| With the rapid development of human society and economy,a large number of nutrients enter the water environment,causing the slow flow water body to encounter seasonal algae outbreak,which seriously threatens the water quality safety of urban residents.Ultrafiltration(UF)can completely intercept algal cells and some extracellular metabolites(EOM)by virtue of its efficient interception ability.At present,UF has become an effective means to treat algaeladen water.However,the deposition of algal cells and their metabolites on the membrane surface will cause serious membrane fouling,which will increase the energy consumption of ultrafiltration and shorten the service life of ultrafiltration membrane,which limits the wide application of ultrafiltration in engineering.Therefore,exploring the effective mitigation strategy of membrane fouling is the top priority in the field of ultrafiltration membrane treatment of algae-laden water.Algal cells and EOM are the main pollutants in the ultrafiltration process of algae-laden water.Therefore,taking the algal source materials of high algal water as the starting point,this paper carries out the ultrafiltration experimental research on algal cells alone,EOM alone and mixed pollution,and explores the characteristics and mechanism of membrane fouling induced by the three in the ultrafiltration process.It is found that the three types of pollutants will lead to the sharp decline of ultrafiltration water production flux and the formation of membrane fouling.Under the condition of mixed pollution,the interaction between algae cells and organic matter leads to the deposition of filter cake layer on the membrane surface,which is more dense and the decline of specific flux is more significant;Both algal cells and EOM alone can cause serious membrane fouling resistance.The reversible pollution formed by algal cells and EOM accumulation on the membrane surface can be removed by hydraulic flushing;The irreversible pollution caused by algal cell residues and small molecular organics in EOM entering the membrane pores or adsorbing on the membrane surface is difficult to be removed by hydraulic means.In practical engineering application,it is necessary to avoid the rupture of algal cells and the release of intracellular organic matter.Based on the fact that the above algal membrane pollutant will cause serious membrane fouling,this paper uses the UV radiation enhanced ferrous ion activated sulfite(UV / Fe(Ⅱ)/S(Ⅳ))system to pretreat algae-laden water,and investigates the influence of the pretreatment system on water purification efficiency and membrane fouling.From the perspective of fluorescent material removal,the fluorescence intensity of organic matter increases after UV activated sulfite(UV / S(Ⅳ))pretreatment,and the removal of organic matter by ferrous ion(Fe(Ⅱ))pretreatment is not obvious.The use of UV / Fe(Ⅱ)/ S(Ⅳ)pretreatment is conducive to the removal of organic matter,but the UV radiation time needs to be controlled.Too long UV radiation may cause the rupture of algal cells and the release of organic matter.From the perspective of flux and fouling resistance,UV / Fe(Ⅱ)/ S(Ⅳ)pretreatment is conducive to alleviate the decline of ultrafiltration membrane flux and gradually reduce the reversible resistance at a certain sulfite concentration;When the concentration of sulfite continues to increase,the oxidation increases,resulting in the rupture of algal cells and the increase of irreversible membrane fouling resistance.From the mechanism analysis of the mixing model,when the sulfite concentration is low,the membrane hole blockage and filter cake blockage coexist.When the concentration gradually increases,the time of filter cake blockage is delayed or even there is no filter cake blockage.EOM is an important substance causing ultrafiltration membrane fouling.In this paper,UV / Fe(Ⅱ)/ S(Ⅳ)system was also used to treat EOM solution to investigate the effect of this pretreatment system on water purification efficiency and membrane fouling in the process of ultrafiltration.From the perspective of fluorescent material removal,UV / S(Ⅳ)pretreatment will cause more intense fluorescent effect.Ferrous pretreatment alone has limited ability to remove fluorescent substances,but it can significantly reduce the fluorescent effect of organic substances under UV / Fe(Ⅱ)/ S(Ⅳ)pretreatment.From the perspective of flux and pollution resistance,UV / Fe(Ⅱ)/ S(Ⅳ)can alleviate the decline of membrane flux at the critical concentration of ferrous,but the mitigation efficiency is limited.The reversible resistance of membrane decreases with the increase of sulfite concentration,but it will cause serious irreversible fouling.The mechanism analysis from the mixing model is mainly membrane hole blockage and filter cake blockage.When the concentration gradually increases,the time of filter cake blockage is delayed.The overall results show that in the UV / Fe(Ⅱ)/ S(Ⅳ)pretreatment system,the oxidation of sulfate radical and the coagulation of in-situ Fe(Ⅲ)make a great contribution to the mitigation of membrane fouling. |
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