Using UV/H2O2 pre-oxidation combined with an optimised disinfection scenario to control CX3R-type disinfection by-product formation

Leaching of organic matter and iodine, formation of iodinated disinfection by-products and toxic risk from Laminaria japonica during simulated household cooking

Iodinated disinfection by-products (I-DBPs) exhibited potential health risk owing to the high toxicity. Our recent study demonstrated that I-DBPs from Laminaria japonica (Haidai), the commonly edible seaweed, upon simulated household cooking condition were several hundred times more than the concentration of drinking water. Here, the characterization of Haidai and its leachate tandem with the formation, identification and toxicity of I-DBPs from the cooking of Haidai were systemically investigated. The dominant organic matter in Haidai leachate were polysaccharides, while the highest iodine specie was iodide (∼90% of total iodine). Several unknown I-DBPs generated from the cooking of Haidai were tentatively proposed, of which 3,5-diiodo-4-hydroxybenzaldehyde was dominant specie. Following a simulated household cooking with real chloraminated tap water, the presence of Haidai sharply increased aggregate iodinated trihalomethanes, iodinated haloacetic acids, and total organic iodine concentrations to 97.4 ± 7.6 μg/L,16.4 ± 2.1 μg/L, and 0.53 ± 0.06 mg/L, respectively. Moreover, the acute toxicity of Haidai soup to Vibrio qinghaiensis sp.-Q67 was around 7.3 times higher than that of tap water in terms of EC50. These results demonstrated that the yield of I-DBPs from the cooking of Haidai and other seaweed should be carefully considered.

Disinfection by-product precursors introduced by sandstorm events: Composition, formation characteristics and potential risks

Sandstorms, a natural meteorological event, occur repeatedly during the dry season and can accumulate large amounts of natural/anthropogenic pollutants during the deposition process, potentially introducing disinfection by-product (DBP) precursors into surface waters. In this study, the characteristics of sandstorm-derived dissolved organic matter (DOM) and its DBP formation potential were elucidated. Overall, sandstorm-derived DOM mainly consisted of low-molecular-weight, low-aromaticity, high-nitrogen organic matter, with a dissolved organic carbon (DOC) release yield of 14.4 mg-DOC/g. The halogenated DBP formation potential (calculated as total organic halogen) of sandstorm-derived DOM was comparable to that of surface water, while the normalized DBP-associated toxicity was 1.96 times higher. Similar to DOM introduced by other depositional pathways, sandstorm-derived DOM also had higher yields of highly cytotoxic DBPs (haloacetaldehydes [HALs], haloacetonitriles [HANs] and halonitromethanes [HNMs]). The average atmospheric deposition flux for DOM during the sandstorm event (50.4 ± 2.1 kg km-2 day-1) was 6.95 times higher than that of dry deposition, indicating a higher probability of contaminant input. Simultaneously, the estimation revealed that the sandstorm will increase the formation potential of toxicity forcing agents, such as HALs, HANs and HNMs, in surface water by 3.87%, 2.39% and 9.04%, respectively. Considering the high frequency of sandstorm events and the sorption of other organic pollutants by sand and dust, the impact of sandstorms on surface water quality should be of concern.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Identification of key precursors contributing to the formation of CX3R-type disinfection by-products along the typical full-scale drinking water treatment processes

Identification and characterization of disinfection by-product (DBP) precursors could help optimize drinking water treatment processes and improve the quality of finished water. This study comprehensively investigated the characteristics of dissolved organic matter (DOM), the hydrophilicity and molecule weight (MW) of DBP precursor and DBP-associated toxicity along the typical full-scale treatment processes. The results showed that dissolved organic carbon and dissolved organic nitrogen content, the fluorescence intensity and the SUVA₂₅₄ value in raw water significantly decreased after the whole treatment processes. Conventional treatment processes were in favor of the removal of high-MW and hydrophobic DOM, which are important precursors of trihalomethane and haloacetic acid. Compared with conventional treatment processes, Ozone integrated with biological activated carbon (O₃-BAC) processes enhanced the removal efficiencies of DOM with different MW and hydrophobic fractions, leading to a further decrease in almost all DBP formation potential and DBP-associated toxicity. However, almost 50% of the detected DBP precursors in raw water has not been removed after the coagulation-sedimentation-filtration integrated with O₃-BAC advanced treatment processes. These remaining precursors were found to be mainly hydrophilic and low-MW (< 1.0 kDa) organics. Moreover, they would largely contribute to the formation of haloacetaldehydes and haloacetonitriles, which dominated the calculated cytotoxicity. Since current drinking water treatment process could not effectively control the highly toxic DBPs, the removal of hydrophilic and low-MW organics in drinking water treatment plants should be focused on in the future.

A novel solar-activated chlorine dioxide process for atrazine degradation in drinking water

New technologies using advanced oxidation processes (AOPs) with low energy-input to address the presence of micro-contaminants and the formation of disinfection byproducts (DBPs) are required for drinking water safety. In this work, the activation of chlorine dioxide with solar (solar/ClO₂ process), a type of renewable and inexhaustible energy, was developed to degrade atrazine (ATZ) and control the formation of DBPs. Results revealed that solar/ClO₂ process was effective in degrading ATZ. Hydroxyl radicals (•OH) and chlorine radicals (Cl•) produced in solar/ClO₂ process were found to be the predominant agents for ATZ degradation with contribution rates of 55.9% and 44.1%, respectively, based on radical quenching tests and competition kinetics. Reaction pH did not affect the total amount of Cl• and •OH (i.e., [•OH]_exp) and [Cl•]_exp), while the conversion of Cl• to •OH was responsible for the depressed ATZ degradation efficiency with the increasing pH in solar/ClO₂ process. The presence of bicarbonate (HCO₃^-), chloride (Cl^-) and humic acid (HA) retarded the ATZ degradation mainly due to they decreased [•OH]_exp) and [Cl•]_exp. Using the UPLC-MS/MS analysis, six degradation intermediates of ATZ were tentatively identified, and the three-stage degradation pathway as well as the stepwise detoxification of ATZ were confirmed by the condensed Fukui function (CFF) calculation and ECOSAR prediction. Applying solar/ClO₂ as a pretreatment of HA-containing water, the formation of DBPs during post-chlorination was significantly reduced. However, the presence of ATZ during solar/ClO₂ pretreatment of HA significantly lowered the control efficiency of DBPs. The major degradation intermediate, i.e., deethyldeisopropylhydroxyatrazine (DEIHA), of ATZ could incorporate into HA and therefore providing more precursors for DBPs. The acute toxicity recorded by the behavior of zebrafish larvae revealed that using chloramine instead of chlorine downstream the solar/ClO₂ pretreatment of ATZ and HA could significantly reduce the acute toxicity by decreasing the formation of total DBPs. This study demonstrated the great potential of applying solar/ClO₂ process followed by chloramination to simultaneously degrade micro-contaminants and reduce DBPs formation as well as toxic risk in practical applications.

Enhanced cyanogen chloride formation after UV/PS and UV/H2O2 pre-oxidation and chlorination in natural river water

Ultraviolet/persulfate (UV/PS) and Ultraviolet/hydrogen peroxide (UV/H₂O₂) have attracted much attention in recent years as advanced oxidation processes for water treatment. However, it is not all clear how these two methods affect the formation of cyanogen chloride (CNCl) in the subsequent water chlorination process. In this study, it was found that both UV/H₂O₂ and UV/PS pre-oxidation promoted the formation of CNCl in six actual water samples collected from urban rivers. Glycine, uric acid, arginine and histidine were investigated as the model compounds to explore the effects of different methods on the production of CNCl. The results showed that compared with chlorination alone, pre-oxidation by UV/H₂O₂ and UV/PS can reduce the production of CNCl for glycine and uric acid by up to 95% during post-chlorination process. However, they can greatly promote the formation of CNCl for arginine and histidine by up to 120-fold. In a more detailed investigation, pre-oxidation of histidine formed highly reactive intermediates to chlorine, leading to increased CNCl formation and chlorine consumption. The results showed that the precursors of CNCl was altered after pre-oxidation, and need to be re-evaluated.

Formation of halogenated macromolecular organics induced by Br- and I- during plasma oxidation/chlorination of DOM: Highlighting competitive mechanisms

Understanding the effects of halogens on the production of macromolecular disinfection byproducts (DBPs) is critical for drinking water safety. The effects of Br^- and I^- on the chemical diversity of dissolved organic matter (DOM) during plasma preoxidation and the subsequent formation of macromolecular halogenated DBPs after chlorination were deciphered. Plasma preoxidation changed DOM diversity from aromatic component-oriented to lignin and tannin component-oriented, resulting in 62.0% and 21.2% decreases in N-DBPs (C_kH_nO_mN_zCl_x formulas) and C-DBPs (C_kH_nO_mCl_x formulas) after chlorination, respectively. Br^- could induce the formation of organobromine compounds (OBrCs) during plasma oxidation; however, the intensities of OBrCs decreased by 56.3% (CHO formulas) and 75.2% (CHON formulas) after further chlorination. OBrCs still accounted for 79.8% of the total organohalogen compounds (OXCs, X=Cl or Br) due to the higher substitutability of bromine. I^-promoted OIC production in the DOM preoxidation process, and OICs acted as intermediates to form OClCs during chlorination. When Br^-and I^-coexisted, Br^- promoted OIC production in the DOM preoxidation process; therefore, more OBrCs and OClCs were generated due to intermediates of OICs in subsequent chlorination. Connections between OXCs and their precursors were established using network computation. The precursors of OClCs were located in the aromatic structure region (0.2 < H/C ≤ 0.7; O/C ≤ 0.67); those of OBrCs and OICs were located in the lignin (0.7 < H/C ≤ 1.5; 0.1 < O/C < 0.67) and tannin (0.6 ≤ H/C ≤ 1.5, 0.67 < O/C < 1.0) regions with relatively greater H/C and O/C ratios, respectively.

Role of UV-based advanced oxidation processes on NOM alteration and DBP formation in drinking water treatment: A state-of-the-art review

Oxidative treatment of drinking water has been practiced for more than a century. UV-based advanced oxidation processes (UV-AOPs) have emerged as promising oxidative treatment technologies to eliminate recalcitrant chemicals and biological contaminants in drinking water. UV-AOPs inevitably alter the properties of natural organic matter (NOM) and affect the disinfection byproduct (DBP) formation in the post-disinfection. This paper provides a state-of-the-art review on the effects of UV-AOPs on the changes of NOM properties and the consequent impacts on DBP formation in the post-chlorination process. A tutorial review to the connotations of NOM properties (e.g., bulk properties, fractional constituents, and molecular structures) and the associated state-of-the-art analytical methods are firstly presented. The impacts of different radical-based AOPs on the changes of NOM properties together with the underlying NOM-radical reaction mechanisms are discussed. The impacts of alteration of NOM properties on DBP formation in the post-chlorination process are then reviewed. The current knowledge gaps and future research needs are finally presented, with emphases on the needs to strengthen the comparability of research data in literature, the accuracy in quantifying the reactive moieties of NOM, and the awareness of unknown DBPs in oxidative water treatment processes. The review and discussion improve the fundamental understanding of NOM-radical and NOM-chlorine chemistry. They also provide useful implications on the engineering design and operation of next-generation drinking water treatment plants.

Modeling carbonate/bicarbonate and nitrate disturbance during secondary effluent disinfection by UV/H2O2 and UV/ozone

The disinfection of effluents has been considered the main step to inactivate pathogenic organisms to prevent the spread of waterborne diseases. The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct treatment. The objective of this study was to develop a simple and practical mathematical model to simulate the disturbance of inorganic anions (CO₃^2-/HCO₃^- and NO₃^-) during secondary effluent disinfection by UV/H₂O₂ and UV/O₃. The pathogenic agents chosen for this study were total coliforms and E. coli. To build the mathematical model, a modification of the Chick model (referred to as 'Modified Chick Model') was proposed by employing a weighted average in the calculation of the kinetic constant. Both treatments were affected by the presence of the anions. However, with the highest NO₃^- concentration, less inhibition of disinfection was observed in the UV/H₂O₂. The use of the arithmetic means to calculate the value of k, as indicated by the Chick model, demonstrates a lesser precision in the prediction of the microorganisms' concentrations. On the other hand, using the Modified Chick Model, a better prediction of the inactivation of the microorganisms was obtained, which can be confirmed by the validation performed.

Does Snowfall Introduce Disinfection By-product Precursors to Surface Water?

Snow with large specific surface area and strong adsorption capacity can effectively adsorb atmospheric pollutants, which could/might lead to the increase of disinfection by-product (DBP) precursors in surface water. In this study, the contents and characteristics of dissolved organic matter (DOM) in meltwater were investigated, and DBP formation and the DBP-associated cytotoxicity index during chlorination of meltwater was first explored. Overall, meltwater exhibited high nitrogen contents. Meltwater-derived DOM was mainly composed of organics with low molecular weights, low aromaticity, and high unsaturated degrees. DBP formation potentials and cytotoxicity indexes in chlorinated meltwater were positively correlated with air quality index and were significantly impacted by snowfall stages. The trihalomethane and haloacetic acid yields from meltwater were relatively low, while yields of highly cytotoxic DBPs, especially halonitromethanes (6.3-10.8 μg-HNMs/mg-DOC), were significantly higher than those of surface water (1.7 μg-HNMs/mg-DOC). Notably, unsaturated nonaromatic organic nitrates in meltwater were important precursors of halonitromethanes. The actual monitoring results showed that snowfall significant increased the haloacetaldehydes and nitrogenous DBP formation levels of surface water. Considering increased DBP formation and DBP-associated toxicity, it was demonstrated that DOM derived from snowfall in atmosphere-polluted areas could deteriorate surface water quality and pose potential risks to drinking water.

Insights into the formation and mitigation of iodinated disinfection by-products during household cooking with Laminaria japonica (Haidai)

Iodinated disinfection by-products (I-DBPs) have attracted extensive interests because of their higher cytotoxicity and genotoxicity than their chlorinated and brominated analogues. Our recent studies have firstly demonstrated that cooking with seaweed salt could enhance the formation of I-DBPs with several tens of μg/L level. Here, I-DBP formation and mitigation from the reaction of disinfectant with Laminaria japonica (Haidai), an edible seaweed with highest iodine content, upon simulated household cooking process was systematically investigated. The total iodine content in Haidai ranged from 4.6 mg-I/g-Haidai to 10.0 mg-I/g-Haidai, and more than 90% of iodine is soluble iodide. During simulated cooking, the presence of disinfectant simultaneously decreased iodide by 15.0-32.8% to 2.7-5.8 mg/L and increased total organic iodine by 1.3-10.9 times to 0.5-1.8 mg/L in Haidai soup, proving I-DBP formation. The concentrations of iodinated trihalomethanes and haloacetic acids were at the levels of several hundreds of μg/L and several μg/L, respectively, which are 2-3 orders and 1-2 orders of magnitude more than those in drinking water. Effects of key factors including disinfectant specie, disinfectant dose, temperature and time on I-DBP formation were also ascertained, and temperature and disinfectant specie played a decisive role in the formation and speciation of I-DBPs. In order to avoid the potential health risk from the exposure of I-DBPs in Haidai soup, it is prerequisite to soak and wash dry Haidai sample over 30.0 min before cooking, which could effectively remove major soluble iodide. In general, this study provided the new insight into I-DBP formation from daily household cooking with Haidai and the corresponding enlightenment for inhabitants to eat Haidai in daily life.

Degradation of sulfadiazine by UV/Oxone: roles of reactive oxidative species and the formation of disinfection byproducts

Sulfadiazine (SDZ) is a typical persistent sulfonamide antibiotic, which has been widely detected in natural drinking water sources. The degradation of SDZ by UV/Oxone (potassium monopersulfate compound) was explored in this study. The results showed that Cl^- can effectively activate PMS to promote rapid degradation of SDZ in the Oxone process by forming chlorine in the system. Radical quenching tests suggested that radical oxidation, including HO^•, SO₄^•-, and reactive chlorine species (RCS), played an important role by UV/Oxone. It further verified that concentration and distribution of HO^•, SO₄^•-, and RCS were pH-dependent; RCS act as a major contributor at pH 6.0 and pH 7.0 to degrade SDZ in this process. The SDZ degradation rate was firstly increased and then decreased by Cl^- and HCO₃^- (0-10 mM); HA (0-10 mg L^-1) exhibited insignificant influence on SDZ degradation. The degradation pathways of SDZ during UV/Oxone and formation pathways of five disinfection byproducts during subsequent chlorination were proposed. The possible DBP precursors formed by SO₂ extrusion, hydroxylation, and chlorination of SDZ during UV/Oxone pre-oxidation.

Underlying mechanisms of promoted formation of haloacetic acids disinfection byproducts after indometacin degradation by non-thermal discharge plasma

Indometacin (IDM), as a kind of non-steroidal anti-inflammatory drugs, has ecological and health risks, which is the potential precursor of chlorination disinfection byproducts (DBPs). Non-thermal discharge plasma was attempted to eliminate IDM and control subsequent DBPs formation. Satisfactory removal performance for IDM was realized by the plasma oxidation; almost 100% of IDM was removed within 2 min. Relatively greater removal efficiency was gained at a higher plasma voltage and a lower pH level. Electron paramagnetic resonance spectrometer revealed that reactive species ·OH, O₂·^-, and ¹O₂ were responsible for IDM decomposition. Based on analyses of Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, three-dimensional fluorescence spectrum, and gas chromatography-mass spectrometer, attacks of reactive species resulted in sequence breakages in functional groups of IDM, leading to production of small molecular alcohols, acids, and amines. Possible decomposition pathways of IDM were proposed. The produced acetamide and 1H-indol-5-ol were important precursors of DBPs. Formation and toxicity of nitrogen-containing DBPs were dramatically inhibited after IDM degradation; however, those of haloacetic acids were strengthened. The relevant roadmaps among DBPs and degradation intermediates were figured out. This study revealed the underlying mechanisms of IDM degradation by discharge plasma and its potential risks in chlorination disinfection.

Analytical characterization of nucleotides and their concentration variation in drinking water treatment process

Nucleotides, as the basic building blocks of nucleic acids, widely exist in aqueous environment. In this study, we developed a solid phase extraction-high performance liquid chromatography-tandem mass spectrometry (SPE-UPLC-MS/MS) method for the analysis of 5'-adenosine monophosphate (AMP), 5'-uridine monophosphate (UMP), 5'-cytidine monophosphate (CMP) and 5'-guanosine monophosphate (GMP). The method achieved limits of detection (LODs) of 0.1-1.0 ng/L, and recoveries of 85-95% for the four tested nucleotides. The occurrence and concentrations of the four nucleotides in water from eight representative drinking water treatment and distribution systems in China were determined using this method. All four nucleotides were detectable in water treatment plant (WTP) influent and effluent, at concentrations of up to 30 ng/L and with occurrence frequency of around 90%. The concentrations of identified nucleotides increased 3-10 times after 10 km of water age in the water distribution system. Biological filters and coagulation increased the concentrations of nucleotides, conversely, active carbon, ozonation, and ultrafiltration membrane removed nucleotides in water. The effects of active carbon and coagulation were further confirmed using laboratory-controlled experiment. In addition, monochlorinated nucleotides were identified as the chlorination products of nucleotides.

Pilot-scale and mechanistic study of the degradation of typical odors and organic compounds in drinking water by a combined UV/H2O2-BAC process

Odor problems are challenging issues in water treatment. Advanced oxidation has a significant degradation effect on these odors; however, some issues, such as oxidant residues and disinfection byproducts, exist in the use of advanced oxidation in actual water treatment. Because of the above issues, a combined advanced oxidation process has emerged-the UV/H₂O₂ -biological activated carbon (BAC) process can play a strong oxidizing role in advanced oxidation and uses the physical adsorption and biological effects of activated carbon. However, there have been few studies on the odor degradation mechanism and characteristics of activated carbon biofilms in actual water treatment. This paper systematically studied the organic and odor substances removal effects and mechanism of a pilot combined UV/H₂O₂-BAC process. The results showed that UV/H₂O₂-BAC technology had a good removal effect on odor substances under long-term stable operation. The concentrations of geosmin (GSM) and 2-methylisoborneol (2-MIB) after systemic treatment were below 5 ng/L. The removal rates of DOC, UV₂₅₄ and H₂O₂ by the combined process were 53.60%, 73.08% and 60.20%, respectively. The results of full-scan determination of GSM and 2-MIB degradation by gas chromatography-mass spectrometry (GC-MS) were consistent with those of front-track analysis. The diversity, richness and evenness of microorganisms in the lower activated carbon layer were higher than those in the middle and upper activated carbon layers. The greater the difference in the carbon layer height was, the greater the difference in the biological community structure.

Elevated risk of haloacetonitrile formation during post-chlorination when applying sulfite/UV advanced reduction technology to eliminate bromate

The formation of haloacetonitriles (HANs) during chlorination after sulfite/ultraviolet (UV) treatment of bromate (BrO₃^-) in the presence of amino acids (AAs) was investigated. During sulfite/UV treatment, the primary species hydrated electrons (e_aq^-) and hydrogen atom radicals (H) dominated the reduction of BrO₃^- to bromide (Br^-), whereas the sulfite anion radicals (SO₃^-) and H degraded AAs to produce the intermediates HN=C(CH₃)-COOH, CH₃-CH=NH, and CH₃-C≡N via α‑hydrogen abstraction and NH₂-hydrogen abstraction mechanisms. During post-chlorination, Br^- was converted to HBrO/BrO-, and the HN=C(CH₃)-COOH, CH₃-CH=NH, and CH₃-C≡N groups featured higher bromine utilization factor (BUF) and chlorine utilization factor (CUF) values than AAs, enhancing the formation of dibromoacetonitrile (DBAN) and dichloroacetonitrile (DCAN). The energetic feasibility of the transformation pathway, that is, HN=C(CH₃)-COOH, CH₃-CH=NH, and CH₃-C ≡ N formation via hydrogen abstraction by SO₃^- and H and their further conversion to HANs, was proved by density functional theory calculations, which showed stepwise negative Gibbs free energy changes (ΔG < 0). The effects of pH and water matrices (e.g., HCO₃^-, Cl^-, Fe³⁺, and natural organic matter) were comprehensively evaluated. Although 72% of BrO₃^- was removed by sulfite/UV treatment in the presence of AAs, the cytotoxicity index (CTI) and genotoxicity index (GTI) during post-chlorination increased by 213% and 125%, respectively, due to the formation of 24 CX₃R-type disinfection by-products (DBPs), especially brominated DBPs. Accordingly, more attention should be given to the formation of brominated DBPs during post-chlorination when using sulfite/UV processes to remove BrO₃^- in the presence of AAs. As a solution, using monochloramine instead of chlorine as a disinfectant after the sulfite/UV process could significantly lower the CTI and GTI values by alleviating the formation of brominated DBPs.

Influence of chemical speciation on enrofloxacin degradation by UV irradiation: Kinetics, mechanism and disinfection by-products formation

Fluoroquinolones (FQs) were frequently detected in aqueous environment. The UV irradiation have been reported as an efficient method for FQs degradation. This study investigated the influence of chemical speciation on enrofloxacin (ENR) photolysis process by UV irradiation. The results showed that chemical speciation of ENR significantly affected the photodegradation kinetics, and the highest degradation rate was observed in the zwitterion form. Presence of natural organic matter (NOM) and inorganic anions had different degrees of influences on ENR photodegradation for three chemical speciation of ENR. The contribution of ¹O₂ on ENR degradation in neutral and alkalinity condition was significantly higher than that in acidic condition. The cation and zwitterion of ENR was beneficial to the formation of trichloromethane (TCM) and haloacetonitrile (HAN) during the chlorination alone. Compared with the chlorination of ENR, the UV pretreatment respectively caused 4.06-fold and 3.14-fold decrease in TCM formation at acidic and neutral reaction condition during subsequent chlorination. Also the decrease in HAN formation at neutral and alkalinity condition was found after UV treatment followed by chlorination. The UV pretreatment caused higher yield of HAN in the subsequent chlorination at acidic condition than that at neutral and alkalinity condition. Through the UV pretreatment at neutral condition, the generated concentration of halonitromethane (HNM) reached the maximum value during the subsequent chlorination. Potential toxic risk analysis showed the toxicity decreased in zwitterion form of ENR, while toxicity increased in cationic and anionic form after UV irradiation pretreatment.

Understanding the influence of pre-ozonation on the formation of disinfection byproducts and cytotoxicity during post-chlorination of natural organic matter: UV absorbance and electron-donating-moiety of molecular weight fractions

Pre-ozonation can reduce the formation of disinfection byproducts (DBPs) and related adverse effects during subsequent chlorination, but the change of each molecular weight (MW) fraction during each step of combined pre-ozonation and post-chlorination has not been well illustrated. In this study, it was investigated in terms of electron-donating-moieties (EDMs) and UVA₂₅₄ for a representative natural organic matter from Suwanee river (SRNOM). Pre-ozonation suppressed the post-chlorination of SRNOM through oxidation of almost all EDMs (>85%) and UVA₂₅₄ (>90%) in high MW fractions (HMW, >3.2 kDa) and moderate EDMs (43%) and UVA₂₅₄ (72%) in medium MW fractions (MMW, 1.0-3.2 kDa). Furthermore, pre-ozonation led to comparable abatements of EDMs and UVA₂₅₄ for HMW fractions, but lower abatement of EDMs than UVA₂₅₄ for MMW fractions. However, when t-BuOH was used as an ^•OH-quencher, pre-ozonation led to a few instances in which there were higher abatements of EDMs than UVA₂₅₄ for the MMW fraction. These findings suggested that the HMW fraction dominantly underwent ring-cleavage of phenols via O₃- or ^•OH-oxidation. Differently, the MMW fraction underwent ring-cleavage of phenols and quinones-formation via O₃-oxidation, but occasionally underwent hydroxylation and hydro-phenol formation via ^•OH-oxidation. Because of forehand elimination of reactive moieties (e.g. EDMs), pre-ozonation obviously inhibited the formation of representative DBPs (67%-84% inhibition), total organic chloride (51% inhibition) and cytotoxicity (31% inhibition), but may have promoted the formation of carbonyl-DBPs (trichloroacetone and chloral hydrate). When compared with UVA₂₅₄, EDMs would better for surrogate of DBPs formation. EDM abatement surrogated the formation of total organic chlorine (TOCl) and cytotoxicity following a two-stage phase, possibly because the speciation of DBPs and transformation products varied with the abatement of EDMs.

The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/H2O2/O3 technology

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H₂O₂/O₃ was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H₂O₂/O₃ is higher than by UV/H₂O₂ or UV/O₃ which can reach 95% at the UV dose of 400 mJ/cm². An alkaline environment reduces the oxidation efficiency of UV/H₂O₂/O₃ technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO₃^-, SO₄^2-, Cl^- and NO₃^- are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H₂O₂/O₃ is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H₂O₂/O₃ was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.

Ultrasound-enhanced coagulation for Microcystis aeruginosa removal and disinfection by-product control during subsequent chlorination

Ultrasound techniques have gained increased interest in environmental remediation because of their promising performance and reagent-free nature. This study investigated the effects of ultrasound-coagulation on Microcystis aeruginosa removal, disinfection by-product (DBP) formation during subsequent chlorination, and acute toxicity and DBP-associated toxicity variations in chlorinated effluents. Compared with coagulation using polymeric aluminum chloride (5 mg-Al/L) alone, ultrasound-coagulation showed significantly enhanced turbidity removal, with the removal ratio increasing from 51% to 87%-96%. Although the addition of ultrasound may not substantially improve and even deteriorate the coagulation removal of DOC following the leakage of intracellular organic matter, the significantly improved DBP control was achieved as the cells dominated DBP formation. With the addition of ultrasound, the chlorine demand, aggregate DBP concentration and total organic halogen concentration reductions in the chlorinated M. aeruginosa solution increased from 15%, 47% and 52% (coagulation alone), respectively, to 56%-78%, 56%-80% and 68%-89%. The enhanced DBP mitigation was mainly attributed to the enhanced algal removal. Similarly, the acute toxicity and DBP-associated toxicity of chlorinated effluents further decreased from 100% and 0.0092 (coagulation alone) to 30%-88% and 0.0029-0.0060. Therefore, ultrasound-enhanced coagulation is a promising strategy for urgent algal removal, DBP mitigation and toxicity abatement.

Simultaneous mitigation of disinfection by-product formation and odor compounds by peroxide/Fe(II)-based process: Combination of oxidation and coagulation

To remove disinfection by-product (DBP) precursors and mitigate odor compounds, peroxide (peroxymonosulfate and persulfate)/Fe(II)-based process was applied as a combination of coagulation and oxidation. Compared with traditional Fe-based salt coagulation (FeSO₄ and FeCl₃), peroxide/Fe(II)-based process was more efficient in dissolved organic carbon, UV₂₅₄ and turbidity removal, and peroxymonosulfate showed better performance than persulfate. The better coagulation performance arose from a combination of enhanced neutralization and different characteristics of flocs. Even though the combined process would increase the bromine substitution factor of DBPs, DBP formation and DBP-associated toxicity after peroxide/Fe(II)-based process were 9.2-38.8% and 5.2-27.2% lower than that after conventional Fe(III) coagulation. Both enhanced dissolved organic matter removal and oxidation of DBP precursors played vital roles in DBP control. Conventional Fe-based salt coagulation could hardly remove odor compounds (less than 10%, generally), whereas 28.2-84.9% of odor compounds were degraded during peroxide/Fe(II)-based process, due to free radical formation. This study demonstrated that PMS/Fe(II)-based process might be a promising treatment process for simultaneous DBP control and odor removal in source water.

Formation of Hydrogen Peroxide from O-(H2O)n Clusters

Hydrogen peroxide (H₂O₂) has recently received much attention as a safe and clean energy carrier for hydrogen molecules. In this study, based on direct ab initio molecular dynamics (AIMD) calculations, we demonstrated that H₂O₂ is directly formed via the photoelectron detachment of O^-(H₂O)_n (n = 1-6) (water clusters of an oxygen radical anion). Three electronic states of oxygen atoms were examined in the calculations: O(X)(H₂O)_n (X = ³P, ¹D, and ¹S states). After the photoelectron detachment of O^-(H₂O)_n (n = 1) to the ¹S state, a complex comprising O(¹S) and H₂O, O(¹S)-OH₂, was formed. A hydrogen atom of H₂O immediately transferred to O(¹S) during an intracluster reaction to form H₂O₂ as the final product. Simulations were run to obtain a total of 33 trajectories for n = 1 that all led to the formation of H₂O₂. The average reaction time of H₂O₂ formation was calculated to be 57.7 fs in the case of n = 1, indicating that the reaction was completed within 100 fs of electron detachment. All the reaction systems O(¹S)(H₂O)_n (n = 1-6) indicated the formation of H₂O₂ by the same mechanism. The reaction times for n = 2-6 were calculated to range between 80 and 180 fs, indicating that the reaction for n = 1 is faster than that of the larger clusters, that is, the larger the cluster size, the slower the reaction is. The reaction dynamics of the triplet O(³P) and singlet O(¹D) potential energy surfaces were calculated for comparison. All calculations yielded the dissociation product O(X)(H₂O)_n → O(X) + (H₂O)_n (X = ³P and ¹D), indicating that the O(¹S) state contributes to the formation of H₂O₂. The reaction mechanism was discussed based on the theoretical results.

Effect of oxidation ditch and anaerobic-anoxic-oxic processes on CX3R-type disinfection by-product formation during wastewater treatment

The high chlorine dosages in wastewater treatment plants during the COVID-19 pandemic may result in increased formation of disinfection by-products (DBPs), posing great threat to the aquatic ecosystem of the receiving water body and the public health in the downstream area. However, limited information is available on the effect of biological wastewater treatment processes on the formation of CX₃R-type DBPs. This study investigated the effect of oxidation ditch (OD) and anaerobic-anoxic-oxic (AAO), two widely used biological wastewater treatment processes, on the formation of five classes of CX₃R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs) and halonitromethanes (HNMs), during chlorination. Experimental results showed that biological treatment effectively reduced the dissolved organic carbon (DOC) and UV₂₅₄, while it increased the dissolved organic nitrogen (DON), and therefore the ratio of DON/DOC. In addition, increases in the contents of soluble microbial product- and humic acid-like matters, and the transformation of high molecular weight (MW) fractions in the dissolved organic matter into low MW fractions were observed after OD and AAO processes. Although biological treatment effectively decreased the formation of Cl-THMs, Cl-HAAs, Cl-HANs and Cl-HNMs, the formation of DBCM, DBAA, BDCAA, DBCAA, DCAL, TCAL and DBAN (where C = chloro, B = bromo, D = di, T = tri) all increased significantly, due to the increased formation reactivity. Moreover, biological treatment increased the ratio of bromide/DOC and bromine incorporation into THMs, HAAs and DHANs except for HALs and THANs. Different from previous studies, this study revealed that biological treatment increased the formation of some DBPs, especially brominated DBPs, despite the efficient removal of organic matters. It provides insights into the DBP risk control in wastewater treatment, particularly during the COVID-19 pandemic.

Polymer brush-grafted cotton fiber for the efficient removal of aromatic halogenated disinfection by-products in drinking water

Apart from the activated carbon, other functional adsorbents are usually not frequently reported for the removal of disinfection by-products (DBPs) in drinking water. In this study, a novel polymer brush-grafted cotton fiber was prepared and for the first time used as adsorbents for the efficient removal of aromatic halogenated DBPs in drinking water in the column adsorption mode. Poly (glycidyl methacrylate) (PGMA) was grafted onto the surface of cotton fibers via UV irradiation, and then diethylenetriamine was immobilized on the PGMA polymer brush through amination reaction to obtain the aminated cotton fibers (ACFs). The adsorption performance of the prepared ACF was investigated with eight aromatic halogenated DBPs via dynamic adsorption experiments. The results revealed that ACF showed significantly longer breakthrough point (38,500-225,500 BV) for aromatic halogenated DBPs compared with the granular activated carbon (150-500 BV). Thomas model was used to fit the breakthrough curves, and the theoretical value of the maximum adsorption capacity ranged from 14.76 to 89.47 mg/g. The enhanced adsorption performance of the ACF for aromatic halogenated DBPs was mainly due to the formation of hydrogen bonds. Additionally, the partially protonated amine groups also improved the adsorption performance. Furthermore, the ACF also showed remarkable stability and reusability.

Removal of the precursors of regulated DBPs and TOX from surface waters and wastewater effluents using mixed anion exchange resins

Both organic and inorganic precursors play important roles in the formation and speciation of disinfection by-products (DBPs). This study aimed to investigate the efficacy of three different anion exchange resins for removing both organic and inorganic DBP precursors simultaneously in a single treatment system. Resins in the single (Purolite®-Br, MIEX®-Br, and MIEX®-Gold) and mixed (Purolite®-Br with MIEX®-Gold and MIEX®-Br with MIEX®-Gold) application modes were tested and compared for the removal of dissolved organic carbon (DOC), bromide (Br^-), and iodide (I^-) from a raw source water and a treated wastewater effluent. Uniform formation condition (UFC) tests were conducted to measure the concentrations of trihalomethanes (THM4), haloacetic acids (HAA9), haloacetonitriles (HAN6), and total organic halides (TOX): total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI) before and after the anion exchange resin treatments. The anion exchange treatment substantially lowered the DOC, UV₂₅₄ absorbing matter, dissolved nitrogen (DN), Br^-, and I^-. Consequently, the formation of THM4, HAA9, HAN6, and TOX in the examined chlorinated water samples were reduced significantly. The maximum reduction in THM4 and TOX (66-69% and 61%, respectively) from wastewater effluent was achieved by the mixed resin system, which also reduced the THM4 and TOX by 77% and 77%, respectively, from raw source water. Overall, mixed resin systems (a DOC-selective and a Br-selective resin) resulted in lower amounts of THM4 and HAA9 formation during subsequent chlorination with lower bromine incorporation as compared to single resin systems. Furthermore, they exhibited lower TOBr formation, while TOI formation was not detected.

Covalent organic frameworks as an efficient adsorbent for controlling the formation of disinfection by-products (DBPs) in chlorinated drinking water

2,5-Dimethyl-p-phenylenediamine-1,3,5-triformylphloroglucinol covalent organic frameworks (PATP COF) were prepared and used as novel adsorbent for controlling the formation potential (FP) and reducing the toxic potential of both carbonaceous disinfection by-products (C-DBPs) and nitrogenous DBPs (N-DBPs) during their subsequent chlorination. During the PATP COF adsorption pretreatment process, the FP of C-DBPs, N-DBPs and total organic halogen (TOX) were reduced by 86.5, 75.4 and 81.1%, respectively. These removal efficiencies were significantly higher when compared with those obtained using a traditional activated carbon (AC) adsorption pretreatment process (42.7, 19.4 and 28.7%, respectively). By comprehensive toxicity calculations, a significant reduction in both the acute and chronic toxic potential of C-DBPs and N-DBPs were observed during the PATP COF adsorption process (with reduction rates of ~85 and ~ 75% observed for the C-DBPs and N-DBPs, respectively), which were comparable to the removal efficiencies observed for C-DBPs FP and N-DBPs FP by weight, suggesting the simultaneous and effective control of DBPs FP and their toxic potential. Cycling tests and stability trial also showed the excellent reusability, wide pH adaptability, and high stability of PATP COF, demonstrating its great potential application to the treatment of drinking water.

Removal of CX3R-type disinfection by-product precursors from rainwater with conventional drinking water treatment processes

In addition to surface water and groundwater, rainwater is used as an important drinking water source in many parts of the world, especially in areas with serious water pollution or insufficient water resources. Conventional drinking water treatment technologies can remove dissolved organic matter and therefore reduce the formation of disinfection by-products (DBPs) during subsequent disinfection using surface water or groundwater as drinking water sources. However, little information has been known about the effect of conventional water treatment processes on DBP formation when rainwater is used as drinking water source. This study evaluated CX₃R-type DBP precursors removal from rainwater by conventional drinking water treatments and the corresponding decrease of CX₃R-type DBP (trihalomethanes (THMs), haloaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs)) formation and toxicity during the subsequent chlor(am)ination. The result showed that both sand filtration (SF) and activated carbon filtration (GAC) were able to remove DBP precursors and GAC outperformed SF, but no DBP precursors removal was observed during coagulation-sedimentation treatment. Among all treatments, SF + GAC was the most effective for DBP precursors removal, with removal efficiencies of 64.2% DOC, 98% DON and 76.6% UV₂₅₄. Correspondingly, both SF and GAC decreased the formation of THMs, HALs, HANs and HAMs, and GAC performed better than SF. The combination of SF and GAC, especially SF + GAC, greatly decreased DBP formation, with average reduction of 79.2% and 85% during chlorination and chloramination respectively. After different treatments, the comprehensive toxicity risk of CX₃R-type DBPs was all reduced, among which GAC + SF exhibited superior performance. Generally, the main contribution of integrated toxicity was HANs during chlor(am)ination. The formation potential of THMs, HALs, HANs and HAMs and the corresponding integrated toxicity were greater during chlorination than that during chloramination. Therefore, the combination of GAC and chloramination was promising in mitigating the comprehensive toxicity risk of THMs, HALs, HANs and HAMs for rainwater.

Kinetic mechanism of ozone activated peroxymonosulfate system for enhanced removal of anti-inflammatory drugs

Peroxymonosulfate (PMS) was employed as an activator of ozone (O₃) to degrade non-steroidal anti-inflammatory drugs (NSAIDs) (aspirin (ASA) and phenacetin (PNT)) in study. The combination of PMS in O₃ system promoted the O₃ decomposition and NSAIDs removal significantly. O₃ molecule, hydroxyl radical (OH) and sulfate radical (SO₄^-) were responsible for the removal of target pollutants in O₃/PMS system. The second-rate constants between O₃, OH and SO₄^- with ASA were determined to be 7.32, 4.18 × 10⁹ and 3.46 × 10⁸ M^-1·s^-1, and 37.3, 4.99 × 10⁹ and 5.64 × 10⁸ M^-1·s^-1 for PNT, respectively. The pattern of pollutant removal and contributions of oxidative species were fitted by experiments and two models. Nevertheless, the wide variety of two models suggested that a comprehensive model for O₃/PMS based on a first-principles approach was not yet possible, due to the number of radicals and subsequent chain reaction, such as SO₅^- or O₃^-. In addition, the formation of five typical CX₃R -type disinfection by products was evaluated from post‑chlorine tests and theoretically calculation by frontier electron density calculation. The calculated toxicity of typical CX₃R -type DBPs was found to decrease with the increase of pH. The results of this study provide a basis for exploring the mechanism of pollutant degradation in O₃ system.

Formation, speciation and toxicity of CX3R-type disinfection by-products (DBPs) from chlor(am)ination of 2,4-diaminobutyric acid (DAB)

2,4-diaminobutyric acid (DAB), a newly identified algal toxins in water, pose a great threat to human health. DAB may react with chlorine or chloramine to produce CX₃R-type disinfection by-products (DBPs) during water treatment processes. This study mainly investigated the formation and speciation of DBPs from chlor(am)ination of DAB. The results revealed that haloacetic acids (HAAs), trihalomethanes (THMs) and haloacetonitriles (HANs) were the main kinds of CX₃R-type DBPs generated from DAB during chlor(am)ination, of which dichloroacetic acid yielded the highest. The formation and total toxicity of four CX₃R-type DBPs from DAB during chloramination was significantly lower than that during chlorination at each Cl₂:N molar ratio. However, more formation of Br-THMs and I-THMs were observed during chloramination in the presence of Br^-/I^-. Futhermore, the effects of chlor(am)ine dosage, solution pH, reaction time, and the concentration of Br^- and I^- on the formation and speciation of CX₃R-type DBPs were also evaluated during chlor(am)ination. The plausible formation pathways of CX₃R-type DBPs from DAB were proposed and verified by theoretical calculation. The quantum chemistry calculations indicate that 1N in DAB and 8N in 2,4-diaminochlorobutyric acid (C₄H₉O₂N₂Cl) were more likely to be attacked by electrophiles, supporting the proposed pathway schemes.