Formation Of Haloacetonitriles Research Articles

Halogenation of Anilines: Formation of Haloacetonitriles and Large-Molecule Disinfection Byproducts.

Aniline-related structures are common in anthropogenic chemicals, such as pharmaceuticals and pesticides. Compared with the widely studied phenolic compounds, anilines have received far less assessment of their disinfection byproduct (DBP) formation potential, even though anilines and phenols likely exhibit similar reactivities on their respective aromatic rings. In this study, a suite of 19 aniline compounds with varying N- and ring-substitutions were evaluated for their formation potentials of haloacetonitriles and trihalomethanes under free chlorination and free bromination conditions. Eight of the aniline compounds formed dichloroacetonitrile at yields above 0.50%; the highest yields were observed for 4-nitroaniline, 3-chloroaniline, and 4-(methylsulfonyl)aniline (1.6-2.3%). Free bromination generally resulted in greater haloacetonitrile yields with the highest yield observed for 2-ethylaniline (6.5%). The trihalomethane yields of anilines correlated with their haloacetonitrile yields. Product analysis of aniline chlorination by liquid chromatography-high-resolution mass spectrometry revealed several large-molecule DBPs, including chloroanilines, (chloro)hydroxyanilines, (chloro)benzoquinone imines, and ring-cleavage products. The product time profiles suggested that the reaction pathways include initial ring chlorination and hydroxylation, followed by the formation of benzoquinone imines that eventually led to ring cleavage. This work revealed the potential of aniline-related moieties in micropollutants as potent precursors to haloacetonitriles and other emerging large-molecule DBPs with the expected toxicity.

Response of a source water quality through a heavy precipitation event: Nutrients, dissolved organic matter and their DBPs formation

To better understand the influence of heavy precipitation event on water supply security, the change of nutrients, dissolved organic matter (DOM) and their corresponding disinfection by-products (DBPs) generation in river were investigated through a heavy precipitation event. The results show that short-term sustained heavy precipitation causes additional load on the river. Significant temporal variations and increases in dissolved oxygen (DO), turbidity, dissolved organic carbon (DOC) and molecular weight of raw water were observed during the heavy precipitation, and dissolved organic nitrogen (DON) showed a remarkably decline with the continuation of precipitation. The molecular weight and aromaticity of DOM increased dramatically with the continuous superposition of precipitation and flow, and the proportion of hydrophobic fraction increased during the study period. Four different fluorescent components were identified, including humic-like (C1, C2 and C3), and protein-like fluorophore C4. Heavy precipitation events affected the mobilization of DOM, while the generation of DBPs increased by 4%–47% during the chlorination, and the elevated river level further increased the DBPs formation. In particular, the HOA fraction was the main contributor of DBPs (up to 70%). The risk of haloacetic acids (HAAs) generation caused by heavy rainfall was concentrated in the river runoff producing and regression periods for both hydrophobic and hydrophilic fractions of DOM. Humification index (HIX) was positively correlated with the yield level of TCM, DCAA, TCAA, and DCAN during chlorination. Chlorination disinfection of raw water during river runoff producing and regression period is likely to increase the haloacetonitriles formation potential (HANsFP), thus posing a vital threat to water supply safety, while chloramination disinfection may significantly relieve the threat. This study provides a theoretical basis for the direct/indirect link between short-term precipitation events and their impact on water quality.

Degrading surface-water-based natural organic matter and mitigating haloacetonitrile formation during chlorination: Comparison of UV/persulfate and UV/hydrogen peroxide pre-treatments

Haloacetonitriles (HANs) are unregulated disinfection by-products that are more toxic than regulated species. Therefore, efficient decomposition of HAN precursors prior to disinfection is crucial for allaying the potential HAN-induced health risks. This study investigated the key roles of ultraviolet-activated persulfate (UV/PS) treatment in alleviating HAN formation. The effects of UV/PS treatment were evaluated by correlating with the characteristics of organic matter in surface water and comparing with conventional UV/H2O2 treatment. Upon irradiating raw water samples and a Suwannee River humic acid solution spiked with 10 mM PS or H2O2 with 254 nm UV light, UV/PS treatment was found to be more potent than UV/H2O2 in mitigating the HAN production and degrading organic substances; moreover, UV/PS treatment effectively decreased the dissolved organic nitrogen (DON) content. In contrast, UV/H2O2 treatment did not induce any noticeable reduction in DON level. Furthermore, both UV/PS and UV/H2O2 treatments reduced the dichloroacetonitrile (DCAN) formation potential (FP), leading to strong correlations with the degradation of aromatic and humic-acid-like compounds. Notably, UV/PS treatment efficiently decreased the FP of bromochloroacetonitrile (BCAN) and dramatically reduced that of dibromoacetonitrile (DBAN) after a sharp increase; however, UV/H2O2 treatment gradually increased the DBAN-FP. Bromide was activated by sulfate radicals during UV/PS treatment, negatively correlating with the BCAN-FP and DBAN-FP, indicating that the formation of reactive bromine species increased the DBAN-FP; however, excessive oxidation possibly led to the recovery of inorganic bromine for decreasing the BCAN-FP and DBAN-FP. Additionally, UV/PS treatment effectively suppressed toxicity owing to its high reduction rate for brominated HANs; in contrast, UV/H2O2 treatment resulted in less significant BCAN and DBAN reductions, leading to minimal net reduction in toxicity. Overall, UV/PS treatment was remarkably effective at diminishing the toxicity of brominated HANs, underscoring its potential to mitigate drinking-water-related health risks.

Response mechanisms of pipe wall biofilms in water supply networks under different disinfection strategy pressures and the effect of mediating halogenated acetonitrile formation

Residual chlorine and biofilm coexistence is inevitable in drinking water transmission and distribution networks. Understanding the microbial response and its mediated effects on disinfection byproducts under different categories of residual chlorine stress is essential to ensure water safety. The aim of our study was to determine the response of pipe wall biofilms to residual chlorine pressure in chlorine and chloramine systems and to understand the microbially mediated effects on the formation and migration of haloacetonitriles (HANs), typical nitrogenous disinfection byproducts. According to the experimental results, the biofilm response changes under pressure, with significant differences noted in morphological characteristics, the extracellular polymeric substances (EPS) spatial structure, bacterial diversity, and functional abundance potential. Upon incubation with residual chlorine (1.0 ± 0.2 mg/L), the biofilm biomass per unit area, EPS, community abundance, and diversity increased in the chloramine group, and the percentage of viable bacteria increased, potentially indicating that the chloramine group provides a richer variety of organic matter precursors. Compared with the chloramine group, the chlorination group exhibited increased haloacetonitrile formation potential (HANFP), with Rhodococcus (43.2%) dominating the system, whereas the prediction abundance of metabolic functions was advantageous, especially with regard to amino acid metabolism, carbohydrate metabolism, and the biodegradation and metabolism of foreign chemicals. Under chlorine stress, pipe wall biofilms play a stronger role in mediating HAN production. It is inferred that chlorine may stimulates microbial interactions, and more metabolites (e.g., EPS) consume chlorine to protect microbial survival. EPS dominates in biofilms, in which proteins exhibit greater HANFP than polysaccharides.

Overlooked Contribution of the Indole Moiety to the Formation of Haloacetonitrile Disinfection Byproducts

Haloacetonitriles (HANs) are a group of disinfection byproducts with high toxicity and frequent occurrence. Past studies have focused on the free amine groups, especially those in amino acids, as HAN precursors. This study reports, for the first time, that the indole moiety such as that in the tryptophan side chain is also a potent precursor for the most common HANs dichloroacetonitrile, bromochloroacetonitrile, and dibromoacetonitrile. 3-Indolepropionic acid, differing from tryptophan only in the absence of the free amine group, formed HANs at levels 57-76% of those by tryptophan at a halogen/nitrogen molar ratio of 10. Experiments with tryptophan-(amino-15N) showed that the indole contributed to 28-51% of the HANs formed by tryptophan. At low oxidant excess (e.g., halogen/precursor = 5), 3-indolepropionic acid even formed more HANs than Trp by 3.5-, 2.5-, and 1.8-fold during free chlorination, free bromination, and chlorination in the presence of bromide (0.6 mg/L), respectively. Indole's HAN formation pathway was investigated by exploring the chlorination/bromination products of 3-indolepropionic acid using liquid chromatography-orbitrap high-resolution mass spectrometry. A total of 22 intermediates were detected, including pyrrole ring-opening products with an N-formyl group, 2-substituted anilines with different hydroxyl/halogen substitutions, and an intermediate with a postulated non-aromatic ring structure.

Removal of carbonaceous and nitrogenous disinfection by-product precursors in biological activated carbon process of drinking water: Is service life a pivotal factor?

Biological activated carbon (BAC) process is commonly used for drinking water treatment. Granular activated carbon (GAC) serving as the initial filter media can be converted to BAC with biofilm development during extending service life. Consequently, GAC/BAC effectiveness for disinfection by-product (DBP) precursors removal varies over service life. Effluents of full-scale ozonation and BACs operated for 1–3 months (1-month GAC), 4–6 months (4-month BAC), and about 7 years (7-year BAC) were analyzed. All BACs were efficient in fluorescence components removal, with decreasing efficiency in the order of 1-month GAC > 4-month BAC > 7-year BAC. Accordingly, reduction ratios of total DBPs concentration formed in post-chlorination dropped from 39% to 21% and 8% by BACs with different ages. Due to varied toxic potencies of DBPs, toxicities reduction was not completely related to DBPs concentration reduction. Haloacetonitriles (HANs) group accounted for small proportion of DBPs concentration but drove both of cytotoxicity and genotoxicity. Hence, the precursor removals of carbonaceous (C-) DBPs and nitrogenous (N-) DBPs were further compared in detail. 1-month GAC exhibited relatively higher effectiveness for protein-like components removal than humic-like component removal, for HANs formation reduction than trihalomethanes (THMs) formation reduction, and for HANs cytotoxicity reduction than THMs cytotoxicity reduction. A similar pattern was observed for 4-month BAC, while 7-year BAC exhibited the opposite pattern. Given the complexity of real water, this full-scale study provides valuable insights into the differences in precursor removals of C-DBPs and N-DBPs by BACs with different ages, which is critical for advancing our understanding of BAC process.

Enhanced formation of haloacetonitriles during chlorination with bromide: Unveiling the important roles of organic bromamines

The formation of brominated disinfection byproducts (Br-DBPs) is an emerging issue in drinking water disinfection because its toxicity is tens to hundreds of times higher than that of chlorinated analogues and because of the widespread presence of bromide in source water. However, the mechanism and pathways of Br-DBPs formation remain unclear. In this study, we used glycine, alanine, and serine as model precursors and observed that brominated haloacetonitriles (Br-HANs) were more likely to be formed than brominated trihalomethanes. The results showed that there is not only one important way to HAN formation in the presence of bromide. We propose that organic bromamines, similar to organic chloramines, play a significant role in the formation of Br-HANs. Both the experimental and theoretical results confirmed that the decay of organic bromamines was faster than that of organic chloramines, which verified our assumption. The effect of the pH was investigated to further confirm the role of organic bromamines. In addition, we found that the formation of Br-HANs was significantly inhibited when monochloramine was used as a disinfectant, because the formation of organic bromamines was blocked. However, the formation of Br-HANs was promoted during the UV/chlorine process because of the faster decay of organic bromamines under UV photolysis. Overall, our study reveals the formation mechanism of Br-HANs and provides an alternative method to prevent Br-HAN formation.

Characterization of DBP precursor removal by magnetic ion exchange resin using spectroscopy and high-resolution mass spectrometry

The characteristics of dissolved organic matter (DOM) play an important role in the formation and speciation of carcinogenic disinfection byproducts. This study investigated changes in the characteristics and reactivity of DOM caused by the magnetic ion exchange resins, MIEX® DOC and MIEX® GOLD, using fluorescence excitation-emission matrix (EEM) with parallel factor (PARAFAC) analysis and Orbitrap mass spectrometry (Orbitrap MS) with unknown screening analysis. A five-component PARAFAC model was developed and validated from 208 EEMs of raw and MIEX®-treated water samples. The two resins exhibited preferential removal of the humic-like components (67–87% removal) and successfully removed protein-like components to a lesser extent (5–61% removal). Unknown screening analysis indicated removal of most condensed aromatic structures and lignin-like features that had high O/C values and refractory characteristics of lipid-like features by MIEX® treatments. MIEX® preferentially removed DOM molecules with more oxidized and shorter CH2 chains. The two resins had similar performance in trihalomethanes formation potential removal, but MIEX® GOLD achieved greater haloacetonitriles formation potential removal owing to its larger pore opening. Over 100 CHOCl DBP features were commonly found in all the samples while tens of CHOCl DBPs were uniquely formed in the samples with and without pre-treatments by MIEX®. Treatments by MIEX® before chlorination resulted in more intermediate CHOCl DBPs formed after chlorination compared to chlorinated raw waters. By optical spectroscopic analysis together with Orbitrap MS molecular characterization, we were able to confirm both quantitative and qualitative changes in DOM properties by MIEX® treatment related to DBP formation.

Characteristics and chlorine reactivity of biochar-derived dissolved organic matter: Effects of feedstock type and pyrolysis temperature

Increasing biochar application worldwide may release more biochar-derived dissolved organic matter (BDOM) to the source water for drinking water supply. However, it is unclear how feedstock types and pyrolysis temperatures for biochar production would affect the characteristics and chlorine reactivity of BDOM. Here, we studied the spectroscopic characteristics of BDOM pyrolyzed from pine needle, wheat straw, walnut shells, alfalfa, pig manure, and sludge derived biochars at 300, 500, and 700 °C, as well as the formation potential of disinfection byproducts (DBPs) and their bulk toxicity after BDOM chlorination. The N/C ratio of biochar was higher for N-rich than C-rich feedstocks. Optical analyses indicated that BDOM aromaticity was highest at 700 °C, while the impact of pyrolysis temperature on the molecular weight of BDOM varied greatly among feedstocks. Increasing pyrolysis temperature caused consistently decreased BDOM reactivity toward haloketone formation but did not show consistent impacts on the other DBPs. Among feedstocks, the N-rich sludge showed the highest specific haloacetonitrile formation potential of BDOM at any given pyrolysis temperature. The DBP formation potential from biochar was consistently highest at 300 °C and was higher for N-rich than C-rich feedstocks. The microtoxicity of DBP mixture was highest for the BDOM derived from sludge produced at 300 °C. This study highlights the high variations in characteristics and chlorination reactivity of BDOM with varying feedstocks and pyrolysis temperatures, which implies that more attention should be paid to the environmental impacts of the intensive application of low-temperature biochar from N-rich feedstock such as sludge.

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 (eaq−) 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.

Molecular-Level Insights into the Formation of Traditional and Novel Halogenated Disinfection Byproducts

Dissolved organic matter (DOM) composition influences the formation of disinfection byproducts (DBPs) during drinking water treatment, yet the role of DOM composition at the molecular level in forming both known and novel DBPs has not been established. We characterized the composition of DOM from drinking water utilities that draw from surface (n = 4) and groundwaters (n = 14), focusing on groundwater because the reactivity of its DOM is poorly understood. We quantified the formation of targeted DBPs, identified novel high molecular weight (HMW) halogenated DBPs, and analyzed DOM transformation after reaction with free available chlorine. Characterization by UV–visible spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) reveals a high degree of variability in DOM composition and reactivity with chlorine, particularly among groundwater samples. Despite the variability in DOM composition, novel DBPs with up to three halogens are compositionally similar among all waters and are positively correlated with trihalomethane and, to a lesser extent, haloacetonitrile formation. These relationships demonstrate that some low molecular weight DBPs and novel DBPs detected by FT-ICR MS share similar aromatic precursors, providing evidence that DBPs such as trihalomethanes are a useful proxy for the formation of their HMW counterparts.

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.

Contribution of wastewater- versus non-wastewater-derived sources to haloacetonitriles formation potential in a wastewater-impacted river

Population growth and urbanization have led to the increasing presence of treated wastewater effluents in downstream drinking water sources. Drinking water sources influenced by organic matter from upstream wastewater treatment plant (WWTP) effluents are thought prone to the formation of haloacetonitriles (HANs), a group of nitrogenous disinfection by-products (DBPs) that can exhibit higher toxicity than currently regulated carbonaceous DBPs. We develop a framework for studying the HAN formation potential (HAN-FP) considering the WWTP and non-WWTP related sources of HAN precursors, and apply this framework to a representative WWTP-impacted river, the Illinois River, USA. A spatiotemporally-resolved river hydrodynamic and water quality model is developed using HEC-RAS to quantify the contribution of WWTP versus non-WWTP sources of HAN-FP precursors. Results show that non-WWTP sources of HAN-FP are considerable, accounting for up to 78% of HAN-FP concentration. Moreover, the contribution of the two sources varies due to streamflow discharge variability. During lower flows, the contribution of WWTPs drives the high concentration of HAN-FP and during higher flows, the contribution of non-WWTP sources becomes dominant. As a result, a high risk of HAN-FP may exist persistently (HAN-FP concentration is always larger than 9.7 μg/L in this study), not only during low flows but also during high flows due to both wastewater- and non-wastewater-derived HAN-FP sources.

DBP formation and toxicity alteration during UV/chlorine treatment of wastewater and the effects of ammonia and bromide

The UV/chlorine process is efficient for the abatement of micropollutants; yet, the formation of disinfection by-products (DBPs) and the toxicity can be altered during the treatment. This study investigated effluent organic matter characterization, DBP formation and toxicity alteration after the UV/chlorine treatment of wastewater; particularly, typical water matrix components in wastewater, namely, ammonia and bromide, were studied. The raw wastewater contained low levels of ammonia (3 µM) and bromide (0.5 µM). The UV/chlorine treatment efficiently eliminated 90 – 94% of fluorescent components. Compared with chlorination alone, a 20 min UV/chlorine treatment increased the formation of trihalomethanes (THMs), haloacetic acids (HAAs), chloral hydrate (CH), haloacetonitriles (HANs), trichloronitromethane (TCNM) and haloacetamides (HAcAms) by 90 – 508%. In post-chlorination after the UV/chlorine treatment, the formation of CH, HANs, TCNM and HAcAms increased by 77 – 274%, whereas the formation of both THMs and HAAs increased slightly by 11%. Meanwhile, the calculated cytotoxicity and genotoxicity of DBPs increased considerably after the UV/chlorine treatment and in post-chlorination, primarily due to the increased formation of HAAs and nitrogenous DBPs (N-DBPs). However, the acute toxicity of the wastewater to Vibrio fischeri and genotoxicity determined by the umu test decreased by 19% and 76%, respectively, after the 20 min UV/chlorine treatment. An additional 200 µM ammonia decreased the formation of all detected DBPs during the UV/chlorine treatment and 24 h post-chlorination, except that TCNM formation increased by 11% during post-chlorination. The acute toxicity of wastewater spiked with 200 µM ammonia was 32% lower than that of raw wastewater after the UV/chlorine treatment, but the genotoxicity was 58% higher. The addition of 1 mg/L bromide to the UV/chlorine process dramatically increased the formation of brominated DBPs and the overall calculated cytotoxicity and genotoxicity of DBPs. However, the acute toxicity and genotoxicity of the wastewater decreased by 7% and 100%, respectively, when bromide was added to the UV/chlorine treatment. This study illuminated that UV/chlorine treatment can decrease acute and geno- toxicities of wastewater efficiently.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO2), ozone (O3), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV254) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV254 abatement ranked in the order O3 > Mn(VII) > Fe(VI)/ClO2, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO2 > Fe(VI) > O3 and two phases were observed. At low specific ClO2, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV254 compared to the EDC was observed (~ 8% EDC abatement per 1% UV254 abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV254 and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV254 (~ 0.9–1.2% EDC abatement per 1% UV254 abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O3 abated the relative UV254 more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO2 and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O3 pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants, trihalomethane formation was poorly correlated with both EDC and UV254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV254 measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.

Chlorination of soil-derived dissolved organic matter: Long term nitrogen deposition does not increase terrestrial precursors of toxic disinfection byproducts

Terrestrial dissolved organic matter (DOM) in forested watersheds is a known precursor of disinfection byproducts (DBPs) in drinking water. Although the characteristics of terrestrial DOM may change with increasing nitrogen (N) deposition in forests, how these changes alter formation potential and toxicity of DBPs remains unexplored. We analyzed the speciation and toxicity of DBPs from chlorination of DOM derived from soils (O, A, and B horizons) in an experimental temperate forest with 22 years of N addition. With long-term N addition, the DOM reactivity toward the formation of trihalomethanes (from 27.7–51.8 to 22.8–31.1 µg/mg-dissolved organic carbon (DOC)) and chloral hydrate (from 1.25–1.63 to 1.14–1.36 µg/mg-DOC) decreased, but that toward the formation of haloketones increased (from 0.23–0.26 to 0.26–0.33 µg/mg-DOC). The DOM reactivity toward the formation of haloacetonitriles was increased in the deeper soil but reduced in the surface soil. The DBP formation potential of DOM draining from a certain area of forest soils (in µg-DBP/m2-soil) was estimated to be reduced by 20.3% for trihalomethanes and increased by 37.5% for haloketones and have minor changes for haloacetonitriles and chloral hydrate (both <7%). Furthermore, the DBPs from chlorination of the soil-derived DOM showed lowered microtoxicity with N addition possibly due to reduced brominated DBP formation. Overall, this study highlights that N deposition may not increase drinking water toxicity through altering terrestrial DOM characteristics.

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.

Estimation of haloacetonitriles formation in water: Uniform formation conditions versus formation potential tests

To date, several studies have used formation potential (FP) tests to examine the presence of HAN precursors in water and wastewater. However, given the decomposition of HANs with time at elevated free chlorine levels, FP test results do not provide meaningful results. We conducted side-by-side FP and uniform formation condition (UFC) experiments to demonstrate that, in order to obtain practical, meaningful, and representative information about HANs formation and their precursors during chlorination, it is important to conduct experiments and report results under UFC [or simulated distribution system (SDS)] conditions.The results confirmed higher HAN formation under UFC than FP tests during chlorination of the tested two surface water and three wastewater effluent samples, indicating HAN decomposition at high chlorine conditions of FP tests. In addition, the well reported ratio (~10%) of HAN/THM from previous studies was more consistent with the UFC results but was lower than 10% in the FP results. On the other hand, HAN formation during chloramination of the same samples were lower under the UFC than FP conditions. Furthermore, FP tests under both chlorination and chloramination resulted in lower bromine substitution factor.We concluded that reporting results of HANs FP tests are not representative, and future studies should focus on UFC or distribution system specific (SDS) experiments for chlorination. However, chloramination FP tests may still provide some information about the HAN precursors in waters.

Low water treatability efficiency of wildfire-induced dissolved organic matter and disinfection by-product precursors

Wildfire could alter both the quantity and composition of terrestrial organic matter exported into source water, and water treatability of fire-impacted dissolved organic matter (DOM) could be different from its unburned counterpart. Currently, there is no standard protocol to treat wildfire-impacted source water. To identify the best treatment practices in handling post-fire runoffs, we conducted a systematic controlled study using leachates of unburned white fir (Abies concolor) and Ponderosa pine (Pinus ponderosa) and black and white ashes (collected immediately and one year after the 2013 Rim Fire, California) to evaluate coagulation and oxidation strategies for controlling disinfection byproducts (DBPs) formation. Results showed that the efficiency (%) of alum coagulation in removing dissolved organic carbon and nitrogen followed the order of litter > ash immediately after the fire > ash one year after the fire. Alum coagulation was less effectiveness in removing DOM and DBP precursors in ash leachates, compared to litter leachates. This may be attributed to the loss of side chains and the decrease of DOM molecular weight during the wildfire, thus inducing lower removal efficiency of the DOM and DBP precursors during the alum coagulation. Considering use of brominated flame retardants by firefighters, the addition of bromide (Br−) (100 μg/L) greatly increased the formation of haloacetonitriles by chlorine, and this increase was relatively lower in ash leachates. The influence of reaction time and pH on DOM reactivity was similar among the leachates of litter and ash samples. Our results show that alum coagulation followed by chloramination at alkaline pH is an effective strategy for reducing post-fire DBP formation in drinking water.

Impact of chlorination and pre-ozonation on disinfection by-products formation from aqueous suspensions of cyanobacteria: Microcystis aeruginosa, Anabaena aequalis and Oscillatoria tenuis

The influence of the pre-ozonization on the formation of disinfection by-products (DBPs) upon chlorination for fresh waters containing three common cyanobacteria, namely Microcystis aeruginosa, Anabaena aequalis and Oscillatoria tenuis at 10,000 cells/mL is reported. Specifically, the formation carbonaceous-DBPs (C-DBPs) (trihalomethanes (THMs), haloacetic acids (HAAs) and haloketones (HKs)) and nitrogenous-DBPs (N-DBP) (haloacetonitriles (HAN) and trichloronitromethane (TCNM)) has been determined as a function of the pH (6.5 or 8.0 and bromide ion concentration (300 μg/L). The main C-DBPs were THMs and HAAs with negligible formation of HKs accompanied by minor amounts of HANs in the absence of TCNM. Pre-ozonation of the aqueous cyanobacteria suspensions does not allow a control over all the DBPs. In fact, pre-ozonation increases THM formation and generates TCNM, has low influence on HAAs and only decreases the formation of HANs. The overall conclusion of this work is that pre-ozonation of waters containing a relatively low concentration of common fresh water cyanobacteria is not an appropriate process to decrease DBP formation from chlorine. Cyanobacteria removal from raw water before chlorination or ozonation should reduce DBP formation.