Enhanced Organic Wastewater Treatment Performance Of Coal-based Carbon Membranes And Their Loading With Metal Oxide Catalysts By Integrating Electrochemical Advanced Oxidation

Due to the escalating population growth and rapid industrialization,water shortage has become one of the serious global challenges,controlling the discharge of wastewater and reducing its pollution to environment have become urgent issues.In recent years,membrane separation,as an advanced separation technology with high efficiency and energy saving,has been widely used in the field of water treatment.However,as for organic wastewater treatment,a considerable amount of organic pollutants with high concentration and high chemical oxygen demand(COD)always cause a great load to the membrane treatment system and seriously affect its treatment efficiency and service life.To circumvent the above problem,microfiltration carbon membranes with abundant pore structure,stability and great electrical conductivity were used in this paper as the separation membrane and coupling with electrochemical advanced oxidation technology to improve the organic wastewater treatment performance of membrane process.On this basis,the electrochemical activity was further enhanced by loading metal oxide catalysts on carbon membrane,the treatment performance and membrane anti-fouling ability by synergistic effects of membrane separation and electrocatalysis for organic pollutants removal from wastewater were investigated.Specific research results are as follows:(1)The separation and membrane anti-fouling performance of conductive carbon membrane integrated with electrochemical advanced oxidation for oily wastewater treatment were investigated.Results showed that the permeability of the membrane was significantly enhanced under the help of the electrochemical reactions.Under the optimal operating parameters(voltage of 2.0 V,electrode distance of 4.25 cm,electrolyte concentration of 5 g/L,flow rate of 1.2 mL/min),the initial permeability was almost twice that of uncharged CM,and the permeability decline rate was only 28.52%after 8 h treatment.The results of membrane fouling index analysis indicated that the relief of membrane fouling by electrochemical reactions mainly lied in the inhibition of reversible surface fouling,so as to reduce the probability of oil droplets adhering to the membrane surface.Meanwhile,the high selectivity was also maintained,that the oil and COD removal efficiency could reach 97.63%and 81.89%respectively.The Gas Chromatography-Mass Spectrometer(GC-MS)analysis of the types and contents of the petroleum hydeocarbon components(normal-alkanes and polycyclic aromatic hydrocarbons)in the oily wastewater before and after treatment demonstrated that the large-sized oil droplets could be degraded into small-sized by-products,proving that the anodic oxidation reactions on CM were the key to improve the separation performance and anti-fouling ability of the membrane.(2)A dynamic electrodeposition method was developed to prepare CuO/carbon electrocatalytic membrane effectively.The influence of the electrocatalyst distribution on membrane electrocatalytic activity was explored,and the pollutants removal performance as well as membrane anti-fouling ability by membrane separation integrated with electrocatalysis were investigated.Results showed that the dynamic electrodeposited CuO/carbon electrocatalytic membrane(DECuO/CM)owned greater ability for small-sized pollutants removal than original carbon membrane(CM)and the conventional electrodeposited CuO/carbon membrane(CECuO/CM).Rhodamine B(RhB),COD and total organic carbon(TOC)removal efficiency of the DECuO/CM were 9.0-20.2 and 1.4-1.5 times higher than that of the CM and CECuO/CM.Meanwhile,the permeability of DECuO/CM was also much higher than that of CM and CECuO/CM.The treatment system with DECuO/CM showed the best energy saving advantages when the same amount of RhB was removed from wastewater,energy consumption for DECuO/CM treatment could be tremendously saved by 33.2%than that of CECuO/CM treatment,95.3%than that of electric CM treatment and even 99.3%than that of barely microfiltration.Moreover,the coupling of the electrocatalysis and membrane separation could further improve the removal efficiency and anti-fouling performance when treating wastewater containing large-sized pollutants.The removal efficiency of DECuO/CM remained above 99.8%throughout the whole oily wastewater treatment process,its permeability enhanced 66.59-fold when compared to that of CM,and the permeability decline rate was only 33.98%after 24 h treatment.(3)Taking advantage of the high electrocatalytic activity and great stability of anatase TiO2 in highly acidic solution,the TiO2/carbon electrocatalytic membrane(TiO2/CM)was prepared by dynamic electrodeposition method for highly acidic organic wastewater treatment.Results showed that the TiO2 electrocatalytic synthetic effect could significantly improve the CM treatment performance for acid RhB wastewater treatment,the removal efficiency of TiO2/CM enhanced about 155-fold under the voltage of 2.5 V,comparing to that of uncharged TiO2/CM.The outstanding acid-tolerant property and long service life of TiO2/CM were showed since the permeability of TiO2/CM could reach 421.95 L/(m2·h·bar)and the removal efficiency was 97.35%after 6 h highly acidic(pH=1)RhB wastewater treatment.The electrochemical property characterization analysis proved that there was almost no loss of electrochemical activity and conductivity of TiO2/CM in such a highly acidic environment.TiO2/CM also demonstrated wide applicability when removing four typical organic pollutants(RhB,phenol,tetracycline and oil)from highly acidic wastewater respectively,the removal efficiency>92%were obtained.High temperature pyrolysis was conducive to the regeneration of the permeability of TiO2/CM,the permeability regeneration rate could reach 100%after pyrolysis process.(4)A series of well-defined morphological different ZnO nanoparticles including nanorods(NRs),nanoflowers(NFs)and nanoplates(NPs)were dynamically electrodeposited on CM to prepare the ZnO/carbon electrocatalytic membranes.The formation and growth mechanism of ZnO nanoparticles were investigated,and the influence of electrocatalyst morphology on the organic wastewater treatment performance of electrocatalytic membranes was revealed.Results showed that there was a significant correlation between the morphology-controlled property and the treatment performance of electrocatalytic membrane.Compared with ZnO NFs/CM and ZnO NPs/CM,ZnO NRs/CM showed the best amoxicillin(AMX)treatment performance(removal efficiency of 99.5%)due to its largest electrocatalytic surface area,fastest electron transfer rate and highest hydroxyl radical generation rate.When increasing the applied voltage in the treatment system,the removal of AMX molecules by ZnO NRs/CM revealed various stages of adsorption,direct oxidation and indirect oxidation successively,in which the·OH generation capacity played the key role,the·OH generation rate could reach 4.56×10-10 M-1s-1 under the applied voltage of 2.0 V.Besides,ZnO NRs/CM demonstrated preferable treatment performance for mixed antibiotics and natural organics removal and recovery of the permeability and selectivity by membrane regeneration process,proving that ZnO NRs/CM had great stability,wide applicability and reusability,which exhibited certain practical application potential.