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.     

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 (TOTNH₃) 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.     

Biodegradation of natural and synthetic estrogens by nitrifying activated sludge and ammonia-oxidizing bacterium Nitrosomonas europaea

This report describes the uses of nitrifying activated sludge (NAS) and ammonia-oxidizing bacterium Nitrosomonas europaea to significantly degrade estrone (E1), 17beta-estradiol (E2), estriol (E3), and 17alpha-ethynylestradiol (EE2). Using NAS, the degradation of estrogens obeyed first-order reaction kinetics with degradation rate constants of 0.056 h(-1) for E1, 1.3 h(-1) for E2, 0.030 h(-1) for E3, and 0.035 h(-1) for EE2, indicating that E2 was most easily degraded. Then, we confirmed that E2 was degraded via E1 by NAS. With/without the ammonia oxidation inhibitor, it was observed that ammonia-oxidizing bacteria in conjunction with other microorganisms in NAS degraded estrogens. Using N. europaea, the degradation of estrogens reasonably obeyed zero-order reaction kinetics, and no remarkable difference is present among the four estrogens degradation rates and it was found that E1 was not detected during E2 degradation period. We suggested that E2 was degraded to E1 in NAS could be caused by other heterotrophic bacteria, not by ammonia-oxidizing bacteria.     

Inhalation exposure to THMs from drinking water in south Taiwan

Trihalomethanes (THMs) are important disinfection byproducts (DBPs) in drinking water. To understand the magnitude of exposure to THMs for the people in southern Taiwan, models are used to estimate the inhalation exposure associated with drinking water based on raw water quality. Two parts of models are used in this study, one for estimating THM concentration from raw water quality, and one for estimating inhalation exposure to people. Important raw water quality and operational parameters, including TOC, UV254, pH, temperature, chlorine dosage, and water residence time of a major water treatment plant in south Taiwan were collected. An empirical THM formation model was then employed to predict the THM concentration at consumers' dwellings based on the parameters collected. Differences between the predicted results and experimental data were found to be small, indicating that the model is appropriate. The predicted THM concentration distribution was served as input parameters for the exposure models. Three major scenarios associated with probable inhalation exposure of THMs, including shower, pre- and post-cooking activities, and cooking processes, were considered in the exposure models. The model results show that the mean inhalation exposure of THMs for shower, pre- and post-cooking activities, and cooking processes are 26.4, 1.56, 3.29 micrograms/day, respectively. The total inhalation exposure (summation of the three scenarios) was found to be comparable with that for direct ingestion, indicating that inhalation is an important pathway for THM exposure from drinking water.     

Trihalomethane formation by chlorination of ammonium- and bromide-containing groundwater in water supplies of Hanoi, Vietnam

The occurrence and the fate of trihalomethanes (THMs) in the water supply system of Hanoi City, Vietnam was investigated from 1998 to 2001. The chlorination efficiency, THM speciation, and, THM formation potential (THMFP) was determined in the water works and in tap water. With regard to THM formation, three types of groundwater resources were identified: (I) high bromide, (II) low bromide, and (III) high bromide combined with high ammonia and high dissolved organic carbon (DOC) concentrations. Under typical treatment conditions (total chlorine residual 0.5-0.8 mg/L), the total THM formation was always below WHO, EU, and USEPA drinking water standards and decreased in the order type I > type II > type III, although the THMFP was > 400 micrograms/L for type III water. The speciation showed > 80% of bromo-THMs in type I water due to the noticeable high bromide level (< or = 140 micrograms/L). In type II water, the bromo-THMs still accounted for some 40% although the bromide concentration is significantly lower (< or = 30 micrograms/L). In contrast, only traces of bromo-THMs were formed (approximately 5%) in type III water, despite bromide levels were high (< or = 240 micrograms/L). This observation could be explained by competition kinetics of chlorine reacting with ammonia and bromide. Based on chlorine exposure (CT) estimations, it was concluded that the current chlorination practice for type I and II waters is sufficient for > or = 2-log inactivation of Giardia lamblia cysts. However, in type III water the applied chlorine is masked as chloramine with a much lower disinfection efficiency. In addition to high levels of ammonia, type III groundwater is also contaminated by arsenic that is not satisfactory removed during treatment. N-nitrosodimethylamine, a potential carcinogen suspected to be formed during chloramination processes, was below the detection limit of 0.02 microgram/L in type III water.     

Lake sediments as potential sources of trihalomethane precursors

Trihalomethanes (THMs) form when chlorine reacts with certain naturally-occurring organic molecules (THM precursors) during the disinfection of drinking water. THMs are believed to have significant carcinogenic and mutagenic properties. The elucidation of THM precursor sources is important because source management may lower costs and increase effectiveness of in-plant treatments. This study investigated the importance of lake and reservoir sediments as a THM precursor source.

Sediments collected from littoral and profundal areas of Lake Rockwell Reservoir (Portage County, Ohio) and from a nearby natural lake (East Twin Lake) were kept in the dark for 21 days at 20°C to estimate release rates of THM precursors. All sediments had significant THM precursor releases relative to non-sediment controls. Anaerobic conditions produced significantly less precursors than during an aerobic incubation. Littoral sediment precursor release rate (μg THMs/m²/day) was significantly greater than precursor release rates for lake and reservoir profundal sediments. The importance of sediment THM precursor release relative to other sources is discussed.     

Occurrence, oral exposure and risk assessment of volatile organic compounds in drinking water for Izmir

Concentrations of volatile organic compounds (VOCs) were measured in the drinking water in Province of Izmir, Turkey, and associated health risks due to ingestion of these compounds were investigated using population weighted random samples. A total of 100 houses were visited in different districts of Izmir and drinking water samples were collected from consumers' drinking water source. Questionnaires were administered to one participant in each house to determine demographics and drinking water consumption rates. Oral exposure and risks were estimated for each participant and Izmir population by deterministic and probabilistic approaches, respectively. The four trihalomethane (THM) species (i.e., chloroform, bromodichloromethane, dibromochloromethane, and bromoform), benzene, toluene, p-xylene, and naphthalene were the most frequently detected VOCs with concentrations ranging from below detection limit to 35 microg/l. The risk estimates were found to be less than the values reported in the literature with few exceptions. Noncarcinogenic risks attributable to ingestion of VOCs for Izmir population were negligible, whereas the mean carcinogenic risk estimates for bromodichloromethane and dibromochloromethane were above the de minimis level of one in a million (10(-6)). For all VOCs, the concentrations measured in metropolitan area were greater than those in other districts. All THM species were detected in higher concentrations in tap water, whereas nontap water contained more benzene, toluene, p-xylene, and naphthalene. Therefore, the concentrations of the latter four compounds and associated risks increased with increasing income and education level since bottled water was used in larger proportions within these subgroups. The results of this study showed that oral exposure to drinking water contaminants and associated risks may be higher than the acceptable levels even if the concentrations fall below the standards.     

Disinfection by-product formation after biologically assisted GAC treatment of water supplies with different bromide and DOC content

Chlorination of drinking water in the presence of bromide and dissolved organic carbon (DOC) leads to the formation of brominated and chlorinated disinfection by-products (DBP). The concentration of bromide ions in the raw water is a significant factor in the speciation of DBP formed, and causes shifts in trihalomethane (THM) formation from chlorinated to brominated species. Drinking water treatment techniques that remove organic contaminants without affecting bromide ion concentrations cause increases in the brominated THM. For the present study, three water supplies containing different DOC and ambient bromide concentrations were filtered through biologically assisted granular activated carbon (BGAC). Similar to adsorption and coagulation treatment, this treatment does not remove bromide from drinking water; also, THMFP (trihalomethane formation potential) analysis indicated that the chlorinated effluent contained higher concentrations of brominated THM in comparison to the influent. Although BGAC may increase the brominated THM, which may be more toxic than the chlorinated THM, the overall reduction of THMFP by DOC removal far exceeds this negative change, thereby producing a much less toxic finished drinking water. This work is part of a study to make high DOC surface waters on the Canadian prairie safe and palatable for small volume users (individuals or small communities).     

Formation of carbonaceous and nitrogenous disinfection by-products from the chlorination of Microcystis aeruginosa

Formation of carbonaceous disinfection by-products (C-DBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), chloral hydrate (CH), and nitrogenous disinfection by-products (N-DBPs), including haloacetonitriles (HANs) and trichloronitromethane (TCNM) from chlorination of Microcystis aeruginosa, a blue-green algae, under different conditions was investigated. Factors evaluated include contact time, chlorine dosages, pH, temperature, ammonia concentrations and algae growth stages. Increased reaction time, chlorine dosage and temperature improved the formation of the relatively stable C-DBPs (e.g., THM, HAA, and CH) and TCNM. Formation of dichloroacetonitrile (DCAN) followed an increasing and then decreasing pattern with prolonged reaction time and increased chlorine dosages. pH affected DBP formation differently, with THM increasing, HKs decreasing, and other DBPs having maximum concentrations at certain pH values. The addition of ammonia significantly reduced the formation of most DBPs, but TCNM formation was not affected and 1,1-dichloropropanone (1,1-DCP) formation was higher with the addition of ammonia. Most DBPs increased as the growth period of algal cells increased. Chlorination of algal cells of higher organic nitrogen content generated higher concentrations of N-DBPs (e.g., HANs and TCNM) and CH, comparable DCAA concentration but much lower concentrations of other C-DBPs (e.g., THM, TCAA and HKs) than did natural organic matter (NOM).     

Degradation of aniline and chloroanilines by sunlight and microbes in estuarine water

The relative importance in estuarine water of photolysis and microbial degradation on aniline and a series of chloroanilines (p-chloroaniline, 2,4-dichloroaniline, and 2,4,5-trichloroaniline) was determined. Photolysis was important for all compounds with photo-transformation half-lives in surface estuarine water ranging from 2 to 125 h. Photolysis rates were lower in estuarine water relative to distilled water, which we speculate was due to quenching of excited states by humics. There was no microbial degradation of chloroanilines during short-term incubations (up to 3 days). The half-lives of aniline in estuarine water was 27 and 173 h in the light and dark (microbial), respectively. Photolysis and microbial degradation rate constants decreased in winter. The winter decrease in photolysis rates correlated to a decrease in surface irradiance while the microbial degradation decrease correlated to the temperature decrease. There was rapid microbial degradation of the chloroamilines and aniline photoproducts. The mineralization of photoproducts of chloroanilines was carried out by bacteria, while microbes larger than 3 μm, e.g. algae, were responsible for the bioaccumulation of the compounds.     

Cancer risk assessment from trihalomethanes in drinking water

This study intends to calculate the lifetime cancer risks resulting from intakes of trihalomethanes (THMs) in drinking water based on the presence of each THM species. The slope factors for each THM species are used, combined with exposure model and Monte Carlo simulations, to calculate the cancer risks with consideration of different exposure routes (oral ingestion, inhalation and dermal absorption). The results revealed that the highest risk comes from the inhalation exposure to chloroform during showers, which also dominates the total risk associated with chloroform exposure. For dichlorobromomethane and chlorodibromomethane, inhalation exposure also plays an important role for total risks; however, contribution from the oral consumption cannot be ignored for these two compounds. Bromoform contributes the least cancer risk among the four THM species, with a risk factor two orders of magnitude smaller than the other three THM species. For all of the four THM species, exposure from dermal absorption is not significant when compared with oral ingestion and inhalation exposures. This study also uses the THMs data collected from Taiwan to calculate the cancer risks associated with THM exposures in different areas of Taiwan. Due to the variations of the THMs compositions, it is observed that higher concentrations of total THMs do not necessarily lead to higher cancer risks. Areas with higher bromide concentration in raw water and often with higher total THM concentration may actually give lower cancer risk if the THMs formed shift to bromoform. However, this also leads to the violation of THM standards since bromoform has much higher molecular weight than chloroform. Based on the results of the cancer risks calculated from each THM species, the regulatory issue of the THMs was also discussed.     

Haloacetic acids in drinking water in the United Kingdom

We measured concentrations of haloacetic acids (HAAs) in the water supply in regions covered by three water companies in the UK Approximately 30 samples in each region were obtained for analysis of both THMs and HAAs to assess the levels of HAAs and the relationship between HAAs and THMs, temperature, pH, free and total chlorine. We have found that there is a range of HAA levels in drinking water with the means ranging from 35-95mug/l and a maximum concentration of 244mug/l. In two out of the three regions there was a high correlation between total THMs and total HAAs, but whereas the HAA and THM levels in one of these companies were approximately equal, in another company the HAA levels were 3-4 times higher than the THM levels. In the third region there was no correlation between total THMs and total HAAs even though the average levels were approximately equal. The ratio of total THM and total HAAs levels was significantly correlated with temperature, pH, free and total chlorine. Overall total THM levels are therefore not considered to be a good indicator of HAA levels. Epidemiological studies using total THM levels should be taking this into account in the interpretation of their results, and regulatory authorities when setting water guidelines.     

Haloacetic acids and trihalomethanes in finished drinking waters from heterogeneous sources

Trihalomethanes (THM) and haloacetic acids (HAA) are the most frequent chlorination by-products (CBP) in finished drinking waters. Traditionally, THM have been used as surrogates for CBP although the quantitative association between THM and other CBP is not well established. This problem is addressed in the present study from the analysis of THM and HAA in drinking water samples from four Spanish regions, representing areas with very different CBP composition, e.g. between 86 and 8.0 microg/l of THM and 50-3.0 microg/l of HAA.The resulting dataset exhibit a statistically significant correlation between total THM and HAA (Pearson's correlation coefficient, r(p)=0.815,p<0.0005). Furthermore, specific HAA are highly correlated with specific THM or their combinations. Accordingly, multivariate linear regression analysis of the concentrations observed show that the levels in total and specific HAA can be predicted from the THM content. These results are relevant for epidemiological studies on health effects from CBP exposure since they usually involve comparison of populations consuming waters of very distinct quality.     

Toxicity evaluation of surface water treated with different disinfectants in HepG2 cells

It is well known that water disinfection through chlorination causes the formation of a mixture of disinfection by-products (DBPs), many of which are genotoxic and carcinogenic. To demonstrate the formation of such compounds, a pilot water plant supplied with water from Lake Trasimeno was set up at the waterworks of Castiglione del Lago (PG, Italy). The disinfectants, continuously added to pre-filtered lake water flowing into three different basins, were sodium hypochlorite, chlorine dioxide and peracetic acid, an alternative disinfectant used until now for disinfecting waste waters, but not yet studied for a possible use in drinking water treatment. The aim of this study was to evaluate the formation during the disinfection processes of some toxic compounds that could explain the genotoxic effects of drinking waters. Differently treated waters were concentrated by solid-phase adsorption on silica C(18) columns and toxicity was assessed in a line of human hepatoma cells (HepG2), a metabolically competent cellular line very useful for human risk evaluation. The seasonal variability of the physical-chemical water characteristics (AOX, UV 254 nm, potential formation of THM, pH and temperature) made indispensable experimentation with water samples taken during the various seasons. Autumn waters cause greater toxicity compared to those of other seasons, in particular dilution of the concentrate at 0.5l equivalent of disinfected waters with chlorine dioxide and peracetic acid causes a 55% reduction in cellular vitality while the cellular vitality is over 80% with the all other water concentrates. Moreover it is very interesting underline that non-cytotoxic quantities of the autumnal water concentrates cause, after 2h treatment, a decrease in GSH and a statistically significant increase in oxygen radicals, while after prolonged treatment (24h) cause a GSH increase, without variations in the oxygen radical content. This phenomenon could be interpreted as the cellular adaptation response to an initial oxidative stress.     

Measuring the concentrations of drinking water disinfection by-products using capillary membrane sampling-flow injection analysis

A capillary membrane sampling-flow injection analysis method is presented for selectively measuring the concentrations of total trihalomethanes (THMs) and total haloacetic acids (HAAs) in drinking water. The method is based on the reaction between nicotinamide and THM or HAA species to yield a fluorescent product. Two configurations are presented, one selective for total THMs and another selective for total HAAs. The construction of a capillary membrane sampler is described, and the results of method detection limit, accuracy and precision studies are reported for each method. Interference, selectivity and linearity studies are reported as well as the effect of temperature and ionic strength changes. Drinking water samples were analyzed by each proposed method and the results were compared to USEPA methods 502.2 and 552.3.     

Kinetics and mechanisms of formation of bromophenols during drinking water chlorination: assessment of taste and odor development

Halophenols are often reported as off-flavor causing compounds responsible for medicinal taste and odor episodes in drinking water. To better understand and minimize the formation of 2-bromophenol and 2,6-dibromophenol which have low odor threshold concentrations (OTCs, 30 and 0.5 ng/L, respectively) a kinetic data base for the chlorination and bromination of phenols was established by combination of kinetic measurements and data from literature. Second-order rate constants for the reactions of chloro- and bromophenols with chlorine and bromine were determined over a wide pH range. The second-order rate constants for bromination of phenols are about three orders of magnitude higher than for chlorination. A quantitative structure activity relationship (QSAR) showed a good comparability of second-order rate constants from this study with those published previously for different phenol derivatives. The quantification of product distribution of the formed halophenols demonstrated that chlorine or bromine attack in ortho position is favored with respect to the para position. A kinetic model was formulated allowing us to investigate the influence of chlorine dose and some water quality parameters such as the concentration of phenol, ammonia, bromide and the pH on the product distribution of halophenols. The kinetic model can be applied to optimize drinking water chlorination with respect to phenol-born taste and odor problems. In general, high chlorine doses lead to low concentrations of intermediate odorous chlorophenols and bromophenols. An increase in the ammonia or phenol concentration leads to a higher consumption of HOCl and therefore greater final concentration of intermediate bromophenols. The presence of higher bromide than phenol concentration also facilitates the rapid bromination pathway which leads to further bromination of 2,6-dibromophenol to higher brominated phenols. Laboratory-scale experiments on taste and odor formation due to the chlorination of phenol- and bromide-containing waters have confirmed the trend of the model calculations.     

Formation of disinfection by-products in indoor swimming pool water: the contribution from filling water natural organic matter and swimmer body fluids

The contribution and role of different precursors in the formation of three class of disinfection by-products (DBPs) [trihalomethanes (THMs), haloacetic acids (HAAs), and halonitromethanes (HNMs)] in swimming pool waters were examined using filling waters obtained from five drinking water treatment plant (WTP) effluents and three body fluid analogs (BFAs). BFAs exerted higher chlorine demands as compared to natural organic matter (NOM) in filling waters. BFAs exhibited higher HAA formation potentials than THM formation potentials, while the opposite was observed for the filling water NOM. There was no appreciable difference in the HNM formation potentials of BFAs and filling water NOM. Different components in the BFAs tested exhibited different degree and type of DBP formation. Citric acid had significantly higher THM and HAA yields than other BFA components. The effect of temperature was greater on THM formation, whereas the effect of contact time had more impact on HAA formation. Experiments with filling waters collected from WTP effluents at three different times showed more variability in HAA than THM formation at the WTPs studied.     

Trihalomethanes formation in point of use surface water disinfection with chlorine or chlorine dioxide tablets

In remote or underdeveloped areas, natural disaster emergencies and armed conflict zones, point‐of‐use surface water disinfection with chlorine tablets provides microbiologically safe water, but disinfection by‐products such as trihalomethanes (THMs) are formed. While the health risks from THMs are much less than the risks from consuming microbiologically unsafe water, it is nonetheless desirable to understand and minimise THM formation. We show that THM concentrations in surface water samples from the Northern British Isles disinfected with chlorine tablets increased with contact time, in some cases to significantly exceed EU, US EPA and WHO drinking water guidance values after more than an hour. More stagnant water from ponds and lochs had higher THM formation than river water. Doubling the chlorine tablet dose slightly enhanced THM formation, and passing water through coffee filter paper reduced it. Chlorine dioxide tablets produced minimal amounts of THMs.     

Volatile halogenated hydrocarbons in Belgian drinking waters

A comparative study was carried out to determine levels of volatile halogenated hydrocarbons, especially trihalomethanes (THM) in different Belgian drinking waters, prepared from both ground and surface waters. In addition to examining raw and treated water leaving the production plants, changes in haloform concentration during transport in the distribution system were also studied. Only a slight decrease of haloform concentration after decompression in water towers and reservoirs occurred and was rapidly compensated by on going chlorination by residual free chlorine.Despite of the very different conditions used for chlorination in the plants studied, a fairly clear relation was found between total THM content in the finished waters and TOC-values of the raw waters, indicating that the primary organic load was the determining factor for haloform formation.