Experimental Study On Percarbonate Oxidation-enhanced Coagulation To Alleviate Algal Source Membrane Fouling

With the rapid development of society and industrialization,people are facing increasingly severe challenges of the water environment crisis.Water eutrophication is one of the important factors that affect the safety of drinking water and increase the burden on urban water treatment systems.The resulting algae outbreak will seriously affect the quality of the tap water and endanger people's lives and health.How to efficiently treat high algae water has gradually become a research hotspot in recent years.Ultrafiltration(UF)has high-efficiency physical separation capabilities and can effectively trap macromolecular pollutants such as algae cells.In addition,UF process also has a series of advantages such as small footprint,low operating cost and pressure.However,severe membrane fouling during algal-laden water treatment will increase energy consumption and shorten the service life of the membrane,which seriously restricts the further development and application of UF.Therefore,this study focused on the mitigation of membrane fouling caused by algal-laden water during UF process through pretreatment.Two oxidation-coagulation systems(Polyaluminum chloride-percarbonate and Ferrous sulfate-percarbonate)were used for the pretreatment of Microcystis aeruginosa and its extracellular organic matters(EOM)and algal cells.The effects of the two systems on the mitigation of membrane flux reduction and membrane fouling resistance were investigated,the removal of organics that caused membrane fouling was analyzed,and the mechanism of mitigating membrane fouling was discussed.The study proved that the dosing method(PACl/SPC)of polyaluminum chloride(PACl)and sodium percarbonate(SPC)at the same time achieved the best treatment effect while individual PAC1 and SPC treatment had poor treatment effect on algal pollutants removal.The final specific flux of the algal solution was increased to 0.838,and the irreversible and reversible membrane fouling were alleviated by 90.5%and 92.8%respectively after PACl/SPC treatment.The effluent protein removal rate could reach about 80%while the removal rate of humic acid substances was slightly lower,which was about 30%.After PACl/SPC treatment,the DOC content of the effluent was reduced by 21.4%.The types and quantities of contaminants on the membrane surface were significantly reduced.The accumulation of algal cells on the membrane surface has been significantly mitigated.Ferrous sulfate-percarbonate(Fe²⁺/SPC)also showed high treatment efficiency during algal-laden water treatment.The final specific flux was greatly increased from 0.097 to 0.965,and the mitigation efficiency of irreversible and reversible pollution resistance reached 71.9%and 98.6%after Fe²⁺/SPC pre-treatment.The final flux after EOM contamination increased from0.511 to 0.941 after Fe²⁺/SPC pre-treatment.The result of fluorescence excitation-emission matrix(EEM)spectrum showed that over 80%of protein substances in algal source pollutants were removed.The result of UV₆₈₅ showed that the removal rate of algae cells reached 88.1%.The surface of the membrane was covered by porous flocs,which could enhance the permeate rate.And the number of algal cells was greatly reduced,which was showed by scanning electron microscope(SEM)results.And Fe²⁺/SPC system also had a good removal effect on the trace pollutant bisphenol A and the removal rate reached 85.3%.Finally,the mechanism of the two systems to alleviate the membrane fouling caused by algal-laden water was studied.The results showed that hydroxyl radicals(HO·)with strong oxidizing were produced during two pre-treatment processes,which could effectively remove organic pollutants in algal-laden water.PACl/SPC treatment could make the zeta potential of the algal solution closer to 0 m V,destroy its colloidal stability and enhance the flocculation effect.The results of the filtration model fitting revealed that the main fouling mechanism during UF filtration process caused by algal solution was cake filtration.After PACl/SPC and Fe²⁺/SPC treatment,the main fouling mechanism in the UF process was turned from cake filtration into standard blockage,which could effectively delay the formation of the cake layer,and alleviate membrane fouling.In summary,the two oxidation-coagulation systems based on percarbonate(PACl/SPC and Fe²⁺/SPC)used in this study could effectively alleviate the serious membrane fouling during algal-laden water treatment,which could provide theoretical support for the further development and application of algal-laden water treatment.