist of texts s p e c i f i c a l l y written for plant operations and process control, a r t i c l e s from magazines, and research publications from journals. The USEPA has published troubleshooting guides and process control manuals for municipal 26 2 V treatment works. ' Additional troubleshooting information was gained from the Water Po l l u t i o n Control Federation publications on design and operation of treatment f a c i l i t i e s as well as t h e i r monthly series, Operations Forum. Much of his work can be referenced to previous work by A l West of the Environmental 2 8 Protection Agency i n the early 1970's. Other reference materials are c i t e d as they appear. Although much of the raw information used was based on written material, most of the key process control points were gained from personal conversation with Dr. B i l l Oldham, Department of C i v i l Engineering U.B.C., and Mr. G i l Bradshaw of the Environmental Protection Service. 6 8 5.2 Knowledge Development After the raw information was obtained, the expert system, which i s a model of the operational aspects of a treatment plant, was assembled. Before the actual knowledge bases were written, an outline was formed which was developed into the o v e r a l l framework for the system. The f i r s t phase of the outline involved i d e n t i f y i n g the unit operations and processes i n the treatment plant and treatment plant problems. The treatment plant problems divided into two f i e l d s : one that dealt with unit operations and processes, and another with common operational and e f f l u e n t problems. The unit operations were sub-divided and the purposes of each outlined. They were examined i n d i v i d u a l l y and problems were i d e n t i f i e d . The key information that would di s t i n g u i s h what problem or problems were present was i d e n t i f i e d . Parameters examined included those within the unit operation and external to i t . The values of the parameters are the information that would have to be obtained i n t e r a c t i v e l y through the expert system. F i n a l l y , the corrective actions were correlated to the problems i d e n t i f i e d using the parameters. Linking the correct actions to the problem i s the basic role of the expert system. The f i n a l r e s u l t was a diagnostic or l o g i c flowsheet for each unit operation or process that outlined a l l the possible problems, the information required to determine what problems were present, and possible solutions to the i d e n t i f i e d problems. 69 A s i m i l a r process was developed for common operational problems and common effluent v i o l a t i o n s . Each l o g i c structure or tree represents a small independent expert system. The next step was to write the rules that would transform the lo g i c structure into a l o g i c system i n the expert system. Starting with the smallest trees, the rules were coded and knowledge base f i l e s written. Once the coding was keyed into the f i l e s , i t was debugged for l o g i c and syntax errors. Then the l o g i c was tested using the tracing feature i n the FRO s h e l l . The tr a c i n g feature puts a small window i n the bottom of the computer screen that relays the inference path and goals. This allows the user to see exactly what the expert system i s t r y i n g to determine and to locate errors i n the rule l o g i c . The completed small expert system knowledge bases were now ready to be linked together using a menu structure and l i n k i n g rules i n the main knowledge base f i l e , treat.kb. The look and f e e l of the system i s a function of designing a menu structure for an intended user group. One of the goals of the system was to make i t simple enough that a person unfamiliar with wastewater treatment f a c i l i t i e s could operate the expert system, understand what the system i s doing, and learn about the treatment process. At the same time, the system should be designed to be useful to someone f a m i l i a r with wastewater treatment and that person should be able to quickly f i n d an area that he or she i s interested i n and examine i t thoroughly with the system. In order to provide 70 both concepts, the expert system was divided into two d i f f e r e n t f i e l d s with the i n i t i a l system query of whether the user wants to examine a general or a s p e c i f i c area of i n t e r e s t . Menus according to each f i e l d are provided. The s p e c i f i c menu l i s t s the unit operations. If the operator knew the problem was i n the secondary c l a r i f i e r s , he or she would sel e c t that area from the menu and the diagnostics on that unit operation would begin. The general problem menu choice invokes a secondary menu that deals with t o t a l plant problems. Most of these general problems deal with the activated sludge process and ef f l u e n t v i o l a t i o n s . The s i z e and scope of a perceived problem often requires the expert system to examine more than one area of the treatment plant i n order to f u l l y diagnose the problem. This may require examining d i f f e r e n t logic structures and loading more than one knowledge base f i l e . This process i s c a l l e d l i n k i n g . It i s accomplished by providing rules that make the expert system examine unit operations and processes related to the current problem. These rules load other knowledge base f i l e s and assign new system goals. This system i s not an a n a l y t i c a l model but instead i s based on a he u r i s t i c or rule-based system that uses observational data. The expert system i s a representation of the model treatment plant 29 30 and i t s operation developed i n Section 3.0. H i l l , Hobson and 71 West have published a r t i c l e s on the co r r e l a t i o n of v i s u a l observations to activated sludge process operation. Similar v i s u a l observations are used i n the expert system to provide additional information. Common observational data used to i d e n t i f y problems includes: o activated sludge floe type and s e t t l e a b i l i t y o aeration tank foaming and foam type o secondary c l a r i f i e r observations o microbiological examination. These observations are used i n conjunction with monitoring e f f l u e n t BOD and TSS le v e l s , and BOD and F/M loading rates to determine the condition of the activated sludge process. These same c h a r a c t e r i s t i c s have been used i n the WASTES system to develop a controller/diagnostics routine. The knowledge base i n t e r a c t i v e l y records observations and by consulting the domain knowledge and i n f e r r i n g through the rule structure suggests probable causes and remedies for common activated sludge problems. The basis for the process control system i n WASTES i s i l l u s t r a t e d i n Table III. 5.3 Completing the Knowledge Bases With basic system structure and knowledge bases completed, attention was focused on f u l l y developing the system. The content of each knowledge base was reviewed and most f i l e s were s i m p l i f i e d and reduced i n si z e . Reducing the o v e r a l l s i z e of the combined knowledge bases allows a l l the program and knowledge 72 t-3 cr CD h o CJ CD 10 CO n o 3 ft n o o iQ I— o c CO CD a cr •< > CA t-3 W cn CLARIFIER SOLIDS CONDITION SLUDGE SETTLE RELATIVE F/M LOADING CLARIFIER SLUDGE BLANKET OTHER CONDITIONS IDENTIFIED PROBLEM RECOMMENDED ACTION BILLOWING THROUGHOUT CLARIFIER AREA SLOW SLOW SLOW HIGH LOW INCREASED SLOWLY FOAMING FILAMENT. ORGANISMS F/M TOO HIGH F/M TOO LOW BULKING SLUDGE DECREASE WASTAGE INCREASE WASTAGE INVESTIGATE CAUSES CHECK B BILLOWING IN PARTS OF CLARIFIER AREA INCREASED RAPIDLY INCREASED RAPIDLY INCREASED SLOWLY TOO HIGH PUMPS NOT WORKING PIPES CLOGGED WIND/NO COVER CHECK EFFLUENT WEIRS BROKEN RSF PUMPS RSF TOO LOW RSF TOO LOW RSF TOO LOW WEIRS NOT LEVEL REPAIR OR BACK-UP PUMPS INCREASE RSF INCREASE RSF INCREASE RSF ADD COVER OR WIND BREAK LEVEL EFFLUENT WEIRS CHECK C CLUMPS AND MATS OF RISING SOLIDS FAST LOW LOW BLACK SOLIDS BROWN OR TAN SOLIDS SEPTIC OR LOW DO DENITRIFICATION INCREASE RSF DECREASE WASTAGE ASH-LIKE SOLIDS ON CLARIFIER SURFACE FAST GREASE IN INFLUENT BEGINNING DENITR. CHECK PRIMARY CLARIFIERS CHECK C DISPERSED SOLIDS OR CLOUDY EFFLUENT SLOW/NORM. FAST FAST HIGH LOW INACTIVE ROTIFERS PLANT START-UP FOAMING FOAMING TOXIC LOADING F/M TOO HIGH F/M TOO LOW F/M TOO HIGH DECREASE WASTAGE DECREASE WASTAGE INCREASE WASTAGE NO WASTAGE FOR 10 DAYS base f i l e s to f i t on one 5.25" floppy disk, and reduced the response time for f i l e loading and disk read/write operations. This kept the system portable, convenient and compatible with a wide v a r i e t y of computers. Continued use and t e s t i n g revealed that further streamlining was necessary i n order that the knowledge presented was accurate and easy to understand. The i n i t i a l system was several smaller expert systems t i e d together. Integrating the domains together by adding more l i n k s would f i l l out the system. Several knowledge bases were added l i k e float.kb and odour.kb to deal with a common problem over the en t i r e plant process. The float.kb knowledge base deals with f l o a t i n g material and the odour.kb knowledge base deals with odour i n a l l unit operations. Large rules had been written i n an e f f o r t to get most accurate representation of the t r e e - l i k e l o g i c structure. Unfortunately these large rules were very d i f f i c u l t to debug, edit and re-program. Most of the rules were broken down into numerous smaller rules making the l o g i c structure c l e a r e r and more readable without changing the siz e of the program. While the WASTES system was being developed, the FRO s h e l l was also constantly updated. Changes i n the p r i n t s t r i n g structure i n the FRO s h e l l permitted enhanced formatting but necessitated changes i n a l l knowledge bases. New user features were added including explain and show functions. These features enhanced the WASTES system considerably by displaying more information on what the expert system i s doing. While the expert system has remained dedicated as a diagnostic and s o l u t i o n -oriented program, further e f f o r t has been made to round out the 74 knowledge bases by providing relevant information to the user at a l l l e v e l s i n the system. Statements have been added at most l o g i c a l points to provide detailed solution choices. In cases where a solution i s not developed the system suggests alter n a t i v e s or other areas to examine before the expert system i s consulted again. 5.4 Knowledge Logic Structures This section i s a breakdown of the in d i v i d u a l knowledge bases i n terms of the function and lo g i c used. Each section i s designed to the following format: Knowledge Base: Name of the knowledge base f i l e used by WASTES Purpose: A Description of the goals of the knowledge base f i l e . Problems: A l i s t the major problems addressed by the knowledge base. Parameters: The information WASTES uses to determine the solution to the problems. Solutions: A l i s t of the possible actions ava i l a b l e to solve or remedy the problems. Logic Structure: A flowchart i l l u s t r a t i n g the rule structure of the knowledge base. The l o g i c structure for each process or operation being investigated, proceeds from s t a r t to f i n i s h i n the order that i t i s represented by the expert system (see Figure 10). The diamond 75 shapes are questions or rules that denote nodes i n the system. The rectangles represent rules that produce general information. The "STORE" command indicates information that i s stored by the system and used l a t e r . The PRINT "information" are samples of the information relayed to the user by the system. The "LINK" statement beside some of the shapes show where that knowledge base l i n k s to other knowledge bases i n the WASTES system. The preceding subsections introduce each knowledge base and give a general description as to what the knowledge base performs. The problems, described i n point form, l i s t the various problems that the knowledge base can solve. The parameters are a l i s t of the information that WASTES w i l l use to determine one or more of the solutions l i s t e d below. These l i s t s are i n point form and appendix 1 contains the actual f i l e l i s t i n g which complements each subsections. The flowcharts describe the l o g i c process that the expert system uses for each knowledge base, where l i n k s occur between knowledge bases, and the structure of queries that WASTES uses to extract information from the user of the system. More deta i l e d results and p r i n t strings are given i n the corresponding knowledge base l i s t i n g i n appendix 1. 76 5.4.1 Knowledge Base; LIFT.KB Purpose: Diagnose and troubleshoot raw sewage l i f t f a c i l i t i e s at wastewater treatment plants. Problems; o not operational o excessive noise o reduced discharge Parameters: o type of l i f t pump o number of i n s t a l l e d and on-line l i f t pumps o condition of pump Solutions: Correct condition o discharge - put more pumps on-line;use back-up pump(s) o operation - repair or shut down o noise - servicing 77 START STORE GRAVITY FEED CENTRIFUGAL SCREW PRINT "CHECK DRIVE ASSEMBLY, MOTOR, CONTROLLER, OR BREAKER" YES PRINT "CHECK CAVITATION, WEAR, DEBRIS, SUBMERGENCE, LUBRICATION PRIMING, OR BEARINGS" PRINT "CHECK MOTOR SPEED. DEBRIS, HEAD, AIR LEAKS, OR LIFT" Figure 10 - LIFT.KB Logic Structure 78 5.4.2 Knowledge Base: RACKS.KS Purpose: Preliminary treatment diagnostics of the unit operations of bar 32 screens and shredding devices. Problems: Inadequate debris removal from racks o Build-up on racks creates backwater and head loss Debris disposal o debris at t r a c t s f l i e s and creates odours o excessive debris a disposal problem Shredder operation o poor operation might hamper downstream operations l i k e scum removal and clogged aerators Parameters: o number of i n f l u e n t channels o cleaning frequency of bar racks o type of bar racks o condition of shredder and shredded so l i d s Solutions: o increase cleaning frequency o bypass channel o change bar rack design o i n s t a l l shredding device o r e p a i r shredder blades o repair mechanical problems 79 5 . 4 . 3 K n o w l e d g e B a s e : G R I T . K B P u r p o s e : D i a g n o s t i c s o f s e d i m e n t a t i o n a n d a e r a t e d g r i t t a n k s u s e d t o 33 34 r e m o v e s a n d , g r i t a n d g r a v e l f r o m t h e t r e a t e d s e w a g e . ' P r o b l e m s : I n a d e q u a t e g r i t r e m o v a l o c l o g s l u d g e r e m o v a l p i p e s o r u i n pump i m p e l l e r s o c e m e n t i n g e f f e c t i n p r i m a r y s l u d g e o w e a r a n d a b r a s i o n o n b e a r i n g s o l o s s o f a v a i l a b l e v o l u m e i n p r i m a r y c l a r i f i e r s a n d s l u d g e d i g e s t e r s C l o g g e d / b r o k e n g r i t r e m o v a l m e c h a n i s m o b u i l d - u p o f g r i t i n c h a m b e r r e d u c e s g r i t r e m o v a l P a r a m e t e r s : o t y p e o f g r i t t a n k o n u m b e r o f i n s t a l l e d a n d o n - l i n e g r i t t a n k s o c o n d i t i o n o f r e m o v a l m e c h a n i s m o s u f f i c i e n t g r i t r e m o v a l S o l u t i o n s : o b y p a s s f a u l t y t a n k o r a i s e e f f l u e n t w e i r o a d j u s t g r i t r e m o v a l m e c h a n i s m o r e p a i r g r i t r e m o v a l m e c h a n i s m o r e s e t c i r c u i t b r e a k e r 8 1 00 c h CD so tt) f o o n-n c fl ft d n (D STORE STORE # OF TANKS ONLINE & INSTALLED TYPE OF GRIT TANKS YES RESET? > NO PRINT "BYPASS TANK OR REPAIR" YES < ^ W ^ O F ^ ^ > AERATED SETTLING PRINT "DECREASE AERATION OR OR INCREASE WEIR HDGHT" PRINT "REMOVE CLOG AND CHECK SYSTEM" PRINT "INSURE GRIT IS REMOVED DAILY" 5.4.4 Knowledge Base: MICRO,KB Purpose: To diagnose the common operational problems that occur with 35 microscreens. Problems: o accumulation of solids i n inf l u e n t chamber o loss of so l i d s through screen o slime build-up o e r r a t i c rotation Parameters: o drum rotation speed and condition o condition of so l i d s at microscreen o drive system and c i r c u i t breaker o number of i n s t a l l e d and on-line microscreens Solutions: o increase drum speed o repair drum screen o re p a i r drive unit and/or motor o bypass faul t y microscreen o i n s t a l l spray washers 83 00 •fl I— C H (D Co n JO o CO f o U3 o Ui f t c o f t c h a> STORE ASK # OF INSTALLED AND ONLINE UNITS PRINT "CHECK MOTOR AND-DRIVE ASSEMBLY" •NO BYPASS < ^ U M ^ R O W T C ^ > YES -STORE - BUILD—UP LOSS-CHECK CAUSE OF SOLIDS LOSS NORMAL PRINT "INCREASE DRUM SPEED OR ADD CAPACITY" REPAIR -SCREEN < AREA ^ UNKNOWN ' SKIRT PRINT "REPAIR DRUM SKIRT PRINT "REPAIR DRUM SCREEN" END "NO PRINT "CHECK UNIT OVER AGAIN" CHECK SUME? YES • REPAIR ^ C t t E ^ M O F -BYPASS PRINT "INSTALL SPRAY WASHERS 5.4.5 Knowledge Base; CLAR.KB Purpose: To diagnose the operation of the primary and secondary c l a r i f i e r s 36 37 38 including sludge and scum removal. ' ' Problems: Loss of so l i d s o hydraulic or solids overloading o inadequate sludge removal o weir placement o secondary currents due to flow, wind and temperature Mechanical problems o sludge pumping o scraper mechanism operation Scum removal o inadequate removal o clogged weirs o excess f l o a t i n g solids Parameters: o type of c l a r i f i e r s o number of i n s t a l l e d and on-line c l a r i f i e r s o sludge scraper operation o sludge pumping operation o flow into c l a r i f i e r s o condition of scum removal o type of solids loss ( i f any) o a i r and wastewater temperature (secondary only) Solutions: o bypass c l a r i f i e r ( s ) o r e p a i r motor/drive assemblies o increase sludge pumping o l e v e l effluent weirs o provide more c l a r i f i c a t i o n capacity o check i n l e t d i f f u s e r s o increase aeration i n activated sludge tanks (secondary only) o provide cover over c l a r i f i e r s o use back-up sludge pumps 85 00 ON I— C n 4^  I n > to o I— o CO rt H c o rt C h CD STORE STORE LINK START ASK TYPE OF PRIMARY CLARIFIERS ASK # OF INSTALLED ANO ONLINE CLARIFIERS CHECK DIGESTER SUPERNATANT CHECK PRELIMINARY OPERATIONS RACKS.KB CHECK SCUM REMOVAL SOUDS PRINT "BYPASS CLARIFIER OR PUMP DILUTE SLUDGE" ROTATING-PRINT "CHECK FOR BENT PLOWS. TOO MUCH SLUDGE. OR GRIT BUILD-UP" PRINT "SHOULD BE ROTATING -AT 0.02 - 0.06 RPM" GOTO SOLIDS CLUMP R E - C H E C K SYSTEM-SMELL H2S? CHECK COVER TEMPERATURE; FLOWS PRINT "HYDRAULIC OVERLOADING" PRINT "ADD CAPACITY AND INCREASE AERATION IN 5ECON0ARY" CHECK WEIR5 SCRAPER OPERATION R E - C H E C K SYSTEM L. C O R R E C T E D ? > Y E S -PRINT "INADEQUATE SLUDGE PUMPING-.IN CREASE RATE" PRINT "BALANCE FLOWS TO ALL CLARIFIERS" • Y E S Y E S PRINT "PUMP SYSTEM FAILURE CHECK CLARIFIERS ANO USE B A C K - U P EQUIP." 5.4.6 Knowledge Base; RBC.KB Purpose; Diagnose and troubleshoot the rotating b i o l o g i c a l contactor (RBC) treatment system that provides BOD removal from municipal wastewater.39 Problems; o organic overloading o excessive sloughing o broken shaft/media o mechanical drive/motor problems o to x i c loadings Parameters: o condition and color of RBC biomass o v i s u a l inspection o speed of rotation (RPM) Solutions; o bypass part of flow around 1st stage o increase/decrease RPM o add aeration o r e p a i r or replace broken shaft/media o check solids i n c l a r i f i e r s 87 00 00 ua c H CD 50 00 n to f o o co rt H O rt C H CD YES I BYPASS AND REPAIR-YES I BYPASS AND REPAIR -PRINT EAKER" EXCESSIVED SLOUGHINC NORMAL LINK < feK RBC RPMJ> 2. ' 1<RPM<2 PRINT "ADJUST RPM" PRINT "POSSIBLE AIDS INCLUDE INCREASED AERATION BAFFLING AND INCREASED RPM" LOAD PC.KB AND SOLVE PRIMARY SOUDS PRINT "ORGANIC OVERLOADING" PRINT "POSSIBLE TOXIC LOADING— ALLOW SYSTEM RECOVERY" YES -ACTIVE PRINT "CHECK FOR REDDISH FILM ON LAST STAGES" • YES MTRIFY? NO PRINT "PREVENTATIVE MAINTANENCE" 5.4.7 Knowledge Base; FLOAT•KB P u r p o s e ; Determines the cause or source of f l o a t i n g s o l i d s or scum on the 40 primary c l a r i f i e r s , aeration tanks and secondary c l a r i f i e r s . Problems; o scum or s o l i d s on the primary c l a r i f i e r s o foam on the aeration tanks o scum, foam or solids on the secondary c l a r i f i e r s Parameters; o unit operation with problem o type of sol i d s or scum o source of foam or scum o loss of s o l i d s from unit operation Solutions; o check loading on aeration tanks o check sludge wastage from primary c l a r i f i e r s o check sludge wastage from secondary c l a r i f i e r s o i n s t a l l b a f f l e s at aeration outlet o check preliminary unit operations o check primary c l a r i f i e r scum removal 89 O • f l iQ C n CD •fl f o > •-3 03 O iQ H-O Ui r+ H e o rt C h ro MOSTLY DEBRIS MOSTLY FOAM PRINT "INSTALL BAFFLES IN AERATION TANKS" YES" PRINT "CHECK SOUDS IN CLARIFIERS AERATION TANKS" SECONDARY CLARIFIERS < ^ L O C A ^ PRIMARY CLARIFIERS-AERATION TANKS SCUMMY DARK BROWN < FOAM TYPET> WHITE BILLOWING" LIGHT BROWN PRINT "NORMAL FOR AVERAGE ACTIVATED SLUDGE SYSTEM" LOAD PC.KB AND SOLVE PRIMARY SCUM UNK PRINT "CAUSES COULD BE OVERLOADING START-UP, OR TOXIC LOADING" LOAD PC.KB AND SOLVE PRIMARY SCUM UNK PRINT "NORMAL FOR UNDERLOADED ACTIVATED SLUDGE SYSTEM" LOADING AND WASTE SOUDS CHECK U N K END 5.4.8 Knowledge Base; ODOUR.KB Purpose; Diagnoses source of disagreeable odours from treatment plant and d i r e c t s action to source of problems. Problems: Disagreeable odour from: o aeration tanks o anoxic reactor o primary c l a r i f i e r s o secondary c l a r i f i e r s Parameters: o l o c a t i o n of odour o subjective type of odour Solutions: o increase aeration i n aeration tanks o check primary sludge wastage o check secondary sludge wastage o add pre-aeration 91 START STORE AERATION TANKS ANOXIC REACTORS PRIMARY CLARIFIERS SECONDARY CLARIFIERS PRINT "NORMAL CONDITIONS FOR OPERATION" ANOXIC REACTORS< AREA > AERATION TANKS PRINT "NORMAL CONDITION" PRINT "CHECK SOUDS, INFLUENT CONDITIONS" PRIMARY < CLARIFIERSJ> SECONDARY PRINT "CHECK D.O. LEVELS AND SOUDS CONDITION" PRINT "LOW D.O. CONDITIONS" CHECK AERATION SYSTEM AND D.O. UNK 5.4.9 Knowledge Base: TREAT.KB The TREAT.KB knowledge base contains the menu system, basic plant lay-out questions, and the diagnostics for the activated sludge system and the aeration system 41/ 4 2/ 43 ,and the secondary c l a r i f i e r s . 4 4 Part 1: Aeration System  Problems: o unbalanced aeration o clogged aerators o broken a i r piping/compressors o low DO o high DO o f a u l t y mechanical aerators o overmixing Parameters: o v i s u a l inspection o DO meter inspection o type of aerators Solutions: o re p a i r of piping/compressors o balance valving o clean/replace/adjust aerators o increase/decrease aeration (DO) o check motors/drives/circuit breaker/power PART 2: Activated Sludge Process Control Problems: o excess effluent BOD o excess effluent suspended so l i d s o excess effluent NH4 o excess effluent N O 3 o improper organic loading (F/M) o improper wastage o improper return s o l i d s flow o secondary sludge pumping o scraper mechanism operation 93 o inadequate scum removal o clogged weirs Parameters; o color of activated sludge floe o r e l a t i v e MLSS concentration o type and color of aeration tank foam o r e l a t i v e F/M loading o BOD t e s t results o type of s o l i d s loss ( i f any) o sludge s e t t l i n g c h a r a c t e r i s t i c s o microbiological observations o process type o n i t r i f i c a t i o n / d e n i t r i f i c a t i o n expected 4 5 o number of i n s t a l l e d and on-line secondary c l a r i f i e r s o sludge scraper operation and type o sludge pumping operation o sludge blanket thickness o plant flow o condition of scum removal o a i r and wastewater temperature o sludge disposal method Solutions: o increase/decrease wasting o change wastage (F/M) control method o increase/decrease return so l i d s flow o bypass secondary c l a r i f i e r ( s ) o r e p a i r motor/drive assemblies o l e v e l e ffluent weirs o provide more c l a r i f i c a t i o n capacity o check i n l e t diffusers/balance flows o check DO requirements o provide cover over c l a r i f i e r s o use back-up sludge pumps o process modifications and additions 94 CHECK C O M P R E S S O R ; AIR LINES CONTROLLER C H E C K AERATOR TYPE 1 C H E C K R A C K S . K B AND R E P L A C E AERATORS C H E C K AND R E P L A C E AERATORS ' INCREASE BITE OR INCREASE S P E E D OR DURATION" PRINT "DECREASE BITE DURATION OR SPEED" PRINT "INCREASE BITE DURATION OR S P E E D " END PRINT "INCREASE AERATION" BELOW IN RANGE ABOVE PRINT "DECREASE AERATION" START / CHECK COLOR OF CHECK TEMP. FOAM. / SLUDGE, MLSS AND AERATION TANK COLOR STORE STORE GO TO S.S. PRINT "INCREASE RECYCLE OR REACTOR VOLUME" POST PRINT "INCREASE REACTOR VOLUME" ^XHIGtN^ <mUIENT N03^ > PRINT "INCREASE MLSS BY DECREASING WASTING" YES PRINT "HIGH E.S.S. WILL RESULT IN HIGH E.B.OD." CONTROLLER TABLE CHECK CLARIFIERS SOLIDS LOADINGS CHECK SECONDARY CLARIFER BLT CHECK WASTING FROM SYSTEM 1 I CHECK AIR AND W.W. TEMPERATURE T MICROSCOPIC CHECK FOR ORGANISMS CHECK PROCESS DESIGN T r NO I PRINT "MAINTAIN MINIMUM BLT' „ RETURN _ SAME<SLUDGE FLOW> DECREASE-INCREASE • PRINT "DECREASE RSF -10-15 X " • PRINT "INCREASE RSF 10-15 X' CHECK MECHANICAL SYSTEMS CHECK ACTIVATED SLUDGE SETTLEABILITY CHECK § OF ONLINE AND INSTALLED CLARIFIERS ACTIVATED SLUDGE PHYSICAL PROPERTIES CHECK RELATIVE F / M LOADING CHECK RETURN SLUDFE aOW SYSTEM CONDITION OF CLARIFIER SUSPENDED SOLIDS BILLOWING ALL AREAS BILLOWING SOME AREAS ASH-UKE SOUDS CLUMPS AND MATS OF SOUDS CLOUDY EFFLUENT DISPERSED SOUDS TABLE 3 - CONTROLLER LOGIC VO ~4 C H CD K J o > o rt < rt CD a C/J i—• c a cQ CD •d n o o CD CO co o o 3 rt H O •3 03 PRINT "USE MCRT" • MCRT-MLSS CONTROLLER TABLE PRINT "BALANCE FLOWS TO ALL CLARIFIERS" • Y E S < B A L A N C E D ? . > N ° -YES I PRINT "WASTE FROM RSF' PRINT "BYPASS CLARIFIER OR PUMP DILUTE SLUDGE" PRINT "SHOULD BE ROTATlNC AT 0.02-0.06 RPM OR MOVINC AT 0.3-1.0 M/MIN" ROTATING/MOVING ERRATICALLY I PRINT "CHECK FOR BENT PLOWS. TOO MUCH SLUDGE. OR CRJT BUILD-UP' GO TO PUMPS SAME WASWX^> INCREASE PRINT "DECREASE MCRT OR MLSS" DECREASE PRINT "INCREASE MCRT OR MLSS" PUMPS PRINT "USE BACK-UP" PRINT "USE BACK-UP AND CHECK FOR CLOCS" YES CHECK f OF INSTALLED AND ONUNE CLARIFIERS CHECK TYPE OF SECONDARY CLARIFIERS Chapter 6.0 Results The r e s u l t of the research i s a completed functional expert system capable of demonstrating the potential of combining a knowledge-rich domain, wastewater treatment plant operations and process control, and a powerful f l e x i b l e expert system s h e l l . The diskette i n Appendix 4 contains the functioning WASTES system, the r e s u l t of the work undertaken. I n i t i a l l y , research determined whether process control and troubleshooting procedures could be used i n conjunction with h e u r i s t i c or rule-based programs i n comparison to the bulk of systems modeling research which took more numerical approaches. It was found that although the h e u r i s t i c f i e l d i s r e l a t i v e l y new, there i s currently extensive research underway and increasing volumes of available information. This research represented a new d i r e c t i o n for the analysis of wastewater treatment plant operations. In general, most of the i n i t i a l research time was spent on gathering the domain knowledge to put into the system. The development time to produce the WASTES expert system was reduced by s e l e c t i n g a capable, f u l l - f e a t u r e d expert system s h e l l . The s h e l l was not overly complicated, d i f f i c u l t to use or ed i t , and i t had a user interface that suited t h i s research. The research has progressed through several milestones. Afte r the i n i t i a l investigations and decision to go ahead with the 98 d i r e c t i o n of the research, the f i r s t was reached when the framework for the system was completed and the raw information was gathered and edited, and getting the system operational and l o g i c a l . This required extensive debugging though each part of the system and checking the output of the s h e l l against the l o g i c a l structure intended i n i t s design. Once the information was placed i n the knowledge bases and used, the c e r t a i n l i m i t a t i o n s of the expert system and the knowledge bases system became apparent. From the hardware perspective, the si z e of the WASTES knowledge bases were too large for the computer's 640 Kb memory and caused the FRO system to f a i l . The WASTES system also had too many hard disk read-write operations, which slowed the program down u n t i l i t was inoperable. To solve t h i s problem the large single knowledge base was broken down into smaller associated domains. The single Treat.kb i s loaded and executed by the s h e l l , but only loads the other related f i l e s as required by the system i n response to the user's input. The process of breaking down the larger domain into small applications that could be r e a d i l y inputted, debugged and then linked together had other benefits. The smaller domains, i n the form of separate ".kb" f i l e s , could be e a s i l y checked for errors i n syntax and l o g i c . Since debugging was the most time consuming task, breaking the system up, as well as the tr a c i n g feature of the s h e l l , led to faster development of the system. The separation of the larger domain into smaller domains also 99 benefited the system development because the process stream i n the model treatment plant was composed of unit operations with s p e c i f i c purposes and in d i v i d u a l operations. These unit operations were developed as complete knowledge bases before the entire system was assembled. Each smaller domain could be run as a separate knowledge base and i n d i v i d u a l errors i n the l o g i c and p r i n t statements could be corrected. The tr a c i n g feature of the FRO s h e l l was invaluable and f a c i l i t a t e d the development of the large WASTES system by finding errors r e l a t i v e l y e a s i l y . F i n a l l y , the system was put together and linked using a feature of the s h e l l that loaded the f i l e s and would involve the new information with the exi s t i n g knowledge base i n the computer memory. The user interface depends on the rule structure, the amount of knowledge contained i n the system, and the querying structure of the s h e l l . What information the user of the system receives from the expert system also depends on t h i s interface, as well as his own c a p a b i l i t i e s of understanding the information presented. The rule structure determined the order i n which information was imparted from the user to the system. By the nature of the knowledge base and the s h e l l , the system moves from general to s p e c i f i c , from problem to solution. It solves problems by asking increasingly s p e c i f i c questions that narrow the possible solutions to a single i n d i v i d u a l solution. The system does not give the most probable solution, but the solution determined by 100 the answers the user has returned. This method requires that every branch of the l o g i c structure have a conclusion that f i t s the l o g i c that reaches that point. The l o g i c for the activated sludge process c o n t r o l l e r best represents t h i s as a l l conditions lead to a solution. If the l o g i c determines that no r e a l s o l u t i o n can be determined then the system must return that information. This i s the major drawback of using a deterministic rather than a p r o b a b l i s t i c system. It was compensated by the fact that the FRO s h e l l would ask questions i n the order they were read from the knowledge base. Using that f a c t , I could bias the s h e l l by invoking the most probable s i t u a t i o n f i r s t , decreasing to the least probable. This bias was based on my own development of the knowledge base structure and not on any mathematical p r o b a b i l i t i e s developed i n the s h e l l . If p r o b a b i l i t y was used i n the s h e l l , I doubt that there would be as large a scope of information i n the knowledge bases. The computer hardware lim i t a t i o n s would have reduced the scope of my research and fundamentally altered the goals of the research i f I had not broken the system into smaller related knowledge bases. One of the goals was to produce a system that embraced a f a i r l y wide domain of knowledge about a s p e c i f i c f i e l d , wastewater treatment plant operations. However, there i s a minimum amount of information and depth within the expert system that must be developed so that i t assumes the i n t e r a c t i v e c h a r a c t e r i s t i c that makes i t unique. A narrow scope or f i e l d e n t i t l e s a domain to possess a l o t of knowledge within the 101 subject area without a large s i z e . A wider scope requires an increased s i z e to maintain the sense and f e e l of the in t e r a c t i v e expert system, and present the technical information and knowledge. The WASTES system i s large because the scope of the domain i s wide and there was attention to providing the interactiveness and correct information i n a l l areas of the knowledge bases. The interactiveness of the expert system i s a function of i t s querying c a p a b i l i t i e s . The FRO system provides menus and accepts user input which increases the range and f l e x i b i l i t y of user responses. An e f f o r t was made to use question statements rather than fact statements i n the WASTES knowledge bases. By u t i l i z i n g question statements, the knowledge base i s larger but provides a more f l e x i b l e and intere s t i n g system. One of the o r i g i n a l goals was to i n e f f e c t replace the operator with t h i s i n t e l l i g e n t expert system to run the treatment plant. It quickly became apparent that there are several obstacles to face, besides the domain being so large and diverse for t h i s one system. One problem i s that treatment operations are s i t e - s p e c i f i c and unique to each location; accurate systems would have to be designed for each plant. Without adequate s i z e , these expert systems would not possess the depth of knowledge necessary to deal with a l l types of plants and t h e i r problems. Without d e t a i l 102 and accuracy, the p r a c t i c a l i t y and usefulness of these systems are reduced considerably. The a v a i l a b i l i t y and consistency of the domain knowledge proved to be another l i m i t a t i o n . The source of raw information was generally written data from other people who had investigated wastewater treatment plant operations and v i s u a l aspects of activated sludge process control. Other sources, such as interviewing operators and other experts, often provided information that was contrary to other previous information. The knowledge engineer determines what was correct and relevant i n the face of c o n f l i c t i n g information. This requires the knowledge engineer to have access to an expert with the f i e l d he or she i s attempting to reduce into a workable expert system. Another problem encountered i s that i n many cases i n the WASTES system there are no hard solutions to the problems. The problem faced i s i n fact unanswerable given the avail a b l e information. This requires the knowledge developer to engineer a system that provides answers for these d i f f i c u l t questions that s a t i s f y the user and d i r e c t him to further areas to investigate for more information. It also leads the researcher to investigate the use of p r o b a b i l i t y and uncertainty, for which the FRO s h e l l i s f u l l y capable of representing using Dempster-Shafer theory. The use of a system l i k e WASTES as a teaching t o o l became apparent considering the lack of coherent process control 103 information and the poor medium that exists i n t r a n s f e r r i n g t h i s knowledge or s k i l l to new operators. A new operator generally learns his trade by experience, reading and course work. An expert system could be used to i n t e r a c t i v e l y i l l u s t r a t e the basics of plant operations and activated sludge process control to students operators. An expert system combined with real-time graphics could i l l u s t r a t e process changes as flow and loadings changed and the function of the various unit operations based on the actual f a c i l i t y ' s operational data and operator knowledge. Interactive changes i n operation i n the treatment plant operation would be simulated by the program and v i s u a l l y displayed. The system could describe the sampling and monitoring required to provide process control data i n conjunction with other v i s u a l information. The software and processing power required to develop these sophisticated programs i s available. Education and t r a i n i n g systems i s the one application using expert systems that has the highest potential for p r a c t i c a l commercial a p p l i c a t i o n and could provide the greatest benefits. 104 Chapter 7.0 Conclusions This research involved the development of an expert system from raw information to a demonstration l e v e l i n a new ap p l i c a t i o n domain: wastewater treatment. Researching and assembling the raw information, i d e n t i f y i n g the v i t a l pieces of knowledge, and developing the l o g i c structure were the i n i t i a l accomplishment i n t h i s research. Coding the information into the knowledge bases and t e s t i n g , both the whole system and each of i t s parts, was the most time consuming task. The f i n a l accomplishment i s presenting a functioning system, enclosed on a diskette i n Appendix 4, that demonstrates the applications of expert systems i n the f i e l d of wastewater treatment operations, with respect to diagnosis, problem solution and control of the treatment operations. The amount of knowledge involved i n the f i e l d of wastewater treatment, both design and operations, and the type of knowledge, that much of i t i s experience-based, proves i t ideal for development of expert systems applications. The a b i l i t y of the system to begin at a general l e v e l and work down to s p e c i f i c problems or circumstances by way of the inference of the expert system i l l u s t r a t e s i d e a l l y the diagnostics of problem-solving wastewater treatment problems. The system contains a great deal of information that can be presented to the user i n a way that promotes understanding of the reasoning and lo g i c behind a decision. This feature of the expert system broadly supports the idea of u t i l i z i n g systems l i k e WASTES as t r a i n i n g and development tools to support the transfer 105 of human knowledge and understanding of a f i e l d l i k e wastewater treatment operations and diagnostics. 106 Chapter 8.0 Recommendations There are several recommendations with regards to future research i n the f i e l d of expert systems applications for wastewater treatment plant operation. The f i r s t recommendation i s to incorporate some aspects of uncertainty into the wastes system using the shell-based uncertainty system i n the FRO s h e l l . 4 6 The key areas would be i n activated sludge process control and problem determination. The system could return the most l i k e l y problem, the user could choose to accept t h i s or ask for the next l i k e l y problem based on s t a t i s t i c a l r e s u l t s . The use of p r o b a b i l i t y would also reduce the r i g i d tree structure of the present WASTES system, allowing for a wider range of possible problems and sol u t i o n . The second recommendation would be to f i e l d t e s t the system at an operating wastewater treatment plant, customizing the system to the problems i d e n t i f i e d at the f a c i l i t y . In t h i s case, just a small part of the whole process could be investigated i n conjunction with developing the p r o b a b l i s t i c s h e l l . The addition of further information i n the areas of actual numerical data would be advantageous i n developing a f u l l e r process control program. The e x i s t i n g s h e l l could also be applied to other research i n the Environmental Engineering Group at U.B.C. such as: 107 o municipal waste l a n d f i l l s i t i n g requirements o toxic waste treatment option determination o lab-scale process c o n t r o l l e r s using personal computers o b i o l o g i c a l phosphorus removal process control o b i o l o g i c a l phosphorus removal process design. In the area of teaching ( s p e c i f i c a l l y with regards to treatment plant operations), these i n t e l l i g e n t systems could educate pote n t i a l plant operators and environmental engineers i n the fundamentals of treatment plant operation and process control by demonstration and interactive displays. The base of knowledge involving b i o l o g i c a l phosphorus removal could also be developed using expert systems. It would be an ideal area to develop both c o n t r o l l e r s and design systems u t i l i z i n g p i l o t plant f a c i l i t i e s . Other research, such as l a n d f i l l s i t i n g , impact assessment and monitoring, could e a s i l y be adapted and used i n expert systems. 108 Chapter 9.0 Endnotes 1 Beck, M.B., "Modelling and Control Studies of the Activated Sludge Process at Norwich Sewage Works", Trans. Inst. MC,  Vol. 6, No. 3, July 1984. 2 Prog. Water Tech. Vol. 9 Nos. 5/6, pg. 562 3 Automatica Vol. 16, 1980, pg. 698 4 Jenkins, W.O., "Activated Sludge Process Control By Operator Experience", Department of C i v i l Engineering, Imperial  College, London, 1982. 5 Maeda, K., "A Knowledge Based System for the Wastewater Treatment Process", IFAC 9th T r i e n n i a l World Congress, 1984. 6 Johnson, D.M., "Diagnosis of Wastewater Treatment Processes", Computer Applications i n Water Resources, pgs. 601-608, 1985. 7 Journal of Computing i n C i v i l Engineering Vol. 1 No. 4, pg. 300-301 8 Water Po l l u t i o n Control Federation, MOP/11 Operation of  Wastewater Treatment Plants: a manual of p r a c t i c e, 1979 pg.23. 9 United States Environmental Protection Agency, Process Control Manual for Aerobic B i o l o g i c a l  Treatment F a c i l i t i e s , 1977, EPA-430/9-77-006. pg. 11-94. 10 Metcalf and Eddy,Inc., Wastewater Engineering  Treatment/Disposal/Reuse, McGraw-Hill, 2nd Ed., 1979, pg. 336. 11 Metcalf and Eddy,Inc., pgs. 336, 350. 109 12 WCPF, MOP/11, pg. 119. 13 Hobson, T., "Process Control Fundamentals Part V -Measuring Aeration Basin Dissolved Oxygen", Operations Forum, Oct 1986, pg. 32. 14 WPCF, MOP/11, pg. 125 15 United States Environmental Protection Agency, Operational Control Procedures for the Activated Sludge  Process, Part 1 - Observations, EPA-330/9-74-001 A, 1973. 16 Hobson, T., "Process Control Fundamentals Part X - Sludge Quality Approach", Operations Forum, Mar 1987, pg. 27. 17 Kay, G.H., "Operation of an Overloaded Activated Sludge Plant", Senior Course for Sewage Works Operators, 1969, pg. L-27. 18 Metclaf and Eddy,Inc., pg. 421. 19 Hobson, T., "Process Control Fundamentals Part VIII - More on Sludge Wasting", Operations Forum, Jan 1987, pg. 19. 20 Hobson, T., "Process Control Fundamentals Part IX -Return Sludge Flow Control", Operations Forum, Feb 1987, pg. 28. 21 Metcalf and Eddy,Inc., pg. 413-414. 22 Hobson, T., "Process Control Fundamentals Part VI -Microscopic Examination of Activated Sludge and Control of Aeration Rates", Operations Forum, Nov 1986, pg. 24. 23 Eikelboom, D.H. and van Buijsen, H.J.J., Microscopic  Sludge Investigation Manual, TNO Research I n s t i t u t e f or Environmental Hygiene, Netherlands, Report A94a, Feb 1981. 110 24 Adapted from Figure 11-20, WPCF, MOP/11, pg. 143. 25 WCPF, MOP/11, pg. 144. 26 United States Environmental Protection Agency, F i e l d Manual for Performance Evaluation and  Troubleshooting at Municipal Wastewater Treatment  F a c i l i t i e s , 1978, EPA-430/9-78-001. 27 E.P.A., Process Control Manual for Aerobic B i o l o g i c a l  Treatment F a c i l i t i e s , 1977, EPA-430/9-77-006. 28 E.P.A., Operational Control Procedures for the Activated  Sludge Process. 29 H i l l , W.R., "Activated Sludge Process and Troubleshooting -Concepts and Applications", Operations Forum, J u l 1984, pg. 10-19. 30 Hobson, T., "Process Control Fundamentals", Operations  Forum, May 1986, pg.24-27. 31 United States Environmental Protection Agency, Operational Control Procedures for the Activated Sludge  Process - Parts 1 - 3b and Appendix, EPA-330/9-74-001, 1973. 32 WPCF, MOP/11, pg. 49-59. 33 Metcalf and Eddy,Inc. pg. 322-330. 34 WPCF, MOP/11, pg. 61-67. 35 E.P.A., F i e l d Manual for Performance Evaluation and  Troubleshooting at Municipal Wastewater Treatment  F a c i l i t i e s , pg. 14-42. 36 E.P.A., F i e l d Manual for Performance Evaluation and  Troubleshooting at Municipal Wastewater Treatment  F a c i l i t i e s , pg. 42-55. Ill 37 WPCF, MOP/11, pg. 69-77. 38 E s l e r , J.K. and M i l l e r , T.J., " C l a r i f i e r Tune-up", Operations Forum, Jan 1987, pg. 7-11. 39 United States Environmental Protection Agency, Summary of Design Information on Rotating B i o l o g i c a l  Contactors, EPA-430/9-84-008, 1984. 40 Zickefoose, C S . and Vass, R., "Foam and Scum - Causes and Cures", Operations Forum, Sept 1986, pg. 26-29. 41 E.P.A., Operational Control Procedures for the Activated Sludge Process - Parts I , I I , I l i a , I l l b and appendix. 42 E.P.A., Process Control Manual for Aerobic B i o l o g i c a l  Treatment F a c i l i t i e s . 43 E.P.A., F i e l d Manual for Performance Evaluation and  Troubleshooting at Municipal Wastewater Treatment  F a c i l i t i e s , pg. 55-77. 44 E.P.A., F i e l d Manual for Performance Evaluation and  Troubleshooting at Municipal Wastewater Treatment  F a c i l i t i e s , pg. 110-118. 45 Water Po l l u t i o n Control Federation, Nutrient Control  Manual of Practice # 7. 46 Caselton, W.F., Froese, T.M., Russell, A.D., Luo, W., "Belief Input Procedures for Dempster-Shafer based Expert Systems", Third International Conference on Applications of  A r t i f i c i a l Intelligence i n Engineering, Los Angeles, August 1988. 112 Chapter 10.0 Appendix 1 - WASTES Knowledge Base F i l e L i s t i n g 10.1.1 LIFT.KB % LIFT PUMPS rule ' l i f t pumps' i f p r i n t $~15 "r5| Raw sewage l i f t pump interactive unit operation diagnosis.$ and ( ('ask l i f t ' i s 'gravity feed from sewers' and print $"15 "r5| Gravity feed into treatment f a c i l i t y - no l i f t pumps.$ and succeed) or ('ask l i f t ' i s 'centrifugal pumps' and 'ask units' i s A and 'ask pump flow' i s B and ' l i f t 2' and succeed) or ('ask l i f t ' i s 'screw pumps' and 'ask units' i s A and 'ask pump flow' i s B and ' l i f t 3' and succeed)). ru l e ' l i f t 2' i f ( ('work pump' i s true and p r i n t $"15 "r5| L i f t pump may not be operating due to:| a) Blown breaker, therefore reset.| b) Defective c o n t r o l l e r i n wet well.| c) Defective motor or drive assembly.| If pump i s s t i l l inoperative, use back-up unit(s).|"p$) or succeed) and ( ('noisy pump' i s true and p r i n t $"15 "r5| A noisy ce n t r i f u g a l pump may be due to:| a) Cavitation. e) Poor l u b r i c a t i o n . | b) Incomplete priming. f) Worn bearings or impellers. | c) Clogged intake b e l l . g) Poor foundation and vi b r a t i o n | d) Incomplete submergence.|"p$) or succeed) and ( ('reduced pump' i s true and p r i n t $"15 "r5| Reduced discharge from a cent r i f u g a l pump may be due to:| a) A i r ca v i t a t i o n . f) Too high suction l i f t . | b) Clogged impeller. g) Clogged piping. | c) Too low motor speed. h) A i r leaks i n suction l i n e . | 113 d) Too high discharge head.'-i) P a r t i a l l y closed valving.| e) Worn or improper impellers.|~p$) or succeed) and p r i n t $~15 "r5| Maintain pumps and drive units and rotate on-line and back-up units for uniform wear.|| Centrifugal raw sewage l i f t pumps functioning properly.$. r u l e ' l i f t 3' i f ( ('work pump' i s true and p r i n t $~15 ~r5| L i f t pump may not be operating due to:| a) Blown breaker, therefore reset.| b) Defective c o n t r o l l e r i n wet well.| c) Defective motor or drive assembly.| If pump i s s t i l l inoperative, use back-up unit(s).|~p$) or succeed) and ( ('reduced pump' i s true and p r i n t $"15 ~r5| Reduced discharge from a screw pump may be due to:| a) Poor seal between screw and casing due to wear or improper| • • ' i n s t a l l a t i o n . | b) Use of a non-covered casing with more splashing and less volume| •••per revolution than an enclosed screw pump.|~p$) or succeed) and ( ('noisy pump' i s true and p r i n t $"15 ~r5| Noisy screw pumps may be due to:| a) G r i t and rocks caught between the screw and the casing.| b) Worn or poorly lubricated bearings.~p$) or succeed) and p r i n t $"15 ~r5| Screw l i f t pumps can pass most solids found i n raw wastewater before screening and g r i t removal but wet well should have a g r i t trap and clean-out for large s o l i d s . | | Raw sewage screw l i f t pumps functioning properly.~p$. •ask l i f t ' ask $"15 "r5| How i s the wastewater l i f t e d to the head of the f a c i l i t y ? $ a l t ('gravity feed from sewers', 'screw pumps 1, 1 c e n t r i f u g a l pumps') expl ($Selecting gravity feed assumes there are no l i f t pumps i n s t a l l e d i n the f a c i l i t y . $ ) . 114 'ask units' ask $~15 "r5| How many pumps are insta l l e d ? (on-line and back-up)$. 'ask pump flow' ask $~15 ~r5|. What percent of the design peak flow i s serviced by one pump?| i . e . 4 pumps @ 30% = 120% peak design flow.$. 'noisy pump' ask $"15 "r5| Are any of the pumps making an unknown noise or sound?$ a l t yn. 'reduced pump' ask $"15 ~r5| Are any of the pumps operating with a reduced discharge?$ a l t yn. 'work pump1 ask $"15 "r5| Are any of the pumps not working?$ a l t yn. 115 10.1.2 RACKS.KB % INFLUENT CHANNELS, RACKS, AND SHREDDERS rule 'solve racks and shredders' i f p r i n t $"15 "r5| Preliminary treatment interactive unit operation diagnosis|$ and ('# of i c ' i s A and A >= 1 and ( ('type rack' i s 'fixed bar' and ( ('shredder' i s true and '# of shred' i s B) or succeed) and 'fixed rack 1' and 'fixed rack 2' and 'shredder 1' and succeed) or ('type rack' i s 'moving or chain' and 'moving rack 1' and succeed)) and succeed) or (print $"15 "r5| There i s no preliminary treatment i n s t a l l e d i n the current plant.|$ and succeed). rul e 'fixed rack 1' i f ('ask racks' i s fals e and p r i n t $"15 "r5| Debris removal from racks and screens i s O.K.|$) or (print $"15 "r5| Increase the frequency of cleaning the bar racks by:| a) If cleaned manually, get s t a f f to clean and check the racks| ••"more frequently.| b) If cleaned mechanically, reduce the timer duration on the| ••'raking mechanism.| p$). rule 'fixed rack 2' i f ('dual racks' i s fals e and p r i n t $"15 "r5| Insure that screening are removed d a i l y to prevent the build-up of obnoxious odours, f l i e s , and insects.| If debris suddenly accumulates, check upstream sources and storm sewer connections, i f plant receives combined flows.|"p$) or (print $"15 "r5| Consider i n s t a l l i n g an i n - l i n e dual rack and screen system| - i n i t i a l coarse bar rack: 20 to 100 mm clear spacing.| 116 - f i n e r screen downstream: 2 to 6 mm clear spacing.| Both angled 30 to 40 degrees into the flow.| This system w i l l perform better and prevent clogging of pumps and other equipment than a single rack system.|| Insure that screening are removed d a i l y to prevent the build-up of obnoxious odours, f l i e s , and insects.| If debris suddenly accumulates, check upstream sources and storm sewer connections, i f plant receives combined flows.|"p$). rul e 'shredder 1' i f ('shredder' i s false and ( ('check s o l i d s ' i s true and p r i n t $"1 " r | I n s t a l l shredder(s) for disposal of excessive s o l i d s c o l l e c t e d by the screen i n s t a l l e d i n the plant.| Insure that the coarse bar rack i s i n s t a l l e d upstream of the shredder(s) to prevent damage by logs and heavy debris.|"p$) or ('shredder 4'))) or 'shredder 2'. rule 'shredder 2' i f ('ask shredder' i s false and 'shredder 3') or ('ask shredder' i s true and 'shredder 4'). rule 'shredder 3' i f ('reset rack 1' i s fals e and p r i n t $"15 "r5| a) Bypass non-functioning shredder to other channel rack.| b) Remove non-functioning shredder for f u l l s e r v i c i n g . | c) Manually rake the screens or racks to remove the s o l i d s accumulated.|"p$ and 'shredder 4') or (print $"15 "r5| The shredder i s operating, checking solids.|$ and 'shredder 4'). rule 'shredder 4' i f ('ask racks' i s false and p r i n t $"15 "r5| No s o l i d s build-up on racks recorded.|| The preliminary unit operations i n the influent channel(s) are functioning properly.| p$) or ( ('shredder' i s true and ( ('coarse' i s fa l s e and p r i n t $"15 "r5| Check the shredder blades and replace worn and/or broken teeth to 117 i n s u r e s o l i d s a r e s h r e d d e d a n d do n o t c o l l e c t o n r a c k ( s ) . | " p $ ) o r s u c c e e d ) ) o r p r i n t $"15 " r 5 | S o l i d s b u i l d - u p o n r a c k s r e c o r d e d . | | T h e p r e l i m i n a r y u n i t o p e r a t i o n s i n t h e i n f l u e n t c h a n n e l ( s ) a r e f u n c t i o n i n g p r o p e r l y . | p $ ) . r u l e ' m o v i n g r a c k 1' i f ( ' a s k a t t a c h e d ' i s f a l s e a n d '# o f i c 1 i s A a n d p r i n t $ T h e r e a r e $ , A , $ i n f l u e n t c h a n n e l s w i t h m o v i n g r a c k s i n s t a l l e d . | " t B y p a s s r a c k a n d r e p a i r w o r n o r b r o k e n l i n k o n s c r e e n c h a i n . | " p $ ) o r ' m o v i n g r a c k 2 ' . r u l e ' m o v i n g r a c k 2 ' i f ( ' a s k r o l l ' i s t r u e a n d p r i n t $"15 " r 5 | I n s u r e t h a t s c r e e n i n g a r e r e m o v e d d a i l y t o p r e v e n t t h e b u i l d - u p o f o b n o x i o u s o d o u r s , f l i e s , a n d i n s e c t s . | I f d e b r i s s u d d e n l y a c c u m u l a t e s , c h e c k u p s t r e a m s o u r c e s a n d s t o r m s e w e r c o n n e c t i o n s , i f p l a n t r e c e i v e s c o m b i n e d f l o w s . | | T h e p r e l i m i n a r y u n i t o p e r a t i o n s i n t h e i n f l u e n t c h a n n e l ( s ) a r e f u n c t i o n i n g p r o p e r l y . | p$) o r ( ' a s k r o l l ' i s f a l s e a n d ( ( ' r e s e t r a c k 2 ' i s f a l s e a n d p r i n t $"15 " r 5 | I f t h e u n i t was jammed a n d d i d n o t r e s e t y o u m i g h t h a v e damaged t h e m o t o r a n d / o r d r i v e g e a r a s s e m b l y . | Remove i t f o r r e p a i r a n d b y p a s s t o o t h e r r a c k ( s ) . | " p $ ) o r ( ' r e s e t r a c k 2 ' i s t r u e a n d p r i n t $"15 " r 5 | I n s u r e t h a t s c r e e n i n g a r e r e m o v e d d a i l y t o p r e v e n t t h e b u i l d - u p o f o b n o x i o u s o d o u r s , f l i e s , a n d i n s e c t s . | I f d e b r i s s u d d e n l y a c c u m u l a t e s , c h e c k u p s t r e a m s o u r c e s a n d s t o r m s e w e r c o n n e c t i o n s , i f p l a n t r e c e i v e s c o m b i n e d f l o w s . | | T h e p r e l i m i n a r y u n i t o p e r a t i o n s i n t h e i n f l u e n t c h a n n e l ( s ) a r e f u n c t i o n i n g p r o p e r l y . | p $ ) ) ) . ' s h r e d d e r ' a s k $"15 " r 5 | A r e t h e r e s h r e d d i n g d e v i c e s l i k e a c o m m i n u t o r s o r b a r m u n i t o r s i n s t a l l e d i n 118 the i n f l u e n t channels?$ a l t yn. 'ask shredder' ask $"15 "r5| Are the i n s t a l l e d shredding device(s) operating?$ a l t yn. 'type rack' ask $"15 "r5| What type of racks or screens are i n s t a l l e d i n the plant?$ a l t ('fixed bar', 'moving or chain'). 'ask attached' ask $"15 "r5| Is the chain rack attached to the drive sprocket at the top of the rack?$ a l t yn. 'ask r o l l ' ask $"15 "r5| Is the chain rack revolving and removing debris?$ a l t yn. 'ask racks* ask $"15 "r5| Are the racks or screens clogged with debris?$ a l t yn. 'dual racks' ask $"15 "r5| Do you have a single bar rack or screen i n s t a l l e d i n the plant?$ a l t yn. 'check s o l i d s ' ask $"15 "r5| Are excessive so l i d s being co l l e c t e d by the racks and screens without a comminutor?$ a l t yn. 'reset rack 1' ask $"15 "r5| Check: a) Debris jams i n the shredder blades| b) Failure of the motor or reducer gears| c) Reset of the power breaker| Does the unit work now?$ a l t yn. 'reset rack 2' ask $"15 "r5| Check: a) Debris jams i n the chain| b) Failu r e of the motor or reducer gears| c) Reset of the power breaker| 119 Does the unit work now?$ a l t yn. 'coarse' ask $"15 "r5| Are the s o l i d s c o l l e c t e d on the rack being ground up and not collecting?$ a l t yn. 120 10.1.3 GRIT.KB % GRIT TANKS rule 'solve g r i t tanks' i f ('grit a 1 i s A and ' g r i t b' i s B and A >= 1 and B >= 1 and p r i n t $"15 "r5| G r i t removal int e r a c t i v e unit operation diagnosis.$ and 'solve g r i t l a ' and 'solve g r i t lb') or p r i n t $"15 "r5| There are no g r i t tanks i n s t a l l e d i n the current plant configuration.$. rule 'solve g r i t l a ' i f ('grit removal' i s fa l s e and ( ('reset g r i t ' i s f a l s e and p r i n t $"15 "r5| If the g r i t c o l l e c t i o n unit was jammed and did not reset you might have damaged the motor and /or drive gear assembly.$ and ( ('grit a' i s A and ' g r i t b' i s B and A > B and p r i n t $"15 "r5| Bypass to other g r i t tank(s) while present tank repaired.$) or succeed)) or ('reset g r i t ' i s true and p r i n t $"15 "r5| Now that the g r i t tank i s working.$ and succeed)) or succeed). ru l e 'solve g r i t lb' i f 'solve g r i t 2' or 'solve g r i t 3'. ru l e 'solve g r i t 2' i f 'ask g r i t type' i s 'velocity s e t t l i n g trough' and ( ('stone' i s fa l s e and ( ('sandy pipes' i s true and p r i n t $"15 "r5| a) Raise outlet weir to provide longer retention.| b) Increase scraper speed and g r i t washer auger speed| •••or decrease timer i n t e r v a l on mechanical c o l l e c t o r to remove| 121 •••amounts of co l l e c t e d g r i t i n chambers.| c) Provide b a f f l e s to increase detention time i n tank. Sedimentation g r i t tank operation functioning properly. "p$) or ('sandy pipes' i s fa l s e and p r i n t $"15 "r5| a) Remove clog from pipe or auger.| b) F i x scraper for better c o l l e c t i o n of g r i t . | Then:| a) Raise outlet weir to provide longer retention.| b) Increase scraper speed and g r i t washer auger speed| •••or decrease timer i n t e r v a l on mechanical c o l l e c t o r to remove] •••excessive amounts of co l l e c t e d g r i t i n chambers.| c) Provide b a f f l e s to increase detention time i n tank. Sedimentation g r i t tank operation functioning properly. p$)) or ('stone' i s true and p r i n t $"15 "r5| a) Insure that c o l l e c t e d g r i t i s removed d a i l y to prevent the •••build-up of obnoxious odours, f l i e s , and insects.| b) If g r i t suddenly accumulates, check upstream sources and storm •••sewer connections, i f plant receives combined flows.[\ Sedimentation g r i t tank operation functioning properly. p$))). r u l e 'solve g r i t 3' i f 'ask g r i t type' i s 'aerated chamber' and ( ('stone' i s fals e and ( ('sandy pipes' i s fa l s e and p r i n t $"15 "r5| a) Reduce a i r supply to aerated chamber to increase detention •••time and increase removal of g r i t . | b) Increase scraper speed and g r i t washer auger speed or ••'decrease timer i n t e r v a l on mechanical c o l l e c t o r to remove •••excessive amounts of co l l e c t e d g r i t i n chambers.| c) Provide b a f f l e s to increase detention time i n tank.|| Aerated g r i t tank operation functioning properly."p$) or ('sandy pipes' i s true and p r i n t $"15 "r5| a) Remove clog from pipe or c o l l e c t i o n auger.| b) Fix clogged aerators.| Then:| a) Reduce a i r supply to aerated chamber to increase detention •"•time and increase removal of g r i t . | b) Increase scraper speed and g r i t washer auger speed or •••decrease timer i n t e r v a l on mechanical c o l l e c t o r to remove •••excessive amounts of co l l e c t e d g r i t i n chambers.| c) Provide b a f f l e s to increase detention time i n tank.|| Aerated g r i t tank operation functioning properly."p$)) or ('stone' i s true and p r i n t $"15 "r5| a) Insure that c o l l e c t e d g r i t i s removed d a i l y to prevent the 122 •••build-up of obnoxious odours, f l i e s , and insects.| b) If g r i t suddenly accumulates, check upstream sources and storm •••sewer connections, i f plant receives combined flows.|| Aerated g r i t tank operation functioning properly."p$))). 'reset g r i t ' ask $"15 "r5| Check:| a) Debris jams i n the unit| b) F a i l u r e of the motor or reducer gears| c) Reset of the power breaker| Does the unit work now?$ a l t yn. ' g r i t removal' ask $"15 "r5| Is the g r i t tank operating.| Is aeration occurring or i s the mechanical scraper operating?$ a l t yn. 'stone' ask $"15 "r5| Is the g r i t being s u f f i c i e n t l y removed from the raw sewage flow?$ a l t yn. 'sandy pipes' ask $"15 "r5| Is the removal auger clogged or i s the mechanical scraper functioning?$ a l t yn. 123 10.1.4 MICRO.KB % MICROSCREENS rule 'solve microscreens' i f ('micro a' i s A and 'micro b' i s B and A >= 1 and B >= 1 and p r i n t $"15 "r5| Microscreen i n t e r a c t i v e unit operation diagnosis.$ and 'microscreen 1' and 'microscreen 4') or p r i n t $"15 "r5| There are no microscreens i n s t a l l e d i n the current f a c i l i t y configuration.$. rule 'microscreen 1* i f ('ask microscreen' i s true and ( ('type rotate' i s true and p r i n t $"15 "r5| Check b e l t drive on microscreen for slippage.$) or ('type rotate' i s fa l s e and ( ("screen s o l i d s ' i s 'build-up of so l i d s ' and p r i n t $"15 "r5| To remove build-up of s o l i d s : | a) Increase drum speed s l i g h t l y , note that large increases i n | •••drum speed d r a s t i c a l l y reduce so l i d s removal e f f i c i e n c y . | b) Add another unit i f capacity of unit i s overloaded.|"p$ and succeed) or ('screen s o l i d s ' i s 'normal removal s o l i d s ' and succeed) or ('screen s o l i d s ' i s 'loss of s o l i d s ' and 'microscreen 2 ' ))))) or ('microscreen 3' and succeed). rul e 'microscreen 2' i f 'microscreen 2a' or 'microscreen 2b' or 'microscreen 2c' or (print $"15 "r5| Unknown s o l i d s , check for leakage.$ and succeed). r u l e 'solve microscreen 2a' i f 'check screen' i s true and 'check seals' i s fa l s e 124 and p r i n t $"15 "r5| Repair screen and f i x s k i r t seals to prevent loss of s o l i d s through| and around or under microscreen.|"p$ and ( ("micro a' i s A and 'micro b' i s B and B > A and p r i n t $"15 "r5| a) Bypass microscreen to remove and repair screen and seals.| b) Use other on-line unit(s).|"p$) or succeed). rul e 'microscreen 2b' i f 'check screen' i s fal s e and 'check seals' i s fa l s e and p r i n t $"15 "r5| Repair s k i r t seals on unit.| Bypassing of microscreen i s probably unnecessary.|"p$. rul e 'microscreen 2c' i f 'check screen' i s true and 'check seals' i s true and p r i n t $"15 "r5| Repair screen to prevent loss of s o l i d s through microscreen unit.|"p$ and ( ('micro a' i s A and 'micro b' i s B and B > A and p r i n t $"15 "r5| a) Bypass microscreen to remove and repair screen.| b) Use other on-line unit(s).|"p$) or succeed). rul e 'microscreen 3' i f p r i n t $"15 "r5| Check the microscreen for:| a) broken drive b e l t or chain| b) burned out motor or reducing gear box| c) bearing f a i l u r e i n unit.|"p$ and ( ('micro a' i s A and 'micro b' i s B and B > A and p r i n t $"15 "r5| Bypass non-functioning microscreen and use other on-line unit(s).|"p$) or succeed) and succeed. 125 rule 'microscreen 4' i f ('slime' i s true and p r i n t $"15 "r5| I n s t a l l spray washers or scrapers to remove slime accumulating on screen surface.|Slime could clog microscreen and lead to a b u i l d -up of s o l i d s and prevent proper flow through the screen.|"p$) or p r i n t $"15 "r5| Microscreen(s) unit operation functioning properly.$. 'ask microscreen* ask $"15 "r5| Is the microscreen drum rotating?$ a l t yn. 'type rotate' ask $"15 "r5| Is the drum rotating e r r a t i c a l l y ? $ a l t yn. 'screen s o l i d s ' ask $"15 "r5| What i s the condition of the sol i d s at the unit?$ a l t ('loss of s o l i d s ' , 'build-up of s o l i d s ' , 'normal removal of s o l i d s ' ) . 'check screen* ask $"15 "r5| Are there any s p l i t s or holes i n the drum screen?$ a l t yn. 'check seals' ask $"15 "r5| Do the seals appear i n t a c t with no leakage of s o l i d s around or under the microscreen drum?$ a l t yn. 'slime' ask $"15 "r5| Is there a b u i l d up of slime on the screen?$ a l t yn. 1 2 6 10.1.5 CLAR.KB % PRIMARY CLARIFIERS rule 'solve primary c l a r i f i e r s ' i f ('pc a' i s A and A >= 1 and 'pc b' i s B and ( ('type of pc' i s ' c i r c u l a r ' and p r i n t $"15 "r5| C i r c u l a r primary c l a r i f i e r i n t e r a c t i v e unit operation diagnosis.$ and 'primary scum' and 'scraper c' and 'primary s o l i d s ' and 'balance primary' and p r i n t $"15 "r5| C i r c u l a r primary c l a r i f i e r ( s ) functioning properly.$) or ('type of pc' i s 'rectangular' and p r i n t $"15 "r5| Rectangular primary c l a r i f i e r i n t e r a c t i v e unit operation diagnosis.$ and 'primary scum' and 'scraper r' and 'primary s o l i d s ' and 'balance primary' and p r i n t $"15 "r5| Rectangular primary c l a r i f i e r ( s ) functioning properly.$))) or p r i n t $"15 "r5| There are no primary c l a r i f i e r s i n s t a l l e d i n the plant.$. rule 'primary scum' i f ('ask scum' i s true and ( ( ('super' i s true and p r i n t $"15 "r5| Check digester supernatant levels for possible withdrawal of f l o a t i n g scum layer.$) or succeed) and ( ('float' i s true and p r i n t $"15 "r5| Check the preliminary unit operations to ensure that debris i s co l l e c t e d and/or i s being shredded e f f e c t i v e l y . $ and load $racks.kb$ and 1 solve racks and shredders') or succeed) and ( ('weeds' i s true 127 and p r i n t $"15 "r5| P u l l weeds and clean weirs out, e s p e c i a l l y i n summer.$) or succeed) and ( ('weir* i s true and p r i n t $"15 "r5| Repair:| a) Scum draw-off weirs and skimmer.| b) Scum c o l l e c t i o n box and scrapers.| To c o l l e c t and remove the f l o a t i n g scum and grease on the primary c l a r i f i e r ( s ) . | " p $ ) or succeed) and p r i n t $"15 "r5| The scum may also be f l o a t i n g sludge i n d i c a t i n g septic conditions i n the c l a r i f i e r . $ ) ) or p r i n t $"15 "r5| No loss of scum from primary c l a r i f i e r ( s ) . $ and succeed. rule 'scraper c' i f ('ask rotate' i s 'rotating' and p r i n t $"15 "r5| Scraper should be rotating at 0.02 to 0.06 RPM for proper operation.|"p$ and succeed) or ('ask rotate' i s 'not rotating' and ( ('reset scraper 1' i s true and succeed) or ('reset scraper 1' i s f a l s e and p r i n t $"15 "r5| Possible solutions are:| a) Bypass primary c l a r i f i e r to other unit(s) and repair scraper arm. b) Continue using c l a r i f i e r , but pump d i l u t e primary sludge to| •••sludge handling f a c i l i t i e s u n t i l scraper arm i s repaired and •••prepare for some sol i d s loss into aeration tank(s).|"p$ and succeed))) or ('ask rotate' i s 'rotating but e r r a t i c a l l y ' and p r i n t $"15 ~r5| Scraper should be rotating at 0.02 to 0.06 RPM for proper operation. Check f o r : | a) Bent or broken sludge plow on scraper ariru b) Build-up of g r i t and sediment due to i n s u f f i c i e n t g r i t •••removal. Check the g r i t tank(s) operation. c) Slippage of drive belts on c o l l e c t i o n arm. d) Build-up of c o l l e c t e d sludge.|"p$ 128 and succeed). ru l e 'scraper r' i f ('ask t r a v e l ' i s 'moving' and p r i n t $"15 "r5| Chain scraper or t r a v e l l i n g bridge should be moving at 0.3 - 1.0 meters per minute for proper operation.|"p$ and succeed) or ('ask t r a v e l ' i s 'not moving' and ( ('reset scraper 2' i s true and succeed) or ('reset scraper 2' i s f a l s e and p r i n t $"15 "r5| Possible solutions are:| a) Bypass primary c l a r i f i e r to other unit(s) and repair scraper arm. | b) Continue using c l a r i f i e r , but pump d i l u t e primary sludge to| •••sludge handling f a c i l i t i e s u n t i l scraper arm i s repaired.| •••and prepare for some loss of s o l i d s into aeration tank(s).|"p$ and succeed))) or ('ask t r a v e l ' i s 'moving but e r r a t i c a l l y ' and p r i n t $"15 "r5| Chain scraper or t r a v e l l i n g bridge should be moving at 0.3 - 1.0 meters per minute for proper operation.| Check for:| a) Broken f l i g h t or worn sprockets.| b) Build-up of g r i t and sediment due to i n s u f f i c i e n t g r i t ••-removal.Check the g r i t tank(s) operation.| c) Slippage of drive belts on drive sprockets.| d) Build-up of co l l e c t e d sludge slowing scraper boards.|"p$ and succeed). ru l e 'primary s o l i d s ' i f ( ('ESS type 1' i s A and A i s 'no s o l i d s i n e f f l u e n t ' and p r i n t $"15 "r5| No loss of s o l i d s from primary c l a r i f i e r ( s ) . $ and succeed) or A i s true or p r i n t $"15 ~r5| Cannot determine type of s o l i d s loss from primary c l a r i f i e r . | Check conditions and query system again to t r y to f i n d a cause.|"p$). rul e 'loss of s o l i d s throughout the area' i f ('peak pflow' i s A and 'current pflow' i s B 129 and A < B and p r i n t $~15 "r5| Hydraulic overloading of c l a r i f i e r ( s ) . | Plant design flow = $,A,$ m3/second.| Present plant flow = $,6,$ m3/second.| Possible solutions:! a) Bring back-up c l a r i f i e r ( s ) on-line to increase _ h r t and decrease| •••weir loading rates allowing s o l i d s to s e t t l e . | b) Increase aeration to assimilate heavier organic loading on| ••-the activated sludge biomass.|"p$ and succeed) or ('primary wastage* and succeed). rul e 'loss of solids i n some areas' i f ('cover' i s f a l s e and p r i n t $"15 "r5| Wind-induced currents over uncovered c l a r i f i e r ( s ) could be creating currents carrying s o l i d s to surface.| Possible solutions:! a) Provide wind breaks around c l a r i f i e r ( s ) . | b) Cover c l a r i f i e r ( s ) . | c) Increase aeration to assimilate heavier organic loading on| ••*the activated sludge biomass.|"p$ and succeed) or ('ask a i r temp' i s X and 'ask ww temp' i s Y and X < Y and p r i n t $"15 "r5| Differences between a i r and wastewater temperatures could cause wastewater to r i s e causing loss of s o l i d s . | Wastewater temperature = $,B,$ °C.| Present a i r temperature = $,X,$ °C.| Possible solutions:! a) Check i n l e t d i f f u s e r s to insure i n f l u e n t i s d i s t r i b u t e d evenly| • • • i n c l a r i f i e r ( s ) . | b) Provide s u f f i c i e n t b a f f l i n g to d i s t r i b u t e flow.| c) Increase aeration to assimilate heavier organic loading on| ••'the activated sludge biomass.|"p$ and succeed) or ('balance primary' and succeed) or (( ('ask rotate' i s 'rotating') or ('ask t r a v e l ' i s 'moving')) and p r i n t $"15 "r5| Solids loss due to probable effluent weir imbalance which causes 130 s o l i d s to surge and billow i n areas of increased flow.| Solutions:| a) Use surveyor's l e v e l to sight and l e v e l e f f l u e n t weirs.| b) Increase aeration to assimilate heavier organic loading on| •••the activated sludge biomass.| "p$ and succeed) or (( ('ask rotate' i s 'rotating but e r r a t i c a l l y ' ) or ('ask t r a v e l ' i s 'moving but e r r a t i c a l l y ' ) ) and p r i n t $"15 "r5| Solids overloading of c l a r i f i e r ( s ) that i s jamming sludge removal scrapers.| Sludge removal scrapers are moving e r r a t i c a l l y . | " p $ and 'primary wastage' and succeed) or ('loss of sol i d s throughout the area' and succeed). rule ' r i s i n g clumps and mats of s o l i d s ' i f 'describe smell' i s true and p r i n t $"15 "r5| C l a r i f i e r s o l i d s condition indicates that s o l i d s losses are due to r i s i n g sludge caused by anaerobic or septic conditions.! Solids are r i s i n g i n clumps and mats and odour indicates septic conditions.|"p$ and 'primary wastage' and succeed. rule 'primary wastage' i f ( ('wspumps' i s true and p r i n t $"15 "r5| Wastage operating but i n s u f f i c i e n t removal rates.| Possible solutions:| a) Increase wastage from the c l a r i f i e r . | b) Increase aeration i n activated sludge unit to assimilate ••'higher organic loading.|"p$ and succeed) or ( ('check pump' i s true and p r i n t $"15 "r5| Wastage operating but i n s u f f i c i e n t removal rates.] Possible solutions:! a) Increase wastage from the c l a r i f i e r . | b) Increase aeration i n activated sludge unit to assimilate ••'higher organic loading.|"p$ and succeed) or ("check pump' i s fa l s e and p r i n t $"15 "r5| Sludge wastage system f a i l u r e . | F a i l e d sludge wastage pumps, clogged wastage piping or f a i l e d 131 sludge plows or scrapers.| Possible solutions:| a) Bypass c l a r i f i e r with clogged sludge withdrawal pipes or pumps| b) Use back-up pumps i f only sludge pump f a i l u r e . | c) Repair pumps or unplug wastage pipes.| d) Increase aeration to assimilate heavier organic loading on| ••*the activated sludge biomass.|"p$ and succeed))). rule 'balance primary' i f ( ('pc b' i s A and ( (A >= 2 and succeed) or (print $"15 "r5| Only one c l a r i f i e r on-line or installe d . | $ and f a i l ) ) and 'ask balance' i s fals e and p r i n t $"15 "r5| Unbalanced flows to on-line c l a r i f i e r s can cause surges of s o l i d s | Try to balance flows to the operational c l a r i f i e r s by:| a) Checking wastage rates and durations for the d i f f e r e n t wastage ••-pumps.| b) Balancing inflows between the on-line c l a r i f i e r s by • • • t h r o t t l i n g flows at s p l i t t e r box and increasing head losses to •••reduce the effects of surges i n the in f l u e n t channels.|"p$ and succeed) or (print $"15 "r5| Flows to on-line c l a r i f i e r s equal.| No possible s o l i d s losses due to surging.|"p$)). 'ask scum' ask $"15 "r5| Is there a build-up of co l l e c t e d scum on the c l a r i f i e r and/or i s i t overloading into the secondary system?$ a l t yn. 'ask windy' ask $"15 "r5| Are there winds i n excess of 15 km/h at the plant site?$ a l t yn expl ($Wind could create currents i n the c l a r i f i e r ( s ) strong enough to carry s o l i d s up and over the weirs.$). 'ask a i r temp' ask $"15 "r5| What i s the current a i r temperature outside the f a c i l i t y ? (°C)$ expl ($1 would l i k e to compare the wastewater 132 temperature with the a i r temperature so see i f temperature currents could be causing a loss of s o l i d s . $ ) . 'ask ww temp' ask $"15 "r5| What i s the current wastewater temperature entering the c l a r i f i e r ( s ) ? (°C)$ expl ($1 would l i k e to compare the wastewater temperature with the a i r temperature so see i f temperature currents could be causing a loss of s o l i d s . $ ) . 'ask balance' ask $"15 "r5| Are the wastewater flows to the on-line c l a r i f i e r s approximately equal?$ a l t yn. 'wspumps' ask $"15 "r5| Is sludge wastage occurring from the primary c l a r i f i e r ( s ) ? $ a l t yn. 'check pump' ask $"15 "r5| Check the sludge wastage pumps.| Make sure a l l pumps are operational.! Check the pumps for debris jams.| Check and reset pump breakers.| Check sludge wastage pipes for clogs or r e s t r i c t i o n s caused by debris or accumulated g r i t . | Is the wastage system O.K.?$ a l t yn. 'ESS type 1' ask $"15 "r5| What i s the condition of the sol i d s at the c l a r i f i e r overflow weir(s)?$ a l t ('loss of sol i d s throughout the a r e a 1 , 'loss of sol i d s i n some areas', ' r i s i n g clumps and mats of s o l i d s ' , 'no so l i d s i n effluent*) expl ($The condition of the so l i d s i n the primary c l a r i f i e r ( s ) helps the system determine corrective actions.$). 'cover' ask $"15 "r5| Is there a cover over the c l a r i f i e r or some sort of wind buffer protecting the c l a r i f i e r ? $ a l t yn. 133 'ask t r a v e l ' ask $"15 "r5| What i s the chain scraper or t r a v e l l i n g bridge scraper doing?$ a l t ('moving', 'not moving', 'moving but e r r a t i c a l l y ' ) expl ($The action of the scraper helps the system determine what i s wrong i n the c l a r i f i e r ( s ) and the proper corrective actions.$). 'ask rotate* ask $"15 "r5| What i s the c i r c u l a r sludge c o l l e c t i o n scraper arm doing?$ a l t ('rotating', 'not rotating', 'rotating but e r r a t i c a l l y ' ) expl ($The action of the scraper helps the system determine what i s wrong i n the c l a r i f i e r ( s ) and the proper corrective actions.$). 'super' ask $"15 "r5| Is there anaerobic digester supernatant pumped to the head of the plant above the primary c l a r i f i e r ? $ a l t yn. ' f l o a t ' ask $"15 "r5| Does the scum have a l o t of paper, rags, and other debris?$ a l t yn. 'weeds' ask [nl,$ Are there weeds or al g a l build-ups i n the scum c o l l e c t i o n weirs?$] a l t yn. 'weir' ask $"15 "r5| Is there a blockage or problem with the scum removal mechanism caused by c o l l e c t e d grease or debris?$ a l t yn. 'reset scraper 1* ask $"15 "r5| Check:| a) Debris jams i n the bottom of the c l a r i f i e r . | b) Bent or broken plow.| c) Failu r e of the motor or reducer gears.| d) Reset of the power breaker.| Does the unit work now?$ a l t yn. 'reset scraper 2' ask $"15 ~r5| 134 Check:| a) Debris jams i n the bottom of the c l a r i f i e r . | b) Broken f l i g h t . | c) F a i l u r e of the motor or reducer gears| d) Reset of the power breaker| Does the unit work now?$ a l t yn. "describe smell' ask $"15 "r5| Is the odour over the surface l i k e rotten eggs or sulfides?$ a l t yn expl ($The presence of s u l f i d e - l i k e odours i s usually an in d i c a t i o n of anaerobic or septic conditions i n the c l a r i f i e r ( s ) . ) . 135 10.1.6 RBC.KB rule 'solve rbc' i f p r i n t $"15 "r5| RBC units require l i t t l e operator control and provide excellent treatment, however RBCs can operate poorly i f they are not maintained properly and adjustments are not made for process co n t r o l . The following i s a concise diagnosis of an RBC system.|"p$ and 'rbc 1' and 1rbc 2'. rule 'rbc 1' i f ('ask turn' i s true and succeed) or ( ( ('broken shaft' i s true and p r i n t $"15 "r5| Bypass broken RBC unit and repair or replace broken shaft.$) or succeed) and ( ('media' i s true and p r i n t $"15 ~r5| Bypass broken RBC unit and repair or replace media/disc connection.$) or succeed) and p r i n t $"15 "r5| Check for f a i l u r e s i n the following:| a) Drive and motor system.| b) Check and lubricate a l l bearings.| c) Check the power breaker and reset i f thrown.|"p$ and succeed). rul e 'rbc 2' i f ( ('ask condition' i s 'shaggy grey white' and ( ('high EBOD' i s true and p r i n t $"15 "r5| Bio f i l m condition and effluent BOD indicate that RBC stage i s organ i c a l l y overloaded.|"p$ and 'rbc 3' ) or (print $"15 "r5| Check i n f l u e n t BOD and "p$ Condition could indicate overloading, e f f l u e n t BOD over composited samples. and 'rbc 4')) or ('ask condition' i s 'grey brown slime' and p r i n t $"15 "r5| Bi o f i l m condition i s normal for domestic wastewaters.|"p$ and 'rbc 4') or ('ask condition' i s 'excessive amount of sloughed 136 s o l i d s ' and ( ('ask rpm' i s true and p r i n t $"15 "r5| Proper operation indicates: 1 < RPM < 2 , therefore adjust motor and drive reducers for proper r o t a t i o n a l speed.|"p$) or succeed) and ( ('high EBOD' i s true and p r i n t $"15 "r5| B i o f i l m sloughing condition and high e f f l u e n t BODindicates that RBC stage i s organically overloaded.|"p$ and 'rbc 3') or (print $"15 "r5| Excessive sloughed so l i d s could be i n d i c a t i n g a toxic loading has entered the plant.|Examine c l a r i f i e r s o l i d s under microscope for protozoa.|"p$ and ( ('rotifer' i s true and p r i n t $"15 "r5| Toxic loading most l i k e l y cause of s o l i d s loss and s t i l l present i n the plant wastewater.|Maintain operation and f i n d upstream source of contaminant.|"p$ and 'rbc 4') or (print $"15 "r5| Toxic loading most l i k e l y cause of s o l i d s loss and has probably l e f t the system.|Maintain operation and f i n d upstream source of contaminant.|"p$) and 'rbc 4')))))) . r u l e 'rbc 3' i f ( ('bypass' i s true and p r i n t $"15 "r5| Bypassing flow around overloaded stage w i l l reduce organic loading rate and allow stage to recover.| a) Monitor composited influent and e f f l u e n t BOD l e v e l s . | b) Expect some amount of sloughed s o l i d s as stage recovers.|"p$ and 'rbc 4') or p r i n t $"15 "r5| Bypass flow i s not available, therefore the following could also be used to reduce the organic loading:| a) I n s t a l l supplemental aeration to r a i s e DO i n bulk l i q u i d and | •••increase organic removal rates.| b) I n s t a l l b a f f l i n g to reduce the hydraulic loading, hence the| •••organic loading on the b i o f i l m . | c) Increase the r o t a t i o n a l speed of the RBC.| d) Increase capacity of the plant by i n s t a l l i n g more RBC units| • * *or higher density media.|"p$ and 'rbc 4') . 137 rule 'rbc 4' i f ( ('ask condition' i s 'excessive amount of sloughed s o l i d s ' and p r i n t $"15 "r5| Sloughing s o l i d s from RBC unit, checking condition of s o l i d s i n f i n a l c l a r i f i e r . $ and load $CLAR.KB$ and 'primary solids') or succeed) and ( ('ask n i t r i f y f i l m ' i s true and p r i n t $"15 "r5| N i t r i f y i n g conditions i n RBC plant are t y p i f i e d by the presence of t h i n reddish b i o f i l m on the fourth and l a s t stage.|High density media should be used i n t h i r d and fourth stages to insure f u l l n i t r i f i c a t i o n of influent.|"p$) or succeed) and p r i n t $"15 "r5| As part of regular maintenance:| a) Check the drive and motor system. b) Check and lubricate a l l bearings. c) Inspect a l l RBC shafts and shaft/media connections.! •••(Area of highest f a i l u r e i n a l l RBC plants.)] d) Check or i n s t a l l adequate venting to prevent corrosion."P$ and succeed. 'ask n i t r i f y f i l m ' ask $"15 "r5| Is the RBC plant designed to n i t r i f y ? $ a l t yn. 'bypass' ask $"15 "r5| Can you bypass part of the flow to another stage to reduce the organic loading on the overloaded RBC stage?$ a l t yn. 'ask rpm' ask $"15 "r5| Is the r o t a t i o n a l speed of the RBC shaft > 2 rpm or < 1 rpm?$ a l t yn. 'broken shaft' ask $"15 "r5| Does the non-rotating RBC have a broken shaft?$ a l t yn. 'media' ask $"15 "r5| Has the media broken away from the RBC shaft?$ 138 a l t yn. 'ask turn' ask $"15 "r5| Are the a l l RBC media and shafts turning?$ a l t yn. 'ask condition' ask $"15 "r5| What best describes the physical condition of the RBC biofilm?$ a l t ('shaggy grey white', 'grey brown slime', 'excessive amount of sloughed s o l i d s ' ) expl ($WASTE uses the v i s u a l condition of the b i o f i l m an indicator of the organic loading and of possible toxic loading into the RBC unit.$). 139 10.1.7 FLOAT.KB % FLOATABLES rule 'solve foam or scum' i f 'ask what' i s A and A i s true. r u l e 'scum on the primary c l a r i f i e r ( s ) ' i f load $CLAR.KB$ and 'primary scum'. rule 'foam on the aeration tank(s)' i f ( ('type of foam' i s 'white billowing foam' and p r i n t $"15 "r5| White billowing foam can be present:| a) During plant start-up ( f i r s t two weeks)| b) If there has been a toxic loading to plant| c) If the process i s organically overloaded|"p$ and 'loading 1' and 'waste s o l i d s ' and succeed) or ('type of foam' i s ' l i g h t tan or brown foam' and p r i n t $"15 "r5| This foam i s t y p i c a l of normally loaded activated sludge aeration tank(s).| If foam builds up re a d i l y , i n s t a l l e f f l u e n t sprayers to reduce volume.|"p$ or ('type of foam' i s 'dark brown foam' and p r i n t $"15 "r5| This type of foam i s t y p i c a l of underloaded or extended aeration-type activated sludge aeration tanks.|If you are not operating i n extended aeration mode, check your wastage requirements and increase wasting.| p$)). ru l e 'foam or scum on the secondary c l a r i f i e r ( s ) ' i f 'second foam or scum'. rule 'second foam or scum' i f ('what foam' i s 'scum, so l i d s and other f l o a t i n g debris' and p r i n t $"15 "r5| Checking possible sources of scum on the secondary c l a r i f i e r ( s ) . $ and ( ('foam loss' i s true and p r i n t $"15 "r5| One possible source of scum i s from aeration basin foam.| I n s t a l l b a f f l e s of a weir to keep foam out of e f f l u e n t channels i n the aeration tank(s).|"p$) or succeed) and ( (print $"15 "r5| 140 One possible source of scum i s from the primary c l a r i f i e r ( s ) or the preliminary operations of screening and shredding.|"p$ and load $CLAR.KB$ and 'primary scum') or succeed) and ( ('clumps' i s true and p r i n t $"15 "r5| One possible source of scum i s from r i s i n g s o l i d s i n the secondary c l a r i f i e r ( s ) . | " p $ ) or succeed) and succeed) or ('what foam' i s 'foam with no debris and l i t t l e s o l i d s * and p r i n t $"15 "r5| Possible source of scum i s from aeration basin foam.| I n s t a l l b a f f l e s of a weir to keep foam out of e f f l u e n t channels i n the aeration tank(s).|"p$ and succeed). 'foam lo s s ' ask $"15 "r5 | l s foam coming through c l a r i f i e r i n l e t weirs from the aeration tank(s)?$ a l t yn. 'what foam' ask $"15 "r5| What appears to be on the surface of the c l a r i f i e r ( s ) ? $ a l t ('scum, sol i d s and other f l o a t i n g debris', 'foam with no debris and l i t t l e s o l i d s ' ) expl ($Scum and other so l i d s are usually paper, p l a s t i c products, grease and organics discharged i n sewage.|Foam i s usually the r e s u l t of the build-up of foam from the aeration tank(s).$). 'ask what' ask $"15 "r5| What appears to be the problem?$ a l t ('scum on the primary c l a r i f i e r ( s ) ' , 'foam on the aeration tank(s)', 'foam or scum on the secondary c l a r i f i e r ( s ) ' ) expl ($WASTE would l i k e to know where the problem i s so i t can suggest the proper corrective action.$). 141 10.1.8 ODOUR.KB % ODOURS rule 'solve smell' i f ('gas 1' or 'gas 2') and succeed. rule 'gas 1' i f ( ('area' i s 'aeration tank(s)' and 'smell' i s true and p r i n t $"15 "r5| That odour i s an in d i c a t i o n of low dissolved oxygen or DO i n the reactor and anaerobic conditions could exist.|"p$ and 'check DO') or ('area' i s 'anoxic reactor' and 'smell' i s true and p r i n t $"15 "r5| Due to the anaerobic nature of anoxic reactors used to d e n i t r i f y the wastewater that i s a common odour.|"p$) or ('area' i s 'primary c l a r i f i e r ( s ) ' and 'smell' i s true and p r i n t $"15 "r5| That odour indicates septic conditions.! a) Check condition of primary c l a r i f i e r s o l i d s . | b) Check for septic wastewater from sewerage system.| c) Check anaerobic digester supernatant i f pumped to plant ••-headworks above primary c l a r i f i e r ( s ) . | d) If odours p e r s i s t , add pre-aeration to wet sump or i n f l u e n t | ••'channels to sweeten wastewater.| p$) or ('area' i s 'secondary c l a r i f i e r ( s ) ' and 'smell' i s true and p r i n t $"15 "5r| That odour indicates septic conditions.! a) Check condition of secondary c l a r i f i e r s o l i d s . j b) Check for septic conditions i n reactor.| c) If odours p e r s i s t , add pre-aeration to wet sump or i n f l u e n t | •••channels to sweeten wastewater.("p$)). rule 'gas 2' i f ('area' i s 'aeration tank(s)' and p r i n t $"15 "r5| That odour i s t y p i c a l of a properly operating activated sludge basin with an adequate DO level.|"p$) or ('area' i s 'primary c l a r i f i e r ( s ) ' and p r i n t $"15 "r5| That odour i s normal and i f the odour becomes a c r i d or l i k e 142 s u l f i d e s there are septic conditions i n the wastewater or c l a r i f i e r . | " p $ ) or ('area' i s 'secondary c l a r i f i e r ( s ) ' and p r i n t $"15 "r5| That odour i s normal and i f the odour becomes a c r i d or l i k e s u l f i d e s there are septic conditions i n the wastewater or c l a r i f i e r . | " p $ ) or ('area' i s 'anoxic reactor' and p r i n t $"15 "r5| A well mixed reactor should have no odours associated with i t as long as the influent i s not anaerobic or septic.|"p$). 'smell' ask $"15 "r5| What does i t smell l i k e rotten eggs or sulfides?$ a l t yn expl ($The presence of that smell means that anaerobic or septic conditions e x i s t i n the area and operational corrections have to be made.$). 'area' ask $"15 "r5| What area of the plant are the odours from?$ a l t ('aeration tank(s)', 'anoxic reactor', 'primary c l a r i f i e r ( s ) ' , 'secondary c l a r i f i e r ( s ) ' ) expl ($WASTES would l i k e to know what area i n the plant the odours are coming from so i t can suggest corrective action i f any.$). 143 10.1.9 TREAT.KB %************ WASTE TREATMENT EXPERT SYSTEM ********************% % % %************************** GOAL *******************************% % % goal run. % % % %************************* RULES *******************************% rule 'run' i f 'setup' and 'solve *. rul e 'solve' i f ('ask user' i s 'part' and 'unit' i s A and A i s true) or ('ask user' i s 'system' and 'whole' i s true). 'ask user' ask $"15 "r5| Do you want to select a treatment problem or pick a selected unit operation, or do you want to t r y the whole system ?$ a l t ('process or unit operation', 'secondary activated sludge system') r a i t ('part','system') expl ($WASTES i s t r y i n g to determine whether you want to look at. S p e c i f i c problem or unit operation, or| the activated sludge treatment system.$). rul e 'section' i f 'unit' i s 'A' and 'A' i s true. 'unit' ask $"15 "r5| Select a system or unit operation from the l i s t and WASTES w i l l diagnose the problem and attempt to f i n d a solution.$ a l t ('rack(s) and shredder(s)', ' l i f t pump(s)', ' g r i t tank(s)', 'microscreen(s)', 'primary c l a r i f i e r ( s ) ' , 'aeration tank(s)', 'RBC(s)', •secondary c l a r i f i e r ( s ) ' , ' a l l unit operations') expl ($WASTES wants to know what operation or system you would l i k e to diagnose or troubleshoot.|If you want to check a l l the unit operations i n s t a l l e d i n WASTES, choose #9.$). 144 rule 'rack(s) and shredder(s) 1 i f load $racks.kb$ and 'solve racks and shredders'. rul e ' l i f t pump(s)' i f load $lift.kb$ and ' l i f t pumps'. rule ' g r i t tank(s)' i f load $grit.kb$ and 'solve g r i t tanks'. rul e 'microscreen(s)' i f load $micro.kb$ and 'solve microscreens'. rul e 'primary c l a r i f i e r ( s ) ' i f load $clar.kb$ and 'solve primary c l a r i f i e r s ' . r u l e 'aeration tank(s)' i f 'ask aeration' i s A and A i s true. 'ask aeration' ask $"15 "r5| What function of the aeration tank(s) would you l i k e to look at ?$ a l t ('aeration and mixing system', 'foaming problems', 'DO levels i n aeration tank(s)', 'aeration odour', 'activated sludge process contr o l ' , ' a l l aeration tank systems') expl ($WASTES would l i k e to know what area of the aeration system you would l i k e to look a t . | l f you want to look at the whole system, choose #6, a l l aeration tank systems.$). rule 'aeration and mixing system' i f 'solve aeration/mixing'. rule 'foaming problems' i f 'loading'. r u l e 'DO levels i n aeration tank(s)' i f 'check DO'. rule 'aeration odour' i f load $odour.kb$ and 'solve smell'. r u l e 'activated sludge process control' i f 'activated sludge'. 145 rule ' a l l aeration tank systems' i f 'foaming problems' and 'aeration and mixing system' and 'activated sludge process control'. rule 'RBC(s)' i f load $RBC.kb$ and 'solve rbc'. rule 'secondary c l a r i f i e r ( s ) ' i f 'secondary floe c l a r i f i e r s ' . r u l e ' a l l unit operations' i f 'rack(s) and shredder(s)' and ' l i f t pump(s)' and ' g r i t tank(s)' and 'microscreen(s)' and 'primary c l a r i f i e r ( s ) ' and 'aeration tank(s)' and 'RBC(s)'. rule 'whole' i f 'excess primary s o l i d s ' and 'aeration and mixing system' and 'foam or scum problems' and 'odour' and 'activated sludge process con t r o l ' . r u l e 'excess primary s o l i d s ' i f load $clar.kb$ and 'primary s o l i d s ' and 'balance primary'. rul e 'foam or scum problems' i f load $float.kb$ and 'solve foam or scum'. rule 'odour' i f load $odour.kb$ and 'solve smell'. f a i l i s f a l s e , succeed i s true. '# of shred' ask $"15 "r5| In how many influent channels are there shredding devices i n s t a l l e d ?$. '# of i c ' ask $"tHow many influent channels enter the plant from the sewer system ?$. 146 'average pflow' ask $"15 "r5| What i s the average design flow of the treatment plant i n m3/s ?$. 'peak pflow' ask $"15 "r5| What i s the peak design flow of the treatment plant i n m3/s ?$. 'current pflow' ask $"15 "r5| What i s the current treatment plant flow i n m3/s ?$. ' g r i t a' ask $"15 "r5| How many g r i t tank(s) are i n s t a l l e d i n the plant ?$. ' g r i t b' ask $"15 "r5| How many g r i t tank(s) are operating ?$. 'ask g r i t type' ask $"15 "r5| What type of g r i t tank(s) are i n s t a l l e d i n the plant ?$ a l t ('velocity s e t t l i n g trough', 'aerated chamber') expl ($Different g r i t tanks have d i f f e r e n t problems. |Select the type of g r i t tanks i n s t a l l e d i n your f a c i l i t y . $ ) . 'micro a' ask $"15 "r5| How many microscreen(s) are i n s t a l l e d i n the plant ?$. 'micro b* ask $"15 "r5| How many microscreen(s) are operating ?$. 'pc a' ask $"15 "r5| How many primary c l a r i f i e r ( s ) are i n s t a l l e d at the plant ?$. 'pc b' ask $"15 "r5| How many primary c l a r i f i e r ( s ) are operating ?$. 'type of pc' ask $"15 "r5| What type of primary c l a r i f i e r ( s ) are i n s t a l l e d i n the plant ?$ a l t ('circular *, 'rectangular') expl ($1 think you know the difference between the two shapes !|Enter the type you have i n s t a l l e d at your n f a c i l i t y . $ ) . 147 'sc a' ask $"15 "r5| How many secondary c l a r i f i e r s are i n s t a l l e d ?$. 'sc b' ask $"15 "r5| How many secondary c l a r i f i e r s are operating ?$. 'average flow' ask $"15 "r5| What i s the average design flow of the aeration tank(s) i n m3/s ?$. 'peak flow' ask $"15 "r5| What i s the peak design flow of the aeration tank(s) i n m3/s ?$. 'current flow' ask $"15 "r5| What i s the current plant flow i n m3/s ?$. %************************ SCREEN SET_UP ************************% rul e setup i f p r i n t $"118| Welcome tol WASTES WAStewater Treatment Expert System (C) Barry Chilibeck Version 3.0 15 "r5| This program i s intended to a s s i s t i n the diagnosis and correction of common problems encountered i n the operation of wastewater treatment f a c i l i t i e s . It should be used only as a reference and guide. The purpose of WASTES i s to i l l u s t r a t e the ap p l i c a t i o n of expert systems to the f i e l d of wastewater treatment.||Completed as p a r t i a l requirement for the degree of Masters of Applied Science, Environmental Engineering, Department of C i v i l Engineering, University of B r i t i s h Columbia, 1990, by Barry Chilibeck. >l I I I I I I I I I I I I I ||||||||$. % ACTIVATED SLUDGE SYSTEM rule 'activated sludge' i f p r i n t $"15 "r5| In order to change the condition of the activated sludge process, the operator usually has 3 basic variables which he can vary:|| "c20 1) Aeration rates i n the aeration tank(s)| "c20 2) Return s o l i d s flow "c20 3) Wastage of s o l i d s . 148 Regardless of the method of process control used, these variable are manipulated to correct effluent and plant problems. The suggested solutions to user-selected system problems w i l l be offered i n terms of adjustments or corrections to one or more of the operator-controlled variables.|"p$ and 'loading' and 'excess secondary effluent suspended s o l i d s ' and p r i n t $"15 "r5| Process control operations completed.||Checking mechanical systems i n secondary c l a r i f i e r ( s ) and pumping systems.$ and 'pumps' and 'secondary floe c l a r i f i e r s ' . r u l e 'loading' i f ('loading 1' or 'loading 2'). rul e 'inc miss' i f succeed. r u l e 'dec miss' i f succeed. r u l e 'inc return' i f succeed. rul e 'dec return' i f succeed. rul e 'loading 1' i f 'ebod' i s true and ( ('ibod' i s false and ( (' r o t i f e r ' i s true and p r i n t $"15 "r5| Inactive protozoa could be an i n d i c a t i o n that a toxic slug loading has entered the plant and disrupted the b i o l o g i c a l system.|Retain biomass to speed plant recovery.|"p$) or ( ('type of foam" i s 'white billowing foam') or ('floe' i s 'darker') or ('MLSS' i s 'lower') and p r i n t $"15 "r5| Conditions indicate that the process i s o r g a n i c a l l y overloaded.| Increase MLSS by decreasing wastage from the process.| If there i s excessive foaming insure grease or other i n d u s t r i a l surfactants are not entering the aeration tank(s) and i n s t a l l sprays to reduce foam build-up.|"p$) or ('temp' i s true and p r i n t $"15 "r5| Reduced wastewater temperatures decrease the biomass a b i l i t y to 149 digest organics.|Reduce wasting to increase MLSS.|"p$) or (print $"15 "r5| Check in f l u e n t COD and BOD and reduce wasting to build-up MLSS.|Also check metal concentrations i n influent.|"p$)) and succeed) or p r i n t $"15 "r5| I n s u f f i c i e n t MLSS for present loading, probably excessive wasting.| Increase MLSS by decreasing wastage from the process.| If there i s excessive foaming insure grease or other i n d u s t r i a l surfactants are not entering the aeration tank(s) and i n s t a l l sprays to reduce foam build-up.|"p$) and 'inc miss' and 'wastage' and succeed. rul e 'loading 2' i f p r i n t $"15 "r5| S u f f i c i e n t biomass available i n aeration tank(s) for increased loading.| Maintain MLSS, wasting rates and aeration.|"p$ and succeed. rul e 'excess secondary effluent BOD' i f ( ('ebod' i s true and ( ('ess' i s true and 'excess secondary e f f l u e n t suspended s o l i d s ' i s true and succeed) or ('loading' i s true and succeed)) and succeed) or succeed). rul e 'excess secondary effluent suspended s o l i d s ' i f ( ('ess' i s true and p r i n t $"15 "r5| High ef f l u e n t suspended solids w i l l probably r e s u l t i n high e f f l u e n t BOD values.|Diagnose ef f l u e n t suspended solids.$ and 'ESS type 2' i s A and A i s true and succeed) or succeed). rul e 'normal - e x i t i n g along entire length of weir' i f ('sludge s e t t l e * i s 'slow s e t t l i n g ' and 'fmload' i s 'high' and 'bltspeed' i s 'slowly' and p r i n t $"15 "r5| 150 Conditions indicate that the process i s organically overloaded.| Increase MLSS by decreasing wastage from the process.| Check that grease or other i n d u s t r i a l surfactants are not entering the aeration tank(s) and i n s t a l l sprays to reduce foam build-up.|"p$ and 'inc miss' and 'wastage' and succeed) or ('sludge s e t t l e ' i s 'slow s e t t l i n g ' and 'fmload' i s 'low' and 'bltspeed' i s 'slowly' and p r i n t $"15 "r5| F/M loading: low.| Condition of aeration tank(s) suggest that MLSS concentrations are high r e l a t i v e to the organic loading and endogenous r e s p i r a t i o n i s occurring.| Increase wastage to decrease biomass i n aeration tank(s).|"p$ and 'dec miss' and 'wastage' and succeed) or ("sludge s e t t l e ' i s 'slow s e t t l i n g ' and 'filament' i s true and 'solve filament' and succeed) or ('return pump' i s true and succeed) or ("normal - ex i t i n g only i n discrete areas of weir' and succeed). rule 'return pump' i f ('ask return pump' i s true and ( ('sir' i s 'above' and p r i n t $"15 "r5| In s u f f i c i e n t secondary c l a r i f i e r capacity.|Solids loading rates are too high at design flows.|Increase loading capacity by increasing capacity or reducing loading|~p$ and succeed) or ('ofr' i s true and p r i n t $"15 "r5| Hydraulic overloading of secondary c l a r i f i e r ( s ) . | Solutions:| a) Bring back-up c l a r i f i e r ( s ) on-line to increase o v e r a l l hydraulic| retention time and reduce overflow rates.| b) Bypass part of plant flow to reduce flow through the plant.| c) I n s t a l l b a f f l i n g i n secondary c l a r i f i e r ( s ) to improve hydraulic capacity.| d) Equalize sewage inflows and inplant flow streams.|"p$) and succeed)) or ("ask return pump' i s fals e and 'bltspeed' i s 'quickly' and p r i n t 151 $"15 "r5| Solids overloading of secondary c l a r i f i e r ( s ) due to return s o l i d s system f a i l u r e . | a) Use back-up or supplemental pumps to remove s o l i d s from secondary c l a r i f i e r ( s ) . | b) Check for clogged return pumps or return sludge l i n e s . | c) Bring back-up c l a r i f i e r ( s ) on-line.|"p$ and succeed). rule 'normal - e x i t i n g only i n discrete areas of weir* i f ('cover' i s fals e and ' b i t ' i s 'high' and p r i n t $"15 "r5| Wind-induced currents over uncovered secondary c l a r i f i e r ( s ) could be creating currents carrying s o l i d s to surface and over weirs.| Possible solutions:] a) Provide wind breaks around c l a r i f i e r ( s ) . | b) Cover c l a r i f i e r ( s ) . | " p $ and succeed) or ('ask a i r temp' i s X and 'ask ww temp' i s Y and X < Y and p r i n t $"15 "r5| Differences between a i r and wastewater temperatures could cause wastewater to r i s e causing loss of so l i d s i n secondary c l a r i f i e r ( s ) . | Possible solutions:! a) Check i n l e t d i f f u s e r s to insure influent i s d i s t r i b u t e d evenly i n secondary c l a r i f i e r ( s ) . | b) Provide s u f f i c i e n t b a f f l i n g to d i s t r i b u t e flow.|"p$ and succeed) or ('balance secondary' and succeed) or ( ( ('ask rotate c' i s 'rotating') or ('ask t r a v e l r' i s 'moving')) and ' b i t ' i s 'high' and p r i n t $"15 "r5| Solids loss due to probable effluent weir imbalance which causes s o l i d s to surge and billow i n areas of increased flow.| Use surveyor's l e v e l to sight and l e v e l e f f l u e n t weirs.|"p$ and succeed) or ( ( ('ask rotate c' i s 'rotating but i r r a t i c a l l y " ) or ('ask t r a v e l r' i s 'moving but i r r a t i c a l l y ' ) ) and p r i n t $"15 "r5| Solids overloading of c l a r i f i e r ( s ) that i s jamming sludge removal scrapers.| Sludge removal scrapers are moving i r r a t i c a l l y . | " p $ and 'inc return' and 'return s o l i d s ' and succeed) 152 or ('normal - ex i t i n g along entire length of weir' i s true and succeed). ru l e 'ash-like s o l i d s on the surface' i f p r i n t $"15 "R5| Ash on surface could be caused by excessive grease entering aeration tanks from primary operations or the beginning of d e n i t r i f i c a t i o n i n the c l a r i f i e r ( s ) . | " p $ and ' r i s i n g clumps and mats of s o l i d s ' and succeed. ru l e ' r i s i n g clumps and mats of s o l i d s ' i f ( ('ask n i t r i f y ' i s true and p r i n t $"15 "r5| Excessive so l i d s retention times i n the secondary c l a r i f i e r ( s ) i s causing d e n i t r i f i c a t i o n of n i t r i f i e d biomass.| Increase return s o l i d s rates to eliminate s o l i d s blanket|"p$ and 'inc return 1 and ( ('ask denit' i s true and p r i n t $"15 "r5| D e n i t r i f i c a t i o n i n the secondary c l a r i f i e r ( s ) due to i n s u f f i c i e n t d e n i t r i f i c a t i o n i n anoxic reactor.|Increase c l a r i f i e r recycle to remove sol i d s blanket.|Adjust return s o l i d s rate so no s o l i d s blanket forms.|"p$ and 'excess secondary e f f l u e n t N03' and succeed) or p r i n t $"15 "r5| D e n i t r i f i c a t i o n i n the secondary c l a r i f i e r ( s ) due to excessive s o l i d s retention time.|Adjust return s o l i d s rate so no s o l i d s blanket forms.|Check for i n s u f f i c i e n t sludge removal or plugged recycle.|"p$ and succeed) and 'return s o l i d s ' and succeed) or p r i n t $"15 "r5| Solids could be due to i n s u f f i c i e n t removal by scrapers or sludge c o l l e c t i n g on side walls of c l a r i f i e r ( s ) . | Inspect sludge c o l l e c t o r s and clean side walls.|"p$ and ( ('color of s o l i d s ' i s 'tan or brown' and p r i n t $"15 "r5| P a r t i a l d e n i t r i f i c a t i o n i n the secondary c l a r i f i e r ( s ) due to increased temperature and/or s u f f i c i e n t MCRT.| Increase wastage to decrease MLSS and MCRT.|"p$ and 'dec miss' and 'wastage') or ('color of s o l i d s ' i s 'black' and p r i n t $"15 "r5| 153 Solids color and condition indicate probable septic condition i n the secondary c l a r i f i e r ( s ) . | Increase return rate and DO levels i n aeration tank(s).|"p$ and 'inc return' and 'return s o l i d s ' ) ) and succeed). ru l e 'cloudy e f f l u e n t - dispersed s o l i d s ' i f ( ('sludge s e t t l e ' i s 'slow s e t t l i n g ' ) or ('sludge s e t t l e ' i s 'normal') and ( ('rot i f e r ' i s true and p r i n t $"15 ~r5| Inactive protozoa could be an in d i c a t i o n that a toxic slug loading has entered the plant and disrupted the b i o l o g i c a l system.|Retain biomass to speed plant recovery.|"p$ and 'inc miss' and 'wastage' and succeed) or succeed) and ( ('fmload' i s 'high' and p r i n t $"15 "r5| Conditions indicate that the process i s or g a n i c a l l y overloaded.| Increase MLSS by decreasing wastage from the process.| Check that grease or other i n d u s t r i a l surfactants are not entering the aerationtank(s) and i n s t a l l sprays to reduce foam build-up.|"p$ and 'inc miss' and 'wastage' and succeed) or succeed)) or ('sludge s e t t l e ' i s 'fast s e t t l i n g ' and ( ('fmload' i s 'high' and p r i n t $"15 "r5| Conditions indicate that the process i s or g a n i c a l l y overloaded.| Increase MLSS by decreasing wastage from the process.| Check that grease or other i n d u s t r i a l surfactants are not entering the aeration tank(s) and i n s t a l l sprays to reduce foam build-up.|"p$ and 'inc miss' and 'wastage' and succeed) or succeed) and ( ('fmload' i s 'low' and p r i n t $"15 "r5| Condition of aeration tank(s) suggest that MLSS concentrations are high r e l a t i v e to the organic loading and endogenous re s p i r a t i o n within the biomass i s occurring.|Probable cause of cloudy effluent i s underloaded process.|Increase wastage to decrease biomass i n aeration tank(s).|"p$ and 'dec miss' 154 and 'wastage' and succeed) or succeed)) or (print $"15 "r5| Check inf l u e n t conditions or preliminary treatment operations.|"p$ and succeed). rul e 'excess secondary effluent NH3' i f p r i n t $"15 "r5| Conditions of loading and/or temperature have changed i n the aeration tank(s)to reduce the b i o l o g i c a l a b i l i t y to n i t r i f y i n f l u e n t ammonia.|Increase MLSS and sludge age by reducing wasting.|"p$ and 'inc miss' and 'wastage' and succeed. r u l e 'excess secondary effluent N03' i f ('type denit' i s ' p r e d e n i t r i f i c a t i o n ' and p r i n t $"15 "r5| Loss of nitrates could be due to:|| a) I n s u f f i c i e n t n i t r a t e recycle to anoxic zone.| b) I n s u f f i c i e n t anoxic reactor volume.| c) Increased n i t r a t e levels ( n i t r i f i c a t i o n r a t e ) . | d) High DO levels i n recycle.||$ and p r i n t $"15 "r5| Possible solutions:| Increase n i t r a t e recycle.| Check inf l u e n t ammonia loadings and necessary anoxic zone volume.|Increase anoxic reactor volume.|Decrease DO i n aerobic recycle.|Check c l a r i f i e r for continued d e n i t r i f i c a t i o n . | " p $ and succeed) or ('type denit' i s ' p o s t d e n i t r i f i c a t i o n ' and p r i n t $"15 "r5| Loss of nitrates could be due to:| | a) I n s u f f i c i e n t anoxic reactor volume.| b) Increased n i t r a t e levels ( n i t r i f i c a t i o n r a t e ) . | c) I n s u f f i c i e n t carbon for d e n i t r i f y i n g heterotrophs.| d) High DO levels i n aerobic reactor passing through to anoxic| reactor.||$ and p r i n t $"15 "r5| Possible solutions:| Check inf l u e n t ammonia loadings and necessary anoxic zone volume.| Supply supplemental carbon or raw sewage bypass to anoxic zone.| Increase anoxic reactor volume.| Check c l a r i f i e r for continued d e n i t r i f i c a t i o n . | " p $ 155 and succeed). rule 'balance secondary' i f ( ('sc b' i s A and A >= 2 and 'ask balance 2' i s fa l s e and p r i n t $"15 "r5| Unbalanced flows to on-line c l a r i f i e r s can cause surges of s o l i d s . | Try to balance flows to the operational c l a r i f i e r s by:| a) Checking return pumping rates and durations.! b) Balancing inflows between the on-line c l a r i f i e r s by throttling|uuuflows at s p l i t t e r box and increasing head losses to reduce the effects of surges i n the i n f l u e n t channels.|"p$ and succeed) or succeed). rul e 'return s o l i d s ' i f ( ('bit' i s 'high' or 'low' and ( ('inc return* i s true and p r i n t $"15 "r5| Increase return rates by 10 to 15 % over present flow.$) or ('dec return' i s true and p r i n t $"15 "r5| Decrease return rates by 10 to 15 % over present flow.| Insure that s o l i d s blanket does not exceed 1/3 of the c l a r i f i e r ( s ) depth.|$)) and p r i n t $"15 "r5| Adjust return s o l i d s rate so that a minimum blanket i s maintained i n the secondary c l a r i f i e r ( s ) over the varying flow conditions.! Thick sludge blankets i n the c l a r i f i e r ( s ) w i l l : | a) plug return s o l i d s pipes| b) jam sludge scrapers on c l a r i f i e r bottom(s)| c) tend to become septic or d e n i t r i f y and cause r i s i n g solids.|"p$ and ( ('ask n i t r i f y ' i s true and p r i n t $"15 "r5| When the process i s controlled for n i t r i f i c a t i o n no sludge blanket should develop i n the secondary c l a r i f i e r ( s ) . | T h e sludge would quickly deplete the available DO and begin to d e n i t r i f y the availab l e n i t r a t e s , causing r i s i n g solids.|"p$) or succeed) and ( ('ask denit' i s true and p r i n t $"15 "r5| When the process i s controlled for d e n i t r i f i c a t i o n no sludge blanket should develop i n the secondary c l a r i f i e r ( s ) . | I n single sludge systems, nitrates that are not recycled or are not d e n i t r i f i e d could d e n i t r i f y i n the secondary c l a r i f i e r ( s ) causing 156 r i s i n g solids.|~p$) or succeed) and succeed) or (print $~15 ~r5| Return s o l i d s rate so sludge blankets are not b u i l t up i n the secondary c l a r i f i e r ( s ) . $ ) ) . r u l e 'wastage' i f 'wastage 1' or 'wastage 2' or p r i n t $'15 ~r5| Maintain wasting at current rates.|$. ru l e 'wastage 1' i f 'inc miss' i s true and ( ('where wastage' i s 'tank' and p r i n t $"15 ~r5| Increase MCRT by decreasing the volume of mixed l i q u o r wasted from the aeration tank(s).]This w i l l increase MLSS le v e l s i n the aeration tank(s).$) or ('where wastage' i s 'rflow' and p r i n t $~15 ~ r | Increase MCRT by decreasing wastage to increase MLSS l e v e l s . | I suggest wasting from the aeration tank(s) due to t h e i r uniform MLSS as compared to the uneven s o l i d s l e v e l s experienced i n the return s o l i d s flow.$) or ('where wastage' i s 'both' and p r i n t $"15 ~r5| I suggest wasting from the aeration tank(s) due to t h e i r uniform MLSS.|Increase MCRT by decreasing the volume of mixed l i q u o r wasted from the aeration tank(s).|This w i l l increase MLSS l e v e l s i n the aeration tank(s).$) and succeed) and succeed. r u l e 'wastage 2' i f 'dec miss' i s true and ( ('where wastage' i s 'tank' and p r i n t $"15 ~r5 Decrease MCRT by increasing the volume of mixed l i q u o r wasted from the aeration tank(s).]This w i l l decrease MLSS l e v e l s i n the aeration tank(s).$) or ('where wastage' i s 'rflow' and p r i n t $"15 "r5| Decrease MCRT by increasing wastage to decrease MLSS l e v e l s . | I suggest wasting from the aeration tank(s) due to t h e i r uniform MLSS as compared to the uneven sol i d s l e v e l s experienced i n the 157 return s o l i d s flow.$) or ('where wastage' i s 'both' and p r i n t $"15 "r5| I suggest wasting from the aeration tank(s) due to t h e i r uniform MLSS.| Decrease MCRT by increasing the volume of mixed l i q u o r wasted from the aerationtank(s).|This w i l l decrease MLSS le v e l s i n the aeration tank(s).$)) and p r i n t $~15 "r5| Decrease MCRT by 10% per MCRT, that i s allow s u f f i c i e n t time for biomass to adjust to new conditions before re-adjusting wastage rates.$ and ( ( ('where waste' i s 'tank') or ('where waste' i s 'both') and 'sludge' i s true and p r i n t $"15 "r5| Large volumes of waste sol i d s are possible when wasting occurs from the aeration tank(s).|Stagger wasting over s h i f t s to continuously process sludge.|Possibleneed for increased sludge handling capacity.$ and succeed) or succeed) and p r i n t $"15 "r5| Generally, an increase i n organic or NH3 loadings are accompanied by an increasein MLSS levels and an increased DO demand. The inverse i s also true.|At a l l times, maintain minimum DO requirements and check aeration and compressor systems.$. rule 'pumps' i f ( ('waste pump' i s true and succeed) or ('waste pump' i s fal s e and p r i n t $"15 "r5| MLSS pumping system f a i l u r e . | a) Use back-up or supplemental pump(s) to r e c i r c u l a t e MLSS for | d e n i t r i f i c a t i o n or wastage.| b) Return so l i d s underflow can be wasted as control option.| c) Check for general pump f a i l u r e s and power breakers.|~p$ and succeed)) and ( ('ask return pump' i s true and succeed) or ('ask return pump' i s fal s e and p r i n t $"15 "r5| Return so l i d s pumping system f a i l u r e . | a) Use back-up or supplemental pumps to remove s o l i d s from | secondary c l a r i f i e r ( s ) . | b) Check for clogged return pumps or return sludge l i n e s . | c) Bring back-up c l a r i f i e r ( s ) on-line.|"p$ 158 and succeed)). rule 'solve filaments' i f p r i n t $"15 "r5| Bulking sludge due to filamentous organisms can cause serious problems inwastewater treatment plants. Older technology uses the following:|| a) c h l o r i n a t i o n - 2 to 3 kg per 1000 kg MLSS per day| b) nutrient addition to follow the r a t i o 100:5:1:0.5 (BOD:N:P:Fe)| c) change i n DO - either low to high or high to low| d) change i n pH - either increase or decrease||$ and p r i n t $"15 "r5| These control practices are intended to k i l l or change the conditions thought to be s p e c i f i c to the filamentous organisms. They can and should be used to control bulking i n the short-term. However, bulking has been found to occur over a wide range of conditions i n wastewater treatment plants and more permanent control practices can be applied.|"p|$ and p r i n t $"15 "r5| Five major b i o l o g i c a l control practices are suggested to reduce the p o s s i b i l i t y of producing conditions favorable to filamentous bulking sludges:|| 1) The use of very long (L:W 6 20:1) plug flow reactors to minimize back-mixing.| 2) Compartmentalization of a b i o l o g i c a l reactor to reduce | back-mixing and produce a high-to-low F/M gradient throughout the reactor.| 3) The operation of the f i r s t zone of reactor i n a f u l l y aerobic conditions : DO 6 2.0 mg/L OUR:DO 6 25:1 while under a | high F/M loading (6 3 kg BOD/kg MLSS/day).|$ and p r i n t $"15 "r5| 4) The operation of the f i r s t zone of reactor i n a near-anaerobic conditions : DO 6 0.2 mg/L OUR:DO 6 500:1 while under a | high F/M loading (6 3 kg BOD/kg MLSS/day).| while under a high F/M loading (6 3 kg BOD/kg MLSS/day).| 5) Anaerobic treatment of the return s o l i d s before re-entering the reactor and mixing with the raw wastewater.||"p$ and ( ('type tank' i s 'completely mixed reactor' and p r i n t $"15 "r5| CMAS reactors tend to promote a bulking sludge due to the concept of t h e i r design. The ov e r a l l low substrate concentration and reaction rate favors filamentous organisms.|Suggested action:|$ and p r i n t $"15 "r5| a) Separate and compartmentalize the CMAS reactors to produce a plugflow type reactor with a high-to-low F/M gradient.| b) Aeration - should use automatic DO control with |"p$) or ('type tank' i s 'plug flow reactor' 159 and p r i n t $"15 "r5| PFAS reactors can be r e t r o f i t t e d quite e a s i l y to compartmentalize the reactor basin and prevent back-mixing.|Suggested action:| a) Compartmentalize - b a f f l e s should cover -f 90% of the| cross-section and can f l o a t on the surface or span the tank for support.| b) Aeration - should use automatic DO control with coarse bubble| d i f f u s e r s and capacity of 200% required a i r . | c) Mixing - minimum a i r i n f i r s t compartment for mixing or use of mechanical mixers to suspend MLSS.| d) Loading - Influent into f i r s t compartment should give F/M loading 3 kg BOD/kg MLSS per day.|"p$)). r u l e 'secondary floe c l a r i f i e r s ' i f (print $"15 "r5| Secondary C l a r i f i e r Interactive Unit Operation Diagnosis||This session checks the secondary c l a r i f i e r s and clarifier-dependant systems."p$ and 'sc a' i s A and A >= 1 and 'sc b' i s B and B >= 1 and A >= B and ( ('type sc' i s ' c i r c u l a r ' and 'rotating plow*) or ('type sc' i s 'rectangular' and 'chain and f l i g h t ' ) ) and 'excess secondary effluent suspended s o l i d s ' and 'balance secondary' and succeed) or (print $"15 "r5| There are no secondary c l a r i f i e r ( s ) i n s t a l l e d i n the plant.$ and succeed). rul e 'rotating plow' i f ('ask rotate c' i s 'rotating' and p r i n t $"15 "r5| Scraper should be rotating at 0.02 to 0.06 RPM for proper operation.$ and succeed) or ('ask rotate c' i s 'not rotating' and ( ('reset scraper 1' i s true and succeed) or ('reset scraper 1' i s fa l s e and p r i n t $"15 "r5| Possible solutions are:| a) Bypass secondary c l a r i f i e r to other unit(s) and repair| scraper arm.| 160 b) Continue using c l a r i f i e r , but pump d i l u t e activated sludge to| sludge handling f a c i l i t i e s u n t i l scraper arm i s repaired.|"p$ and succeed))) or ('ask rotate c' i s 'rotating but i r r a t i c a l l y ' and p r i n t $"15 "r5| Scraper should be rotating at 0.02 to 0.06 RPM for proper operation. Check for: a) Bent or broken sludge plow on scraper arm.| b) Slippage of drive belts or worn gear drives on c o l l e c t i o n arm. | c) Build-up of col l e c t e d sludge.| "p$ and succeed). rule 'chain and f l i g h t ' i f ('ask t r a v e l r' i s 'moving' and p r i n t $"15 "r5| Chain scraper or t r a v e l l i n g bridge should be moving at 0.3 - 1.0 meters per minute for proper operation.$ and succeed) or ('ask tr a v e l r' i s 'not moving' and ( ('reset scraper 2' i s true and succeed) or ('reset scraper 2' i s fa l s e and p r i n t $"15 "r5| Possible solutions are:| a) Bypass secondary c l a r i f i e r to other unit(s) and repair| scraper arm.| b) Continue using c l a r i f i e r , but pump d i l u t e activated sludge to| sludge handling f a c i l i t i e s u n t i l scraper arm i s repaired.|"p$ and succeed))) or ('ask moving r' i s 'moving but i r r a t i c a l l y ' and p r i n t $"15 "r5| Chain scraper or t r a v e l l i n g bridge should be moving at 0.3 - 1.0| meters per minute for proper operation.| Check for:| a) Broken f l i g h t or worn sprockets.| b) Slippage of drive belts on drive sprockets.| c) Build-up of col l e c t e d sludge slowing scraper boards.|"p$ and succeed). 'temp' ask $"15 "r5| Has the inf l u e n t wastewater temperature decreased and remained lower than normal?$ a l t yn. 'fmload' ask $"15 "r5| 161 What i s the current F/M loading on the aeration tank(s)?$ a l t ('< 0.5','0.5 - 0.2','> 0.2') r a i t ('high', 'normal','low 1) expl ($The process loading on the aeration tanks helps WASTES determine whether the process i s under or overloaded.| Changing the l i m i t s i n the question 'fmload' customizes the l i m i t s to a s p e c i f i c process or f a c i l i t y . $ ) . 'ofr' ask $'l5'r5| Is the c l a r i f i e r ( s ) overflow rate above design flow(s)?$ a l t yn. 'waste pump' ask $'15 'r5| Are the pump(s) for wastage of MLSS from the aeration tank(s) operating?$ a l t yn. 'ask return pump' ask $'15 'r5| Are the return s o l i d s pump(s) operating and i s there flow back to the aeration tank(s)?$ a l t yn. 'floe' ask $'15 'r5| Under microscopic observation, what i s the color of the b i o l o g i c a l f l o e r e l a t i v e to normal conditions?$ a l t ('lighter', 'same', 'darker'). 'sludge' ask $'15 r5| Do the sludge handling or treatment methods used at the plant have a limi t e d capacity to the amount of waste sludge that can be processed?$ a l t yn. 'ask blanket' ask $'15 'r5| Are the secondary c l a r i f i e r ( s ) and return s o l i d s flow controlled so that a sludge blanket develops on the bottom(s).$ a l t yn. 'type of scraper' ask $'15 'r5| What type of sludge c o l l e c t o r i s i n s t a l l e d i n the secondary c l a r i f i e r ( s ) ? $ a l t ('rotating plow-type', 162 'chain and f l i g h t ' ) . 'type sc' ask $"15 "r5| What type of secondary c l a r i f i e r ( s ) are i n s t a l l e d i n the plant?$ a l t ( 1 c i r c u l a r ' , 'rectangular'). 'MLSS' ask $"15 "r5| What do you think the present MLSS concentration i s compared to normal loading conditions i n the aeration tank(s)?$ a l t ('higher', 'same', 'lower'). 'ask n i t r i f y ' ask $"15 "r5| Is the plant purposely n i t r i f y i n g i n fluent ammonia for e f f l u e n t requirements ? $ a l t yn. 'ask denit' ask $"15 "r5| Is the plant purposely d e n i t r i f y i n g to remove nitrogen from the ef f l u e n t for effluent requirements?$ a l t yn. 'type tank' ask $"15 "r5| What type of mixing regime or tank design i s used at the plant?$ a l t ('completely mixed reactor', 'plug flow reactor'). 'color of MLSS' ask $"15 "r5| What describes the color of the mixed liquor i n the aeration tank(s) as compared to normal conditions?$ a l t ('lighter', 'same', 'darker'). 'type of foam' ask $"15 "r5| What best describes the color and type of foam present on the surface of the aeration tank(s) at the present time?$ a l t ('white billowing foam', 'l i g h t tan or brown foam', 'dark brown foam'). 'where wastage 1 ask $"15 "r5| Where can b i o l o g i c a l s o l i d s wasted or removed from the system?$ 163 a l t ('aeration tank(s)','secondary c l a r i f i e r underflow','both') r a i t ('tank *,'rflow','both') expl ($WASTES would l i k e to know where you waste s o l i d s from youractivated sludge process so I can estimate the changes needed to correct your system.$). 'sludge s e t t l e ' ask $'15 'r5| What best describes the s e t t l i n g a b i l i t y of the activated sludge mixed liq u o r entering the secondary c l a r i f i e r ( s ) ? $ a l t ('slow s e t t l i n g ' , 'normal s e t t l i n g ' , 'fast s e t t l i n g ' ) . ' b i t ' ask $'15'r5| Where i s the pos i t i o n of the sludge blanket i n the c l a r i f i e r ( s ) ? $ a l t ('high*, 'low', 'none'). 'bltspeed' ask $'l5'r5| How d i d the l e v e l of the sludge blanket change?$ a l t ('quickly (minute/hours)', 'slowly (days)') r a i t ('quickly', 'slowly'). ' s i r ' ask $'l5~r5| What i s the current s o l i d s loading rate on the c l a r i f i e r ( s ) r e l a t i v e to the design so l i d s loading rate?$ a l t ('above', 'at or below'). 'filament' ask $'15 'r5j Does a microscopic examination of the activated sludge show masses of filamentous organisms present?$ a l t yn. 'ess' ask $'15 'r5| Does the effluent from secondary c l a r i f i e r ( s ) contain excess suspended solids?$ a l t yn. 'ESS type 2' ask $'15 'r5( 164 What do the so l i d s appear l i k e at the c l a r i f i e r overflow weir(s)?$ a l t ('normal - ex i t i n g along entire length of weir', 'normal - ex i t i n g only i n discrete areas of weir", 'ash-like solids on the surface', ' r i s i n g clumps and mats of s o l i d s ' , 'cloudy effluent - dispersed s o l i d s ' ) . 'ebod' ask $"15 "r5| Is the BOD of the plant effluent above normal levels?$ a l t yn. 'ibod' ask $"15 "r5| Has the organic loading or F/M of the process increased?$ a l t yn. ' r o t i f e r ' ask $"15 "r5| Does a microscopic examination show inactive r o t i f e r protozoa?$ a l t yn. 'cover' ask $"15 "r5| Is there a cover over the c l a r i f i e r or some sort of wind buffer protecting the c l a r i f i e r ? $ a l t yn. 'ask t r a v e l r' ask $"15 "r5| What i s the chain scraper or t r a v e l l i n g bridge scraper doing?$ a l t ('moving', 'not moving', 'moving but i r r a t i c a l l y ' ) . 'ask rotate c' ask $"15 "r5| What i s the c i r c u l a r sludge c o l l e c t i o n scraper arm doing?$ a l t ('rotating', 'not rotating', 'rotating but i r r a t i c a l l y ' ) . 'reset scraper c' ask $"15 "r5| Check: a) Debris jams i n the bottom of the c l a r i f i e r ) b) Bent or broken plow.| c) F a i l u r e of the motor or reducer gears| d) Reset of the power breaker| Does the unit work now?$ a l t yn. 'reset scraper r' ask 165 $"15 "r5| Check: a) Debris jams i n the bottom of the c l a r i f i e r | b) Broken f l i g h t . | c) F a i l u r e of the motor or reducer gears| d) Reset of the power breaker| Does the unit work now?$ a l t yn. 'color s o l i d s ' ask $"15 "r5| What do the r i s i n g s o l i d s look like?$ a l t ('tan or brown', •black'). 'ask balance 2' ask $"15 "r5| Are the wastewater flows to the on-line secondary c l a r i f i e r s approximately equal?$ a l t yn. 'type denit' ask $"15 "r5| What type of d e n i t r i f i c a t i o n system employing an anoxic zone being used?$ a l t ( ' p r e d e n i t r i f i c a t i o n ' , ' p o s t d e n i t r i f i c a t i o n ' ) . % AERATION AND MIXING SYSTEMS rule 'solve aeration/mixing' i f ('type aer' i s 'diffused a i r ' and p r i n t $"15 "r5| Diffused aeration of activated sludge tanks.$ and 'aeration present' and 'aeration uniform' and 'check DO') or ('type aer' i s 'mechanical' and ( MLSS' ('ask bubbles' i s 'to provide DO and mix the and p r i n t $ 1 5 r5| Mechanical aeration of activated sludge tanks.$ and 'aeration mechanical' and 'solve DO mechanical') or ('ask bubbles' i s 'only to mix the MLSS' and p r i n t $"15 "r5| Mechanical aeration of activated sludge tanks.$ and 'mix mechanical'))). rule 'aeration present' i f ('ask present' i s f a l s e 166 and p r i n t $"15 "r5| a) Check your compressor(s) to see i f they are operating.| b) Examine the piping and valve system to see i f there are any s p l i t casings, blown gaskets, or frozen valves.| c) If using DO c o n t r o l l e r , check readings.|"p$ and ( ('ask a i r loss' i s 'piping system f a i l u r e ' and p r i n t $"15 "r5| If the f a i l u r e i s on a main a i r supply conduit to a tank:| a) Reduce compressor output to minimum.| b) Close valves leading to aeration tank(s).| (Closing valves under pressure could cause more damage)| c) Use aeration piping bypass to supply the tank.| d) If no bypass i s available, provide aeration through mechanical means:| mechanical aerators, pumping and spraying the MLSS.| Provide DO to the biomass and prevent reactor upset or f a i l u r e . | p $ ) or ('ask a i r loss' i s 'compressor f a i l u r e ' and p r i n t $"15 "r5| a) Close valving to prevent backflow into compressor and use other i n s t a l l e d compressors or back-up units to meet DO demand of aeration tank(s).| b) Immediately get compressor or motor and drive unit serviced.|"p$) or ('ask a i r loss' i s 'controller f a i l u r e ' and p r i n t $"15 "r5| a) Check i n s t a l l e d DO probes operation.| b) I n s t a l l DO probe self-checking i n c o n t r o l l e r software.|"p$))) or succeed. rul e 'aeration uniform' i f ('ask uniform 1 i s 'excessive a g i t a t i o n and splashing' and ( ('ask head' i s 'coarse bubble d i f f u s e r ' and p r i n t $"15 "r5| Reduce agitat i o n and splashing by:| a) I n s t a l l i n g fine d i f f u s e r heads on some or a l l of the aeration units.| b) I n s t a l l spargers to break up the coarse a i r bubbles.|"p$) or ('ask head' i s 'fine bubble d i f f u s e r ' and p r i n t $"15 "r5| Check the positioning of the aeration heads r e l a t i v e to the aeration tank walls to ensure they are not too close.|"p$)) and p r i n t $"15 "r5| Reduced aeration rates could solve excessive a g i t a t i o n and splashing.| Check the mixing condition a f t e r the aeration tank(s) have had a 167 period of time to s e t t l e down.| Check and monitor:| a) DO level s throughout aeration tank.| b) MLSS mixing conditions.|"p$ and succeed) or ('ask uniform' i s 'uniform and thoroughly mixed' and succeed) or ('ask uniform' i s 'non-uniform with dead spots of s e t t l i n g MLSS' and p r i n t $"15 "r5| Non-uniform aeration leads to dead spots i n the tank and reduced e f f i c i e n c y of removal.| Balance the a i r supply to aeration heads by adjusting the a i r flow valves at the aeration tank(s).|"p$ and ('ask a i r balance' i s true and p r i n t $"15 "r5| Insure that a l l aeration tanks are balanced and check a i r flow meters to insurethat a l l aeration tanks are receiving equal flow.|"p$ and succeed) or ('ask a i r balance' i s fa l s e and p r i n t $"15 "r5| L i f t aerators out that are experiencing continued poor a i r flow and inspect for:| a) aerators clogged with rags or debris.| b) dark, d i r t y aerators.|"p$ and ( ('ask clog' i s true and p r i n t $"15 "r5| Aerators clogged with debris, check the preliminary unit operation racks and shredders.$ and load $racks.kb$ and 'racks and shredders') or ('ask clog' i s fa l s e and p r i n t $"15 "r5| Remove the aeration head and replace with new one.$ and ( ('ask head' i s 'fine bubble d i f f u s e r ' and p r i n t $"15 "r5| Probable cause of f a i l u r e i s d i r t y a i r therefore replace or i n s t a l l a i r f i l t e r s on compressors.! Fine bubble d i f f u s e r s are prone to clogging and could be replaced with medium or coarse bubble d i f f u s e r s but with increased a i r flow necessary and at reduced transfer e f f i c i e n c i e s . | " p $ ) or succeed)))) and succeed). ru l e 'aeration mechanical' 168 i f ('ask present' i s fal s e and p r i n t $"15 "r5| Check the following on the mechanical aerators:| a) Power supply main breakers.| b) Power connections to aerators.| c) Motor breaker and reducer drive for jams.|"p$ and ('ask s t i r ' i s true and p r i n t $"15 "r5| Now that the aerator i s functioning.$ and succeed) or ('ask s t i r ' i s fa l s e and p r i n t $"15 "r5| Remove the aerator from the tank for s e r v i c i n g . | a) Replace with back-up aerator.| b) If there i s no back-up aerator available, increase aeration| with other units i n s t a l l e d i n the tank by:| - lowering them into the MLSS and increasing the b i t e of the| impellers| - increasing the duration of operation of the other aerators| - increasing the speed of the units| c) Monitor DO lev e l s and l e v e l of mixing i n tank.|"p$)) or ( ('ask uniform' i s 'excessive a g i t a t i o n and splashing' and p r i n t $"15 "r5| Decrease the a g i t a t i o n and splashing by:| a) I n s t a l l i n g shields or covers around impellers to reduce spray| and wash. b) Reduce b i t e of impellers and i n s t a l l d r a f t tubes to r e t a i n | mixing and aeration| Wait an hour before testing bulk DO lev e l s i n MLSS.|"p$) or ('ask uniform' i s 'uniform and thoroughly mixed' and succeed) or ("ask uniform' i s 'non-uniform with dead spots of s e t t l i n g MLSS' and p r i n t $"15 "r5j Increase the aeration and mixing of the mechanical aerators by:| a) Lowering them into the MLSS and increasing the b i t e of the| uuuimpellers.| b) Increasing the duration of operation of the other aerators.| c) Increasing the speed of the units.| d) I n s t a l l d r a f t tubes to improve c i r c u l a t i o n of MLSS.| e) Bring additional aerators on-line i n the tank.| Wait an hour before testing bulk DO lev e l s i n MLSS.|"p$)) and succeed. rule 'mix mechanical' i f ('ask mix' i s true and ('ask uniform' i s 'uniform and thoroughly mixed' and p r i n t 169 $"15 "r5| Good mixing i s essential for suspended MLSS.$) or ('ask uniform' i s 'excessive a g i t a t i o n and splashing' and p r i n t $"15 "r5| Excessive agita t i o n w i l l : | a) Entrain a i r into the MLSS and reduce the a b i l i t y to e n i t r i f y . | b) Cause excessive shearing of the b i o f l o c creating c l a r i f i c a t i o n problems.| Therefore:| a) Reduce the mixing power input or motor speed.| b) Decrease the on duration time on some of the mixers.|"p$) or ('ask uniform' i s 'non-uniform with dead spots of s e t t l i n g MLSS' and p r i n t $"15 "r5| I n s u f f i c i e n t mixing w i l l allow the MLSS to s e t t l e and reduce removal e f f i c i e n c y . | a) Increase the mixing power input or motor speed.| b) Increase the on duration time on some of the mixers.|"p$)) or ('ask mix' i s fals e and ('ask uniform' i s 'uniform and thoroughly mixed' and p r i n t $"15 "r5| Good mixing i s essential for suspended MLSS.$) or ('ask uniform' i s 'excessive a g i t a t i o n and splashing' and p r i n t $"15 "r5| Excessive agita t i o n can shear the sludge floes causing ash on the surface of the c l a r i f i e r ( s ) . | Therefore:| a) Reduce the mixing power input or motor speed.| b) Decrease the on duration time on some of the mixers.|"p$) or ('ask uniform' i s 'non-uniform with dead spots of s e t t l i n g MLSS' and p r i n t $"15 "r5| I n s u f f i c i e n t mixing w i l l allow the MLSS to s e t t l e and reduce removal e f f i c i e n c y . | a) Increase the mixing power input or motor speed.| b) Increase the on duration time on some of the mixers.|"p$)). rule 'check DO' i f ('type aer' i s 'diffused a i r ' and 'solve DO diffused' and succeed) or ('type aer' i s 'mechanical' and 'solve DO mechanical' and succeed). 'ask DO high' i s 1.8. 'ask DO low' i s 1.4. 170 rule 'solve DO diffused' i f 'ask DO' i s A and ( ('ask DO low" i s X and A < X and p r i n t $"15 "r5| DO l e v e l s are too low for stable aerobic conditions i n dispersed! growth biomass:| a) Increase aeration by increasing the a i r flow to the aeration | tank(s).| b) If automated DO control i s used, decrease the DO setpoint| on the controller.|"p$) or ('ask DO high* i s Y and 'ask DO low' i s X and A >= X and A =< Y and p r i n t $"15 "r5| DO l e v e l s are good for stable aerobic conditions i n dispersed growth biomass and economical a i r use for f a c i l i t y operation.|"p$) or ('ask DO high' i s Y and A > Y and p r i n t $"15 "r5| DO l e v e l s are too high for economical a i r use for f a c i l i t y operation:| a) Decrease aeration by decreasing the a i r flow to the aeration| tank(s).| b) If automated DO control i s used, increase the DO setpoint| on the controller.|"p$)). rule 'solve DO mechanical' i f 'ask DO' i s A and ( ('ask DO low' i s X and A < X and p r i n t $"15 "r5| DO l e v e l s are too low for stable aerobic conditions i n dispersed growth biomass considering mechanical aeration i s used.| Increase the aeration and mixing of the mechanical aerators by:| a) Lowering them into the MLSS and increasing the b i t e of the| impellers.| b) Increasing the duration of operation of the other aerators.| c) Increasing the speed of the units.| or you can bring additional aerators on-line i n the tank.|"p$) or ('ask DO high' i s Y and 'ask DO low' i s X and A >= X and A =< Y and p r i n t $"15 "r5| DO l e v e l s are good for stable aerobic conditions i n dispersed 171 growth biomass and economical power use for f a c i l i t y operation.|"p$) or ('ask DO high' i s Y and A > Y and p r i n t $"15 "r5| DO le v e l s are too high for economical power use for f a c i l i t y operation.| Decrease the aeration and mixing of the mechanical aerators by:| a) Raising them out of the MLSS and decreasing the b i t e of the| impellers.| b) Decreasing the duration of operation of the other aerators.| c) Decreasing the speed of the units.| or you can take additional aerators o f f - l i n e i n the tank.|"p$)). 'ask DO' ask $"15 "r5| What i s the current mean bulk dissolved oxygen content i n the aeration tank(s) expressed i n mg/L ? -> enter a one decimal place number $ expl ($WASTES would l i k e to know the current DO so i t can compare i t to the low and high values and suggest c o r r e c t i v e action i f necessary.$). 'ask s t i r ' ask $"15 "r5| Did the aerator r e s t a r t and i s now functioning?$ a l t yn. 'ask clog' ask $"15 "r5J Is the aeration head functioning properly now a f t e r cleaning?$ a l t yn. 'ask head' ask $"15 "r5| What type of diffused a i r head i s i n s t a l l e d i n the aeration tanks?$ a l t ('fine bubble d i f f u s e r " , 'coarse bubble d i f f u s e r ' ) . 'type aer' ask $"15 "r5| What type of equipment i s i n s t a l l e d i n the activated sludge tank(s)?$ a l t ('diffused a i r ' , 'mechanical'). 'ask a i r balance' ask $"15 "r5| Did the a i r flow adjustment work or i s the aeration s t i l l v a riable perhaps 172 with a i r escaping out the blow-off legs on the aerators?$ a l t yn. 'ask bubbles' ask $"15 "r5| The the purpose of the mechanical mixing i n s t a l l e d i n the tank is?$ a l t ('to provide DO and mix the MLSS', 'only to mix the MLSS'). 'ask present' ask $"15 "r5| Are a l l the units i n s t a l l e d i n the tank(s) functioning?$ a l t yn. 'ask a i r loss' ask $"15 "r5| What appears to be the cause of the apparent lack of a i r to supply the aerators i n the tank(s)?$ a l t ('failed compressed a i r piping system', 'compressor f a i l u r e ' , 'controller f a i l u r e ' ) . 'ask uniform' ask $"15 "r5| What best describes the condition of the aeration tank(s)?$ a l t ('non-uniform with dead spots of s e t t l i n g MLSS', 'uniform and thoroughly mixed", 'excessive agitation and splashing') expl ($WASTES uses th i s description as a i n d i c a t i o n of the mixing provided by the aeration system and bases cor r e c t i v e action on the r e s u l t . $ ) . 'ask DO high' ask $"15 "r5| What i s the upper l i m i t for the DO range on the aeration tank(s) expressed i n mg/L ? -> enter a one decimal place number $. 'ask DO low' ask $"15 "r5| What i s the lower l i m i t for the DO range on the aeration tank(s) expressed i n mg/L ? -> enter a one decimal place number $. 'ask mix ' ask $"15 "r5| Is the mixing i n an anoxic d e n i t r i f i c a t i o n reactor?$ a l t yn. 173 Chapter 11.0 Appendix 2 Microscopic Examination of Activated Sludge 1.0 Introduction The d a i l y examination of the activated sludge mixed l i q u o r and the secondary c l a r i f i e r e f f l u e n t i s a powerful diagnostic t o o l a v a i l a b l e to the treatment plant operator. The presence, predominance, and condition of c e r t a i n types of microorganisms can help determine: o Filamentous bulking sludge o Organic overloading o Organic underloading o Toxic loading o Overall treatment e f f i c i e n c y . The following t u t o r i a l i s a general guide to help you d i s t i n g u i s h the various types of microorganisms present i n the activated sludge system. 2.0 Visual Examination Microscopic examination of the activated sludge mixed l i q u o r and f i n a l c l a r i f i e r e f f l u e n t can be done on a standard phasecontrast l i g h t microscope with an available magnification of 500 X. The mixed l i q u o r sample should be fresh and always taken from the same areas of the tanks. Assuming that the set-up and operation of the microscope and samples i s known, the time for a d a i l y v i s u a l analysis and recording of the c h a r a c t e r i s t i c s should only take 15 minutes. A sample observation sheet i s attached as a 174 reference. 2.1 I n i t i a l Observations The mixed liquor should be placed i n a 1.0 l i t e r beaker and suspended by s t i r r i n g . The observations should be done by eye or hand lens to record the following: o colour of the sludge o odour of the sludge o any trapped gases or unknown s o l i d s o sludge s e t t l i n g t e s t 2.2 Low Power Observations The next observation should be done under low magnification (100-200 X) for: o shape, s i z e , and structure of the sludge floe o presence of filamentous organisms o type of inorganic inclusions i n the floe o i d e n t i f i c a t i o n and observation of protozoa i n the mixed liquor. 2.3 High Power Observations The f i n a l observations should be made under high power (400 - 500 X) to d e t a i l : o composition of floes o nature of dispersed bacteria o i d e n t i f i c a t i o n of f l a g e l l a t e s and filamentous bacteria (diameter > 1 ym) 175 3.0 Results A l l observations are subjective and what I would say i s dark brown, you could say i s l i g h t black thus the key to rendering good observational results i s consistency and o b j e c t i v i t y . Try to be consistent i n when you sample, where you sample, and who samples. One person should do the microscopic analysis and interpret the r e s u l t s , i n a way become the resident expert of that plant's microbial population. The form at the end of the guide serves as a sample of examination guide. 3.1 Macroscopic Observations The observations of mixed liquor colour and odour, combined with the operational observations of the aeration tanks and secondary c l a r i f i e r and results of the simple s e t t l i n g test help determine the observational data for the WASTES system. The information gathered i s used to determine the type, condition, and loading of the treatment process. 176 4 . 0 S a m p l e O b s e r v a t i o n s S h e e t DATE: : MIXED LIQUOR • TIME: SETTLED S L U D G E • LOCATION: OTHER: TANK #: A. V ISUAL OBSERVATIONS ( 1 . 0 I S E T T L E O M E T E R ) C O L O R : T R A P P E D G A S E S • ODOR: : OTHER: B. ACTIVATED S L U D G E ELOC O B S E R V A T I O N S L A R G E LACY E L O C S • DARK • PIN E L O C S • LIGHT • N O R M A L E L O C S • IRREGULAR • El LAMENTS • D I S P E R S E D . • P R O T O Z O A ACTIVE • INACTIVE • C. DETAILED OBSERVATIONS ( 4 0 0 - 5 0 0 X ) A P P R O X . ELOC SIZE: (,um) P R O T O Z O A : T Y P E N U M B E R 177 Chapter 12.0 Appendix 3 - WASTES User Manual This i s a guide of how to use WASTES, wastewater treatment expert system, and FRO, the accompanying system s h e l l . 1. System Requirements An IBM or compatible personal computer with at lea s t 256 Kb of RAM memory. An i n s t a l l e d hard disk drive i s preferred due to the amount of reading and writing to disk while the system operates, but a single floppy disk w i l l work and the system w i l l be slower. 2. Loading the system Turn the computer on and making sure that any memory-resident are not loaded to maximize the available memory for the expert system and minimize the amount of reading and writing to disk. a. I n s t a l l WASTES on a hard disk drive. Copy a l l the f i l e s from either the high density or the standard floppy disk to a subdirectory on the hard disk, i . e . C:\waste. The f i l e s copied should be: FRO.EXE RACKS.KB CLAR.KB FLOAT.KB FRO.IDB GRIT.KB MICRO.KB ODOUR.KB FRO.POO LIFT.KB RBC.KB TREAT.KB b. On floppy disk systems ins e r t the system disk into the disk drive with the correct dos prompt. c. To begin WASTES type " f r o " and enter at the dos prompt i n the correct subdirectory and disk drive: C>fro <enter> or A>fro <enter> If you are not using a mouse, use: C>fro /n <enter> or A>fro /n <enter> d. A frame should appear on your monitor with key d e f i n i t i o n s along the top border. 178 3. FUNCTION KEY DEFINITIONS a. Before you begin... Before you press a key to continue, notice the along the top of the frame are d e f i n i t i o n s for the function keys on the keyboard: These are the function keys for the Fro system. You w i l l also notice that some of the d e f i n i t i o n s have been blanked out by a row of dots. This means that the function i s not act i v e . Here are explanations of the function keys: F l : HELP This key provides a help function for the knowledge base. Pressing the key provides information on what area of the knowledge base you are presently i n . F2: FILES or EXPLAIN The context of t h i s key changes between FILES and EXPLAIN, depending on the status of the system. The FILES function prompts the user to enter the name of a knowledge base to be loaded into the FRO system. The EXPLAIN function i s active when the system i s asking a question. It provides a window of information concerning the question. F3: EXECUTE Used a f t e r the FILES command, t h i s key executes the top l e v e l goal i n the loaded knowledge base and begins the WASTES system. 179 F4: SAVE This function i s also used a f t e r the FILES command. It saves the loaded knowledge base i n two binary f i l e s , FRO_SAVE.IDB and FRO_SAVE.P00. When FRO i s re-started, these f i l e s are automatically loaded and the top l e v e l goal i s executed. F5; TRACE The TRACE function invokes a l o g i c t r a c i n g window along the bottom of the screen. Inside the screen, the in d i v i d u a l statements and goals are stepped through as the FRO system works through the knowledge base. The space bar steps through the ind i v i d u a l operations i n the s h e l l allowing the user an idea of the l o g i c developed i n the knowledge base. The F5 key toggles the trace function on and o f f . F6: Quit The QUIT function ends the in t e r p r e t i v e session and returns you to the DOS prompt. To end the session at any point, press t h i s key. To re- s t a r t WASTES, type fro <enter>. 4. Using WASTES Press F2 and type treat.kb <enter>. Once the system returns the statement: loaded You have two options before you press F3 and execute the program. One, you can press F4 and save the knowledge base i n binary and r e - s t a r t the program. This i s the option allows the system to load much faster, cutting disk read operations and shortening response times. Second, you can press any key to continue and use the system as i t i s . Whatever options you choose, execution of the program w i l l begin with: 180 Welcome t o WASTES W A S t e w a t e r T r e a t m e n t E x p e r t S y s t e m (C) B a r r y C h i l i b e c k . . V e r s i o n 3.0 f o l l o w e d b y a s h o r t p r o g r a m d e s c r i p t i o n a n d t h e f i r s t s y s t e m q u e s t i o n . T h e e x p l a i n f u n c t i o n s h o u l d be p r e s e n t a t t h e f i r s t q u e s t i o n . I n W A S T E S , t h e e x p l a i n f u n c t i o n c a n p r o v i d e t h r e e d i f f e r e n t p i e c e s o f i n f o r m a t i o n . F i r s t , i t c a n e x p a n d o n t h e q u e s t i o n p o s e d b y t h e s y s t e m b y s u p p l i n g a m o r e d e t a i l e d d e s c r i p t i o n . S e c o n d , i t c a n e x p l a i n how t h i s q u e s t i o n r e l a t e s t o t h e l o g i c o f t h e k n o w l e d g e b a s e a n d d e v e l o p m e n t o f t h e r u l e s t o s u p p o r t a g o a l . L a s t , i t c a n e x p l a i n what p i e c e s o f i n f o r m a t i o n i t h o p e s t o g a i n f r o m e a c h o f t h e d i f f e r e n t p o s s i b l e r e s p o n s e s . O p e r a t i n g t h e s y s t e m i s v e r y s i m p l e , j u s t a n s w e r t h e q u e s t i o n s a n d c h o o s e w h a t y o u w o u l d l i k e t o q u e r y o r t r o u b l e s h o o t . Y o u c a n a n s w e r q u e s t i o n s b y e n t e r i n g t h e number o f y o u r s e l e c t i o n . W i t h t h e mouse y o u s i m p l y move t h e p o i n t e r t o y o u r s e l e c t i o n , i t b e c o m e s h i g h l i g h t e d , a n d y o u p r e s s t h e mouse b u t t o n t o s e l e c t i t . T h e e a s i e s t way t o u n d e r s t a n d how t h e e x p e r t s y s t e m s h e l l a n d t h e k n o w l e d g e b a s e o p e r a t e s i s t o u s e t h e m . T r y d i f f e r e n t r e s p o n s e s t o t h e q u e s t i o n s a n d e x p e r i m e n t w i t h a l l o f t h e o p t i o n s a v a i l a b l e t o y o u . I f t h e s y s t e m c h a i n s t h r o u g h a l l t h e p o s s i b l e r u l e s a n d s o l v e s t h e t o p l e v e l g o a l i t p r i n t s : * * * S e s s i o n C o m p l e t e d * * * a n d t h e k n o w l e d g e b a s e i s f i n i s h e d . T h e s y s t e m i s n o t f o o l - p r o o f a n d t h e r e may be some e r r o r s , e s p e c i a l l y o n d i f f e r e n t P C s . I f i t h a n g s s i m p l y r e - s t a r t a n d t r y a g a i n . A t t a c h e d w i t h t h i s m a n u a l i s a r e v i e w s h e e t . Y o u r comments a n d c r i t i c i s m s w i l l h e l p me 181 improve WASTES and give me new ideas on what to include or develop with the system. I hope you can take some time to use the system and complete the review sheet. REVIEW SHEET a. Did you think that there were any conclusions that you did agree with? Any errors or omissions? b. What did you think about using the system? Was i t easy to understand? Were a l l the questions worded c l e a r l y ? 182 Did you learn something about what might be involved i n operating a f u l l wastewater treatment f a c i l i t y ? In general, do you think that systems s i m i l a r to t h i s would make good teaching tools? Are there any other comments you would l i k e to add? 183 Chapter 13.0 Appendix 4 - WASTES System Diskette 184 

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