Study On Membrane Fouling Control And Mechanism Of EfOM Ultrafiltration For Secondary Effluent Of The Municipal Wastewater Treatment Plant

Under the conditions of the increasing shortage of water resources and rapid increase in water use,the ultrafiltration process has broad application prospects in advanced sewage treatment.However,the problem of ultrafiltration membrane pollution still restricts the application of membrane filtration technology in advanced sewage treatment projects.Natural Organic Matters（NOM）and Soluble Microbial Products（SMPs）contained in secondary effluent organic matter（Effluent Organic Matter,EfOM）can cause irreversible membrane fouling in the ultrafiltration process.Using a pretreatment process before membrane filtration can not only improve the removal efficiency of organic pollutants but also control the pollution of ultrafiltration membranes caused by EfOM.This topic mainly studies the pretreatment processes of ultraviolet activation of potassium persulfate（UV/PS）,ultraviolet activation of hydrogen peroxide（UV/H₂O₂）,and pre-oxidation-enhanced coagulation to control the pollution of ultrafiltration membrane caused by EfOM and its pollution Mechanism of action.The test results show that the secondary effluent EfOM of the municipal sewage treatment plant is dominated by dissolved organic matter less than 3 k Da,and the hydrophilic matter accounts for the largest proportion of the organic matter.The secondary effluent EfOM contains four different types of fluorescent components,which can be expressed as soluble microbial products,aromatic protein substances,fulvic acids,and humic acids.Direct ultrafiltration secondary effluent leads to a rapid decrease in the permeability of the ultrafiltration membrane,and the accumulation of pollutants on the membrane surface causes serious membrane fouling.At this time,the membrane resistance is dominated by reversible resistance.Direct use of ultrafiltration membrane filtration has a poor removal effect on organic pollutants and has little effect on the removal of fluorescent components.In terms of organic matter removal and ultrafiltration membrane pollution control,the effect of UV/PS pretreatment is better than that of UV/H₂O₂.UV/PS pretreatment can significantly degrade or mineralize EfOM.Under the condition of higher PS dosage,the removal rate of DOC and UV₂₅₄ is higher than that of single pretreatment.UV/PS pretreatment changes the characteristics of the organics in the secondary effluent,increases the proportion of small molecular organics and hydrophilic components,and reduces the content of fluorescent substances to effectively alleviate pollution.The free radical that UV/PS plays a leading role in the control of pollution caused by EfOM is sulfate radical(SO4^-·),and the conversion of sulfate radical to hydroxyl radical（HO·）has a negative impact on the control of EfOM pollution.When the secondary effluent is pretreated by UV/PS,the membrane fouling mechanism caused by EfOM shifts from continuous pore blockage and filter cake filtration to single standard blockage.Separate coagulation pretreatment has a limited mitigation effect on membrane flux decline,and it is not effective in EfOM pollution control,while pre-oxidation-enhanced coagulation pretreatment can slow down the decrease of membrane specific flux in the secondary effluent process of ultrafiltration,and can it has the effect of improving the reversibility of pollution.With the addition of a lower dose of coagulant,the effect of mitigating ultrafiltration membrane pollution has been improved.In addition,pre-oxidation-enhanced coagulation pretreatment can significantly remove EfOM in the secondary effluent,and the organic matter removal rate is significantly improved.In summary,in the control of ultrafiltration membrane pollution caused by EfOM,UV/PS pretreatment has a significant effect,and its effect increases with the increase of the dosage of oxidant PS,and it has performed in pollutant mineralization.Outstanding performance,UV/PS pretreatment can effectively alleviate membrane pollution caused by EfOM.The UV/PS pre-oxidation treatment process has low equipment requirements and can be applied to most sewage treatment plants based on ultraviolet disinfection for advanced sewage treatment.The research results of this paper can provide theoretical support for the secondary effluent of municipal wastewater treatment plants in the advanced treatment project of ultrafiltration membrane method.