Municipal sludge pyrolysis for biochar production: mechanism and performance under self-generated atmosphere

Abstract

With the continuous growth of municipal sludge production, its harmless and resourceful treatment has become a significant environmental challenge. This study proposed a pyrolysis method based on a self-gas isolation model, which utilized the gas generated from sludge pyrolysis to create anoxic environments for simple biochar preparation. Orthogonal experiments were conducted to investigate the effects of pyrolysis temperature (500–700°C) and duration (0.5–2 h) on the physicochemical properties of biochar. Results showed that with increasing temperature and extended time, the sludge weight loss rate rose from 41.7% to 48.7%, while organic element content (C, N, H, S) decreased. The mineral phases underwent transformation, with functional groups like Si-O-Si and Fe-O remaining stable, whereas aliphatic C-H and amide II bands gradually disappeared. SEM (Scanning Electron Microscope) revealed significantly enhanced pore structure and increased specific surface area in pyrolysis samples. The proposed biochar preparation method removes partial organic matter, forming a stable porous biochar structure dominated by silicon and iron elements. This research provides valuable insights and guidance for simple biochar preparation from municipal sludge