Catalytic Oxidation With CuO@CNF For Degradation Of Natural Organic Matter And Mitigation Of Membrane Fouling

With the continuous improvement of drinking water quality standards and sewage effluent quality requirements,traditional water treatment processes hold certain limitations.Today,ultrafiltration technology has gradually been industrialized and applied on a large scale in the field of modern water treatment due to its excellent retention of macromolecular organic matter,suspended solids and colloids.However,the fouling of ultrafiltration membranes is a great obstacle to the widespread application of ultrafiltration technology.At present,a variety of means have been explored to alleviate membrane fouling,including coagulation,oxidation,and membrane material modification.Among them,oxidation pretreatment is proved to be an effective pretreatment method before ultrafiltration membrane.In this study,modified carbon nanofibers（CuO@CNF）were used to catalyze the oxidation of potassium hydrogen persulfate（PMS）as a pretreatment method to investigate the degradation of organic pollutants during the pretreatment reaction of CuO@CNF/PMS.The control efficiency of CuO@CNF/PMS pretreatment system on membrane fouling caused by typical organic matter and natural surface water was investigated.The synergistic mechanism between CuO@CNF and PMS was revealed,and the mechanism of CuO@CNF/PMS pretreatment system to control membrane fouling was analyzed from multiple perspectives.First,a stable method was explored to support copper oxide（CuO）on carbon nanofibers（CNFs）.and the morphological and structural characteristics of CuO@CNF were characterized by transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）.and other methods.The results showed that CuO was tightly loaded on the CNF rod-like fibers,and the distribution was uniform,with the dispersibility significantly improved.Meanwhile,methylene blue（MB）was used as the target pollutant to characterize the catalytic performance of CuO@CNF.The results showed that CuO@CNF had significantly improved adsorption and catalytic oxidation capacity compared with CuO and CNF.The types of free radicals generated by the CuO@CNF/PMS process were identified by electron paramagnetic resonance detection（EPR）.The results showed that^·OH,SO₄^·-,O₂^·-,and ~1O₂ coexisted in the CuO@CNF/PMS process,indicating that both free radical and non-radical pathways existed in the degradation process of typical organic matter.Secondly,the removal effect of CuO@CNF/PMS on typical natural organic matter was explored,and the feasibility of CuO@CNF/PMS process for oxidative pretreatment before ultrafiltration was proved.The research results showed that compared with CNF,CuO@CNF holds a significantly higher number of surface defects and disorder,which could notably promote the oxidative decomposition of PMS,effectively improve the reaction rate of catalyzing PMS and shorten the reaction time.In addition,CNF/PMS,CuO/PMS and CuO@CNF/PMS processes were all effective on reducing the organic matter content in the raw water,among which the CuO@CNF/PMS system possessed the most obvious degradation effect.And in the effluent of the ultrafiltration membrane,CuO@CNF/PMS process could further reduce the DOC concentration.In addition,the CNF/PMS,CuO/PMS and CuO@CNF/PMS pretreatment presented certain control effects on membrane fouling caused by humic acid,sodium alginate and mixed organics.It was noted that CuO@CNF/PMS held the best effect on alleviating membrane fouling,with the terminal flux of 0.75-0.9.However,CNF/PMS and CuO/PMS pretreatment aggravated the membrane fouling caused by bovine serum albumin,while CuO@CNF/PMS played a significant role in mitigating the membrane fouling caused by bovine serum albumin.It was obvious that CuO@CNF/PMS pretreatment could be utilized as an effective means to control membrane fouling caused by typical organics.Finally,in order to investigate the effect of CuO@CNF/PMS process on removing organic matter in natural water and mitigating membrane fouling,the Yellow River water was selected as the target water for pretreatment.The mechanism of CuO@CNF/PMS pretreatment to alleviate membrane fouling was explained by means of model fitting,molecular weight distribution of organic matter,Zeta potential,particle size distribution,and Fourier infrared spectroscopy characterization of the membrane.As for adsorption capacities,CuO@CNF performed far more excellent compared with CNF and CuO.At the same time,comparing the effects of the three catalysts on the removal of organic matter by PMS,the oxidation efficiencies were ranked as:CuO@CNF/PMS>CuO/PMS>CNF/PMS.After pretreated by CuO@CNF/PMS and passing through the membrane,the terminal flux after three filtration cycles was 0.61,with the reversible fouling resistance reduced by 89.6%,indicating mitigation of membrane fouling effectively achieved.Therefore,the CuO@CNF/PMS process also held a significant mitigation effect on membrane fouling caused by natural water.In this study,CuO@CNF/PMS process was proposed as a pretreatment method before ultrafiltration membranes.And CuO@CNF was prepared by using CNF as a carrier,which solved the shortcomings of the self-adsorption effect of carbon nanofibers and the poor self-dispersion of copper oxide.Combined with ultrafiltration membrane treatment,it provided ideas for alleviating membrane fouling and improving the practical application scale of ultrafiltration technology in water treatment.