Regulated Disinfection By-products Research Articles

Characterisation of the formation of halobenzoquinone disinfection by-products in typical water sources at different water quality stages

As an emerging class of uncontrolled disinfection by-products, halobenzoquinones (HBQs) are 3 to 4 orders of magnitude more cytotoxic and genotoxic than regulated disinfection by-products.

Toward the Development of an Electromechanical Ion-Specific Conveyer Belt

Bromide (Br−) is ubiquitous both in natural waters and those impacted by anthropogenic activities, such as, the discharge of treated or untreated wastewaters, releases from coal-fired power plants and hydraulic fracturing operations, and sea water intrusion. The development of methods for the extraction and purification of Br−, particularly from Br− -rich brines, is regarded as of great economic interest owed to the uses of bromine in many industrial processes. In fact, the removal of Br- from drinking water is beneficial from a public health perspective, as it can lead to the formation of regulated disinfection byproducts (DBPs) during water treatment. Although various alternatives have recently been proposed to remove halide anions, such as bromide, from drinking water, none of them have proven sufficiently effective for large-scale application (see e.g. Ref. 1).The present contribution describes a strategy for the removal and purification of bromide from an aqueous solution containing chloride in amounts that closely mimic those found in natural brine sources. As will be described, this tactic relies on the selective electrosorption of Br− on Au, an inert metal electrode material from such a synthetic brine, and its subsequent desorption into a second aqueous solution devoid of Br−.The all glass multi compartment cell employed for these experiments ‘shown schematically in the figure above consists of a central cylindrical cup filled with 0.01 HClO4 supporting electrolyte, which houses the reference, RE, and counter electrodes connected on either side to two identical cups of smaller diameter, C1 and C2 are separated from the central cup by glass frits so that diffusion between C1 and C2 is negligible. At the start of a regular experiment, C1 is filled with a solution containing 28 mM KCl and 12.5 mM KBr, the synthetic brine, in the supporting electrolyte, and C2 is filled with only supporting electrolyte. In the initial stage of this protocol, a gold foil is immersed in C1, which together with the RE and CE would form a conventional 3-electrode cell and a potential of 1.3 V vs RHE is then applied to the Au foil using a potentiostat to induce anion adsorption for ca.10 s. which is sufficient for Br-(aq) and Cl-(aq) to achieve their equilibrium coverages under the specific conditions of the experiment, as represented by the blue arrow. Based on the results of independent optical measurements, Br-(aq) would be the predominant ion adsorbed on the Au surface at this high potential. Subsequently, the Au foil is emersed from the solution without disconnecting the potentiostat, immersed into C2, and a potential of 0.2 V applied, which is just positive of the onset of hydrogen evolution but negative enough for adsorbed Br- to fully desorb, as represented by the red arrow. This process is then repeated tens of times, at the end of which the composition of the solution in C2 is analyzed using the methylene blue (MB) spectroscopic method described by Uraisin, et al. (2) to determine specifically Br-(aq), and a slightly modified Mohr’s turbidimetry technique, which employs K2CrO4 as the indicator, to determine the total amount of Br-(aq) and Cl-(aq).Four independent runs involving 50 to 75 sequential transfers were performed in order to assess the efficiency of this process, and found to yield an increase in the Br-(aq) concentration from an initial 30% in C1, up to higher than 75% in C2. Overall, the efficiency of this process can be increased by a corresponding increase in the area of the electrode. Alternatively, one can envision a continuous process involving a segmented electrode in the form of a belt and appropriate potential controls, that would be continuously emersed and immersed into C1 and C2, acting as a virtual ionic conveyer. Various aspects of this unique technology and its prospects for large scale implementation will be discussed. Acknowledgements This work was supported by a grant from NSF, CHE-1412060 References Sanchez-Polo, J. Rivera-Utrilla, E. Sahli, U. von Gunten, Ag-Doped Carbon Aerogels For Removing Halide Ions In Water Treatment, Water Res., 41, 2007,1031-1037Uraisin, T. Takayanagi, M. Oshima, D. Nacapricha, S. Motomizu, Kinetic-Spectrophotometric Method For The Determination Of Trace Amounts Of Bromide In Seawater, Talanta, 68, 2006, 951-956 Figure 1

Overlooked inorganic DBPs in trichloroisocyanuric acid (TCCA) disinfected indoor swimming pool: Evidences from concentration, cytotoxicity, and human health risk

Trichloroisocyanuric acid (TCCA) is a popular disinfectant for swimming pools in China. However, the occurrence and importance of regulated disinfection byproducts (DBPs) in TCCA-disinfected swimming pools are less understood. This study analyzed 12 regulated DBPs (4 trihalomethanes (THMs), 5 haloacetic acid (HAAs), bromate, chlorate, and chlorite) in 85 swimming pool water samples and 17 input tap water samples from one swimming pool for 17 days continuously. Considering water temperature, pH, free chlorine, total chlorine, and urea, most of swimming pool water samples were within the water quality limits for China. Total concentrations of THMs, HAAs, and inorganic DBPs of 20.4–42.2, 82.0–229, and 100–729 μg/L in the swimming pool, and 16.6–28.3, 8.2–12.8, and 64.4–95.6 μg/L in the tap water, indicating inorganic DBPs are the dominant swimming pool and drinking water pollutants. Cancer risk values of regulated DBPs in swimming pools and input tap water are 2.7E-05 and 8.1E-05, respectively, and exceed the US EPA's threshold (1.0E-06). The non-cancer risk is below the US EPA's threshold. Following TCCA disinfection, the concentration and calculated cytotoxicity of regulated DBPs had a 3.6-fold and 1.9-fold increase, respectively. Inorganic DBPs contribute to the calculated concentration and cancer risks of DBPs in swimming pools and tap water at sufficient concentrations warranting regulation. This study provides data on 12 regulated DBPs in TCCA-disinfected indoor swimming pools, highlighting the importance of inorganic DBPs from evidences of concentration, cytotoxicity, and cancer risk for the first time.

Maternal exposure to nitrosamines in drinking water during pregnancy and birth outcomes in a Chinese cohort

Maternal exposure to regulated disinfection by-products (DBPs) during pregnancy has been linked with adverse birth outcomes. However, no human studies have focused on drinking water nitrosamines, a group of emerging unregulated nitrogenous DBPs that exhibits genotoxicity and developmental toxicity in experimental studies. This cohort study included 2457 mother-infant pairs from a single drinking water supply system in central China, and maternal trimester-specific and entire pregnancy exposure of drinking water nitrosamines were evaluated. Multivariable linear and Poisson regression models were used to estimate the associations between maternal exposure to nitrosamines in drinking water and birth outcomes [birth weight (BW), low birth weight (LBW), small for gestational age (SGA) and preterm delivery (PTD)]. Elevated maternal N-nitrosodimethylamine (NDMA) exposure in the second trimester and N-nitrosopiperidine (NPIP) exposure during the entire pregnancy were associated with decreased BW (e.g., β = −88.6 g; 95% CI: −151.0, −26.1 for the highest vs. lowest tertile of NDMA; p for trend = 0.01) and increased risks of PTD [e.g., risk ratio (RR) = 2.16; 95% CI: 1.23, 3.79 for the highest vs. lowest tertile of NDMA; p for trend = 0.002]. Elevated maternal exposure of N-nitrosodiethylamine (NDEA) in the second trimester was associated with increased risk of SGA (RR = 1.80; 95% CI: 1.09, 2.98 for the highest vs. lowest tertile; p for trend = 0.01). Our study detected associations of maternal exposure to drinking water nitrosamines during pregnancy with decreased BW and increased risks of SGA and PTD. These findings are novel but require replication in other study populations.

Pilot Study of Pollution Characteristics and Ecological Risk of Disinfection Byproducts in Natural Waters in Hong Kong.

Increased disinfection efforts in various parts of China, including Hong Kong, to prevent the spread of the novel coronavirus may lead to elevated concentrations of disinfectants in domestic sewage and surface runoff in Hong Kong, generating large quantities of toxic disinfection byproducts. Our study investigated the presence and distribution of four trihalomethanes (THMs), six haloacetic acids (HAAs), and eight nitrosamines (NAMs) in rivers and seawater in Hong Kong. The concentrations of THMs (mean concentration: 1.6 µg/L [seawater], 3.0 µg/L [river water]), HAAs (mean concentration: 1.4 µg/L [seawater], 1.9 µg/L [river water]), and NAMs (mean concentration: 4.4 ng/L [seawater], 5.6 ng/L [river water]) did not significantly differ between river water and seawater. The total disinfection byproduct content in river water in Hong Kong was similar to that in Wuhan and Beijing (People's Republic of China), and the total THM concentration in seawater was significantly higher than that before the COVID‐19 pandemic. Among the regulated disinfection byproducts, none of the surface water samples exceeded the maximum index values for THM4 (80 μg/L), HAA5 (60 μg/L), and nitrosodimethylamine (100 ng/L) in drinking water. Among the disinfection byproducts detected, bromoform in rivers and seawater poses the highest risk to aquatic organisms, which warrants attention and mitigation efforts. Environ Toxicol Chem 2022;41:2613–2621. © 2022 SETAC

Transformation mechanisms of acetaldehyde and its substituted aldehydes into the corresponding nitriles and (N-chloro)amides during chloramination: A computational study.

As an alternative disinfectant to free chlorine, monochloramine reduces the formation of regulated disinfection byproducts (DBPs); however, it also contributes to the formation of highly toxic nitrogenous DBPs (N-DBPs), especially through the aldehyde pathway. The current understanding of aldehyde pathway mechanisms is limited. In this study, the transformation pathways of acetaldehyde and its substituted aldehydes into the corresponding nitriles and (N-chloro)amides during chloramination were investigated using quantum chemical calculations. Consistent with previous studies, 1-chloroamino alcohol first forms in the chloramination of aldehydes and then undergoes competitive dehydration and HCl elimination branch reactions to generate the nitrile and (N-chloro)amide, respectively. Iminol was found to be a key intermediate for (N-chloro)amide formation. Moreover, the results indicated that acetaldehydes substituted with electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) are beneficial to the formation of the respective nitriles and N-chloro-amides, while those substituted with conjugated groups (CGs) are favourable for both. Based upon the above results, in addition to acetaldehyde, other aldehydes, such as propionaldehyde, glycolaldehyde, 3-butenal, and phenylacetaldehyde, which are the α-H of acetaldehydes substituted with -CH3, -OH, -CH=CH2, and -C6H5 groups, respectively, are potential precursors of toxic nitriles and (N-chloro)amides during chloramination. Thus, more attention should be given to these aldehydes. The findings of this work are helpful for further understanding the aldehyde pathway mechanisms and predicting potential precursors of toxic nitriles and (N-chloro)amides during chloramination.

A new chloramine recovery method in nitrifying water without “chlorine burn”

A better alternative to breakpoint chlorination (BPC) or “chlorine burn” to recover from nitrification is proposed. The BPC involves adding chlorine to achieve Cl/N mass ratios more than 7.5 g-Cl2/g-NH4+-N to convert to free chlorinated system. Thus, it is operationally complex and increases the chance of the formation of regulated disinfection by-products (DBPs). Reverting the system back to (mono)chloraminated system is also operationally complex. All these processes require informing public and disruption to service. We tested three Cl/N mass ratios (5.5:1, 7.5:1, 10:1) and three predetermined reaction times (breakpoint reaction time). After the breakpoint reaction time, the samples were rechloraminated (2.5 mg/L at a Cl/N mass ratio of 4.5:1) twice. The second rechloramination was carried out when chloramine had reached 1.0 mg/L. The improvement was evaluated based on the ability of the method to improve chloramine stability, suppress nitrification, and reduce active bacterial cells. Results showed a Cl/N ratio of 5.5:1 (a new method) followed by two rechloramination doses achieved the same improvement as the traditional Cl/N ratio of 10:1 and one rechloramination. Major factor controlling the effectiveness of the new method relies on the ability of the disinfectant to deactivate chloramine-decaying proteins present in nitrified water. The new method does not need the conversion to a free chlorinated system and thus significantly minimises the operational complexity, disruption to service and potential to form DBPs. It offers a potentially novel solution but needs optimisation and testing in a continuous flow system.

Superfast degradation of micropollutants in water by reactive species generated from the reaction between chlorine dioxide and sulfite

Chlorine dioxide (ClO2) is used as an oxidant or disinfectant in (waste)water treatment, whereas sulfite is a prevalent reducing agent to quench the excess ClO2. This study demonstrated that seven micropollutants with structural diversity could be rapidly degraded in the reaction between ClO2 and sulfite under environmentally relevant conditions in synthetic and real drinking water. For example, carbamazepine, which is recalcitrant to standalone ClO2 or sulfite, was degraded by 55%–80% in 10 s in the ClO2/sulfite process at 30-µM ClO2 and 30-µM sulfite concentrations within a pH range of 6.0–11.0. Results from experiments and a kinetic model supported that chlorine monoxide (ClO·) and sulfate radicals (SO4·–) were generated in the ClO2/sulfite process, while hydroxyl radical generation was insignificant. Apart from radicals, dichlorine trioxide (Cl2O3) was generated and largely contributed to micropollutant degradation, supported by experimental results using stopped-flow spectrometry and quantum chemical calculations. The impacts of pH, sulfite dosage, and water matrix components (chloride, bicarbonate, and natural organic matter) on micropollutant abatement in the ClO2/sulfite process were evaluated and discussed. When treating the real potable water, the concentrations of organic (five regulated disinfection byproducts) and inorganic byproducts (chlorite and chlorate) formed in the ClO2/sulfite process were all below the drinking water standards. This study disclosed fundamental knowledge advancements relevant to the reaction mechanisms between ClO2 and sulfite, and highlighed a novel process to abate micropollutants in water and wastewater.

Optimize Water Treatment Aeration Processes With Real‐Time THM Data

Trihalomethanes (THMs), the most common type of regulated disinfection byproducts (DBPs), can be a challenge for water utilities. A utility that fails to reduce the presence of THMs once they've been created risks violating regulatory compliance and jeopardizing public health. Online THM analyzers were recently installed at the City of San Luis Obispo, Calif., water treatment plant to monitor water quality in real time.

Total organic halogen in two drinking water supply systems: Occurrence, variations, and relationship with trihalomethanes

The spatiotemporal presence of overall disinfection by-products (DBPs) in two full-scale drinking water supply systems (DWSSs) were investigated using quantification of total organic halogen (TOX). The relationships of TOX with water quality parameters (especially the most regulated DBPs, trihalomethanes (THMs)) were also evaluated. The TOX levels ranged between 2.6 and 70.3 μg Cl/L and between 46.6 and 205.9 μg Cl/L in raw water and distribution water, respectively. The TOX concentration in water increased by an average of nine times after water treatment and varied slightly during distribution, suggesting that TOX in drinking water was mainly formed during chlorination disinfection rather than distribution. No clear seasonality in TOX level was observed. Positive correlations were found between raw water dissolved organic carbon (DOC) with an increase in TOX in treated water and between DOC level with TOX content in distributed water, emphasizing a key role of organics in TOX formation. Chloroform (TCM) was the dominant THM, followed by bromodichloromethane (BDCM) in the drinking water, and the levels of the other two measured THMs (dibromochloromethane and bromoform) were negligible. THM2 (sum of TCM and BDCM) made up average of 18% of the TOX, and was weakly correlated with TOX content (rs = 0.321; P < 0.05), implying that THM is not a suitable surrogate measure for TOX in drinking water. This study provides basic data on the occurrence and variation of TOX within conventional DWSSs and highlights the importance of using TOX measurements to obtain more accurate information about DBP occurrence, for exposure assessment and regulatory determination.

Removal of disinfection by-product precursors by Al-based coagulants: A comparative study on coagulation performance

Coagulation is well-established for controlling regulated disinfection by-products (DBPs), but its effectiveness for controlling unregulated DBPs remains unclear. The efficiency of coagulation in controlling unregulated DBPs requires clarification owing to their relatively high toxicity. In this study, three Al-based coagulants, aluminum sulfate (Alum), polyaluminum chloride (PAC), and a novel type of covalently bond hybrid coagulant (CBC, synthesized using AlCl3) were selected, and the coagulation performance of these Al-based coagulants in controlling DBPs and DBP-associated toxicity was compared over 5 classes of DBPs, including trihalomethanes, haloacetic acids, haloacetaldehydes, haloacetonitriles, and halonitromethanes. The results showed that Alum was the least efficient in removing DBP precursors among the three coagulants. The effectiveness of CBC and PAC for DBP control varied with the characteristics of source waters. CBC had an advantage in water with a low content of humic acids, and reduced DBP concentration and DBP-associated toxicity by 47% and 25%, respectively. For water rich in aromatic organics, CBC might serve as DBP precursors at a high-required dosage, suggesting that a trade-off between enhanced DBP control and serving as DBP precursors should be considered for CBC coagulation; PAC achieved the most reduction in DBP concentration and DBP-associated toxicity by 50% and 34%, respectively.

Effects of harmful algal blooms on regulated disinfection byproducts: Findings from five utility case studies

AbstractDuring a cyanobacterial harmful algal bloom (HAB) event, drinking water treatment systems face the challenge of balancing acute and chronic health risks by treating the potentially toxin‐producing HAB and simultaneously managing for disinfection byproduct (DBP) formation. To explore the relationship between HAB events and DBP formation, a unique full‐scale study, including paired source water and finished water monitoring, was conducted at five drinking water utilities with HAB‐impacted source waters. Results confirm bench‐scale findings that HAB events in source water contribute to increases in DBP precursors. However, unlike results from laboratory studies, source water HAB‐related parameters and finished water DBPs were not consistently correlated at the five study utilities. These different outcomes suggest regulated DBP formation in utilities with HAB‐impacted source water is complex and influenced by a variety of site‐specific conditions, including source water conditions and data available for operational decision‐making, timing of treatment adjustments, and key operational choices.

Effectiveness of peracetic acid and EarthTec QZ for controlling zebra and quagga mussels in drinking water treatment plants on Lake Ontario

Abstract Prechlorination is the most common strategy for zebra and quagga mussel control in drinking water treatment plant intakes in the Great Lakes region. Although effective and inexpensive, chlorine can form regulated disinfection byproducts. Two potential alternatives to prechlorination were evaluated for mussel control: peracetic acid (PAA) and EarthTec QZ, a copper-based product. Pilot-scale experiments were conducted to test EarthTec QZ for veliger control and to evaluate the efficiency of PAA and EarthTec QZ for adult mussel control. EarthTec QZ doses of 30, 60, and 120 μg/L as copper ions demonstrated dose-dependent veliger control at 12 °C. PAA doses of 5, 10, and 25 mg/L were effective for adult mussel control at the low water temperatures tested (4 °C). Results from this study indicate that PAA and EarthTec QZ may be an alternative to prechlorination.

Regulated disinfection byproduct formation over long residence times

Design and operation of drinking water treatment plants and associated distribution systems with long residence times are complicated by the formation of regulated disinfection byproducts (DBPs), comprised of total trihalomethanes (TTHM) and five haloacetic acids (HAA5). Treated water dissolved organic carbon (DOC) concentrations, the unit processes required to meet those DOC concentrations, and disinfection strategies (e.g., booster chlorination) are the primary design and operational considerations that can require extensive testing or modeling to determine. In this study, twelve different treated drinking waters were generated at the bench-scale using ferric chloride coagulation and granular activated carbon adsorption from four parent raw waters collected from the San Juan River representing spring runoff, monsoon, and low flow events. Treated drinking waters with DOC concentrations of 0.9, 1.4, and 1.9 mg/L were tested for regulated DBP formation under simulated distribution system (SDS) conditions over residence times as long as 56 days and compared to 7-day formation potential (FP) testing. SDS free chlorine concentrations were maintained between 0.2 and 1.0 mg/L as Cl2 through periodic booster chlorination. Maximum SDS TTHM and HAA5 concentrations were 0.208 and 0.074 mg/L, respectively, with formation consistently varying by approximately ±20% across the four different parent raw waters despite having been treated to the same three DOC concentrations. An average of four existing TTHM models consistently underpredicted TTHM formation by approximatively 20%. Long considered a conservative measure of DBP formation, FP testing also underpredicted SDS DBP formation at 56 days by approximately 40% on average. The DBP testing approach presented in this study allowed for the development of several significant linear relationships for predicting DBP concentrations based on treated water ultraviolet light absorbance at 254 nm, water temperature, and cumulative free chlorine demand.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO2), ozone (O3), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV254) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV254 abatement ranked in the order O3 > Mn(VII) > Fe(VI)/ClO2, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO2 > Fe(VI) > O3 and two phases were observed. At low specific ClO2, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV254 compared to the EDC was observed (~ 8% EDC abatement per 1% UV254 abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV254 and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV254 (~ 0.9–1.2% EDC abatement per 1% UV254 abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O3 abated the relative UV254 more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO2 and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O3 pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants, trihalomethane formation was poorly correlated with both EDC and UV254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV254 measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.

Predicting unregulated disinfection by-products in small water distribution networks: an empirical modelling framework.

Disinfection is used to deactivate pathogens in drinking water. However, disinfectants react with natural organic matter present in water to form disinfection by-products (DBPs). While a few of these DBPs have been studied extensively and are regulated in many countries, new unregulated DBPs (UR-DBPs) have also recently been identified in drinking water. The UR-DBPs are considered to be more toxic than regulated DBPs (R-DBPs). To understand the occurrence of UR-DBPs in a water distribution network (WDN), this research presents an approach to predicting the behaviour of emerging UR-DBPs such as dichloroacetonitrile (DCAN), trichloropropanone (TCP), and trichloronitromethane (TCNM) in WDNs. Water quality data, generated by sampling and laboratory analysis of 12 small communities, was used to develop predictive models. A framework was also proposed alongside the predictive models to estimate the concentration of emerging UR-DBPs under limited water quality sampling information. Moreover, the relationship between emerging UR-DBP concentrations and their identified predictors was further observed and evaluated by developing contour profiles. DCAN and TCP predictive models have coefficient of determination (R2) > 85%, whereas for TCNM model, the R2 was > 65%. Water quality parameters including water temperature, turbidity, conductivity, and dissolved organic carbon concentrations were identified as key predictors. Similarly, trichloroacetic acid and bromodichloromethane were identified as key predictors among DBP families, to predict the occurrence of emerging UR-DBPs. Developed models and relationships between the UR-DBPs and predictors can help water utilities and regulators to manage the occurrence of UR-DBPs in small WDNs.

Trihalomethane precursors: Land use hot spots, persistence during transport, and management options

To meet drinking water regulations, rather than investing in costly treatment plant operations, managers can look for ways to improve source water quality; this requires understanding watershed sources and fates of constituents of concern. Trihalomethanes (THMs) are one of the major classes of regulated disinfection byproducts, formed when a specific fraction of the organic carbon pool—referred to as THM precursors—reacts with chorine and/or bromine during treatment. Understanding the source, fate, timing and duration of the organic compounds that react to form THMs will allow identification of targeted and effective management actions. In this study we evaluated THM precursor contributions from multiple land use categories and hydrologic contexts, including novel data for urban land uses that demonstrate strong potential to release water with high THM formation potential (THMFP; median 618 μg L−1): greater than storm runoff integrated across a mixed-use (1/3 natural, 2/3 agricultural) watershed (median 460 μg L−1), irrigation runoff from agricultural systems (357 μg L−1), or runoff from a natural forested (median 123 μg L−1) and shrubland/grassland (median 259 μg L−1) watersheds. While individual storm events released high THM precursor concentrations over short periods, dry season agricultural irrigation as well as urban landscapes have the potential to release water high in THM precursors for several months. Experimental bioassays and sampling along 333 miles of the California Aqueduct confirmed bioavailability and photooxidation potential of less than 10% for THM precursors, suggesting that rivers with residence times of days to weeks may act as THM precursor conduits, shuttling THM precursors from hundreds of miles away to drinking water intakes with minimal degradation. This finding has considerable implications for water managers, who may therefore consider THM precursor management strategies that target even sources located far upstream.

Effects of ozonation on halogenated acetaldehydes and trihalomethanes formation: Strategy of process control for a full-scale plant

Ozonation provides several advantages during the drinking water treatment process, including controlling the formation of regulated disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). However, ozonation can lead to the formation of bromate and unregulated halogenated acetaldehydes (HALs). In order to better understand the effects of ozonation on the formation and speciation of different DBPs and on the quality of drinking water, high-frequency water quality monitoring was conducted in a Canadian full-scale drinking water treatment plant (DWTP). We collected samples during a period when the DWTP underwent changes to their ozonation strategies: applying only post-ozonation (Post-O3) and only pre-ozonation (Pre-O3), and a transition period comprising two-stage (pre- and post-) ozonation and no-ozonation. In this case study, four different phases of disinfection were examined chronologically: Phase 1 (P1), Post-O3 with Post-Cl2; Phase 2 (P2), Pre-O3 and Post-O3 with Post-Cl2; Phase 3 (P3), Post-Cl2 only; Phase 4 (P4), Pre-O3 with Post-Cl2. In finished water, we observed that ozonation significantly effected the removal of total nitrogen (TN) and aromatic content (UV-254, SUVA) only, but not the removal of TOC. Total ozone dosage (Pre-O3 + Post-O3) appeared to be a contributing factor for HAL formation. Compared to non-ozonated water (chlorination only), concentrations of chloral hydrate (CH, the most prevalent HAL) were double in ozonated water. Dibromoacetaldehyde (DBAL) formed only in the presence of pre-ozonation. Ozonation effectively reduced the formation of total THMs, whereas more brominated THMs were formed with higher ozone dosages.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4–27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Methyl chloride produced during UV254 irradiation of saline water

Ultraviolet (UV) irradiation is widely used for water treatment due to its effectiveness against a wide range of waterborne pathogens with minimal production of regulated disinfection byproducts. However, in this study, the formation of methyl chloride (CH3Cl) from guaiacol and chloride was observed during UV254 irradiation. The results indicated that direct photolysis of guaiacol produced an arenium ion, and the reactive methoxy group was further transformed to CH3Cl in the presence of chloride. O-quinone was detected as the primary product of the degradation of guaiacol resulting from UV254 irradiation. Other organic compounds containing methoxy, ethoxy, or methylamino groups with structures that are similar to guaiacol were also demonstrated to generate halocarbons in aqueous chloride or bromide solution under UV254 irradiation. Scavenging experiments and removal of oxygen demonstrated that neither oxygen nor chlorine radicals were involved in CH3Cl formation. In seawater samples, CH3Cl was also detected in the presence or absence of added organic matter. These results demonstrate that CH3Cl can be formed during UV254 irradiation in saline water and that attention should be paid to this compound and structurally-related compounds in the application of UV254 processes.