Study On The Control Law And Mechanism Of Algae-derived Membrane Fouling In MIEX-UF Integrated Process

With the emission of more nitrogen and phosphorus,the phenomenon of widespread eutrophication in fresh water results in seasonal algae blooms of many drinking water resources.Ultrafiltration?UF?process is the core of the third generation of drinking water treatment technology,and inevitably faces the membrane fouling when dealing with algae-polluted drinking water..Transparent Extracellular particles in algae water is a special kind of Extracellular Polymeric Substances,which could be stained by Alcian blue and comprise acidic polysaccharide and protein.Studies have shown that TEP are closely associated with the membrane fouling caused by algae.Although extensive research work has been conducted to better explore TEP from the oceans under various conditions,little has been known about the effects of TEP on membrane fouling in algae-polluted drinking water.In our experiments microcystis aeruginosa which is the most common algal in bloom was chosen as a representative.The influence of TEP on UF membrane fouling caused by algae was studied.It was found that the membrane fouling caused by the dead algae was the most serious in different growth stages,and was closely related to TEP in the algae.Further research showed that the combined TEP exacerbated membrane reversible fouling,while free TEP exacerbated membrane irreversible fouling.Moreover,the free TEP with colloidal scale had an obvious linear relationship with irreversible membrane resistance.Studies about the effects of Ca²⁺ and pH on membrane fouling caused by TEP showed that Ca²⁺ could promote the transformation of dissociated TEP from colloidal size to partical size and reduced the irreversible pollution of UF membrane.The acid pH value will significantly aggravate the UF membrane fouling,and the alkaline pH value will reduce membrane fouling.The existance of Na+ can significantly aggravate the membrane fouling.On the above research,the rule and mechanism of membrane irreversible fouling caused by algae in the integrated MIEX-OF process were further studied.For membrane irreversible fouling caused by free TEP,the control of hydraulic and chemical irreversible membrane fouling by the integrated MIEX-UF process in four consecutive cycles were explored and it was found that the accumulation rate of the hydraulic irreversible pollution decreased by 39.94%and that of chemical irreversible pollution was reduced by 20.10%compared with UF alone.The Confocal Laser Scanning Microscopy?CLSM?observation showed that the accumulation of irreversible pollutants in the membrane surface and section could be effectively reduced by the integrated MIEX-UF process.The mechanism analysis of membrane fouling control in the integrated process showed that the MIEX dynamic layer formed on the surface of UF membrane was the most important.Micro interface forces analysis found that the interface force between MIEX and TEP was significantly higher than that between PVDF membrane and TEP,which means a stronger affinity between MIEX and TEP.As a result,TEP could be captured preferentially by MIEX when it crosses the resin dynamic layer and the amount of TEP that reach the membrane surface and membrane pores were reduced.Furthermore,the higher affinity between MIEX and TEP could make those pollutants accumulated on the UF membrane surface are more easily stripped with the resin dynamic layer during backwashing,which could enhance the hydraulic backwashing effect.