Biodegradation of haloacetic acids by bacterial enrichment cultures

Perspectives and understanding on the occurrence, toxicity and abatement technologies of disinfection by-products in drinking water

Disinfection by-products (DBPs) are one of the significant emerging contaminants that have caught the attention of researchers worldwide due to their pervasiveness. Their presence in drinking water, even in shallow concentrations (in levels of parts per billion), poses considerable health risks. Therefore, it is crucial to understand their kinetics to understand better their formation and persistence in the water supply systems. This manuscript demonstrates different aspects of research carried out on DBPs in the past. A systematic approach was adopted for the bibliographical research that started with choosing appropriate keywords and identifying the most relevant manuscripts through the screening process. This follows a quantitative assessment of the extracted literature sample, which included the most productive and influential journal sources, the most widely used keywords, the most influential authors active in the research domain, the most cited articles, and the countries most actively engaged in the research field. Critical observations on the literature sample led to the qualitative assessment, wherein the past and current research trends were observed and reported. Finally, we identified the essential gaps in the available literature, which further led to recommending the course ahead in the research domain. This study will prove fruitful for young and established researchers who are or wish to work in this emerging field of research.

Analysis of rainwater storage and use recommendations: From the perspective of DBPs generation and their risks

As a vital freshwater resource, rainwater is usually stored in water cellars in arid regions to solve the daily drinking water problems of the population. However, the status of disinfection by-products (DBPs) generation in cellar water under intermittent disinfection conditions is unclear. Therefore, we investigated the formation and distribution characteristics of DBPs in cellar water under intermittent disinfection conditions for the first time. The results demonstrated that six categories of DBPs were selected for detection after chlorination, including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), haloacetonitriles (HANs), halonitromethanes (HNMs), and nitrosamines (NAs), among which HAAs, HKs, and HANs were the major DBPs. Only bromoacetic acid (MBAA), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) showed an increasing trend of accumulation as the number of disinfections increased. Meanwhile, the precursor composition was gradually transformed from humic substances to amino acids, and both organic substances were the main precursors of HAAs. The health risk assessment showed that the main carcinogenic and non-carcinogenic risks of cellar water were contributed by NAs and HAAs, respectively, and children are more susceptible to the risks than adults. The best time to drink cellar water is after approximately 12 days of storage, when the total carcinogenic risk is the minimum.

Beneficial role of pre- and post-ozonation in a low rate biofiltration-ultrafiltration process treating reclaimed water

Previous studies have shown that the combination of biological and ozone oxidation processes can achieve a greater performance in treating natural surface water than each process individually. In this work, we designed and tested an ozonation-gravity-driven up-flow slow rate (0.01 m/h) biofiltration-ozonation (O₃-GUSB-O₃) process for the pre-treatment of reclaimed water prior to ultrafiltration (UF), with the aim of producing high quality drinking water and a significantly reduced degree of UF fouling. Results showed that O₃ coupled with GUSB can effectively remove aromatic compounds (∼ 84.8%), dissolved organic carbon (DOC, ∼ 83.4%), and biopolymers in surface water. In addition, post-ozonation greatly contributed to the reduction of the UF membrane fouling (∼ 6 times greater flux). With regard to the disinfection by-product formation potential (DBPFP) of the final treated water, both trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were greatly reduced (86.4% and 84.8% for THMs and HAAs, respectively). The relationship between DBPFP and various spectral indexes revealed that aromatic compounds and amino acids were more likely to generate DBPs during the disinfection stage. Among these, humic substances were more likely to generate THMs, while low molecular weight carboxylate and carbonyl organic compounds were associated with the generation of HAAs. Moreover, the dosage of O₃ during the post-ozonation stage was found to influence directly the generation of DBPs. Overall, this study has conducted a detailed evaluation of a novel multi-ozone biofilter UF process for treating surface water, and the results provide a valuable basis for subsequent studies at larger scale to demonstrate the potential of the treatment process for practical applications.

Biphenyl-degrading Bacteria Isolation with Laser Induced Visualized Ejection Separation Technology and Traditional Colony Sorting

In this work, biphenyl was used as carbon source to enrich microorganisms from polychlorinated biphenyls (PCBs)-contaminated paddy soil samples, and the taxonomic structures in both of the soil samples and the fourth-generation enrichments were examined with high-throughput sequencing. Single cells were isolated from the enrichments via single cell sorting technology named Laser Induced Visualized Ejection Separation Technology (LIVEST) and also traditional single colony sorting, and the genera of the isolates were identified using 16S rRNA sequencing. The results from high-throughput sequencing present that enrichment from generation to generation can considerably change the microbial community. Comparing the two sorting methods, the LIVEST is more time-saving and cell-targeted for microbial resource exploration. Based on the further verification of biphenyl degradation, it was found that some strains belonging to genera Macrococcus, Aerococcus and Metabacillus are capable in degrading biphenyl, which have not been reported yet.

Rapid removal of trace haloacetic acids from drinking water by a continuous adsorption process using graphene oxide

Significant health risks are caused by trace levels of haloacetic acids (HAAs) in drinking water. We used graphene oxide (GO), a high-performance absorbent, to remove monochloroacetic acid (MCAA), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). 31.6%, 27.1% and 30.2% of MCAA, DCAA and TCAA in drinking water could be rapidly removed within 2 min by the interaction of intermolecular hydrogen bonds between GO and HAAs. On the other hand, as a type of weak interaction, intermolecular hydrogen bonds are easy to fracture, which leads to the recovery of GO. The removal efficiency of MCAA, DCAA and TCAA monotonously decreased with increasing pH from 3 to 11. Temperature was not an important influence on the removal efficiency of HAAs, and only affected the interaction of intermolecular hydrogen bonds between GO and HAAs. A continuous adsorption process was used for further improving the removal efficiency of HAAs, and the concentration of total HAAs decreased from 436 to 52.5 μg L^-1 after five adsorption processes. The total contact time was just 2.25 min, which was faster than other reported adsorbents, and total HAAs could be decreased by 88%. The innovative process in this study provides an effective method for application of GO to rapidly remove HAAs in drinking water.

Natural Treatment Systems and Importance of Social Cost Benefit Analysis in Developing Countries: A Critical Review

This review article attempts to analyse the social issues that impact the performance of natural treatment systems (NTSs). An NTS is a decentralised wastewater treatment system found to be appropriate in developing countries due to its affordability and lower technicity. However, if socio-economic and institutional issues of community are ignored then NTSs may turn out to be unsuitable for developing countries. The article also takes a critical view on the extant literature which ignores the social cost of NTSs. The social cost of NTSs may be high as a decentralised system requires the engagement of various governmental agencies, research institutes and the community. The cost of engagement may make NTSs a socio-economically unattractive proposition. The article discusses the variables to be considered for the social cost-benefit analysis. It also discusses the implications of social cost-benefit analysis for appreciating the incentives and net benefits for collective actions at the community level. Social cost-benefit analysis can help overcome the initial difficulty of high financial cost and usher sustainability.

Pyrogenic carbon-promoted haloacetic acid decarboxylation to trihalomethanes in drinking water

Drinking water disinfection by chlorination or chloramination can result in the formation of disinfection byproducts (DBPs) such as haloacetic acids (HAAs) and trihalomethanes (THMs). Pyrogenic carbonaceous matter (PCM), such as activated carbon (AC), is commonly used as an ostensibly inert adsorbent to remove HAAs from water. HAA degradation has been mainly attributed to biological factors. This study, for the first time, revealed that abiotic HAA degradation in the presence of PCM could be important under water treatment conditions. Specifically, we observed complete destruction of Br3AA, a model HAA, in the presence of powder AC at pH 7 within 30 min. To understand the role of PCM and the reaction mechanism, we performed a systematic study using a suite of HAAs and various PCM types. We found that PCM significantly accelerated the transformation of three HAAs (Br3AA, BrCl2AA, Br2ClAA) at pH 7. Product characterization indicated an approximately 1:1 HAA molar transformation into their respective THMs following a decarboxylation pathway with PCM. The Br3AA activation energy (Ea) was measured by kinetic experiments at 15-45 °C with and without a model PCM, wherein a significant decrease in Ea from 25.7 ± 3.2 to 13.6 ± 2.2 kcal•mol-1 was observed. We further demonstrated that oxygenated functional groups on PCM (e.g., -COOH) can accelerate HAA decarboxylation using synthesized polymers to resemble PCM. Density functional theory simulations were performed to determine the enthalpy of activation (ΔH‡) for Br3AA decarboxylation with H3O+ and formic acid (HCOOH). The presence of HCOOH significantly lowered the overall ΔH‡ value for Br3AA decarboxylation, supporting the hypothesis that -COOH catalyzes the C-C bond breaking in Br3AA. Overall, our study demonstrated the importance of a previously overlooked abiotic reaction pathway, where HAAs can be quickly converted to THMs with PCM under water treatment relevant conditions. These findings have substantial implications for DBP mitigation in water quality control, particularly for potable water reuse or pre-chlorinated water that allow direct contact between HAAs and AC during filtration as well as PAC fines traveling with finished water in water distribution systems. As such, the volatilization and relative low toxicity of volatile THMs may be considered as a detoxification process to mitigate adverse DBP effects in drinking water, thereby lowering potential health risks to consumers.

THMs, HAAs and NAs production from culturable microorganisms in pipeline network by ozonation, chlorination, chloramination and joint disinfection strategies

Disinfection is an indispensable process to inactivate pathogens, while unexpected disinfection by-products (DBPs) would also be formed between the reaction of residual disinfectants and microorganisms in the water distribution system (WDS). However, there are few studies referring to the formation of DBPs and DBPs-associated toxicity under various disinfection methods based on microorganisms in the real WDS. In addition, the main contributors of bacterial communities or components that generate DBPs are unclear. In this study, the formation of trihalomethanes (THMs), halo-acetic acids (HAAs), nitrosamines (NAs) from culturable microorganisms in pipeline network by ozonation(O₃), chlorination (Cl₂), chloramination (NH₂Cl) and joint disinfection methods were compared, meanwhile, their calculated toxicities under different oxidation scenarios were also discussed. Moreover, 16S ribosomal ribonucleic acid (rRNA) gene sequencing was used to identify the main microbial communities. The results demonstrated that THMs and HAAs increased with increasing disinfectant dosages, while the quantity of NAs (mainly nitroso dimethylamine (NDMA)) was not significantly related to disinfectant dosages for each disinfection strategy. Chloroform (TCM) and dichloroacetic acid (DCAA) were the dominant THMs and HAAs species, respectively. NDMA existed in the samples before disinfections, which may due to the metabolic activity of microorganisms. Pre-O₃ increased THMs formation during subsequent Cl₂ and NH₂Cl treatment. However, pre-O₃ effectively reduced HAAs produced by subsequent chlorination. O₃/Cl₂ disinfection had the highest DBPs formation potential (DBPFP) (883.6 nM), while its calculated toxicity was similar to that in Cl₂ disinfection treatment. Pseudomonas was the most abundant bacterial genus in biofilm of WDS pipeline. This study can aid in an optimal disinfection strategy for water treatment plants to reduce the toxicity of DBPs caused by biomass in pipelines and ensure water quality safety.

Evidence-based analysis on the toxicity of disinfection byproducts in vivo and in vitro for disinfection selection

Disinfection is a key step in drinking water treatment process to prevent water-borne infections. However, reactions between chlorine, one of the most common disinfectants, and natural organic matter (NOM) often lead to the formation of hazardous disinfection byproducts (DBPs). However, the cytotoxicity of some DBPs is still poorly understood. Such knowledge is critical for proper selection of disinfection processes. We investigated the effects of DBPs on mouse acute liver injury. The exacerbation of liver damage increased with the DBPs concentrations, likely due to the increased hepatic macrophages. Haloacetonitriles (HANs) and haloketones (HKs) are more toxic to Human Hepatocellular (Hep3B) cells than trihalomethanes (THMs). Cytotoxicity of DBPs were governed by the halogen type (brominated DBPs > chlorinated DBPs) and the numbers of halogen atoms per molecule. Then, we used the pilot-scale WDS to study the best conditions for reducing the formation of DBPs. The result showed that the formation of DBPs followed the order: stainless-steel (SS) > ductile iron (DI) > polyethylene (PE) pipe. Higher flowrate promoted the formation of DBPs in all three pipes. The results suggest that the formation of DBPs in chlorine disinfection can be reduced by using PE pipes and low flow rate in water distribution systems (WDS).

Disinfectant residual stability leading to disinfectant decay and by-product formation in drinking water distribution systems: A systematic review

Secondary disinfectants, such as chlorine and chloramine, have been widely applied to minimise microbial risks in drinking water during distribution. Key challenges have included the maintenance of stable concentrations of disinfectant residuals and the control of disinfection by-products that may form as a consequence of residual decay processes. Many factors may influence disinfectant residual stability and the consequential formation of by-products. Thus predictions of disinfectant stability and by-product formation are multifactorial problems, complete with numerous complications of parameter co-dependence and feedback amplification of some key parameters. The aim of this review was to derive an understanding of how disinfectant residual stability in drinking water distribution systems is impacted by various influencing factors such as water quality and operational parameters. Factors known to influence disinfectant stability and by-product formation were critically reviewed. A systematic review method was applied to identify 1809 journal articles published in the two decades from January 1998 to December 2017. From the initial screening, 161 papers were selected for detailed assessment. Important factors were identified to include temperature, water age, piping material, corrosion products, pH, hydraulic condition, disinfectant residual type and dosage and microbial activity. Microbial activity is a particularly complex parameter on which to base predictions since many factors are known to influence the degree and nature of such activity. These include temperature, water age, piping material, corrosion products, nutrients, natural organic matter, hydraulic condition and disinfectant residual type and dosage. Disinfectant types and dosages were found to be among the most important factors. Many knowledge gaps and research needs still remain, including the need for a more complete understanding of the factors that influence the production of nitrogenous disinfection by-products.

Understanding the impact of water distribution system conditions on the biodegradation of haloacetic acids and expression of bacterial dehalogenase genes

The objective of this study is to evaluate the influence of water distribution system conditions (pH, total organic carbon, residual chlorine, and phosphate) on haloacetic acids (HAAs) biodegradation. A series of batch microcosm tests were conducted to determine biodegradation kinetics and collected biomass was used for real time quantitative reverse transcription polymerase chain reaction analyses to monitor how these drinking water distribution system conditions affect the relative expression of bacterial dehalogenase genes. It was observed that tested water distribution system conditions affected HAA biodegradation with different removal efficiencies (0-100%). HAA biodegradation was improved in tested samples with TOC (3 mg/L) and pH 8.5 compared to those of TOC (0 mg/L) and pH 7, respectively. However, slight improvement was observed with the increased PO₄ concentration (3.5 mg/L), and the presence of residual chlorine even at low concentration prohibited biodegradation of HAAs. The observed trend in the relative expression of dehII genes was compatible with the HAA biodegradation trend. Overall relative expression ratio of dehII genes was lower at pH 7, phosphate (0.5 mg/L), and TOC (0 mg/L) in comparison with pH 8.5, phosphate (3.5 mg/L), and TOC (3 mg/L) in the same experimental conditions.

CATALOGIC 301C model - validation and improvement

In Europe, REACH legislation encourages the use of alternative in silico methods such as (Q)SAR models. According to the recent progress of Chemical Substances Control Law (CSCL) in Japan, (Q)SAR predictions are also utilized as supporting evidence for the assessment of bioaccumulation potential of chemicals along with read across. Currently, the effective use of read across and QSARs is examined for other hazards, including biodegradability. This paper describes the results of external validation and improvement of CATALOGIC 301C model based on more than 1000 tested new chemical substances of the publication schedule under CSCL. CATALOGIC 301C model meets all REACH requirements to be used for biodegradability assessment. The model formalism built on scientific understanding for the microbial degradation of chemicals has a well-defined and transparent applicability domain. The model predictions are adequate for the evaluation of the ready degradability of chemicals.

Effects of plumbing systems on human exposure to disinfection byproducts in water: a case study

Disinfection byproducts (DBPs) in water distribution systems (WDS) are monitored for regulatory compliance, while populations are exposed to DBPs in tap water that may be different due to stagnation of water in plumbing pipes (PP) and heating in hot water tanks (HWT). This study investigated the effects of water stagnation in PP and HWT on exposure and risk of DBPs to humans. Trihalomethanes (THMs) in PP and HWT were observed to be 1.1-2.4 and 1.6-3.0 times, respectively, to THMs in the WDS, while haloacetic acids (HAAs) were 0.9-1.8 and 1.2-1.9 times, respectively, to HAAs in the WDS. The chronic daily intakes of DBPs from PP and HWT were 0.6-1.8 and 0.5-2.3 times the intakes from WDS. The cancer risks from PP and HWT were 1.46 (0.40-4.3) and 1.68 (0.35-5.1) times the cancer risks from WDS. The findings may assist in regulating DBPs exposure concentrations.

Disinfection byproduct formation during biofiltration cycle: Implications for drinking water production

The goal of this study was to investigate the potential of biofiltration to reduce the formation potential of disinfection byproducts (DBPs). Particularly, the work investigates the effect of the duration of the filter cycle on the formation potential of total trihalomethanes (TTHM) and five species of haloacetic acids (HAA5), dissolved oxygen (DO), organic carbon, nitrogen and total phosphorous concentrations along with biofilm coverage of the filter media and biomass viability of the attached cells. The study was conducted on a full-scale biologically active filter, with anthracite and sand media, at the Britannia water treatment plant (WTP), located in Ottawa, Ontario, Canada. The formation potential of both TTHMs and HAA5s decreased due to biofiltration. However the lowest formation potentials for both groups of DBPs and or their precursors were observed immediately following a backwash event. Hence, the highest percent removal of DBPs was observed during the early stages of the biofiltration cycle, which suggests that a higher frequency of backwashing will reduce the formation of DBPs. Variable pressure scanning electron microscopy (VPSEM) analysis shows that biofilm coverage of anthracite and sand media increases as the filtration cycle progressed, while biomass viability analysis demonstrates that the percentage of cells attached to the anthracite and sand media also increases as the filtration cycle progresses. These results suggest that the development and growth of biofilm on the filters increases the DPB formation potential.

Seasonal evaluation of the presence of 46 disinfection by-products throughout a drinking water treatment plant

In this work, we studied a total of 46 regulated and non-regulated disinfection by-products (DBPs) including 10 trihalomethanes (THMs), 13 haloacetic acids (HAAs), 6 halonitromethanes (HNMs), 6 haloacetonitriles (HANs) and 11 aldehydes at different points in a drinking water treatment plant (DWTP) and its distribution network. Determining an increased number of compounds and using accurate, sensitive analytical methodologies for new DBPs can be useful to overcome some challenges encountered in the comprehensive assessment of the quality and safety of drinking water. This paper provides a detailed picture of the spatial and seasonal variability of DBP concentrations from raw water to distribution network. Samples were collected on a monthly basis at seven different points in the four seasons of a year to acquire robust data for DBPs and supplementary quality-related water parameters. Only 5 aldehydes and 2 HAAs were found in raw water. Chlorine dioxide caused the formation of 3 new aldehydes (benzaldehyde included), 5 HAAs and chloroform. The concentrations of DBPs present in raw water were up to 6 times higher in the warmer seasons (spring and summer). The sedimentation process further increased their concentrations and caused the formation of three new ones. Sand filtration substantially removed aldehydes and HAAs (15-50%), but increased the levels of THMs, HNMs and HANs by up to 70%. Chloramination raised the levels of 8 aldehydes and 7 HAAs; also, it caused the formation of monoiodoacetic acid, dibromochloromethane, dichloroiodomethane and bromochloroacetonitrile. Therefore, this treatment increases the levels of existing DBPs and leads to the formation of new ones to a greater extent than does chlorine dioxide. Except for 5 aldehydes, the 23 DBPs encountered at the DWTP exit were found at increased concentrations in the warmer seasons (HAAs by about 50% and THMs by 350%).

Electrochemical removal of haloacetic acids in a three-dimensional electrochemical reactor with Pd-GAC particles as fixed filler and Pd-modified carbon paper as cathode

The reductive removal of haloacetic acids (HAAs) in a three-dimensional electrochemical continuous reactor with Pd-granular activated carbon (Pd-GAC) particles as fixed filler and Pd-modified carbon paper (Pd-C) as cathode was studied in this research. Pd-C electrode was prepared from PdCl2 via electrodeposition onto carbon paper. Pd-GAC particles were prepared by the impregnation of Pd(2+) ions onto GAC. Efficient electrocatalytic reduction of HAAs in this reactor was exhibited. Effects of current density, initial HHAs concentration, and hydraulic retention time on the HHAs removal were investigated. Under the current density of 0.3 mA/cm(2), HAAs with initial concentration of 120 μg/L were reduced to be less than 60 μg/L with hydraulic retention time of 20 min. Electron transfer and HAAs diffusion both played an important role in controlling the electro-reduction process under the conditions of current density less than 0.6 mA/cm(2) with an initial HAAs concentration ranging from 120 to 600 μg/L. However, the HAAs diffusion became the primary rate-limiting step when the current density was higher than 0.6 mA/cm(2). The Pd(0) and Pd(2+) species were detected by X-ray photoelectron spectroscopy. The stability of the electrochemical reactor in the reduction removal of HAAs was also exhibited.

Reducing and verifying haloacetic acids in treated drinking water using a biological filter system

This study focused on reducing the haloacetic acid (HAA) concentrations in treated drinking water. HAA has been thought to be one possible nutrient supporting heterotrophic bacteria regrowth in drinking water. In this study, experiments were conducted using a pilot-scale system to evaluate the efficiency of biological filters (BF) for reducing excess HAA concentrations in water. The BF system reduced the total HAA concentration and the concentrations of five HAA species in the water. Dichloroacetic acid (DCAA), monobromoacetic acid (MBAA) and dibromoacetic acid (DBAA) were the three main HAA5 species that were present in the treated drinking water in this investigation. Combined, these three species represent approximately 77% of the HAA5 in the finished water after BF. The verification of the empirical HAA equation for the outlet in the BF system indicated linear relationships with high correlation coefficients. The empirical equation for the HAA5 concentrations in the finished water was established by examining other nutrients (e.g., dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm wavelength (UV254), and ammonia nitrogen) that can reduce pathogenic contamination. These findings may be useful for designing advanced processes for conventional water treatment plants or for managing water treatment and distribution systems for providing high-quality drinking water.

Identification of dichloroacetic acid degrading Cupriavidus bacteria in a drinking water distribution network model

AIMS

Bacterial community structure and composition of a drinking water network were assessed to better understand this ecosystem in relation to haloacetic acid (HAA) degradation and to identify new bacterial species having HAA degradation capacities.

METHODS AND RESULTS

Biofilm samples were collected from a model system, simulating the end of the drinking water distribution network and supplied with different concentrations of dichloroacetic and trichloroacetic acids at different periods over the course of a year. The samples were analysed by culturing, denaturing gradient gel electrophoresis (DGGE) and sequencing. Pipe diameter and HAA ratios did not impact the bacterial community profiles, but the season had a clear influence. Based on DGGE profiles, it appeared that a particular biomass has developed during the summer compared with the other seasons. Among the bacteria isolated in this study, those from genus Cupriavidus were able to degrade dichloroacetic acid. Moreover, these bacteria degrade dichloroacetic acid at 18°C but not at 10°C.

CONCLUSIONS

The microbial diversity evolved throughout the experiment, but the bacterial community was distinct during the summer. Results obtained on the capacity of Cupriavidus to degrade DCAA only at 18°C but not at 10°C indicate that water temperature is a major element affecting DCAA degradation and confirming observations made regarding season influence on HAA degradation in the drinking water distribution network.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first demonstration of the HAA biodegradation capacity of the genus Cupriavidus.

Influence of bacterial extracellular polymeric substances on the formation of carbonaceous and nitrogenous disinfection byproducts

Considering the regulatory presence of residual chlorine in water distribution systems, untreated organic matter may not be the sole contributor to disinfection byproduct (DBP) formation, given the presence of microbial biofilm with extracellular polymeric substances (EPS). This study investigated the influence of bacterial EPS on the formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs), reacting chlorine with Pseudomonas strains that produce different quantities and composition of EPS. When biomass is reacted in excess to chlorine, both C-DBPs and N-DBPs were produced without preference for speciation. However, under an excess of chlorine compared to biomass, increased EPS content led to enhanced formation of DBPs. The DBP yield of haloacetic acids (HAAs) was higher than that of trihalomethanes where dichloroacetic acid was dominant in HAA species. Additionally, chemical composition of EPS influenced the yields of DBPs. The N-DBP yield from P. putida EPS was two times higher than that of P. aeruginosa EPS, which suggested that higher organic nitrogen content in EPS contributes to higher N-DBP yield. Moreover, time-based experiments revealed that DBP formation from biomass occurs rapidly, reaching a maximum in less than four hours. Combined results suggest that bacterial EPS have significant roles in both the formation and fate of DBPs.

Heterotrophic bacteria in drinking water distribution system: a review

The microbiological quality of drinking water in municipal water distribution systems (WDS) depends on several factors. Free residual chlorine and/or chloramines are typically used to minimize bacterial recontamination and/or regrowth in WDS. Despite such preventive measures, regrowth of heterotrophic (HPC) and opportunistic bacteria in bulk water and biofilms has yet to be controlled completely. No approach has shown complete success in eliminating biofilms or HPC bacteria from bulk water and pipe surfaces. Biofilms can provide shelter for pathogenic bacteria and protect these bacteria from disinfectants. Some HPC bacteria may be associated with aesthetic and non-life threatening diseases. Research to date has achieved important success in understanding occurrence and regrowth of bacteria in bulk water and biofilms in WDS. To achieve comprehensive understanding and to provide efficient control against bacteria regrowth, future research on bacteria regrowth dynamics and their implications is warranted. In this study, a review was performed on the literature published in this area. The findings and limitations of these papers are summarized. Occurrences of bacteria in WDS, factors affecting bacteria regrowth in bulk water and biofilms, bacteria control strategies, sources of nutrients, human health risks from bacterial exposure, modelling of bacteria regrowth and methods of bacteria sampling and detection and quantification are investigated. Advances to date are noted, and future research needs are identified. Finally, research directions are proposed to effectively control HPC and opportunistic bacteria in bulk water and biofilms in WDS.

Chlorine residuals and haloacetic acid reduction in rapid sand filtration

It is quite rare to find biodegradation in rapid sand filtration for drinking water treatment. This might be due to frequent backwashes and low substrate levels. High chlorine concentrations may inhibit biofilm development, especially for plants with pre-chlorination. However, in tropical or subtropical regions, bioactivity on the sand surface may be quite significant due to high biofilm development--a result of year-round high temperature. The objective of this study is to explore the correlation between biodegradation and chlorine concentration in rapid sand filters, especially for the water treatment plants that practise pre-chlorination. In this study, haloacetic acid (HAA) biodegradation was found in conventional rapid sand filters practising pre-chlorination. Laboratory column studies and field investigations were conducted to explore the association between the biodegradation of HAAs and chlorine concentrations. The results showed that chlorine residual was an important factor that alters bioactivity development. A model based on filter influent and effluent chlorine was developed for determining threshold chlorine for biodegradation. From the model, a temperature independent chlorine concentration threshold (Cl(threshold)) for biodegradation was estimated at 0.46-0.5mgL(-1). The results imply that conventional filters with adequate control could be conducive to bioactivity, resulting in lower HAA concentrations. Optimizing biodegradable disinfection by-product removal in conventional rapid sand filter could be achieved with minor variation and a lower-than-Cl(threshold) influent chlorine concentration. Bacteria isolation was also carried out, successfully identifying several HAA degraders. These degraders are very commonly seen in drinking water systems and can be speculated as the main contributor of HAA loss.

Performance and biofilm activity of nitrifying biofilters removing trihalomethanes

Nitrifying biofilters seeded with three different mixed-culture sources removed trichloromethane (TCM) and dibromochloromethane (DBCM) with removals reaching 18% for TCM and 75% for DBCM. In addition, resuspended biofilm removed TCM, bromodichloromethane (BDCM), DBCM, and tribromomethane (TBM) in backwash batch kinetic tests, demonstrating that the biofilters contained organisms capable of biotransforming the four regulated trihalomethanes (THMs) commonly found in treated drinking water. Upon the initial and subsequent increased TCM addition, total ammonia nitrogen (TOTNH(3)) removal decreased and then reestablished, indicating an adjustment by the biofilm bacteria. In addition, changes in DBCM removal indicated a change in activity related to DBCM. The backwash batch kinetic tests provided a useful tool to evaluate the biofilm's bacteria. Based on these experiments, the biofilters contained bacteria with similar THM removal kinetics to those seen in previous batch kinetic experiments. Overall, performance or selection does not seem based specifically on nutrients, source water, or source cultures and most likely results from THM product toxicity, and the use of GAC media appeared to offer benefits over anthracite for biofilter stability and long-term performance, although the reasons for this advantage are not apparent based on research to date.

The production and degradation of trichloroacetic acid in soil: results from in situ soil column experiments

Previous work has indicated that the soil is important to understanding biogeochemical fluxes of trichloroacetic acid (TCA) in the rural environment, in forests in particular. Here, the hydrological and TCA fluxes through 22 in situ soil columns in a forest and moorland-covered catchment and an agricultural grassland field in Scotland were monitored every 2 weeks for several months either as controls or in TCA manipulation (artificial dosing) experiments. This was supplemented by laboratory experiments with radioactively-labelled TCA and with irradiated (sterilised) soil columns. Control in situ forest soil columns showed evidence of net export (i.e. in situ production) of TCA, consistent with a net soil TCA production inferred from forest-scale mass balance estimations. At the same time, there was also clear evidence of substantial in situ degradation within the soil ( approximately 70% on average) of applied TCA. The laboratory experiments showed that both the formation and degradation processes operate on time scales of up to a few days and appeared related more with biological rather than abiotic processes. Soil TCA activity was greater in more organic-rich soils, particularly within forests, and there was strong correlation between TCA and soil biomass carbon content. Overall it appears that TCA soil processes exemplify the substantial natural biogeochemical cycling of chlorine within soils, independent of any anthropogenic chlorine flux.

Biodegradation of haloacetic acids by bacterial isolates and enrichment cultures from drinking water systems

Biodegradation is a potentially important loss process for haloacetic acids (HAAs), a class of chlorination byproducts, in water treatment and distribution systems, but little is known about the organisms involved (i.e., identity, substrate range, biodegradation kinetics). In this research, 10 biomass samples (i.e., tap water, distribution system biofilms, and prechlorinated granular activated carbon filters) from nine drinking water systems were used to inoculate a total of thirty enrichment cultures fed monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), or trichloroacetic (TCAA) as sole carbon and energy source. HAA degraders were successfully enriched from the biofilm samples (GAC and distribution system) but rarely from tap water. Half of the MCAA and DCAA enrichment cultures were positive, whereas only one TCAA culture was positive (two were inconclusive). Eight unique HAA-degrading isolates were obtained including several Afipia spp. and a Methylobacterium sp.; all isolates were members of the phylum Proteobacteria. MCAA, monobromoacetic acid (MBAA), and monoiodoacetic acid (MIAA) were rapidly degraded by all isolates, and DCAA and tribromoacetic (TBAA) were also relatively labile. TCAA and dibromoacetic acid (DBAA)were degraded by only three isolates and degradation lagged behind the other HAAs. Detailed DCAA biodegradation kinetics were obtained for two selected isolates and two enrichment cultures. The maximum biomass-normalized degradation rates (Vm) were 0.27 and 0.97 microg DCAA/ microg protein/h for Methylobacterium fujisawaense strain PAWDI and Afipia felis strain EMD2, respectively, which were comparable to the values obtained for the enrichment cultures from which those organisms were isolated (0.39 and 1.37 microg DCAN/microg protein/h, respectively). The half-saturation constant (Km) values ranged from 4.38 to 77.91 microg DCAA/L and the cell yields ranged from 14.4 to 36.1 mg protein/g DCAA.

Detection and enumeration of haloacetic acid-degrading bacteria in drinking water distribution systems using dehalogenase genes

AIMS

To develop a PCR-based tracking method for the detection of a subset of bacteria in drinking water distribution systems capable of degrading haloacetic acids (HAAs).

METHODS AND RESULTS

Published degenerate PCR primers were used to determine that 54% of tap water samples (7/13) were positive for a deh gene, indicating that drinking water distribution systems may harbour bacteria capable of HAA degradation. As the published primer sets were not sufficiently specific for quantitative PCR, new primers were designed to amplify dehII genes from selected indicator strains. The developed primer sets were effective in directly amplifying dehII genes from enriched consortia samples, and the DNA extracted from tap water provided that an additional nested PCR step for detection of the dehII gene was used.

CONCLUSIONS

This study demonstrates that drinking water distribution systems harbour microbes capable of degrading HAAs. In addition, a quantitative PCR method was developed to detect and quantify dehII genes in drinking water systems.

SIGNIFICANCE AND IMPACT OF THE STUDY

The development of a technique to rapidly screen for the presence of dehalogenase genes in drinking water distribution systems could help water utilities determine if HAA biodegradation is occurring in the distribution system.

Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes

The decomposition of two haloacetic acids (HAAs), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), from water was studied by means of single oxidants: ozone, UV radiation; and by the advanced oxidation processes (AOPs) constituted by combinations of O(3)/UV radiation, H(2)O(2)/UV radiation, O(3)/H(2)O(2), O(3)/H(2)O(2)/UV radiation. The concentrations of HAAs were analyzed at specified time intervals to elucidate the decomposition of HAAs. Single O(3) or UV did not result in perceptible decomposition of HAAs within the applied reaction time. O(3)/UV showed to be more suitable for the decomposition of DCAA and TCAA in water among the six methods of oxidation. Decomposition of DCAA was easier than TCAA by AOPs. For O(3)/UV in the semi-continuous mode, the effective utilization rate of ozone for HAA decomposition decreased with ozone addition. The kinetics of HAAs decomposition by O(3)/UV and the influence of coexistent humic acids and HCO(3)(-) on the decomposition process were investigated. The decomposition of the HAAs by the O(3)/UV accorded with the pseudo-first-order mode under the constant initial dissolved O(3) concentration and fixed UV radiation. The pseudo-first-order rate constant for the decomposition of DCAA was more than four times that for TCAA. Humic acids can cause the H(2)O(2) accumulation and the decrease in rate constants of HAAs decomposition in the O(3)/UV process. The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2mgTOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO(3)(-) concentration of 1.0mmol/L.

Characterization of a recombinant thermostable dehalogenase isolated from the hot spring thermophile Sulfolobus tokodaii

A putative dehalogenase, L-HAD(ST), from the thermophile Sulfolobus tokodaii, was cloned and expressed in Escherichia coli. The recombinant enzyme catalyzes the stereospecific dehalogenation of L-2-haloacids with similar levels of activity as its homolog from mesophiles. L-HAD(ST) remains fully active after being incubated for 4 h at 70 degrees C and tolerates extreme pH conditions ranging from 4 to 10. Furthermore, it can be purified conveniently without the usage of any chromatography method. The high expression yield and easy purification procedure make the recombinant dehalogenase an excellent candidate for biotechnological applications.

The formation and fate of chlorinated organic substances in temperate and boreal forest soils

BACKGROUND, AIM AND SCOPE

Chlorine is an abundant element, commonly occurring in nature either as chloride ions or as chlorinated organic compounds (OCls). Chlorinated organic substances were long considered purely anthropogenic products; however, they are, in addition, a commonly occurring and important part of natural ecosystems. Formation of OCls may affect the degradation of soil organic matter (SOM) and thus the carbon cycle with implications for the ability of forest soils to sequester carbon, whilst the occurrence of potentially toxic OCls in groundwater aquifers is of concern with regard to water quality. It is thus important to understand the biogeochemical cycle of chlorine, both inorganic and organic, to get information about the relevant processes in the forest ecosystem and the effects on these from human activities, including forestry practices. A survey is given of processes in the soil of temperate and boreal forests, predominantly in Europe, including the participation of chlorine, and gaps in knowledge and the need for further work are discussed.

RESULTS

Chlorine is present as chloride ion and/or OCls in all compartments of temperate and boreal forest ecosystems. It contributes to the degradation of SOM, thus also affecting carbon sequestration in the forest soil. The most important source of chloride to coastal forest ecosystems is sea salt deposition, and volcanoes and coal burning can also be important sources. Locally, de-icing salt can be an important chloride input near major roads. In addition, anthropogenic sources of OCls are manifold. However, results also indicate the formation of chlorinated organics by microorganisms as an important source, together with natural abiotic formation. In fact, the soil pool of OCls seems to be a result of the balance between chlorination and degradation processes. Ecologically, organochlorines may function as antibiotics, signal substances and energy equivalents, in descending order of significance. Forest management practices can affect the chlorine cycle, although little is at present known about how.

DISCUSSION

The present data on the apparently considerable size of the pool of OCls indicate its importance for the functioning of the forest soil system and its stability, but factors controlling their formation, degradation and transport are not clearly understood. It would be useful to estimate the significance and rates of key processes to be able to judge the importance of OCls in SOM and litter degradation. Effects of forest management processes affecting SOM and chloride deposition are likely to affect OCls as well. Further standardisation and harmonisation of sampling and analytical procedures is necessary.

CONCLUSIONS AND PERSPECTIVES

More work is necessary in order to understand and, if necessary, develop strategies for mitigating the environmental impact of OCls in temperate and boreal forest soils. This includes both intensified research, especially to understand the key processes of formation and degradation of chlorinated compounds, and monitoring of the substances in question in forest ecosystems. It is also important to understand the effect of various forest management techniques on OCls, as management can be used to produce desired effects.

Identification and degradation characterization of hexachlorobutadiene degrading strain Serratia marcescens HL1

A bacterium (strain HL1) capable of growing with hexachlorobutadiene (HCBD) as sole carbon and energy sources was isolated from a mixture of soil contaminated with HCBD and activated sludge obtained from petrochemical plant wastewater treatment plant by using enrichment culture. Biochemical characteristics and phylogenetic analysis based on 16S rDNA sequence indicate that strain HL1 clearly belongs to Serratia marcescens sp. Resting cells of strain HL1 were found to remove HCBD from culture fluids with the concomitant release of chloride ion under aerobic conditions. The ranges of pH value and temperature for satisfactory growth of strain HL1 cells were from 7.0 to 8.0 and 25 to 30 degrees C, respectively. Capability of resting cells to degrade HCBD was induced by HCBD in the culture fluids. HCBD (20mg/l) was removed from culture fluids by resting cells in 4 d without lag phase, but for 50mg/l and 80mg/l HCBD 7 days were needed with lag phase. Growth of strain HL1 cells was inhibited by HCBD at the concentration up to 160mg/l. First order kinetics could be fitted to the biodegradation of HCBD by HL1 cells after lag phase at initial concentrations of 20, 50, and 80mg/l. Strain HL1 also showed strong capacity to degrade chloroprene, trichloroethylene, tetrachloroethylene, and vinyl chloride at solely initial concentration of 50mg/l. Results could offer useful information for the application of strain HL1 in bioremediation or control of HCBD-polluted environment.

Dechlorination of disinfection by-product monochloroacetic acid in drinking water by nanoscale palladized iron bimetallic particle

Nanoscale palladized iron (Pd/Fe) bimetallic particles were prepared by reductive deposition method. The particles were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM), transmission electron microscope (TEM), and Brunauer-Emmett-Teller-nitrogen (BET-N2) method. Data obtained from those methods indicated that nanoscale Pd/Fe bimetallic particles contained alpha-Fe0. Detected Pd to Fe ratio by weight (Pd/Fe ratio) was close to theoretical value. Spherical granules with diameter of 47 +/- 11.5 nm connected with one another to form chains and the chains composed nanoscale Pd/Fe bimetallic particles. Specific surface area of particles was 51 m2/g. The factors, such as species of reductants, Pd/Fe ratio, dose of nanoscale Pd/Fe bimetallic particles added into solutions, solution initial pH, and a variety of solvents were studied. Dechlorination effect of monochloroacetic acid by different reductants followed the trend: nanoscale Pd/Fe bimetallic particles of 0.182% Pd/Fe > nanoscale Fe > reductive Fe. When the Pd/Fe ratio was lower than 0.083%, increasing Pd/Fe ratio would increase dechlorination efficiency (DE) of MCAA. When the Pd/Fe ratio was higher than 0.083%, increasing Pd/Fe ratio caused a decrease in DE. Adding more nanoscale Pd/Fe bimetallic particles to solution would enhance DE. The DE of MCAA decreased as initial pH of solution increased.

Biodegradation of dibromoneopentyl glycol by a bacterial consortium

Dibromoneopentyl glycol (DBNPG) is a brominated flame retardant that is used as an additive during the manufacture of plastic polymers and as a chemical intermediate for other flame retardants. It is classified as not readily biodegradable and based on experimental studies in animals is believed to be a carcinogen. We have demonstrated, to the best of our knowledge for the first time, the complete biodegradation of DBNPG under aerobic conditions. Total organic carbon (TOC) analysis indicates the complete mineralization of DBNPG. DBNPG biodegradation was accompanied by the release of bromide into the medium, probably due to a biological debromination reaction by bacterial consortia. A denaturing gradient gel electrophoresis (DGGE) analysis of PCR amplified 16S rRNA gene was used, to characterize the bacterial consortia involved in DBNPG biodegradation. At least seven bacterial species were found to be involved in this process, among them species with similarity to strains that are known for their dehalogenating ability.

Modeling of trihalomethane cometabolism in nitrifying biofilters

The computer program AQUASIM was used to model biofilter experiments seeded with Lake Austin, Texas mixed-culture nitrifiers. These biofilters degraded four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Apparent steady-state data from the biofilter experiments and supporting batch experiments were used to estimate kinetic parameters for TCM, DBCM and ammonia degradation. Subsequently, the model was verified against other experimental biofilter data. To allow for full-scale simulations, BDCM and TBM rate constants were estimated using data from batch kinetic studies. Finally, the model was used to simulate full-scale filter performance under different filter surface loading rates and THM speciation seen in practice. Overall, total THM removals ranged from 16% to 54% in these simulations with influent total THM concentrations of 75-82microg/L, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality.

Novel aerobic perchloroethylene degradation by the white-rot fungus Trametes versicolor

Perchloroethylene (PCE) is one of the most important groundwater pollutants around the world. It is a suspected carcinogen and is believed to be recalcitrant to microbial degradation. We report here, for the first time, aerobic degradation of PCE by the white rot fungus, Trametes versicolor, to less hazardous products. Aerobic degradation rate of PCE was 0.20 and 0.28 nmol h(-1) mg(-1) dry weight of fungal biomass. Trichloroacetic acid (TCA) was identified as the main intermediate using [2-13C]-PCE as the substrate. Chloride released and TCA produced were stoichiometric with PCE degradation. Our studies using 1 -aminobenzotriazole (ABT), an inhibitor of cytochrome P-450, suggested that a cytochrome P-450 system may be involved in PCE degradation by T. versicolor. These results are of particular interest because TCA production from PCE has not been reported to date in bacteria or fungi.

Mineralisation of 2,6-dichlorobenzamide (BAM) in dichlobenil-exposed soils and isolation of a BAM-mineralising Aminobacter sp

Mineralisation of the groundwater contaminant 2,6-dichlorobenzamide (BAM), a metabolite from the herbicide 2,6-dichlorobenzonitrile (dichlobenil), was studied in soil samples obtained from 39 locations previously exposed to dichlobenil. Rapid BAM mineralisation was detected in samples from six locations with 5.2-64.6% of the added BAM mineralised within 48-50 days. From one location rapid BAM mineralisation was observed in soil samples down to a depth of 2 m below the surface. One location with fast BAM mineralisation showed significant dichlobenil degradation activity with 25.5% of the added dichlobenil being mineralised within 50 days. By inoculating soil showing the fastest mineralisation of BAM into a mineral medium with BAM as the only carbon and nitrogen source an enrichment culture was established. Community analysis based on extracted DNA revealed a change of the bacterial community but without any clear indication of key members within the BAM-mineralising culture. Parallel cultivation resulted for the first time in the isolation of a BAM-mineralising bacterium, identified as an Aminobacter sp.

Electrochemical dechlorination of chloroacetic acids (CAAs) using hemoglobin-loaded carbon nanotube electrode

Hemoglobin (Hb) was immobilized on carbon nanotube (CNT) electrode to catalyze the dechlorination of chloroacetic acids (CAAs), and the electrocatalytic behaviors of the Hb-loaded electrode for the dechlorination of trichloroacetic acid (TCAA) were studied by cyclic voltammetry and constant-potential electrolysis technique. An Hb-loaded packed-bed flow reactor was also constructed for bioelectrocatalytic dechloriantion of CAAs from drinking water. The results showed that the reduced heme of Hb immobilized on CNT electrode was easily regenerated, and Hb exhibited a stable and high activity for reductive dechlorination of CAAs with significant lowering of overpotential. TCAA could be reduced at -0.450 V (vs. saturated calomel electrode (SCE)) with catalysis of Hb-loaded electrode and its dechlorination was stepwise, following the pathway of TCAA-->dichloroacetic acid (DCAA)-->monochloroacetic acid (MCAA)-->acetic acid. It was also found that all CAAs, e.g., TCAA, DCAA and MCAA, could be dechlorinated completely at -0.450 V. The removal of 30.0 mM TCAA and DCAA is ca. 40% and 31%, respectively, with electrolysis for 100 min at -0.600 V (vs. SCE) using the Hb-loaded packed-bed flow reactor. The dechlorination activities of CAAs follow the decreasing order: TCAA>DCAA>MCAA, and the average current efficiency is over 90%.

Degradation of drinking water disinfection byproducts by synthetic goethite and magnetite

Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface. Fe(II), a potent reductant when associated with iron oxide surfaces, can mediate the reduction of halogenated organic compounds. Batch experiments were performed to investigate the kinetics and pathways of the degradation of selected chlorinated disinfection byproducts (OBPs) by Fe(II) in the presence of synthetic goethite and magnetite. Trichloronitromethane was degraded via reduction, while trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldyde hydrate were transformed via both hydrolysis and reduction. Chloroform and trichloroacetic acid were unreactive. Observed pseudo-first-order reductive dehalogenation rates were influenced by DBP chemical structure and identity of the reductant. Fe(II) bound to iron minerals had greater reactivity than either aqueous Fe(II) or structural Fe(II) present in magnetite. For DBPs of structure Cl3C-R, reductive dehalogenation rate constants normalized by the surface density of Fe(II) on both goethite and magnetite correlated with the electronegativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1-trichloropropanone.

Biodegradation of monochloroacetic acid used as a sole carbon and energy source by Xanthobacter autotrophicus GJ10 strain in batch and continuous culture

Batch and continuous mode degradation of monochloroacetic acid used as a sole carbon and energy source in the concentration range of 0.9-48.4 mM by pure culture of Xanthobacter autotrophicus GJ10 was investigated. The substrate was completely degraded in each flask in batch system. Partial substrate inhibition occurred at the concentrations exceeding 25.4 mM. Temporary accumulation of glycolic acid in the medium indicated that dehalogenation was undergoing faster than further utilization of glycolate. Three different carbon substrates were used for inoculum preparation--1,2-dichloroethane, tri-sodium citrate and a nutrient broth. The fastest growth on monochloroacetate occurred for 1,2-dichloroethane-grown inoculum. The assays of haloacid dehalogenase in crude extract indicated that the bacteria grown on 1,2-dichloroethane possessed higher level of the enzyme. The response of the GJ10 culture towards spikes of 20 mM monochloroacetate was tested in 2.5-1 continuously stirred tank fermentor. The substrate was readily utilized within 7-8 h. Continuous degradation of monochloroacetate in the fermentor was demonstrated for monochloroacetate concentration of 20 mM and dilution rate 0.016 h(-1). Quantitative agreement between the amount of monochloroacetate introduced and chloride released was found. The results demonstrated that the strain X. autotrophicus GJ10 might be suitable for biodegradation of monochloroacetate contaminated media.