Multi-chamber membrane capacitive deionization coupled with peroxymonosulfate to achieve simultaneous removal of tetracycline and peroxymonosulfate reaction byproducts.

Advanced oxidation technologies based on peroxymonosulfate (PMS) have been extensively applied for the degradation of antibiotics. However, the degradation process inevitably introduces SO42- and other sulfur-containing anions, these pollutants pose a huge threat to the water and soil environment. Addressing these concerns, this study introduced PMS oxidation into a multi-chamber membrane capacitive deionization (MC-MCDI) device to achieve simultaneous tetracycline (TC) degradation and removal of PMS reaction byproduct ions. The experimental results demonstrated that when the TC solution (40 mg L-1) was pre-adsorbed for 10 min, the voltage was 1.2 V and the concentration of PMS solution added was 4 mg mL-1, the removal efficiency of TC and ion can reach 77.4 % and 46.5 % respectively. Furthermore, the activation process of PMS in MC-MCDI/PMS system and the reactive oxygen (ROS) that mainly produce degradation were deeply investigated. Finally, liquid chromatography-mass spectrometry (LC-MS) was employed to identify intermediates of TC degradation, propose potential degradation pathways, and analyze the toxicities of the intermediates. In addition, in five cycles, the MC-MCDI/PMS system demonstrated excellent stability. This study provides an effective strategy for treating TC wastewater and a novel approach for simultaneous TC degradation and desalination.

Characterizing the roles of pretreatment methods for model suspensions in the membrane fouling process: The case of yeast and kaolin.

Model suspensions are important substances for characterizing fouling processes to study the mechanism of membrane fouling, thus, choosing a suitable standard suspension is critical for researches on membrane fouling processes. The pretreatment methods of model suspensions have long been neglected, which can alter the physical and chemical properties and affect fouling results. This study compared four different pretreatment methods (centrifuging and drying, magnetic stirring, ultrasonic processing, and dissolving in buffer solution) and found effects on size distribution, dispersion stability, pH variation over time, and fouling properties. Among the characterization of model suspensions, different pretreatment methods led to various changes in physical and chemical properties in this study. Membrane filtration experiments showed that these four pretreatments changed the rate of membrane fouling. The results of the analysis of filtration flux for suspensions indicated that for ultrasonic processing of all suspensions and magnetic stirring of kaolin suspensions, pore blocking was the main mechanism, while cake formation was dominant for the others. Therefore, special attention should be placed on different pretreatment methods and selecting appropriate model foulants. Finally, some guidance on selecting appropriate model foulants was given in the study.

Characterizing synergistic effect of coagulant aid and membrane fouling during coagulation-ultrafiltration via in-situ Raman spectroscopy and electrochemical impedance spectroscopy.

The polymer coagulant aid can effectively enhance the coagulation-ultrafiltration (C-UF) process for the purification of drinking water. However, when coagulant aid entered the filtration, it may also cause serious membrane fouling as polymer. In-situ Raman spectroscopy and electrochemical impedance spectroscopy(EIS) were applied to monitor the effects of coagulant aids on the membrane. The causes of fouling were assisted discussed through stage cleaning of the membrane. The equivalent circuit fitting was performed on the EIS data and the Raman spectral data were statistically analyzed after peak fitting. EIS and the cluster analysis of Raman spectroscopy provided an earlier feedback on membrane fouling layers compared to flux. The cause of membrane fouling was explained via variation of characteristic functional groups obtained by Raman spectroscopy. When the molecular weight of the coagulant aid was 160 times,80 times and 16 times larger than the MWCO of the UF membrane, the equivalent circuit obtained by fitting the EIS of the UF system satisfied Rs + c(QpRp), Rs(QcRc)(QpRp) and Rs(Qt(Rc(QpRp))) respectively. Partial correlation analysis showed that the corresponding factors causing irreversible fouling of membrane were humic acid(HA), HA and coagulant aids, coagulant aids. Combined with the mean roughness (Ra) of membrane, the coagulant aid performed differently in the cleaning of contaminated membrane and also affected the cleaning of HA.