•A nano ZVI-activated persulfate (nZVI-PS) process efficiently degraded BDE-47.•The role of metal ions in the nZVI-PS process was investigated.•Cu(II) improves the performance of nZVI-PS due to a synergistic effect with Fe.•Integration of nZVI and PS might be used for in situ degradation of PBDEs.A nano zerovalent iron activated by persulfate process (nZVI-PS) was applied to degrade 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), which is representative of the polybrominated diphenyl ethers (PBDEs) found in electronic waste (e-waste) sites. The influences of Cu(II), Zn(II), and Ni(II) ions, which are co-present in electronic wastes were evaluated on the degradation process. Electron paramagnetic resonance (EPR) and quenching studies indicates that sulfate radicals (SO4−) and hydroxyl radicals (HO) were both responsible for the degradation of BDE-47 during the treatment. Zn(II) and Ni(II) inhibited BDE-47 degradation, possibly due to their negative reduction potentials leading to surface adsorption on or complexation with nZVI. Cu(II), however, enhanced the degradation of BDE-47. Characterization of the nZVI surface reveals that the catalytic activity of Cu(II) could be attributed to the synergistic effect of Cu(0)-Cu(III) and Fe(II)-Fe(III) redox pairs, which favored the continuous decomposition of PS and thus BDE-47 degradation. Overall, these findings indicate that nZVI can be used as an effective activator of PS for removal of the lower brominated BDEs (e.g., tetra-BDE) and the role of metal ions cannot be neglected, which provides a significant implication for the use of nZVI-PS system in e-waste contaminated site.Download high-res image (92KB)Download full-size image

•The occurrence of 17 C- and N-DBPs was investigated in drinking water in Shenzhen, South China.•The level of haloacetamides was 0.1–3.1 μg/L and that of trihaloacetaldehydes was 0.1–11.4 μg/L.•12-month sampling results indicated the seasonal variation with highest levels in spring.•Trihalomethane levels can be used as indicator of haloacetonitriles and haloacetamides levels.A 12-month sampling program was conducted throughout a drinking water distribution system in Shenzhen and the data from 251 samples provide a comprehensive picture of the spatial and seasonal variability of 17 species disinfection by-products (DBPs) in a city with subtropical monsoon climate. The carbonaceous disinfection by-product (C-DBPs) included four trihalomethanes (THMs), three trihaloacetaldehydes (THAs) and two haloketones (HKs). Their median concentrations over the entire period were 19.9 μg/L, 3.4 μg/L and 1.4 μg/L, respectively. The nitrogenous DBPs (N-DBPs) monitored were four haloacetonitriles (HANs) and four haloacetamides (HAcAms). Their median levels were 2.0 μg/L and 1.5 μg/L, respectively. Low levels of brominated DBP species (bromine substitution factors ≤ 0.5) were observed. The BSF of each DBP class followed the trend: THMs ≈ DHAcAms > DHANs > THAs. All the DBP concentrations showed clear seasonal variations with the highest average concentrations in spring. Correlation analyses showed that the THMs and CH levels in Shenzhen drinking water could be used as statistical indicators of the levels of unregulated N-DBPs (0.4 < r < 0.7, p < 0.5). The results supplement the database of DBP occurrence in drinking water in China, and provide an important reference data set for DBP occurrence in cities with a subtropical monsoon climate around the world.Download high-res image (154KB)Download full-size image

•3NOM* was the major specie accounting for indirect photolysis of acetaminophen.•Dissolved oxygen played dual roles in acetaminophen photodegradation.•O2- suppressed the photodegradation by transferring electrons to the oxidative intermediates.•The photodegradation mechanism involving 3NOM*, oxygen and O2- was proposed.The photolysis of acetaminophen, a widely used pharmaceutical, in simulated natural organic matter solutions was investigated. The triplet states of natural organic matter (3NOM*) were found to play the dominant role in its photodegradation, while the contributions from hydroxyl radicals and singlet oxygen were negligible. Dissolved oxygen (DO) plays a dual role. From anaerobic to microaerobic (0.5 mg/L DO) conditions, the degradation rate of acetaminophen increased by 4–fold. That suggests the involvement of DO in reactions with the degradation intermediates. With increasing oxygen levels to saturated conditions (26 mg/L DO), the degradation rate became slower, mainly due to DO's quenching effect on 3NOM*. Superoxide radical (O2-) did not react with acetaminophen directly, but possibly quenched the intermediates to reverse the degradation process. The main photochemical pathways were shown to involve phenoxyl radical and N-radical cations, finally yielding hydroxylated derivatives, dimers and nitrosophenol. A reaction mechanism involving 3NOM*, oxygen and O2- is proposed.Download high-res image (345KB)Download full-size image

N-Nitrosodimethylamine (NDMA) is an emerging disinfection byproduct, and we show that use of chlorine dioxide (ClO2) has the potential to increase NDMA formation in waters containing precursors with hydrazine moieties. NDMA formation was measured after oxidation of 13 amines by monochloramine and ClO2 and pretreatment with ClO2 followed by postmonochloramination. Daminozide, a plant growth regulator, was found to yield 5.01 ± 0.96% NDMA upon reaction with ClO2, although no NDMA was recorded during chloramination. The reaction rate was estimated to be ∼0.0085 s–1, and on the basis of our identification by mass spectrometry of the intermediates, the reaction likely proceeds via the hydrolytic release of unsymmetrical dimethylhydrazine (UDMH), with the hydrazine structure a key intermediate in NDMA formation. The presence of UDMH was confirmed by gas chromatography–mass spectrometry analysis. For 10 of the 13 compounds, ClO2 preoxidation reduced NDMA yields compared with monochloramination alone, which is explained by our measured release of dimethylamine. This work shows potential preoxidation strategies to control NDMA formation may not impact all organic precursors uniformly, so differences might be source specific depending upon the occurrence of different precursors in source waters. For example, daminozide is a plant regulator, so drinking water that is heavily influenced by upstream agricultural runoff could be at risk.

Nitrogenous disinfection byproducts (N-DBPs) such as haloacetonitriles (HANs) and halonitromethanes (HNMs) are formed during water chlorination. Preozonation is sometimes applied to control trihalomethane (THM) formation, but this may risk promoting the formation of HNMs and HANs. The role of ozone in the formation of HANs and HNMs in natural waters remains unclear. The nitrogen sources involved in HAN and HNM formation during the chloramination of dissolved organic matter (DOM) with and without preozonation were evaluated using 15N-labeled monochloramine. The origin of the nitrogen involved in HAN formation was found to depend on the ratio of dissolved organic carbon to nitrogen. In nitrogen-rich solutions HAN nitrogen was mainly from DOM constituents. The formation of 15N-labeled dichloroacetontrile (DCAN) accounted for approximately 30% of the DCAN produced from all hydrophilic acidic and neutral isolates, which have low carbon to nitrogen ratios, while it reached over 50% for the hydrophobic acidic, basic, and neutral isolates with high carbon to nitrogen ratios. Unlabeled trichloronitromethane (TCNM) accounted for over 90% of the total TCNM produced from most of the isolates. The remaining less than 10% of the TCNM was probably generated through an aldehyde pathway. Preozonation reduced DCAN but enhanced the yield of TCNM. The destruction of amino acids and amine structures and subsequent formation of nitro groups by preozonation may help explain the reduced DCAN and increased TCNM formation.

•5 confirmed TPs and 19 tentatively identified TPs were found from UV/chlorine treatment of CBZ.•The CBZ degradation pathways from reaction with hydroxyl and chlorine radicals are proposed.•The kinetics of four products was evaluated under the variation of chlorine dose, pH and NOM.•The tests with bioluminescence inhibition showed the decreased toxicity.Carbamazepine (CBZ) is one of the pharmaceuticals most frequently detected in the aqueous environment. This study investigated the transformation products when CBZ is degraded by chlorine under ultraviolet (UV) irradiation (the UV/chlorine process). Detailed pathways for the degradation of CBZ were elucidated using ultra-high performance liquid chromatography (UHPLC)−quadrupole time-of-flight mass spectrometry (QTOF-MS). CBZ is readily degraded by hydroxyl radicals (HO) and chlorine radicals (Cl) in the UV/chlorine process, and 24 transformation products were identified. The products indicate that the 10,11-double bond and aromatic ring in CBZ are the sites most susceptible to attack by HO and Cl. Subsequent reaction produces hydroxylated and chlorinated aromatic ring products. Four specific products were quantified and their evolution was related with the chlorine dose, pH, and natural organic matter concentration. Their yields showed an increase followed by a decreasing trend with prolonged reaction time. CBZ-10,11-epoxide (I), the main quantified transformation product from HO oxidation, was observed with a peak transformation yield of 3–32% depending on the conditions. The more toxic acridine (IV) was formed involving both HO and Cl with peak transformation yields of 0.4–1%. All four quantified products together amounted to a peak transformation yield of 34.5%. The potential toxicity of the transformation products was assayed by evaluating their inhibition of the bioluminescence of the bacterium Vibrio Fischeri. The inhibition increased at first and the decreased at longer reaction times, which was in parallel with the evolution of transformation products.Download high-res image (213KB)Download full-size image

Chlorine dioxide (ClO2) is an alternative to chlorine in water treatment due to its more limited formation of chlorinated disinfection by-products (DBPs). However, on-site generation of ClO2 often involves the production of free chlorine, unreacted reagents or side-reaction products. The disinfectant is thus a mixture of ClO2 and chlorine. The focus of this study was on the role of the mixed ClO2/chlorine oxidant in the changes of the precursors of DBPs including trihalomethanes (THMs), chloral hydrate (CH), haloketones (HKs), haloacetonitriles (HANs), halonitromethanes (HNMs), chlorite and chlorate. The influence of bromide ions in water was also included. The ratio of ClO2 to chlorine was found to significantly affect the DBPs formed, depending on the water sample's properties. In the three waters tested, THMs formation was the least at a ClO2 to chlorine mass ratio of 1:0.5 or 1:0.8. Both decreases and increases in the formation of CH and HKs after ClO2/chlorine pre-oxidation were observed compared with using ClO2 alone. The formation of HANs and TCNM was the least at a ClO2 to chlorine mass ratio of 1:0.5 or 1:0.8, although in the GM water sample no trend was apparent. In the presence of bromide, more bromine incorporation was found after ClO2/chlorine pre-oxidation than when ClO2 alone was used or without pre-oxidation at all. With an increase in the chlorine fraction in the mixed oxidant, less chlorite was formed; chlorate formation was enhanced instead. Therefore, the ratio of ClO2 to chlorine needs to be monitored and adjusted to obtain the best control of DBP formation.