Xiaowei Liu

Advanced oxidation processes are effective for removing emerging contaminants from water, but the use of catalysts or chemicals increases costs and may cause secondary pollution. In this study, a circulating atomized microdroplet system (denoted as CAMS) that operates without any chemical additives was developed to achieve the highly efficient degradation of norfloxacin (NFX). The degradation process of NFX followed pseudo-first-order kinetics, with a rate constant of 0.087 min⁻1 which is 5000 times higher than that in the corresponding bulk phase. This remarkable degradation performance is attributed to the spontaneous generation of reactive oxygen species within the microdroplets, including hydrogen peroxide, hydroxyl radicals, singlet oxygen, and superoxide radicals. These species drive a dual-channel directed oxidation pathway by targeting the electron-rich piperazine ring and the electron-deficient quinolone core the NFX molecule. Our findings advance the mechanistic understanding of multi-species synergistic oxidation driven by microdroplet interfacial chemistry, and provides a novel strategy for the green strategy for the treatment of complex water matrices contaminated with emerging contaminants.

The long-term sustainability of beneficial effects resulting from the modification of polyamide thin-film composite (PATFC) membranes with zwitterionic poly(sulfobetaine methacrylate) (pSBMA) and silver nanoparticles (AgNPs) in real-world application scenarios remains uncertain. This study used response surface methodology and innovative anti-biofouling evaluation method to optimize the conditions for AgNP- and pSBMA-co-modified PATFC membranes, with reverse osmosis seawater desalination as the test application scenario. A 180-day continuous seawater treatment test was conducted to evaluate the long-term sustainability of anti-biofouling resistance. Results indicated that loading AgNPs before grafting pSBMA enhanced their stability during use and cleaning. Co-modification under optimal conditions led to a 6.3% improvement in membrane flux reduction over long-term operation. The effect of AgNPs was significant for 30 days, while pSBMA remained effective until the end of the test. Water contact angle measurements, confocal laser scanning microscopy, and quorum sensing signal molecule analysis revealed anti-bioflouling improvements due to the hydration layer and electrostatic barrier from pSBMA, as well as quorum sensing inhibition and disinfection from AgNPs. These findings confirm the discount effectiveness and feasibility of the pSBMA and AgNPs co-modification technique during long working time, offering valuable insights into modification operations and anti-biofouling mechanisms.

The viewpoints on whether high concentrations of chloride ion (Cl⁻) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl⁻ concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ), and phenol (PN) by Cl⁻-activated PMS (denoted as Cl⁻/PMS) were investigated. Results showed that Cl⁻ could effectively activate PMS for the complete removal of CBZ, SDZ, and PN with reaction kinetic constants of 0.4516 min⁻¹, 0.01753 min⁻¹, and 0.06805 min⁻¹, respectively. Parameters such as PMS dose, Cl⁻ concentration, solution pH, and initial concentrations of organic pollutants that affect the degradation efficiencies of the Cl⁻/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl⁻/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ was proposed. Though higher toxic chlorinated by-products were generated, the Cl⁻/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contain high concentrations of Cl⁻.

The S(IV)–Fe(II)/PM pretreatment has demonstrated preliminary potential as an effective ultrafiltration (UF) pretreatment technology. However, a comprehensive understanding of its impact on UF membrane fouling control and the dynamic evolution of membrane fouling during prolonged operation is still lacking. In this study, a relatively prolonged fouling experiment was conducted. Results revealed that the S(IV)–Fe(II)/PM pretreatment exhibited superior performance over Al(III) coagulation pretreatment in mitigating the transmembrane pressure difference and addressing both reversible and irreversible membrane fouling. The application of a cluster analysis method to classify membrane fouling evolution stages further confirmed that S(IV)–Fe(II)/PM pretreatment effectively decelerated the rate of membrane fouling evolution. The surface cake layer of UF membranes pretreated with S(IV)–Fe(II)/PM exhibited greater looseness and smoothness. It also showed better results than Al(III) coagulation pretreatment in reducing the accumulation of organic foulants, controlling the Si content and reducing the total microorganisms and live microorganisms in the UF feed water. Variance Partitioning Analysis indicated that the combined contribution of organic, inorganic, and biological foulants was the most significant for UF membranes after S(IV)–Fe(II)/PM pretreatment (50.4%) and UF membranes after Al(III) coagulation pretreatment (70.2%). These findings underscore the efficacy of S(IV)–Fe(II)/PM pretreatment in controlling UF membrane fouling under prolonged operation.

The viewpoints on whether high concentration of chloride ion (Cl⁻) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl⁻ concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ) and phenol (PN) by Cl⁻ activated PMS (denoted as Cl⁻/PMS) were investigated. Results showed that Cl⁻ could effectively activate PMS for complete removal of CBZ, SDZ and PN with reaction kinetic constants of 0.4516 min^− 1, 0.01753 min^− 1 and 0.06805 min^− 1, respectively. Parameters such as PMS dose, Cl⁻ concentration, solution pH, and initial concentrations of organic pollutants that affecting the degradation efficiencies of the Cl⁻/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl⁻/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ were proposed. Though higher toxic chlorinated by-products were generated, the Cl⁻/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contains high concentration of Cl⁻.