Impact of UV/H2O2 pre-oxidation on the formation of haloacetamides and other nitrogenous disinfection byproducts during chlorination

Use of coupled wavelength ultraviolet light-emitting diodes for inactivation of bacteria in subsea oil-field injection water

The development of subsea injection water disinfection systems will enable the novel exploration of offshore oilfields. Ultraviolet light emitting diodes (UV-LEDs) with peak wavelengths at 255 nm, 280 nm, 350 nm, and combinations of 255 nm and 350 nm, and 280 nm and 350 nm were investigated in this study to determine their efficiency at disinfecting saprophytic bacteria, iron bacteria, and sulfate reducing bacteria. Results show that UV-LEDs with peak wavelengths at 280 nm were the most practical in this domain because of their high performance in both energy-efficiency and reactivation suppression, although 255 nm UV-LEDs achieved an optimal germicidal effect in dose-based experiments. The use of combined 280 nm and 350 nm wavelengths also induced synergistic bactericidal effects on saprophytic bacteria.

Effective and sensitive determination of eleven disinfection byproducts in drinking water by DLLME and GC-MS

The aim of this study was to optimize the dispersive liquid-liquid microextraction (DLLME) parameters for simultaneous analysis through DLLME-gas chromatography-mass spectrometry (GC-MS) of six iodo-trihalomethanes, four haloacetonitriles, and one halonitromethane, which are residual disinfection products found in drinking water. Eleven disinfection by-product (DBPs) remaining in aqueous samples were extracted and concentrated using a simple, rapid, and environmentally friendly DLLME method, and then analyzed simultaneously by GC-MS. The optimized DLLME parameters were a sample volume of 5 mL, 100 μL of dichloromethane as the extraction solvent, 1 mL of methanol as the dispersion solvent, an extraction time of 60 s, and 1.5 g of sodium chloride for the salting out effect. The enrichment factor values obtained using the established DLLME-GC-MS method were 19.8-141.5, and the limit of detection and limit of quantification were 0.22-1.19 μg/L and 0.75-3.98 μg/L, respectively. The calibration curves had correlation coefficients (r²) of 0.9958-0.9992 in the concentration range of 0.5-40 μg/L, and they exhibited good linearity in quantitative analysis. This new method could be useful for analyzing eleven DBPs that remain in drinking water.

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes

Chloride ion (Cl^-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl^- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H₂O₂ processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl^- is present to the rate when Cl^- is not present (designated as r_R^Cl-/ r_R) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, r_R^Cl-/ r_R, can be no larger than 60%. Hence, Cl^- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H₂O₂ process, we found that Cl^- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl^- will adversely impact organic compounds destruction by the UV/PS and UV/H₂O₂ processes.

Impact of ClO2 pre-oxidation on the formation of CX3R-type DBPs from tyrosine-based amino acid precursors during chlorination and chloramination

ClO₂ is frequently used as a pre-oxidant in water treatment plants. However, the effects of ClO₂ pre-oxidation on disinfection by-product (DBP) formation, especially the highly toxic nitrogenous DBPs, during subsequent chlor (am)ination have not been studied thoroughly. There is also limited information about DBP formation from combined amino acids (AAs), which are more abundant than free AAs in source waters. Many typical DBPs (including representative N-DBPs) have a similar structure of "CX₃R" (X = H, Cl, Br or I). In the study, tyrosine and forms representing its reactivity in combined AAs (tyrosine tert-butyl ester and Boc-tyrosine) were selected as model precursors. The formation of various regulated and unregulated CX₃R-type DBPs from ClO₂ pre-oxidation and subsequent chlor (am)ination were studied at a wide-range of ClO₂ and chlor (am)ine doses (ClO₂/precursors and chlor (am)ine/precursors are at the range of 0-2.5 and 1-20 [Mol/Mol], respectively). Chloroform and chloral hydrate (CH) yields increased with chlorine dose, while haloacetonitrile and haloacetamide maximized at median chlorine dose (Cl₂/Precursors = 10). All DBP yields increased with chloramine dose. ClO₂ pre-oxidation increased chloroform, haloacetonitrile, trichloronitromethane and CH yields during chlorination, but ClO₂ increased chloroform, CH, trichloroacetamide while decreased dichloroacetonitrile and trichloronitromethane yields during chloramination. The overall toxicity of the formed DBPs was evaluated by cytotoxicity index (CTI). ClO₂ pre-oxidation increased CTI from all precursors during post-chlorination while reduced it during post-chloramination. Results imply that ClO₂ is probably more suitable for use in combination with chloramination disinfection, rather than chlorination, in the integrated control of CX₃R-type DBPs from source waters abundant in AAs.

Degradation of polyvinyl alcohol (PVA) by UV/chlorine oxidation: Radical roles, influencing factors, and degradation pathway

Polyvinyl alcohol (PVA) is widely used in industry but is difficult to degrade. In this study, the synergistic effect of UV irradiation and chlorination on degradation of PVA was investigated. UV irradiation or chlorination alone did not degrade PVA. By contrast, UV/chlorine oxidation showed good efficiency for PVA degradation via generation of active free radicals, such as OH and Cl. The relative importance of these two free radicals in the oxidation process was evaluated, and it was shown that OH contributed more to PVA degradation than Cl did. The degradation of PVA followed pseudo first order kinetics. The rate constant k increased linearly from 0 min^-1 to 0.3 min^-1 with increasing chlorine dosage in range of 0 mg/L to 20 mg/L. However, when the chlorine dosage was increased above 20 mg/L, scavenging effect of free radicals occurred, and the degradation efficiency of PVA did not increase much more. Acidic media increased the degradation efficiency of PVA by UV/chlorine oxidation more than basic or neutral media because of the higher ratio of [HOCl]/[OCl^-], higher free radical quantum yields, and the lower free radical quenching effect under acidic conditions. Results of Fourier Transform Infrared Spectroscopy showed that carbonyl groups in degradation products were formed during UV/chlorine oxidation, and a possible degradation pathway via alcohol to carbonyl was proposed.

Comparative study of the formation of brominated disinfection byproducts in UV/persulfate and UV/H2O2 oxidation processes in the presence of bromide

The objective of this research was to compare the transformation of Br^- and formation of brominated byproducts in UV/persulfate (PS) and UV/H₂O₂ processes. It was revealed that Br^- was efficiently transformed to free bromine which reacted with humic acid (HA) or dihydroxybenzoic acid resulting in the formation of brominated byproducts such as bromoacetic acids (BAAs) in UV/PS system. In contrast, no free bromine and brominated byproducts could be detected in UV/H₂O₂ system, although the oxidization of Br^- was evident. We presumed that the oxidation of Br^- by hydroxyl radicals led to the formation of bromine radicals. However, the bromine radical species could be immediately reduced back to Br^- by H₂O₂ before coupling to each other to form free bromine, which explains the undetection of free bromine and BAAs in UV/H₂O₂. In addition to free bromine, we found that the phenolic functionalities in HA molecules, which served as the principal reactive sites for free chlorine attack, could be in situ generated when HA was exposed to free radicals. This study demonstrates that UV/H₂O₂ is more suitable than UV/PS for the treatment of environmental matrices containing Br^-. Graphical abstract Graphical abstract.

Effects of pre-oxidation and adsorption on haloacetonitrile and trichloronitromethane formation during subsequent chlorination

In this study, the effects of pre-oxidants permanganate (PM), persulfate (PS), hydrogen peroxide (PO), and ozone (OZ)) and/or adsorption on pseudoboemite-chitosan shell magnetic nanoparticles (ACMNs) on haloacetonitrile (HAN) and trichloronitromethane (TCNM) formation from aspartic acid (Asp; positive charge) and/or histidine (His; negative charge) were compared. Asp and His apparently do not interact in aqueous solution during chlorination. Asp and/or His can undergo partially oxidation by PM, but are recalcitrant to direct oxidation by PS and PO. Pre-oxidation with OZ decreases the formation of HANs but increases the formation of TCNM. ACMN prefers to adsorb Asp over His in the competitive sorption of coexisting Asp and His because of attractive electrostatic interactions. The rank order for the effect of the pre-oxidants and ACMN adsorption on dichloroacetonitrile and trichloroacetonitrile formation is OZ and ACMN adsorption > PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption; that for the effect of the pre-oxidants and ACMN adsorption on TCNM formation is PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption > OZ and ACMN adsorption. The favored adsorption of Asp over His by ACMN is weakened by pre-oxidation.

The shadow of dichloroacetonitrile (DCAN), a typical nitrogenous disinfection by-product (N-DBP), in the waterworks and its backwash water reuse

Dichloroacetonitrile (DCAN) is one of nitrogenous disinfection by-products (N-DBPs) with strong cytotoxicity and genotoxicity. In this study, the formation potential (FP) of DCAN was investigated in the samples of six important water sources located in the Yangtze River Delta. The highest formation concentration of DCAN was 9.05 μg/L in the water sample taken from Taihu Lake with the lowest SUVA value. After the NOM fractionation, the conversion rate of hydrophilic fraction to DCAN was found the highest. Subsequently, a waterworks using Taihu Lake as water source was chosen to research the FP variations of DCAN in the treatment process and backwash water. The results showed that, compared to the conventional treatment process, O/biological activated carbon (BAC) process increased the removal efficiency of DCAN from 21.89% to 50.58% by removing aromatic protein and soluble biological by-products as main precursors of DCAN. The DCAN FP in the effluent of BAC filters using old granular activated carbon was higher than that in the influent and the DCAN FP of its backwash water was lower than that in raw water. In the backwash water of sand filters, the DCAN FP higher than raw water required the recycle ratio less than 5% to avoid the accumulation of DCAN.

Control of aliphatic halogenated DBP precursors with multiple drinking water treatment processes: Formation potential and integrated toxicity

The comprehensive control efficiency for the formation potentials (FPs) of a range of regulated and unregulated halogenated disinfection by-products (DBPs) (including carbonaceous DBPs (C-DBPs), nitrogenous DBPs (N-DBPs), and iodinated DBPs (I-DBPs)) with the multiple drinking water treatment processes, including pre-ozonation, conventional treatment (coagulation-sedimentation, pre-sand filtration), ozone-biological activated carbon (O₃-BAC) advanced treatment, and post-sand filtration, was investigated. The potential toxic risks of DBPs by combing their FPs and toxicity values were also evaluated. The results showed that the multiple drinking water treatment processes had superior performance in removing organic/inorganic precursors and reducing the formation of a range of halogenated DBPs. Therein, ozonation significantly removed bromide and iodide, and thus reduced the formation of brominated and iodinated DBPs. The removal of organic carbon and nitrogen precursors by the conventional treatment processes was substantially improved by O₃-BAC advanced treatment, and thus prevented the formation of chlorinated C-DBPs and N-DBPs. However, BAC filtration leads to the increased formation of brominated C-DBPs and N-DBPs due to the increase of bromide/DOC and bromide/DON. After the whole multiple treatment processes, the rank order for integrated toxic risk values caused by these halogenated DBPs was haloacetonitriles (HANs)≫haloacetamides (HAMs)>haloacetic acids (HAAs)>trihalomethanes (THMs)>halonitromethanes (HNMs)≫I-DBPs (I-HAMs and I-THMs). I-DBPs failed to cause high integrated toxic risk because of their very low FPs. The significant higher integrated toxic risk value caused by HANs than other halogenated DBPs cannot be ignored.

Kinetic removal of haloacetonitrile precursors by photo-based advanced oxidation processes (UV/H2O2, UV/O3, and UV/H2O2/O3)

The objective of the study is to evaluate the performance of conventional treatment process (i.e., coagulation, flocculation, sedimentation and sand filtration) on the removals of haloacetonitrile (HAN) precursors. In addition, the removals of HAN precursors by photo-based advanced oxidation processes (Photo-AOPs) (i.e., UV/H₂O₂, UV/O₃, and UV/H₂O₂/O₃) are investigated. The conventional treatment process was ineffective to remove HAN precursors. Among Photo-AOPs, the UV/H₂O₂/O₃ was the most effective process for removing HAN precursors, followed by UV/H₂O₂, and UV/O₃, respectively. For 20min contact time, the UV/H₂O₂/O₃, UV/H₂O₂, and UV/O₃ suppressed the HAN formations by 54, 42, and 27% reduction. Increasing ozone doses from 1 to 5 mgL^-1 in UV/O₃ systems slightly improved the removals of HAN precursors. Changes in pH (6-8) were unaffected most of processes (i.e., UV, UV/H₂O₂, and UV/H₂O₂/O₃), except for the UV/O₃ system that its efficiency was low in the weak acid condition. The pseudo first-order kinetic constant for removals of dichloroacetonitrile precursors (k'_DCANFP) by the UV/H₂O₂/O₃, UV/H₂O₂ and standalone UV systems were 1.4-2.8 orders magnitude higher than the UV/O₃ process. The kinetic degradation of dissolved organic nitrogen (DON) tended to be higher than the k'_DCANFP value. This study firstly differentiates the kinetic degradation between DON and HAN precursors.

Production of trihalomethanes, haloacetaldehydes and haloacetonitriles during chlorination of microcystin-LR and impacts of pre-oxidation on their formation

Microcystins (MCs) in drinking water have gained much attention due to their adverse health effects. However, little is known about the impact of pre-oxidation in the formation of disinfection by-products (DBPs) during the downstream chlorination of MCs. The present study examined the formation of both carbonaceous and nitrogenous DBPs from chlorination of MC-LR (the most abundant MC species) and evaluated the impact of permanganate (PM), hydrogen peroxide (H₂O₂) and chlorine dioxide (ClO₂) pre-oxidation on the DBP formation in chlorination. Higher yields of chloroform (CF) (maximum 43.0%) were observed from chlorination of MC-LR than free amino acids which are included in MC-LR structure. Chloral hydrate (CH) and dichloroacetonitrile (DCAN) were also produced from the chlorination of MC-LR, and the latter one was formed probably due to the chlorination of peptide bonds. A high pH favored the production of CF and CH, but inhibited the formation of DCAN. In the presence of bromide, bromo-DBPs could be produced to pose a threat. For example, 0.58μg/L of tribromoacetaldehyde was produced from the chlorination of MC-LR at Br^-=200μg/L. PM and ClO₂ pre-oxidation could both reduce the DBP formation from MC-LR. In contrast, H₂O₂ appeared not to significantly control the DBP formation.

The determination and fate of disinfection by-products from ozonation-chlorination of fulvic acid

Ozonation of fulvic acid (FA) can result in diverse intermediate oxidation by-products, significantly affecting disinfection by-product (DBP) formation following chlorination. The objective of this study was to provide insight into ozone reaction intermediates and reveal the possible formation pathway of DBPs from ozonation of FA due to the formation of intermediate oxidation by-products. Aldehydes, aromatic acids, short-chain acids, chloroform, and dichloroacetic acid were detected at various ozone dosage additions. Aromatic acids were studied by using solid-phase extraction-ultra high-performance liquid chromatography (SPE-UPLC). This new analytical approach enables the extraction and analysis of highly polar carboxylic acids that are difficult to measure using conventional methods. The results showed that formaldehyde, acetaldehyde, glyoxal, methyl-glyoxal, fumaric, malonic protocatechuic, 3-hydroxybenzoic, and benzoic acid were predominant oxidation by-products. The yields of the four aldehydes increased steadily with ozone dosage. When ozone dosage was 2∼2.5 mg/l, the amount of carboxylic acids was largest, and the total amount of the carboxylic acids was about 5∼10 times higher than that of the aldehydes. Besides, hydroxybenzoic acids are the major precursor, although they have low content in ozone reaction solution, they have a great contribution to the DBP formation. This study provides a new perspective on ozonation natural organic matter, which contributes to understand the other sources of DBPs and thus broadens the knowledge of drinking water treatment.

Increase of cytotoxicity during wastewater chlorination: Impact factors and surrogates

Toxic and harmful disinfection byproducts (DBPs) were formed during wastewater chlorination. It was recently suggested that cytotoxicity to mammalian cells reflects risks posed by chlorinated wastewater. Here, ATP assays were performed to evaluate the cytotoxicity to mammalian cells. Chlorination significantly increased cytotoxicity of treated wastewater. Factors affecting cytotoxicity formation during wastewater chlorination were investigated. Quenching with sodium thiosulfate and ascorbic acid decreased the formed cytotoxicity, while ammonium kept the cytotoxicity stable. The chlorine dose required for the maximum cytotoxicity increase was dramatically affected by DOC and ammonia concentrations. The maximum cytotoxicity increase, defined as the cytotoxicity formation potential (CtFP), occurred when wastewater was treated for 48h with a chlorine dose of 2·DOC+11·NH₃N+10 (mg-Cl₂/L). During chlorination, the amounts of AOX formation was found to be significantly correlated with cytotoxicity formation when no DBPs were destroyed. AOX formation could be used as a surrogate to estimate cytotoxicity increase during wastewater chlorination. Besides, the CtFP of 14 treated wastewater samples was assessed ranged from 5.4-20.4mg-phenol/L. The CtFP could be estimated from UV₂₅₄ of treated wastewater because CtFP and UV₂₅₄ were strongly correlated.

Formation of iodo-trihalomethanes, iodo-acetic acids, and iodo-acetamides during chloramination of iodide-containing waters: Factors influencing formation and reaction pathways

This study investigated systematically the factors influencing the formation of iodinated disinfection by-products (I-DBPs) during chloramination of I^--containing waters, including reaction time, NH₂Cl dose, I^- concentration, pH, natural organic matter (NOM) concentration, Br^-/I^- molar ratio, and water matrix. Among the I-DBPs detected, iodoform (CHI₃), iodoacetic acid (IAA), diiodoacetic acid (DIAA), triiodoacetic acid (TIAA), and diiodoacetamide (DIAcAm) were the major species produced from reactions between reactive iodine species (HOI/I₂) and NOM. A kinetic model involving the reactions of NH₂Cl auto-decomposition, iodine species transformation and NOM consumption was developed, which could well describe NH₂Cl decay and HOI/I₂ evolution. Higher concentrations of CHI₃, IAA, DIAA, TIAA, and DIAcAm were observed in chloramination than in chlorination, whereas IO₃^- was only formed significantly in chlorination. Maximum formation of I-DBPs occurred at pH 8.0, but acidic conditions favored the formation of iodinated haloacetic acids and DIAcAm. Increasing Br^-/I^- molar ratio from 1 to 10 did not increase the total amount of I-DBPs, but produced more bromine-substituting species. In addition, chloramination of 18 model compounds indicated that low-SUVA₂₅₄ (specific ultraviolet absorbance at 254nm) NOM generally favored the formation of I-DBPs compared to high-SUVA₂₅₄ NOM. Finally, potential pathways for I-DBPs formation from chloramination of NOM were proposed.

Understanding and exploring the potentials of household water treatment methods for volatile disinfection by-products control: Kinetics, mechanisms, and influencing factors

This study systematically evaluates the capabilities of five types of household water treatment (HWT) methods (including boiler heating, microwave irradiation, pouring, stirring, and shaking) on the removals of four regulated trihalomethanes (THM₄) and three iodinated halomethanes (IHMs) under a variety of conditions simulative of residential uses. Overall, the results clearly showed promising capabilities of all five HWT methods in controlling volatile disinfection by-products (DBPs), and heating with a boiler was the most effective approach among all methods due to the synergistic effects of water turbulence and bubbling phenomena. A contemporary boiler equipped with an automatic switch-off function reduced on average 92% of seven halomethanes (HM₇) at favourable conditions. The removal increased significantly with increasing initial concentrations and the rates correlated well with the logarithmic Henry's law constants and molecular weights of compounds, with triiodomethane being the most refractory species. Meanwhile, the importance of water handling habits was revealed, including power input, operation time, volume, heating/cooling speed, cooling method, and capping conditions. The findings hence explored the potentials of HWTs on DBP control and pointed out a potential limit to DBP epidemiology studies that do not consider water handling habits.

Formation and speciation of haloacetamides and haloacetonitriles for chlorination, chloramination, and chlorination followed by chloramination

The formation of haloacetamides (HAcAms) and haloacetonitriles (HANs) from a solution containing natural organic matter and a secondary effluent sample was evaluated for disinfection by chlorination, chloramination, and chlorination followed by chloramination (Cl₂NH₂Cl process). The use of preformed monochloramine (NH₂Cl) produced higher concentrations of HAcAms and lower concentrations of HANs than chlorination, while the Cl₂NH₂Cl process produced the highest concentrations of HAcAms and HANs. These results indicate that the Cl₂NH₂Cl process, which inhibited the formation of regulated trihalomethanes compared with chlorination, enhanced the formation of HAcAms and HANs. For disinfection in the presence of bromide, brominated dihaloacetamides and dihaloacetonitriles were formed, and the trends were similar to those observed for chlorinated species in the absence of bromide. The degrees of bromine substitution of dihaloacetamides and dihaloacetonitriles were highest for chlorination, followed by the Cl₂NH₂Cl process and then by the NH₂Cl process. For the Cl₂NH₂Cl process, HAN formation kept gradually increasing with prechlorination time increasing from 0 to 120 min, while HAcAm formation increased only until it reached a maximum at around 10-30 min. These results suggest that the prechlorination time could be reduced to control the formation of HAcAms and HANs. During chloramination, the formation of HAcAms and HANs was lower when using preformed NH₂Cl than when chloramines were formed in situ, with higher formation of HAcAms and HANs when chlorine was added before ammonia than vice versa for the secondary effluent; this finding suggests that preformed NH₂Cl could be used to inhibit the formation of HAcAms and HANs during chloramination.

An efficient strategy for full mineralization of an azo dye in wastewater: a synergistic combination of solar thermo- and electrochemistry plus photocatalysis

An efficient strategy for full mineralization of azo dye in wastewater.

Copper increases reductive dehalogenation of haloacetamides by zero-valent iron in drinking water: Reduction efficiency and integrated toxicity risk

The haloacetamides (HAcAms), an emerging class of nitrogen-containing disinfection byproducts (N-DBPs), are highly cytotoxic and genotoxic, and typically occur in treated drinking waters at low μg/L concentrations. Since many drinking distribution and storage systems contain unlined cast iron and copper pipes, reactions of HAcAms with zero-valent iron (ZVI) and metallic copper (Cu) may play a role in determining their fate. Moreover, ZVI and/or Cu are potentially effective HAcAm treatment technologies in drinking water supply and storage systems. This study reports that ZVI alone reduces trichloroacetamide (TCAcAm) to sequentially form dichloroacetamide (DCAcAm) and then monochloroacetamide (MCAcAm), whereas Cu alone does not impact HAcAm concentrations. The addition of Cu to ZVI significantly improved the removal of HAcAms, relative to ZVI alone. TCAcAm and their reduction products (DCAcAm and MCAcAm) were all decreased to below detection limits at a molar ratio of ZVI/Cu of 1:1 after 24 h reaction (ZVI/TCAcAm = 0.18 M/5.30 μM). TCAcAm reduction increased with the decreasing pH from 8.0 to 5.0, but values from an integrated toxic risk assessment were minimised at pH 7.0, due to limited removal MCAcAm under weak acid conditions (pH = 5.0 and 6.0). Higher temperatures (40 °C) promoted the reductive dehalogenation of HAcAms. Bromine was preferentially removed over chlorine, thus brominated HAcAms were more easily reduced than chlorinated HAcAms by ZVI/Cu. Although tribromoacetamide was more easily reduced than TCAcAm during ZVI/Cu reduction, treatment of tribromoacetamide resulted in a higher integrated toxicity risk than TCAcAm, due to the formation of monobromoacetamide (MBAcAm).

Role of NOM molecular size on iodo-trihalomethane formation during chlorination and chloramination

Natural organic matter (NOM) is the major precursor for the generation of disinfection byproducts (DBPs) during disinfection, but the role of the NOM molecular size on the formation of iodinated DBPs (I-DBPs) is still unclear. The objective of this study was to evaluate the function of the NOM molecular size on the formation of iodo-trihalomethane (I-THMs) during chlorination and chloramination. Humic acid was adopted as the NOM matrix and fractionated into four molecular weight (MW) groups. Various parameters, including iodide, bromide, NOM concentrations, pH, and pre-chlorination time, were investigated for each MW fraction. During chlorination, high MW fractions (i.e., MW > 100 K Da and 50 K < MW < K00 K Da) produced more I-THMs compared with small MW fractions (i.e., MW < 3 K Da and 3 K < MW < 50 K Da). With the increase in the I(-) or NOM concentration, the formation of I-THMs increased for small MW fractions, while a slight reduction occurred for high MW fractions during chlorination. Higher pH resulted in more I-THM formation for small MW fractions, while the opposite was true for high MW fractions during chlorination. Compared to small MW fractions, bromide was relatively more reactive with high MW fractions in the formation of I-THMs during chlorination. During chloramination, the I-THM yields decreased with the increasing NOM concentration for high MW fractions. The concentration of bromine-containing I-THMs decreased with increasing pH for all MW fractions during chloramination. Additionally, with the prolongation of pre-chlorination time, the total amount of I-THMs decreased remarkably for MWs higher than 3 K Da, while a slight change for MW lower than 3 K Da occurred during chloramination. The results from this study suggest that the molecular weight of the NOM plays an important role in the formation of I-THMs during chlorination and chloramination.

Water temperature significantly impacts the formation of iodinated haloacetamides during persulfate oxidation

The use of persulfate oxidation processes is receiving increasing interest for the removal of aquatic contaminants. However, it is unknown whether its application in the presence of iodide has the potential to directly form iodinated DBPs. This study investigated formation of six chlorinated, brominated and iodinated di-haloacetamides (DHAcAms) during persulfate oxidation in the presence of bromide and iodide. Formation of the same DHAcAms during chlorination was monitored for comparison. Persulfate oxidation of natural water formed diiodoacetamide (DIAcAm), and heat-activated persulfate, at 45 °C and 55 °C, generated bromoiodoacetamide (BIAcAm) and dibromoacetamide (DBAcAm), besides DIAcAm. At an ambient iodide concentration of 0.3 μM, total DHAcAms increased slightly from 0.43 to 0.57 nM as the water temperature increased from 4 °C to 35 °C, respectively (only DIAcAm detected), then significantly increased to 1.6 nM at 55 °C (DIAcAm, BIAcAm and DBAcAm detected). Equivalent total DHAcAm concentrations in the presence of 3.0 μM iodide were 0.5, 0.91 and 2.1 nM, respectively. Total DHAcAms formed during chlorination, predominantly dichloroacetamide (DCAcAm) and bromochloroacetamide (BCAcAm), were always significantly higher than that during persulfate oxidation. However, an integrated risk assessment showed the toxicity resulting from the DHAcAms was higher during persulfate oxidation than chlorination. An increase in water temperature from 25 °C to 55 °C significantly increased the integrated toxic risk values for both persulfate oxidation and chlorination. Use of persulfate oxidation should be weighed against the formation of high-toxicity iodinated HAcAms in waters with high ambient iodide concentrations.

Fully solar-driven thermo- and electrochemistry for advanced oxidation processes (STEP-AOPs) of 2-nitrophenol wastewater

The STEP (Solar Thermal Electrochemical Process) for Advanced Oxidation Processes (AOPs, combined to STEP-AOPs), fully driven by solar energy without the input of any other forms of energy and chemicals, is introduced and demonstrated from the theory to experiments. Exemplified by the persistent organic pollutant 2-nitrophenol in water, the fundamental model and practical system are exhibited for the STEP-AOPs to efficiently transform 2-nitrophenol into carbon dioxide, water, and the other substances. The results show that the STEP-AOPs system performs more effectively than classical AOPs in terms of the thermodynamics and kinetics of pollutant oxidation. Due to the combination of solar thermochemical reactions with electrochemistry, the STEP-AOPs system allows the requisite electrolysis voltage of 2-nitrophenol to be experimentally decreased from 1.00 V to 0.84 V, and the response current increases from 18 mA to 40 mA. STEP-AOPs also greatly improve the kinetics of the oxidation at 30 °C and 80 °C. As a result, the removal rate of 2-nitrophenol after 1 h increased from 19.50% at 30 °C to 32.70% at 80 °C at constant 1.90 V. Mechanistic analysis reveals that the oxidation pathway is favorably changed because of thermal effects. The tracking of the reaction displayed that benzenediol and hydroquinone are initial products, with maleic acid and formic acid as sequential carboxylic acid products, and carbon dioxide as the final product. The theory and experiments on STEP-AOPs system exemplified by the oxidation of 2-nitrophenol provide a broad basis for extension of the STEP and AOPs for rapid and efficient treatment of organic wastewater.

PPCP degradation by UV/chlorine treatment and its impact on DBP formation potential in real waters

The ultraviolet/chlorine (UV/chlorine) water purification process was evaluated for its ability to degrade the residues of pharmaceuticals and personal care products (PPCPs) commonly found in drinking water sources. The disinfection byproducts (DBPs) formed after post-chlorination were documented. The performance of the UV/chlorine process was compared with that of the UV/hydrogen peroxide (UV/H2O2) process in treating three types of sand-filtered natural water. Except caffeine and carbamazepine residues, the UV/chlorine process was found to be 59-99% effective for feed water with a high level of dissolved organic carbon and alkalinity, and 27-92% effective for water with a high ammonia content. Both chlorine radicals and hydroxyl radicals were found to contribute to the observed PPCP degradation. The removal efficiencies of chlorine- and UV-resistant PPCPs such as carbamazepine and caffeine were 2-3 times greater than in the UV/H2O2 process in waters not enriched with ammonia. UV/chlorine treatment slightly enhanced the formation chloral hydrate (CH), haloketone (HK) and trichloronitromethane (TCNM). It reduced haloacetonitrile (HAN) formation during the post-chlorination in comparison with the UV/H2O2 process. In waters with high concentrations of ammonia, the UV/chlorine process was only 5-7% more effective than the UV/H2O2 process, and it formed slightly more THMs, HKs and TCNM along with reduced formation of CH and HAN. The UV/chlorine process is thus recommended as a good alternative to UV/H2O2 treatment for its superior PPCP removal without significantly enhancing DBP formation.

Impact of anionic ion exchange resins on NOM fractions: Effect on N-DBPs and C-DBPs precursors

The formation potential of carbonaceous and nitrogenous disinfection by-products (C-DBPs, N-DBPs) after ion exchange treatment (IEX) of three different water types in multiple consecutive loading cycles was investigated. Liquid chromatography with organic carbon detector (LC-OCD) was employed to gauge the impact of IEX on different natural organic matter (NOM) fractions and data obtained were used to correlate these changes to DBPs Formation Potential (FP) under chlorination. Humic (-like) substances fractions of NOM were mainly targeted by ion exchange resins (40-67% removal), whereas hydrophilic, non-ionic fractions such as neutrals and building blocks were poorly removed during the treatment (12-33% removal). Application of ion exchange resins removed 13-20% of total carbonaceous DBPs FP and 3-50% of total nitrogenous DBPs FP. Effect of the inorganic nitrogen (i.e., Nitrate) presence on N-DBPs FP was insignificant while the presence of dissolved organic nitrogen (DON) was found to be a key parameter affecting the formation of N-DBPs. DON especially the portion affiliated with humic substances fraction, was reduced effectively (∼77%) as a result of IEX treatment.

Contribution of the Antibiotic Chloramphenicol and Its Analogues as Precursors of Dichloroacetamide and Other Disinfection Byproducts in Drinking Water

Dichloroacetamide (DCAcAm), a disinfection byproduct, has been detected in drinking water. Previous research showed that amino acids may be DCAcAm precursors. However, other precursors may be present. This study explored the contribution of the antibiotic chloramphenicol (CAP) and two of its analogues (thiamphenicol, TAP; florfenicol, FF) (referred to collectively as CAPs), which occur in wastewater-impacted source waters, to the formation of DCAcAm. Their formation yields were compared to free and combined amino acids, and they were investigated in filtered waters from drinking-water-treatment plants, heavily wastewater-impacted natural waters, and secondary effluents from wastewater treatment plants. CAPs had greater DCAcAm formation potential than two representative amino acid precursors. However, in drinking waters with ng/L levels of CAPs, they will not contribute as much to DCAcAm formation as the μg/L levels of amino acids. Also, the effect of advanced oxidation processes (AOPs) on DCAcAm formation from CAPs in real water samples during subsequent chlorination was evaluated. Preoxidation of CAPs with AOPs reduced the formation of DCAcAm during postchlorination. The results of this study suggest that CAPs should be considered as possible precursors of DCAcAm, especially in heavily wastewater-impacted waters.

The enhanced removal of carbonaceous and nitrogenous disinfection by-product precursors using integrated permanganate oxidation and powdered activated carbon adsorption pretreatment

Pilot-scale tests were performed to reduce the formation of a range of carbonaceous and nitrogenous disinfection by-products (C-, N-DBPs), by removing or transforming their precursors, with an integrated permanganate oxidation and powdered activated carbon adsorption (PM-PAC) treatment process before conventional water treatment processes (coagulation-sedimentation-filtration, abbreviated as CPs). Compared with the CPs, PM-PAC significantly enhanced the removal of DOC, DON, NH3(+)-N, and algae from 52.9%, 31.6%, 71.3%, and 83.6% to 69.5%, 61.3%, 92.5%, and 97.5%, respectively. PM pre-oxidation alone and PAC pre-adsorption alone did not substantially reduce the formation of dichloroacetonitrile, trichloroacetonitrile, N-nitrosodimethylamine and dichloroacetamide. However, the PM-PAC integrated process significantly reduced the formation of both C-DBPs and N-DBPs by 60-90% for six C-DBPs and 64-93% for six N-DBPs, because PM oxidation chemically altered the molecular structures of nitrogenous organic compounds and increased the adsorption capacity of the DBP precursors, thus highlighting a synergistic effect of PM and PAC. PM-PAC integrated process is a promising drinking water technology for the reduction of a broad spectrum of C-DBPs and N-DBPs.

Nitrogenous disinfection byproducts in English drinking water supply systems: Occurrence, bromine substitution and correlation analysis

Despite the recent focus on nitrogenous disinfection byproducts in drinking water, there is limited occurrence data available for many species. This paper analyses the occurrence of seven haloacetonitriles, three haloacetamides, eight halonitromethanes and cyanogen chloride in 20 English drinking water supply systems. It is the first survey of its type to compare bromine substitution factors (BSFs) between the haloacetamides and haloacetonitriles. Concentrations of the dihalogenated haloacetonitriles and haloacetamides were well correlated. Although median concentrations of these two groups were lower in chloraminated than chlorinated surface waters, median BSFs for both in chloraminated samples were approximately double those in chlorinated samples, which is significant because of the higher reported toxicity of the brominated species. Furthermore, median BSFs were moderately higher for the dihalogenated haloacetamides than for the haloacetonitriles. This indicates that, while the dihalogenated haloacetamides were primarily generated from hydrolysis of the corresponding haloacetonitriles, secondary formation pathways also contributed. Median halonitromethane concentrations were remarkably unchanging for the different types of disinfectants and source waters: 0.1 μg · mgTOC(-1) in all cases. Cyanogen chloride only occurred in a limited number of samples, yet when present its concentrations were higher than the other N-DBPs. Concentrations of cyanogen chloride and the sum of the halonitromethanes were not correlated with any other DBPs.

Peptide bonds affect the formation of haloacetamides, an emerging class of N-DBPs in drinking water: free amino acids versus oligopeptides

Haloacetamides (HAcAms), an emerging class of nitrogenous disinfection by-products (N-DBPs) of health concern, have been frequently identified in drinking waters. It has long been appreciated that free amino acids (AAs), accounting for a small fraction of the dissolved organic nitrogen (DON) pool, can form dichloroacetamide (DCAcAm) during chlorination. However, the information regarding the impacts of combined AAs, which contribute to the greatest identifiable DON portion in natural waters, is limited. In this study, we compared the formation of HAcAms from free AAs (tyrosine [Tyr] and alanine [Ala]) and combined AAs (Tyr-Ala, Ala-Tyr, Tyr-Tyr-Tyr, Ala-Ala-Ala), and found that HAcAm formation from the chlorination of AAs in combined forms (oligopeptides) significantly exhibited a different pattern with HAcAm formation from free AAs. Due to the presence of peptide bonds in tripeptides, Tyr-Tyr-Tyr and Ala-Ala-Ala produced trichloroacetamide (TCAcAm) in which free AAs was unable to form TCAcAm during chlorination. Moreover, peptide bond in tripeptides formed more tri-HAcAms than di-HAcAms in the presence of bromide. Therefore, the peptide bond may be an important indicator to predict the formation of specific N-DBPs in chlorination. The increased use of algal- and wastewater-impacted water as drinking water sources will increase health concerns over exposure to HAcAms in drinking water.