[Disinfection By-products in Drinking Water and Their Control Strategies: A Review].

Disinfection by-products(DBPs) are secondary pollutants generated by the reaction of disinfectants with organic or inorganic precursors during drinking water disinfection. DBPs have received considerable global attention due to their carcinogenic, teratogenic, and mutagenic characteristics. Focusing on drinking water, this paper introduces the main classification and research history of DBPs, and then summarizes the concentration levels of common DBPs in drinking water, and DBPs regulatory compliance in global drinking water standards. Further, the control strategies for DBPs in drinking water, including source control, process control, DBPs removal and integrated control are introduced together with the advantages and disadvantages. Finally, a summary and review of the current level and future trends of DBPs research in China are presented with the proposed control strategies. On the one hand, when evaluating the control effect of a process or technology, the DBPs concentration and comprehensive toxicity should be considered; on the other hand, in order to realize the efficient control of DBPs in drinking water, the focus should be on the integrated methods coupling different DBPs control methods.

Enhancing trace acrylamide analysis by bromine derivatization coupled with direct-immersion solid-phase microextraction in drinking water.

Acrylamide is a neurotoxic and genotoxic compound. It is abundant in drinking water because of the usage of polyacrylamide. Its high polarity and small molecular weight characteristics make it difficult to be extracted and analysed. In this study, a novel method was optimized for the determination of trace acrylamide in drinking water. The optimized method, uses bromine derivatization, can avoid false analysis of co-extractives and precursors effectively by transferring acrylamide to 2-bromopropenamide. The 2-bromopropenamide was extracted from water samples using DI-SPME and further analysed by GC-MS. This optimized method uses CAR/PDMS coating SPME fibre to extract at 55°C for 45 min after the addition of 12 g Na2SO4, and then desorbs the extractions in GC injector at 260°C for 3 min. The detection limit was 0.05 µg/L with linearity ranging from 0.5 to 500 µg/L. The repeatability and reproducibility relative standard deviation were 7.30% and 8.50%, respectively. The spiking recovery of tap water samples ranged from 100% to 106%. These results confirmed that this novel method was more precise and accurate than the previously reported SPME methods that used to analyse trace acrylamide in drinking water. The concentrations of acrylamide in the collected samples from clarification and filtration units were 0.80 and 0.71 g/L respectively.

Comparison of different disinfection processes for controlling disinfection by-product formation in rainwater.

With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO4) and potassium ferrate (K2FeO4), ultraviolet/hydrogen peroxide (UV/H2O2), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO4 pre-oxidation, better reduction of almost all DBPs was observed during K2FeO4 pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO4 and K2FeO4. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H2O2. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater.

Enhanced ronidazole degradation by UV-LED/chlorine compared with conventional low-pressure UV/chlorine at neutral and alkaline pH values.

Ultraviolet light-emitting diodes (UV-LEDs) are promising alternatives to conventional low-pressure UV (LPUV) lamps, mainly because they contain no toxic mercury and have a potential for less energy consumption and longer lifetime. In this study, UV sources including UV-LEDs (265, 275 and 285 nm) and LPUV (254 nm) were compared in UV/chlorine degradation of an organic contaminant, ronidazole (RNZ). UV-LED/chlorine performed better than LPUV/chlorine at neutral and alkaline pH values for RNZ degradation considering the fluence-based rate constant. However, the wall plug efficiencies of UV-LEDs are relatively low at present and must reach about 20-25% to achieve the same electrical energy per order as the LPUV in UV/chlorine degradation of RNZ at pH 7.5 and 9. Neither the contribution of radical (HO· or Cl·) nor the quantum yield of chlorine could explain the different RNZ degradation rate by UV/chlorine at different wavelengths and pH values, while the chlorine photolysis rate should be the key factor for these phenomena. The effects of common co-existing substances in real water (chloride, bicarbonate and natural organic matter) on UV/chlorine degradation of RNZ were similar at different UV wavelengths. Opposite to other oxidants or reductants, the molar absorption coefficient of chlorine increases when the UV wavelength increases from 254 to 285 nm at neutral and alkaline pH, which makes UV-LED/chlorine one of the best choices for UV-LED-based advanced oxidation/reduction processes.

[Removal Efficiency of Trichloroacetamide by UV/Sodium Sulfite].

Haloacetamides (HAcAms) are an emerging class of nitrogenous disinfection by-products (N-DBPs) with high cytotoxicity and genotoxicity, which are widely detected in drinking water. The toxicity of trichloroacetamide (TCAcAm) is significantly higher than traditional DBPs. In this study, ultraviolet (UV) treatment was combined with sodium sulphite (Na2SO3) to remove TCAcAm from water. The effects of different light intensities, different agent dosages (Na2SO3), and pH conditions on the removal of TCAcAm by UV/Na2SO3 advanced reduction process were investigated. The results showed that TCAcAm could be rapidly degraded by the UV/Na2SO3 system. The degradation effect was directly proportional to light intensity, dosage of Na2SO3, and pH. Moreover, the pH had a significant effect on the reaction rate and degradation rate. As the pH increased from 6 to 9, the degradation rate of TCAcAm increased from 12.8% to 99.6%, in 120 min. The removal rate of TCAcAm reached 99.4% when the UV light intensity, pH, Na2SO3 dosage, and reaction time were 450 µW·cm-2, 9, 1.00 mmol·L-1, and 30 min, respectively. The experimental results indicated that the UV/Na2SO3 system is an efficient advanced reduction process for the removal of TCAcAm, and it has the potential to reduce other halogenated DBPs. Therefore, it could be used for the degradation of halogenated DBPs in the treatment of drinking water.

Effect of UV wavelength on humic acid degradation and disinfection by-product formation during the UV/chlorine process.

The efficiency of the ultraviolet (UV)/chlorine process strongly depends on UV wavelength because chlorine photolysis and its subsequent radical formation are highly wavelength-dependent. This study compared the degradation of humic acid (HA) during the UV/chlorine process by low pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 310 nm). The results indicated that HA degradation followed the pseudo-first-order kinetics, and the fluence-based degradation rate constants (kobs) were significantly affected by UV wavelength and solution pH. HA degradation decreased greatly with increasing solution pH during the UV/chlorine process at 254 nm, while the opposite trend was observed at 275 and 310 nm. In the meantime, kobs decreased in the order of 275 nm > 254 nm > 310 nm at pH > 7.0. The changes of chlorine molar absorption coefficients at different UV wavelengths resulted in the variation of chlorine photodecay rates (kobs, chlorine), and the synergistic effects of kobs, chlorine and chlorine quantum yields (Φchlorine) affected HA reduction. The formation of disinfection by-products (DBPs) during the UV/chlorine process was also evaluated. A significant suppression on DBP formation and DBP-associated calculated theoretical cytotoxicity were observed at 275 nm high UV fluence and alkaline pHs. These findings in this study demonstrate that UV wavelength at 275 nm is more suitable for HA degradation by the UV/chlorine advanced oxidation process in practical applications.

Effect of UV irradiation on iodinated trihalomethane formation during post-chloramination.

Ultraviolet (UV) irradiation has been widely used in drinking water treatment processes, but its influence on the formation of disinfection by-products (DBPs), especially the emerging iodinated trihalomethanes (I-THMs) during post-chloramination remains unclear. This study evaluated the impact of low pressure (LP) UV treatment on the formation of I-THMs during post-chloramination through two pathways. The first pathway is through the transition of DOM structure and composition during UV-chloramination, resulting significant increase of I-THM formation with increasing UV dosage in different dissolved organic matter (DOM)-containing water (49.7%-90.5% at 1160 mJ/cm2). With the application of excitation emission matrix-parallel factor analysis (EEM-PARAFAC), we found that I-THM formation in UV-chloraminated water correlated well with two ratios of three PARAFAC humic-like components (C3/C2 and C1/C2, R2 = 0.958-1.000), suggesting that the ratios of fluorescent components can be used as reliable indicators for I-THM formation. Moreover, the shift in these fluorescent components is crucial for I-THM formation during UV-chloramination. Another pathway for UV irradiation to affect I-THM formation during post-chloramination is through the transformation of iodine species. Large amounts of reactive iodine species (HOI/I2 and I3-) can be generated directly in the mixed iodine system by UV light, leading to the enhancement of iodine utilization factor (IUF) (up to 0.040) after post-chloramination. These results suggest that UV application to DOM-containing water may induce changes in organic precursors and iodine species so as to enhance I-THM formation during post-chloramination.

Degradation of acrylamide during chlorination as a precursor of haloacetonitriles and haloacetamides.

Acrylamide is a monomer of polyacrylamide, which is widely used in the water treatment process as a flocculant. The degradation kinetics and formation of disinfection by-products (DBPs) during acrylamide chlorination were investigated in this study. The reaction between chlorine and acrylamide followed a pseudo-first-order kinetics. A kinetic model regarding acrylamide chlorination was established and the rate constants of each predominant elementary reaction (i.e., the base-catalyzed reaction of acrylamide with ClO- as well as the reactions of acrylamide with HOCl and ClO-) were calculated as 7.89×107M-2h-1, 7.72×101M-1h-1, and 1.65×103M-1h-1, respectively. The presence of Br- in water led to the formation of HOBr and accelerated the rate of acrylamide degradation by chlorine. The reaction rate constant of acrylamide with HOBr was calculated as 1.33×103M-1h-1. The degradation pathways of acrylamide chlorination were proposed according to the intermediates identified using ultra-performance liquid chromatography and electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Five chlorinated DBPs including chloroform (CF), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAcAm), and trichloroacetamide (TCAcAm) were identified during acrylamide chlorination. The formation of CF, DCAN, DCAcAm, and TCAcAm kept increasing, while that of TCAN increased and then decreased with increasing reaction time. As the chlorine dosage increased from 0.75 to 4.5mM, DCAN became the dominant DBP. Large amounts of CF, DCAN, and TCAN were formed at basic pHs. The hydrolysis of DCAN and TCAN led to the formation of DCAcAm and TCAcAm, respectively. The results of this study elucidated that acrylamide can be a precursor for the formation of haloacetonitriles (HANs) and haloacetamides (HAcAms) during drinking water treatment.

Iodinated trihalomethane formation during chloramination of iodate-containing waters in the presence of zero valent iron.

Iodide (I-) and iodinated X-ray contrast media (ICM) are the primary iodine sources for the formation of iodinated disinfection byproducts (I-DBPs), and iodate (IO3-) is believed to be a desired sink of iodine in water. This study found that highly cytotoxic iodinated trihalomethanes (I-THMs) also can be generated from iodate-containing waters (without any other iodine sources) in the presence of zero valent iron (ZVI) during chloramination, which could be a big issue in the wide usage of iron pipes. The effect of major factors including ZVI dosage, NH2Cl and IO3- concentrations, initial pH, Br-/IO3- molar ratio, phosphate concentration, iron corrosion scales (goethite and hematite) on the formation of I-THMs were investigated. Formation of I-THMs from IO3- increased with the increase of ZVI dosage, IO3- and NH2Cl concentrations. Chloramines can also remarkably accelerate the reduction of IO3- by ZVI. Peak I-THM formation was found at pH 8. As the Br-/IO3- molar ratio increased from 0 to 20, I-THM formation considerably enhanced, especially for the bromine-incorporated species. Goethite and hematite enhanced the formation of I-THMs in the presence of ZVI. Additionally, a significant suppression on I-THM formation was observed with the addition of phosphate. Considering that a large number of water distribution networks contain unlined cast iron pipes, transformation of IO3- in the presence of ZVI during chloramination may contribute to the formation of I-THMs in such systems.

Chlor(am)ination of iopamidol: Kinetics, pathways and disinfection by-products formation.

The degradation kinetics, pathways and disinfection by-products (DBPs) formation of iopamidol by chlorine and chloramines were investigated in this paper. The chlorination kinetics can be well described by a second-order model. The apparent second-order rate constants of iopamidol chlorination significantly increased with solution pH. The rate constants of iopamidol with HOCl and OCl- were calculated as (1.66 ± 0.09) × 10-3 M-1 s-1 and (0.45± 0.02) M-1 s-1, respectively. However, the chloramination of iopamidol fitted well with third-order kinetics and the maximum of the apparent rate constant occurred at pH 7. It was inferred that the free chlorine (i.e., HOCl and OCl-) can react with iopamidol while the combined chlorine species (i.e., NH2Cl and NHCl2) were not reactive with iopamidol. The main intermediates during chlorination or chloramination of iopamidol were identified using ultra performance liquid chromatography - electrospray ionization-mass spectrometry (UPLC-ESI-MS), and the destruction pathways including stepwise deiodination, hydroxylation as well as chlorination were then proposed. The regular and iodinated DBPs formed during chlorination and chloramination of iopamidol were measured. It was found that iodine conversion from iopamidol to toxic iodinated DBPs distinctly increased during chloramination. The results also indicated that although chloramines were much less reactive than chlorine toward iopamidol, they led to the formation of much more toxic iodinated DBPs, especially CHI3.

Formation of organic chloramines during chlor(am)ination and UV/chlor(am)ination of algae organic matter in drinking water.

Surface water are frequently subjected to problems of algal blooms and release of algae organic matter (AOM) from the algae cells, which cause many water quality issues. This study investigated the formation of organic chloramines and nitrogenous disinfection by-products (N-DBPs) during chlor(am)ination and UV/chlor(am)ination of AOM in drinking water. AOM caused higher organic chloramine formation than humic acid and fulvic acid during chlor(am)ination. The formation of organic chloramines increased first and then decreased with the increase of free chlorine dosage, but kept increasing with the increase of NH2Cl dosage. During AOM chlorination, the formation of organic chloramines kept decreasing as the reaction time went by, and the maximum organic chloramine proportion (79.1%) in total chlorine occurred at 8 h. However, during AOM chloramination, the formation of organic chloramines increased first, decreased in the following and then increased again as the reaction time went by, and the maximum organic chloramine proportion (22.1%) in total chlorine occurred at 24 h. UV irradiation pretreatment did not effectively influence organic chloramine formation during AOM chlor(am)ination, but accelerated the degradation of organic chloramines during chloramination. Besides, UV pretreatment enhanced the formation of N-DBPs during the subsequent chlor(am)ination of AOM, especially dichloroacetonitrile.

[Composition of NOM in raw water of Danjiangkou Reservoir of South-to-North Water Diversion Project and comparison of efficacy of enhanced coagulation].

The best enhanced coagulation conditions for the raw water of Danjiangkou Reservoir of South-to-North Water Diversion Project and the molecular weights as well as hydrophobicity composition of Natural organic matter (NOM) in the water were investigated in this study. The results showed that the NOM in the raw water of Danjiangkou Reservoir of South-to-North Water Diversion Project was mainly composed of the fraction with a molecular weight of < 1 000 and transphilic components. Dissolved organic carbon (DOC, 39.98%) and UV254 (39.10%) were the major components. And the fraction with a molecular weight of < 1 000 had the highest contents of THMFP and N-DBPFP. In the raw water of Danjiangkou Reservoir, the sum of transphilic and hydrophobic fractions was up to 80%, and the hydrophobic fraction was the minimum contributor of the NOM, but the THMFP of the hydrophobic fraction had the highest percentage. And when the raw water of Danjiangkou Reservoir was treated using polymeric ferric sulfate (PFS, 4 mg x L(-1)) and poly-acrylamide (PAM, 0.4 mg x L(-1)) , the optimal removal rates of turbidity, DOC, UV254 and THMFP were 76.33%, 25.57%, 37.78% and 23.16%, respectively. The results of this paper can provide theoretical and technological basis for upgrading of the process and operation optimization of original drinking water treatment plants in the intake area of South-to-North Water Diversion Project.

[Formation of Disinfection By-Products During Chlor(am)ination of Danjiangkou Reservoir Water and Comparison of Disinfection Processes].

This study discussed the formation of volatile carbonaceous disinfection by-products (DBPs) and nitrogenous DBPs during chlor(am) ination of Danjingkou Reservoir water which was the source of the Middle Route Project of South-to-North Water Diversion Project. The effects of disinfection methods, disinfectant dosage, reaction time, pH values and bromide ion concentration were investigated. And the disinfection parameters were optimized. Four DBPs, including chloroform (CF), bromodichloromethane (BDCM), dichloroacetonitrile(DCAN) and trichloronitromethane(TCNM), were observed during the chlorination. But only CF and TCNM were detected during the chloramination of water. The disinfection by-product (DBP) concentration from chlorination is 7. 5 times higher than that from chloramination, and the yield of DBPs from short time chlorination then chloramination is in between the first two methods. All kinds of DBPs detected increased with the dosage of increasing chlorine, but the increases slowed down when the dosage was higher than 2 mg . L -1. The formation of CF varied a little as the dosage of chloramine increasing. TCNM was detected when the chloramine dosage was greater than 2 mg . L -1. As reaction time going on, chlorine decayed much faster than chloramine, while DBP formation under chlorination was faster than that of chloramination. THM produced by chlorine increased with the increasing pH, while chloramination showed no obvious changes. As the bromide ion increasing, the species of DBPs transformed from chlorinated DBPs to brominated ones, and the total yield of DBPs increased during both chlorination and chloramination, but the former one was obviously more than that of the latter one. In order to reduce the risk of DBP formation, the chloramination is suggested in the treatment of water from Danjiangkou Reservoir. And if chlorination is applied, the disinfectant dosage should be controlled seriously.

Photochemical degradation of ciprofloxacin in UV and UV/H2O2 process: kinetics, parameters, and products.

Photochemical degradation of fluoroquinolone ciprofloxacin (CIP) in water by UV and UV/H2O2 were investigated. The degradation rate of CIP was affected by pH, H2O2 dosage, as well as the presence of other inorganic components. The optimized pH value and H2O2 concentration were 7.0 and 5 mM. Carbonate and nitrate both impeded CIP degradation. According to liquid chromatography-tandem mass spectrometry analysis, four and 16 products were identified in UV and UV/H2O2 system, respectively. Proposed degradation pathways suggest that reactions including the piperazinyl substituent, quinolone moiety, and cyclopropyl group lead to the photochemical degradation of CIP. Toxicity of products assessed by Vibrio qinghaiensis demonstrated that UV/H2O2 process was more capable on controlling the toxicity of intermediates in CIP degradation than UV process.

Formation of nitrogenous disinfection by-products from pre-chloramination.

A sampling survey investigated the formation of nitrogenous disinfection by-products (N-DBPs) and carbonaceous DBPs (C-DBPs) from pre-chloramination, an increasingly common treatment strategy in China for regulated C-DBP control, followed by subsequent conventional water treatment processes, i.e., coagulation, sedimentation, and filtration. Dihalogenated N-DBPs typically peaked in the summer and early autumn with a relatively higher temperature, with the maximum levels of dichloroacetamide (DCAcAm), dichloroacetonitrile (DCAN), bromochloroacetonitrile, dibromoacetonitrile and dichloroacetone at 1.8, 6.3, 6.0, 2.6 and 1.8µgL(-1) in the finished water, respectively. Also, the levels of all the dichlorinated N-DBPs were correlated with the ratio of dissolved organic nitrogen (DON) to dissolved organic carbon, implying autochthonous DON played an essential role in the formation of these DBPs. In contrast, the yields of trihalogenated DBPs [chloroform (CF), trichloronitromethane (TCNM) and trichloroacetone (TCAce)] appeared not to be significantly affected by seasons. CF and DCAN were the dominant species in trihalomethanes (THMs) and dihaloacetonitriles (DHANs), respectively. Bromine was more readily incorporated into DHANs to form brominated DBPs than THMs during pre-chloramination. Although pre-chloramination can ensure the finished water to meet with the current Chinese THM regulatory limits, the increased levels of TCNM and TCAce may be a new water quality concern.

Comparison of inclined plate sedimentation and dissolved air flotation for the minimisation of subsequent nitrogenous disinfection by-product formation.

The formation of disinfection by-products (DBPs), including both nitrogenous disinfection by-products (N-DBPs) and carbonaceous disinfection by-products (C-DBPs), was investigated upon chlorination of water samples following two treatment processes: (i) coagulation-inclined plate sedimentation (IPS)-filtration and (ii) coagulation-dissolved air flotation (DAF)-filtration. The removal of algae, dissolved organic nitrogen (DON), dissolved organic carbon (DOC) and UV(254) by coagulation-DAF-filtration was superior to coagulation-IPS-filtration. On average, 53%, 53% and 31% of DOC, DON and UV(254) were removed by coagulation-DAF-filtration process, which were higher than 47%, 31% and 27% of that by coagulation-IPS-filtration process. Additionally, coagulation-IPS-filtration performed less well at removing the low molecular weight organics than coagulation-DAF-filtration process. The concentrations of chloroform, dichloroacetamide (DCAcAm) and dichloroacetonitrile (DCAN) formed during chlorination after coagulation-DAF-filtration reached their maximum values of 13, 1.5 and 4.7µgL(-1), respectively, and were lower than those after coagulation-IPS-filtration with the maximum detected levels of 17, 2.9 and 6.3µgL(-1). However, the trichloronitromethane (TCNM) concentration after the two processes was similar, suggesting that DON may have less of a contribution to TCNM formation than DCAcAm and DCAN.

Precursors of dichloroacetamide, an emerging nitrogenous DBP formed during chlorination or chloramination.

Haloacetamides (HAcAms) are an emerging class of nitrogenous disinfection byproducts (N-DBPs). However, there is a limited understanding about the precursors of HAcAms. In this study, we screened the precursors of dichloroacetamide (DCAcAm), the most commonly identified HAcAm in chlorinated or chloraminated drinking water. DCAcAm formation potential (FP) of raw water samples collected in different months from a reservoir in China was determined during chlorination, and the highest DCAcAm FP typically occurred in the summer samples. Dissolved organic matter (DOM) in a representative summer raw water sample was separated into six fractions by a series of resin elutions. Among them, hydrophilic acid (HiA) DOM showed the maximum DCAcAm FP, followed by hydrophilic bases (HiB) and, to a much lower extent, hydrophobic acids (HoA). Fluorescence excitation-emission matrix (EEM) spectra revealed that a mass of protein-like substances in the HiA fraction, made up of amino acids (AAs), were the likely DCAcAm precursors. Finally, we investigated the DCAcAm yields of 20 AAs during chlorination. Among them, seven AAs (aspartic acid, histidine, tyrosine, tryptophan, glutamine, asparagine, phenylalanine) could form DCAcAm during chlorination, with the corresponding DCAcAm yields of 0.231, 0.189, 0.153, 0.104, 0.078, 0.058, and 0.050 mmol/mol AA.

Formation of haloacetamides during chlorination of dissolved organic nitrogen aspartic acid.

The stability of haloacetamides (HAcAms) such as dichloroacetamide (DCAcAm) and trichloroacetamide (TCAcAm) was studied under different experimental conditions. The yield of HAcAms during aspartic acid (Asp) chlorination was measured at different molar ratio of chlorine atom to nitrogen atom (Cl/N), pH and dissolved organic carbon (DOC) mainly consisted of humic acid (HA) mixture. Ascorbic acid showed a better capacity to prevent the decay of DCAcAm and TCAcAm than the other two dechlorinating agents, thiosulfate and sodium sulfite. Lower Cl/N favored the DCAcAm formation, implying that breakpoint chlorination might minimize its generation. The pH decrease could lower the concentration of DCAcAm but favored dichloroacetonitrile (DCAN) formation. DCAcAm yield was sensitive to the DOC due to higher chlorine consumption caused by HA mixture. Two possible pathways of DCAcAm formation during Asp chlorination were proposed. Asp was an important precursor of DCAN, DCAcAm and dichloroacetic acid (DCAA), and thus removal of Asp before disinfection may be a method to prevent the formation of DCAcAm, DCAN and DCAA.

Formation of chloroform during chlorination of alanine in drinking water.

Currently, dissolved nitrogenous organic matters in water, important precursors of disinfection by-products (DBPs), are of significant concern. This study was to explore the formation of chloroform (CF) during chlorination of alanine (Ala), an important nitrogenous organic compound commonly present in water sources. Our results indicated that the CF yield reached a maximum value of 0.143% at the molar ratio of chlorine atom to nitrogen atom (Cl/N)=1.0 over a Cl/N range of 0.2-5.0 (pH=7.0, reaction time=5d, and initial Ala=0.1mM). At an acidic-neutral condition (pH 4-7), the formation of CF was suppressed. However, the highest CF yield (0.227%) occurred at weakly alkaline condition (pH 8.0) (initial Ala=0.1mM, and Cl/N=1.0). The increase of Br(-) in water can increase total trihalomethanes (THMs) and bromo-THMs. However, the bromo-THMs level reached a plateau at Br(-)/Cl>0.04. Finally, based on the computation of frontier electron density and identification and measurement of key intermediates during Ala chlorination, we proposed a formation pathway of CF from Ala chlorination: Ala-->monochloro-N-alanine (MC-N-Ala)-->acetaldehyde (AAld)-->monochloroacetaldehyde acetaldehyde (MCAld)-->dichloroacetaldehyde (DCAld)-->trichloroacetaldehyde (TCAld)-->CF.

[Factors affecting formation of THMs during dissolved organic nitrogen acetamide chlorination in drinking water].

Chlorination disinfection greatly reduced bacteria and virus in drinking water. However, there is an unintended consequence of disinfection, the generation of chemical disinfection by-products (DBPs). Dissolved organic nitrogen (DON) as the important precursor of DBPs is of current concern. As acetamide (AcAm) occur in important bimolecular, we studied formation pathways for THMs during chlorination of model AcAm. The experiments are designed by Plackett-Burman and Box-Behnken methods. Factors affecting formation of THMs such as AcAm initial concentration, chlorine dosage, pH, temperature, Br(-) concentration and contact time were investigated. The results indicate that AcAm initial concentration, pH and temperature have little effects on formation of THMs. On the contrary, three other factors have important effects on formation of THMs, especially Br(-) concentration. The capacity of THMs generation varies very little when Br(-) has a constant concentration. Generation amount of THMs attach maximum under the condition that dosage of active chlorine, Br(-) concentration and contact time is 8.77 mg/L, 0.77 mg/L and 6.20 h respectively. Bromine ion plays a catalysis role on THMs formation. Controlling the concentration of bromine ion can reduce total generation amount of THMs via AcAm. Bromine partition coefficient tends to increasing along with contact time lapse. Controlling chlorination reaction time can lower the cancer risk. At last, the pathway is proposed for THMs formation via AcAm, and the catalysis mechanism of Br(-) was addressed.