The Contribution of Biofilm to Nitrogenous Disinfection ByProduct Formation in Full-Scale Cyclically-Operated Drinking Water Biofilters PDF Download
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Author: Caroline Di Tommaso
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Biofiltration can be effective for disinfection by-product (DBP) precursor control, however few studies have considered its role in the potential formation of DBPs. The objective of this study was to determine the contribution of biofilm-related materials to form nitrogen-containing DBPs upon chloramination and to determine the influence of cyclical biofilter operation on DBP precursor removal. Biologically active media was sampled from a full-scale biofilter operating under cold-water conditions (3.6 ± 0.5°C) and its components were extracted with a cation exchange resin into a phosphate buffering solution. N-nitrosodimethylamine (NDMA) and haloacetonitrile (HAN4) formation potential tests conducted on extracted biofilm yielded 0.80 ± 0.27 ng NDMA/g media and 18.7 ± 3.3 ng dichloroacetonitrile (DCAN)/g media. However, an analysis of NDMA formation potential and biological surrogates in the effluent of a full-scale cyclically-operated biofilter did not show release of NDMA precursors during filter start-up after stagnation periods of 6 hours or more.
Author: Caroline Di Tommaso
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Biofiltration can be effective for disinfection by-product (DBP) precursor control, however few studies have considered its role in the potential formation of DBPs. The objective of this study was to determine the contribution of biofilm-related materials to form nitrogen-containing DBPs upon chloramination and to determine the influence of cyclical biofilter operation on DBP precursor removal. Biologically active media was sampled from a full-scale biofilter operating under cold-water conditions (3.6 ± 0.5°C) and its components were extracted with a cation exchange resin into a phosphate buffering solution. N-nitrosodimethylamine (NDMA) and haloacetonitrile (HAN4) formation potential tests conducted on extracted biofilm yielded 0.80 ± 0.27 ng NDMA/g media and 18.7 ± 3.3 ng dichloroacetonitrile (DCAN)/g media. However, an analysis of NDMA formation potential and biological surrogates in the effluent of a full-scale cyclically-operated biofilter did not show release of NDMA precursors during filter start-up after stagnation periods of 6 hours or more.
Author: Fei Feng
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Previous studies have reported that biofilm extracted from full-scale biofilters can serve as nitrogenous disinfection by-product (N-DBP) precursors. Detached biofilm could escape during filter ripening and form N-DBP upon chloramination. This study examined the potential breakthrough of biofilm and N-DBP precursors during filter ripening at two water treatment plants (WTPs). The presence of biofilm was estimated by total adenosine triphosphate levels (tATP); N-DBP formation potential (FP) tests were conducted to quantify N-nitrosodimethylamine (NDMA) and haloacetonitrile precursors. While tATP peaks in filter effluent were observed post backwash at both WTPs, temporary increases of effluent NDMA FP were only observed during filter ripening where particle-associated NDMA precursors served as the dominant contributor. Overall, biofilters examined in this study demonstrated a consistent removal of NDMA FP regardless of the filter ripening process.
Author: Zhikang Wang
Publisher:
ISBN:
Category : Biofilms
Languages : en
Pages : 283
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Book Description
Since biofilm has been implicated in the deterioration water quality and the increase of public health risks, various efforts have been made to minimize biofilm regrowth in drinking water distribution systems. Although traditional water treatment processes can greatly remove a large fraction of disinfection by-products (DBPs) precursors, a small portion of natural organic matter (NOM) may still enter water distribution systems. Untreated NOM can serve as nutrients for biofilm growth while also consuming maintained disinfection residuals, which can result in microbial contamination in drinking water. To suppress biofilm formation, water utilities maintain disinfectant residuals for the distribution system. However, upon disinfectant addition, toxic DBPs are inevitably produced. Biofilm and its secreted extracellular polymeric substances (EPS) produce toxic DBPs, due to the very similar chemical composition compared to traditional investigated DBP precursors. This research investigated the role of biofilm on DBP formation and decay in simulated drinking water distribution systems with four objectives. The first objective was to investigate the influence of chemical composition and quantity of bacterial EPS on the biosorption of NOM in drinking water. Results indicated that both protein and polysaccharide based EPS adsorbed existing NOM. Biosorption capacity was mainly determined by divalent ion (Ca2+ and Mg2+) concentrations. Mechanistically, the presence of a diffuse electrical double layer inhibited NOM biosorption by potential energy barriers, however, presence of divalent ions in the aquatic environment enhanced biosorption processes, permitting functional group interactions between EPS and NOM. In addition, hydrophobic interactions, EPS characteristics and quantity can also be used to explain biosorption results. Bridging between hydrophilic carboxyl groups on alginate EPS and NOM appeared to be the dominant form of biosorption, while hydrophobic interactions enhanced biosorption for protein-based EPS. The second and third objectives of this study were to investigate the role of biofilm EPS on the formation of both carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs). DBP yield (formation potential) tests of both bacterial culture and extracted EPS indicated that the chemical composition and quality of EPS played a critical role for DBP formation. In general, protein based EPS possessed higher DBP yields compared to polysaccharide based EPS, especially for N-DBPs. To further determine the relative contribution of each biomolecule in EPS to DBP formation and speciation, detailed chemical compositions of biomolecules in EPS (amino acids, polysaccharide monomers, and fatty acids) from both pure culture and mixed species biofilm isolated from a water utility were analyzed. DBP yield results from both extracted EPS and EPS surrogates (amino acids and polysaccharide monomers) indicated that proteins in EPS have a greater impact on DBP formation, where amino acids containing unsaturated organic carbon or conjugated bonds in R-group produced higher amount of DBPs. However, DBP yields of polysaccharide monomers were lower than those of tested amino acids groups and the DBP yields were not significantly influenced by their chemical structures. The last objective of this study was to understand the influence of biofilm on DBP formation and decay in a simulated water distribution system using lab scale annular reactors. For Cl2 disinfection at 0.5 mg L-1 Cl2 residual concentration, no obvious DBP formation was observed. This was mainly due to the combination of low DBP formation, DBP volatilization, and biodegradation. However, when high Cl2 residuals were maintained, the formations of both C-DBPs and N-DBPs increased dramatically beyond the DBP formation potential of the feed solution. This suggests higher Cl2 residual not only reacted with humic acid (HA) in feed solution but also reacted with biofilm and produced extra DBPs, especially the high formation of N-DBPs (haloacetonitriles). For NH2Cl disinfection, the DBP levels were much lower than those of Cl2 disinfection and differences in DBP formation were not significant under different NH2Cl residual concentrations. Combined results suggested that biofilm can impact both C-DBP and N-DBP formation and decay in water distribution systems, where biomolecules in EPS affect DBP speciation.
Author: Mehrnaz Mirzaei Barzi
Publisher:
ISBN: 9780494437469
Category :
Languages : en
Pages : 210
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Over the past century chlorine has been a reliable disinfectant to reduce transmission of waterborne diseases in drinking water. Concerns about chlorination have increased since it was discovered in the 1970s that use of chlorine in drinking water produces trihalomethanes (THMs), when chlorine reacts with natural organic matter (NOM), which has been observed in increased levels in surface water during the past decades. THM and other disinfection by-products (DBPs) such as some of the haloacetic acids (HAAs) and some nitrosamines are considered probable human carcinogens by USEPA. Since DBPs are still formed even when using alternative disinfectants such as chloramines, treatment processes by which disinfection by-product precursors are removed continue to be studied. Many researchers have demonstrated that the use of pre-ozonation/biological processes in the production of drinking water has the potential to decrease levels of disinfection by-products in finished water more than conventional treatment alone. Two of the parameters which affect the efficiency of DBP precursor removal in biofilters are filter media and filter flow rate. In this research, the biofiltration process was examined using pilot-scale filters receiving ozonated water to determine the relative effectiveness of these parameters for influencing the removal of natural organic matter. The research presented in this thesis initially focuses on determining the effects of flow rate and filter media including GAC (granular activated carbon) and anthracite on decreasing the levels of THM, HAA and nitrosamine precursors in biologically active filters. In the second part, the performances of full-scale and pilot-scale filters at the Mannheim Water Treatment Plant were compared. THM and HAA precursor removal was found to decrease when loading rates were increased, likely due to associated shorter contact times in the filters. Also, higher THM and HAA precursor removal was always observed in the GAC filters than in the anthracite filters. However, removal of nitrosamines was not affected by flow rate or the type of filter media. In general, the pilot-scale filter performance was representative of full-scale filter performance, especially in regards to THM precursor and chlorine demand removal. Statistical evaluation and interpretation of the data for HAA and NDMA precursor removal was more difficult, likely due to the low concentrations of these DBPs which was near their method detection limits (MDLs) and also because of some operational problems with pilot filter #1. Despite these limitations, the results of this study add to the literature concerning the use of different types of media to support biofiltration and reduce DBP precursor concentrations during drinking water treatment.
Author: Steven Lane Percival
Publisher: CRC Press
ISBN: 1420041940
Category : Science
Languages : en
Pages : 241
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Book Description
The development of biofilms and their role in public health - particularly drinking water - is often overlooked. Ideal for anyone interested in water related issues, Microbiological Aspects of Biofilms and Drinking Water presents an overview of the public health effects associated with drinking water. It highlights the microbiological aspects relat
Author: K. Clive Thompson
Publisher: Royal Society of Chemistry
ISBN: 1782620885
Category : Medical
Languages : en
Pages : 368
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Book Description
Covering the latest developments in themes related to water disinfection by-products, this book brings the academic and industry researchers right up to date.
Author: Amina K. Stoddart
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Natural organic matter (NOM) is a complex mixture of organic material ubiquitous in natural waters. NOM can affect nearly all aspects of drinking water treatment. It can exert a demand on treatment chemicals, promote regrowth in distribution systems and can form genotoxic and/or carcinogenic disinfection by-products (DBPs) when exposed to disinfectant. Biofiltration is one treatment strategy that has potential to provide additional removal of NOM following coagulation. In biofiltration, bacteria indigenous to the source water form biofilms on filter media and use organic material as an energy source. This type of biological treatment within a filter has advantages over filtration with relatively biologically inert granular media because of its potential to provide additional NOM removal through biodegradation. This thesis investigated conversion of full-scale anthracite-sand drinking water filters to biofilters through the removal of prechlorination. Results showed that filters operated in direct filtration mode could be converted in this way to reduce DBP formation in the plant effluent and distribution system without compromising water quality or filter performance. Biomass monitoring using adenosine triphosphate (ATP) showed that filter media biomass increased as a result of conversion. Further interpretation of the biomass data with a growth model demonstrated that consistency in biomass sampling within the context of the operational state of the filter or following significant process changes was critical information for long-term performance assessment. A concurrent pilot-scale investigation tested nutrient, oxidant and filter media enhancement strategies with the goal of improving NOM removal and further reducing DBP formation. Results showed that nutrient and oxidant addition could increase the filter biomass and alter the microbial community, but would not improve NOM removal or further reduce DBP formation potential. Ultimately, despite reductions in DBP formation and increases in biofilter biomass, NOM removal across the biofilters remained unchanged with conversion and enhancements, posing a challenge for process monitoring. A novel method to measure oxygen demand was optimized for use in a drinking water matrix and used to evaluate NOM removal and transformation in the biofilters.
Author: Robert M. Clark
Publisher: DIANE Publishing
ISBN:
Category : Drinking water
Languages : en
Pages : 336
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Author: Michael James McKie
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Drinking water biofiltration research has increased dramatically in the past decade as new monitoring techniques have become available, resulting in widespread implementation at municipal treatment facilities. However, biofiltration is still considered a "black-box" technology which offers limited process control. This research examined biofiltration using a variety of techniques to develop a practical understanding of the underlying biological processes and provide guidance for improved design and operation. This research focussed on three primary topics: i) modelling processes critical to biofiltration, ii) applying biological monitoring to improve treatment, and iii) demonstrating benefits beyond providing improved water quality. Initial studies evaluated the application of a biofilter scaling model to determine the significance of biofilm shear loss and mass transport resistance with respect to a variety of biomass (density, function, and community composition) and water quality (organics, nutrients, disinfection by-product formation potential) parameters. Biofilm shear loss was observed to be the critical design parameter when scaling biofilter processes from pilot- to bench-scale, as enzyme activity, indicative of biological function, was not equivalent to pilot filters when mass transport resistance was deemed to have primacy. Subsequent studies further examined enzyme activity as a monitoring parameter for biofilter function; esterase and phosphatase were identified as being quantifiable and meaningful. Combining enzyme activity and filter empty bed contact time (EBCT) was defined as "Effective Activity". Effective esterase activity was observed to correlate to carbon removal whereas effective phosphatase activity was correlated with phosphate removal. These relationships were observed for a range of pre-treatments (coagulation, pre-ozonation, ultrafiltration, UV), filter media (granular activated carbon, anthracite or sand) and operating conditions (EBCT, daily shutdown) suggesting that effective activity may serve as a useful design and operation parameter. Finally, two water treatment facilities were examined to determine potential energy cost savings associated with cyclical biofilter operation. It was shown that production costs could be reduced by >20% by scheduling production during low energy cost periods (e.g. 10 PM - 7 AM). This research demonstrated that monitoring biofilter enzyme activity may allow for optimal design and operation when compared to other monitoring parameters. Cyclically operated biofilters may dramatically reduce operating costs without impacting water quality.
Author:
Publisher:
ISBN:
Category : Bacterial growth
Languages : en
Pages : 72
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