Coupling of KMnO4-assisted sludge dewatering and pyrolysis to prepare Mn,Fe-codoped biochar catalysts for peroxymonosulfate-induced elimination of phenolic pollutants

Conversion of waste sludge into biochar-based catalysts has been considered as a feasible alternative for sludge treatment, and dewatering of waste sludge is a key process for further treatment and disposal. In this study, KMnO4 was used as both a chemical conditioner to assist Fe-rich sludge dewatering and a chemical modifier to incorporate Mn oxides into the biochar catalysts. Results showed that the sludge dewatering was substantially improved when KMnO4 dosage was above 13% DS (dry sludge), and more than 99% of Mn was retained in the sludge cake. After pyrolysis of the sludge cake, a series of Mn,Fe-codoped biochar catalysts (assigned to x-Mn-FeBC) were obtained. The catalysts could activate peroxymonosulfate (PMS) well for complete removal of phenolic contaminants including phenol, bisphenol A (BPA) and 2,4-dichlorophenol (DCP) over a wide pH range (2.5–12) with the co-existence of water constituents. After 5 consecutive cycles, the catalytic performance of 13%-Mn-FeBC was decreased by half, but it could be fully recovered by simple calcination at 600 oC. It was proposed that radical and non-radical oxidation processes worked together for organic degradation, but non-radical pathways involving 1O2 oxidation and electron transfer between PMS and organic played more crucial roles. This study proposed a novel sludge treatment process by combining enhanced sludge dewatering with efficient catalyst preparation, and the as-prepared catalysts were promising in PMS activation and organic degradation.