Polymer flocculants, traditionally used with primary coagulant to enhance flocculation and sedimentation, are used in the coagulation-/microfiltration process as well assuming they can improve membrane performance similarly. However, there are several uncertainties concerning the use of polymer flocculants in the coagulation-microfiltration process. First, polymer flocculants may not have measurable effect on turbidity removal, because microfiltration membranes can remove significantly smaller particles than those removed by the conventional treatment process. Second, the effect of using polymer flocculants on NOM removal has been controversial. Although a number of studies reported improved NOM removal when polymers were used, others reported no or negative impact of polymers on NOM removal. Third, polymer flocculants are high molecular weight organic compounds. When carried over to membrane residual polymers can potentially foul the membranes. Finally, the use of polymer flocculants will change floc properties (i.e. size, fractal dimension, and stickiness) and subsequently bring uncertain effect on cake layer resistance. Therefore, the role of polymer flocculants in coagulation-microfiltration system needs to be carefully assessed for system optimization. In the reported research, three types of polymer flocculants with different charge and molecular weights were tested for comprehensively evaluating the impact of polymer flocculants on the performance of coagulation-microfiltration of surface water. Operation conditions such as inline filtration, direct filtration, and filtration with sedimentation were included. Two membrane reactors were designed to study the mechanism through which polymer flocculants affect the performance of coagulation-microfiltration systems. The result demonstrated that the use of polymer flocculants provides little to no benefit to turbidity and NOM removal in most cases, but pDADMACs can enhance NOM removal if applied properly; All polymer flocculants significantly increased membrane fouling except for pDADMACs when sedimentation proceeds MF; Polymer flocculants increase deposition/attachment of floc particles on the membrane surface through both adsorption of residual polymer on the membrane surface and polymer molecules on the floc particle surface; Even though polymers form larger and more fractal floc particles, they did not have notable impact on cake layer structure.

<p>Mercury contamination in aquatic ecosystems is a concern as anaerobic aquatic sediments are the primary regions of methylmercury production in freshwater and coastal regions. Methlymercury is a bioaccumulative neurotoxin, and human exposure to methylmercury can result in impaired functioning of the central nervous system and developmental disabilities in children. To minimize the risk of human exposure to methylmercury, it is important to be knowledgeable of the various sources which can supply mercury to aquatic ecosystems as well as have a complete understanding of the biogeochemical processes which are involved in methylmercury production in aquatic systems. In this dissertation work, both mercury biogeochemical speciation in anaerobic aquatic sediments and sources of mercury to aquatic systems were addressed. </p><p>The biogeochemical speciation of mercury is a critical factor which influences the fate and transformation of mercury in aquatic environments. In anaerobic sediments, mercury chemical speciation is controlled by reduced sulfur groups, such as inorganic sulfide and reduced sulfur moieties in dissolved organic matter (DOM). The formation of mercury sulfide nanoparticles through stabilization by dissolved organic matter (DOM) was investigated in precipitation studies using dynamic light scattering. Mercury sulfide nanoparticles (particle diameter < 100 nm) were stabilized through precipitation reactions that were kinetically hindered by DOM. To further investigate the interaction between DOM and metal sulfides, similar precipitation studies were performed using zinc sulfide and a number of DOM isolates (humic and fulvic acids) representing a range of DOM properties. The results of these experiments suggest that the mechanism of metal sulfide particle stabilization may be electrostatic or electrosteric, depending on the nature of the DOM molecule.</p><p>The mercury that is methylated in aquatic systems enters these environments via a number of sources, including atmospheric deposition, landscape runoff and other industrial and municipal activities. In two separate field studies, two potential sources of mercury to aquatic systems were investigated: landscape runoff and coal combustion products. The mercury loading to aquatic environments from these sources and their potential for transformation to methylmercury were investigated.</p><p>Landscape runoff from a Duke University campus catchment (Durham, NC) was identified as a source of mercury to a stream-wetland. The source of mercury to the runoff was likely from a `legacy' source of mercury; the historic application of mercury fungicide compounds to turf grass during the 20th century. Downstream of the point where the runoff was discharged to the stream-wetland, methylmercury concentrations were detected in stream sediments (up to 11% of total mercury), suggesting that this legacy mercury could be transformed to methylmercury. </p><p>The environmental impact of coal combustion products (CCPs) with respect to mercury and methylmercury was also investigated in a river system (Roane County, TN) that was inundated with fly ash and bottom ash from the Tennessee Valley Authority Kingston coal ash spill in 2008. Elevated total mercury and methylmercury sediment concentrations (relative to upstream sediments) were detected in regions impacted by the ash spill, and our biogeochemical data suggested that the ash may have stimulated methylmercury production in river sediments.</p><p>The results of this dissertation work address the formation of mercury sulfide (along with zinc sulfide) nanoparticles in anaerobic aquatic sediments. In the current mercury methylation paradigm, dissolved mercury species such as Hg(SH)02(aq) and HgS0(aq) are assumed to be the only mercury species that are available for methylation. The results of this dissertation work suggests that in previous studies, HgS0(aq) may have been mistaken as mercury sulfide nanoparticles which may be formed in under supersaturated conditions (with respect to HgS(s)) where DOM is present. Mercury sulfide nanoparticles are a mercury biogeochemical species that has been largely ignored in the research literature and whose role in the mercury biogeochemical cycle and in mercury methylation remains to be investigated.</p><p> This dissertation work also identifies potential sources of mercury to aquatic systems, namely, landscape runoff and CCPs. Atmospheric deposition is currently considered to be the major source of mercury to inland aquatic water bodies compared to sources such as landscape runoff and CCPs. However, in the watershed studied in this dissertation, landscape runoff was identified as a larger source of mercury than atmospheric deposition, suggesting that these so-called `minor' sources may actually be major sources of mercury to watersheds depending on land usage, and should be considered in watershed models. Furthermore, the environmental hazards of mercury-associated with CCPs has typically been determined through leaching experiments, such as the Toxicity Characteristic Leaching Procedure (TCLP), which are not representative of environmental conditions and do not predict that CCPs may influence mercury methylation in aquatic sediments. Thus, in this dissertation work, we suggest that leaching protocols such as the TCLP should be re-evaluated. </p><p>Overall, this dissertation work will be useful in future studies examining mercury speciation and bioavailability to methylating bacteria in aquatic sediments, and the formation of metal sulfide nanoparticles in aquatic systems. Additionally, data on sources of mercury will be useful in developing policies for the regulation of these sources and in assessing the risk to human health from mercury methylation.</p> / Dissertation

<p>Methylmercury is a bioaccumulative neurotoxin that severely endangers human health. Humans are exposed to methylmercury through consumption of contaminated aquatic fish. To date, effective strategies for preventing and remediating methylmercury contamination have remained elusive, mainly due to the lack of knowledge in regard to how methylmercury is generated and degraded in the aquatic environment. The goal of this dissertation was to study the mechanisms of two transformation processes that govern the fate of methylmercury in natural settings: microbial mercury methylation and methylmercury photodegradation. The role of mercury speciation (influenced by environmental conditions) in determining the reactivity of mercury in these biological and photochemical reactions was the focus of this research.</p><p>Methylmercury production in the aquatic environment is primarily mediated by anaerobic bacteria in surface sediments, particularly sulfate reducing bacteria (SRB). The efficiency of this process is dependent on the activity of the methylating bacteria and the availability of inorganic divalent mercury (Hg(II)). In sediment pore waters, Hg(II) associates with sulfides and dissolved organic matter (DOM) to form a continuum of chemical species that include dissolved molecules, polynuclear clusters, amorphous nanoparticles and after long term aging, bulk-scale crystalline particles. The methylation potential of these mercury species were examined using both pure cultures of SRB and sediment slurry microcosms. The results of these experiments indicated that the activity of SRB was largely determined by the supply of sulfate and labile carbon, which significantly influenced the net methylmercury production in sediment slurries. The availability of mercury for methylation decreased during aging. Dissolved Hg-sulfide (added as Hg(NO3)2 and Na2S) resulted in the highest methylmercury production. Although the methylation potential of humic-coated HgS nanoparticles decreased with an increase in the age of nanoparticle stock solutions, nano-HgS was substantially more available for microbial methylation relative to microparticulate HgS, possibly due to the smaller size, larger specific surface area and more disordered structure of the nanoparticles. Moreover, the methylation of mercury derived from nanoparticles cannot be explained by equilibrium speciation of mercury in the aqueous phase (<0.2 <em>f</em>Ým, the currently-accepted approach for assessing mercury bioavailability for methylation). Instead, the methylation potential of mercury sulfides appeared to correlate with the extent of dissolution and their reactivity in thiol ligand exchange. Additionally, partitioning of mercury to a diverse group of bulk-scale mineral particles and colloids (especially FeS) may be an important process controlling the mercury speciation and subsequent methylmercury production in natural sediments.</p><p>In surface waters, sunlight degradation is believed to be the predominant pathway for the decomposition of methylmercury. The mechanism of this process was investigated in a series of photodegradation experiments under natural sunlight and UV-A radiation, and in the presence of DOM and selective quenchers for photo-generated reactive intermediates. The results suggested that singlet oxygen generated from photosensitization of DOM drove the photodecomposition of methylmercury. The rate of methylmercury degradation depended on the type of methylmercury (CH3Hg+) binding ligand present in the water. CH3Hg -thiol (e.g., glutathione, mercaptoacetate, DOM) complexes were significantly more reactive in photodegradation compared to other methylmercury complexes (CH3HgCl or CH3HgOH), which may be because thiol-binding can effectively decrease the activation energy and thus enhance the reactivity of methylmercury molecules toward the Hg-C bond breaking process. These findings challenge the long-accepted view that water chemistry characteristics do not affect the kinetics of methylmercury sunlight degradation, and help explain recent field observation that methylmercury photodegradation occurred rapidly in freshwater lakes (where CH3Hg-DOM dominate methylmercury speciation) but relatively slowly in sea water (where CH3Hg-Cl control methylmercury speciation).</p><p>Overall, this dissertation has demonstrated that chemical speciation of inorganic mercury and methylmercury determines their availability for microbial methylation and sunlight degradation, respectively. The abundance of these available mercury species is influenced by a variety of environmental parameters (e.g., DOM). This dissertation work contributes mechanistic knowledge toward understanding the occurrence of methylmercury in the aquatic environment. This information will ultimately help construct quantitative models for accurately predicting and assessing the risks of mercury contamination.</p> / Dissertation

Previous research indicates that pharmaceutically active compounds (PhACs) and endocrine-disrupting compounds (EDCs) are poorly removed during conventional drinking water treatment processes including coagulation; however, removal efficiency increases in the presence of natural organic matter (NOM). Therefore, this project investigates the link between various NOM types with EDC/PhAC removal. Bench-scale coagulation tests were conducted on three different source waters spiked with environmentally relevant levels (nominally 1000 ng/L) of EDCs/PhACs. Two different coagulants were used: polyaluminum chloride (PACl) and aluminum sulphate (alum). NOM was characterized using size exclusion liquid chromatography-organic carbon detection (LC-OCD). Results for Lake Ontario, Otonabee and Grand River water indicate that certain EDCs/PhACs are significantly removed during coagulation while others increase in concentration. Concurrently, particular NOM fractions (biopolymers and humic substances) are also being removed. Solvents used for EDC/PhAC spiking (acetone and acetonitrile) did not affect coagulation, but contributed to low molecular weight neutral and hydrophobic NOM fractions.

Previous research indicates that pharmaceutically active compounds (PhACs) and endocrine-disrupting compounds (EDCs) are poorly removed during conventional drinking water treatment processes including coagulation; however, removal efficiency increases in the presence of natural organic matter (NOM). Therefore, this project investigates the link between various NOM types with EDC/PhAC removal. Bench-scale coagulation tests were conducted on three different source waters spiked with environmentally relevant levels (nominally 1000 ng/L) of EDCs/PhACs. Two different coagulants were used: polyaluminum chloride (PACl) and aluminum sulphate (alum). NOM was characterized using size exclusion liquid chromatography-organic carbon detection (LC-OCD). Results for Lake Ontario, Otonabee and Grand River water indicate that certain EDCs/PhACs are significantly removed during coagulation while others increase in concentration. Concurrently, particular NOM fractions (biopolymers and humic substances) are also being removed. Solvents used for EDC/PhAC spiking (acetone and acetonitrile) did not affect coagulation, but contributed to low molecular weight neutral and hydrophobic NOM fractions.

<p>The existence of trihalomethanes (THMs) in a drinking water plant of Nicaragua has been investigated in order to see whether the concentration exceeded the maximum contaminant level recommended by the environmental protection agency of the United States (USEPA) and the Nicaragua guidelines. The influence of pH, temperature, chlorine dose and contact time on the formation of THMs were studied. The contents of organic matter measured by surrogate parameters such as total organic carbon, dissolved organic carbon, ultraviolet absorbance and specific ultraviolet absorbance were also determined in order to show which type of organic matter is most reactive with chlorine to form THMs. Models developed by other researchers to predict the formation of trihalomethanes were tested to see whether they can be used to estimate the trihalomethane concentration. In addition, empirical models were development to predict the THM concentration of the drinking water plant analysed. The raw water was treated by conventional and enhanced coagulation and these processes were compared with regard to the removal of natural organic matter (NOM). The significance of the results was assessed using statistic procedures.</p><p>The average concentration of THMs found at the facility is below the USEPA and Nicaragua guideline values. Nevertheless the maximum contaminant level set by USEPA is sometimes exceeded in the rainy season when the raw water is rich in humic substances. Comparison between the water treated by conventional and enhanced coagulation shows that enhanced coagulation considerably diminished the trihalomethane formation and the value after enhanced coagulation never exceeded the guidelines. This is because enhanced coagulation considerably decreases the organic matter due to the high coagulant dose applied. The study of the trihalomethane formation when varying pH, time, temperature and chlorine dose using water treated by conventional and enhanced coagulation showed that higher doses of chlorine, higher pH, higher temperature and a longer time increases the formation of THMs. However, combinations of two and three factors are the opposite. The predicted THM formation equations cannot be used for the water at this facility, since the results shown that the measured THM differs significantly from the THM concentration predicted. Two empirical models were developed from the data for enhanced coagulation, using linear and non-linear regression. These models were tested using the database obtained with conventional coagulation. The non-linear model was shown to be able to predict the formation of THMs in the Boaco drinking water plant.</p>

Research in the use of ozone in water treatment conducted by many authors support the idea that the nature and characteristics of natural organic matter (NOM) present in raw water determines the efficiency of ozonation in water purification. An ozone contact chamber was designed and made to allow pre-ozonation of water to take place. The concentration of ozone in the chamber was determined using the Indigo method. For the duration of one year, water samples were collected from four different sampling sites and analyzed to determine their overall ecological status with regard to several variables such as pH, chlorophyll-a, SAC254, turbidity, DOC, algal species composition and sum of NOM. Two dams sites and two riverine sites were chosen, Hartbeespoort Dam (a hyper-eutrophic impoundment), Boskop Dam (a mesotrophic impoundment), Midvaal Water Company at Orkney and Sedibeng Water at Bothaville. The samples were treated in Jar Tests with FeCI3 and the same variables were measured. Preozonation followed by Jar Tests was performed on each sample at twoconcentrations of ozone and the variables were measured to examine the efficiency of ozonation. In general, the ph was high and stayed the same for all the samples and for all the treatments. DOC was variable and showed no relationship to any other variable or to the treatments. Hartbeespoort Dam was found to be a eutrophic impoundment characterized by high algal bloom of the cyanobacteria Microcystis sp., Turbidity, SAC254, and the sum of NOM were lower than for the riverine sites but higher than for Boskop Dam. The NOM constituted more intermediate molecular weight(1MW)and low molecular weight (LMW) fractions than the riverine sites. Ozone was effective in reducing chlorophyll-a, turbidity and SAC254 from Hartbeespoort Dam, but the presence of large numbers of algal cells interferes with its efficiency. Release of cell-bound organics after ozonation can lead to increases instead of decreases in these variables. Jar Test results demonstrate that ozonation improves water quality when compared to conventional treatment although the interference of algal cells can alter results. Boskop Dam is a mesotrophic impoundment characterised by low productivity, low SAC254, tow turbidity and low sum of NOM. However, it has a large portion of the LMW fraction of NOM present. This LMW fraction affects the treatment process as this fraction is not acted upon by ozone. Therefore it was found that ozonation did not improve the quality of the water when compared to conventional treatment. The two riverine sites, Midvaal and Sedibeng were similar to each other. Both sites had high algal productivity with high chlorophyll-a values indicative of algal blooms observed at certain times. These blooms consisted either of members of Bacillariophyceae or Chlorophyceae. High turbidity and SAC254 was observed during the rainy season and was related to the high percentage HMW and IMW fractions of NOM present. There was correlation between the turbidity and SAC254 of these sites leading to the assumption that the turbidity of the river is due to the presence of HMW humic fractions of NOM. Ozonation was effective in improving water quality with respect to turbidity, SAC254 and chlorophyll-a removal, both on its own and after conventional treatment when combined with a coagulant. However, the species of algae present affects ozonation as members of Bacillariophyceae are not affected by the actions of ozone because of the presence of a silica frustule whereas members of Chlorophyceae are easily removed by ozone. In general, ozone acts upon the HMW and LMW fractions of NOM causing them to breakdown into smaller fractions. Ozone has no effect on samples that have a high percentage of the LMW fraction of NOM. This LMW fraction is more readily removed by conventional treatment than by ozonation. The presence of large numbers of algal cells as well as the species of cells can negatively affect the treatment process with regard to ozone. / Thesis (M. Environmental Science (Water Science))--North-West University, Potchefstroom Campus, 2007.

This research addresses the potential ecotoxicity of two emerging carbonaceous materials: C 60 and biochar. The use of these materials is rapidly increasing, as well as their potential for widespread applications. Thus, information about unintended consequences associated the widespread use, incidental or accidental release, and disposal of these emerging materials is needed. The environmental impacts of C 60 , its stable water suspension (nC 60 ), and biochar are assessed here using bacteria and earthworms as model receptors. The antibacterial activity of nC 60 can be mitigated by the presence of natural organic matter as a soil constituent or dissolved in the water column. Sorption to soil might decrease the bioavailability of nC 60 and thus its toxicity to bacteria. Aqueous organic matter also may mitigate nC 60 toxicity. Pristine C 60 showed toxicity to the earthworm's reproduction and was rapidly bioaccumulated by earthworms, although to a lower extent than smaller phenanthrene molecules that are more hydrophobic; thus, the large molecular size of C 60 hinders its bioaccumulation. Less bioaccumulation occurred at higher C 60 concentration in soil, which is counterintuitive and reflects that higher C 60 concentrations that exceed the soil sorption capacity exist as larger precipitates that are less bioavailable. Earthworms avoided soils amended with high concentrations of dry biochar, and experienced significant weight loss after 28-day exposure. The avoidance response was likely to avert desiccation rather than to avoid potential toxicants (i.e., PAHs formed during biochar production by pyrolysis) or nutrient scarcity. By wetting the biochar to field capacity before exposing the worms, this adverse effect can be completely mitigated. Overall, this research provides a foundation for ecotoxicity assessment associated with exposure to C 60 or biochar, and establishes a method by which other emerging materials can be evaluated for their potential environmental impacts.

Research has shown biological filtration can be a successful treatment for manganese (Mn) removal from groundwater and surface water. In this study, bench-scale direct biofiltration was used to remove Mn and dissolved organic carbon (DOC) from a pH 6 surface water source in Halifax, Canada. The removal of Mn in pH 6 surface water was significantly (? = 0.05) removed with 200-300 µg/L phosphorus (P), and 500 µg/L hydrogen peroxide (H2O2). DOC removal was significantly (? = 0.05) improved with granular activated carbon (GAC) media, P enhancement at 200-300 µg/L, and H2O2 enhancement at 500 µg/L. Mn was likely removed by biological oxidation and physical adsorption to biogenic Mn and iron (Fe) oxides. These results show direct biofiltration of surface water at pH 6 can remove Mn below the 50 µg/L aesthetic guideline from a Mn loading of over 1 mg/L. Further research is required to verify the microbial mechanism.

Natural organic matter (NOM) is present in all surface waters as a result of decaying vegetation, biological activity, and organic soil. Alternative NOM removal processes such as anion exchange resins (AERs) have shown NOM removals typically ranging between 50 to 90%, with up to 99% removal achieved in some cases. The first portion of this study evaluated the performance of two AERs; a conventional Type 1 AER and magnetic ion exchange resin (i.e. MIEX®) for NOM removal from surface water quantified by UV254, dissolved organic carbon (DOC), and specific UV absorbance (SUVA). Samples were also characterized for chloride, sulphate, and chloride-to-sulphate mass ratio (CSMR) to provide additional information on water quality characteristics of AER treated waters. Overall, the results showed that both AERS were effective for removing NOM. However, the MIEX® resin provided greater removal of NOM with shorter contact times compared to the conventional resin investigated. Water treated with MIEX® resin showed significantly higher chloride and lower sulphate concentrations than the conventional AER. Higher CSMR values were found with MIEX® treated water compared to conventional AER system, although both resins showed CSMR much greater than 0.5, which can increase galvanic corrosion effects with lead. Bench-scale jar tests were conducted to investigate the impact of temperature on the efficacy of three NOM removal treatment technologies; enhanced coagulation with alum, MIEX® and a combined MIEX® treatment followed by coagulation with a low dose of alum. Higher settled water turbidity was observed during cold water operating conditions for all three processes. At cold-water operating conditions, DOC removal was reduced with combined MIEX® -Alum treatment, and UV254 removal was impacted for both MIEX® and MIEX® -Alum processes. The combined MIEX®-Alum process was found to provide the lowest THMFP and HAAFP at both temperatures to concentrations lower than current regulatory maximum acceptable concentration (MAC) guidelines in Canada. Surface charge analysis experiments were performed at bench-scale using synthetic water containing humic acid to determine the relationship between NOM and the charge of AER-treated waters. Further bench and pilot-scale studies were performed to investigate the use of surface charge measurements to monitor and optimize NOM removal during treatment with AER systems. Strong correlations were observed between UV254 and respective charge measurements (i.e. ZP, SC) of AER-treated synthetic and raw waters. The results of this research has shown that it is possible to use charge to optimize the MIEX® process for NOM removal. Additionally, it was found that SC measurements could be used as an operational tool for AER processes, where deviations in SC from optimum treatment would indicate the requirement for fresh resin addition or resin regeneration.