The activation of peroxymonosulfate by biochar derived from anaerobic and aerobic iron-containing excess sludge

The excess sludge from municipal sewage treatment plants is rich in Fe (III) due to chemical dephosphorization. The activation of peroxymonosulfate (PMS) by biochar derived from anaerobic and aerobic iron-containing excess sludge was studied systematically in this research. Fe (III)-containing excess sludge was cultured in an anaerobic environment for conversion of partial Fe (III) to Fe (II), which was further carbonized to prepare biochar labeled AnSx@Fe. Meanwhile, aerobic sludge with different Fe (III) content was directly carbonized to produce biochar labeled AeS@Fe. For biochar (AnS20@Fe-15%) prepared from 15% Fe(III)-containing anaerobic cultured 20 days sludge, the relative contents of Fe (III) and Fe (II) were 21.26% and 78.74%, which were 31.03% and 68.97% for biochar (AeS@Fe-10%) prepared from 10% Fe (III)-containing aerobic sludge. Fe (III) can be reduced to Fe (II) by both anaerobic culture and carbonization. Their removal rates of tetracycline (TC) through 60 min PMS activation were 97% and 98%, with TOC (Total organic carbon) removal of 61.8% and 53.4% respectively. The reactive species including sulfate radical (·SO4-), hydroxyl radical (·OH) and singlet oxygen (¹O₂) were produced during PMS activation. After O₂-aeration treatment of both AeS@Fe and AnSx@Fe, the relative content of Fe (II) was decreased and group C = O was disappeared, which resulted in reduction of ·SO4-, ·OH and ¹O₂. The generation of ·SO4- and ·OH was dominated by the Fe (II) activation and the ¹O₂ generation was originated from graphite type N and C = O. Direct carbonization of aerobic and anaerobic sludge is a feasible method to produce biochar for PMS activation.