A novel approach for simultaneous improvement of dewaterability, post-digestion liquor properties and toluene removal from anaerobically digested sludge

Abstract Anaerobically digested sludge (ADS) is a major product of anaerobic digestion a widely used and economically viable microbial process used in wastewater treatment plants (WWTP) to break down biodegradable material in the absence of oxygen. Although anaerobic digestion is considered environmentally safe, the sludge often possesses undesirable properties including resistance to dewatering and high concentrations of harmful or deleterious compounds. Toluene is one of the hazardous products of anaerobic digestion that can be harmful to humans and the environment. In previous studies, it was demonstrated that persulfates: peroxydisulfate (PDS, S 2 O 8 2− ) and peroxymonosulfate (PMS, HSO 5 − ) could be successfully used in the sludge treatment process. In this study, it was demonstrated that elevated temperatures from meso- or thermophilic digestion could activate persulfate creating highly reactive sulfate and hydroxyl radicals. These radicals can oxidize toluene and other organic matter in ADS thereby improving its dewaterability. Furthermore, supernatant obtained after oxidation treatment was conditioned by struvite precipitation in order to remove ammonium nitrogen and phosphates. The results of this study indicate large improvements in ADS properties after PDS treatment in comparison to PMS or temperature conditioning alone.