Nitrogenous Disinfection By-products Research Articles

Effects of KMnO4/NaHSO3 pre-oxidation on the formation potential of disinfection by-products during subsequent chlorination

Bisulfite-activated permanganate oxidation (PM/BS) technology is an emerging oxidation process that can rapidly oxidize organic contaminants and degrade some permanganate-resistant organic contaminants. For the first time, the influences of PM/BS technology as a pre-oxidation process on the formation potentials of disinfection by-products (DBPFPs) during chlorination of humic acid (HA) solution and three natural water samples were investigated. The results revealed that PM/BS pre-oxidation only slightly affected the DBPFPs of HA in the absence of Br- although it changed the structure of HA according to the fluorescence characterization result. With the presence of Br-, PM/BS pre-oxidation enhanced the generation of trihalomethanes but inhibited that of nitrogenous DBPs (N-DBPs) during chlorination of HA. The toxic risk analysis showed that the toxicity of the generated DBPs from chlorinating HA solution without Br- only changed slightly after PM/BS pre-oxidation but it was decreased by 14% in the presence of 150 μg/L Br− due to PM/BS pre-oxidation. This should be associated with the inhibiting effect of PM/BS pre-oxidation on the generation of N-DBPs and several haloacetic acids in the presence of Br-. Because of the complex matrix of natural water samples, PM/BS pre-oxidation had minor influence on the amount and the potential toxicity of DBPs generated during chlorination. The above results suggested that PM/BS technology could be an alternative of the drinking water pretreatment.

Microbial degradation of typical amino acids and its impact on the formation of trihalomethanes, haloacetonitriles and haloacetamides during chlor(am)ination

Nitrogenous disinfection by-products (N-DBPs) in chlorinated drinking water are receiving increasing attention due to their elevated toxicities. An effective strategy to control the formation of N-DBPs is to reduce their nitrogenous precursors (e.g., amino acids [AAs], believed to be the important N-DBP precursors) before disinfection. So far, little information is available about the effectiveness of conventional microbial degradation at controlling the formation of N-DBPs. In this study, the biodegradability of 20 AAs was investigated, and the impacts of microbial degradation for the selected 6 typical AAs on the formation of N-DBPs (haloacetonitriles and haloacetamides) and traditional carbonaceous DBP (chloroform) were investigated. The results indicated that glycine, arginine, aspartic acid, asparagine, alanine and serine were susceptible to biodegradation, and the formation potentials (FPs) of DBPs were remarkably reduced after biodegradation. The highest chloroform FP reduction rates from tryptophan and tyrosine were 85.4% and 56.2%, respectively. The FPs of dichloroacetonitrile and trichloroacetamide were also reduced after biodegradation of the all selected AA samples during chlor(am)ination. Dichloroacetamide FPs decreased continuously with incubation time during chlorination for phenylalanine, asparagine, aspartic acid, and the mixed AAs, and the highest reduction rates were 78.7%, 74.6%, 46.7% and 35.3% respectively. The results of integrated toxicity analysis indicated that the pre-treatment of microbial degradation significantly decreased the integrated toxicity of DBPs formed from AAs. Moreover, the microbial community analysis revealed that Proteobacteria was predominant at phylum level in the mixed AA sample, and the dominant genera were Acinetobacter and Pseudomonas. Proteobacteria may play an important role in controlling DBP precursor.

A novel molecularly imprinted polymer-solid phase extraction method coupled with high performance liquid chromatography tandem mass spectrometry for the determination of nitrosamines in water and beverage samples

Nitrosamines (NAs) as a group of emerging nitrogenous disinfection byproducts were present in drinking water at ng/L levels. Accurate measurements of NAs at such a trace level in samples is a challenging task. Solid phase extraction (SPE), which is used in the sample pretreatment, plays a critical role in the analysis of NAs in water. In this study, a highly selective and sensitive method for the determination of five less polar NAs, namely nitrosodiethylamine nitrosopiperidine, nitrosodi-n-propylamine, nitrosodibutylamine and nitrosodiphenylamine, in water and beverage samples was developed. A new molecularly imprinted polymer (MIP) was synthesized and used as sorbents in SPE for the sample preparation. Prepared samples were analyzed using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Satisfactory recoveries were obtained at three different concentrations (5, 20, and 50 ng/L, n = 3) in the range of 93–107% with relative standard deviations of 3.1–9.8%. Limit of detection and limit of quantitation for the five NAs were in the range of 0.2–0.7 ng/L and 0.6–2.1 ng/L, respectively. Method precisions ranged from 4.9% to 10.5%. This novel method of MIP-SPE coupled with HPLC-MS/MS was successfully applied to the determination of these five NAs in different types of water and beverages samples.

Analytical methods for conventional and emerging disinfection by-products in fresh-cut produce

The formation of toxic disinfection by-products (DBPs) is among the main concerns in the use of chlorine sanitizers for washing fresh and fresh-cut produce to minimize microbial cross-contamination. Even so, robust analytical methods for measuring various DBPs in produce have been lacking. This study has established two liquid-liquid extraction methods, followed by gas chromatography with electron capture detection, to measure 32 conventional and emerging DBPs in different produce types including lettuce, cabbage and strawberry. Good recoveries (50–130%) were achieved for most DBPs in the different produce. The method detection limits were in the range of 0.3–10 ng/g for trihalomethanes, haloacetic acids, nitrogenous DBPs, and other carbonaceous DBPs. Preliminary screening analysis indicated one-third of the target DBPs were found in unwashed produce, and washing with chlorine significantly promoted DBPs’ formation and concentrations in the produce. The developed analytical methods will be useful tools for future research on food DBPs.

Transformation and fate of dissolved organic nitrogen in drinking water supply system: A full scale case study from Yixing, China

The transformation of dissolved organic nitrogen (DON) in the drinking water treatment plants could be closely associated with nitrogenous disinfection by-product (N-DBP) formation. In this study, we have assessed the molecular transformation of DON and its impact on N-DBP formation in a full scale drinking water treatment plant. Based on the result of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, DON compounds with low molecular weight (<1 kDa) were classified as CHON, CHON2 and CHON3 according to the number of nitrogen atoms. Via the analytical window of van Krevelen diagrams, we found that the molecular structural features of CHON, CHON2 and CHON3 were not altered before the chlorination process. In detail, the CHON2 and CHON3 compositions were concentrated on the regions assigned to a lignin-structure while CHON compositions were also distributed in other compounds including proteins, carbohydrates and tannin. Furthermore, CHON formation was more difficult to be removed before the V-filter process. For N-DBP, chlorine-containing DON (Cl-DON) composition was likely to be removed through flocculation and sedimentation processes, whereas N-nitrosamine compounds were removed in V-filter and biological activated carbon filter processes. The health risks of aromatic structure N-nitrosamines due to the pre-chlorination of the raw water should be further studied.

Impact of UV irradiation on Chlorella sp. damage and disinfection byproducts formation during subsequent chlorination of algal organic matter

The frequent occurrence of algal blooms in surface water has attracted more and more attention, which caused many water quality problems, including disinfection byproducts (DBPs). Algal organic matter (AOM) including intracellular organic matter (IOM) and extracellular organic matter (EOM), was a well-known precursor to DBPs formation in drinking water. This study evaluated the effect of ultraviolet (UV) irradiation on the cell integrity, IOM release and DBPs formation during subsequent chlorination of Chlorella sp. Results showed the damage rates of algal cells increased to 40.1% after the high UV irradiation of 528 mJ/cm2, which contributed to the release of IOM. In addition, UV irradiation was effective in reducing the formation of haloacetic acids (HAAs) both in AOM and IOM, but promoted the formation of nitrogenous DBPs (N-DBPs) from AOM in subsequent chlorination. Furthermore, neutral pH exerted a positive effect on the formation of DBPs. UV irradiation decreased the bromine substitution factor (BSF) value of AOM at a high bromide level. The BSF values increased with increasing of the concentration of bromide. Moreover, more amino acids and low molecular weight precursors were produced after UV irradiation in filtered supernatant, which contributed to the formation of N-DBPs with algal chlorination. Overall, this information demonstrated pre-oxidation of UV irradiation could be used to treat the algal-rich drinking water.

The contribution of biofilm to nitrogenous disinfection by-product formation in full-scale cyclically-operated drinking water biofilters

Biofiltration has been shown to be effective for disinfection by-product (DBP) precursor control, however few studies have considered its role in the potential formation of DBPs. Biofilm is composed of heterogeneous bacteria as well as extracellular polymeric substances (EPS). The objective of this study was to determine the contribution of biofilm-related materials such as EPS to form nitrogen-containing DBPs upon chloramination, and to determine the influence of cyclical (scheduled on-off) biofilter operation on DBP precursor removal. Biologically active media was sampled from a full-scale biofilter operating under cold-water conditions (3.6 ± 0.5 °C) and extracted using a cation exchange resin into a phosphate buffer solution. Biomass concentrations, as determined using adenosine triphosphate (ATP) measurements, remained stable at 298 ± 55 ng ATP/g media over the trial period. N-nitrosodimethylamine (NDMA) and haloacetonitrile (HAN4) formation potential (FP) tests conducted under uniform formation conditions (UFC) using extracted biofilm yielded 0.80 ± 0.27 ng NDMA/g media and 18.7 ± 3.3 ng dichloroacetonitrile (DCAN)/g media. Further analyses of extracted biofilm using fluorescence spectroscopy and liquid chromatography-organic carbon detection indicated the presence of proteins above 20 kDa and humic-like substances. Extracted proteins (93.5 ± 8.1 μg/g media) correlated well (R = 0.90) with UV 280 measurements, indicating that spectrophotometry may serve as a valuable tool to quantify proteins in extracted biofilms. While substances in biofilms can serve as NDMA and DCAN precursors, the full-scale cyclically-operated biofilter that was examined did not show release of NDMA precursors during start-up following stagnation periods of 6 h or more. These biofilters consistently removed 6.9 ± 4.3 ng/L of NDMA precursors; typical NDMA UFC-FP of biofilter effluent was 8.5 ± 2.6 ng/L.

Speciation and seasonal variation of various disinfection by-products in a full-scale drinking water treatment plant in East China

Abstract The objective of this research was to study the occurrence and seasonal variations of disinfection by-products (DBPs), including traditional carbonaceous and emerging nitrogenous DBPs, in a full-scale drinking water treatment plant (DWTP) for nearly 2 years. The removal efficiencies of each DBP through the treatment processes were also investigated. This DWTP takes raw water from the Yangtze River in East China. The quality of the raw water used in this DWTP varied with different seasons. The results suggested that DBP concentrations of the finished water were higher in spring (82.33 ± 15.12 μg/L) and summer (117.29 ± 9.94 μg/L) with higher dissolved organic carbon (DOC) levels, but lower in autumn (41.10 ± 5.82 μg/L) and winter (78.47 ± 2.74 μg/L) with lower DOC levels. Due to the increase of bromide concentration in spring and winter, more toxic brominated DBPs increased obviously and took up a greater proportion. In this DWTP, DBP concentrations increased dramatically after pre-chlorination, especially in summer. It is noteworthy that the removal of DBPs during the subsequent treatment was more obvious in spring than in the other three seasons because the pH value is more beneficial to coagulation in spring.

Removal of pharmaceuticals and personal care products by two-stage biofiltration for drinking water treatment

Contamination of drinking water with pharmaceuticals and personal care products (PPCPs) is an issue of health concerns. To effectively control the level of PPCPs in drinking water, a pilot study employing two parallel trains of two-stage biofiltration, i.e., a sand/anthracite (SA) biofilter coupled with a biologically-active granular activated carbon (GAC) post-filter contactor, was conducted as a post-treatment after coagulation in a drinking water treatment plant. Results showed the biofiltration process could effectively remove PPCPs with an average removal of 53.4%, where the GAC contactor played the dominant role to remove 48.1% of the total PPCPs. The molecular properties determined the removability of individual PPCPs, i.e., smaller molecules with simpler structure connectivity were more likely to be removed. Based on the quantitative structure-property relationships (QSPRs) analysis, a simple regression model was proposed to predict the removability of each PPCP across the biofiltration process. The drinking water equivalent level (DWEL) quotient method was developed to assess the health risks of detected PPCPs in water samples. The biofiltration process showed efficient capacity to reduce the health risks of PPCPs with an average removal of 79%, and the PPCPs in the effluents generally would not pose adverse health effects. Pearson correlation analysis explored the possible role of nitrogenous PPCPs (N-PPCPs) as the precursors of nitrogenous disinfection byproducts (N-DBPs) in drinking waters. Aromatic nitrogen in PPCPs was found to be a significant descriptor for the formation potential of trichloroacetonitrile (TCAN). In addition, it was found that pre-filter chlorination could slightly improve the biofiltration of PPCPs.

Synergistic removal of ammonium by monochloramine photolysis

The presence of ammonium (NH4+) in drinking water treatment results in inhibition of disinfection efficiency and formation of nitrogenous disinfection by-products. Our previous study found monochloramine (NH2Cl) photolysis under 254 nm UV irradiation can be effective for removal of NH4+; however, the mechanisms of NH4+ degradation in this process were unknown. The kinetics and fundamental radical chemistry responsible for NH4+ removal in the UV/NH2Cl process were investigated in this study. The results showed that the pseudo first-order rate constant for NH4+ degradation in the UV/NH2Cl process ranged between 3.6 × 10-4 to 1.8 × 10-3 s-1. Solution pH affected radical conversion and a higher NH4+ degradation efficiency was achieved under acidic conditions. The effects of chloride were limited; however, the presence of either bicarbonate or natural organic matter scavenged radicals and inhibited NH4+ removal. NH2Cl photolysis generated an aminyl radical (NH2•) and a chlorine radical (Cl•) that further transformed to a chlorine dimer (Cl2•-) and a hydroxyl radical (HO•). The second-order rate constants for Cl• and Cl2•- reacting with NH4+ were estimated as 2.59 × 108 M-1s-1 and 3.45 × 105 M-1s-1 at pH 3.9, respectively. Cl•, Cl2•-, and HO• contributed 95.2%, 3.5%, and 1.3% to NH4+ removal, respectively, at the condition of 3 mM NH2Cl and pH 7.5. Major products included nitrite and nitrate, possibly accompanied by nitrogen-containing gases. This investigation provides insight into the photochemistry of NH4+ degradation in the UV/NH2Cl process and offers an alternative method for drinking water production.

Degradation of haloacetonitriles with UV/peroxymonosulfate process: Degradation pathway and the role of hydroxyl radicals

Haloacetonitriles (HANs), a specie of new emerging halogenated nitrogenous disinfection by-products (N-DBPs) including trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), monochloroacetonitrile (MCAN) and dibromoacetonitrile (DBAN), were more cytotoxic and genotoxic than the conventional DBPs. In this study, kinetics and mechanisms in the oxidization of HANs by UV/peroxymonosulfate (PMS) process were investigated. The degradation of chloroacetonitriles (CANs) in UV/PMS process was more remarkable than UV alone, PMS alone and UV/H2O2 process. And the order of the rates of degradation of HANs was followed: TCAN > DCAN > MCAN, while DBAN was remarkably degraded by UV alone. The degradation of DCAN was accelerated by humic acid and Cl−, while suppressed by bicarbonate. Scavenging experiments showed that hydroxyl radical (radOH) was the predominant species in the reaction. According to the gas chromatography/mass spectrometer (GC/MS) analysis, the breakage of CCl bond was the dominant pathways in degradation of CANs.

Nitrosamines: A review of formation pathways, precursors, control, and occurrence in drinking water

Nitrogenous disinfection by-products (N-DBPs) are emerging by-products that may be present in drinking water as by-products of water treatment plant (WTP) operations. Nitrosamines are N-DBPs that form by reaction of chloramine with certain organic nitrogen-containing compounds; however, the exact processes and environments in which nitrosamines form are still not well understood. Organic nitrogen precursors react within the WTP and distribution system, forming the toxic by-products during chloramination, or while in distribution. To best control the formation potential of nitrosamines, precursors must be removed from source water prior to chloramine disinfection. These nitrosamine forming precursors are abundant in source waters worldwide, presenting a need for further study of the mechanisms that reduce the formation potential of nitrosamines in chloramination WTPs.

The fates of aromatic protein and soluble microbial product-like organics, as the precursors of dichloroacetonitrile and dichloroacetamide, in drinking water advanced treatment processes

Dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) are two typical nitrogenous disinfection by-products (N-DBPs) with strong cytotoxicity and genotoxicity.

Activated carbon adsorption for removal of the nitrogenous disinfection byproduct phenylacetonitrile from drinking water

Activated carbon adsorption for removal of the nitrogenous disinfection byproduct phenylacetonitrile from drinking water

Trace determination and occurrence of eight chlorophenylacetonitriles: An emerging class of aromatic nitrogenous disinfection byproducts in drinking water

Two chlorophenylacetonitriles (CPANs) (2-chloro- and 3,4-dichlorophenylacetonitrile), representatives of an emerging class of aromatic nitrogenous disinfection byproducts, were recently identified in chlor(am)inated drinking water with liquid/liquid extraction and gas chromatography/mass spectrometry (GC/MS). Due to their high cytotoxicity, they are potentially significant drinking water contaminants. The detection limit for these two CPANs with the previous method was 100 ng L−1. To search for additional CPAN isomers, a more sensitive method for the simultaneous determination of eight CPANs was developed using solid-phase extraction (SPE)-GC/MS. GC/MS parameters and SPE pre-concentration conditions, including SPE cartridge, eluent type, eluent volume, and sample pH, were optimized. Under optimized conditions, the new method had method detection limits, method quantification limits, and precision ranging from 0.15 to 0.37 ng L−1, 0.50–0.95 ng L−1, and 5.8%–11%, respectively. The recoveries of the eight CPANs ranged from 92% to 102%. The concentrations of the eight CPANs in nine finished drinking waters were determined to be at concentrations ranging from 0.5 to 155 ng L−1. Seven CPANs were detectable in all samples. CPANs were detected at concentrations between 0.8 and 155 ng L−1 in chlorinated waters, and from 0.5 to 15 ng L−1 in chloraminated waters. Across all waters, the sum of all CPANs in chloraminated waters was 13% of that in chlorinated systems.

Effect of reduced sulfur group on the formation of CX3R-type disinfection by-products during chlor(am)ination of reduced sulfur compounds

Previous studies have examined the effects of peptide bond and unsaturated bond on the formation of disinfection by-products (DBPs). However, limited information has been available for the impact of reduced sulfur group on the formation of DBPs. This study investigated the formation of carbonaceous and nitrogenous DBPs (C-DBPs and N-DBPs) with a similar structure of ''CX3R'' (X = H, Cl, Br or I, R = functional group), including trihalomethanes, haloacetaldehydes, haloketones, haloacetonitriles, haloacetamides and halonitromethanes, during chlor(am)ination of three reduced sulfur compounds (RSCs), such as N-acetylcysteine, glutathione and glutathiol. Results showed that all DBPs except dichloroacetonitrile (DCAN) continuously increased with increasing Cl2 or NH2Cl doses in this study. The chlor(am)ination of three RSCs with lower disinfectant doses (the molar ratio of disinfectant to precursor ≤5) generated low DBPs compare to non-RSCs. More chloroform was observed in alkaline condition, while weak acidic condition was in favor of DCAN and dichloroacetamide formation. The results of frontier electron density calculation reported that the much higher reactivity for Cl2 and NH2Cl toward reduced sulfur group in RSCs protects other groups, which account for the formation of CX3R-type DBPs. This phenomenon has important environmental implications. When RSCs are present in the water, Cl2 or NH2Cl will reacts preferably with them rather than non-RSCs to form RSO3H as the major products. Hence, the trade-offs of between the products generated upon S-chlorination, which account for the formation RSO3H, and alkyl halogenation and N-chlorination, which account for the formation of CX3R-type DBPs, influence the formation of CX3R-type DBPs.

Simultaneous analysis of haloacetonitriles, haloacetamides and halonitromethanes in chlorinated waters by gas chromatography-mass spectrometry

Nitrogenous classes of disinfection by-products (DBPs), such as haloacetamides (HAAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), while generally present at lower concentrations in disinfected waters than carbonaceous DBPs, such as trihalomethanes or haloacetic acids, have been shown to be more detrimental to human health. While several methods have been shown to be suitable for the analysis of some nitrogenous DBPs (N-DBPs) in disinfected waters, many are unable to quantify HAAms, the most detrimental to health of these three N-DBP classes. Here, we report the first method for the simultaneous analysis of twenty-five N-DBPs (nine HANs, nine HNMs and seven HAAms) in disinfected waters using liquid-liquid extraction followed by gas chromatography-mass spectrometry. The use of a programmable temperature vaporiser injector minimises degradation of the thermally labile HNMs, while avoiding the concomitant decreases in HANs and HAAms which occur when using lower injector temperatures. Extraction parameters, including sample pH, solvent volume, salt addition and sample pre-concentration, were investigated to determine the optimal conditions across all target N-DBPs. Good detection limits were achieved for all analytes (0.8–1.7 μg L−1) and both laboratory and instrumental runtimes were significantly reduced compared to previous methods. The method was validated for the analysis of N-DBPs in drinking, swimming pool and spa waters, and concentrations of up to 41 μg L−1 of some N-DBPs were measured in some pools.

Weak magnetic field accelerates chloroacetamide removal by zero-valent iron in drinking water

Chloroacetamides (CAMs) as a class of highly toxic nitrogenous disinfection by-products (N-DBPs) have been widely detected in drinking water. It has been reported that weak magnetic field (WMF) could improve the removal ability of zero-valent iron (ZVI) to some pollutants, but CAMs removal by ZVI coupled with WMF has never been studied. This study through oxic batch experiments was executed to investigate the effect of WMF on trichloroacetamide (TCAM) removal by different doses of ZVI under different pH levels and to explore how WMF works on TCAM removal for the first time. The results showed that the WMF improved TCAM removal by ZVI and the strengthening effect of WMF was more significant at lower ZVI dose or higher pH conditions. The formation of trichloroacetic acid indicated the occurrence of TCAM hydrolysis. Chlorine mass balance was observed in TCAM and its potential products, dichloroacetamide, monochloroacetamide, and chloride, indicating these were all the products and a dechlorination process occurred when TCAM contacted with ZVI. By calculating the yields of hydrolytic products and dechlorinated products, it was determined that dechlorination of TCAM was the dominant reaction for TCAM removal by ZVI with and without WMF, while hydrolysis reaction played a minor role. Mechanism analysis showed that the WMF promoted TCAM hydrolysis through impacting the electromigration within the oxide scale and improving the migration of paramagnetic oxygen to the surface of magnetized ZVI. Taken together, ZVI coupled with WMF is a potential effective technology for TCAM removal in effluent of chlorination.

Insight into carbamazepine degradation by UV/monochloramine: Reaction mechanism, oxidation products, and DBPs formation

UV/monochloramine (NH2Cl) process has attracted some attention for the elimination of contaminants of emerging concern as a novel advanced oxidation process. However, there is still much uncertainty on the performance and mechanisms of UV/NH2Cl process because of its complexity and generation of various species of radicals, including NH2•, HO•, Cl• and other reactive chlorine species (RCS). The mechanism and influence factors of degradation of carbamazepine (CBZ) in the UV/NH2Cl process were investigated, and a synergistic effect was observed. Degradation of CBZ under all investigated conditions followed pseudo-first order kinetics. The corresponding rate constant increased along with the dosage of NH2Cl, and was affected significantly by the presence of bicarbonate and natural organic matter. The process has little pH-dependency, while the specific contribution of RCS and HO• changed with solution pH, and RCS always act as a major contributor to the degradation of CBZ. Eleven byproducts of CBZ were identified and their respective evolution profiles were determined. The participation of UV in chloramination can reduce the formation of nitrogenous DBPs, but promote the formation of carbonaceous DBPs. Furthermore, when influent, sand filtered, and granular activated carbon filtered water was respectively used as background, degradation of CBZ was inhibited to different degree and more disinfection byproducts (DBPs) were generated, compared to deionized water. The electrical energy per order for degradation of CBZ in the UV/NH2Cl process was also calculated to obtain some preliminary cost information.

Formation characteristics of carbonaceous and nitrogenous disinfection by-products depending on residual organic compounds by CGS and DAF

Allogenic organic matter (AOM) composed of extracellular and intracellular organic matter (EOM and IOM) is a major precursor of halogenated carbonaceous and nitrogenous disinfection by-products (C-DBPs and N-DBPs) upon chlorination. The EOM and IOM extracted from Microcystis aeruginosa were analyzed based on bulk parameters and organic fractions with different molecular weight by liquid chromatography with organic carbon detection (LC-OCD). It investigated the efficiency of a conventional gravity system (CGS) and dissolved air flotation (DAF) in the removal of organic precursors, together with measurement of the formation of four major trihalomethanes (THMs) and haloacetonitriles (HANs) in treated water upon chlorination. The results showed that EOM accounted for 59% of building blocks and humic substances, whereas for IOM, 54% were low molecular weight (LMW) neutrals. Both CGS and DAF showed 57-59% removal of dissolved organic carbon (DOC) from EOM and IOM. Regarding DON removal, DAF was found to be more effective, i.e., 8% higher than CGS for EOM. Moreover, the removal of LMW acids and neutrals (not easy to remove and are major precursors of DBPs) from EOM and IOM by DAF was higher than from CGS. The amounts of DBPs measured in all the samples treated for interchlorination were much lower than in the samples for prechlorination. Although the precursors of EOM had a higher concentration than in IOM, THMs and HANs were detected for IOM at a higher concentration, which might be attributed to higher amounts of aromatic, aliphatic moisture and protein compounds in the IOM. Comparatively, DAF showed lower THM and HAN values than CGS water, particularly for IOM. Also, DAF showed a sharp decrease in THMs and an insignificant increase in HANs according to time.