Xian Lu

Degradation of diclofenac by UV-activated persulfate process: Kinetic studies, degradation pathways and toxicity assessments

Diclofenac (DCF) is the frequently detected non-steroidal pharmaceuticals in the aquatic environment. In this study, the degradation of DCF was evaluated by UV-254nm activated persulfate (UV/PS). The degradation of DCF followed the pseudo first-order kinetics pattern. The degradation rate constant (kobs) was accelerated by UV/PS compared to UV alone and PS alone. Increasing the initial PS dosage or solution pH significantly enhanced the degradation efficiency. Presence of various natural water constituents had different effects on DCF degradation, with an enhancement or inhibition in the presence of inorganic anions (HCO3- or Cl-) and a significant inhibition in the presence of NOM. In addition, preliminary degradation mechanisms and major products were elucidated using LC-MS/MS. Hydroxylation, decarbonylation, ring-opening and cyclation reaction involving the attack of SO4•- or other substances, were the main degradation mechanism. TOC analyzer and Microtox bioassay were employed to evaluate the mineralization and cytotoxicity of solutions treated by UV/PS at different times, respectively. Limited elimination of TOC (32%) was observed during the mineralization of DCF. More toxic degradation products and their related intermediate species were formed, and the UV/PS process was suitable for removing the toxicity. Of note, longer degradation time may be considered for the final toxicity removal.

Degradation of 2,4-dichlorophenol from aqueous using UV activated persulfate: kinetic and toxicity investigation

2,4-DCP is a high-toxicity phenol compound, which is difficult to remove, harmful to the health of people and seriously influences the aquatic ecosystems. In this study, the degradation of 2,4-DCP using UV/persulfate (UV/PS) process was investigated for the first time. The results showed pseudo-first-order rate constants of 2,4-DCP photo-degradation by UV/PS was 35.1 × 10−3 min−1. The reaction rate constants increased with pH increasing from 5 to 7 and then decreased at pH 8. Different anions (Cl−, HCO3− and NO3−) in water presented different effects on the photo-degradation reaction. The photo-degradation rates of 2,4-DCP in three actual water conditions (Xidong water works, Xijiu reservoir, Henshan reservoir) were higher than in the ultrapure water. Two possible (hydroxylated and dechlorinated) pathways for the degradation of 2,4-DCP by UV/PS were proposed. The luminescent bacteria inhibition rate greatly decreased with the concentration of 2,4-DCP decreasing in the reaction process.

Control of disinfection by-product derived from humic acid using MIEX process: optimization through response surface methodology

This work investigated the removal of humic acid (HA) as the precursor of disinfection by-product (DBP) using a magnetic ion exchange (MIEX) resin. The Box–Behnken design of response surface methodology (RSM) was used to evaluate the effect of process variables (initial pH, MIEX dose and reaction time) and their interaction for HA removal. Specific ultraviolet absorbance (SUVA) removal was selected as the response value. The analysis of variance (ANOVA) of the quadratic model demonstrated that the model was significant, and the optimum conditions were obtained as pH 2.3, MIEX resin dosage 0.95 mL L−1, and reaction time 59.18 min. At these applied optimum conditions, 39.74% SUVA removal from an initial SUVA value of 10.06 L mg−1 m−1 was achieved. Also the reduction in DBP (chloroform, dichloroacetic acid and trichloroacetic acid) formation potentials was about 76%, 73% and 80%, respectively. The MIEX process was effectively optimized by RSM with a desirability value of 1.0. After the process optimization, the MIEX treatment was proven to be a good option for controlling the DBP derived from HA.

Impact of preoxidation of UV/persulfate on disinfection byproducts by chlorination of 2,4-Di-tert-butylphenol

UV/persulfate (UV/PS) has been as an efficient method to remove many organic contaminants in water. However, little is known about the impact of UV/PS pretrement on the formation of disinfection byproducts (DBPs) during chlorination of 2,4-Di-tert-butylphenol (2,4-D). This research evaluated that UV/PS preoxidation of 2,4-D greatly decreased the DBPs generation during following chlorination. In the 2,4-D solution without any treatment system (O system), trichloromethane (TCM) as the only detected DBP increased with the increase of chlorine dosage. While the formation of TCM declined with the increase of PS dosage in the PS and UV/PS preoxidation systems and decreased the estimated toxicity accordingly. And it was found the residual PS in system could combine free chlorine to further oxidize 2,4-D. And intermediate products were analysed by high-performance liquid chromatography combined with triple quadrupole mass spectroscopy analysis. In the presence of bromine, the bromodichloromethane augmented first and then slowly decreased while dibromochloromethane and tribromethane increased both in O and UV/PS systems with the increase of [Br-]. Bromine substitution was decreased by preoxidation of UV/PS. UV/PS could decrease the total-DBPs formation when used in the real water matrix contained 100 μg/L 2,4-D.