Civil and Environmental Engineering

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The Critical Role of Chemical Pre-Treatment in Ensuring Cryptosporidium Removal by Filtration of High Quality Source Water
(University of Waterloo, 2019-05-01) Lee, Kristina M.; Emelko, Monica; Anderson, William B.
Drinking water utilities reliant on surface water utilize chemically-assisted filtration (CAF) as a key barrier against the passage of protozoan pathogens, like Cryptosporidium spp. oocysts, to treated water. The goal of this work was to enable system-specific and potentially dynamic assessment of oocyst removal by CAF by using zeta potential as a tool for rapid operational feedback. Specifically, this work focused on systems utilizing high quality, low turbidity (typically <1 NTU) source water, with relatively low C. parvum oocyst concentrations and applied full scale coagulant doses (typically <5 mg/L). In these systems, the formation of settleable flocs is not a necessity because source water turbidities are already low and frequently meet treated water criteria. Rather, coagulation is used to enable particle removal through physico-chemical (i.e., chemically -assisted) filtration, as indicated by filter effluent turbidities that may or may not be indicative of optimal particle destabilization and removal by CAF. Accordingly, the identification of “optimal” coagulant doses can be challenging, and becomes even more challenging when process performance is being assessed, such as when Cryptosporidium oocysts are added to filter influents to evaluate their removal by CAF processes. In Phase 1 of this work, the role of oocyst coagulation during CAF performance demonstrations was investigated. It was demonstrated that appropriate coagulation of oocyst seed suspensions is critical to reflecting “well-operated” CAF performance. A protocol for ensuring optimal coagulation of oocyst seed suspensions during such performance demonstrations was developed and demonstrated at pilot-scale. Here, zeta potential was useful in identifying the coagulant doses needed for maximal particle destabilization and removal by CAF. This pilot-scale approach was then validated using lower, environmentally relevant oocyst concentrations (and much longer pilot-scale investigations) during which the entire filtered volume of water was evaluated. Using this protocol, it was demonstrated that a minimum of 3-log oocyst removal could be achieved by CAF (essentially direct filtration) at a variety of operational conditions. During Phase 2 of this work, the protocol developed in Phase 1 was used to evaluate oocyst passage through CAF processes with different filter designs (bed depths, water temperature) at various operational conditions (suboptimal coagulation, filter ripening, end-of-run operation, and hydraulic surges). Here, because of the high quality, low turbidity source water, adequate coagulation was the dominant control for risk, in contrast to many reported investigations in which more deteriorated source water was investigated and operational period within the filter cycle was a more dominant control over oocyst passage through the CAF process. Here, with the exception of suboptimal coagulation conditions, the pilot-scale filters consistently achieved >3-log C. parvum oocyst removal in an essentially directly filtration mode. Thus, this work demonstrated the critical importance of (1) appropriate particle destabilization by coagulation prior to CAF of low turbidity, low DOC source waters, (2) coagulation of oocysts prior to their addition to filter influent streams during CAF performance demonstrations, and (3) zeta potential as a useful tool for ensuring adequate particle destabilization in situations (i.e. treatment of low turbidity, low DOC source waters) in which extensive particle settling is not likely. In doing so, this work further highlights that Cryptosporidium spp. oocyst removal credits of >2.5 log may be warranted for “well-operated” direct filtration processes.
Granular Activated Carbon for the Removal of Seasonally Present Microcystin-LR
(University of Waterloo, 2017-04-20) Chennette, Victoria; Anderson, William B.; Peldszus, Sigrid; Huck, Peter
Microcystin-LR (MC-LR) is a potent hepatotoxin, produced by cyanobacteria. MC-LR is the most commonly regulated cyanotoxin. MC-LR typically occurs seasonally in late summer in temperate regions, such as the North American Great Lakes region. Nutrient and temperature conditions lead to the annual formation of cyanobacterial blooms, most notably in shallower Lake Erie. Adsorption using granular activated carbon (GAC) is a promising treatment technology for the removal of cyanotoxin MC-LR. The operation of a GAC contactor on a seasonal basis, and the storage of GAC between annual events were the focus of this work. A typical GAC in the study geographic area, Calgon Filtrasorb ® 300 (F300), was selected for this work. In order to simulate one season of use, the F300 was preloaded with 20,000 bed volumes of post-filtration Lake Ontario water from a full-scale drinking water treatment plant. The preloading period was determined from the volume of water passed through the full-scale plant when cyanobacterial metabolites geosmin and 2-methylisoborenol had historically been detected. During preloading the water quality was consistent in terms of Total (TOC) and dissolved (DOC) organic carbon. The largest contributor to natural organic matter (NOM) was humics as determined by liquid chromatography organic carbon detection (LC-OCD). The virgin and preloaded F300 were evaluated in terms of ultimate capacity and kinetics for MC-LR adsorption. The bottle point method was used, with samples taken daily for the first ten days, and every two days following until less than 1% change in percentage removal was observed. MC-LR was quantified using LC-MS/MS (liquid chromatography tandem mass spectrometry). The virgin F300 reached equilibrium after 18 days, and the preloaded reached equilibrium after 49 days. The preloaded and virgin F300 did not show significantly different Freundlich isotherm parameters, indicating that the preloaded F300 was not significantly exhausted following one season of preloading. This finding should be interpreted with caution, as there may be differences which are not detectable at the selected confidence level. The preloaded F300 was then stored under four conditions for eight months (the typical portion of the year in which cyanobacterial blooms are uncommon in temperate regions). Storage conditions included high moisture content (HMC) and low moisture content (LMC), to represent the bottom and top, respectively, of a drained GAC contactor. Two fully saturated conditions were explored; the F300 was stored completely submerged in post-filtration water from the full scale facility, and the F300 was stored fully submerged in a 20 g/L salt (sodium chloride) solution. In addition, a continuous operational control located at the full-scale pant was maintained at the same hydraulic loading rate as the full-scale filters in order to simulate a GAC contactor which remained in service year round. The time to equilibrium for each carbon was evaluated; the salt storage samples reached equilibrium (less than 1% change in percent removal) after 41 days, and displayed the fastest kinetics for MC-LR removal. The submerged storage method displayed the slowest kinetics, and reached equilibrium after 57 days. At the 95% confidence level, all of the stored F300 Freundlich isotherm parameters were significantly different from the continuous operational control, indicating that there may be a benefit from storage under any of the considered conditions. When the broader prediction intervals are considered, there was no significant difference in any of the predicted MC-LR solid phase concentrations when considering various MC-LR liquid phase concentrations. This finding indicates that non-detectable differences may be present, due to the data quality. When compared with the virgin and preloaded F300, the continuous operational control is distinct from the virgin and preloaded isotherm parameters at the 95% confidence level. At the 95% confidence level, the virgin, preloaded and LMC stored carbon parameters for MC-LR removal are not distinct. Although capacity for MC-LR cannot be directly determined simply by examining the Freundlich parameters, the results suggest that the storage of the F300 under LMC conditions provides a benefit in terms of equilibrium capacity. Overall, this research indicates that there is a benefit in terms of capacity and kinetics from the storage of the preloaded F300, under any of the considered conditions. There is an indication that the LMC storage may provide the most benefit, however additional confirmation is required to establish this finding with statistical significance.
Improving the Understanding of Factors Influencing Cryptosporidium Removals Reported for Granular Media Filtration
(University of Waterloo, 2016-01-13) Zhou, Ye; Huck, Peter; Anderson, William B.
Cryptosporidium is an important waterborne protozoan pathogen which has been implicated in several large gastrointestinal disease outbreaks attributable to inadequate treatment of drinking water. Unfortunately, Cryptosporidium oocysts, the life cycle phase found in water, are highly resistant to conventional disinfectants such as chlorine and chloramines. As such, rapid granular filtration (preceded by adequate coagulation) serves as an important barrier against the passage of Cryptosporidium oocysts. However, a wide range of Cryptosporidium removals, from 1.4 log to 5.8 log, have been reported from various pilot- and full-scale filtration investigations (with or without removals by clarification), with the reasons behind the substantial variability not well understood. The disparity in published data leads to uncertainty in developing expectations for the removals that can be reasonably achieved by filtration processes. To further complicate the interpretation of these studies, there is still some uncertainty involved with accurate oocyst enumeration. The objective of this research is to investigate reasons behind the substantial variability in oocyst removals reported in the literature by attempting to link them to differences in raw water characteristics, coagulant conditions, filter design, filter operation, and analytical and experimental methods. This research included two components: (1) a thorough review of the literature, and (2) the development, distribution, and analysis of a questionnaire to access industry knowledge and insights that might not necessarily be reflected in the peer-reviewed literature. An up-to-date review of published studies was conducted with the intent of identifying the potential effects of a variety of factors as they relate to the determination of Cryptosporidium oocyst removals by granular media filtration. However, the amount of detail contained in published studies is still somewhat limited and the current data pool is not sufficiently extensive to definitively identify reasons behind the substantial variability in removal data. As an outcome of the review, it was felt that views from drinking water professionals on the factors which may have an impact on reported Cryptosporidium removals by granular media filters would enhance research into this important topic. In developing the questionnaire, thirty-three influencing factors were identified, and these fall into six groups. In total, 39 completed questionnaires were returned, representing a response rate of 35%. In addition, 260 open-ended comments were collected. Statistics from the background survey revealed that the majority of respondents could be considered to be sufficiently knowledgeable to be able to provide valuable input (with more than 70% of respondents having direct involvement in research on Cryptosporidium or/and surrogate removals through filtration). From the questionnaire, consensus was reached that the most influential factors were optimized coagulant dose (95% of respondents rated it as having a strong influence) and filter effluent turbidity (81% rated it as having a strong influence), while the least influential were Cryptosporidium species and the use of chlorinated backwash water (0% rated them as being strongly influential). A weighting system was developed to evaluate the overall influence of an identified factor on Cryptosporidium removal through filtration and a sensitivity analysis was conducted to evaluate the robustness of the weighting system. The weighting system ranked the importance of optimized coagulant dose, filter effluent turbidity, Cryptosporidium oocyst detection limit, Cryptosporidium recovery adjustment, and Cryptosporidium spike concentration as the five most influential factors (in that order). For most findings, the questionnaire results demonstrated consistency with literature results. This research narrowed down the factors contributing to uncertainty in developing expectations for Cryptosporidium removals in a given situation, by ranking the influence of each of a number of factors. It also identified some potentially important issues/factors whose effects have not yet been assessed, and provided useful information and some speculation which may not have been reflected in published studies. However, it may not be possible to single out any one factor which accounts for a substantial portion of the variability; in fact, the reported differences may not be attributable to any single factor, but rather a group of factors.
Pre-Treatment Evaluation Prior to Ultrafiltration in Secondary Effluent Treatment for Water Reuse
(University of Waterloo, 2015-12-17) Aly, Samia; Huck, Peter; Anderson, William B.
Reusing wastewater can assist in solving water shortage problems, reduce the amount of wastewater discharged to surface water bodies and, by extension, alleviate its adverse effects on humans and the environment. Organics found in wastewater can be removed through biological treatment, however, if secondary effluent is to be reused for potable or some nonpotable applications, some form of advanced treatment is required. Membranes are often used to further treat these effluents for water reuse as they require only a small footprint and can provide a high quality treated water. They are also robust as is relates to dealing with feed waters of varying composition. However, due to the accumulation of rejected contaminants and certain natural organic matter (NOM) constituents on membrane surfaces and within pores, fouling can be an important shortcoming of this technology. Small improvements in the reduction of foulants can translate into substantial improvements in production quantity and cost savings. As such, it is worth the investment of time and research into common pre-treatment methods to identify technologies that can reduce foulant accumulation on membranes. The primary objective of this study was to extend previous research which investigated the use of ultrafiltration (UF) membranes for secondary effluent treatment for water reuse purposes. The most appropriate UF pre-treatment method was identified by comparing three different pre-treatment process modes (biofiltration, in-line coagulation, and a combination of the two processes). In parallel, the primary UF membrane foulant types found in a secondary effluent with high biopolymer content were identified, as well as those removed by the pre-treatment methods used in this research. In this study, aerobic biofilters typically used in drinking water treatment, were investigated for improving the characteristics of Waterloo Wastewater Treatment Plant treated secondary effluent for reuse. Two biofilters, one containing sand and the other containing anthracite, were operated under identical conditions (empty bed contact time [EBCT] of 60 min & hydraulic loading rate [HLR] of 0.75 m/h). Four different coagulants (alum, polyaluminum chloride [PACl], ferric chloride, and ferric sulfate) with a no coagulant control and two different dosages (0.5 and 5.0 mg/L) of each were investigated for their potential to remove UF foulants. To investigate the effect of combining in-line coagulation prior to biofiltration for improving UF performance, one biofilter (containing anthracite media) and one coagulant (1.0 mg/L ferric sulfate) were selected. The organic compound fractions found in secondary effluent, were quantified by Liquid Chromatography-Organic Carbon Detection (LC-OCD) analyses in all water samples before and after each treatment step. Data revealed that both biofilters reduced dissolved organic carbon (DOC), especially the high molecular weight biopolymer fraction, which was reduced by 25-30%. However, the biopolymer concentrations in the biofiltered secondary effluent were somewhat higher than in river and lake water sources, so even with these reductions the biopolymer levels in the effluent of the biofilters were higher than would typically be seen using those sources as biofilter feed. The reduction of organic compounds attributable to biodegradation occurred in the upper layer of the biofilter as confirmed by the highest consumption of dissolved oxygen and biomass concentrations at that location. The higher removals of different DOC fractions achieved by sand appear to be attributable to the increased amount of attached biomass (measured as ATP). Physical properties of secondary effluent were also improved after biofiltration, and turbidity in the effluent of the biofilters did not exceed 1.0 NTU despite influent values ranging from 1.1 to 10.3 NTU. To investigate the impact of pre-treatment methods, UF experiments were conducted with both secondary effluent (as collected from the full-scale plant) and after pre-treatment processes. To assess the development of UF fouling rates, changes in transmembrane pressure through UF runs were monitored and measured every 10 sec. Biofiltration effectively improved the performance of UF by reducing fouling development. The observed reduction in TMP was attributed to the removal of biopolymers (especially the protein component) and turbidity through biofiltration. Under the investigated conditions, sand as a biofilter media performed better than anthracite for reducing UF fouling. When the UF membrane was fed with biofilter effluents, both the reversible and irreversible fouling were correlated with biopolymer concentrations in feed water. Particulate matter was also weakly correlated with reversible fouling. In-line coagulation experiments demonstrated a sustainable reduction in both reversible and irreversible fouling, and coagulant type and dosage had a major impact in improving the performance of UF. Fouling reduction by in-line coagulation was primarily attributed to the alteration of organic composition of secondary effluent and/or the size modification of particles that contributed to membrane pore blocking. The most substantial impact of in-line coagulation was observed for the irreversible fouling reduction, which is more important for sustainable operation of membranes. The higher of the two coagulant dosages tested improved foulant removal and additional reduction of membrane reversible and irreversible fouling rates. Under the conditions investigated, ferric-based coagulants were better for UF fouling control than the aluminum-based coagulants. In-line coagulant provided additional removal of particles and organics through biofilter. In this instance it appears as if the negative surface charge of colloids and organics surface is reduced by charge neutralization resulting in larger compounds being produced and rejected by straining processes through the biofilter. In-line coagulation prior to biofiltration further improved membrane performance by reducing fouling and enhancing the removal of particles and DOC fractions (biopolymer and humic substances) through UF. Biofilter hydraulic performance was relatively unaffected by the upstream addition of coagulant. This study demonstrated that biofiltration and in-line coagulation can, under the investigated conditions, remove some treated wastewater constituents which have been associated with membrane fouling, and negatively affect other advanced treatments for water reuse. The integration of the two pre-treatment processes provided additional fouling reduction and a better UF permeate water was produced than that of the individual pre-treatments.
Removal of microplastics during drinking water treatment: Linking theory to practice to advance risk management
(University of Waterloo, 2024-10-22) Gomes, Alice; Emelko, Monica B.; Anderson, William B.
Microplastics (MPs) have emerged in the past decade as widespread contaminants that are harmful to human and ecosystem health. While their removal from water may be similar to those of other particulate contaminants, its characterization is complicated because MPs can undergo weathering, photolysis, and microbial degradation in the natural environment, resulting in the presence of functional groups (e.g., carbonyl, hydroxyl) on their surfaces, which may affect their removal during drinking water treatment. Given that studies using seeded polystyrene microspheres/MPs as surrogates for oocysts have shown good (but sometimes variable) removals through conventional drinking water treatment composed of coagulation, flocculation and sedimentation (CFS) followed by filtration, MPs are likely to be well removed in optimized conventional drinking water treatment plants. While many studies have focused on the removal of larger (i.e., >50 µm sized microplastics), investigations of the removal of smaller sized (<10 μm) microplastics by drinking water treatment processes have been limited largely to case studies in which foundational mechanisms necessary for maximizing treatment performance have only been superficially investigated, if at all. To address this gap, the study focused on whether MPs removal by conventional chemical pretreatment (i.e., coagulation, flocculation, and sedimentation) with alum aligns with the removal of other particles, including Cryptosporidium oocysts, for which particle destabilization is essential for removal. The study aimed to advance knowledge through three main objectives: (1) characterize MPs removal by CFS with different particle destabilization mechanisms and compare it to other important particulate contaminants (i.e., Cryptosporidium spp. oocysts), (2) evaluate the effect of particle size on MPs removal by CFS, and (3) assess the influence of weathering on MPs removal by CFS. To evaluate MPs removal by chemical pretreatment reliant on (1) adsorption and charge neutralization and (2) enmeshment in precipitate (i.e., sweep flocculation) particle destabilization mechanisms, bench-scale investigations of alum-based CFS (i.e., jar tests) were conducted with synthetic water using pristine and weathered PS microplastics of 1, 5 and 10 μm diameter. Several synthetic raw water matrices were explored to identify scenarios in which both particle destabilization mechanisms were clearly discerned. The final synthetic raw water was composed of deionized water spiked with sodium carbonate and kaolin (70 NTU) at pH 7.0. To demonstrate that MPs removal by CFS aligns with coagulation theory, sixteen alum doses between 0–38.8 mg/L were used to evaluate MPs removal by CFS. Turbidity reduction was also evaluated, and zeta potential was analyzed to identify maximal particle destabilization. MPs removal increased with particle size, aligning with gravitational settling theory. MPs removal during CFS with optimized particle destabilization was generally consistent with reported removals of other particles, including Cryptosporidium spp. oocysts during optimized chemical pretreatment, thereby suggesting that similar approaches for risk management may be relevant to MPs. Notably, differences in pristine and weathered MPs removal by CFS were not significant under the conditions investigated, thereby suggesting that weathering does not affect MPs removal when particle destabilization by coagulant addition is optimized. This study bridges the gap between the theories of conventional drinking water treatment and concerns regarding the potential passage of MPs through drinking water treatment plants, demonstrating that MPs can be removed in the same manner as other colloidal particles using conventional chemical pretreatment and—by well-recognized theory-based extension—physico-chemical filtration.
Removal of Organic Matter by Classical Biofiltration: Mechanistic Insights Regarding "Biodegradation"
(University of Waterloo, 2019-10-03) Thompson, Joan; Emelko, Monica; Anderson, William B.
Pilot-scale biofiltration experiments were conducted at the Region of Waterloo’s Mannheim Drinking Water Treatment Plant to inform the scientific and operational understanding of drinking water treatment by biologically-active GAC/sand filtration processes. Three dual-media granular activated carbon (GAC)/sand biofilters and one multi-media GAC-capped anthracite/sand biofilter media configuration were investigated. Both new GAC and GAC that had been biologically active for five years were used. The performance differences between a new, highly adsorptive GAC filter that is undergoing biological acclimation, and a biofilter that is stacked with older, biologically-active GAC media were investigated to increase the mechanistic understanding of natural organic matter (NOM) removal by biofiltration. The performance of a cost-effective, new GAC-capped anthracite/sand biofilter compared to a GAC/sand biofilter also was investigated. Performance was assessed using adenosine tri-phosphate (ATP) concentration associated with attached biomass in the filter media, dissolved organic carbon (DOC), UVabsorbance, and characterization by liquid chromatography-organic carbon detection (LC-OCD) fractionation. The filters were monitored for their performance in headloss accumulation and turbidity removal. Water from the full-scale water treatment plant was coagulated, flocculated, clarified by settling, and then ozonated. It was then directed to the pilot plant filters, which contained the same depth of media, but were operated separately from the full-scale plant. The experiments were conducted from June to September 2018, during warm water conditions (18–27°C). As expected, the new GAC/sand filter removed substantially more DOC, UV-absorbing compounds, and humic substances than did the biologically-active GAC. There was also a typical pattern of biological acclimation in this filter, as there was high DOC removal, followed by a decline, and then a steady-state period. DOC removal during the steady-state period in the new filter was 25 to 30% on average, which was significantly higher than that in the filter containing media that had been biologically active for five years (13% on average), suggesting that DOC removal might decline over years of service. Interestingly, the new GAC/sand filter did not out-perform the biologically-active GAC/sand filter in biopolymer removal, possibly due to the size (>20 kDa) and shape of these compounds. This observation also suggests that biodegradation of biopolymers (in contrast to other compounds) occurs directly in biologically-active GAC filters, and not necessarily by bioregeneration (freeing up of adsorptive sites). Further, compared to biologically-active GAC/sand, there was no outright disadvantage to running a GACcapped anthracite/sand biofilter. One month into the experiment, the backwashing procedure was altered to improve filter run times. The increased vigorousness caused the biofilm in the GAC-capped anthracite/sand filter to decrease temporarily, and it also caused a brief decrease in the DOC removal, whereas the GAC/sand biofilter was not affected by the backwashing change. Overall, it was found that (1) the new GAC filter demonstrated a trend in DOC removal that was expected, with the added finding that the biodegradation or adsorptive capacity declines over a period of several years after acclimation (2) adsorption did not enhance the removal of biopolymers, though they were removed by biofiltration, indicating that biodegradation may occur directly and not necessarily by bioregeneration (adsorption and desorption by biodegradation), and (3) as configured, the GAC/sand biofilter was more effective in removing DOC than the GAC-capped anthracite biofilter.
Treatment of the Cyanotoxins Cylindrospermopsin, Microcystin-LR, and Anatoxin-a by Activated Carbon in Drinking Water
(University of Waterloo, 2017-08-23) Liu, Yanting; Anderson, William B.; Peldszus, Sigrid
Cyanotoxins are known to cause human and animal illness, in some cases resulting in death, and their presence in drinking water is a potential risk to public health. Cylindrospermopsin (CYL), microcystin-LR (MC-LR), and anatoxin-a (ANTA) are among the most detected and studied cyanotoxins in North American surface water. While microcystin is regulated in drinking water in most North American jurisdictions, lower maximum contaminant limits may be coming as well as the potential addition of CYL and ANTA as regulated contaminants. Powdered and granular activated carbon (PAC and GAC) may be cost-effective barriers for extracellular cyanotoxins in conventional drinking water treatment plants but not all carbons and toxins have been studied. Even less information is available at PAC contact times that are relevant to practice. The primary objective of this research was to investigate the adsorption behavior (rate and capacity) of CYL, MC-LR, and ANTA during treatment with PAC and GAC. Adsorption of CYL, MC-LR, and ANTA was investigated using three commercially available PACs: coal-based COL-PL60-800 (Carbon Activated Corporation), wood-based BG-HHM (Calgon Carbon), and coconut-based WPC® (Calgon Carbon). Initially adsorption was studied in ultrapure water to establish baseline performance and for inter-lab comparisons now and in the future. The BG-HHM (wood) and the WPC (coconut) adsorbed CYL the fastest, the BG-HHM (wood) adsorbed MC-LR the fastest, while the BG-HHM (wood) and WPC (coconut) adsorbed ANTA the fastest. Adsorption capacity was evaluated under both equilibrium and non-equilibrium conditions (0.5 h and 1 h contact times). At equilibrium, the BG-HHM (wood) had the highest CYL capacity, the COL-PL60-800 (coal) had the highest MC-LR capacity, and the WPC (coconut) had the highest capacity for ANTA adsorption. Interestingly, PAC had substantially different capacities under non-equilibrium conditions which serve to more accurately simulate PAC contact times typically available in full-scale water treatment plants. Under non-equilibrium conditions, the wood-based BG-HHM outperformed the other two PACs with the highest capacity for the all three cyanotoxins investigated in this study. The adsorption of CYL, MC-LR, and ANTA was then investigated using Lake Erie water (adjusted to pH 7) collected from the Elgin Area Water Treatment Plant (Southern Ontario, Canada), again using the same PAC products as studied in the ultrapure water investigations. The BG-HHM (wood) adsorbed CYL and MC-LR the fastest, whereas the WPC (coconut) adsorbed ANTA the fastest. At equilibrium, the COL-PL60-800 (coal) had the greatest CYL capacity, the BG-HHM (wood) had the highest MC-LR capacity, and the WPC (coconut) and BG-HHM (wood) retained the greatest and similar capacity for ANTA. Under non-equilibrium conditions, the BG-HHM (wood) had the highest capacity for CYL and MC-LR, while the WPC (coconut) performed best for ANTA removal. Compared to the ultrapure water results, a substantial reduction in adsorptive capacity and a slight decrease in the rate of adsorption were observed in Lake Erie water. To describe the competitive adsorption of cyanotoxins and dissolved natural organic matter (NOM) in Lake Erie water, a competitive adsorption model, the simplified equivalent background compound model (SEBCM), was successfully utilized in this study to predict PAC dose to achieve target removals of each of CYL, MC-LR and ANTA under non-equilibrium conditions (0.5 h contact time). Based on the SEBCM results, an economic analysis was conducted and it was found that the BG-HHM (wood) was the most cost-effective alternative for CYL and MC-LR removal, while none of the selected PACs in this study was an effective barrier for ANTA. CYL adsorption was then investigated in ultrapure water using three virgin GACs, including coal-based F-300® (Calgon Carbon), wood-based C Gran (Norit), and coconut-based Aqua Carb (Siemens), and a preloaded coal-based F-300, previously prepared by Vlad (2015). Among all virgin GACs, the C Gran (wood) adsorbed CYL the fastest, while the F-300 (coal) was slowest. The F-300 (coal) retained the highest equilibrium capacity, while the C Gran (wood) had the lowest. Comparing the performance of virgin and preloaded F-300 (coal), both the rate of adsorption and capacity deteriorated as a result of preloading. Overall, PAC adsorption for CYL and MC-LR is a promising treatment option. Further investigations are required to explain differences observed for ANTA removal by PAC in this study vs. that reported by Vlad (2015). In the case of CYL adsorption by GAC, bench-scale testing has demonstrated that larger scale investigations are justified (at pilot- or full-scale in the event of a bloom). At present, the price and availability of the cyanotoxins is such that larger scale experiments may be cost prohibitive. Additional bench-scale PAC and GAC studies in other water sources are warranted.

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Browsing Civil and Environmental Engineering by Author "Anderson, William B."