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Haloacetonitriles (HANs) are the most frequently found nitrogenous disinfection by-products (N-DBPs) in water. This study investigated the degradation of HANs, including dibromoacetonitrile (DBAN), monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) in the UV/persulfate process. DBAN was efficiently degraded by the direct UV photolysis, while chlorinated HANs (CANs) were more efficiently degraded by the UV/persulfate process than by the UV or UV/H 2 O 2 process. The degradation kinetics of MCAN, DCAN and TCAN by SO 4 − followed second order kinetics at the rate constants of 7.48 (±0.58) × 10 7 M −1 ·s −1 , 6.36 (±0.16) × 10 7 M −1 ·s −1 and 2.43 (±0.15) × 10 7 M −1 ·s −1 , respectively, which were 10 times higher than those by OH. The degradation rates increased with increasing persulfate dosages and temperatures, but were suppressed by natural organic matter and bicarbonate. The degradation of CANs in the UV/persulfate process was initiated by hydrogen abstraction and C C bond breakage by SO 4 − instead of C Cl bond cleavage, and followed by subsequent oxidation and hydrolysis to produce Cl − , NO 3 − , CO 2 and H 2 O. This study demonstrates that SO 4 − is more suitable than OH for the degradation of CANs, but the effective dehalogenation of aliphatic halogenated compounds by SO 4 − still requires at least one hydrogen or carbon atom connecting to an alpha carbon. [ABSTRACT FROM AUTHOR]

The UV/persulfate process is an effective advanced oxidation process (AOP) for the abatement of a variety of micropollutants via producing sulfate radicals (SO 4 •-). However, when this technology is used to reduce target pollutants, the precursors of disinfection byproducts (DBPs), such as natural organic matter (NOM) and organic nitrogen compounds, can be altered. This study systematically investigated the DBP formation from NOM and five model compounds after UV/H 2 O 2 and UV/persulfate treatments followed with 24 h chlorination. Compared to chlorination alone, the yields of trichloromethane (TCM) and dichloroacetonitrile (DCAN) from NOM decreased by 50% and 54%, respectively, after UV/persulfate treatment followed with chlorination, whereas those of chloral hydrate (CH), 1,1,1-trichloropropanone (1,1,1-TCP) and trichloronitromethane (TCNM) increased by 217%, 136%, and 153%, respectively. The effect of UV/H 2 O 2 treatment on DBP formation shared a similar trend to that of UV/persulfate treatment, but the DBP formation was higher from the former. As the UV/persulfate treatment time prolonged or the persulfate dosage increased, the formation of TCM and DCAN continuously decreased, while that of CH, 1,1,1-TCP and TCNM presented an increasing and then decreasing pattern. SO 4 •- activated benzoic acid (BA) to form phenolic compounds that enhanced the formation of TCM and CH, while it deactivated resorcinol to decrease the formation of TCM. SO 4 •- reacted with aliphatic amines such as methylamine (MA) and dimethylamine (DMA) to form nitro groups, which significantly increased the formation of TCNM in post chlorination, and the rate was determined to be higher than that of HO•. This study illuminated the diverse impacts of the structures of the precursors on DBP formation after UV/persulfate treatment, and DBP alteration depended on the reactivity between SO 4 •- and specific precursor. Image 1 • SO 4 •- oxidation decreased the TCM and DCAN formation but increased the TCNM and CH formation from NOM chlorination. • SO 4 •- oxidation dramatically increased the TCNM formation from aliphatic amines. • SO 4 •- activated benzoate but deactivated resorcinol to form TCM and CH. • SO 4 •- oxidation showed differences from HO• in DBP alteration from NOM and model compounds. • DBP alteration by UV/persulfate treatment depended on the precursor structures and water matrices. [ABSTRACT FROM AUTHOR]

• The interaction of SO 4 ·– and chloride produces HO· and reactive chlorine species (RCS). • The transient intermediates of gemfibrozil reacting with RCS, SO 4 ·– and HO· were identified by laser flash photolysis. • RCS and SO 4 ·– attack gemfibrozil mainly via hydrogen abstraction and/or electron transfer, but HO· via addition. • Increased HO· and RCS levels changed the product species and abundances in UV/PDS/Cl–. • UV/PDS/Cl– induced much lower acute toxicity than UV/PDS and UV during gemfibrozil degradation. The radical chemistry of SO 4 ·– is strongly affected by its interaction with chloride in natural waters, during which SO 4 ·– can be converted to HO· and reactive chlorine species (RCS). This study investigated the effects of chloride on gemfibrozil (GFRZ) transformation via the UV/peroxydisulfate (PDS) process, elucidating the kinetics, degradation pathways and solution toxicity. The pseudo-first-order rate constants (k ′) of GFRZ by UV/PDS changed slightly from 1.0 × 10−3 s−1 to 9.3 × 10−4 s−1 as the chloride content increased from 0 to 10 mM because the increase in HO· and RCS levels compensated for the decrease in SO 4 ·– concentration. However, the transformation pathways in the presence of chloride changed significantly. From the transient absorption spectra, we inferred that RCS and SO 4 ·– attacked GFRZ mainly through hydrogen abstraction and/or electron transfer, while HO· interacted with the GFRZ aromatic ring by addition. Hydroxylation, carboxylation and cleavage products were enhanced in UV/PDS/Cl– compared to UV/PDS through the addition of HO· and the cleavage of C O bonds by RCS, and total organic chlorine (TOCl) was undetectable. Interestingly, the acute toxicity was lowest in UV/PDS/Cl–, with an inhibition percentage of 1% at 30 min. The higher inhibition percentages in UV/PDS (13%) and UV alone (53%) at 30 min likely resulted from the stronger capacity of HO· and RCS to oxidize aldehydes to carboxylic groups and cleave C O bonds, respectively, than that of SO 4 ·–. This study provides a better understanding of contaminant transformation mechanisms under UV/PDS treatment at chloride levels present in natural waters. [Display omitted] [ABSTRACT FROM AUTHOR]

Degradation of three lipid regulators, i.e., gemfibrozil, bezafibrate and clofibric acid, by a UV/chlorine treatment was systematically investigated. The chlorine oxide radical (ClO • ) played an important role in the degradation of gemfibrozil and bezafibrate with second-order rate constants of 4.2 (±0.3) × 10 8  M −1  s −1 and 3.6 (±0.1) × 10 7  M −1  s −1 , respectively, whereas UV photolysis and the hydroxyl radical (HO • ) mainly contributed to the degradation of clofibric acid. The first-order rate constants ( k ′) for the degradation of gemfibrozil and bezafibrate increased linearly with increasing chlorine dosage, primarily due to the linear increase in the ClO • concentration. The k ′ values for gemfibrozil, bezafibrate, and clofibric acid degradation decreased with increasing pH from 5.0 to 8.4; however, the contribution of the reactive chlorine species (RCS) increased. Degradation of gemfibrozil and bezafibrate was enhanced in the presence of Br − , whereas it was inhibited in the presence of natural organic matter (NOM). The presence of ammonia at a chlorine: ammonia molar ratio of 1:1 resulted in decreases in the k ′ values for gemfibrozil and bezafibrate of 69.7% and 7%, respectively, but led to an increase in that for clofibric acid of 61.8%. Degradation of gemfibrozil by ClO • was initiated by hydroxylation and chlorine substitution on the benzene ring. Then, subsequent hydroxylation, bond cleavage and chlorination reactions led to the formation of more stable products. Three chlorinated intermediates were identified during ClO • oxidation process. Formation of the chlorinated disinfection by-products chloral hydrate and 1,1,1-trichloropropanone was enhanced relative to that of other by-products. The acute toxicity of gemfibrozil to Vibrio fischeri increased significantly when subjected to direct UV photolysis, whereas it decreased when oxidized by ClO • . This study is the first to report the transformation pathway of a micropollutant by ClO • . [ABSTRACT FROM AUTHOR]

The UV/chlorine process is an emerging advanced oxidation process (AOP) that produces various reactive species, such as hydroxyl radicals (HO ) and reactive chlorine species (RCS). The effects of the treatment conditions, such as chlorine dosage and pH, and the water matrix components of natural organic matter (NOM), alkalinity, ammonia and halides, on the kinetics and reactive species in the degradation of four micropollutants, metronidazole (MDZ), nalidixic acid (NDA), diethyltoluamide (DEET) and caffeine (CAF), by the UV/chlorine process were investigated. The degradation of MDZ and CAF was primarily attributable to HO and ClO , respectively, while that of NDA was primarily attributable to both ClO and CO 3 - . HO , Cl and CO 3 − are important for the degradation of DEET. The second-order rate constants for ClO with CAF and CO 3 − with NDA were determined to be 5.1 (±0.2) × 10 7 M −1 s −1 and 1.4 (±0.1) × 10 7 M −1 s −1 , respectively. Increasing chlorine dosage slightly changed the contribution of HO but linearly increased that of ClO to micropollutant degradation. Increasing pH decreased the contribution of either HO or Cl but not that of ClO . Both NOM and bicarbonate decreased the contributions of HO and Cl , whereas NOM but not bicarbonate significantly decreased that of ClO . The contribution of either HO or Cl first rose and then fell as the molar ratio of ammonia to chlorine increased from 0 to 1:1, while that of ClO decreased. The co-presence of high concentrations of Cl − and Br − enhanced the contribution of ClBr − and BrCl. [ABSTRACT FROM AUTHOR]

[Display omitted] • Freshwater-level Cl− alters radical chemistry and PPCP degradation in UV/PDS. • Cl− (≤1000 μM) converts SO 4 •− to HO• and Cl 2 •− at pH 7. • Alkaline pH promotes the transformation from SO 4 •− and Cl•/Cl 2 •− to HO•. • Cl− inhibits 18 PPCP degradation but promotes other 5 PPCP abatement at pH 7. • HO• dominates PPCP degradation rather than Cl•/Cl 2 •− at freshwater-level Cl−. Chloride (Cl−) affects the sulfate radical (SO 4 •−)-based advanced oxidation processes for application. This study investigated the effects of Cl− at freshwater levels (5–1000 μM) on radical chemistry and pharmaceuticals and personal care products (PPCPs) degradation in a UV/peroxydisulfate (UV/PDS) process. By using radical probes and a kinetic model, SO 4 •− was converted to chlorine radical (Cl•), and Cl• was subsequently transformed to hydroxyl radical (HO•). The SO 4 •− concentration monotonically decreased by 56.8–91.7% at 5–1000 μM Cl− at pH 7, and that of HO• increased by 127–419%. Cl•/Cl 2 •− formation was less prevalent at ≤ 100 μM Cl−, but Cl 2 •− was notable at 1000 μM Cl−. Increasing pH promoted the transformation from SO 4 •− to HO• and drove the conversion from Cl•/Cl 2 •− to HO•, resulting in less Cl•/Cl 2 •− at pH 10. Increasing Cl− from 10 to 1000 μM decreased the pseudo-first-order rate constants (kʹ s) of 18 PPCPs from 1.6% to 93.9% but increased the kʹ s of 5 other PPCPs by 2.5–33.4%, compared to those without Cl−. Cl− (1000 μM) primarily transformed SO 4 •− to HO• and Cl• with the conversion ratios of 89.8% and 0.7%, respectively. Therefore, the contributions of HO• increased from 16–65.9% to 83.6–99.5%, and those of SO 4 •− decreased from 10.2–62.6% to < 8.6%, as Cl− rose from 10 to 1000 μM. This study demonstrated that at freshwater levels, Cl− primarily drove the conversion from SO 4 •− to HO•, emphasizing the importance of HO• in PPCP degradation in the UV/PDS process. [ABSTRACT FROM AUTHOR]

• Br− converts SO 4 •− to HO• and bromine radicals and also scavenges HO• in UV/PDS. • Bromine radicals are much higher than SO 4 •− and HO• at pH 7 but lower at pH 10. • Cl− and Br− converts SO 4 •− to HO• but chlorine radicals are negligible. • Br− at several μM levels promote some micropollutant degradation in UV/PDS. Bromide (Br−) is a typical scavenger to sulfate radical (SO 4 •−) and hydroxyl radical (HO•), which simultaneously forms secondary reactive bromine species (RBS) such as Br• and Br 2 •−. This study investigated the effects of Br− at fresh water levels (~μM) on the radical chemistry in the UV/peroxydisulfate (UV/PDS) process by combining the degradation kinetics of probe compounds (nitrobenzene, metronidazole, and benzoate) with kinetic model. Br− at 1 − 50 μM promoted the conversion from SO 4 •− to HO• and RBS in the UV/PDS process. At pH 7, the concentration of SO 4 •− monotonically decreased by 31.5 – 94.8% at 1 – 50 μM Br−, while that of HO• showed an increasing and then decreasing pattern, with a maximum increase by 171.7% at 5 μM Br−. The concentrations of Br• and Br 2 •− (10−12 − 10−10 M) were 2 – 3 orders of magnitude higher than SO 4 •− and HO•. Alkaline condition promoted the conversion from SO 4 •− to HO•, and drove the transformation from RBS to HO•, resulting in much lower concentrations of RBS at pH 10. Br− at 1 μM and 5 μM decreased the pseudo-first-order reaction rates (kʹ s) of 15 pharmaceuticals and personal care products (PPCPs) by 15.2 – 73.9%, but increased kʹ s of naproxen and ibuprofen by 13.7 – 57.3% at pH 7. The co-existence of 10 − 1000 μM Cl− with 5 μM Br− further promoted the conversion from SO 4 •− to HO• compared to Br− alone. Bicarbonate consumed SO 4 •− and HO• but slightly affected RBS, while natural organic matter (NOM) exerted scavenging effects on HO• and RBS more significantly than SO 4 •−. This study demonstrated that Br− at fresh water levels significantly altered the radical chemistry of the UV/PDS process, especially for promoting the formation of HO•. [Display omitted] [ABSTRACT FROM AUTHOR]