Study On Ultrafiltration Membrane Fouling Control By Magnetic Biochar(Beads) Activated Peroxymonosulfate

Due to the increase of natural organic matter（NOM）,refractory trace emerging pollutants and pathogenic microorganisms in surface water,the conventional water purification process has encountered challenges in ensuring water quality safety.Therefore,it will be a trend and inevitable to apply the third generation of membrane separation technology with ultrafiltration（UF）as the core to the water purification process.However,in the actual operation,the serious membrane fouling caused by humic substances,polysaccharides and other NOMs prevalent in water sources has become a bottleneck restricting the use and popularization of the membrane process.This topic is based on the efficient and complete oxidative degradation of organic matter by sulfate radical-based advanced oxidation processes（SR-AOPs）,a green and economical modified biochar catalytic material was prepared for activating peroxymonosulfate（PMS）as a pretreatment process of UF to mitigate ultrafiltration membrane fouling caused by NOM.This study may provide an effective strategy for membrane fouling control and resource utilisation of waste biomass.Firstly,based on waste coffee grounds,powdered magnetic biochar（Fe-BC）was prepared by co-precipitation for activation of peroxymonosulfate（PMS）as a pretreatment process for UF process.Results showed that the average removal rates of humic acid（HA,10 mg/L）were 55.23%and 73.55%,at the Fe-BC dosage of 300mg/L and PMS dosage of 300 mg/L and 900 mg/L,respectively.Radical quenching experiments showed that Fe-BC/PMS pretreatment could remove HA by both radical and non-radical pathways,with·OH and SO₄^-·contributing 26.74%and 9.85%respectively.The increase in the hydrophilic component of the system after pretreatment and the removal of dissolved organic carbon（DOC）both had a positive effect on the mitigation of membrane fouling.The Fe-BC/PMS pretreatment significantly reduced the total（44%）and reversible（61%）ultrafiltration membrane fouling after five filtration cycles at a relatively high flux of 200 L/m²·h,and the Fe-BC and PMS dosage of 100 mg/L.The results of the combined fouling models fit showed that the pretreatment oxidatively degrades large molecular weight organics to small molecules,resulting in a shift from complete blocking to standard blocking.Therefore,it can be seen that the Fe-BC/PMS pretreatment system can mitigate ultrafiltration membrane fouling caused by HA by reducing the membrane treatment load and reducing complete blocking.Secondly,another material was prepared by the"gel-calcination"method using alginate-embedded waste coffee grounds:magnetic biochar-iron cross-linking alginate beads（MBCA-beads）,which were used to activate PMS as a pretreatment method for UF process.Results demonstrated that membrane fouling caused by HA can be completely alleviated at a speed of 3 rpm,and dosages of 0.5 g and 25 mg/L for MBCA-beads and PMS,respectively.When the simulated contaminants were HA（10mg/L）and sodium alginate（SA,5 mg/L）,the MBCA-beads/PMS pretreatment removed 98%of UV₂₅₄ and 68%of DOC under the same conditions as above,while the increase in TMP was almost zero.The main mechanisms for HA and SA removal were radicals oxidation and coagulation with in situ generated Fe（III）.The contribution of·OH was about 14.83%and the joint effect of SO₄^-·and coagulation accounted for about 50%.The results of the combined membrane fouling models showed that pretreatment mitigates HA-SA induced membrane fouling mainly by reducing cake layer fouling and intermediate blocking.Finally,the MBCA-beads/PMS combined UF process was used to treat actual river water,and the results showed that after 10 hours of pretreatment,the total fouling of the ultrafiltration membrane was significantly reduced by 50%and the hydraulic reversible fouling was reduced by 60%.In addition the trend in membrane fouling index showed that this pretreatment still had the ability to mitigate membrane fouling over longer filtration times.In summary,the pretreatment system of coffee grounds-based magnetic biochar（beads）in combination with PMS can effectively remove typical NOM from water and significantly alleviate membrane fouling,which has good prospects for application in membrane water treatment.