Research On The Separation Of DOM In Municipal Wastewater By UF+RO Membrane Integration Technology And Membrane Fouling Mechanism

Promoting urban sewage treatment and reuse is an important means to alleviate the shortage of water resources and build a water-saving society.However,the widespread implementation of urban sewage treatment and reuse,first of all to ensure the safety of reuse of sewage.The components of the influent water in the urban sewage treatment plant are relatively complex,and even after the secondary treatment,the effluent still contains a large amount of dissolved organic matter（DOM）.The DOM may cause the generation of potentially harmful disinfection by-products（DBPs）in the subsequent chlorine disinfection process.Therefore,the removal of certain toxic and hazardous substances such as DOM has become one of the problems that need to be solved urgently for urban wastewater reuse.Membrane technologies include microfiltration（MF）,ultrafiltration（UF）,nanofiltration（NF）and reverse osmosis（RO）technologies.Membrane technology is a new technology that has been widely applied to the advanced treatment of municipal wastewater in recent years.It has the advantages of good treatment effect and small floor space.In order to ensure the water quality of the effluent while reducing membrane fouling,two or more membrane technologies are usually integrated.At present,there are few researches on the characteristics of DOM and the membrane fouling mechanism in the treatment of urban sewage by membrane integration technology.Based on the above issues,UF+RO membrane integrated technology was used to treat the secondary effluent of the municipal wastewater treatment plant,and the process parameters such as FeCl₃ addition amount,pH,membrane pressure and recovery rate were optimized,and the integrated process under the optimal process parameters was investigated.Removal of COD and DOC.The DOM of UF membrane and RO membrane unit effluent was characterized by UV-Vis absorbance,molecular weight distribution analysis,hydrophilicity and hydrophobicity distribution analysis,and three-dimensional fluorescence spectral characterization,and the mechanism of DOM removal by integrated process was analyzed.Investigate the mechanism of membrane fouling caused by DOM on UF+RO.Concluded as follow:（1）The optimal operating parameters of the UF+RO membrane integrated process are:FeCl₃ added in an amount of 40 mg/L,influent pH of 8,UF membrane pressure of 0.04 MPa,recovery rate of 40%;RO membrane pressure is 0.3MPa,recovery rate 50%.The removal rates of COD and DOC under UF+RO conditions were stable at 88.66%and 80.78%over the long term.（2）UF+RO interception of characteristic DOM is mainly in RO.UF+RO has a near100%rejection rate for macromolecule DOM,and also has a very high rejection rate for small molecule DOM.UF has a certain rejection rate for the hydrophobic component,and the hydrophilic component and transitional hydrophilic component are hardly trapped by the UF membrane and are mainly separated in the RO.UF+RO mainly uses RO to retain fulvic acids,humic acids,tyrosines and tryptophans.The efficiencies of UF+RO for DOM interception were humic acid>fulvic acid>tyrosine>tryptophan.The undissolved DOM in the UF+RO effluent is mainly small molecules,hydrophobic and proteinaceous DOMs.（3）DOM with unsaturated double bonds and DOM with aromaticity are the main substances that cause UF+RO process membrane fouling.The DOM,which easily leads to the production of disinfection by-product THMs,is also the main substance that causes UF+RO membrane fouling.Humic The membrane fouling of UF+RO mainly acts on RO.The DOM with molecular weight less than 1k,hydrophobic organic acid HPO-A and fulvic acid DOM contributed a lot to membrane fouling of UF+RO.