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The Accuracy and precision of ORP monitoring in bio-nutrient removal processes Zhou, Jianpeng 1993-12-31

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THE ACCURACY AND PRECISION OF ORP MONITORING INBIO-NUTRIENT REMOVAL PROCESSESByJIANPENG ZHOUB. Eng. (Civil Engineering), Tsinghua University, China.M. Eng. (Environmental Engineering), Tsinghua University, China.A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF APPLIED SCIENCEinTHE FACULTY OF GRADUATE STUDIESCIVIL ENGINEERINGWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAJanuary 1993© JIANPENG ZHOU, 1993In presenting this thesis in partial fulfilment of the requirements for an advanced degree atthe University of British Columbia, I agree that the Library shall make it freely availablefor reference and study. I further agree that permission for extensive copying of thisthesis for scholarly purposes may be granted by the head of my department or by hisor her representatives. It is understood that copying or publication of this thesis forfinancial gain shall not be allowed without my written permission.Civil EngineeringThe University of British Columbia2324 Main MallVancouver, CanadaV6T 1Z4Date:t`-^1711-^ 77_JAbstractIt is important to have complete denitrification in the anoxic zone to provide good con-ditions for phosphorus removal in a bio-nutrient removal process. The objective of thisresearch was to examine the possibility of using oxidation reduction potential (ORP) asa means of assessing the completeness of denitrification in the anoxic zone.First, the reliability and sensitivity of ten probes were tested and evaluated. Next,ORP values in complete denitrification conditions from biological systems with differentinitial NO concentrations and denitrification rates were collected and the usefulness ofthese redox values was assessed.Batch testing was used in this research. The Remote Data Acquisition and ControlSystem, an automated data log-in system, was used to collect redox values. ORP probeswere tested in quinhydrone buffer solutions. The biological systems in the anoxic testswere proportional combinations of mixed liquors from the anaerobic zone, aerobic zone,and the return sludge line of the UBC bio-nutrient removal process, so that differentinitial NO concentrations were obtained. Sodium acetate (NaAc) was added to thesystems of carbon addition tests in order to achieve different denitrification rates.The probe test results indicated that measured ORP values were linearly relatedto standard ORP values of the tested quinhydrone solutions. Adjustment factors weredeveloped based on this relationship for each probe.In the ORP vs time curves of biological batch tests, knees characteristic of the min-imum first derivative were observed. At these knees, the NO removal efficiencies werefound to be 92.6 % on average in anoxic tests, and to be 96.2 % in carbon additiontests. Redox values at the knees had an average of -28 my (adjusted value), with a stan-dard deviation of +8 my (adjusted value). When redox values reached -44 my (adjustedvalue), the lower limit of the 95% confidence interval, the biological system was still agood environment for phosphorus removal in the process.Adjusting measured redox values is not necessary in order to achieve the conclusionabout using ORP values to control a denitrification process. The -42 my, the lower limitof the 95% confidence interval from measured redox values, is suggested to be used as adenitrification control guideline. However, probe testing is still considered necessary.It was concluded that ORP monitoring can be used as a control tool in a denitri-fication process. Probe test procedures, including testing solutions, adjustment factorsdevelopment, and testing frequency are recommended in the research.Table of ContentsAbstractList of Tables^ viiiList of Figures xiList of Abbreviations^ xiiiAcknowledgements^ xiv12INTRODUCTIONLITERATURE REVIEW132.1 Oxidation-Reduction Potential Measurement ^ 32.2 The Application Possibilities of ORP Measurement ^ 52.3 ORP as a Control Parameter in Waste Treatment Processes ^ 62.4 ORP Monitoring in Bio-nutrient Removal Processes ^ 73 EXPERIMENTAL DESCRIPTION 93.1 Research Objectives ^ 93.2 UBC Bio-nutrient Removal Process Introduction ^ 103.2.1^Process scheme ^ 103.2.2^Process mechanism 123.3 Experimental Set-up ^ 133.3.1^Data log-in system 13iv3.3.2 QBASIC program ^  133.3.3 Batch testing apparatus  ^153.3.4 ORP probes and probe maintenance ^  153.4 Analytical Parameters and Techniques  183.4.1 NO (NO and NOn ^  183.4.2 MLSS and MLVSS  183.4.3 pH  ^193.4.4 Temperature  ^193.4.5 Chemical oxygen demand ^  193.5 Data Analysis Techniques  194 RESULTS^ 204.1 Probe Testing Results ^  204.1.1 Introduction  ^904.1.2 Probe test 1 (March 4, 1991)  ^224.1.3 Probe test 2 (April 4, 1991)  ^924.1.4 Probe test 3 (May 7, 1991)  ^224.2 Anoxic Batch Tests (Without External Chemical Addition) ^ 294.2.1 Introduction  ^294.2.2 Anoxic batch test 1 (March 11, 1991) ^ 304.2.3 Anoxic batch test 2 (March 21, 1991) 344.2.4 Anoxic batch test 3 (March 28, 1991) ^ •44.3 Anoxic Batch Tests (With External Carbon Addition) ^364.3.1 Introduction  ^364.3.2 Carbon addition test 1 (February 1, 1991) ^ 374.3.3 Carbon addition test 2 (February 7, 1991) 374.3.4 Carbon addition test 3 (March I, 1991)  ^425 DISCUSSION^ 445.1 Introduction  445.2 Evaluation of Probe Testing Results ^  445.2.1 The Probe's behaviour in quinhydrone buffer solutions ^ 455.2.2 Redox value adjustment ^  465.2.3 Evaluation of probe testing results  ^505.3 Redox Values for Complete Denitrification Conditions ^ 505.3.1 Defining ORP values for complete denitrification conditions ^505.3.2 Measured ORP values at the knees ^ 515.3.3 NO, levels at the knees  ^565.3.4 The possibility of using ORP as a control parameter ^ 585.4 The Necessity of Adjusting Measured ORP Values ^  646 CONCLUSIONS and RECOMMENDATIONS^ 686.1 Conclusions  ^686.1.1 Probe testing experiments  ^686.1.2 The accuracy and precision of ORP monitoring ^ 696.1.3 The necessity of adjusting measured ORP values  706.2 Recommendations ^  71Bibliography^ 72viAppendices^ 75A Results of Probe Test 2 and Probe Test 3^ 75B Results of Anoxic Batch Test 2 and Anoxic Batch Test 3^88C Results of Carbon Addition Test 2 and Carbon Addition Test 3^95viiList of Tables4.1 Nominal ORP values of reference quinhydrone solutions ^ 214.2 Buffer solutions' compositions  ^214.3 Experimental conditions for probe test 1 ^  224.4 Experimental conditions for probe test 2  924.5 Experimental conditions for probe test 3 ^  994.6 Mixed liquor combinations ^  294.7 Process characteristics on March 11, 1991  ^304.8 Experimental conditions for anoxic batch test 1  ^314.9 Process characteristics on March 21, 1991 ^ 354.10 Experimental conditions for anoxic batch test 2  ^354.11 Process characteristics on March 28, 1991 ^ 354.12 Experimental conditions for anoxic batch test 3  ^364.13 Process characteristics on February 1, 1991  ^384.14 Experimental conditions for carbon addition test 1  ^384.15 Process characteristics on February 7, 1991  ^424.16 Experimental conditions for carbon addition test 2 ^ 424.17 Process characteristics on March 1, 1991  ^434.18 Experimental conditions for carbon addition test 3 ^ 435.1 ORP values: Avg, Std and SD (probe test 1) (my)  465.2 Adjustment ratios (probe tests 1 to 3)  ^485.3 Measured ORP values at the knees (DM, AT1) (my)^ 54viii5.4 Measured ORP values at the knees (DM, AT2) (my) ^ 545.5 Measured ORP values at the knees (DM, AT3) (my)  555.6 Measured ORP values at the knees (DM, CA1) (my) ^ 555.7 Measured ORP values at the knees (DM, CA2) (my)  555.8 Measured ORP values at the knees (DM, CA3) (my) ^ 555.9 Measured NO at the knee position (AT 1-3) ^  565.10 Measured NO at the knee position (CA 1-3)  565.11 Initial NO levels and removal efficiencies (anoxic tests 1-3) ^575.12 Initial NO levels and removal efficiencies (carbon tests 1-3)  ^575.13 Adjusted ORP values at the knees (DM, AT1) (my) ^ 585.14 Adjusted ORP values at the knees (DM, AT2) (my)  595.15 Adjusted ORP values at the knees (DM, AT3) (my) ^ 595.16 Adjusted ORP values at the knees (DM, CA1) (my)  595.17 Adjusted ORP values at the knees (DM, CA2) (my) ^ 595.18 Adjusted ORP values at the knees (DM, CA3) (my)  605.19 Avg and Std at the redox knees (AT 1-3 and CA 1-3) ^ 605.20 NO (adjusted ORP value is -12 my, AT1) ^  615.21 NO (adjusted ORP value is -28 my, AT3)  625.22 NO (adjusted ORP value is -44 my, AT1) ^  625.23 NO (adjusted ORP value is -44 my, AT2)  625.24 NO (adjusted ORP value is -44 my, AT3) ^  635.25 NO (adjusted ORP value is -44 my, CA1)  635.26 NO (adjusted ORP value is -44 my, CA2) ^  635.27 NO (adjusted ORP value is -44 my, CA3)  635.28 NO (measured ORP value is -42 my, AT1) ^  655.29 NO (measured ORP value is -42 my, AT2)  65ix5.30 NOT (measured ORP value is -42 my, AT3) ^  655.31 NO (measured ORP value is -42 my, CA1)  665.32 NO (measured ORP value is -42 my, CA2) ^  665.33 NO (measured ORP value is -42 my, CA3)  66List of Figures3.1 UBC bio-nutrient removal process ^  113.2 Data log-in system scheme  143.3 Batch test apparatus  ^163.4 ORP probe ^  174.1 Probe test 1.1 (pH 4.03): (A) Probes (1-5). (B) Probes (6-10) ^234.2 Probe test 1.2 (pH 6.30): (A) Probes (1-5). (B) Probes (6-10) ^244.3 Probe test 1.3 (pH 7.06): (A) Probes (1-5). (B) Probes (6-10) ^254.4 Probe test 1.4 (pH 7.78): (A) Probes (1-5). (B) Probes (6-10) ^264.5 Probe test 1.5 (pH 8.78): (A) Probes (1-5). (B) Probes (6-10) ^274.6 Probe test 1.6 (pH 9.85): (A) Probes (1-5). (B) Probes (6-10) ^284.7 Anoxic batch test 1.1 (ratio 0)  ^314.8 Anoxic batch test 1.2 (ratio 1)  ^324.9 Anoxic batch test 1.3 (ratio 2)  ^324.10 Anoxic batch test 1.4 (ratio 3)  ^334.11 Anoxic batch test 1.5 (ratio 4)  ^334.12 NO test results (anoxic test 1)  ^344.13 Carbon addition test 1.1 (control)  ^394.14 Carbon addition test 1.2 (20 mg/L)  ^394.15 Carbon addition test 1.3 (40 mg/L)  ^404.16 Carbon addition test 1.4 (60 mg/L)  ^404.17 Carbon addition test 1.5 (80 mg/L)  ^41xi4.18 NO test results (carbon addition test 1)  ^415.1 Measured ORP values vs pH (probe test 1) ^  475.2 Measured ORP values vs standard ORP values (probe test 1) ^ 495.3 Anoxic test 1.1: first derivatives vs time  ^525.4 Anoxic test 1.1: first derivatives vs time (Avg 5)  ^535.5 Anoxic test 1.1: first derivatives vs time (Avg 10)  ^53xiiList of AbbreviationsAT: anoxic testAvg: averageCA: carbon addition testCOD: chemical oxygen demandDM: the derivative methodDO: dissolved oxygenmin: minuteMLSS: mixed liquor suspended solidMLVSS: mixed liquor volatile suspended solidNOT: a comprehensive measure of both NO3- and NO2-ORP: oxidation reduction potentialSD: standard valueStd: standard deviationUBC: the University of British ColumbiaVFA: volatile fatty acidNote: in this thesis the term "redox value" means the same as "ORP value".AcknowledgementsI gratefully acknowledge the following persons for their guidance and support during mystudies and research at the University of British Columbia.Dr. William. K. Oldham, Professor of the Civil Engineering Department at theUniversity of British Columbia, and Mr. Frederick A. Koch, Research Associate of thebio-P research group for their guidance and advice throughout my research.Dr. D. S. Mavinic and Dr. K. J. Hall, Professors of the Civil Engineering Departmentat UBC for serving on my committee and for their recommendations.Susan C. Harper and Paula D. Parkinson, Environmental Engineering LaboratoryTechnicians for their help during my experiments. John Wong, Civil Engineering Elec-tronics Technician for his help in setting up the data log-in system and preparation ofthe computing program.Fellow graduate students, Dave G. Wareham and Patrick F. Coleman for their valu-able discussion and help on the research. Patrick Duffy, UBC graduate student, for hishelp with the English in this thesis.Friendship from fellow graduates Andrew De Boer, James T-Y Ting has made myUBC life really enjoyable.Special thanks go to my sister Jianping Zhou for her consistent encouragement andhelp in my UBC life.The Environmental Engineering Group in the Department of Civil Engineering atthe University of British Columbia is gratefully acknowledged for providing the financialsupport through the operation grant of the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC).xivChapter 1INTRODUCTIONIt is important to remove nitrogen and phosphorus from municipal and industrial wastew-ater, especially when the wastewater is discharged into inland water systems such as lakesand rivers; nitrogen and phosphorus are major elements which are responsible for exces-sive growth of aquatic plants and algae, or eutrophication. Eutrophication can havedetrimental effects on aquatic life and the usefulness of the water resource. Among thecurrently employed methods of nitrogen and phosphorus removal, the biological methodhas advantages over chemical methods, as it has fewer chemical requirements and lowersludge production. The biological method is often more cost effective (US EPA, 1975).People have studied biological nutrient removal processes from different aspects suchas nutrient removal mechanisms (nitrification, denitrification, and phosphorus removal),process alternatives, and process controls. One current area of research interest is thedevelopment of automated control systems for bio-nutrient removal processes. In a pro-cess such as that shown in Figure 3.1, the aerobic zone is nitrate rich because of thenitrification. When denitrification is required, it is necessary to recycle the mixed liquorsfrom the aerobic zone to the anoxic zone, because denitrification will occur in the anoxiczone. It is important to have good control of the denitrification process in the anoxic zoneto guarantee that no significant quantity of nitrate is recycled from the anoxic zone tothe anaerobic zone by the anoxic recycling line. Nitrates could jeopardize the favourableconditions necessary for phosphorus removal in the process. It is generally realised thatdetection of nitrate concentrations in the anoxic zone is an important step in overall1Chapter 1. INTRODUCTION^ 2process control.Since nitrate probes are very expensive and are far from problem free when usedin sewage treatment plants, indirect measures of nitrate presence are potentially useful.Previous research indicated that oxidation reduction potential (ORP), or redox value,might be able to be used as a control parameter. ORP probes are sensitive to the nitratecouple, commercially available and inexpensive.The first part of this research involved the testing of individual probes for suitability.ORP probes were tested in quinhydrone buffer solutions and evaluated by comparing themeasured values to the standard values of each buffer solution.In the second part of this thesis, biological systems were used in batch tests to inves-tigate the possibilities of the redox measurement in a bio-nutrient removal process. Theeffect of different initial nitrate levels and different denitrification rates on redox values,in complete denitrification conditions, were studied.As a result of the data generated, testing procedures for ORP probes were recom-mended.Chapter 2LITERATURE REVIEW2.1 Oxidation-Reduction Potential MeasurementOxidation-reduction potential measurement determines the ratio of oxidants to reduc-tants within a solution. It is different from pH measurements because it is non-specificwith respect to any one compound. What the ORP electrode pairs test is the prevailingnet potential of a solution. This measurement makes it possible to determine the abilityto oxidize or reduce a given species in the solution (ASTM, 1983).Equation (2.1) is used to describe the oxidation reduction potential of a processsolution:Em = E0 + RT ln A'^ (2.1)nF AredEm = the measured oxidation reduction potential relative to a reference half cell (my).E0 = a constant that is dependent to the choice of reference electrode (my).R = universal gas constant (8.314 joules/deg - mole).T = absolute temperature (°C -I- 273.15).n = number of electrons involved in the process reaction.F = Faraday constant (96,464 joules/volt).A0s and Ared = activities of the oxidants and reductant participating in reactions.More detailed redox theory can be found in Petersen (1966), Bates (1973), Broadley(1990), and Wareham (1992).3Chapter 2. LITERATURE REVIEW^ 4Wareham (1992) described typical bacterial electron and energy transport chains, andgave a good picture of the redox measurement from the microbial level. His descriptionindicated that the external ORP value directly reflected the activity of the biologicalmaterials in the system at the cellular level. His belief in the correlation between aparticular ORP value and a given bacterial population agreed with the work of Whitfield(1969).The ORP electrode actually consists of an indicating electrode and a reference elec-trode. The indicating electrode is made of a noble metal; platinum, gold, and silver areamong the commonly used. This electrode is constructed in such a way that only thenoble metal is in contact with the test solution. The contact area should be about 1 cm'(ASTM, 1983). A reference electrode can use a calomel, silver/silver chloride, or otherelectrodes which have a constant potential. Descriptions of how ORP probes functionare presented in ASTM (1983), Coleman (1987), and Wareham (1992).According to ASTM (1983), ORP electrodes generally are not subject to solutioninterference from colour, turbidity, colloidal matter and suspended matter, and so areideally suited to applications in wastewater treatment processes where the above inter-ferences are commonly encountered with nitrate probes.Temperature and pH will change the measured ORP of an aqueous solution. In mostsituations, temperature correction is not done because of its minimal effect and complexnature. Variations in pH are taken into consideration only when the oxidation reductionreaction involves either hydrogen or hydroxyl ions.ASTM (1983) recommended ORP electrode cleaning procedures, and suggested thatas much as a 10 my difference between the experimental readings and the publishedstandard solution values would be acceptable.Chapter 2. LITERATURE REVIEW^ 52.2 The Application Possibilities of ORP MeasurementThe application possibilities of ORP measurement have been researched by Rohlich(1948), Hood (1948), Eckenfelder and Hood (1951), and Nussberger et. al (1953).Rohlich (1948) questioned the usefulness of exact potentials in aerobic and anaerobiczones because the measured ORPs were quite different from one treatment plant toanother, and among probes used in the same tank of a given plant, but he believed thatORP vs time curves could be useful in operational control of a sewage treatment process.Nussberger (1953) generated some ORP-time curves for various activated sludge sys-tems. He intended to use them as guidelines to indicate whether the process was under-loaded or overloaded, underaerated or overaerated. He concluded that ORP measure-ment provided a tool to control aeration in the activated sludge process and to controlthe sewage addition volume at each point in a step aeration process.In a discussion of the paper by Grune and Chueh (1958), Eckenfelder (1958) mentionedthat in experiments to control chlorination of a wastewater containing sulfides, sulfites,and thiosulfates, a sharp break in the ORP-time curve was observed when all the sulphurcompounds were oxidized. This is a supportive observation for possible ORP applicationin automated control systems.O'Rourke et. al (1963) investigated the use of ORP for aiding in the adjustment ofthe air supply to the point of greatest need during periods of heavy organic loads. Inthis case, the ORP electrode was used in the aeration basin.Harrison (1972) argued that overall redox potential was of little value in studies ofgrowing microbial cultures because of the complexity of the biological system.The use of ORP has also been researched in the field of fermentation. Because of thedifficulties in measuring the very low DO (dissolved oxygen) concentrations in an aerobicmicrobial fermentation process by the use of DO probes, ORP probes have received moreChapter 2. LITERATURE REVIEW^ 6attention as a measurement tool to get information about the system. Kjaergaard (1977)concluded that the redox potential was significantly dependent on the concentration ofdissolved oxygen. He also pointed out that it was not possible to "put forward anygeneral laws concerning the exact changes that take place in the redox potential duringmicrobial growth, but the qualitative changes are well known".Radjai et. al (1984) noted, in his research on optimizing the production of amino acidssuch as homoserine, lysine and valine, that specific ORP values generally correspondedto the optimum production rate of the amino acid.2.3 ORP as a Control Parameter in Waste Treatment ProcessesThe application of ORP as a control tool in waste treatment processes has been discussedby several researchers.Poduska and Anderson (1981) noted a high positive ORP value (> +100 my) whenthere was an effective control on hydrogen sulphide odours developed in lagoons storingaerobically digested sludge. A platinum redox electrode with a pH/millivolt meter wasused in their research.Eilbeck (1984) found that the detection of the redox breakpoint (a marked increaseof about 400 my) was helpful in deciding chlorination dosage rates to achieve residualchlorine in the wastewater treatment effluent. He used a gold electrode measured withreference to a saturated KC1 calomel electrode.Watanabe et. al (1985) found that ORP was an effective index for controlling themethanol feed rate to achieve a good denitrification rate in a biological single sludgepre-denitrification process. The results indicated that by maintaining an ORP of -150 +15 my (the electrodes used were not identified in the paper) to manipulate the methanolfeed rate, the effluent NO was maintained below 1 mg/L with variations in the influentChapter 2. LITERATURE REVIEW^ 7flow rate and influent concentrations of NO and COD (chemical oxygen demand).The research of De la Menardiere et. al (1991) was conducted at a full scale activatedsludge system in France. The plant consists of two tanks in series, a non-aerated tankfollowed by an aerated tank. There is a sludge recycle from the secondary settler to thenon-aerated tank. It was found that in the non-aerated tank, when ORP values were inthe range of -230 to -100 my (referring to a conventional hydrogen electrode), phosphaterelease was at a high level of 60 mg/L (as PO41, while an absence of nitrate was observed.In the aeration tank, "correct setting of ORP regulation limits has proved an essentialoperation parameter to ensure good simultaneous C, N, and P removal".ORP's application in aerobic sludge digestion systems was researched by Peddie et. al(1988). It was observed that the ORP profile was reproducible with the cycled operationof alternating aerated and non-aerated conditions in the aerobic digesters. The slopechanges of the ORP profile clearly defined the range of aerobic and anaerobic respirationand fermentation.Wareham (1992) used the distinctive breakpoint occurring in the ORP-time profileand correlated it to nitrate disappearance to control his aerobic/anoxic sludge digestionsystem. He also used the ORP breakpoint to control the addition of sodium acetate tothe reactor in his biological phosphorus removal experiments.2.4 ORP Monitoring in Bio-nutrient Removal ProcessesThe development of biological nutrient removal processes resulted in a significant increaseof interest in ORP research. Comprehensive literature reviews of bio-phosphorus removalhave been presented by Siebritz et. al (1983), Comeau (1984, 1989) ,and Rabinowitz(1985). The information related to nitrogen removal such as biological nitrification anddenitrification can be found in U.S. EPA (1975), and Metcalf and Eddy Inc. (1979).Chapter 2. LITERATURE REVIEW^ 8A significant piece of work about the usefulness of ORP monitoring in the bio-Premoval process was done by Koch and Oldham (1985). Based on a series of laboratorybatch experiments, the correlation between a breakpoint in redox-time curves and theend of denitrification activity was found. They also discovered a second breakpoint inthe ORP-time curve indicating the end of aerobic activity. ORP values observed fromthis research were reported over a range of -40 to -140 my (using a platinum sensor withan Ag/AgC1 reference electrode) for complete nitrate disappearance conditions. Moreprecise ORP values in complete denitrification conditions were not concluded in thereport.Koch et. al (1988) also conducted ORP monitoring in a continuous flow bio-nutrientremoval process. Efforts were made to look for relationships between ORP values andnitrate concentrations in the anoxic reactor, and ortho-phosphate concentrations in bothanoxic and anaerobic reactors. Several relationships were formulated between ORP anddissolved oxygen, nitrate and phosphate concentrations. However, only qualitative con-clusions were given at the end of the paper.This thesis investigated the approach of using measured ORP values as a control toolin a bio-nutrient removal process.Chapter 3EXPERIMENTAL DESCRIPTION3.1 Research ObjectivesThe purpose of this research was to investigate the method of using ORP monitoringto assess the completeness of denitrification in the anoxic zone of a bio-nutrient removalprocess (such as the one shown in Figure 3.1). Since the collected ORP values representthe characteristic combination of both the probe individuality and the tested chemical orbiological system, examinations of probes and their applications in monitoring a biologicaldenitrification process are both conducted.The first objective of this research was to determine if a probe's individual character-istics need to be considered when the ORP values collected from biological batch testswere evaluated.A group of ten probes were tested in a series of quinhydrone buffer solutions whosestandard redox values were pre-determined, and were different. The measured redox val-ues were compared with the standard values to determine the significance of the probes'individual characteristics. The necessity of adjusting the measured redox values is dis-cussed in conjunction with the evaluation of the biological batch results.The second objective of this research was to determine if ORP values collected frombatch tests can be used as indicators of the biological denitrification process. The batchtests were designed to stimulate the biological system in the anoxic zone. Mixed liquorsfrom the aerobic zone, anaerobic zone, and sludge return line were all present in the9Chapter 3. EXPERIMENTAL DESCRIPTION^ 10batch test system. The initial nitrate concentrations and the denitrification rates in thetested batch system were designed to be variable. Their impact on ORP values testedin complete denitrification conditions are used as an approach to assess the applicationpossibility of ORP monitoring.3.2 UBC Bio-nutrient Removal Process Introduction3.2.1 Process schemeThe biological mixed liquor used in experiments was collected from the bio-nutrientremoval process of the UBC pilot plant. Figure 3.1 shows the process configuration.The pilot plant is situated close to the UBC campus, in Vancouver, B.C.. The influentsources include student residences, campus housing, and the university sports centre.The wastewater is pumped into two plastic storage tanks, each with a capacity of 9000L. Sodium bicarbonate was added daily to the storage tanks to increase sewage alkalinityby about 100 mg/L (as CaCO3) , because wastewater in the Vancouver area is low inalkalinity (80 - 120 mg/L as CaCO3), and hence poorly buffered.The influent first passes into an upflow fermenter with a flow rate of 2.5 L/min. Thefermenter has a volume of 400 L. No solids wasting or mixing was conducted in thefermenter during the time when experimental work was performed for this thesis. Thefermented effluent is then fed into the anaerobic zone of the bio-reactor. The 2500 Lvolume rectangular bio-reactor is divided into three zones. They are an anaerobic zone(1/7), an anoxic zone (2/7), and an aerobic zone (4/7).There is a mixed liquor recycle from the anoxic zone to the anaerobic zone which isperformed at a flow rate of 2.5 L/min. Volatile fatty acid (VFA) is added into the anaer-obic zone to enhance the bio-phosphorus removal. The VFA feeding rate is 7 mL/min.Figure 3.1: UBC bio-nutrient removal processChapter 3. EXPERIMENTAL DESCRIPTION^ 12The strength of the VFA stock solution was 3290 mg/L as acetic acid (HAc). The con-centration of HAc added to the influent therefore averaged 9.2 mg/L. There was no mixedliquor recycle from aerobic zone to anoxic zone when the experimental part of this thesiswas being performed. The anaerobic and anoxic zones were kept completely mixed withmechanical mixers.In the aeration zone, coarse bubble aeration through header pipes provides aerationand thorough mixing conditions. The dissolved oxygen (DO) concentration in the aerobiczone was maintained at 2 - 3 mg/L. The mixed liquor from the aerobic zone is wasted atthe rate of 110 L per day.The process ends up in a 500 L secondary clarifier. The sludge is returned from thebottom of the secondary clarifier to the anoxic zone at a flow rate of 2.5 L/min.3.2.2 Process mechanismThe UBC pilot plant process, as shown in Figure 3.1, did not have the mixed liquorrecycle from the aerobic zone to the anoxic zone when this research was conducted. Thenitrate concentration was high in the aerobic zone where organic nitrogen and ammoniain the influent were converted into nitrate by nitrification. A mixed liquor recycle fromthe aerobic zone to the anoxic zone is needed to facilitate the UBC process with efficientnitrate removal. Nitrate can be removed in oxygen-free conditions by denitrification inthe anoxic zone.It is essential to have complete denitrification in the anoxic zone, so as to achieveefficient phosphorus removal in the process when both the aerobic recycle (from theaerobic zone to the anoxic zone) and the anoxic recycle (from the anoxic zone to theanaerobic zone as shown in Figure 3.1) are present. If the residual nitrates in the anoxiczone entered the anaerobic zone by the anoxic recycle line, the denitrifiers would be ableto grow in the anaerobic zone by utilizing the easily available volatile fatty acid providedChapter 3. EXPERIMENTAL DESCRIPTION ^ 13by the fermenter. The competition between denitrifiers and phosphate accumulatorsfor the available simple carbon substrate would have a negative impact on phosphateaccumulators. If nitrates in the anoxic zone continued to enter the anaerobic zone,phosphate accumulating organisms would be reduced in number, and the phosphateremoval process would be jeopardized (Oldham, 1988). It is important to have completedenitrification in the anoxic zone to facilitate efficient phosphate removal.3.3 Experimental Set-up3.3.1 Data log-in systemOxidation reduction potentials were collected by the use of a log-in system called REM-DACS (Remote Data Acquisition and Control System). The system included a 10 channelconnection board, a set of high impedance instrumentation amplifiers, a multi - chan-nel 12 bit analogue to digital converter, and a microcomputer as shown in Figure 3.2.ORP data were collected continuously from as many as 10 channels simultaneously. Theresolution was 0.5 my. Data collected from scanned channels were recorded on disks informatted blocks in digital form for subsequent evaluation and analysis.3.3.2 QBASIC programA QBASIC program was used in the data log-in system. Users could set file names, thechannel scan rate, and the experimental run-time. The channel scan rate decided howfrequently the ORP was to be collected. For each scan interval, the user could decidewhether to record an averaged value or to record an instantaneous value. Users couldalso record the initiating time of each channel. Data log-in termination could be preset.The data files could be imported into Lotus 1-2-3 for analysis and evaluation.oFigure 3.2: Data log-in system schemeChapter 3. EXPERIMENTAL DESCRIPTION ^ 153.3.3 Batch testing apparatusThe testing apparatus used in this research is shown in Figure 3.3. Erlenmeyer flasksof 2.8 L capacity were used in all batch tests. Each flask was sealed with a rubberstopper which was fitted with a rubber septum. Rubber balloons filled with nitrogenwere attached to syringe needles which were pierced through the septum. When samplingstarted, nitrogen was displaced from the the balloon with positive pressure, and pushedthe mixed liquor out of the flask through a sampling tube which was inserted throughthe stopper and went down to the bottom of flask. Nitrogen that replaced any liquidwithdrawn from the flask kept an inert atmosphere above the liquid to prevent air leakageinto the flask. The septum was also used for the injection of chemicals. Each flask had amagnetic stirrer to insure complete mixing condition during the course of the experiment.Each flask was fitted with two ORP probes which were attached to plastic tubes andinserted in the stopper. Duplicate measurements provided direct confirmation of ORPvalues. The collected mixed liquor samples were filtered and refrigerated before analysis.All experiments were conducted at ambient room temperature. No pH adjustment wasapplied in the experiments, but pH and temperature were monitored.3.3.4 ORP probes and probe maintenanceThe ORP probes used in this research were supplied by the Broadley James Corporation,as shown in Figure 3.4.The probe has a 1/8 inch platinum ring located near its tip. The noble metal acceptedand donated electrons, but did not participate in other oxidation/reduction reactions inthe tested system. The reference electrode was a silver metal strip coated with solidAgC1, and the Ag/AgC1 electrode was immersed in KC1 solution. Based on the solubilityproduct principle as shown in Equation (3.1), the concentration of the cation associatedSampling tubeORP probes•^"11II IIClampRubber stoper\ /^Magnetic stirring barTo log-in systemNitrogen balloonon syringe needleSyringe for samplingChapter 3. EXPERIMENTAL DESCRIPTION ^ 162800 mL erlenmeyer flaskFigure 3.3: Batch test apparatusChapter 3. EXPERIMENTAL DESCRIPTION^ 17Figure 3.4: ORP probeChapter 3. EXPERIMENTAL DESCRIPTION^ 1 8with the electrode metal was kept constant, therefore the reference electrode potentialhad a fixed value (Wareham, 1988).Ag(s) AgCl(s) e (3.1)The ORP measured by the probe was the electro-motive force (emf) difference be-tween the ORP metallic indicating electrode and the reference electrode. All ORP valuesshown in this thesis are therefore relative to the Ag/AgC1 electrode. Probes were cleanedwith a distilled water rinse after each test to remove any chemical and biological impuri-ties. Between experiments, probes were kept in storage boots which were filled with 2MKC1 (Broadley, 1990).3.4 Analytical Parameters and Techniques3.4.1 NO (I\To:N- and NOnNO is a comprehensive measure of both NO3- and NO2- in a sample. It is the most impor-tant parameter in assessing a biological denitrification process. NO monitoring in batchtests can inform researchers about the biological denitrification process in flasks. Sampleswere filtered through Whatman *4 filter paper, then analyzed by the Lachat QuickhemAE auto-analyzer (automated cadmium reduction method) (Lachat, 1988. APHA, 1989).The detection limit was 0.05 mg/L (as NO;-N). The instrumental calibration solutions'concentrations ranged from 0.05 mg/L to 20.0 mg/L.3.4.2 MLSS and MLVSSMLSS stands for mixed liquor suspended solid, which is the nonfilterable residue thatremained on the filter after evaporation and dried to a constant weight at 104 °C. MLVSS(mixed liquor volatile suspended solid) is the volatile residue, and is determined byChapter 3. EXPERIMENTAL DESCRIPTION^ 19igniting MLSS at 550 °C (APHA, 1989). MLSS is an indicator of sludge concentrationsin the system. MLVSS can be used to estimate live bacteria in the system (Metcalf kEddy, 1979).3.4.3 pHThe ORP of an aqueous solution is sensitive to pH variation when the oxidation/reductionreaction involves either hydrogen or hydroxyl ions. The ORP generally tends to increasewith an increase in H+ and to decrease with an increase in OH- during such a reac-tion (ASTM, 1983). Bacteria are sensitive to pH conditions too. The pH was testedthroughout experiments by the use of a Cole-Farmer Digi-sense pH meter.3.4.4 TemperatureThe redox potential is dependant on temperature, and all measurements should includea temperature reference to specify the testing conditions (Petersen, 1966). Temperatureswere tested by the use of the same Cole-Parmer Digi-sense pH meter.3.4.5 Chemical oxygen demandChemical oxygen demand (COD) was used as a measurement of the laboratory madecarbon stock solution (NaAc). The COD analysis was conducted in accordance withStandard Methods (APHA, 1989).3.5 Data Analysis TechniquesLotus 1-2-3 (version 2.2) by Lotus Development Corporation was used for the data anal-ysis. Freelance (version 3.01) by Lotus Development Corporation was used for plottingresults.Chapter 4RESULTSExperimental results are presented in three groups. Part one is probe testing results, parttwo is biological batch tests with varied initial nitrate concentrations, and part three isbatch tests with external carbon additions (to create varied denitrification rates).4.1 Probe Testing Results4.1.1 IntroductionThe purpose of probe testing was to verify the reliability of direct values from probes,to determine if the probe tested yielded the true ORP values of the tested solutions. Agroup of ten probes was tested in quinhydrone buffer solution at the same time, althoughonly four of them were going to be used in batch tests.The substance quinhydrone is an equimolar compound of benzoquinone (006H40),and hydroquinone (HOC61-140H). Quinhydrone is slightly soluble in water (ASTM, 1983).The benzoquinone and hydroquinone, which are referred to as Q and H2Q respectively,form a reversible oxidation reduction system with hydrogen ions.H2Q Q 2H+ + 2e^ (4.1)Buffer solutions saturated with quinhydrone have stable oxidation reduction poten-tials. Nominal millivolt redox values for these reference solutions at various temperatures20Chapter 4. RESULTS^ 21Table 4.1: Nominal ORP values of reference quinh drone solutionsBuffer solution pH 4 7Temperature (°C) 20 25 30 20 25 30ORP (my) 268 263 258 92 86 79Reference electrode: silver/silver chlorideTable 4.2: Buffer solutions compositionspH 689Nall2PO4 (mL) 8 1 0Na2HPO4 (mL) 2 9 10are given in Table 4.1 (ASTM, 1983). Excess quinhydrone was used so that solid crys-tals were always present in order to have a saturated quinhydrone solution. Quinhydronewas added into buffer solutions immediately before each experiment, since these referencesolutions are only stable for about 8 hours (ASTM, 1983).Six buffer solutions with different pH values ranging from 4 to 10 were used in probetesting. These buffer solutions have different voltage levels so that probe behaviour atdifferent ORP levels can be studied. BDH Chemicals provided the buffer solutions ofpH 4, 7, and 10. pH 6, 8, and 9 buffer solutions were made by the combination of 0.1M sodium dihydrogen phosphate and 0.1 M disodium hydrogen phosphate according toTable 4.2 (Gabb, 1968).The pH and temperature of the buffer solutions were tested in the experiments. Theten probes were put into the same buffer solution with thorough mixing throughout eachtest. ORPs collected from each probe were logged into the computer in the rate of onereading every 60 seconds. Each test was conducted for 20 minutes. Experimental resultsincluded here were conducted on March 4, 1991, April 4, 1991, and May 7, 1991.Chapter 4. RESULTS^ 22Table 4.3: Experimental conditions for probe test 1pH 4.03 6.30 7.06 7.78 8.78 9.85Temperature (°C) 19.7 20.1 19.5 20.1 20.0 19.4Table 4.4: Experimental conditions for probe test 2pH 4.10 6.32 7.11 7.85 8.85 9.94Temperature (°C) 20.9 21.1 20.8 19.5 19.4 19.44.1.2 Probe test 1 (March 4, 1991)The probe test presented here was done on March 4, 1991. Temperature and pH weremonitored during the experiment. It was observed that during the 20 minutes, pH andtemperatures of the testing system did not change much, and therefore, are taken as theexperimental conditions. The initial test conditions are listed in Table 4.3. The resultsof probe test 1 are shown in Figures 4.1 to 4.6.4.1.3 Probe test 2 (April 4, 1991)Probe test 2 was conducted one month after test 1. The experimental procedures werethe same as those which were used in test 1. The repeatability of probe behaviour inbuffer solution was tested. Test conditions are listed in Table 4.4. Test results can befound in Appendices A-1 to A-6.4.1.4 Probe test 3 (May 7, 1991)Probe test 3 was designed to gather more data for the results analysis. Table 4.5 containsthe test conditions of each chemical solution. The test procedures were the same as thosein test 2. Test results are listed in Appendices A-7 to A-12.Chapter 4. RESULTS^ 23Figure 4.1: Probe test 1.1 (pH 4.03): (A) Probes (1-5). (B) Probes (6-10).• -- 41 --^11 'ND-- --O.^-- -0 -- -0-- -- fr^-^,Q.^ -13- ^ a.. NV' ..9^9^ 0 ^9 ^.  —-o ^ 0 ^9^(A) Probe (1-5) -^-E. -IF  ^-   14215;'140138136a.cc0 13473e 132MI 1301501481461441281261241221200 2 4 6 8 10^12Time (min)14 16 18 20 22 24Probe 1Probe 2---0-  - -Probe  3Probe 4_^_Probe 50 134736.°) 132To>a_cc142140a) 138a$ 130a)15014814614413612812612412001222 4 6 8 10^12Time (min)14 16 18 20 22 24(B) Probes (6-10).0 ^ 0 ^ 0 ^Al- -IL,^0 ^G- -^-- 5- -.AB-- -6- -11^ -a -6- is- -or' II- -sr'^II-^ -6- —  Probe _6Probe 7Probe  8Probe 9—^-Probe 10Chapter 4. RESULTS^ 24Figure 4.2: Probe test 1.2 (pH 6.30): (A) Probes (1-5). (B) Probes (6-10).102E., 100coa)• 98Ta> 960-CC0 942 92M 90a)211010810610488868482800 2 4 6 8 10^12^14Time (min)16 18 20 22 24Probe 1Probe 2Probe 3ElProbe 4—^-Probe 5(A) Probes (1-5)01-^ ^-II^00-,O•^la^.^..._.^• . X3-',^ .^ „-^ • .1I - --0.,^„AI- - 711. - -0 - 111(- - •- - -Or° ....^■^...- 40- -   - --10--4fr 11 - -0-   -^- - -  ^cJ(B) Probes (6-10)14.^ 111- - -lb-^-  41-▪ -   - -41r° 111-^"-pool:Jou ^0 ^ o-tr-^ 0 ^ El ^ D ^ DD El ^ El ^ Era.0 94"CS2 9227it 90a)a)7 98• 96102100110108106104848280088862 4 6 8 10^12^14Time (min)16 18 20 22 24Probe 6Probe 7Probe 8ElProbe 9—^-Probe 10Chapter 4. RESULTS^ 25Figure 4.3: Probe test 1.3 (pH 7.06): (A) Probes (1-5). (B) Probes (6-10).Chapter 4. RESULTS^ 96Figure 4.4: Probe test 1.4 (pH 7.78): (A) Probes (1-5). (B) Probes (6-10).Chapter 4. RESULTS^ 27Figure 4.5: Probe test 1.5 (pH 8.78): (A) Probes (1-5). (B) Probes (6-10).;.74-76O 82ED. -842 -86• -88-90-92-94-96-98-1000 2 4 6 8 10^12^14Time (min)16 18 20 22 24-60-62-64-862^4^6^8 16^18^20^22^2410^12^14Time (min)-90-92-94-96-98-1000-so-62-64-66-68-70> -72-74a)7 -76TO• -78CC -80O -82-o▪ -8472 -86ni2 '88Chapter 4. RESULTS^ 98Figure 4.6: Probe test 1.6 (pH 9.85): (A) Probes (1-5). (B) Probes (6-10).Chapter 4. RESULTS^ 29Table 4.5: Experimental conditions for probe test 3pH 4.06 6.25 7.02 7.75 8.72 9.79Temperature (°C) 19.1 17.4 18.2 18.8 18.4 18.8Table 4.6: Mixed liquor combinationsRatio Aerobic (mL) Anaerobic (mL) Sludge return (mL)0 0 (0) 1867 (2) 933 (1)1 700 (1) 1400 (2) 700 (1)2 1120 (2) 1120 (2) 560 (1)3 1400 (3) 933 (2) 467 (1)4 1600 (4) 800 (2) 400 (1)4.2 Anoxic Batch Tests (Without External Chemical Addition)4.2.1 IntroductionAnoxic batch tests were designed to exam the impact of initial nitrate concentration onthe redox values in complete denitrification conditions. The nitrate levels in the aerobiczone of the UBC process presented in Figure 3.1 was high. The mixed liquor suspensionsin the anoxic batch tests were made by combining 2:x:1 volume ratios of mixed liquorcontents from the anaerobic zone, the aerobic zone, and the return sludge flow. Thevariable aerobic mixed liquor ratio (x) was set at values of 4, 3, 2, 1, and 0 respectivelyin the batch tests to make a total volume of 2800 mL as shown in Table 4.6. In this way,different initial nitrate levels were obtained in flasks.Temperatures and pH were measured for each sample. It was observed that duringthe experiments (which usually lasted no longer than 180 minutes), temperatures andpH did not change significantly. The initial pH and temperatures were taken as constantthroughout the experiment.Chapter 4. RESULTS^ 30Table 4.7: Process characteristics on March 11, 1991NO (mg/L) P0:1 (mg/L) MLSS (mg/L) COD (mg/L)Influent 49Anaerobic zone 0.00 13.92Anoxic zone 0.16 8.66Aerobic zone 10.27 0.00 2950Effluent 10.29 0.05 4 3330 min settling (mL/L) 910The anoxic denitrification experiments presented here were conducted on March 11,1991, March 21, 1991, and March 28, 1991. No external chemicals were added to theflasks. The biological systems in the flasks were kept oxygen free throughout experiments.Probes 3, 4, 5, and 6 were used in these experiments. Each flask had two probes installedwith probes 3 and 4 in one group and probes 5 and 6 in the second group. Samplingfrequency was once every 10 minutes. Samples were filtered by Whatman *4 qualitativefilter paper and then kept in a freezer until they were analyzed. MLSS and MLVSSwere tested for each batch test. Process operation conditions for the experiment days(influent, effluent and process characteristics) were monitored. ORPs were collected atthe rate of one sample every 60 seconds. Tests were terminated manually.4.2.2 Anoxic batch test 1 (March 11, 1991)Anoxic batch test I was conducted on March 11, 1991. Table 4.7 shows the processinformation for the pilot plant on that day. Experimental conditions for the batch testare listed in Table 4.8. Figures 4.7 to 4.11 are experimental results for ratios 0, 1, 2, 3,and 4 respectively. NO analysis results are shown in Figures 4.12.Probe 3Probe 4■■■■.■Chapter 4. RESULTS^ 31Table 4.8: Experimental conditions for anoxic batch test 1Ratio pH Temp. MLSS MLVSS MLVSS/MLSS(°C) (mg/L) (mg/L) (%)0 7.15 14.3 2563 2190 861 7.26 15.2 2690 2280 852 7.21 15.2 2510 2150 863 7.17 14.4 2583 2145 834 7.19 14.1 2460 2067 8410090807060505- 40E 3020P 10> 0cc -10O -20-oEi2 -30Fo -40▪ -502 -60-70-80-90-100-110-1200 10^20^30^40Time (min)Figure 4.7: Anoxic batch test 1.1 (ratio 0)50^60eitlet14110000640.114.-tamotrecotofawic.,70„II! VPirkilOgra4 .-ram-assi evort,opvon.Chapter 4. RESULTS^ 321009080706050E 403020> 10cc^00 -10-0EL' -20Cl) 30nccsa) -402 -50-60-70-80-90-10001009080706050E 4030a)20To> 10cc 00 -10-0E.) -20cci -30a) -402 -50-60-70-80-90100010^20^30^40^50^60^70^80Time (min)Figure 4.8: Anoxic batch test 1.2 (ratio 1)10^20^30^40^50^60^70^80Time (min)Figure 4.9: Anoxic batch test 1.3 (ratio 2)90^100^110^12090^100^110^120Chapter 4. RESULTS^ 33120110100908070S"; 6050g; 402 30a)> 20100 0E-10-20-30a)2 -40-50-60-70-80-90-10001201101009080706050(3°3^40.2 30as> 20cl 100 0'um -10-20coes -30a)2 -40-50-60-70-80-90-10001.^  ^  .• • 4...       co, .10 trii;^.^  44, cat„„),,tv:,),,,;   ^• loe„.10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (min)Figure 4.10: Anoxic batch test 1.4 (ratio 3)10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (min)Figure 4.11: Anoxic batch test 1.5 (ratio 4)4 —--4Ic00'..........^\3 —Chapter 4. RESULTS^ 348Ratio 0Ratio 1Ratio 20Ratio 3Ratio 4--■     ■-0.I^I0^10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (min)Figure 4.12: NOx test results (anoxic test 1)4.2.3 Anoxic batch test 2 (March 21, 1991)Anoxic batch test 2 was a repeat test of anoxic batch test I. In the test 2, the proportionsof mixed liquors were the same as those in the test 1, but it was conducted on a differentday, for which the Process characteristics are presented in Table 4.9. Experimentalconditions can be found in Table 4.10. ORP and NO testing results are included inAppendices B-1 to B-6.4.2.4 Anoxic batch test 3 (March 28, 1991)Anoxic batch test 3 was designed to increase the amount of data available for analysis,because the influence of random errors on the conclusion will be diminished when moredata are used in the analysis. Table 4.11 includes process characteristics. Table 4.12shows experimental conditions. ORP and NO results can be found in Appendices 13-7to B-12.7 —6 Et-5AAA,10••- -^-- •El]^I^I Chapter 4. RESULTS^ 35Table 4.9: Process characteristics on March 21, 1991NO (mg/L) P0-4- (mg/L) MLSS (mg/L) COD (mg/L)Influent 191 333Anaerobic zone 0.22 16.69Anoxic zone 0.06 10.62Aerobic zone 8.40 0.04 2910Effluent 8.17 0.04 2 2530 min settling (mL/L) 910Table 4 10: Experimental conditions for anoxic batch test 2Ratio pH Temp. MLSS MLVSS MLVSS/MLSS(°C) (mg/L) (mg/L) (%)0 7.06 16.5 3080 2573 841 7.15 16.2 3123 2566 822 7.14 16.1 2997 2474 833 7.08 15.9 2867 2450 854 7.10 15.9 3177 2650 83Table 4.11: Process characteristics on March 28, 1991NO (mg/L) PO-4- (mg/L) MLSS (mg/L) COD (mg/L)Influent 67 319Anaerobic zone 0.09 14.66Anoxic zone 0.06 9.10Aerobic zone 7.01 0.02 3310Effluent 6.89 0.04 1 2730 min settling (mL/L) 880Chapter 4. RESULTS^ 36Table 4.12: Experimental conditions for anoxic batch test 3Ratio pH Temp. MLSS MLVSS MLVSS/MLSS(°C) (mg/L) (mg/L) (%)0 7.13 16.0 3033 2543 841 7.19 17.3 3177 2607 822 7.20 17.1 3130 2583 833 7.25 16.0 3010 2490 834 7.18 16.0 3060 2527 834.3 Anoxic Batch Tests (With External Carbon Addition)4.3.1 IntroductionIt is known that a biological denitrification process usually requires the addition of anexternal carbon source to promote the nitrate removal reactions (US EPA, 1975. Metcalfand Eddy, 1979. Narkis et. al, 1979. Watanabe et. al 1985). The effect of carbonconcentration on the rate of denitrification has been modeled in terms of a Monod typeof expression. When methanol serves as the carbon source, the expression is (US EPA,1975):IUD PD(max) Km +^ (4.2)where:,up = growth rate (day-').itD(max) = maximum denitrifier growth rate (day-').M = methanol concentration (mg/L).Km = half saturation constant for methanol (mg/L).The carbon addition tests were designed to investigate the effect of different denitri-fication rates on the redox values measured at the end of the denitrification process.Chapter 4. RESULTS^ 37Sodium acetate (NaAc) is one of many commercially available organic compoundsthat can be used as a readily available carbon source. With the addition of a simpleexternal carbon source, the denitrification rate is increased in the anoxic zone of theprocess. The NaAc stock solution was prepared at a concentration of 9512 mg/L asCOD (testing result).In experiments, the NaAc stock solution was injected into flasks in the volumes whichmade up carbon addition of 0, 20, 40, 60 and 80 mg/L as COD. pH and temperatureswere measured, and did not show great changes in the experiments. In carbon additiontests, the mixed liquor in each flask was the same combination of 467 mL from the returnsludge, 933 mL from the anaerobic zone, and 1400 mL from the aerobic zone. Probes3, 4, 5 and 6 were used, with probes 3 and 4 as one group and probes 5 and 6 as theother group. The external carbon addition experiments presented here were conductedon February 1, 1991, February 7, 1991, and March 1, 1991.4.3.2 Carbon addition test 1 (February 1, 1991)Carbon addition test 1 was conducted on February 1, 1991. Process characteristicson February 1, 1991 are listed in Table 4.13. pH, temperature, MLSS and MLVSS weretested for the initial samples of batch tests and can be found in Table 4.14. The samplingrate was once every 10 minutes. ORP values were automatically averaged and recordedevery 180 seconds. The experiment lasted about 120 minutes. The collected ORPs wereplotted over time. The graphs are presented in Figures 4.13 to 4.17. NO, analysis resultsare presented in Figures 4.18.4.3.3 Carbon addition test 2 (February 7, 1991)Carbon addition test 2 was a repeat test of carbon addition test 1. The carbon dosesapplied in test 2 are the same as those used in test 1, but this test was conducted onChapter 4. RESULTS^ 38Table 4.13: Process characteristics on February 1, 1991NO (mg/L) POTI (mg/L) MLSS (mg/L) COD (mg/L)Influent 45 289Anaerobic zone 0.43 6.85Anoxic zone 0.21 4.67Aerobic zone 8.85 0.05 2830Effluent 8.64 0.02 5 1930 min settling (mL/L) 830Fable 4.14: Experimental conditions for carbon addition test .NaAc(mg/L)pH Temp.(°C)MLSS(mg/L)MLVSS(mg/L)MLVSS/MLSS(%)0 7.05 16.6 3028 2516 8320 6.94 16.2 3034 2470 8140 6.97 16.8 3050 2492 8260 6.79 16.9 3064 2508 8280 7.17 15.6 3244 2616 81Probe 5Probe 6Chapter 4. RESULTS^ 39120110100908070-5.- 60E 50oto 402 30> 20cc 100 073• -1009 -20-302 -40-50-60-70-80-90-1000120110100908070-5.- 60E 50402 30>  20o_cc^100 013, -10{,a -20wal -302 -40-50-60-70-80-90-100010^20^30^40^50^60^70^80Time (min)Figure 4.13: Carbon addition test 1.1 (control)10^20^30^40^50^60^70^80Time (min)Figure 4.14: Carbon addition test 1.2 (20 mg/L)90^100^110^12090^100^110^120Chapter 4. RESULTS^ 408070605040S' 30E20coa)^1 0mTs;> 0cc• -100-20-02 -300coas -4002 -50-60-70-80-90-10008070605040-5,- 30---'^20to'a)^1 0mV 0ct.cc -100 -20-0}1.-)^-30=asas -40C)M -50-60-70-80-90-100010^20^30^40^50Time (min)Figure 4.15: Carbon addition test 1.3 (40 mg/L)10^20^30^40^50Time (min)Figure 4.16: Carbon addition test 1.4 (60 mg/L)60 70 8060 70 80Control20 mg/L-- - 0-- -40  rpg/L60 mg/L--.--80  mg/L-^-\.p\ •\ Chapter 4. RESULTS^ 4180706050405. 302010To'> 0ct.cc -100 -20-30-40C)2 -50-60-70-80-90-1000 10^20^30^40^50Time (min)Figure 4.17: Carbon addition test 1.5 (80 mg/L)60 70 800^10^20^30^40^50^60^70^80^90^100^110Time (min)Figure 4.18: NOx test results (carbon addition test 1)6543210Chapter 4. RESULTS^ 49Table 4.15: Process characteristics on February 7, 1991NO (mg/L) POTi (mg/L) MLSS (mg/L) COD (mg/L)Influent 42 166Anaerobic zone 0.17 6.76Anoxic zone 0.11 3.32Aerobic zone 8.00 0.01 3050Effluent 7.87 0.00 1 1930 min settling (mL/L) 890Table 4.16: Experimental conditions for carbon addition test 2NaAc(mg/L)pH Temp.(°C)MLSS(mg/L)MLVSS(mg/L)MLVSS/MLSS(%)0 7.13 14.5 3200 2590 8120 7.03 16.8 3200 2576 8040 7.16 17.4 3152 2538 8160 7.04 14.0 3347 2687 8080 7.10 17.0 3238 2658 82February 7, 1991. Process characteristics are given in Table 4.15. pH, temperature,MLSS and MLVSS for each test are listed in Table 4.16. The rest of the experimentalconditions of test 2 are the same as those in carbon addition test 1. The ORP and NOtesting results are given in Appendices C-1 to C-6.4.3.4 Carbon addition test 3 (March 1, 1991)Carbon addition test 3 was conducted to create more data for final results analysis. Mostexperimental conditions were the same as those which were used in carbon addition test2, except that test 3 was conducted on March 1, 1991 and the ORP logging rate was onesample every 60 seconds. Process characteristics are in Table 4.17. pH, temperatures,MLSS and MLVSS are listed in Table 4.18. ORP and NO were plotted over time. TheChapter 4. RESULTS^ 43Table 4.17: Process characteristics on March 1 1991NO (mg/L) P0-4" (mg/L) MLSS (mg/L) COD (mg/L)Influent 56 271Anaerobic zone 0.52 10.23Anoxic zone 0.33 7.90Aerobic zone 8.41 0.00Effluent 8.11 0.05 330 min settling ( mL/L) 735Table 4.18: Experimental conditions for carbon addition test 3NaAc(mg/L)pH Temp.(°7)MLSS(ng/L)MLVSS(Ing/L)MLVSS/MLSSM0 7.20 14.2 2210 1813 8220 7.10 13.7 2403 1960 8240 7.14 15.0 2527 2177 8660 7.12 17.0 2413 2056 8580 7.11 15.4 2543 2180 86graphs can be found in Appendices C-7 to C-12.Chapter 5DISCUSSION5.1 IntroductionExperimental results of probe tests and biological batch tests are discussed in this chapter.In the discussion of the probe testing results, measured ORP values are compared withthe standard ORP values of the tested quinhydrone solutions. The relationship betweenmeasured values and standard values is investigated. The necessity of probe testing inorder to properly adjust measured ORP values before the application of ORP values isdiscussed.Biological batch tests examined the effects of initial NO concentrations and deni-trification rates on redox values at complete denitrification conditions. The method ofdefining redox values for complete denitrification conditions is discussed. Redox valuesin complete denitrification conditions are evaluated to examine the possibility of usingthem as a biological denitrification control parameter.5.2 Evaluation of Probe Testing ResultsProbe test 1 will be discussed in detail. Experimental results of probe tests 2 and 3 willalso be discussed.44Chapter 5. DISCUSSION^ 455.2.1 The Probe's behaviour in quinhydrone buffer solutionsA group of ten probes was tested in a series of 6 quinhydrone solutions whose pH valuesranged from 4 to 9. It was observed that measured ORP values were steady over thetesting period shown in Figures 4.1 to 4.5. In Figure 4.6 (probe test 1.6 with a pH valueof 9.85), measured ORP values decreased over 20 minutes. Averages (Avg) and standarddeviations (Std) are taken on measured ORP values collected in probe tests 1.1 to 1.5(Figures 4.1 to 4.5). The results are listed Table 5.1.Petersen (1966) mentioned that quinhydrone buffer solutions have steady ORP valueswhen solutions' pH values are below 9. When the pH is above 9, the high OH- concen-tration in the system will make the reaction shown in Equation (4.1) a irreversible one.Therefore, the probe test 1.6 at pH 9.85 does not have a steady ORP value, and is notincluded in probe testing discussions.The standard deviations (Std) in Table 5.1 are used to evaluate the reliability of thedata log-in system, and to detect any malfunctioning probes. The resolution of the datalog-in system in 0.5 my. In other words, a + 0.5 my difference between the measuredvalue and the true value (in practice, the average is taken as the true value) is acceptable.It is observed that 42% of standard deviations (Std) in Table 5.1 are equal to, or lessthan 0.5 my. 72% of the standard deviations are no more than 1.0 my. These standarddeviations indicated that no extraordinary discrepancy was present in the log-in systemand from ORP probes.The relationship between measured redox values (Avg in Table 5.1) and pH values ofthe corresponding solutions was studied by plotting measured redox values against pHvalues for each probe. This was done to correlate measured redox values with pH values,and furthermore, to correlate measured redox values with standard values. Figure 5.1presents the relationship between measured redox values and pH values. It was observedChapter 5. DISCUSSION^ 46Table 5.1: ORP values: Avg, Std and SD (probe test 1) (my)pH 4.03 6.30 7.06 7.78 8.78Probe Avg Std Avg Std Avg Std Avg Std Avg Std1 268 0.4 142 0.4 97 0.5 51 0.7 -5 1.22 264 0.5 139 0.4 92 1.0 49 0.9 -8 1.13 260 0.5 136 1.3 88 1.1 47 1.0 -9 1.94 261 0.5 137 1.1 91 0.5 48 0.8 -8 1.35 269 0.0 141 0.6 99 0.4 51 0.7 -6 1.16 262 0.0 138 0.6 92 0.3 48 0.6 -8 1.17 269 0.0 140 0.9 98 0.6 47 1.2 -9 1.28 267 0.0 141 0.5 95 0.4 48 1.0 -7 1.29 266 0.5 140 0.5 96 0.5 51 0.7 -6 1.210 266 0.5 140 0.4 97 0.7 49 0.7 -7 1.2SD 266 133 88 46 -12that measured redox values were linearly related to pH values in the quinhydrone buffersolution. (Quinhydrone solutions have lower redox values when pH values are higher).Since the standard redox values (SD) of quinhydrone solution at pH 4.0 and 7.0 aregiven in Table 4.1, by using the linear relationship between redox values and pH values,the standard redox values at pH 4.03, 6.30, 7.06, 7.78 and 8.78 (used in probe test 1)were extrapolated (temperature 20°C), and are listed in Table 5.1. It is observed thatmeasured values from each probe are not necessary the same as the extrapolated standardredox values of that quinhydrone solution. For each probe, at different pH levels, thedifference between measured values and standard values are not constant. For each pHvalue, different probes could have different ORP values on the same quinhydrone solution.5.2.2 Redox value adjustmentThe relationship between measured redox values and standard values was establishedbased on the data listed in Table 5.1, and is presented in Figure 5.2. It was observed(A) Probes (1-5)Probe 1Probe 2Probe 3Probe 4Probe 5Probe 6Probe 7Probe 813Probe 9-- -A --Probe 10(B) Probes (6-10)Chapter 5. DISCUSSION^ 47300 ^280260240 —220 —5"-'E 200 —•180160cc 1400-0 120 —I'F, 100cocp 8060 —4020 —0-203 4^5^6^7^8^9^10pH300280260240220E 200180• 160>ct 1400-0 120pn 100a) 806040200-203^4^5^6^7^8^9^10pHFigure 5.1: Measured ORP values vs pH (probe test 1)Chapter 5. DISCUSSION^ 48Table 5.2: Adjustment ratios (probe tests 1 to 3)Y = bX + aProbe test 1 Probe test 2 Probe test 3Probes b a (my) b a (my) b a (my)1 0.98 8 0.98 11 0.99 32 0.98 5 0.97 8 0.99 03 0.97 3 0.97 5 0.98 -14 0.97 5 0.98 6 0.99 15 0.99 8 0.99 8 0.99 26 0.97 5 0.97 7 0.99 17 1.00 5 0.99 11 1.00 78 0.99 6 0.98 8 1.00 19 0.98 7 0.98 8 0.99 210 0.98 6 0.98 7 1.00 1that a linear relationship exists between measured redox values and standard values inthe pH ranges from 4 to 9.An equation was developed to relate measured redox values to standard values:Y=bX-Fa^ (5.1)Y - measured redox values (my)X - standard redox values (my)b, a - ratiosThe values of b and a can be found in Table 5.2.Probe tests 2 and 3 have similar results to probe test 1. The measured redox valuesare also linearly related to the corresponding standard redox values. The ratios are listedin Table 5.2.■^I0^20^40^60^80^100 120 140 160 180 200 220 240 260 280 300Standard redox values (my)30-0-0300280260240220200180160140120100806040200-20-20Probe 1Probe 2Probe 3Probe 4Probe 5(B) Probes (6-10)Probe 6Probe 7Probe 80Probe 9Probe 10Chapter 5. DISCUSSION^ 49300280260240— 220200S 180co> 160-o0 140 120-o.a.2  1wcz  80 6040200-20-20 0^20^40^60^80^100 120 140 160 180 200 220 240 260 280 300Standard redox values (my)Figure 5.2: Measured ORP values vs standard ORP values (probe test 1)Chapter 5. DISCUSSION^ 505.2.3 Evaluation of probe testing resultsProbe testing results are discussed based on the data listed in Table 5.2. Ratio b in Table5.2 varied from 0.97 to 1.00. Every 100 my change of the solutions' standard values willresult in a minimum 97 my change in measured ORP values.Ratio a is a major contribution to the difference between the measured redox valueand the standard redox value of the tested solution, and to the difference among differentprobes. It was observed that, for each probe test, the difference between ratio a fordifferent probes was in the 0 - 10 my range.The necessity of adjusting measured ORP values before their application will bediscussed based on the redox values of the biological batch tests. Although measuredvalues for individual probes may not be the same as the solution's true value, this kindof difference may, or may not have a critical influence on conclusions of a experiment.The necessity of adjusting measured ORP values has to be examined for the individualexperiment.5.3 Redox Values for Complete Denitrification Conditions5.3.1 Defining ORP values for complete denitrification conditionsThe results of anoxic batch test 1 and carbon addition test 1 are presented in Figures 4.7to 4.11, and Figures 4.13 to 4.17 respectively. It was observed that in each redox valuevs time curve, there is a redox value plateau following the initial rapid ORP decrease. Atthe end of the plateau, redox values were observed to decrease in a faster rate. The slopechange point, when the ORP started to decrease at an increasing rate after the plateau,is defined as the knee.The knee phenomenon is the major interest of this research. The internal relation-ship between redox values and denitrification process in the tested biological system wasChapter 5. DISCUSSION^ 51investigated by examining the ORP values at the knees and the NO levels at the cor-responding time. If redox values at the knees are related to the NO disappearance inbiological systems, then these redox values can be assessed on the possibility of beingused in a denitrification control system.Since the knee in redox monitoring curves is consistent with the point which has theminimum derivative, then taking the derivative of the redox vs time curve is used as themethod to obtain redox values to be used in the discussion of the results. Eye estimationis used to decide the knee position as a confirmation approach of the derivative method,since it is simple and straightforward. The disadvantage of eye estimation method is thatnot every redox curve has a very sharp knee, in which case it is not easy to define theknee's position.The derivative method and the eye estimation method work well for the batch testsystem. They cannot be used however, in a flow through system where measured ORPvalues are indicative of a steady state condition which may or may not represent thepoint of complete denitrification. However, the conclusions from a batch test can beused in a flow through process based on the assumption that the biological condition forcomplete denitrification has the same measured ORP for a batch system and a steadystate condition of a flow through process, when they have the same biological materialsand operational conditions.5.3.2 Measured ORP values at the kneesOn the basis of eye estimation on Figure 4.7, the knee appeared between the 30th and40th minute. The derivative method was used to identify the exact time when theknee appeared. The first derivative was taken on the redox curve (shown in Figure4.7 as an example). Because of the sensitivity of ORP probes and the complexity of abiological system, the plotted data points did not provide a completely smooth curveChapter 5. DISCUSSION^ 52I^■^I^i^I^■^I^■^1^i^1^i^i^■^I^,5^10^15^20^25^30^35^40^45^50^55^60Time (min)Figure 5.3: Anoxic test 1.1: first derivatives vs time420,Es - 1 o-12it-14-16-18-200where the point of inflection was obvious. The effect of these data point irregularitieswas compounded when a first derivative vs time curve was constructed (see Figure 5.3).The irregularities in Figure 5.3 does not represent the characteristics of the curve inFigure 4.7. For example, ORP values are still in the plateau area between the 15th and20th minute, however, the several consecutive derivatives in Figure 5.3 are +4, -3, +2, to-2 (mv/minute) for probe 4, which exaggerate the irregularities of the curve. Averagingevery five points consecutively was done on Figure 5.3 to get Figure 5.4. The irregularitiesin Figure 5.3 were smoothed, and the minimum derivative, when the knee appeared, wasdistinguished, and is shown to occur at the 34th minute.Figure 5.5 is the result of averaging every ten points consecutively. It was observedthat in the time period of the 28th minute to the 35th minute, 7 consecutive points havethe same derivative. In this curve, the minimum derivative can not be identified. Tenpoint averaging will therefore not be used in deciding the position of the knee.40 50 6045 555^10^15^20^25^30^35Time (min)Figure 5.5: Anoxic test 1.1: first derivatives vs time (Avg 10)50 55 6045405^10^15^20^25^30^35Time (min)Figure 5.4: Anoxic test 1.1: first derivatives vs time (Avg 5)Chapter 5. DISCUSSION 53o,p,o,p AA 00000000--E1^.cf-4-6-12-14-16-18-2006420-20 0 0 0 0 0 0 0 0 0 0 0 0 0 06420-14-16-18-200Chapter 5. DISCUSSION^ 54Table 5.3: Measured ORP values at the knees DM, AT1 myRatio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 34 -51 -471 75 -13 -202 98 -29 -243 116 -22 -224 138 -21 -26Table 5.4: Measured ORP values at the knees (DM, AT2)(myRatio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 18 -49 -481 46 -9 -222 62 -31 -253 69 -18 -214 88 -14 -24Although the derivative method cannot be used in a flow through process, the con-clusions that are drawn from batch testing data will build a solid background for theORP's application in a flow through process.It is recommended that five point averaging be used to smooth the first derivativecurve. The corresponding redox values defined in this way are listed in Table 5.4. Deriva-tives of other redox curves have similar results to the one shown in Figure 5.3, and theredox values obtained from the derivative method are listed in Tables 5.4 to 5.8.In Tables 5.3 to 5.8, DM stands for the derivative method, AT stands for an anoxictest, CA stands for a carbon addition test. The listed redox values are measured ORPvalues at the knees as determined by the derivative method. Each batch test used twoprobes (probes 3 and 4, probes 5 and 6). The times listed in Tables 5.3 to 5.8 are usedto decide NO, levels in biological testing systems.Chapter 5. DISCUSSION^ 55Table 5.5: Measured ORP values at the knees (DM, AT3) (my)Ratio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 20 -55 -541 43 -20 -322 59 -36 -303 86 -31 -244 105 -16 -28Table 5.6: Measured ORP values at the knees (DM, CA1) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 75 -5 -1320 52 -12 -2240 36 -12 -2160 35 -24 -3480 33 -45 -36Table 5.7: Measured ORP values at the knees (DM, CA2) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 87 -19 -1120 54 -13 -2540 36 -22 -1660 36 -17 -3180 36 -45 -36Table 5.8: Measured ORP values at the knees (DM, CA3) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 115 -25 -2020 65 -2 -2140 44 -26 -1560 44 -23 -2480 43 -26 -17Chapter 5. DISCUSSION^ 56Table 5.9: Measured NO at the knee position AT 1-3Anoxic test 1 Anoxic test 2 Anoxic test 3Ratio Time(min)NO(mg/L)Time(min)NO(mg/L)Time(min)NO(mg/L)0 34 0.05 18 0.42 20 0.381 75 0.16 46 0.34 43 0.262 98 0.16 62 0.24 59 0.133 116 0.67 69 0.44 86 0.31138 0.53 88 0.35 105 0.10Table 5.10: Measured NO at the knee position (CA 1-3)Carbon test 1 Carbon test 2 Carbon test 3NaAc(mg/L)Time(min)NO(mg/L)Time(min)NO(mg/L)Time(min)NOT(mg/L)0 75 0.07 87 0.10 115 0.6320 52 0.05 54 0.10 65 0.2840 36 0.12 36 0.15 44 0.3160 35 0.04 36 0.07 44 0.3680 33 0.03 36 0.08 43 0.445.3.3 NO, levels at the kneesThe NO levels at the knees are used to exam the relationship between redox values atthe knees and the completeness of the denitrification process in a biological system. NOlevels at the time of the minimum derivative are presented in Tables 5.9 to 5.10. InitialNO levels and NO removal efficiencies are listed in Tables 5.11 and 5.12.It was observed that among measured NO levels in Tables 5.9 and 5.10, 43% of themare lower than 0.15 mg/L, and 90% of them are no more than 0.50 mg/L. The NOTdetection limit is 0.05 mg/L. The NO removal efficiencies are averaged to be 92.6% inanoxic tests 1-3, and to be 96.2% in the carbon addition tests 1-3. The NO testing resultsChapter 5. DISCUSSION^ 57Table 5.11: Initial NO levels and removal efficiencies (anoxic tests 1-3)Anoxic test 1 Anoxic test 2 Anoxic test 3Ratio NO @ t=0(mg/L)% removal@ kneeNO @ t=0(mg/L)% removal@ kneeNO @ t=0(mg/L)% removal@ knee0 2.6498.1 2.21 81.0 2.10 81.91 4.97 96.8 4.28 92.1 3.29 92.12 5.96 97.3 5.24 95.4 4.04 96.83 6.59 89.8 5.29 91.7 4.58 93.24 6.65 92.0 5.17 93.2 5.21 98.1Table 5.12: Initial NOT levels and removal efficiencies (carbon tests 1-3)Carbon test 1 Carbon test 2 Carbon test 3NaAc(mg/L)NO @ t=0(mg/L)% removal@ kneeNO @ t=0(mg/L)% removal@ kneeNO @ t=0(mg/L)% removal@ knee0 4.76 98.54.83 97.9 4.85 87.020 4.75 98.9 4.86 97.9 4.98 94.440 4.74 97.5 4.66 96.8 5.10 93.960 4.58 99.1 4.57 98.5 5.09 92.980 4.77 99.4 4.79 98.3 5.32 91.7Chapter 5. DISCUSSION^ 58Table 5.13: Adjusted ORP values at the knees DM, AT1)(myRatio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 34 -56 -531 75 -21 -262 98 -33 -303 116 -26 -284 138 -29 -32indicate that denitrification processes in biological systems are essentially complete at thetime the knees are present. The knee phenomenon also strongly indicates the internalrelationship between redox values and the denitrification process in a batch test system,because of the relationship between the slope change in redox vs time curves and theNO disappearance in the system.5.3.4 The possibility of using ORP as a control parameterIt was observed in Section 5.2 that the measured ORP values of different probes aredifferent from standard values for the tested solution, and there are differences amongORP probes. Before evaluation of ORP as a denitrification control parameter, measuredORP values listed in Tables 5.3 to 5.8 were adjusted based on the relationship presentedin Equation (5.1), so that these redox values are made to be comparable. Adjustmentfactors used the results of probe test 1 in Table 5.2, since all biological batch tests wereconducted before the end of March, 1992. The adjusted redox values are listed in Tables5.13 to 5.18.In the evaluation of anoxic tests 1-3, the batch test from ratio 0 was not included.A flow through nitrate removal process normally has the aerobic mixed liquors recycledback to the anoxic zone for denitrification. The ratio 0 batch test system did not haveany biological material from the aerobic zone (see Table 4.6), and therefore was not usedChapter 5. DISCUSSION^ 59Table 5.14: Adjusted ORP values at the knees (DM, AT2) (my)Ratio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 18 -54 -541 46 -17 -282 62 -35 -313 69 -22 -274 88 -22 -30Table 5.15: Adjusted ORP values at the knees (DM, AT3) (my)Ratio Time (min) Probe 3 Probe 4 Probe 5 Probe 60 20 -60 -611 43 -28 -382 59 -40 -363 86 -35 -304 105 -24 -34Table 5.16: Adjusted ORP values at the knees (DM, CA1) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 75 -9 -1820 52 -20 -2840 36 -16 -2760 35 -32 -4080 33 -50 -42Table 5.17: Adjusted ORP values at the knees (DM, CA2) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 87 -23 -1620 54 -21 -3140 36 -26 -2160 36 -25 -3780 36 -50 -42Chapter 5. DISCUSSION^ 60Table 5.18: Adjusted ORP values at the knees (DM, CA3) (my)NaAc (mg/L) Time (min) Probe 3 Probe 4 Probe 5 Probe 60 115 -29 -2520 65 -10 -2740 44 -30 -2060 44 -31 -3080 43 -30 -22Table 5 19: Avg and Std at the redox knees AT 1-3 and CA 1-3)Anoxic tests Carbon addition testsRange(my)Averages(my)Std(my)Range(my)Averages(my)Std(my)Test 1 -33 to -21 -28 4 -50 to -9 -28 13Test 2 -35 to -17 -27 6 -50 to -16 -29 11Test 3 -40 to -24 -33 5 -31 to -10 -25 7All tests -40 to -17 -29 6 -50 to -9 -25 10Avg = -28 my^Std = 8 mvin the evaluation of redox values at the knees. The ratio 0 batch test was designed tosimulate the anoxic zone of the process for which no aerobic recycling is done (shown inFigure 3.1). It could be interpreted as a "control" system.Averages and standard deviations (Std) were taken for adjusted redox values in Tables5.13 to 5.18. The averages and standard deviations of redox values at the knees fromanoxic batch tests 1-3 (ratio 1 to 4), and carbon addition tests 1-3 are listed in Table5.19.When the average was taken on all 54 data sets (24 from anoxic tests, 30 from carbonaddition tests), the average is -28 my, and the standard deviation is 8 my. Statistically,the 68% confidence interval is one standard deviation (+ 8mv), and the 95% confidenceinterval is two standard deviation (± 16 my). Therefore any adjusted redox values at theChapter 5. DISCUSSION^ 61Table 5.20: NO (adjusted ORP value is -12 my, AT1)Ratio Time (min) NO (mg/L)1 29 (P5) 29 (P6) 3.42 (P5) 3.42 (P6)2 32 (P3) 36 (P4) 3.75 (P3) 3.44 (P4)3 44 (P3) 41 (P4) 3.76 (P3) 3.81 (P4)4 47 (P5) 47 (P6) 4.80 (P5) 4.80 (P6)knee has a 95% possibility to fall into a range of (-28+16) my, or -12 to -44 my.In deciding which redox value (the upper limit of -12 my, the average of -28 my,or the lower limit of -44 my) should be used as a control guideline of the biologicaldenitrification process, Figures 4.7 to 4.11, and Figures 4.13 to 4.17 were examined.Redox values decreased over the time of the biological denitrification process in all batchtests. Because of the plateau, the time when the adjusted redox values is -12 my willoccur much more quickly than when the knee occurs. The NO in the system is far frombeing removed completely. Table 5.20 lists the time when the adjusted ORP value is -12my (measured ORP values were calculated by using the Equation (5.1) and the ratiosfrom probe test 1 listed in Table 5.2). P3, P4, P5, and P6 stand for probe 3, probe 4,probe 5, and probe 6. Because the ratios a and b are different for different probes, thetime when the same adjusted ORP value of -12 my occurs are different in Table 5.20.NO levels were decided from Figures 4.12 and 4.18 by using the time listed in Table5.20.When the redox value of -28 my (adjusted) is used, biological systems may or maynot be NO low, since the -28 my is an averaged value. In Table 5.21, one batch test(ratio 2) in the anoxic test 3 has a NO of 1.80 mg/L, which does not indicate completedenitrification.The lower limit of -44 my is the most promising redox value that can be used inChapter 5. DISCUSSION^ 62Table 5.21: NO adjusted ORP value is -28 my, AT3Ratio Time (min) NO (mg/L)1 43 (P5) 17 (P6) 0.34 (P5) 1.67 (P6)2 29 (P3) 42 (P4) 1.80 (P3) 1.23 (P4)3 69 (P3) 84 (P4) 1.19 (P3) 0.31 (P4)4 106 (P5) 96 (P6) 0.09 (P5) 0.45 (P6)Table 5.22: NO adjusted ORP value is -44 my, AT1Ratio Time / intervals (min) NO (mg/L)1 83 (P5) / 8 81 (P6) / 6 0.06 (P5) 0.06 (P6)2 101 (P3) / 3 102 (P4) / 4 0.07 (P3) 0.07 (P4)3 123 (P3) / 7 123 (P4) / 7 0.44 (P3) 0.44 (P4)4 144 (P5) / 6 142 (P6) / 4 0.34 (P5) 0.33 (P6)denitrification process control. First, redox values at the knees statistically have 95%possibility to be higher than -44 my in this research, no matter what initial NO levels,or what denitrification rates the batch test systems have. Second, after the knee, redoxvalues decreased in an increasing rate, thus, the time when redox value is -44 my is nottoo much longer than the time when the knee occurs. The time and the correspondingNO levels when the redox value (adjusted) is - 44 my are listed in Tables 5.22 to 5.27.Tables 5.22 to 5.24 include anoxic tests 1 to 3. Tables 5.25 to 5.27 present carbonTable 5.23: NO (adjusted ORP value is -44 my, AT2)Ratio Time / intervals (min) NO (mg/L)1 53 (P5) / 7 50 (P6) / 4 0.46 (P5) 0.51 (P6)2 63 (P3) / 1 65 (P4) / 3 0.23 (P3) 0.24 (P4)3 73 (P3) / 4 73 (P4) / 4 0.34 (P3) 0.34 (P4)4 93 (P5) / 5 90 (P6) / 2 0.23 (P5) 0.31 (P6)Chapter 5. DISCUSSION^ 63Table 5.24: NO (adjusted ORP value is -44 my, AT3Ratio Time / intervals (min) NO (mg/L)1 47 (P5) / 3 45 (P6) / 2 0.15 (P5) 0.21 (P6)2 61 (P3) / 2 61 (P4) / 2 0.07 (P3) 0.07 (P4)3 89 (P3) / 3 90 (P4) / 4 0.31 (P3) 0.31 (P4)4 110 (P5) / 5 107 (P6) / 2 0.06 (P5) 0.08 (P6)Table 5.25: NO (adjusted ORP value is -44 my, CA1)mg/L Time / intervals (min) NO (mg/L)0 99 (P3) / 24 90 (P4) / 15 0.05 (P3) 0.05 (P4)20 69 (P5) / 17 54 (P6) / 2 0.04 (P5) 0.05 (P6)40 48 (P3) / 12 42 (P4) / 6 0.07 (P3) 0.06 (P4)60 42 (P5) / 7 36 (P6) / 1 0.06 (P5) 0.04 (P6)80 42 (P3) / 9 39 (P4) / 6 0.04 (P3) 0.04 (P4)Table 5.26: NO adjusted ORP value is -44 my, CA2mg/L Time / intervals (min) NO (mg/L)0 99 (P3) / 12 99 (P4) / 12 0.05 (P3) 0.05 (P4)20 72 (P5) / 18 63 (P6) / 9 0.06 (P5) 0.14 (P6)40 45 (P3) / 9 48 (P4) / 12 0.05 (P3) 0.05 (P4)60 45 (P5) / 9 39 (P6) / 3 0.08 (P5) 0.08 (P6)80 36 (P3) / 10 39 (P4) / 3 0.08 (P3) 0.07 (P4)Table 5.27: NO (adjusted ORP value is -44 my, CA3)mg/L Time / intervals (min) NO (mg/L)0 119 (P3) / 4 121 (P4) / 6 0.08 (P3) 0.05 (P4)20 81 (P5) / 16 70 (P6) / 5 0.07 (P5) 0.36 (P6)40 49 (P3) / 5 52 (P4) / 8 0.13 (P3) 0.14 (P4)60 49 (P5) / 5 48 (P6) / 4 0.23 (P5) 0.26 (P6)80 46 (P3) / 3 48 (P4) / 5 0.40 (P3) 0.37 (P4)Chapter 5. DISCUSSION^ 64addition tests 1 to 3. The intervals in Tables 5.22 to 5.27 are the time between theposition of the knee and the position of - 44 my (adjusted value). Among the NO levelsin Tables 5.22 to 5.27, 63% of them are not higher than 0.15 mg/L, and 98% of themare lower than 0.50 mg/L. Therefore, -44 my is a good redox value for indicating thecompleteness of the denitrification in the tested systems of this research. When redoxvalues of a biological system reach - 44 my (adjusted value), the denitrification in thesystem can be assumed to be complete.The intervals listed in Tables 5.22 to 5.24 (anoxic tests 1 to 3) have an average of4 minutes with a range of 1 to 8 minutes. In Tables 5.25 to 5.27, the intervals averageis 8 minutes, the range is 0 to 24 minutes. Although the maximum interval in Tables5.25 to 5.27 is 24 minutes, 83% of intervals are not longer than 12 minutes. Therefore,when -44 my is used as a control redox value, and if the knees are taken as the NOdisappearance positions, the biological system will not have been transformed into theanaerobic condition, from the anoxic condition, for a very long period of time. Thephosphorus removal will not be affected in such a denitrification system.5.4 The Necessity of Adjusting Measured ORP ValuesAs discussed in Section 5.2, the measured ORP values are different from the standardvalues. Different probes may have different values for the redox value of the same solution.In Section 5.3, the possibility of using ORP values as a control parameter in assessingthe completeness of a denitrification process was discussed on adjusted redox values withthe consideration that adjusted redox values are closest to the true values of the testedsolutions.The necessity of adjusting measured redox values is examined by investigating the54 data points listed in Tables 5.3 to 5.8 (excluding ratio 0 in anoxic tests 1 to 3). TheChapter 5. DISCUSSION^ 65Table 5.28: NO (measured ORP value is -42 my, AT1Ratio Time / Interval (min) NO (mg/L)1 86 (P5) / 11 83 (P6) / 8 0.06 (P5) 0.06 (P6)2 102 (P3) / 4 102 (P4) / 4 0.07 (P3) 0.07 (P4)3 125 (P3) / 9 126 (P4) / 10 0.43 (P3) 0.43 (P4)4 148 (P5) / 10 144 (P6) / 6 0.37 (P5) 0.34 (P6)Table 5.29: NO (measured ORP value is -42 my, AT2)Ratio Time / Interval (min) NO (mg/L)1 56 (P5) / 10 51 (P6) / 5 0.41 (P5) 0.49 (P6)2 64 (P3) / 2 65 (P4) / 3 0.24 (P3) 0.24 (P4)3 73 (P3) / 4 73 (P4) / 4 0.34 (P3) 0.34 (P4)4 94 (P5) / 6 91 (P6) / 3 0.28 (P5) 0.28 (P6)average is -22 my, and the standard deviation is 10 my. Therefore, the lower limit ofthe 95% confidence interval is (-22-20) my = -42 my. The time when the redox vs timecurves of all batch tests reach -42 my are listed in Tables 5.28 to 5.33. NOT levels atcorresponding time and time intervals between the knees and -42 my positions are listedin Tables 5.28 to 5.33 as well.When the redox value of -42 my (measured value) is used as a control guideline, amongthe NO data listed in Tables 5.28 to 5.33, 59% of them are lower than 0.15 mg/L, andTable 5.30: NO (measured ORP value is -42 my, AT3)Ratio Time / Interval (min) NO (mg/L)1 48 (P5) / 5 46 (P6) / 3 0.12 (P5) 0.18 (P6)2 61 (P3) / 2 61 (P4) / 2 0.07 (P3) 0.07 (P4)3 89 (P3) / 3 91 (P4) / 5 0.31 (P3) 0.32 (P4)4 112 (P5) / 7 108 (P6) / 3 0.13 (P5) 0.08 (P6)Chapter 5. DISCUSSION^ 66Table 5.31: NO, (measured ORP value is -42 my, CA1)mg/L Time / Interval(min) NO (mg/L)0 99 (P3) / 24 93 (P4) /18 0.05 (P3) 0.05 (P4)20 75 (P5) / 23 57 (P6) / 2 0.05 (P5) 0.06 (P6)40 48 (P3) / 12 45 (P4) / 9 0.07 (P3) 0.07 (P4)60 45 (P5) / 10 36 (P6) / 11 0.09 (P5) 0.04 (P6)80 42 (P3) / 9 42 (P4) / 9 0.04 (P3) 0.04 (P4)Table 5.32: NO (measured ORP value is -42 my, CA2mg/L Time / Interval (min) NO (mg/L)0 99 (P3) / 22 99 (P4) / 22 0.05 (P3) 0.05 (P4)20 81 (P5) / 27 66 (P6) / 12 0.06 (P5) 0.11 (P6)40 45 (P3) / 9 48 (P4) / 12 0.05 (P3) 0.05 (P4)60 45 (P5) / 9 42 (P6) / 6 0.08 (P5) 0.08 (P6)80 36 (P3) / 0 39 (P4) / 3 0.08 (P3) 0.07 (P4)Table 5.33: NO (measured ORP value is -42 my, CA3)mg/L Time / Interval (min) NO (mg/L)0 120 (P3) / 5 122 (P4) / 7 0.05 (P3) 0.05 (P4)20 85 (P5) / 20 73 (P6) / 8 0.19 (P5) 0.26 (P6)40 49 (P3) / 5 54 (P4) / 10 0.13 (P3) 0.19 (P4)60 50 (P5) / 6 49 (P6) / 5 0.21 (P5) 0.23 (P6)80 47 (P3) / 4 49 (P4) / 6 0.38 (P3) 0.35 (P4)Chapter 5. DISCUSSION^ 67100% of them are lower than 0.50 mg/L. Therefor, -42 my can be used to indicate theNO disappearance.The intervals between the knee and the -42 my (measured value) position are averagedto be 5 minutes for anoxic tests 1 to 3, and to be 11 minutes for carbon addition tests1 to 3. The maximum interval is 11 minutes for anoxic tests 1 to 3, and 24 minutes forcarbon addition tests 1 to 3. In carbon addition tests 1 to 3, 77% of the intervals are notlonger than 12 minutes. The standard deviation of the 54 data points listed in Tables5.3 to 5.8 (excluding ratio 0) is 10 my, which is 2 my higher than the 8 my standarddeviation determined from the 54 adjusted data in Tables 5.13 to 5.18. It is realizedthat, without adjusting measured ORP values in Tables 5.3 to 5.8, the lower limit of the95% confidence interval is still a good indicator of the completeness of a denitrificationprocess. In this research, the redox value is -42 my, that is, when measured ORP valuesdrops to -42 my, the NO removal in the system can be assumed to be complete, andthe biological system is still a good environment for phosphorus removal because it hasnot been in the anaerobic condition for long.It has to be pointed out that although adjusting measured ORP values is not necessaryin this research, probe testing is still recommended before their application in any processcontrol. One reason is that probe testing can identify any malfuntioning probes. Thesecond reason is that different processes may have different requirements on the accuracyand precision of measured ORP values. Without probe testing, it is not easy to projectwhether the difference between measured ORP values and true values is critical or notin evaluating the use of redox values in a process control system.Chapter 6CONCLUSIONS and RECOMMENDATIONS6.1 ConclusionsBased on results of probe testing experiments, biological batch tests (anoxic batch tests,and carbon addition tests), this research has led to the following conclusions:6.1.1 Probe testing experiments1. The designed probe testing system was reliable and flexible for conducting oxidationreduction potential experiments.2. ORP probes tested in quinhydrone buffer solutions, whose pH values are in therange of 4 to 9, have steady ORP values over the testing time. Standard deviationsof measured ORP values from each probe test were less than 2 my. 43% of themwere no more than 0.5 my, and 72% of them were no more than 1.0 my.3. Measured ORP values from probes may not be equal to the standard value of thetested quinhydrone solution. When the same probe was tested in quinhydronesolutions whose pH values were different, the differences between measured valuesand standard values were not, in general, constant (the differences varied between 2my to 9 my for probe 1). When the same quinhydrone solution was used, differentprobes had different measured ORP values (the differences varied between -6 Invto 3 my for pH 4.03). A linear relationship was developed between measured ORPvalues and standard ORP values of the tested quinhydrone solutions.68Chapter 6. CONCLUSIONS and RECOMMENDATIONS^ 694. Adjustment factors for measured ORP values were developed. The necessity ofadjusting measured ORP value is discussed in Section 6.1.3.6.1.2 The accuracy and precision of ORP monitoring1. The knee phenomenon was observed from the ORP monitoring curves in anoxicand carbon addition batch tests. The knee position is defined as the position onthe curve which exhibits the minimum derivative in a plot of millivolts vs time.2. The knee could be used as an indication of the complete denitrification conditionin the tested biological system. At the time corresponding to the occurrence of theknee, 43% of the tested NO levels were lower than 0.15 mg/L, and 90% of thetested NO were lower than 0.5 mg/L. The average NO removal efficiencies were92.6% in anoxic tests, and 96.2% in the carbon addition tests.3. When the average of the 54 adjusted redox values (24 from anoxic tests excludingratio 0 batch tests, 30 from carbon addition tests) is evaluated, it was found to be- 28 my, and the standard deviation was 8 my. Any adjusted redox values at theknees have a 95% possibility to be above -44 my (adjusted value).4. At -44 my (adjusted value), 63% of NO levels in the system are not higher than0.15 mg/L. 98% of the NO levels are lower than 0.50 mg/L. The denitrificationcan be assumed to be complete when redox values reach -44 my (adjusted value).5. The intervals between knees and the position of -44 my (adjusted value) are 4minutes on average for anoxic tests 1 - 3, and 8 minutes on average for carbon ad-dition tests 1 - 3. The biological system is still in a favourable state for phosphorusremoval in the process.Chapter 6. CONCLUSIONS and RECOMMENDATIONS^ 706. Anoxic batch tests were designed to have different initial NO concentrations. Car-bon addition tests were designed to have different denitrification rates. Redoxvalues collected from these different batch tests generated a guideline of -44 my(adjusted value) which can be used as an indicator of complete denitrification inbiological systems used in this research (other biological systems may not have thesame ORP value at the complete denitrification condition). The knee phenomenonrevealed the internal relationship between redox testing and the NO disappear-ance. Therefore, there is a good possibility that ORP testing can be used as acontrol tool in a denitrification process.6.1.3 The necessity of adjusting measured ORP values1. When adjustment was not applied to the 54 redox values, the average was -22 my,and the standard deviation was 10 my. Comparing this with the standard deviationof 8 my from the adjusted values, it is seen, that, without adjustment, the standarddeviation is only 2 my higher.2. When the -42 my (measured value, the lower limit of the 95% confidence interval)is used as a control guideline, 59% of the NO data are lower than 0.15 mg/L, and100% of NO data are lower than 0.5 mg/L. Thus, -42 my (measured value) can beused as a redox value indicating NO disappearance in the system.3. The time intervals between the knee and the -42 my (measured value) position havean average of 5 minutes for anoxic tests 1 to 3, and 11 minutes for carbon additiontests 1 to 3. The system with -42 my (measured value) redox value is still a goodenvironment for phosphorus removal in the process.Chapter 6. CONCLUSIONS and RECOMMENDATIONS^ 714. On the basis of the results of this research, it is not necessary to adjust measuredORP values to arrive at conclusion 6 in Section 6.1.2 for this specific application.However, probe testing is still recommended before using the ORP probe as acontrol tool. The testing procedures are presented in Section 6.2.6.2 RecommendationsAs a result of this work, the following probe testing procedures are recommended:1. Read the output from the probes in two quinhydrone buffer solutions with twodifferent pH values.2. Determine the standard redox values of the buffer solutions.3. Assume a linear relation between the measured redox values and the standard redoxvalues for each tested probe by using the following equation:Ymeasured = constant(X standard) + constant^(6.1)4. Adjust the measured values (Y) to get the standard value (X), and apply thestandard value in the process control system.5. Recheck the probe compliance with the equation on approximately a monthly basis.BibliographyAmerican Public Health Association (APHA), American Water Works Association(AWWA), and Water Pollution Control Federation (WPCF) (1989). "StandardMethods for the Examination of Water and Wastewater". 17th Ed., Washing-ton, D.C..American Society for Testing and Materials (ASTM) (1983). "Standard Practicefor Oxidation Reduction Potential of Water". Vol 11:01, Section D1498, Water(1), Philadelphia, PA 19103.Bates, R. G. (1973). "Determination of pH: Theory and Practice". 2nd Ed., JohnWiley Si Sons, Inc..Broadley James Corporation (1990). "Electrode Instructions".Coleman, P. (1987). "ORP Measurement in the Laboratory". Memo. Environmen-tal Engineering Laboratory, The University of British Columbia.Comeau Y. (1984). "Biochemical Models for Biological Excess Phosphorus Removalfrom Wastewater". M.A.Sc. Thesis. The University of British Columbia.Comeau Y. (1989). "The Role of Carbon Storage in Biological Phosphate Removalfrom Wastewater". Ph.D Thesis. The University of British Columbia.De la Menardiere M., Charpentier, J., Vachon, A. and G. Martin (1991). "ORPas a Control Parameter in a Single Sludge Biological Nitrogen and PhosphorusRemoval Activated Sludge System". Water S. A.. 17 (2), p123.Eckenfelder, W. W. Jr. and J. W. Hood (1951). "The Application of Oxidation Re-duction Potential to Biological Waste Treatment Process Control". Proceedingsof the 6th Purdue Industrial Waste Conference, Feb 21-23, 1951. Purdue Uni-versity, West Lafayette, Indiana, p221.Eckenfelder, W. W. Jr. (1958). "A Discussion on Redox Potentials in WasteTreatment - Laboratory Experiences and Applications". Sewage and IndustrialWastes. 30 (4), p501.Eilbeck, W. J. (1984) "Redox Control in Breakpoint Chlorination of Ammonia aridMetal Ammine Complexes". Water Research. 18, (1), p21.Gabb, M. H. & W. E. Latchem (1968). "A Handbook of Laboratory Solutions".Chemical Publishing Co. Inc.. New York, N.Y.72Bibliography^ 73Grune, W. N. and Chun-Fei Chueh (1958). "Redox Potentials in Waste Treatment- Laboratory Experiences and Applications". Sewage and Industrial Wastes. 30(4), p479.Harrison, D. E. F. (1972). "Physiological Effects of Dissolved Oxygen Tension andRedox Potential on Growing Populations of Microorganisms". Journal of Ap-plied Chemistry and Biotechnology. Vol. 22, p417.Hood, J. W. (1948). "Measurement and Control of Sewage Treatment Process Ef-ficiency by Oxidation Reduction Potential". Sewage Works Journal. 20 (4),p640.Kjaergard L. (1977). "The Redox Potential: Its Use and Control in Biotechnology".Advances in Biochemical Engineering, Vol.7, Chose, T. K., Fiechter, A. and N.Blakebrough (Editors), Springer - Verleg, Berlin , p131.Koch, F. A. W. K. Oldham (1985). "ORP - A Tool for Monitoring, Control andOptimization of Biological Nutrient Removal Systems". Water Science Tech-nology. 17, 259.Koch, F. A., Oldham, W. K., and H. Z. Wang (1988). "ORP as Tool for Mon-itoring and Control in Bio-nutrient Removal System". Proceedings of JointASCE/CSCE Environmental Engineering Conference, July 12-19, Vancouver,B. C., p162.Lachat Instrument (1988). "Methods Manual for the Quickhem Automated Ion An-alyzer". The Environmental Engineering Laboratory. The University of BritishColumbia.Metcalf Sz Eddy Inc. (1979). "Wastewater Engineering: Treatment. Disposal,Reuse". 2nd Ed., McGraw Hill, Boston, MA.Narkis, N., M. Rebhun and Ch. Sheindorf (1979). "Denitrification at Various Car-bon to Nitrogen Ratios". Water Research. 13, p9398.Nussberger, F. E. (1953). "Applications of Oxidation Reduction Potentials to theControl of Sewage Treatment Processes". Sewage and Industrial Wastes. 25 (9),p1003.Oldham, W. K. (1988). "Report on Previous Work and Description of ProposedResearch". Research Proposal. The University of British Columbia.O'Rourke, J. T., Tomlinson, H. D. and N. C. Burbank. Jr. (1963). "Variation ofORP in an Activated Sludge Plant with Industrial Waste Load". IndustrialWater and Wastes. 8 (6), p15.Peddie, C. C., Koch, F. A., Jenkins, C. J., and D S. Mavinic (1988). -ORP asa Tool for Monitoring and Control of SBR Systems for Aerobic Sludge Diges-tion" Proceedings of Joint ASCE/CSCE Environmental Engineering Confer-ence, July 12-19, Vancouver, B. C., p171.Bibliography^ 74Petersen, G. K. (1966). "Redox Measurements: Their Theory and Technique".Radiometer A/S. Copenhagen, Denmark.Poduska, R. A. and B. D. Anderson (1981). "Successful Storage Lagoon OdourControl". Journal Water Pollution Control Federation. 53 (3), p299.Rabinowitz, B. (1985). "The Role of Specific Substrate in Excess Biological Phos-phorus Removal". Ph.D Thesis. The University of British Columbia.Radjai, M., Hatch, R. T. and T. W. Cadman (1984). "Optimization of AminoAcid Production by Automatic Self-Tuning Digital Control of Redox Potential".Biotechnology and Bioengineering Symposium. No.14, John Wiley & Sons, Inc.,p657.Rohlich, G. A. (1948). "Measurement and Control of Sewage Treatment ProcessEfficiency by Oxidation Reduction Potential - A Discussion". Sewage WorksJournal. 20 (4), p650.Siebritz I., Ekama, G. A. and G. v. R. Marais (1983). "Biological Excess PhosphorusRemoval in the Activated Sludge Process". Research Report. W 47, Dept. ofCivil Engineering, The University of Cape Town.US EPA (1975). "Process Design Manual for Nitrogen Control". Office of Technol-ogy Transfer, Cincinnati, Ohio, USA.Wareham D. G. (1988). "The Use of Oxidation Reduction Potential for Real TimeProcess Control in Sequencing Batch Reactors". Ph.D Research Proposal. TheUniversity of British Columbia.Wareham D. G. (1992). 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"Eh as an Operational Parameter in Estuarine Studies".Limnology and Oceanography. 14 (4), p547.Appendix AResults of Probe Test 2 and Probe Test 375 •(A) Porbes (1-5)Probe 1Probe 2Probe 3Probe 4— -.—Probe 5•_- -0 -^-41-^-.0 ^ 0 ^ 0 ^ 0 ^ .0 ^ 0 ^ 0 ^ 0^ 0 ^ 00 ^0^ G266a.cc0 264I:12 262g 2608 268272E 27025002582562542522782762742802 4 6 a^10^12^14Time (min)16 18 20 22 24Probe 6Probe 7Probe 8Probe 9— -.—Probe 10(B) Probes (6-10)0 264272E 270a) 268266CLCCig 262CI)26025425002582522562742802782762 4 6 8^10^12^14Time (min)16 18 20 22 24.••— • •^43^•^• • 74a At --11-^111- AI- -IV^*-11L--.-^--11-Appendix A. Results of Probe Test 2 and Probe Test 3^ 76Figure A-1: Probe test 2.1 (pH 4.10)150148146144142• 1400 134E 132130128126124122120Probe 6Probe 7Probe 80.Probe 9— -.—Probe 10Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 77(A) Probes (1-5) Probe 1Probe 2Probe 30Probe 4-4Probe 5      - .0-^    •0- 0-^1-- -4P-- -0- -0- -1- 0-^ -41''^- -0 - -1- --or00000 ^9000000000 ^9^ 0 ^00^2^4^6^a^10^12^14^16^18^20^22^24Time (min)148146144142140CDO 134.? 13203 130a.)• 128126124122120 ^0• 138"ra• 136150(B) Probes (6-10)/A' ——a ^9.7--1j ^ J2. ^111 --• •F^or' •-•^•242^4^6^8^10^12^14^16^18^20^22Time (min)Figure A-2: Probe test 2.2 (pH 6.32)(A) Probes (1-5)Probe 1Probe 2Probe 3Probe 4- °-Probe 5_—^ ^-0 -II^IF S.^0^-0^  ^A^-II—0- -IR.^0- -0--0,0".^ -tr"0000 ^ 00000 ^ 0 ^ 0 ^ 90 ^ 0000 ^ 0 110108106104102E 1008 98a. 96CCQ 949290888684822^4 16^18^20^22^246^8^10^12^14Time (min)800Probe 6Probe 7Probe 8Probe 9- 0 -Probe 10(B) Probes (6-10)1021007 9896Cl.CC09492tr)203 9010810610411088868482800 2 4 6 8 10^12^14Time (min)16 18 20 22 24■^.^ ■^, -,^- r'^`lei^1^t^I^I^I^I^1***I^I^4,^....'Ir.^4^,i^'IIIAppendix A. Results of Probe Test 2 and Probe Test 3 ^ 78Figure A-3: Probe test 2.3 (pH 7.11) (A) Probes (1-5)Probe 1Probe 2---0 - -Probe  3Probe 4— -.—Probe 5^0- .0 .7111 -0^ 0- 0- -1IF -111 -0^—111-- 0-^-0 -016^18^20^22^242^4^62^4^6 16^18^20^22^248^10^12^14Time (min)3008^10^12^14Time (min)300(B) Probes (6-10)CI ^A. •,r'111:__,•e......„„A •^*^*^'11".^*^IProbe 6Probe 7Probe 8C.Probe 9— -.—Probe 106058565452E 50Q44Ca.) 42g 4038363432605856545257.500o 48> 46a.cc04442a3 402 38363432Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 79Figure A-4: Probe test 2.4 (pH 7.85)0-6-87g .1016 20 22 2418(A) Probes (1-5),0- - - 0- - - - - -0 - - - 0- - - 0- - - - - -0 - -^- - -^-• •— S — •S .^-a• —• -a ^ o ^ 9^--ar,"•• • • 13^ 0-'-2^4^6^8^10^12^14Time (min)-20010862 -12-14-16-18Probe 1Probe 2Probe 3Probe 4— -.—Probe 5-8-12-14-16-18Appendix A. Results of Probe Test 2 and Probe Test 3^ 801086^ (B) Probes (6-10)42EProbe 6Probe 7Probe 8Probe 9— -.—Probe 10-200 6^8^10^12^14^16Time (min)Figure A-5: Probe test 2.5 (pH 8.85)2^4 18^20^22^24-90-92-94-9e-98-100Probe 6Probe 7Probe 8Probe 9— -4 —Probe 10-60-62-64-66-68-70-72tO-747 -76CO -78CI-CC -800 -82-84-868-880^2^4^6^8^10^12^14^16^18^20^22^24Time (min)2^4^6^a^10^12^14Time (min)-1000(A) Probes (1-5)"  - -'O.-^ -***- —  ^ -ap- —   __EtEL^s.^N._^-o_ "-e, so- - - —   ' -o,se- - -—0...*Probe 1Probe 2Probe 30.Probe 4— -.—Probe 5--neme■ 16^18^20^22^24-60-62-64-66-68-70-72-747 -76> -78Ct.CC -800 432-84-86-88-90-92-94-96-98Appendix A. Results of Probe Test 2 and Probe Test 3^ 81Figure A-6: Probe test 2.6 (pH 9.94)280278276274272 E 270268266a_0 264-g 26232602 258256254252280278276274272.9., 270268CS(B) Probes (6-10)Probe 6Probe 7Probe 8Probe 9- -.-Probe 10-olommolk .0^ 0 ^ 0^ 0 ^. 0^ 0 ^ 0^ J.^9 ^ 0 ^0. • • •9 I^1Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 822500(A) Probes (1-5)Probe 1Probe 2Probe 3Probe 4- -.-Probe 5*^I^4^1^*^I^4^I,^44^4^4.^1^* ^•^ 0^0- 41,- -  -  -- --  - 0- -0- -0 - U- --IF-  13 - - -^l  - — -41e.0- —0 ^0^ 0 ^9^ 0 ^ 0^ 0 ^0^ 0 ^ 9^ 0 ^ 0^ 0 ^ 002^4^6^a^10^12^14Time (min)16^18^20^22^24> 266a_cc0 2641-1?- 2628 2602 2582500^2^4^6^8^10^12^14Time (min)25625425216^18 20^22^24Figure A-7: Probe test 3.1 (pH 4.06)>C1136-CC0 134.g 1327130128->"12212001261241441421401381481461502^4^6^8^10^12^14Time (min)16 18 20 22 24..s —  Probe 1Probe 2Probe 3Probe 4— *—Probe 5(A) Probes (1-5). ^  —   — —  ^  —   —   — —0— —0— —...000000000 ^000000 ^900—01160158156154152150148E 146144> 142CC 1400 138130128126124122120i! 136mu> 1342 132(B) Probes (6-10)Probe 6Probe 7Probe 8Probe 9— • —Probe 100 ^0^ 0  ^ ^..,11---111--11—^0--1111,-,..    ^ Ma  ^ ,M• —ID • —111M---41—.—.*=Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 830^2^4^6^8^10^12^14^16^18^20^22^24Time (min)Figure A-8: Probe test 3.2 (pH 6.25)110108106104102E loo7 99> eea_CC0 94-g 9279088868482'Er(B) Probes(6-10)- -Probe 6Probe 7Probe 8Probe 9—   —Probe 10    ^    ..0 ^ El^ 0 ^ 043 ^ 0-0 ^ 0)11,0S^ 0 ^ 0^ 111   -  Al • -0- •..     - -A^--III--^ID-^   ^-411"^-I/^-1Ir M-^IF^III^   ^-IP.     102L0042) 98> seo_cc0 94g 920310410810611082800^2^4^6^8^10^12^14Time (min)86848816 18 20 22 24Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 84Probe 1Probe 2Probe 3Probe 4— —Probe 5(A) Probes (1-5)- -0-00-0- -0- - 0- - If00   0- -IN^-0-A ***.0 -0- - 111- -^-BEIGB0-A- - 41-..9•-.•--•--•---•----•-- -0 ^ B 800 2^4^6^8^10^12^14^16^18^20^22^24Time (min)Figure A-9: Probe test 3.3 (pH 7.02)6058se5452E 50M 4e*aa.> 46cc0 44424°2„AIL - - e^  - -o-^-o- - - e- -^-e- -o-^ -o,  fir.---Ef....0139 ^ 000130 ^ 0130'^'13 ^ 043 ^ 013''(A) Probes (1-5)Probe 1Probe 2Probe 3Probe 4—Probe 53634322^4^6^8^10^12^14Time (min)30 o16 18 20 22 244e0-CC04442Probe 6Probe 7Probe 8Probe 9— -• —Probe 10-IIII-- -4- -4--  ^ -IF -11/ -111-----111---III-- 0- 4- -4 -4so585854525048co8 403836343230(B) Probes (6-10)Appendix A. Results of Probe Test 2 and Probe Test 3^ 850^2^4^6^8^10^12^14^16^18^29^22^24Time (min)Figure A-10: Probe test 3.4 (pH 7.75)-aA 0-12-14-16-1810864-14-16-18-20(B) Probes (6-10)Probe 6Probe 7Probe 8- -• JO - -•-111, • Probe 9- -.-Probe 10AI -* IAmi■olm■Appendix A. Results of Probe Test 2 and Probe Test 3 ^ 861086(A) Probes (1-5)Probe 1—*—Probe 2Probe 3Probe 4- -.-Probe 5A,^JO_ ...-^..--• - • - -IA-..^..- • - -• - -0- „,-A- -0- ,111k- - 0- - A - - -9- -1*-41C.--, ^-^,- A - -0^.- -Er" .0- --0---  -G , 'or" _ 0- - - 0 - - -0 ,- ."..6 - 0" .0 -0- .0 ^6^ - 'El,.  .,^..•"••. ,,^.. „•• •0Io- - Ar---- -0 - - -0- - - 0' ° .0. ^ -0 ^ 0, ' - .. -^..0^0...  CT^.   — o'- 0 . --200^2^4^6^8^10^12^14^16^18^20^22^24Time (min)0^2^4^6^8^10^12^14^16^18Time (rtlirl)Figure A-11: Probe test 3.5 (pH 8.72)20^22^24Probe 1Probe 2Probe 3Probe 4—-60-62-64-66-68-70-72-74-78-78-80-82-84-86-88-90-922^4^6^8^10^12^14Time (min)-98-1000 16^18^20^22^24- - -Os'0- -Probe 6Probe 7Probe 8Probe 9— -.—Probe 10--■•■■(B) Probes (6-10)1Appendix A. Results of Probe Test 2 and Probe Test 3^ 87-50-52-54-66-58-60-62a) -66co> -68Clec -70-72I -78CD2 -78-80-82-84-86-88-900 2^4^6^8^10^12^14Time (min)16^18^20^22^24Figure A-12: Probe test 3.6 (pH 9.79)Appendix BResults of Anoxic Batch Test 2 and Anoxic Batch Test 388Probe 3Probe 4Probe 5Probe 6Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3^890-10-20-30-50-60>cc -700 -80g -902 -100-110-120-130-140 01101009080706050403020100-10-20-30-40-50-60-70-80-90-100010^20^30Time (min)Figure B-1: Anoxic batch test 2.1 (ratio 0)10^20^30^40^50^60^70^80Time (min)Figure B-2: Anoxic batch test 2.2 (ratio 1)40^5090^100^110^120Probe 3Probe 4Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3 ^9080706050405. 302010oioet -.c;). _20E -30-402 -50-60-70-80-90-1000 10^20^30^40^50^60^70^80Time (min)Figure B-3: Anoxic batch test 2.3 (ratio 2)90^100^110^1201009080706050E  40302O 20> 1013-^0O -10.? -20g  -306 -402-50-60-70-80-90-1000 10^20^30^40^50^60Time (min)Figure B-4: Anoxic batch test 2.4 (ratio 3)70^80^90^100Ratio 0ItRatio 1Ratio 2Ratio 3Ratio 46 1 —^...... .0..•••• •^ - - -a ......^o .... .. .. 4-__,---47-'..;"..-11]•".^1 ,^I^,^I^,111.. \7`..\5s -e,   Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3^9111010090807060504030"a 20>a_ 100-10tg -20-302 -40-50-60-70-80-90-1000 10^20^30^40^50^60^70^80Time (min)Figure B-5: Anoxic batch test 2.5 (ratio 4)90^100^110^12010^20^30^40^50^60^70^80^90 100 110 120 130 140Time (min)Figure B-6: NOx test results (anoxic test 2)Probe 3Probe 4Probe 5Probe 6Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3^920-10-20-30"5-• -40s -50-60tx -700-g -804 -9062 -100-110-120-130-1400 10^20^30Time (min)Figure B-7: Anoxic batch test 3.1 (ratio 0)40^5011010090807060"--)^50•=, 4030al 20>0. 10cc0 °-20-302 -40-50-60-70-80-90-1000 10^20^30^40^50^60Time (min)Figure B-8: Anoxic batch test 3.2 (ratio 1)70^80^90Probe 3Probe 4Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3^9380706050403020100-10-20-30-40-50-60-70-80-90-1000 10^20^30^40^50^60Time (min)Figure B-9: Anoxic batch test 3.3 (ratio 2)70 80 9010090807060-5 50-g- 4030V. 20°- 10cc0 0-10-20M -30-40-50-60-70-800 10^20^30^40^50^60^70^80^90 100 110 120 130 140Time (min)Figure B-10: Anoxic batch test 3.4 (ratio 3)4 73.14.P411.4 4(.4 ?`"42Pola r.:11 2^Pz 1.41, Itej^17 2 `'ett1142.2PeL",P,1 — 'EL94Appendix B. Results of Anoxic Batch Test 2 and Anoxic Batch Test 3140130120110100908070 60S 50.g 40> 30ma' 200 102 015 -10-20g -30-40-50-60-70-80-90-1000 10^20 30^40^50^60^70^80^90 100 110 120 130 140Time (min)Figure B-11: Anoxic batch test 3.5 (ratio 4)6Ratio 0Ratio 1Ratio 2Ratio 3—^-Ratio 4--■•■0 140I^I^ I ^4-^'4 0^10^20^30^40^50^60^70^80^90 100 110 120 130Time (min)Figure B-12: NOx test results (anoxic test 3)Appendix CResults of Carbon Addition Test 2 and Carbon Addition Test 3957010^20^30^40^50^60Time (min)Figure C-1: Carbon addition test 2.1 (control)807060505s. 400-102 -20-30-40-50-600 90 1008010090807060Ss 50Co 4030co> 2010^20^30^40^50^60^70Time (min)Figure C-2: Carbon addition test 2.2 (20 mg/L)-g— -10-20M -30-40-50-60-70-800 80^90^100Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3 ^96Probe 3Probe 4605040302010^20^30^40^50Time (min)Figure C-3: Carbon addition test 2.3 (40 mg/L)a_cc -100-1g -20a)2 -40-50-60-70-800 60^70^80Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3^971009080706050E 40 30a) 2010o_cc^00 -1002 -20U) -30cocl) -402-50-60-70-80-90-1000 10^20^30^40Time (min)Figure C-4: Carbon addition test 2.4 (60 mg/L)50^60Probe 3Probe 4654210Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3^9860504030oz., 20€ io8 om>0.cc -20o2 -30i -50M-60-70-80-90-100 0 10^20^30^40Time (min)Figure C-5: Carbon addition test 2.5 (80 mg/L)50^600^10^20^30^40^50^60^70^80^90^100^110Time (min)Figure C-6: NOx test results (carbon addition test 2)120110100908070E 60;. 50a)= 40> 30a_cc 20O t o, ! 0=.9 -10O -202-30140130120110100905*. 80E 7064 60' 5010^20^30^40^50^60^70Time (min)Figure C-8: Carbon addition test 3.2 (20 mg/L) -102 -20-30-40-50-60-70-800 80 10090Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3 ^99-40-50-60-70-800 10^20^30^40^50^60^70^80^90 100 110 120 130 140Time (min)Figure C-7: Carbon addition test 3.1 (control)Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3^10010101009080706050E 40u, 30a)= 20co> 10a.cr^0.2 -106 -20N-30aia) -402-50-60-70-80-90-10001009080706050.g. 40u)3 3020a_cc 100.,„^05N -100ccs -20a)2 -30-40-50-60-70-80020^30^40^50Time (min)Figure C-9: Carbon addition test 3.3 (40 mg/L)20^30^40^50Time (min)Figure C-10: Carbon addition test 3.4 (60 mg/L)60 70 8060^70120Control20 nc-ig/L40 rEn3g/L60 rn g/L80 mg/L-'aANt...,-,.^',^........1^I^I^I^. --4.---:.^7-^,^1^-:.---.4,---",--^I^,^I 10^20^30^40^50^60^70^80^90^100^110Time (min)Figure C-12: NOx test results (carbon addition test 3)Appendix C. Results of Carbon Addition Test 2 and Carbon Addition Test 3^101807060504030--C.• 20§ 10V.^0cc -100 -20§ -30-402 -50-60-70-80-90-1000 10^20^30^40Time (min)Figure C-11: Carbon addition test 3.5 (80 mg/L)50^605

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