Determination of acid dissociation constants and reaction kinetics of dimethylamine-based PPCPs with O3, NaClO, ClO2 and KMnO4

Algae-containing raw water treatment and by-products control based on ClO2 preoxidation-assisted coagulation/precipitation process

Eutrophication has become a great concern in recent years with the algae blooms in source water resulting in a serious threat posing to the safety of drinking water. Chlorine dioxide (ClO₂) has been served as an alternative oxidant for preoxidation or disinfection during drinking water treatment process due to its high oxidation efficiency and low risk of organic by-products formation. However, the generation of inorganic by-products including chlorite (ClO₂^-) and chlorate (ClO₃^-) has become a potential problem when applied in drinking water treatment. In this study, ClO₂ preoxidation-assisted coagulation/precipitation process was applied to improve the raw water quality, especially algae, turbidity, chemical oxygen demand (COD_Mn), and UV₂₅₄, and explore the formation mechanisms of inorganic by-products. It was found that the polymeric aluminum chloride (PAC) and ClO₂ have shown the best raw water treatment performance with the optimal dosage of 10 mg/L and 0.8 mg/L, respectively. Moreover, the initial pH also has exhibited a notable influence on pollutants treatment and by-products generation. Due to the adverse influence of algae and natural organic matters (NOM) and the generation of by-products, it was significant to investigate their inhibition effect on the water quality and the production of ClO₂^- and ClO₃^- in the ClO₂ preoxidation-assisted coagulation/precipitation process. Moreover, it was applicable of this process to apply for the algae-containing raw water (calculated as Chl.a lower than 50 μg/L) treatment with the ClO₂ dosage of less than 0.8 mg/L to achieve optimum treatment performance and minimum by-products generation.

Fabricating a novel ternary recyclable Fe3O4/graphene/sulfur-doped g-C3N4 composite catalyst for enhanced removal of ranitidine under visible-light irradiation and reducing of its N-nitrosodimethylamine formation potential

A novel ternary recyclable Fe₃O₄/graphene/sulfur-doped g-C₃N₄ (Fe₃O₄/GE/SCN) composite catalyst was synthesized and adopted in a visible-light driven catalytic system for the degradation of ranitidine, which is an important precursor of the emerging disinfection by-product of N-nitrosodimethylamine (NDMA). The addition of GE and Fe₃O₄ significantly improved the interface charge transfer of SCN, increased the light collection efficiency and decreased the photogenerated charge recombination efficiency. Considering both the ranitidine removal efficiency and catalyst recovery, the Fe₃O₄ mass fraction of 20% (20%-Fe₃O₄/GE/SCN) was recommended. Ranitidine (≤2 mg/L) was completely removed in 60 min under the conditions of an initial pH of 7.0 and a 20%-Fe₃O₄/GE/SCN dose of 1.0 g/L, and its degradation fitted well with the pseudo first-order kinetics model. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O₂^-, ·OH and h⁺ participated in the degradation of ranitidine. Ranitidine was removed through the pathways of demethylation and hydroxylation based on the analysis of the detected degradation intermediates, and 57.3% of the NDMA formation potential (FP) was reduced after the reaction. The visible-light driven 20%-Fe₃O₄/GE/SCN catalytic technology is a promising method not only for the control of NDMA FP but also the catalyst could be recovered and reused.

Insights into antimicrobial agent sulfacetamide transformation during chlorination disinfection process in aquaculture water

Antibiotic addition and chlorination are two common processes in fishery culture. Antibiotic residues not only pollute aquaculture water, but are also one of the potential precursors of disinfection by-products (DBPs) during chlorination. The degradation kinetics, products identification and reaction mechanism of sulfacetamide (SFA), a new sulfonamides antibiotics, and potential formation of haloacetic acids (HAAs) in chlorination were explored. The results showed that the degradation of SFA followed pseudo first-order kinetic model, and chlorinating agent dose, pH of water, water temperature, NH4 +, HCO3 - and humic acid (HA) had various effects on the degradation of SFA and the yields of HAAs. The presence of Br- accelerated both the degradation rate of SFA and more formation of Br-DBPs. Through the identification of intermediate products, we proposed the transformation pathway of SFA during the chlorination disinfection process. Namely, in this NaClO disinfection system, the C-S bond between the sulfonyl group and benzene ring, and S-N bond between sulfonyl and acylamino of SFA were broken, and then the primary formed groups were further oxidized to produce intermediates, such as chloroanilines and chlorophenols. And then chlorophenols were subsequently chlorinated to form toxic HAAs. The present study might be of significance for the evaluation of effective degradation of SFA and potential production of halogenate-DBPs (H-DBPs) during the chlorination disinfection process in aquaculture water.