Insight into the mechanisms of trichloronitromethane formation by vacuum ultraviolet: QSAR model and FTICR-MS analysis

Vacuum ultraviolet(VUV) photolysis is recognized as an environmental-friendly treatment process. Nitrate(NO-3) and natural organic matter(NOM) are widely present in water source.We investigated trichloronitromethane(TCNM) formation during chlorination after VUV photolysis, because TCNM is an unregulated highly toxic disinfection byproduct. In this study:(1) we found reactive nitrogen species that is generated under VUV photolysis of NO-3react with organic matter to form nitrogen-containing compounds and subsequently form TCNM during chlorination;(2) we found the mere presence of 0.1 mmol/L NO-3can result in the formation of up to 63.96 μg/L TCNM;(3) we found the changes in pH(6.0-8.0), chloride(1-4 mmol/L), and bicarbonate(1-4 mmol/L) cannot effectively diminish TCNM formation;and,(4) we established the quantitative structure-activity relationship(QSAR) model,which indicated a linear relationship between TCNM formation and the Hammett constant(σ) of model compounds;and,(5) we characterized TCNM precursors in water matrix after VUV photolysis and found 1161 much more nitrogen-containing compounds with higher aromaticity were generated. Overall, this study indicates more attention should be paid to reducing the formation risk of TCNM when applying VUV photolysis process at scale.

Impact of pre-oxidation on the formation of byproducts in algae-laden water disinfection:Insights from fluorescent and molecular weight

Pre-oxidation has been reported to be an effective way to remove algal cells in water, but the released algal organic matter (AOM) could be oxidized and lead to the increment in disinfection by-product (DBP) formation. The relationship between pre-oxidation and AOM-derived DBP formation needs to be approached more precisely. This study compared the impact of four pre-oxidants, ozone (O), chlorine dioxide (ClO), potassium permanganate(KMnO) and sodium hypochlorite (NaClO), on the formation of nitrogenous (N-) and carbonaceous (C-) DBPs in AOM chlorination. The characterization (fluorescent properties,molecular weight distribution and amino acids concentration) on AOM samples showed that the characterization properties variations after pre-oxidation were highly dependent on the oxidizing ability of oxidants. The disinfection experiments showed that Oincreased DBP formation most significantly, which was consistent with the result of characterization properties variations. Then canonical correspondent analysis (CCA) and Pearson’s correlation analysis were conducted based on the characterization data and DBP formation. CCA indicated that C-DBPs formation was highly dependent on fluorescent data. The formation of haloacetic acids (HAAs) had a positive correlation with aromatic protein-like component while trichloromethane (TCM) had a positive correlation with fulvic acid-like component.Pearson’s correlation analysis showed that low molecular weight fractions were favorable to form N-DBPs. Therefore, characterization data could provide the advantages in the control of DBP formation, which further revealed that KMnOand ClOwere better options for removing algal cells as well as limiting DBP formation.

Assessment of solar-assisted electrooxidation of bisphenol AF and bisphenol A on boron-doped diamond electrodes

Bisphenol(BP)analogues in wastewater effluent and groundwater pose a potential threat to human health due to their ability to disrupt steroidogenesis.A new solar-assisted electrochemical process(SECP)was developed and evaluated for the degradation of BP analogues.The effects of quenchers,current density,initial pH,supporting electrolyte,and aqueous matrix on the removal kinetics of bisphenol AF(BPAF)and bisphenol A(BPA)were investigated.The kinetic constants of BPAF,BPA,and bisphenol S(BPS)in the SECP with irradiation intensity of 500 mW cm^(-2) were 0.017±0.002 min^(-1),0.022±0.002 min^(-1),and 0.012±0.001 min^(-1),respectively.The changes in the degradation rates of BPAF,BPA,and BPS in the presence of quenchers indicated the relative contribution of hydroxyl radical(·OH)oxidation,anodic electrolysis,and singlet(^(1)O_(2))oxygenation in the degradation of BPs in the SECP.The enhanced rate of generation of ·OH and ^(1)O_(2) was observed in the SECP compared with those in the conventional electrochemical system.The identification of the transformation products(TPs)of BPAF demonstrated that hydroxylation,ring cleavage,b-scission,and defluorination were the major processes during the oxidation in the SECP.The conversion to fluoride ions(76%)and mineralization of total organic carbon(72%)in the SECP indicated further degradation of TPs.The results from this study improved our understanding of the degradation of BP analogues in the electrooxidation irradiated by solar light and help to establish the application potential of the SECP for the effective degradation of emerging contaminants in wastewater.