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What are the management practices and treatments for the removal of iron and manganese from ‘dewatered’… Lee, Martha 2013

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What are the management practices and treatments for the removal of iron and manganese from ‘dewatered’ water at construction sites in the Lower Mainland?  by Martha Lee  Report prepared at the request of Dillon Consulting Limited in partial fulfillment of UBC Geog 419: Research in Environmental Geography, for Dr. David Brownstein  1  Executive Summary  This paper divides management practices issue into: 1) Treatments for removing iron and manganese and 2) Practices for disposal of iron and manganese. After evaluation, two recommendations are made for removal treatments: 1) Aeration, and 2) Greensand filtration. Aeration is a removal technique that uses atmospheric oxygen and greensand filtration is removal using oxidizing filtration media. For disposal, it is recommended to use irrigation, the watering of vegetated areas. For a more effective outcome, these processes may be used in combination.  This paper aims to provide Dillon Consulting with options for management practices for the discharging of groundwater with high concentrations of naturally occurring iron (Fe) and manganese (Mn) from construction sites. This groundwater is accumulated through ‘dewatering’, the process of extracting groundwater from the soil. Recommendations will be efficient and economically feasible while meeting water quality standards, with particular focus on Richmond. While there are a number of best management practices dealing with ‘dewatered’ water, not all are suitable for Metro Vancouver construction sites. The purpose of this paper is to evaluate the available practices for the Metro Vancouver context.  Background  Context of the Problem  Iron and manganese are common metallic elements found in the earth’s crust. Iron makes up around 5.6% of the earth’s crust (Achterberg et al., 2001) while manganese makes up 0.085-0.95% (Ministry of Environment, 2001). Through weathering, iron and manganese are released and subsequently enter into groundwater systems. In groundwater these metals potentially exist in one of three basic states (Barlokova and Ilavsky, 2010): 2  1. Soluble – as single ions Fe2+ (ferrous) and Mn2+ (manganous) 2. Insoluble – as Fe(OH)3 (ferric) and Mn(OH)4 (manganic) 3. Colloid – as very small particles The state depends on a range of factors including dissolved oxygen concentrations, the pH level of the water, and the presence of inorganic and organic substances (Barlokova and Ilavsky, 2010). Generally iron and manganese exist in a soluble form in groundwater, due to the lack of oxygen, and can exist in relatively high concentrations particularly with increased depth. At the surface, the presence of air usually oxidizes these metals, causing them to precipitate. In fresh surface water, the total concentrations average 0.7 mg/L for iron (WHO, 1996, p.2) and rarely exceed 1.0 mg/L for manganese, usually less than 0.2mg/L (Ministry of Environment, 2001). Seawater has an even lower level, usually 0.05 – 2nM for iron (Achterberg et al., 2001) and 0.002 mg/L for manganese (Ministry of Environment, 2001). Therefore while high iron and manganese concentrations may be naturally occurring in the aquifer, these concentrations are not normal for surface water systems.  Iron and manganese are necessary trace elements for living organisms. However, high concentrations can have a number of negative effects, such as toxicity to aquatic life (Ministry of Environment, 2001; Ministry of Environment, 2008). The severity of these impacts depends on a number of factors including: affected species, pH levels, water hardness, and stage of development for species (Ministry of Environment, 2008; Ministry of Environment, 2001). Iron and manganese are found in very low concentration in natural freshwater ecosystems and many organisms in those systems cannot tolerate high doses of these metals. In contrast, human are much more tolerant of elevated iron and manganese levels. In general, typical concentrations in groundwater pose no health risks to humans, and drinking water standards are for aesthetic and infrastructure objectives. For example, groundwater with high concentrations have an undesirable taste, can clog pipes, and promote iron and manganese bacteria growth.  3  In the Metro Vancouver region, notably higher concentrations of iron and manganese in groundwater are common. For example, groundwater sampling in June 2008 at Horseshoe Slough in Richmond showed total concentrations (dissolved in water and present in particulates) of 26.3 mg/L for iron and 7.33mg/L for manganese, with dissolved concentrations of 14.4 mg/L for iron and 5.59 mg/L for manganese (City of Richmond, 2008). One site in Delta had groundwater with total iron concentrations of 39.3 mg/L and dissolved concentrations of 29.3 mg/L (Dillon Consulting, 2013). These numbers are well in excess of water quality standards, though they may not reflect average concentrations levels throughout the region.  In low-laying areas, such as Richmond and Delta, groundwater exists close to the surface, so, construction sites are more likely to need to remove groundwater during the construction process, and sometimes afterwards for maintenance. This is necessary to ensure a stable foundation, prevent flooding, and prevent groundwater water intrusion (Johnson, 2008). This results in dewatering wastewater with iron and manganese levels that are excess of legal limits. The issue of discharging ‘dewatered’ water is an important concern to Dillon Consulting due to their involvement with a number of construction projects located in Richmond and other low-lying areas of the Lower Mainland and their wish to comply with water quality regulations and limit environmental impact.  Regulatory Framework  Richmond follows the regulatory standards of water quality at federal, provincial, and municipal levels. Guidelines are not legally enforced. They are standards that promote environmentally sensitive development or practices. Systemic violation of guidelines may produce significant adverse impacts on the environment, which may have legal ramifications under other regulations, such as the Fisheries Act in the past, or municipal regulations. Currently, they are as follows:  4  Federal   Canadian Council of Ministers Guidelines (CCME 1987, Health Canada 2012).  Iron   Protection of aquatic life – 0.3 mg/L    Agricultural irrigation water - 5 mg/L    Drinking water – 0.3 mg/L  Manganese   Agricultural irrigation water – 0.2 mg/L    Drinking water – 0.05 mg/L  Provincial (BC)   BC Water Quality Guidelines through the Ambient Aquatic Life and Guidelines for Iron (2008) and the Ambient Aquatic Life Guidelines for Manganese (2001)  Iron   Maximum concentrations (total) – 1.0 mg/L    Maximum concentrations (dissolved) – 0.35 mg/L  Manganese   Chronic limits (depending on water hardness) – 0.7 to 1.9 mg/L    Acute limits (depending on water hardness) – 0.8 to 3.8 mg/L  Municipal   City of Richmond - Bylaw 8475 (2009)   Enforces BC Water Quality Guidelines and/or Canadian Council of Ministers Guidelines  Current Treatment  Numerous technologies exist for the removal of iron and manganese from water. Broadly speaking, this includes equalization tanks, pH adjustment, coagulation and flocculation, settling/clarification, and filtration (Powers, et al. 2007). It is not uncommon for 5  treatments to be used in conjunction with each other and with other best management practices to further reduce iron and magnesium levels. In theory, these technologies should be able to reduce iron and manganese levels to suitable levels. In practice, however, construction sites introduce a number of variables that decrease the efficiency of these systems. Limited space, variable flow rates, and cost are major limiting factors, as well as the lag time associated with many of these technologies. Unlike some other industrial uses of iron or manganese removal, such as drinking water or mining, these systems are usually not permanent.  There is also no shortage of options for disposal of ‘dewatered’ water. Disposal generally occurs after the water has been treated. Current practices include: public sewage systems, sewers, fresh waterways, groundwater recharge, recycling, water use off-site, and solar evaporation. Generally, the most common method of disposal is storm drains due to the low cost and relative ease of permitting process. However, storm drains eventually make their way into freshwater systems and many municipalities, such as Richmond, state wastewater must meet water quality standards to protect ambient aquatic life (Bylaw 8475, 2009).  Currently, Dillon Consulting practices dewatering with wellpoints or surface water ‘trash pumps’. This water is then pumped into an onsite treatment pond. It is then treated with a flocculent, chitosan lactate, a biopolymer derived from chitin. This binds iron and manganese particles together causing them to settle to the bottom of the treatment pond. This is an expensive process and needs a relatively stable settling pond and has a lag time of about an hour. Other techniques that are sometimes employed by Dillon Consulting are pH adjustment, aeration, other flocculants (such as liquid chitosan or chitosan acetate), and chitosan enhanced sand filtration. In practice, the final treatment must consider the size of the project, available space, cost, and local water quality standards.  6  Methods  Recommendation Criteria  Removal treatments and disposal practices for ‘dewatered’ water were examined separately in this project. Removal of iron and manganese is a means of meeting water quality standards while practices of disposal indicate what type of what water quality standards and permitting procedures have to be met. Both were evaluated based on: 1) Effectiveness and 2) Costs. Effectiveness referred to removal treatments and their ability to reduce concentrations of iron and manganese and the systems reliability on a construction site. Costs referred to the overall financial expense of the procedure. Since this paper only overviews possible methods and specifications for any particular operating range were not given, cost will be judge relative to other methods.  It should be noted that the breath of this study was limited by information availability. Only recommendations that were supported by the literature were included, however, this excluded some technologies from the recommendations.  Sources Consulted  Research was conducted primarily through a literature review, supplemented by an interview with an expert in the field. There is a lack of academic literature in this area of study so this study looked at many sources from the “grey” literature (government, organization, and company documents), generally from Canada, the United States, and Australia. These three countries have strong regulatory interest and subsequent technical developments in this issue. Grey literature sources were deemed creditable if corroborated with other sources, properly referenced, and produced by a reliable organization.  7  Only one interview was conducted in this study, due to the difficultly of setting up interviews. It involved a chemical engineer whose specialty is dewatering of construction sites. The interview took place on March 11, 2013 and further information was gathered on March 22, 2013. This study gave interviewees the option to remain anonymous. It was taken. This interview confirmed many of the practices and results found in the literature and helped direct research.  Recommend Options  Aeration  Aeration treatments bring iron and manganese rich water in contact with atmospheric oxygen to oxidize the dissolved metals. The oxygen converts the ferrous and manganous forms of the metals into their insoluble ferric and manganic forms (Jobin and Ghosh, 1972; Václavíková, Vitale, Gallios, & Ivanicová, 2009). The effectiveness of this process depends on the degree of contact between air and water achieved.  There are several methods of aeration, categorized as 1) water into air or 2) air into water. Method selection depends on what material is being removed and its concentrations, among other factors. Two notable aeration methods for iron and manganese removal are waterfall and air diffusion systems. Waterfall systems, such as coke tray aerators, are water into air systems, which break water into a thin film to increase the contact area with air. Air diffusion systems are air into water systems that create contact by pumping pressurized air into water. In theory, air diffusion should be more effective because the speed of rising is slower than the speed of falling, meaning long contact times, the contact area per unit oxygen is maximized because an individual bubble is constantly coming into contact with new water surfaces. This appears to hold in practise, and air diffusors are used by some companies to treat for high concentrations of these metals (Anonymous interview informant, personal communication, March 11, 2013). According to the interview, the system is effective and cost efficient for the removal of iron. Aeration systems can also be joined with other methods if greater removal is needed. 8  The main benefit of aeration systems is they are one of the most cost efficient treatments. This is because the system requires no chemicals and has low maintenance costs, although initial costs may be higher. The lack of chemicals has advantages for post treatment too. It is generally agreed that aeration systems can remove combined concentrations of iron and manganese as high has 10 - 15 mg/L, and some sources suggest numbers as high as 25 mg/L for dissolved iron if the system is well designed (CCE, 2005). Under ideal conditions iron oxidation takes about 15 minutes (American Water Works Association, 2011), however in practice this process normally takes longer.  Concerns with this treatment lie in its selective effectiveness, pH sensitivity, and operational requirements. Kinetically, aeration is slow. While aeration can remove moderate amounts of iron it is significantly less successful with manganese, partly because more oxygen is needed for oxidation than iron and the system generally cannot provide sufficient contact. Organically bound iron and manganese is also difficult to remove (HDR Engineering, 2002). These processes are further retarded by pH levels below 9.5, for only iron removal pH can be lower (NESC, 1998). Under these conditions reaction times for iron can be 20 – 50 minutes and up to 80 for manganese (Giles, 2010). Lime can be added to raise pH levels. In cases of slow reaction rate large reaction tanks may be needed to supply the needed detention times. Other operational requirements of aeration systems include filtration and re-pumping. Filtration is needed with these systems, as sedimentation, particularly in a construction site environment, is unlikely to adequately separate out the metals. This filter must be backwatered. Re-pumping is generally required with these systems although this can be minimized with design.  An aeration method of particular interest is Deferum technology. This technology is a relatively recent and is a based in an intense aeration/gasification and filtration treatment. It claims to accommodate iron levels from 5 - 75 mg/L and manganese levels from 0.05 – 7 mg/L, making it one of a select few systems that can remove high concentrations of iron. If greater levels of manganese removal are needed, the system can be paired with a demagnum system. As these processes are non-reagent, it is more eco-friendly then other 9  high removal technologies. Capacity is of up to 132,500 gallons per day. However, the majority of information for this technology is from the company itself, so further information is needed to know if this technology is practical for construction sites, as affordable as the company claims, and able to perform to the standards suggested.  Manganese Greensand Filtration  Greensand is a product derived from ‘New Jersey greensand’, a zeolite mineral glauconite, which has been coated with manganese oxide, MnO2 (NESC, 1998). This product is catalytic and insoluble in water (Water & Wastes Digest, 2013). It acts as an oxidizing filter medium, removing soluble and insoluble iron and manganese through oxidation and filtration. Oxidation forms precipitates that are then captured in the greensand. Greensand systems usually require a filtration bed of greensand of at least 6076cm (CCE, 2005). For the maintenance of the greensand, anthracite is commonly used as a capping media that is layered on top of the greensand. This layer should have at minimum a depth of 15 cm depth (MassDEP Drinking Water Program, 2011). Without other chemicals added, this process can remove moderate levels of iron and manganese, combined concentrations of up to15 mg/L (Dvorak, Prasai, Skipton, & Woldt, 2007). For example, at a test site in North Vancouver, greensand was able to reduce iron levels from 10.8 mg/L to 0.0146 mg/L, while simple sand filtration only reduced concentrations to 8.52 mg/L (Anonymous interview informant, 2013).  To keep the greensand from exhausting, regeneration is needed. There are two main categories of system designs of greensand filtration 1) continuous regeneration (CR) and 2) intermittent regeneration (IR). As the name suggests, the difference between these systems is how the regenerative oxidizer is added to the system. CR systems are constantly fed by an oxidizer as they operate, while in IR systems an oxidizer is introduced in the backwash cycle. Hence in CR systems pre-oxidation can occur through contact between the oxidizer and raw water. Greensand acts as a buffer to react remaining soluble iron and manganese or excess of the oxidizer. In IR systems oxidation is only through direct contact with the greensand. 10  For the purposes of this paper, CR is the most suitable opinion. CR is used when iron removal is the main goal, irrespective of manganese levels, while IR is used when only manganese is present or manganese levels are higher than iron levels (Rader, 2009). Iron concentrations are generally higher than manganese concentrations in the Lower Mainland. IR systems are also at risk of soluble manganese leakage, not as economically efficient for raw water with high concentrations, and have much longer backwashing period. Finally CR systems are able to harness the oxidizer to further treat raw water therefore increasing their removal capacity.  Common oxidizers for these systems are chlorine and potassium permanganate, KMnO4 (Rader, 2009). While there are cost advantages to using chlorine, KMnO4 is a stronger oxidizer than chlorine, meaning more effective at removing iron and particularly manganese (Raveendran, Ashworth, Chatelier, 2001) and the reaction time is shorter (Evans, Tan, Stegink, & Horstman, 2009). Therefore it is preferred for high concentrations of iron and manganese. Theoretically, dosing demands are 0.94 mg/L KMnO4 per 1mg/L iron and 1.92 mg/L per 1 mg/L of manganese (U.S. Department of the Interior Bureau of Reclamation, 2009). Furthermore, KMnO4 does not product any toxic by-products (Crocker, Heath, & Simpson, 2011).  There are a number of benefits of greensand systems (and greensand systems using KMnO4 for pre-oxidation). It is operationally simple (HDR Engineering, 2002), reliable, and has a proven track record (U.S. Department of the Interior Bureau of Reclamation, 2009). If KMnO4 is used as a pre-oxidizer, reactions are almost instantaneous and high concentrations can be removed (Evans, Tan, Stegink, & Horstman, 2009; HDR Engineering, 2002). While more expensive than simple aeration, this system is more effective and, relative to other high removal chemical treatments, it is low cost (U.S. Department of the Interior Bureau of Reclamation, 2009). Crocker, Heath, & Simpson estimated the cost of this type of system for Attleboro, MA. They estimated a unit price of $4.50/lb for KMnO4, $54.99/cu-ft, and $9.60/cu-ft for anthracite (2011). Regeneration of the greensand means this is mainly a capital cost, although in some cases, regeneration 11  may not be worthwhile (Anonymous interview informant, personal communication, March 11, 2013). Feeding chlorine ahead of KMnO4 can be used as a cost saving measure although residual chlorine must be watched as it is toxic to freshwater systems and there are water quality standards for it.  The drawback of the greensand filtration is the exactness needed for the process. KMnO4 must be exact, and overdosing will lead to the water turning pink. Reactions with the greensand in CR system should act as buffer removing at least some of the excess KMnO4 (Rader, 2009). Monitoring of treated water is needed to make sure there are no residual chemicals. Care must be taken when handing KMnO4 and chlorine as they are harmful. Like most filtration processes backwashing is required. This backwashing necessitates certain pressure and flow rates for proper particular deposit removal (U.S. Department of the Interior Bureau of Reclamation, 2009). Like aeration, and may other removal methods, greensand filtration has pH sensitivities. Alkaline pH levels are desired for iron removal and pH levels greater than 8 for manganese (Aquavarra Research Limited, 2009).  Irrigation  Disposal of ‘dewatered’ wastewater via irrigation is practice that is growing in popularity (Johnson & Vasquez, 2008). Currently it is not a common practice in Metro Vancouver, although there is some use in the interior of BC and in Alberta (Anonymous interview informant, 2013). Based on government documents, it appears to be a more prevalent practice in Australia for both on and off-site irrigation (Sunshine Coast Council, 2008).  This disposal practice has been heralded as ecologically-friendly, shown by its ability to earn LEED points (Johnson & Vasquez, 2008). This practice is also economical (Johnson & Vasquez, 2008). CCME agricultural irrigation guidelines are higher than freshwater standards as the environment is less sensitive.  They are the same as the  irrigation water quality guidelines for greenhouses from the BC Ministry of Agriculture, Fisheries and Food (BCMAFF) (1996). Therefore removal costs are lower. It is 12  necessary to account for irrigation needed to site in question, taking into account season evapotranspiration (Government of Western Australia, 2012). An implication hurdle for this practice in Metro Vancouver is the relative abundance of water provides less incentive to use this practice.  Conclusion  In conclusion, several technologies stood out as being the most useful for removal of iron and manganese from construction sites. Aeration is one of the cheapest methods for removal and with the proper design the system can be relatively effective. The Deferum technology also may be a possible direction and is a direction for future research. Greensand filtration, although greensand itself is expensive, has a relatively low cost for a process as effective as it is. Finally, irrigation is cost-effective and, if water needs are correctly accounted for, effective as well.  Works Cited Achterberg, E.P., Holland, T.W., Bowie, A.R., Mantoura, R.F.C., & Worsfold, P.J. (2001). Determination of iron in seawater. Analytica Chimica Acta, 442(1), 1-14. doi: 10.1016/S0003-2670(01)01091-1 American Water Works Association. (2011). Basic Science Concepts and Applications. Denver, CO: Cobban, B. (Ed.). Anonymous interview informant. (2013). Personal communication, March 11, 2013. Anonymous interview informant. (2013). Personal communication, March 22, 2013. Aquavarra Research Limited. (2009). Iron and Manganese in Water: Occurrence, drinking water standards, treatment options. Casey, T.J. Retrieved from Auckland Council. (2011). Best Management Practice: Dewatering. Retrieved from ts/dewatering.pdf Barlokova, D. & Ilavsky, J. (2010). Removal of Iron and Manganese from Water Using  13  Filtration by Natural Materials. Polish Journal of Environmental Studies, 19(6), 1117-1122. Retrieved from Canadian Council of Ministers Guidelines (CCME), (1987) Canadian Environmental Quality Guidelines Summary Table. Retrieved from City of Abbotsford. (2010). Erosion and Sediment Control (ESC) Bylaw: Best Management Practice. 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Irrigation Water Quality for BC Greenhouses. Retrieved from htm Ministry of Environment.Water Stewardship Division. (2008). Ambient Aquatic Life and Guidelines for Iron. Retrieved from BCguidelines/iron/iron_overview.pdf Ministry of Environment. Water Stewardship Division. (2001). Ambient Aquatic Life and Guidelines for Manganese. Retrieved from ca/wat/wq /BCguidelines/manganese/manganese.html National Environmental Services Center (NESC). (1998). Tech Brief: Iron and Manganese Removal. Retrieved from 15  publications/ ontap/2009_tb/iron_DWFSOM42.pdf Outtrim, P. (2009, June 16 -18). Tarcutta Treatment Plant Iron and Manganese Removal. Paper presented at Queensland Water Industry Operations Workshop, Caloundra, Queensland. Retrieved from papers/09_qld/documents/peterouttrim.pdf Powers, J. P., Corwin, A. B., Schmall, P. C., and Kaeck, W. E. (2007). Construction Dewatering and Groundwater Control: New Methods and Applications (3rd ed.): John Wiley & Sons. Retrieved from ca/web/portal/browse/display?_EXT_KNOVEL_DISPLAY_bookid=3354&Verti calID=0 Rader, L. (2009). How to Operate and Maintain Manganese Greensand Treatment Units. Retrieved from how_to_manganese_greensand.pdf Raveendran, R., Ashworth, B., & Chatelier, B. (2001, Sept. 5-6). Manganese Removal in Drinking Water Systems. Paper presented at Water Industry Operator Association of Australia, Bendigo, Victoria. Retrieved from conference_papers/01/paper12.htm Ricketts, B. D., and Liebscher, H. (1994). The geological framework of groundwater in the Greater Vancouver area. In J.W.H. Monger (Ed.), Geology and Geological Hazards of the Vancouver Region, Southwestern British Columbia (pp. 287-298). Vancouver: Geological Survey of Canada. Sunshine Coast Council. (2008). Erosion and Sediment Control Manual. Queensland, Australia. Retrieved from code=erosion-sediment-manual U.S. Department of the Interior Bureau of Reclamation. (2009). Iron and Manganese Fact Sheet. Water Treatment Engineering Research Team. Retrieved from http://www. U.S. Department of Transportation. Federal Highway Administration. (2008). Best Management Practices for Chemical Treatment Systems for Construction Stormwater and Dewatering by McLaughlin, R. A. and Zimmerman, A. Retrieved from publications /documents/ctsbooklet.pdf Václavíková, M., Vitale, K., Gallios, G.P., & Ivanicová, L. (2009). Water Treatment Technologies for the Removal of High-Toxicity Pollutants. Springer. Retrieved from =V%C3%A1clav%C3%ADkov%C3%A1,+Vitale,+Gallios,+%26+Ivanicov%C3 16  %A1&source=bl&ots=qqOIBeY3rW&sig=DL55hLd_6q87OaTAMKuBblN0rjU &hl=en&sa=X&ei=qQh4UfrUHYnxsgbiw4GACA&redir_esc=y Vigneswaran, S., Visvanathan, C., & Sundaravadivel, M., (2007). Treatment Options for Removal of Specific Impurities from Water. In Vigneswaran, S. (Ed.), Wastewater Recycle, Reuse, and Reclamation – Vol. II (pp. 97-111). Retrieved from Water & Wastes Digest. (2013, March 13). General format. 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