Trihalomethane Precursors Research Articles

Trihalomethanes (THMs) precursor fractions removal by coagulation and adsorption for bio-treated municipal wastewater: Molecular weight, hydrophobicity/hydrophily and fluorescence

Due to concerns over health risk of disinfection byproducts (DBPs), removal of trihalomethanes (THMs) precursor from bio-treated wastewater by coagulation and adsorption was investigated in this study. Ultrafiltration (UF) membranes and nonionic resins were applied to fractionate THMs precursor into various molecular weight (MW) fractions and hydrophobic/hydrophilic fractions. Characteristics of coagulated water and adsorbed water were evaluated by the three-dimensional excitation and emission matrix (3DEEM) fluorescence spectroscopy. Results showed that coagulation and adsorption were suitable for removing different hydrophobic/hydrophilic and fluorescent fractions. Coagulation decreased THMs concentration in hydrophobic acids (HoA) fraction from 59μg/L to 39μg/L, while the lowest THMs concentration (9μg/L) in hydrophilic substances (HiS) fraction was obtained in adsorbed water. However, both coagulation and adsorption were ineffective for removing fractions with MW<5kDa. Although coagulation and adsorption processes could reduce THMs formation, some specific THMs formation potential (STHMFP) in residual dissolved organic matter (DOM) fractions increased in this study. Hydrophobic acid and hydrophilic fractions increased after coagulation treatment, and low MW and hydrophobic fractions increased after adsorption treatment. In addition, active carbon adsorbed more organic matter than coagulant, but brominated disinfection byproducts (Br-DBPs) in adsorbed water turned to the major THMs species after chlorination.

Photocatalysis of THM precursors in reclaimed water: the application of TiO2 in UV irradiation

In this study, ultraviolet (UV) irradiation followed by chlorination was employed for reclaimed water disinfection. In order to reduce trihalomethanes (THMs) from reclaimed water, suspended TiO2 (10 mg/L) was added as photocatalyst in UV process to enhance the removal of THM precursors. Reduction of UV absorbance in 254 nm (UV254), dissolved organic carbon (DOC), and THMs formation was analyzed under different experimental conditions (exposure time, pH, TiO2 doses, and TiO2 forms). Excitation–emission matrix spectra technology was also used to investigate the changes of dissolved organic matters properties during UV and UV-TiO2 process. Expansion of irradiation time resulted in a remarkable decrease in UV254 and THM yields, but showed few influence on DOC removal. THMs yield decreased more than 50% with pH increased from 5 to 9 and rise in TiO2 dosage also presented a positive effect on photocatalytic disinfection. In addition, a dramatic increase in removal rates of UV254, DOC, and THMs was observed when TiO2 doses were increased from 3 to 15 mg/L. In terms of TiO2 form, suspended TiO2 exhibited a better removal capacity on UV254, DOC, and THMs by contrast with TiO2 coated on granular active carbon.

Removal of organic matter and disinfection by-products precursors in a hybrid process combining ozonation with ceramic membrane ultrafiltration

The performance of an integrated process including coagulation, ozonation, ceramic ultrafiltration (UF) and biologic activated carbon (BAC) filtration was investigated for the removal of organic matter and disinfection by-products (DBPs) precursors from micro-polluted surface water. A pilot scale plant with the capacity of 120 m3 per day was set up and operated for the treatment of drinking water. Ceramic membranes were used with the filtration area of 50 m2 and a pore size of 60 nm. Dissolved organic matter was divided into five fractions including hydrophobic acid (HoA), base (HoB) and neutral (HoN), weakly hydrophobic acid (WHoA) and hydrophilic matter (HiM) by DAX-8 and XAD-4 resins. The experiment results showed that the removal of organic matter was significantly improved with ozonation in advance. In sum, the integrated process removed 73% of dissolved organic carbon (DOC), 87% of UV254, 77% of trihalomethane (THMs) precursors, 76% of haloacetic acid (HAAs) precursors, 83%of trichloracetic aldehyde (CH) precursor, 77% of dichloroacetonitrile (DCAN) precursor, 51% of trichloroacetonitrile (TCAN) precursor, 96% of 1,1,1-trichloroacetone (TCP) precursor and 63% of trichloronitromethane (TCNM) precursor. Hydrophobic organic matter was converted into hydrophilic organic matter during ozonation/UF, while the organic matter with molecular weight of 1000–3000 Da was remarkably decreased and converted into lower molecular weight organic matter ranged from 200–500 Da. DOC had a close linear relationship with the formation potential of DBPs.

Effects of ozone as a stand-alone and coagulation-aid treatment on the reduction of trihalomethanes precursors from high DOC and hardness water

This study investigates the effect of ozone as a stand-alone and coagulation aid on the removal of dissolved organic carbon (DOC) from the water with a high level of DOC (13.8 mgL−1) and calcium hardness (270 mgL−1) CaCO3.Natural water collected from the Assiniboine River (Manitoba, Canada) was used in this study.Effectiveness of ozone treatment was evaluated by measurement of DOC, DOC fractions, UV254, and trihalomethane formation potential (THMFP). Additionally, zeta potential and dissolved calcium concentration were measured to discern the mechanism of ozone reactions.Results indicated that 0.8 mg O3/mg DOC ozone stand-alone can cause up to 86% UV254 reduction and up to 27% DOC reduction.DOC fractionation results showed that ozone can change the composition of DOC in the water samples, converting the hydrophobic fractions into hydrophilic ones and resulting in the reduction of THMFP. Also, ozone caused a decrease in particle stability and dissolved calcium concentration. These simultaneous ozonation effects caused improved water flocculation and enhanced removal of DOC. This resulted in reduction of the coagulant dosage when ozone doses higher than 0.2 mg O3/mg DOC were applied prior to coagulation with ferric sulfate. Also, pre-ozonation-coagulation process achieved preferential THMFP removal for all of the ozone doses tested (0–0.8 mg O3/mg DOC), leading to a lower specific THMFP in pre-ozonated-coagulated waters than in the corresponding ozonated waters.

Incidence of Adsorption Process on the Reduction of Trihalomethanes Precursory in Algerian Surface Water

The objective of our work is to test the performance of activated carbon on the elimination of humic substances by adsorption before chlorination in order to reduce the trihalomethane precursor of humic substances for two types of surface waters of Biskra region (South East of Algeria). During the chlorination, the results showed that the potential of consumption chlorine is very high for raw surface water tested and accompanied by a rather significant quantity of the trihalomethanes. The adsorption of humic substances on powder activated carbon showed that the activated carbon whatever its form effectively removes humic substances and the yield could reach 98%. For coupling adsorption / chlorination, the results showed that adsorption induced a significant and even a remarkable reduction in both of potential of chlorine consumption and the training potential of organochlorine compounds especially trihalomethanes.

Effects of chlorination operating conditions on trihalomethane formation potential in polyaluminum chloride-polymer coagulated effluent

In this study, coagulation performance of polyaluminum chloride (PAC) and PAC-lignin acrylamide (PAC+LAM) in reservoir water treatment was contrastively analyzed. Effects of operating conditions including chlorine dose, contact time and pH on the formation potential of trihalomethanes (THMs) during chlorination in coagulated effluent were also investigated. Comparing with PAC, PAC+LAM achieved higher efficiency in the removal of THMs precursors. TTHM yield in unfiltered water samples (UW) was greater than that of filtered water (FW) due to the residual dissolved organic matter (DOM) in the suspended particles or micro flocs. Meanwhile, operating conditions during chlorination had a significant influence on THMs formation potential. With chlorine dose rising, mass ratio of CHCl3 to TTHM increased, whereas that of CHBr2Cl decreased due to higher Cl2/Br− molar ratio. TTHM and CHCl3 levels rose with the increase of pH. Under a given chlorination condition, there was a minor effect of contact time on THM speciation.

Assessing trihalomethanes (THMs) and N-nitrosodimethylamine (NDMA) formation potentials in drinking water treatment plants using fluorescence spectroscopy and parallel factor analysis

The formation of disinfection byproducts (DBPs) is a major challenge in drinking water treatments. This study explored the applicability of fluorescence excitation–emission matrices and parallel factor analysis (EEM–PARAFAC) for assessing the formation potentials (FPs) of trihalomethanes (THMs) and N-nitrosodimethylamine (NDMA), and the treatability of THM and NDMA precursors in nine drinking water treatment plants. Two humic-like and one tryptophan-like components were identified for the samples using PARAFAC. The total THM FP (TTHM FP) correlated strongly with humic-like component C2 (r=0.874), while NDMA FP showed a moderate and significant correlation with the tryptophan-like component C3 (r=0.628). The reduction by conventional treatment was more effective for C2 than C3, and for TTHM FP than NDMA FP. The treatability of DOM and TTHM FP correlated negatively with the absorption spectral slope (S275–295) and biological index (BIX) of the raw water, but it correlated positively with humification index (HIX). Our results demonstrated that PARAFAC components were valuable for assessing DBPs FP in drinking water treatments, and also that the raw water quality could affect the treatment efficiency.

The migration and transformation of dissolved organic matter during the freezing processes of water

This study investigated the partitioning behavior of dissolved organic matter (DOM) in liquid and ice phases, as well as the changes in the optical properties and chlorine reactivity of DOM during the freezing processes of water. DOM was rejected from the ice phase and accumulated in the remaining liquid phase during water freezing. Moreover, the decrease in freezing temperature, as well as the increase in dissolved organic carbon (DOC) concentration of feed water, caused an increase in DOM captured in the ice phase. The ultraviolet-absorbing compounds, trihalomethane precursors, as well as fulvic acid- and humic acid-like fluorescent materials, were more liable to be to be rejected from the ice phase and were more easily retained in the unfrozen liquid phase during water freezing, as compared with organics (on average) that comprise DOC. In addition, it was also found a higher accumulation of these organics in the unfrozen liquid phase during water freezing at higher temperature. The freeze/thaw processes altered the quantity, optical properties, and chlorine reactivity of DOM. The decrease in ultraviolet light at 254nm as well as the production of aromatic protein- and soluble microbial byproduct-like fluorescent materials in DOM due to freeze/thaw were consistently observed. On the other hand, the changes in DOC, trihalomethane formation potential, and fulvic acid- and humic acid-like fluorescence caused by freeze/thaw varied significantly between samples.

Drinking Water Chlorination and Adverse Public Health Outcomes in Algeria

Drinking water supplies continue to be a major source of human disease because many of them remain unsafe and vulnerable. The aim of this study was to investigate the levels of trihalomethanes formation and chemical and microbiological quality through four raw surface waters as well as finished tap waters. The seasonal changes on trihalomethane formation and concentration of organic precursors were examined. Results show that disinfection for Algerian drinking water reduces the risk of pathogenic infection but may pose chemical threat to human health due to high levels of by-products such as trihalomethanes, when the organic and inorganic precursors are present in water. The level of THM precursors vary between different catchment areas and between different water treatment plants, and seasonally. Such work may be interesting to help management strategies and to assist drinking water treatment plants in DBP control processes for increasingly impaired water sources.

Dissolved organic carbon and trihalomethane formation potential removal during coagulation of a typical UK upland water with alum, PAX-18 and PIX-322

This paper considers the removal of dissolved organic carbon (DOC) from a typical UK upland reservoir water using three different coagulants; aluminium sulphate/alum (Al2(SO4)3(aq)), polyaluminium chloride/PAX-18 (Aln(OH)mCl3n-m(aq)) and ferric sulphate/PIX-322 (Fe2(SO4)3(aq)). A comparison of DOC quality including fractional character, colour, specific ultraviolet absorption (SUVA) and molecular weight was made between the source water and the supernatants obtained following its coagulation in each case. Trihalomethane formation potential (THMFP) was compared before and after treatment to assess which coagulant performed best in terms of THM amelioration. The conditions (coagulant dose and pH) required to obtain optimal DOC removal were established using bench-scale jar tests. Statistically significant differences in DOC removal rates were observed between the different coagulants. THMFP removal was linked to a combination of high net DOC removal and the preferential removal of THM precursors. This selectivity may also be responsible for the increase in brominated THM species (BrTHMs) observed following treatment.

Characterization of chromophoric dissolved organic matter and trihalomethane formation potential in a recently constructed reservoir and the surrounding areas – Impoundment effects

Summary The effects of the dam impoundment on the distribution of chromophoric dissolved organic matter (CDOM) were evaluated for a dam reservoir (the Gunwi reservoir) at an early impoundment stage by comparing the characteristics of CDOM and trihalomethane (THM) precursors among the upstream catchment areas, the dam reservoir, and a downstream site. Sampling was conducted for two separate sampling periods of a non-storm event in May and a storm event in August, 2012. The dam reservoir had experienced long-term enrichment of non-biodegradable organic matter since its construction in February, 2010. In May, significant differences were observed in several selected CDOM properties between the upstream catchments and the locations affected by the impoundment (i.e., within the reservoir and the downstream sites). For the storm event, however, such impoundment effects became much less pronounced likely due to elevated input of CDOM with terrestrial origin into the reservoir. Specific THM formation potential (STHMFP) did not show the same spatial distinction as those of CDOM for both sampling periods. Three fluorophore groups were identified from fluorescence excitation–emission matrices (EEMs) of the collected samples by parallel factor analysis (PARAFAC) modeling. Protein-like and microbial humic-like components were relatively more enriched for the impoundment-affected sites compared to the upstream locations, in which terrestrial humic-like component was more dominant. Principal component analysis (PCA) demonstrated that the accumulation of non-biodegradable organic matter in the dam reservoir might be attributed to microbial humification of the algal-derived organic substances originated from either periphytons flushed from upstream stream beds or decomposing algae settled on the bottom of the reservoir, or both.

Trihalomethanes in marine mammal aquaria: Occurrences, sources, and health risks

Disinfecting water containing the high levels of dissolved organic carbon (DOC) commonly generated during pinniped husbandry may cause the formation of carcinogenic disinfection byproducts (DBPs). Little information is available on DBP levels, sources, and health risks in marine mammal aquaria. Using the commonly observed trihalomethanes (THMs) as a DBP indicator, we monitored concentrations for seven months at The Marine Mammal Center in Sausalito, California, one of the largest pinniped rehabilitation facilities in the world. Concentrations of THMs ranged 1.1–144.2 μg/L in pool waters and generally increased with number of animals housed (P < 0.05). To identify the sources of THM precursors in marine mammal aquaria, we intensively monitored the mass flows of potential THM precursors (i.e. food and wastes) in an isolated system with nine individual California sea lions to evaluate the sources and reactivity of dissolved organic carbon (DOC) for 2–5 weeks. The common frozen foods used in feeding pinnipeds, including herring, sardine, and squid, produced an average of 22–34 mg-DOC/g-food in water and 836–1066 μg-THM/g-food after chlorination, whereas the fecal materials, including fresh scat, decomposed scat, and urine, produced 2–16 mg-DOC/g-waste and 116–768 μg-THM/g-waste. Food not eaten by animals could cause a sharp increase of DOC and DBP production and therefore should be removed rapidly from pools. Marine mammal husbandry staff and trainers are at risk (5.16 × 10−4 to 1.30 × 10−3) through exposure of THMs, exceeding the negligible risk level (10−6) defined by the US Environmental Protection Agency.

微粉末活性炭と化学的強化逆洗を組合わせた膜ろ過処理における異臭味物質とトリハロメタン前駆物質の除去性能の向上

本研究は，微粉末活性炭（Supper-powdered activated carbon）と化学的強化逆洗（Chemical enhanced backwashing）を膜ろ過処理に組合わせ，臭気・トリハロメタン生成能の除去ついて評価するため，高濃度に藻類を含有する水源で長期のパイロットスケール膜ろ過実験を行なった．その結果，化学的強化逆洗は膜ファウリングを抑制するとともに，膜ファウリング抑制に必要な前塩素処理を行わないため，膜ろ過水中の消毒副生成物質リスクを低減できることを確認した．また，微粉末活性炭を注入することにより，膜処理では除去されにくいトリハロメタン生成能や臭気物質である2-MIB，ジェオスミンも同時に吸着除去できることを確認した．

DBP formation and speciation in a central anatolian dam water depending on pH, TOC level, fraction and chlorine dose

&lt;p&gt;The effects of pH, NOM concentration, fractions and the chlorine dose on the formation and speciation of THMs and HAAs were determined in Altinapa Dam water (Konya/Turkey). Water sample was isolated and chlorinated at different TOC levels and pH&amp;rsquo;s. The isolate was fractioned; THM and HAA species were measured after chlorination. THM increased with increasing pH (6 to 8) whereas a consistent pH tendency could not be inferred from the HAA changes. CF is the dominant THM specie which exerts up to 91% of the total THM. The majority of total HAAs composed of MCAA, DCAA and TCAA. The hydrophobic fraction was the main THM precursor under the studied conditions although their percentage was lower than hydrophilics, whereas, hydrophilic fraction had significant contribution to HAA formation, in contrast to the general tendency for HAA. High correlation (0.97) was calculated between total THMs and HAAs.&lt;/p&gt;

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride (FeCl3), aluminum sulfate (Al2(SO4)3), polyaluminum chloride (PACl) and composite polyaluminum (HPAC), in order to remove dissolved organic matter (DOM). Considering the disinfection byproduct (DBP) precursor treatability, DOM was divided into five chemical fractions based on resin adsorption. Trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were measured for each fraction. The results showed that hydrophobic acids (HoA), hydrophilic matter (HiM) and hydrophobic neutral (HoN) were the dominant fractions. Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally, HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation. HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions. DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PACl. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PACl under enhanced coagulation could reach 51% and 59% respectively.

Advanced oxidation of bromide-containing drinking water: A balance between bromate and trihalomethane formation control

Addition of H2O2 has been employed to repress bromate formation during ozonation of bromide-containing source water. However, the addition of H2O2 will change the oxidation pathways of organic compounds due to the generation of abundant hydroxyl radicals, which could affect the removal efficacy of trihalomethane precursors via the combination of ozone and biological activated carbon (O3-BAC). In this study, we evaluated the effects of H2O2 addition on bromate formation and trihalomethane formation potential (THMFP) reduction during treatment of bromide-containing (97.6–129.1 μg/L) source water by the O3-BAC process. At an ozone dose of 4.2 mg/L, an H2O2/O3 (g/g) ratio of over 1.0 was required to maintain the bromate concentration below 10.0 μg/L, while a much lower H2O2/O3 ratio was sufficient for a lower ozone dose. An H2O2/O3 (g/g) ratio below 0.3 should be avoided since the bromate concentration will increase with increasing H2O2 dose below this ratio. However, the addition of H2O2 at an ozone dose of 3.2 mg/L and an H2O2/O3 ratio of 1.0 resulted in a 43% decrease in THMFP removal when compared with the O3-BAC process. The optimum H2O2/O3 (g/g) ratio for balancing bromate and trihalomethane control was about 0.7–1.0. Fractionation of organic materials showed that the addition of H2O2 decreased the removal efficacy of the hydrophilic matter fraction of DOC by ozonation and increased the reactivity of the hydrophobic fractions during formation of trihalomethane, which may be the two main reasons responsible for the decrease in THMFP reduction efficacy. Overall, this study clearly demonstrated that it is necessary to balance bromate reduction and THMFP control when adopting an H2O2 addition strategy.

Comparison of conventional technologies and a Submerged Membrane Photocatalytic Reactor (SMPR) for removing trihalomethanes (THM) precursors in drinking water treatment plants

This work evaluates the feasibility of several technologies for the removal of trihalomethanes (THM) precursors, usually humic substances found in real surface water, which are transformed into these potential carcinogens (THMs) during the further disinfection by chlorination. The aim was to compare, an Activated Carbon Bed (ACB), an Ozonation Reactor (OR) and a Submerged Membrane Photocatalytic Reactor (SMPR) with TiO2/UV in terms of reduction efficiency of these THM precursors after chlorination. Taguchi's parameter design methodology was selected to study the most relevant factors that might influence the removal of THM precursors with each technology keeping the number of experiments at minimum. According to the study, OR showed low removal percentages of THM precursors (of 40–50%) while SMPR and ACB were more efficient technologies. SMPR achieved 86% removal of THM precursors when operating at the optimal conditions of TiO2 catalyst concentration of 0.5gL−1 (type PC500® from Cristal Global). ACB attained the 87% removal of THM precursors when Filtracarb® CC60 8×30 (steam activated mineral coal) was used with a hydraulic retention time of 15min.

Seasonal variations of NOM composition and their reactivity in a low humic water

Natural organic matter (NOM) and its potential to form disinfection by‐products (DBPs) during water treatment are of great public health concern. Understanding the seasonal changes in NOM composition and their reactivity in DBP formation could lead to a better treatment of drinking water and a more consistent water quality. NOM from the Terkos Lake was fractionated and characterized by XAD resin adsorption and ultrafiltration (UF) techniques during four different seasons within a year. XAD fraction analysis indicates that the HPI (38%) and the TPI (21%) were the dominant chemical fractions as DOC masses across the sampling period. Moreover, the fractions contributing to the most UV254 absorbance were HPO, which accounted for more than 72% of total UV254. It was found that the percentages of UV254 of HPI and TPI showed significant amount of variation with coefficients of variation of 48% (HPI) and 35% (TPI), respectively. Moreover, it was concluded that the HPO fraction was the primary THM precursor, which contributed more than 48%, and while the primary fraction of HAA precursors was found to be TPI, accounting for more than 47% of total HAAFP with exceptions in January 2011. As obviously seen in this study, the hydrophobic constituents in Terkos Lake water are on the low end of the spectrum in terms of their reactivity to form HAAs. In the context of THM reactivity, the physical properties (i.e., moleculer size) of Terkos Lake NOM are more important than their chemical properties (i.e., aromaticity). On the other hand, the predominant fraction as the source of HAAs precursors was found to be with the TPI and HPI chemical fractions. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 962–971, 2014

Relationships between trihalomethanes, haloacetic acids, and haloacetonitriles formed by the chlorination of raw, treated, and fractionated surface waters

This study examined effects of coagulation and fractionation of natural organic matter on the distribution of trihalomethanes (THM), haloacetic acids (HAA), and haloacetonitriles (HAN) formed in chlorinated water. The precursors of HAA and THM were determined to be associated primarily with the hydrophobic fraction although the hydrophilic fraction is important as well. On the other hand, the precursors of HAN are overwhelmingly hydrophilic with only a negligible contribution of the hydrophobic and transphilic fractions. Higher percentages of HAN were found in the treated waters compared with raw waters, collected from three different full scale water treatment plants. Very strong correlations were found between THM, HAA, and HAN concentrations. Two main correlations between THM and HAN were observed. One was applicable to all raw waters regardless of their fractionation and provenance, while the other was formed by the treated waters, again regardless of their source and fractionation. This result emphasizes that a significant removal of THM and HAA precursors can be achieved via coagulation but it results in a negligible removal of HAN precursors. As a consequence, some changes in treatment trains or operating conditions may need to be considered to minimize the formation of HAN.

Dissolved organic carbon and trihalomethane precursor removal at a UK upland water treatment works

The removal of dissolved organic carbon (DOC) during potable water treatment is important for maintaining aesthetic water quality standards, minimising concentrations of micro-pollutants, controlling bacterial regrowth within distribution systems and, crucially, because it contains a sub-component that can act as trihalomethane (THM) precursors. In this study, the concentration and characteristics of raw water DOC and THM formation potential (THMFP) entering an upland potable water treatment works were analysed over twelve months. Correlations between raw water DOC characteristics, standardised THMFP (STHMFP) and % DOC removal were also investigated. DOC and THM precursor removal during a series of treatment stages was examined over this period, as well as potential selectivity in the removal of DOC fractions, to assess the importance of different treatment stages for DOC removal and THM amelioration. Though THMFP removal remained high and fairly stable throughout the study period (83–89%), the data suggest that this was mostly the result of high DOC removal rates rather than the selective removal of THM precursors. Whilst this chemical agnosticism makes DOC removal more robust, it may make the overall process more vulnerable to exceeding permissible THM concentrations under changing climatic conditions. The kinetics of the reaction between DOC and chlorine appeared to vary seasonally, indicating temporal changes in the proportions of fast- and slow-reacting precursors with implications for THM concentrations at the point of delivery to the consumer. The initial treatment stages, comprising coagulation–flocculation and dissolved air floatation (DAF) were by far the most important in terms of bulk DOC removal and the preferential removal of THM precursors, though, surprisingly, DOC quality was also modified following chlorination and secondary rapid gravity filtration (RGF). Though net THM concentration decreased following initial treatment stages, a doubling in the proportion of brominated THMs (BrTHMs), which are reported to be more carcinogenic, was also observed.