Organic Disinfection By-products Research Articles

Influence of ultrasound enhancement on chlorine dioxide consumption and disinfection by-products formation for secondary effluents disinfection

Chlorine dioxide (ClO2) has been promoted as an alternative disinfectant because of its high disinfection efficiency and less formation of organic disinfection by-products (DBPs). However, particle-associated microorganisms could be protected during the disinfection process, which decreases the disinfection efficiency or increases the required dosage. Besides, the formation of inorganic disinfection by-products is a significant concern in environment health. Ultrasound (US)-combined disinfection methods are becoming increasingly attractive because they are efficient and environmentally friendly. In this study, US was introduced as an enhancement method to identify its influence on ClO2 demand reduction and to minimize the production of potential DBPs for secondary effluents disinfection. Fecal coliform was used as an indicator, and DBPs, including trichloromethane (TCM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), chlorite (ClO2−), and chlorate (ClO3−), were analyzed to observe the potential DBPs formation. Results show that US pretreatment could reduce half of ClO2 dosage compared with ClO2 disinfection alone for the same disinfection efficiency, and that an input power density of 2.64kJ/L pretreatment with the 1.5mg/L ClO2 was enough to meet the discharge requirement in China (i.e., fecal coliform below 1000CFU/L for Class 1A) for secondary effluent disinfection, and the ClO2− concentration in the disinfection effluent was only 1.37mg/L at the same time. Furthermore, the different effects of US on the two processes (US as pretreatment and simultaneous US/ClO2 disinfection) were also analyzed, including deagglomerating, cell damage, and synergistic disinfection as well as degasing/sonolysis. It was proved that the production of TCM, DCAA, and TCAA was insignificantly influenced with the introduction of US, but US pretreatment did reduce the production of ClO2− and ClO3− effectually. In general, US pretreatment could be a better option for disinfection enhancement methods combined with ClO2 in terms of both disinfection efficiency and disinfection by-product formation.

Effect of seawater intrusion on formation of bromine-containing trihalomethanes and haloacetic acids during chlorination

This study quantified the formation and speciation of halogenated organic disinfection byproducts (DBPs) during chlorination as a function of seawater intrusion by spiking fresh groundwater with 0.1% to 2% seawater by volume. The four chlorine- and bromine-containing trihalomethanes (THM4) and the nine chlorine- and bromine-containing haloacetic acids (HAA9) were the DBPs investigated. The bromide concentration increased from 38μgL−1 in fresh groundwater to 974μgL−1 in 2% seawater, and upon chlorination the concentration of THM4 increased from 43 to 206μgL−1 and the concentration of HAA9 increased from 39 to 75μgL−1. At 0.4% seawater and higher the THM4 concentration exceeded the U.S. EPA maximum contaminant level of 80μgL−1. Although the mass concentration of HAA9 increased by nearly a factor of 2 over the seawater range of 0% to 2%, the mass concentration of the five regulated HAAs (i.e., HAA5) remained approximately constant. This is because HAA5 excludes four bromine-containing species. The increase in mass concentrations of THM4 and HAA9 with increasing seawater intrusion was the result of an increased molar formation of DBP species and a shift from chlorinated species to brominated species.

To add or not to add: The use of quenching agents for the analysis of disinfection by-products in water samples

The formation of disinfection by-products (DBPs) is a public health concern due to their potential adverse health effects. Robust and sensitive methods for the analysis of DBPs, as well as appropriate sample handling procedures, are essential to obtain accurate, precise and reliable data on DBP occurrence and formation. In particular, the use of an appropriate quenching agent is critical to prevent further formation of DBPs during the holding time between sample collection and analysis. Despite reports of decomposition of DBPs caused by some quenching agents, particularly sulphite and thiosulphate, a survey of the literature shows that they are still the most commonly used quenching agents in analysis of DBPs. This study investigated the effects of five quenching agents (sodium sulphite, sodium arsenite, sodium borohydride, ascorbic acid, and ammonium chloride) on the stability of seven different classes of DBPs commonly found in drinking waters, in order to determine the most appropriate quenching agent for the different classes of DBPs. All of the quenching agents tested did not adversely affect the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), and thus are suitable for quenching of disinfectant residual prior to analysis of these DBPs. Ascorbic acid was found to be suitable for the analysis of haloacetonitriles (HANs) and haloketones (HKs), but should not be used for the analysis of chlorite. Sodium arsenite, sodium borohydride, and ascorbic acid were all acceptable for the analysis of haloacetaldehydes (HALs). All of the quenching agents tested adversely affected the concentration of chloropicrin. A ‘universal’ quenching agent, suitable for all groups of DBPs studied, was not identified. However, based on the results of this study, we recommend the use of ascorbic acid for quenching of samples to be analysed for organic DBPs (i.e. THMs, HAAs, HANs, HKs, and HALs) and sodium sulphite for analysis of inorganic DBPs. Our study is the first comprehensive study on the effects of quenching agents on the stability of DBPs involving a wide range of DBP classes and quenching agents.

Effect of quenching time and quenching agent dose on total organic halogen measurement

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competitive adsorption existed between halogenated organic DBPs and the excessive arsenite on the activated carbon. This competitive adsorption effect was pronounced within a quenching time of 15 min. After 15 min of quenching, a large fraction of arsenite might have reacted with some easily-reduced halogenated DBPs to become arsenate, which is partially ionized at pH 2 and less likely adsorbed on the activated carbon. In this case, more halogenated organic DBPs could be adsorbed on the activated carbon, resulting in the measured TOX concentrations to be much closer to the actual one contained in the sample. Second, excessive arsenite might lead to reduction or decomposition of halogenated organic DBPs with a prolonged quenching time (>60 min). Thus, to avoid the negative interferences, the appropriate quenching time should be 15–60 min.

Discharges of produced waters from oil and gas extraction via wastewater treatment plants are sources of disinfection by-products to receiving streams

Fluids co-produced with oil and gas production (produced waters) are often brines that contain elevated concentrations of bromide. Bromide is an important precursor of several toxic disinfection by-products (DBPs) and the treatment of produced water may lead to more brominated DBPs. To determine if wastewater treatment plants that accept produced waters discharge greater amounts of brominated DBPs, water samples were collected in Pennsylvania from four sites along a large river including an upstream site, a site below a publicly owned wastewater treatment plant (POTW) outfall (does not accept produced water), a site below an oil and gas commercial wastewater treatment plant (CWT) outfall, and downstream of the POTW and CWT. Of 29 DBPs analyzed, the site at the POTW outfall had the highest number detected (six) ranging in concentration from 0.01 to 0.09μgL−1 with a similar mixture of DBPs that have been detected at POTW outfalls elsewhere in the United States. The DBP profile at the CWT outfall was much different, although only two DBPs, dibromochloronitromethane (DBCNM) and chloroform, were detected, DBCNM was found at relatively high concentrations (up to 8.5μgL−1). The water at the CWT outfall also had a mixture of inorganic and organic precursors including elevated concentrations of bromide (75mgL−1) and other organic DBP precursors (phenol at 15μgL−1). To corroborate these DBP results, samples were collected in Pennsylvania from additional POTW and CWT outfalls that accept produced waters. The additional CWT also had high concentrations of DBCNM (3.1μgL−1) while the POTWs that accept produced waters had elevated numbers (up to 15) and concentrations of DBPs, especially brominated and iodinated THMs (up to 12μgL−1 total THM concentration). Therefore, produced water brines that have been disinfected are potential sources of DBPs along with DBP precursors to streams wherever these wastewaters are discharged.

Simultaneous Compliance of TOC and Turbidity Related to Pathogen Breakthrough and THMs Control by Enhanced Coagulation

Since discovery of harmful disinfection by products (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs) in chlorinated waters the removal of organic DBPs precursors gained priority in drinking water treatment. Historically, coagulation process was arranged to remove turbidity, typically related to pathogens occurrence, but nowadays it is usually optimized/enhanced for total organic carbon (TOC) reduction. This work dealt with the removal of TOC and turbidity by means of enhanced coagulation process using Al2(SO4)3⋅18 H2O and FeCl3⋅6H2O as coagulants for jar test without pH adjustment according to USEPA procedure. 15% of TOC removal required by USEPA D/DBPs rule (1998) was achieved using 30-50 mg l-1 of both coagulants. On the other hand, for compliance with more stringent MCL for total THMs in Italy (30 μg l-1) higher TOC removal (>30%) which needed of higher coagulants doses (80 mg l-1), was obviously required. Those high coagulant doses were also to be used for the compliance with the turbidity standard (<1NTU).

Investigation of the use of Chlorine Based Advanced Oxidation in Surface Water: Oxidation of Natural Organic Matter and Formation of Disinfection Byproducts

AbstractDisinfection byproduct (DBP) formation during the treatment of raw Colorado River Water (CRW) using aqueous chlorine and ultraviolet (UV) light advanced oxidation processes (AOPs) was investigated. Here, CRW was combined with aqueous chlorine from two distinct sources (electrochemically-generated Mixed Oxidant Solution (MOS) and commercial sodium hypochlorite) and then exposed to ultraviolet C (UV-C) and ultraviolet A (UV-A) light. The impact of the treatment process on the structure of (NOM) in the CRW was examined, as well as the resulting production of various halogenated organic Disinfection By-Products (DBPs). Both AOP conditions tested resulted in destruction of chromophoric components of the NOM, while formation of total amounts of haloacetic acids and trihalomethanes was far below the US EPA regulated maximum contaminant level values for these contaminants, even though the UV and chlorine doses used in these studies were much higher than the typical doses used in an actual treatment process.

Effects of Physicochemical Properties of Nanofiltration Membranes on the Rejection of Small Organic DBP Precursors

AbstractIn this study, two types of commercial nanofiltration (NF) membranes (NF70 and NF270) were chosen to remove four model disinfection by-product (DBP) precursors (resorcinol, phloroglucinol, 3-hydroxybenzoic acid, and tannic acid) with different functional groups. The clean NF membranes were also characterized by physicochemical properties of membrane surface charge (determined by streaming potential measurement), hydrophobicity [determined by contact angle measurement), membrane surface morphology (determined by scanning electron microscopy and atomic force microscope (AFM)], surface roughness (determined by AFM), and surface composition (X-ray photoelectron spectroscopy) to validate the NF rejection mechanisms of the DBP precursors. The filtration experiments of the model DBP precursors were assessed under various pH values (3–10), and the removal efficiencies were good at high pH values for both membranes (84–99% at pH 9 and 89–100% at pH 10). Electrostatic repulsion is the prevailing mechanism f...

Monitoring natural organic matter and disinfection by-products at different stages in two South African water treatment plants

Natural organic matter (NOM) is a complex organic material present in natural surface water. NOM can cause problems during water treatment . most notably the formation of toxic disinfection by-products. This study was undertaken in order to assess the effectiveness of some of the water treatment techniques employed by selected water supply companies in South Africa in dealing with NOM. Total organic carbon (TOC) and ultra violet (UV) absorbance at wavelength of 254 nm were measured and used to calculate specific ultra violet absorbance (SUVA), which was used to determine the changes in NOM concentration throughout the water treatment train. Other parameters measured include pH, turbidity, chemical oxygen demand (COD) and conductivity. Water samples were collected from two water treatment plants in South Africa, namely Sedibeng (Balkfontein) and Midvaal. The overall TOC reduction after the water treatment processes was 33% and 30% at Midvaal and Sedibeng, respectively. SUVA values were generally low (<2 ..mg-1.m-1) indicating the presence of aliphatic compounds and less earomaticityf in NOM of the water samples. Water insoluble ƒA-cyclodextrin (ƒA-CD) polyurethanes were then applied to the water to compare TOC reduction in addition to enormalf water treatment processes, and were found to provide up to 19% additional TOC decrease, and UV absorbance reduction was up to 78%. Results obtained using gas chromatography-mass spectrometry (GC-MS) analysis after chlorination, revealed that the water had the potential to form halomethane compounds with chloroform being the most dominant. Again, water-insoluble ƒA-CD polyurethanes were applied to the water as a treatment to remove trihalomethanes (THMs) and were found to efficiently remove up to 95% of THMs formed during the disinfection step. The treatment processes studied have limited ability in dealing with NOM and are not individually effective in NOM removal. Results obtained indicate that the application of ƒA-CD polyurethanes in addition to the water treatment processes may enhance NOM removal in water and significantly reduce the THMs formed.

Penetration of polar brominated DBPs through the activated carbon columns during total organic bromine analysis

Total organic bromine (TOBr) is a collective parameter representing all the brominated organic disinfection byproducts (DBPs) in water samples. TOBr can be measured using the adsorption-pyrolysis method according to Standard Method 5320B. This method involves that brominated organic DBPs are separated from inorganic halides and concentrated from aqueous solution by adsorption onto the activated carbon (AC). Previous studies have reported that some commonly known brominated DBPs can partially penetrate through the AC during this adsorption step. In this work, the penetration of polar brominated DBPs through AC and ozone-modified AC was explored with two simulated drinking water samples and one chlorinated wastewater effluent sample. Polar brominated DBPs were selectively detected with a novel precursor ion scan method using electrospray ionization-triple quadrupole mass spectrometry. The results show that 3.4% and 10.4% of polar brominated DBPs (in terms of total ion intensity) in the chlorinated Suwannee River fulvic acid and humic acid samples, respectively, penetrated through the AC, and 19.6% of polar brominated DBPs in the chlorinated secondary wastewater effluent sample penetrated through the AC. The ozone-modification of AC minimized the penetration of polar brominated DBPs during the TOBr analysis.

Evaluation and improvement of total organic bromine analysis with respect to reductive property of activated carbon

A collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts in a water sample is total organic halogen (TOX), which can be differentiated as total organic chlorine (TOCl), total organic bromine (TOBr) and total organic iodine. The TOX method involves concentration of organic halogens from water by adsorption onto activated carbon (AC). A previous study showed that a portion of TOCl can be reduced to chloride during the adsorption procedure, which can be minimized by ozonation of the AC. In this study, a portion of TOBr was sometimes found to be reduced by AC to bromide, and the reduction was generally less than that of corresponding TOCl. The results suggested that around 10% of brominated Suwannee River fulvic acid was reduced to bromide. However, some brominated amino compounds (especially glycylglycine, phenylalanine, and cytosine) were found to be more reactive with the AC. For the iodinated compounds studied, the reduction to iodide was not significant. The method for the TOBr measurement was improved by using ozonated AC when reduction occurred on the original AC. The improved method was also evaluated on treated wastewater and swimming pool water samples.

Effect of Reductive Property of Activated Carbon on Total Organic Halogen Analysis

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX can be measured with the adsorption-pyrolysis method based on Standard Method 5320B. This method involves concentration of organic halogens from water by adsorption onto activated carbon (AC) and removal of inorganic halides present on the AC by competitive displacement by nitrate ions. Since AC can also act as a reductant, this work studied whether the reduction of chlorinated DBPs by AC occurs during the TOX measurement, to what extent the reduction affects the measurement of TOX, what type of chlorinated DBPs can be reduced by AC, and whether the method for the TOX measurement can be improved. Initially, chlorinated Suwannee River fulvic acid samples were prepared and pretreated with precipitation/dialysis/ultrafiltration to minimize the chloride levels in the samples. It was found that the fractions of TOX in the precipitated, dialyzed, and ultrafiltered samples that were reduced by AC in 5 min were around 13%, 20% and 24%, respectively. The formation of some N-chloroamino compounds and their reactivity with AC were examined. The results indicate that organic chloramines are one type of DBPs in TOX that could be reduced by AC. It was demonstrated that slight oxidation of AC with ozone basically inhibited its reduction for TOX and meanwhile maintained its adsorption capacity for TOX.

A multi-year survey of organic disinfection by-products in drinking waters of Castilla y León, Spain. The need and difficulty to comply with the legal limit of 2009

This article explains the general difficulties of the Spanish source waters and climatic conditions regarding a control of trihalomethanes (THMs), as reflected by the case of Castilla y León, and how the median values of 75 and 163 microg L(-1) of years 1999 and 2002 gave way to the more moderate of 31 and 47 microg L(-1) of years 2006 and 2007, respectively--both the latter being measured during the warmer season. Particular circumstances such as raw surface water--with frequently high total organic carbon (T.O.C) values--being the source for 80% of population served, the moderate-to-high water temperatures during the warm seasons and the high chlorine dosages frequently applied account for such as high levels. The median global value (n = 98) for raw water T.O.C. was 4.26 mg L(-1) (90th percentile of 9.81 mg L(-1)) and a median T.O.C. removal of 30% was observed during the treatment, but with an enormous variety (a 90th percentile in the order of 70%). Regression analysis associated the variables raw water temperature, prechlorination dosage and raw and finished water T.O.C. with the THMs measured in the finished waters and in the distribution systems. A certain linear correlation exists between THMs and haloacetic acids (HAAs) contents. However, a shift on their profile is noticeable with the temperature of the water, so that above 11.12 degrees C, THMs concentration tends to be higher than that of HAAs, and vice versa.

Evaluation of control strategies for disinfection byproducts for small water supplies using ozone as an alternative disinfection process

Batch ozonation experiments were conducted to investigate the effects of various operating options (i.e. additions of acid, ethanol, ammonium ion, and hydrogen peroxide) on the formation of disinfection byproducts (DBPs) in six different source waters. Formation of bromate, total organic bromines, total aldehydes (the sum of 13 aldehydes) was evaluated, assuming they represent three different types of DBPs during ozonation (i.e. inorganic bromine DBPs, organobromine DBPs, and non-brominated organic DBPs, respectively). Among the tested options, acid addition was found to be the best one to control all the three types of DBPs simultaneously on an ozone exposure basis.

Disinfection By-Products (DBPs) in Drinking Water from Eight Systems Using Chlorine Dioxide

Abstract A study was initiated to determine the presence of organic disinfection by-products (DBPs) in drinking water treated with chlorine dioxide (ClO2). One potential advantage for the use of ClO2 as a disinfectant is the reduced formation of organic DBPs. Generally, water treated with ClO2 produces chlorite and chlorate ions, but there is limited information regarding the presence of halogenated organic DBPs. Eight systems that use chlorine dioxide as part of the water disinfection process were investigated. All systems in this study applied chlorine as a primary or secondary disinfectant in addition to ClO2. To evaluate seasonal and spatial variations, water samples were collected during cold water (February to March 2003) and warm water (July to August 2003) months at five sites for each system: raw water (R, before treatment), treated water (T, after treatment but before distribution), and three points along the same distribution line (D1, D2, D3). Sampling and analysis were conducted according to established protocols. A suite of 27 organic DBPs including haloacetic acids (HAA), trihalomethanes (THM), haloacetonitriles (HAN), haloketones, haloacetaldehydes (HA), chloropicrin, and cyanogen chloride were examined. In addition, the concentration of oxyhalides (chlorite and chlorate ions) and auxiliary parameters were also determined. Chlorite was found in treated (T) and distributed (Dx) waters. The chlorite ion levels decreased along the distribution system (T &amp;gt; D1 &amp;gt; D2 &amp;gt; D3). At T sites, the levels ranged from 10 to 870 µg/L (winter), and from 300 to 1,600 µg/L (summer). Chlorite was not found in treated or distributed water in the one system that used ozone. Chlorate ion levels ranged from 20 to 310 µg/L (winter), and 80 to 318 µg/L (summer). Chlorate levels remained relatively constant throughout the distribution system. THM and eight HAA (HAA8) accounted for approximately 85% of the total DBPs (wt/wt) analyzed, followed by total HA (up to 7%) and HAN (3%). THM in distributed water were found at concentrations between 1.8 and 30.6 µg/L (winter), and 3.3 and 93.6 µg/L (summer). For HAA8, the levels ranged from 13 to 52 µg/L (winter), and 16 to 111 µg/L (summer). Chloral hydrate ranged from 0.2 to 5.2 µg/L (winter), and 0.4 to 12.2 µg/L (summer). The temporal and spatial variations observed in previous studies were confirmed in the current study as well.

Formation of oxidation byproducts from ozonation of wastewater

Disinfection byproduct (DBP) formation in tertiary wastewater was examined after ozonation (O 3) and advanced oxidation with O 3 and hydrogen peroxide (O 3/H 2O 2). O 3 and O 3/H 2O 2 were applied at multiple dosages to investigate DBP formation during coliform disinfection and trace contaminant oxidation. Results showed O 3 provided superior disinfection of fecal and total coliforms compared to O 3/H 2O 2. Color, UV absorbance, and SUVA were reduced by O 3 and O 3/H 2O 2, offering wastewater utilities a few potential surrogates to monitor disinfection or trace contaminant oxidation. At equivalent O 3 dosages, O 3/H 2O 2 produced greater concentrations of assimilable organic carbon (5–52%), aldehydes (31–47%), and carboxylic acids (12–43%) compared to O 3 alone, indicating that organic DBP formation is largely dependent upon hydroxyl radical exposure. Bromate formation occurred when O 3 dosages exceeded the O 3 demand of the wastewater. Bench-scale tests with free chlorine showed O 3 is capable of reducing total organic halide (TOX) formation potential by at least 20%. In summary, O 3 provided superior disinfection compared to O 3/H 2O 2 while minimizing DBP concentrations. These are important considerations for water reuse, aquifer storage and recovery, and advanced wastewater treatment applications.

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60–80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.

Effect of multiple GAC reactivations on disinfection byproduct precursor removal

The objective of this study was to compare the adsorption capabilities of the virgin carbon to the twelve and five times reactivated granular activated carbon (GAC). From a water treatment plant operator's perspective, there were very few practical differences in adsorption among the carbons tested for total organic carbon (TOC) and disinfection byproduct (DBP) precursors. However, some overall trends were observed. The GAC that was regenerated 5 times (R5) generally showed greater DBP precursor adsorption than the other GACs especially at the beginning of the runs. In some cases the carbon that was reactivated 12/13 times (R12 and R13) adsorbed slightly less DBP precursors than the other GACs especially in the latter part of the runs. The virgin (V) carbon performed better than the other GACs relative to DBP precursor removal in the latter part of the runs.

Contribution of brominated organic disinfection by-products to the mutagenicity of drinking water

The activity inducing chromosomal aberrations of the mixture of brominated disinfection by-products (DBPs) was approximately three times higher than that of the chlorinated counterparts for the same hypohalous acid dose. With the combination of chromosomal aberration test and a new analytical technique to differentiate total organic chlorine (TOCl) and total organic bromine (TOBr), it was found that TOBr was correlated to the mutagenicity of chlorinated waters. It was also implied that for a bromide-to-TOC ratio of 0.1 (mg/mg C), brominated DBPs could account for at least 29% of the total toxicity of DBPs formed during chlorination. On the other hand, bromate ion, a major ozonation DBP, was not a major contributor to the activity inducing chromosomal aberrations of the water treated with an ozone/chlorine sequential process. Therefore, ozonation is one possible option to reduce the health risk caused by DBPs even in the presence of bromide.

Riverbank filtration: Effect of ground passage on NOM character

Research was conducted to explore the effect of underground travel on the character of the natural organic matter (NOM) originating from river water sources during riverbank filtration (RBF) at three Midwestern US drinking water utilities. Measurements of biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC) showed significant reductions (50 to 90%) in the biodegradable portion of NOM at two of the sites. Specific UV-absorbance (SUVA) values suggested preferential reduction (26% reduction in SUVA) in UV-absorbing NOM at one of the sites but negligible changes in SUVA were observed at the other two sites. XAD-8 characterization was carried out on the river and well waters to investigate possible changes in the character of the NOM. The distribution of dissolved organic carbon (DOC) between the XAD-8 adsorbing (‘hydrophobic’) and non-adsorbing (‘hydrophilic’) fractions was similar between the river and well waters (40 to 70% hydrophilic and 30 to 60% hydrophobic), indicating no significant, consistent, preferential removal of either fraction upon ground passage. SUVA measurements on the separate XAD-8 fractions similarly showed no significant change during bank filtration. Disinfection by-product (DBP) formation testing was performed on the various fractions, keeping the ratio of chlorine:DOC:bromide constant. DBP formation testing showed no preferential formation between the hydrophobic and hydrophilic fractions in either the river or well waters. While the overall concentrations of organic DBP precursors are effectively reduced during bank filtration, the reductions appear to be largely the result of the reduction in NOM concentration rather than a consistent change in NOM character.