Insights into Fe/N co-doped biochar on enhanced dewaterability of anaerobically digested sludge: Heterogeneous oxidation and skeleton builder

Abstract

Although anaerobic digestion is a promising way for valorization of waste activated sludge, the process severely deteriorates the sludge dewaterability. Herein, a novel strategy of iron and nitrogen co-doped biochar (Fe-N-BC) activated peroxydisulfate (PDS) was developed to improve anaerobically digested sludge (ADS) dewaterability. Results showed that Capillary suction time (CST) and moisture content (MC) of ADS after conditioned with Fe-N2-BC-800/PDS system dropped to 43.4 s and 66.8% when the initial pH was 6.0, dose of Fe-N2-BC-800 was 0.6 g/g VS, dose of PDS was 0.9 mmol/g VS, and reaction time was 30 min, respectively. Quantitative analysis indicated that the heterogeneous oxidation initiated by Fe-N2-BC-800 primarily contributed to the enhancement of ADS dewaterability. Mechanistic results revealed that (S•O4−, O•H, and O21were generated as reactive oxygen species (ROS) through multiple active sites of Fe-N2-BC-800 during catalytic reaction. These highly ROS efficiently decomposed extracellular polymeric substances (EPS) and disintegrated ADS cells, thereby releasing bound and intracellular water into free water. Meanwhile, Fe-N2-BC-800/PDS significantly reduced hydrophilic biopolymers, improved hydrophobicity of ADS through adjusting protein secondary structure and enriching hydrophobic groups in sludge pellets. Furthermore, Fe-N2-BC-800 produced rigid and porous drainage routes in ADS as skeleton builder, inducing enhancement of ADS dewaterability combing with the strong oxidation. The proposed Fe-N2-BC-800/PDS treatment offers a novel and promising technology for high-efficiency enhancement of ADS dewaterability, providing a valuable reference for ADS deep dehydration.