Article

EFFECT OF operating conditions on Bromate Removal Efficiency in BAC fitters

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Abstract

This study examined the use of biologically active carbon (BAC) filters for microbial reduction of bromate to bromide. In these filters, abiotic reduction by the activated carbon did not play a significant role in bromate removal. Bromate removal in a BAC filter decreased by 30% after a system perturbation, suggesting that filter history affects bromate removal. Although 25 and 51 mm (1 and 2 in,) inner-diameter BAC filters provided comparable bromate removals for the tested contact times, the larger filter exhibited nitrite production; therefore, system performance must be monitored to prevent such undesirable compounds from entering the water. The mass of bromate removed increased as the influent bromate concentration increased, whereas bromate removal did not change after backwashing. Experimental evidence indicated that increased regrowth would not be observed in the distribution system following BAC filtration with a low influent dissolved oxygen concentration (2 mg/L) in ale tested water.

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... The addition of exogenous organic donor as well as the biodegradation of labile organic matter consume DO in water, allowing for anoxic conditions for the reduction of BrO 3 À and other anions. Bromate reduction to Br À has been reported in BAC in which microorganisms reduced BrO 3 À to Br À (Chuang and Mitch, 2017;Kirisits et al. 2001Kirisits et al. , 2002Kirisits and Snoeyink, 1999;Kirisits et al., 2001;Liu et al., 2012b). Common electron acceptors hindered the reduction of BrO 3 À . ...
... Bromate removal improved when sufficient organic electron donor was added to remove the nitrate and DO present in the surface water, indicating that the poor biodegradability of the DOM may have limited the BrO 3 À removal in that water sample. In a continuous study, Kirisits et al. (2002) found that in these filters, abiotic removal (i.e., adsorption) by the activated carbon in these filters did not play a significant role in BrO 3 À removal. An increase in the removal of the mass of BrO 3 À was observed with an increase in the influent BrO 3 À , whereas the level of BrO 3 À removed did not change after backwashing. ...
... High DO may impair the filter's performance. Kirisits et al., 2002 5 Pilot HAAs GAC bed volume ¼ 40 mL; filter diameter ¼ 1.1 cm; EBCT ¼ 20 min. ...
Article
While disinfection provides hygienically safe drinking water, the disinfectants react with inorganic or organic precursors, leading to the formation of harmful disinfection byproducts (DBPs). Biological filtration is a process in which an otherwise conventional granular filter is designed to remove not only fine particulates but also dissolved organic matters (e.g., DBP precursors) through microbially mediated degradation. Recently, applications of biofiltration in drinking water treatment have increased significantly. This review summarizes the effectiveness of biofiltration in removing DBPs and their precursors and identifies potential factors in biofilters that may control the removal or contribute to formation of DBP and their precursors during drinking water treatment. Biofiltration can remove a fraction of the precursors of halogenated DBPs (trihalomethanes, haloacetic acids, haloketones, haloaldehydes, haloacetonitriles, haloacetamides, and halonitromethanes), while also demonstrating capability in removing bromate and halogenated DBPs, except for trihalomethanes. However, the effectiveness of biofiltration mediated removal of nitrosamine and its precursors appears to be variable. Increased nitrosamine precursors after biofiltration was ascribed to the biomass sloughing off from media or direct nitrosamine formation in the biofilter under certain denitrifying conditions. Operating parameters, such as pre-ozonation, media type, empty bed contact time, backwashing, temperature, and nutrient addition may be optimized to control the regulated DBPs in the biofilter effluent while minimizing the formation of unregulated emerging DBPs. While summarizing the state of knowledge of biofiltration mediated control of DBPs, this review also identifies several knowledge gaps to highlight future research topics of interest.
... To date, although the biological reduction of bromate has been realized in many types of bioreactors, and several attempts have been made to identify bromate-reducing consortia, the phylogenetic characterization of bromate reducers remains inconclusive (Assunção et al., 2011;Davidson et al., 2011;Liu et al., 2012;Zhong et al., 2018). Moreover, although some bromate-reducing bacterial strains that belong to Actinobacteria, Bacteroidetes, Firmicutes, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria have been isolated and identified in previous studies (Hijnen et al., 1995;Kirisits et al., 2002;Davidson et al., 2011;Tamai et al., 2016), the specific bromatereducing pathway has remained unclear. Thus, our work aims to isolate a number of differing bromate-reducing bacteria and to uncover genomic insights into bromate reducers. ...
... Considering that the seed sludge used for anaerobic enrichment was taken from aerobic activated sludge, the enriched bacteria were likely facultative anaerobes. Bacterial isolates belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes have been reported to be involved in bromate reduction (Hijnen et al., 1995;Kirisits et al., 2002;Assunção et al., 2011;Davidson et al., 2011;Liu et al., 2012;Demirel et al., 2014;Zhong et al., 2018), however, to the best of our knowledge, no bromate-reducing bacteria belonging to Enterobacteriaceae have been identified by other groups, although other genera that belonging to Proteobacteria, such as Citrobacter (Assunção et al., 2011), Sphingomonas (Liu et al., 2012), and Denitratisoma (Demirel et al., 2014), have been reported to be involved in bromate reduction. Thus, the cultural isolates here have expanded our understanding of the potential diversity of bromate-reducing bacteria. ...
Article
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Bromate, a possible human carcinogen, can be reduced to innocuous bromide by microorganisms. To characterize bromate reducers, microbes were enriched anaerobically from activated sludge by using bromate as the sole electron acceptor and different carbon sources as the electron donor. Bacteria that showed significant bromate-reducing activity but not coupled to cell growth were isolated. Two whole genomes of the isolates, namely, Raoultella electrica Lac1 and Klebsiella variicola Glu3, were reconstructed by Illumina and Nanopore sequencing. Transcriptomic analysis suggested that neither the respiratory nitrate reductase, the selenate reductase, nor the dimethylsulfoxide reductase was involved in the bromate reduction process, and strain K. variicola Glu3 reduced bromate via a yet undiscovered enzymatic mechanism. The results provide novel phylogenetic insights into bromate-reducing microorganisms and clues in putative genes encoding enzymes related to bromate reduction.
... Given the diverse distribution of nitrate-, sulfate-and (per)chlorate-reducing microorganisms in nature, bromate-reducing microorganisms were also assumed to be phylogenetically diverse in the environment. The amplicons of 16S rRNA gene were usually used as a biomarker to reveal microbial profiles in bromate-reducing bioreactors, such as biological activated carbon (BAC) filters (Davidson et al. 2011;Kirisits et al. 2002;Liu et al. 2012), fixed bed column reactors (Demirel 2016) and rotating biofilm-electrode reactor (RBER) (Zhong et al. 2018) (Table 1). Denaturing gradient gel electrophoresis ...
... (DGGE) were employed as a pioneering method to analyze microbial diversity and to compare the band patterns under different conditions of BAC filters (Kirisits et al. 2002). Later, with the assistance of TA cloning and pyrosequencing, researchers began to uncover the diverse bacterial subdivisions that were responsible for bromate reduction. ...
Article
Bromate is a disinfection byproduct (DBP) that forms during the ozonation of bromide-containing natural water, which may cause health risks to humans. In this review, we provide an overview of the mechanism of bromate formation, microbial communities and bioreactors that are responsible for bromate reduction. Bromate can be formed through two pathways of bromide oxidation by ozone or by Á OH, and it can be removed by biological approaches. Members belonging to phyla of Spirochaetes, Pro-teobacteria, Firmicutes, Actinobacteria, Clostridium, Deinococcus-Thermus and Bacteroidetes have been identified as capable of reducing bromate to bromide. Multiple configurations of biofilm bioreactors have been employed to cultivate microbial communities to perform bromate removal. The rapid development of multiomics has and will continue to accelerate the elucidation of the mechanisms involved in bromate and other DBP conversions, as well as the interaction patterns among different bacterial subdivisions in the bioremoval of DBPs.
... Given the diverse distribution of nitrate-, sulfate-and (per)chlorate-reducing microorganisms in nature, bromate-reducing microorganisms were also assumed to be phylogenetically diverse in the environment. The amplicons of 16S rRNA gene were usually used as a biomarker to reveal microbial profiles in bromate-reducing bioreactors, such as biological activated carbon (BAC) filters (Davidson et al. 2011;Kirisits et al. 2002;Liu et al. 2012), fixed bed column reactors (Demirel 2016) and rotating biofilm-electrode reactor (RBER) (Zhong et al. 2018) (Table 1). Denaturing gradient gel electrophoresis ...
... (DGGE) were employed as a pioneering method to analyze microbial diversity and to compare the band patterns under different conditions of BAC filters (Kirisits et al. 2002). Later, with the assistance of TA cloning and pyrosequencing, researchers began to uncover the diverse bacterial subdivisions that were responsible for bromate reduction. ...
Article
Full-text available
Bromate is a disinfection byproduct (DBP) that forms during the ozonation of bromide-containing natural water, which may cause health risks to humans. In this review, we provide an overview of the mechanism of bromate formation, microbial communities and bioreactors that are responsible for bromate reduction. Bromate can be formed through two pathways of bromide oxidation by ozone or by ·OH, and it can be removed by biological approaches. Members belonging to phyla of Spirochaetes, Proteobacteria, Firmicutes, Actinobacteria, Clostridium, Deinococcus-Thermus and Bacteroidetes have been identified as capable of reducing bromate to bromide. Multiple configurations of biofilm bioreactors have been employed to cultivate microbial communities to perform bromate removal. The rapid development of multiomics has and will continue to accelerate the elucidation of the mechanisms involved in bromate and other DBP conversions, as well as the interaction patterns among different bacterial subdivisions in the bioremoval of DBPs.
... Many countries have implemented regulations in which the maximum contaminant level (MCL) in potable water was set to 10 lg L À1 [4]. Many methods for the removal of bromate from potable water have been proposed including ion exchange [5], nanofiltration [6], UV irradiation [7], photocatalytic degradation [8], coagulation with Al 3+ and Fe 3+ [9], chemical reduction with a variety of reducing agents, such as Fe 2+ [10], biological degradation [11], as well as electrochemical reduction on various cathodes12131415. Bromate has been used as a model anion since 1960 by many researchers, in studies regarding the electron transfer to anionic species [16,17]. ...
Article
Full-text available
The electrochemical removal of bromate on a tin cathode has been studied by both electrochemical techniques, such as cyclic voltammetry and chronoamperometry, as well as by steady-state electrolytic experiments. The reduction of bromate in 2M NaCl takes place efficiently at potentials more negative than �1.4V vs. Ag/AgCl and the rate of the reduction displays a maximum at about �1.8 V, then decreases and consequently it increases again as the potential becomes more negative than �1.9 V. The % removal efficiency of bromate displays a maximum (75.6%) at �1.8 V, while the % selectivity of bromide displays a minimum (70.3%) at the same potential.
... Little is known about the long-term effects of human bromate exposure or the behavior of bromate within the natural environment. The current maximum contaminant level (MCL) of bromate in the US and in European countries is set at 10 mg L À1 (3)(4). ...
Article
The feasibility of nano–Al2O3 for bromate removal from aqueous solution was assessed in the present study. Batch sorption experiments were performed to examine the influence of various experimental parameters such as contact time, initial bromate concentration, temperature, and pH on the sorption of bromate on nano–Al2O3. Kinetic data revealed that the uptake rate of bromate was rapid in the beginning and 50% adsorption was completed within 10 min and equilibrium was achieved within 120 min. Pseudo–second–order kinetic model was fitted well with the kinetics of the sorption process. The sorption potential of nano–Al2O3 for bromate removal was ∼6.0 mg g. The adsorption was found to be an endothermic process and data conform to the Langmuir model.Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science and Technology to view the free supplemental file.
... Bromate poses potential health risks and has been verified to induce renal cell tumors, mesotheliomas of the peritoneum, and follicular cell tumors of the thyroid [5], which has been classified as a possible carcinogen by United States Environmental Protection Agency (US EPA) [6]. The specified maximum contaminant level (MCL) of bromate of 10 μg·L −1 for drinking water has already been implemented in the USA, U.K., Canada, Japan and China [7][8][9]. Thus, it is necessary to reduce the concentration level of bromate in drinking water. ...
... Significant bromate reduction has been doi: 10.2166/ws.2008.098 achieved using biologically activated carbon (Kirisits & Snoeyink 1999; Kirisits et al. 2001 Kirisits et al. , 2002), a suspended growth bioreactor (Butler et al. 2005b), a fixed-film bioreactor (Butler et al. 2006), and a hollow fiber membrane biofilm reactor (Downing & Nerenberg 2007). Despite the effectiveness of biological reduction for treating bromate, little is known about the microbial bromate reduction process. ...
Article
Full-text available
Bromate is a carcinogenic disinfection by-product formed from bromide during ozonation or advanced oxidation. We previously observed bromate reduction in a hydrogen-based, denitrifying hollow fiber membrane biofilm reactor (MBfR). In this research, we investigated the potential existence of specialized bromate-reducing bacteria. Using denaturing gradient gel electrophoresis (DGGE), we compared the microbial ecology of two denitrifying MBfRs, one amended with nitrate as the electron acceptor and the other with nitrate plus bromate. The DGGE results showed that bromate exerted a selective pressure for a putative, specialized bromate-reducing bacterium, which developed a strong presence only in the reactor with bromate. To gain further insight into the capabilities of specialized, bromate-reducing bacteria, we explored bromate reduction in a control MBfR without any primary electron acceptors. A grown biofilm in the control MBfR reduced bromate without previous exposure, but the rate of reduction decreased over time, especially after perturbations resulting in biomass loss. The decrease in bromate reduction may have been the result of the toxic effects of bromate. We also used batch tests of the perchlorate-reducing pure culture, Dechloromonas sp. PC1 to test bromate reduction and growth. Bromate was reduced without measurable growth. Based on these results, we speculate bromate's selective pressure for the putative, specialized BRB observed in the DGGE was not growth related, but possibly based on resistance to bromate toxicity.
... Bromate, which can occur as an impurity within sodium hypochlorite (Stanford, et al., 2013) is also formed as a disinfection by-product when ozone is used on waters containing bromide. As such, most approaches to controlling bromate focus on optimisation of the ozonation process, although some success at reducing bromate has been shown with biological filtration (Kirisits, et al., 2002). Iodide is emerging as a concern because of the toxicity associated with iodinated disinfection by-products (see Section 0). ...
Book
Drinking water quality is of key importance to public health, and the provision of safe drinking water has been recognised as one of the greatest technological and public health advances of the last century. The current system of delivering safe water to consumers in the UK is based upon significant investment in infrastructure and performs at an excellent standard at a very low cost. However, the future challenges of climate change, energy efficiency, population growth, and an aging infrastructure mean that the traditional ways of providing safe water may need to change. If we want to achieve 100% compliance with drinking water standards (at point of use) by 2050 we need considerable research and development in this area. We have created a strategic research programme help us achieve this.
... Furthermore, the bromate specified maximum contaminant level (MCL) of 0.01 mg•L −1 for potable water has already been carried out in the Canada, U.K, Japan, China and USA. [7,8]. Hence, lowering the bromate concentration level in potable water become the imminent matter. ...
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The purpose of this study is to investigate the adsorption performance of bromate in water with magnetic ion exchange (MIEX) resin. In batch experiments, various factors affecting bromate adsorption are discussed, including initial solution pH and concentration, adsorption time, natural organic matter, coexistent anions, stirring intensity, adsorbent dosage, bed volume and ion strength. In addition, the main factors affecting adsorption efficiency of bromate are studied by the response surface methodology. Kinetic data and the sorption equilibrium agree well with the pseudo-first-order model and Langmuir, respectively. To sum up, bromate adsorption on the MIEX resin involves physical adsorption and chemisorption. In addition, the saturated sodium chloride solution can be used to effectively regenerate the MIEX resin. MIEX resin has strong adsorption capacity for bromate is shown by a series of experiments and characterizations, which lays a foundation for the practical application of water treatment in the future.
... Consequently, residual DO might have inhibited bromate reducing microorganisms in the raw lake water. In BAC filters, considerable bromate removal was observed in the presence of measured effluent concentrations of DO and nitrate (Kirisits et al., 2002). As the influent DO increased from 2.1 to 3.2 mg/L; the accumulation of nitrite increased, nitrification resulted in less residual DO and the bromate breakthrough continued to decrease. ...
Article
Disinfection in water treatment and reclamation systems eliminates the potential health risks associated with waterborne pathogens, however it may produce disinfection by-products (DBPs) harmful to human health. Potentially carcinogenic bromate is a DBP formed during the ozonation of bromide-containing waters. To mitigate the problem of bromate formation, different physical/chemical or biological reduction methods of bromate have been investigated. Until now, adsorption-based physical method has proven to be more effective than chemical methods in potable water treatment. Though several studies on biological reduction methods have been carried out in a variety of bioreactor systems, such as in biologically active carbon filters and denitrifying bioreactors, the microbiological mechanisms or biochemical pathways of bromate minimization have not been clearly determined to date. Genetic analysis could provide a broader picture of microorganisms involved in bromate reduction which might show cometabolic or respiratory pathways, and affirm the synergy functions between different contributing groups. The hypothesis established from the diffusion coefficients of different electron donor and acceptors, illustrates that some microorganisms preferring bromate over oxygen contain specific enzymes which lower the activation energy required for bromate reduction. In addition, considering microbial bromate reduction as an effective treatment strategy; field scale investigations are required to observe quantitative correlations of various influencing parameters such as pH, ozone dose, additives or constituents such as ammonia, hydrogen peroxide, and/or chloramine, dissolved organic carbon levels, dissolved oxygen gradient within biofilm, and empty bed contact time on bromate removal or reduction.
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As a potent greenhouse gas with a greenhouse warming potential 28 times that of carbon dioxide over a 100-year timescale, methane has been proven to be utilized as electron donor to remove various of contaminants, e.g. nitrate, nitrite, perchlorate, and chromate from contaminated water. However, microbial bromate reduction supported by methane has not been reported so far. Here, a lab-scale membrane biofilm reactor (MBfR) was set up to explore the feasibility of bromate reduction driven by methane under oxygen-limiting condition. Long-term operational performance demonstrated that a complete bromate (BrO3-) reduction to bromide (Br-) could be achieved, with 100% of bromate removal efficiency under a volume loading of 1 mg Br L-1 d-1. Volatile fatty acids (VFAs) were produced in the reactor (ranging from 1.81 to 27.9 mg/L) under oxygen-limiting condition. High-throughput 16S rRNA gene sequencing indicated that Methanosarcina became the only dominate methane-oxidizing microorganism and the abundance of Dechloromonas increased from 0.9% to 18.0% after feeding bromate. It is hypothesized that under oxygen-limiting conditions methane was oxidized into VFAs, which might be used to reduce bromate by dissimilatory bromate-reducing bacteria (likely Dechloromonas). This study offers a potential technology for bromate removal by using the methane-based MBfR.
Chapter
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Ammonia-based strategies are becoming more popular for mitigating bromate formation during the ozonation of drinking water. Biofiltration presents a cost effective alternative to remove biodegradable organic matter and residual ammonia for utilities targeting a free chlorine residual for secondary disinfection. In this study, we investigated the development of nitrification with pilot-scale biological filters using anthracite/sand and GAC/sand filter media. Sampling ports on the column walls allowed us to examine removal of various water quality constituents over the media depth. During these experiments, sample flow did not exceed 5% of the total flow rate through the filter. Ammonia, nitrite, nitrate, carboxylic acids, bromate, and trihalomethanes were monitored throughout the depth of media. Results showed that CAAs were removed in the upper portion of the media bed while the removal of ammonia was more distributed throughout the bed. Full conversion of ammonia to nitrate was observed in each of the filters. Bromate removal was witnessed within the filters but ambient influent concentrations were less than 15 μg/L. THMs removal was experienced within the filter; however, the total THMs concentration was less than 16 μg/L. Ammonia removal was not impacted during filter ripening. 2009 © American Water Works Association WQTC Conference Proceedings. All Rights Reserved.
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Bromate, an inorganic by-product of ozonation, has been classified as a probable human carcinogen. Bromate is difficult to remove by conventional drinking water treatment, but biological removal of bromate under particular water quality conditions has been demonstrated. Eight bromate-reducing microorganisms were spiked to virgin granular activated carbon filters (influent conditions: 2 mg/L dissolved oxygen [DO], 1 mg/L nitrate, 20 mg/L bromate, pH 7.5) that were operated with a 20-min empty bed contact time (EBCT). Once steady state bromate removal was observed (67%), the influent water quality to the filters was perturbed for four days. One filter was subjected to an increased influent DO concentration of 8 mg/L, and the other filter was subjected to an increased influent nitrate concentration of 5 mg/L. During the perturbation, both filters removed 51% of the influent bromate. The filter perturbed by the DO spike showed no significant change in microbial community, and the filter perturbed by the nitrate spike showed a decrease in the operational taxonomic unit (OTU) corresponding to the bromatereducing Acidovorax sp. After the perturbation, the influent composition was returned to 2 mg/L DO and 1 mg/L nitrate. The filter with the DO perturbation showed 48% bromate removal, which was significantly less than the removal observed before the perturbation. The filter with the nitrate perturbation showed 64% bromate removal, which was very similar to the removal observed before the perturbation. © 2006 American Water Works Association Inorganics Workshop All Rights Reserved.
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Contamination of drinking water with bromate (BrO3 ) at levels ranging from 0.4 to 60 μ g L may be found following ozonation of water containing background bromide (Br). Based on rodent studies, bromate is classified as a “possible human” carcinogen, and drinking water standards of 10–25 μ g L are now implemented in many countries. Bromate is highly soluble, stable in water, and difficult to remove using conventional treatment technologies. This has led to investigations into novel removal techniques, but many have not developed beyond laboratory trials. Analytical advances have recently led to detection of bromate contamination within both rivers and groundwater, which has provided an additional requirement for bromate remediation. This review summarizes bromate environmental characteristics and the regulatory situation, and outlines bromate remediation processes, including filtration, ultraviolet irradiation, catalysis, chemical reduction, activated carbon, and biodegradation. These techniques are evaluated for developmental progress in a potable water system and also for potential application within the natural water environment.
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The objective of the current study was to isolate and characterize several bromate-reducing bacteria and to examine their potential for bioaugmentation to a drinking water treatment process. Fifteen bromate-reducing bacteria were isolated from three sources. According to 16S rRNA gene sequencing, the bromate-reducing bacteria are phylogenetically diverse, representing the Actinobacteria, Bacteroidetes, Firmicutes, and α-, β-, and γ-Proteobacteria. The broad diversity of bromate-reducing bacteria suggests the widespread capability for microbial bromate reduction. While the cometabolism of bromate via nitrate reductase and (per)chlorate reductase has been postulated, five of our bromate-reducing isolates were unable to reduce nitrate or perchlorate. This suggests that a bromate-specific reduction pathway might exist in some microorganisms. Bioaugmentation of activated carbon filters with eight of the bromate-reducing isolates did not significantly decrease start-up time or increase bromate removal as compared to control filters. To optimize bromate reduction in a biological drinking water treatment process, the predominant mechanism of bromate reduction (i.e., cometabolic or respiratory) needs to be assessed so that appropriate measures can be taken to improve bromate removal.
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Bromate (BrO3−), an anion with carcinogenic properties, may be present in drinking water when bromide-containing water is ozonated during treatment or when it is present in surface water used as the source. Experiments showed that the concentration of BrO3− was reduced in a denitrifying bioreactor supplemented with ethanol, when NO3− was almost completely removed. At BrO3− concentrations of 25 and 35 μg/l and a temperature of 12°C the removal rates were 0.6 and 0.8 μg l−1 min−1, respectively. Calculations based on bromate concentration profiles in the bioreactor revealed that contact times of 25–50 min will be necessary to obtain concentrations below 3 μg/l, the 10−5 cancer risk level. Furthermore, intensive post treatment of the filtrate is required to remove biomass and excess ethanol applied for complete denitrification. Therefore, bromate removal in a denitrifying bioreactor does not seem to be a realistic option in drinking water treatment. Soil passage under anoxic conditions as occurring during artificial recharge or river bank filtration may enable BrO3−-removal from (ozonated) surface water.
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Ozone has been proposed for water disinfection because it is more efficient than chlorine for killing microbes and results in much lower levels of carcinogenic trihalomethanes than does chlorination. Ozone leads to formation of hypobromous acid in surface waters with high bromine content and forms brominated organic by-products and bromate. The carcinogenicity and chronic toxicity of potassium bromate (KBrO3) was studied in male B6C3F1 mice and F344/N rats to confirm and extend the results of previous work. Mice were treated with 0, 0.08, 0.4, or 0.8 g/L KBrO3 in the drinking water for up to 100 wk, and rats were provided with 0, 0.02, 0.1, 0.2, or 0.4 g/L KBrO3. Animals were euthanatized, necropsied, and subjected to a complete macroscopic examination. Selected tissues and gross lesions were processed by routine methods for light microscopic examination. The present study showed that KBrO3 is carcinogenic in the rat kidney, thyroid, and mesothelium and is a renal carcinogen in the male mouse, KBrO3 was carcinogenic in rodents at water concentrations as low as 0.02 g/L (20 ppm; 1.5 mg/kg/day). These data can be used to estimate the human health risk that would be associated with changing from chlorination to ozonation for disinfection of drinking water.
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In the presence of bromide, ozonation as applied in water treatment results in the formation of bromate, an ion with carcinogenic properties. The reduction of bromate by mixed bacterial populations as well as pure cultures was studied under laboratory conditions. Bromate was reduced to bromide by a mixed bacterial population with and without a preceding nitrate reduction step in an anaerobically incubated medium with ethanol as the energy and carbon source at 20 and 25 deg C. The predominating bacteria isolated from the batches showing bromate reduction were identified as Pseudomonas spp. Strains of Pseudomonas fluorescens reduced BrO(inf3)(sup-) to Br(sup-) but at a much lower rate than the mixed bacterial population did. Nitrate is a preferred electron acceptor for the bromate-reducing bacteria. Bromate reduction did not occur in the presence of NO(inf3)(sup-), and the rate of bromate reduction was at least 100 times lower than the rate of nitrate reduction. Bromate was completely converted to Br(sup-), indicating that intermediates, e.g., BrO(inf2)(sup-), did not accumulate during bromate reduction.
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This article examines the application of biological treatment strategies to current problems of the water industry. The studies focused on the production of biologically stable water, increased disinfectant stability, and reduced formation of disinfection by-products. Results show that biological processes can meet the practical as well as the regulatory requirements of the industry. Este articulo examina la aplicacion de estrategias de tratamiento biologicós a los próblemas actuales de la industria del agua. Los estudios, enfocados en la producción de un agua biológicamente estable, aumentó la estabilidad del desinfectante y redujo la formacion de subproductos. Los resultados demuestran que los procesos biológicos pueden cumplir con los requisites prácticos lo mismo que con las normas regulatorias de la industria.
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Empirical bromate formation models were developed from observed batch ozonation data to simulate the effects of important water quality characteristics and treatment processes on bromate formation. Data generated from true batch ozonation studies with an orthogonal matrix design, served as the base for development of empirical models for bromate formation. The variables examined include pH, initial bromide concentration, alkalinity, ozone dose, ammonia and dissolved organic carbon level. This array of variables was selected to evaluate the effects of important water quality characteristics and treatment processes on the formation of bromate ion during water ozonation. Limited temperature variation data were also generated. Isolation and fractionation of natural organic matter (NOM) by ultrafiltration and reverse osmosis membrane techniques allowed assessment of source water variations and the role of molecular size on bromate formation. Multiple linear regression of logarithmic transformations was used to generate the models. Results obtained from the empirical models indicate that bromate formation is favored at high pH, initial bromide concentration, alkalinity and high ozone dose. On the other hand, increasing DOC and ammonia concentration decreased bromate formation. The models also indicated that NOM isolated from different water sources have a strong influence on bromate formation upon ozonation of model solutions composed of different membrane isolates. Both internal and external validation of the models demonstrated that the bromate models predicted bromate formation well. Finally, the models indicated that acid addition (pH depression) strategies can be used to control bromate formation.
Article
A simulation and verification study assessing the performance of 10 censored data reconstitution methods was conducted to develop guidance for statistical comparisons among very small samples (n < 10) with below detection limit observations in dredged sediment testing. Censored data methods were evaluated for preservation of power and nominal type I error rate in subsequent statistical comparisons. Method performance was influenced by amount of censoring, data transformation, population distribution, and variance characteristics. For nearly all situations examined, substitution of a constant such as one-half the detection limit equaled or outperformed more complicated methods. Regression order statistics and maximum likelihood techniques previously recommended for estimating population parameters from censored environmental samples generally performed poorly in very small-sample statistical hypothesis testing with more than minimal censoring, due to their inability to accurately infer distributional properties and their consequent low power or high type I error rates.
Article
Ozone oxidizes Br- under water treatment conditions to form HOBr. HOBr reacts further with O3, but only in its ionized form, OBr-. OBr- is oxidized not only to BrO3- but also to a species that regenerates Br-. The results are consistent with the following scheme of reactions: (1) O3 + Br- k1 → O2 + OBr-; (2) O3 + OBr- k2 → 2O2 + BR-; (3) 2O3 + OBr- k3 → 2O2 + BrO3-; where k1 = 160 ± 20 M-1 s-1, k2 = 330 ± 60 M-1 s-1, and k3 = 100 ± 20 M-1 s-1 at 20°C. Thus, a catalytic decomposition of O3 via reactions and 2 is observed. The maximum intermediate HOBr concentration is greater the lower the pH. In the presence of organic matter, HOBr reacts to form bromo organics. Thus, more bromoform was produced with humic acid at pH 6.1 than at pH 8.8. The range of conditions conducive to haloform formation is narrower than during chlorination.
Article
The removal of bromate, an inorganic disinfection by-product, by granular activated carbon (GAC) was investigated in this study. Bromate ion removal from water was observed in the presence of virgin and acid-washed outgassed (AWOG) GAC. In a GAC filter with distilled-deionized water, bromate breakthrough occurred slowly whereas bromate breakthrough occurred very quickly in natural water due to the presence of natural organic matter (NOM) and other anions. NOM adsorption decreased bromate reduction, presumably by blocking bromate reduction sites. The use of a biologically active carbon (BAC) filter with ozonated water, as a pretreatment step to remove NOM, only slightly improved bromate reduction in the subsequent fresh GAC filter. Kinetic studies showed that the presence of chloride, sulfate, bromide, and nitrate causes a decrease in the kinetics of bromate reduction by GAC. These anions may occupy ion exchange sites on the carbon, reducing the rate at which bromate can access the reduction sites. However, when the anions were released from the carbon, the bromate reduction rate increased.
Article
This study investigated the feasibility of using granular activated carbon (GAC) to remove bromate ion (BrO3−) from drinking water through a rapid small-scale column test (RSSCT) method and a pilot-scale study. Results from RSSCT tests indicated that the GAC capacity for BrO3− removal was carbon-specific and dependent on the source water quality and empty bed contact time (EBCT). The presence of dissolved organic carbon (DOC) and anions, such as bromide, nitrate, and sulfate, resulted in poor BrO3− reduction. On the other hand, BrO3− removal was improved by increasing EBCT. The reduction capacity of spent GAC could be completely recovered by thermal regeneration. Under RSSCT conditions, the results showed that preloading with natural water significantly decreased the capacity of GAC for BrO3− removal; whereas in the pilot plant study, a GAC column (operating with 20-min EBCT) preloaded for 110 days achieved a BrO3− removal ranging from 57 to 92% for at least 98 days, and the BrO3− amount removed was found to be proportional to the influent BrO3− concentration. These limited data suggest that if suitable GAC is used, GAC performed in the biological mode may achieve a longer bedlife for BrO3− removal.
Article
The biofilm airlift suspension (BAS) reactor can treat wastewater at a high volumetric loading rate combined with a low sludge loading. Two BAS reactors were operated, with an ammonium load of 5 kg N/(m(3) d), in order to study the influence of biomass and oxygen concentration on the nitrification process. After start-up the nitrifying biomass in the reactors gradually increased up to 30 g VSS/L. Due to this increased biomass concentration the gas-liquid mass transfer coefficient was negatively influenced. The resulting gradual decrease in dissolved oxygen concentration (over a 2-month period) was associated with a concomitantly nitrite build-up. Short term experiments showed a similar relation between dissolved oxygen concentration (DO) and nitrite accumulation. It was possible to obtain full ammonium conversion with approximately 50% nitrate and 50% nitrite in the effluent. The facts that (i) nitrite build up occurred only when DO dropped, (ii) the nitrite formation was stable over long periods, and (iii) fully depending on DO levels in short term experiments, led to the conclusion that it was not affected by microbial adaptations but associated with intrinsic characteristics of the microbial growth system. A simple biofilm model based on the often reported difference of oxygen affinity between ammonium and nitrite oxydizers was capable of adequately describing the phenomena.Measurements of biomass density and concentration are critical for the interpretation of the results, but highly sensitive to sampling procedures. Therefore we have developed an independent method, based on the residence time of Dextran Blue, to check the experimental methods. There was a good agreement between procedures.The relation between biomass concentration, oxygen mass transfer rate and nitrification in a BAS reactor is discussed. (c) 1997 John Wiley & Sons, Inc.
Article
Purified respiratory nitrate reductase from Escherichia coli is able to use either reduced viologen dyes or quinols as the electron donor and nitrate, chlorate, or bromate as the electron acceptor. When reduced viologen dyes act as the electron donor, the enzyme follows a compulsory-order, "Theorell-Chance" mechanism, in which it is an enzyme-nitrate complex that is reduced rather than the free enzyme. In contrast, if quinols are used as the electron donor, then the enzyme operates by a two-site, enzyme-substitution mechanism. Partial proteolysis of the cytochrome b containing holoenzyme by trypsin results in loss of cytochrome b and in cleavage of one of the enzyme's subunits. The cytochrome-free derivative exhibits a viologen dye dependent activity that is indistinguishable from that of the holoenzyme, but it is incapable of catalyzing the quinol-dependent reaction. The quinol-dependent, but not the viologen dye dependent, activity is inhibited irreversibly by exposure to diethyl pyrocarbonate and reversibly by treatment with 2-n-heptyl-4-hydroxyquinoline N-oxide. We conclude that the holoenzyme has two independent and spatially distinct active sites, one for quinol oxidation and the other for nitrate reduction.
Article
The objective of this work was to develop a reliable, rugged high-performance liquid chromatographic (HPLC) method for determination of trace levels of bromate (< 10 micrograms/l) in bottled water. HPLC separation was achieved by ion interaction chromatography using a C-18 reversed-phase column and a mobile phase consisting of methanol/water (20:80, v/v) with tetrabutylammonium acetate as the ion interaction reagent. A post-column reaction based on oxidation of o-dianisidine in acidic solution to a product detected at 500 nm provided selective measurement of the oxidants. The limit of detection and the limit of quantitation were 1 and 3 micrograms/l, respectively. Iodate, chlorite, and nitrite were chromatographically separated from bromate and measured by monitoring the post-column reaction. Chloride and chlorate at levels that might be found in bottled water did not interfere with the determination of bromate. Bromate was detected in bottled waters at concentrations up to 40 micrograms/l.
The Effect of Granular Activated Carbon Surface Chemistry on Bromate Reduction
  • Miller
The Effect of Granular Activated Carbon Surface Chemistry on Bromate Reduction
  • J. Miller
  • V.L. Snoeyink
  • S. Harrell