Combination of magnetic biochar beads and peroxymonosulfate pretreatment process for mitigating ultrafiltration membrane fouling caused by typical natural organic matters in water

To relieve the serious membrane fouling caused by natural organic matter (NOM) in ultrafiltration (UF) process, in this study, magnetic biochar-iron cross-linking alginate (MBCA) beads were prepared using alginate doped with coffee grounds. These MBCA-beads when combined with peroxymonosulfate (PMS) served as an UF pretreatment to alleviate membrane fouling. Results demonstrated that membrane fouling caused by humic acid (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 HA (10 mg/L) and sodium alginate (SA, 5 mg/L) were present together, the MBCA-beads/PMS pretreatment could remove UV254 of 98% and DOC of 68%. 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%. Additionally, the pathways of pretreatment to mitigate HA-SA induced membrane fouling were attributed to the reduced cake layer fouling and intermediate blocking. Finally, when treating real river water, the pretreatment significantly reduced 50% of total fouling, and about 60% of the reversible fouling after 10 h filtration. This also displayed long-lasting membrane fouling mitigation ability.