Graphitic biochar catalysts from anaerobic digestion sludge for nonradical degradation of micropollutants and disinfection

Abstract

The peroxydisulfate (PDS) -based advanced oxidation processes (AOPs) is a promising technology for wastewater treatment and the efficiency primarily depends on the high-performance catalysts. Therefore, it is necessary to develop a green and low-cost biomaterial for PDS activation to drive such a process. In this study, biochar catalysts were produced via pyrolysis of anaerobic digestion sludge (ADS) as effective PDS activators. The biochar derived from ADS (ADSBC) yielded large specific surface areas, a high degree of graphitization and good conductivity, which can be used for effectively oxidizing various pollutants including dyes, estrogens and sulfonamides with PDS in broad pH and temperature ranges. It is showed that PDS activated by ADSBC 1000 can completely remove sulfathiazole in 90 min much higher than that of ADSBC 400 (20.25%). Moreover, the biochar produced under high pyrolysis temperature shows great stability and low biotoxicity due to the limited metals leaching and eliminated persistent free radicals as well as dissolved organic matter. The mechanism of the ADSBCs/PDS system was critically discussed via selectively radical screening tests, solvent exchange (H₂O to D₂O), selectivity to pollutants and electrochemical analysis. These results revealed that the organics were decomposed by a nonradical pathway via electron transfer rather than relying on free radicals or singlet oxygen. More importantly, the biochar-based nonradical oxidation system can leveraged for inactivation of Escherichia coli (E. coli) and diverse bacteria in both simulated and real wastewater. Therefore, this work not only provides an approach to reuse the sludge residue to prepare graphitic biochar catalysts as PDS activators for decontamination of emerging micropollutants, but also expands the practical application of advanced carbocatalysis for bacteria inactivation by nonradical oxidation in real wastewater.