Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment

The biogas residue (BR) from the anaerobic digestion of sludge poses a threat to the environment due to the presence of toxic and hazardous substances. Furthermore, emerging contaminants, such as bisphenol A (BPA), are widespread in domestic and industrial wastewater, requiring efficient and sustainable treatment technologies. In this study, the BR-based biochar was pyrolyzed from urea-modified BR and employed as a catalyst to activate peroxymonosulfate (PMS) for BPA degradation. With BR-based biochar pyrolyzed at 750 °C as a catalyst, 20 mg/L of BPA was completely removed. Free radical detection confirmed that hydroxyl radical (•OH) and sulfate radical (•SO4−) generation decreased with the increase in catalyst reuse times. The X-ray photoelectron spectra showed that the catalyst deactivation mainly resulted from -COOH and C-OH group loss, which acted as active sites for generating •OH and •SO4−, and HCl or NaOH regeneration for catalysts could recover oxygen-containing functional groups, boosting BPA removal from 54.7% to 91.5% and 100%, respectively. Thermal regeneration could only enlarge the catalyst’s specific surface area (SSA) to recover adsorption capacity, but might not restore the free radical generation capability. This research offered a theoretical basis for the sustainable utilization of BR and provided a reference for reusing catalysts in wastewater treatment.