Slow co-pyrolysis of faecal sludge and rice husks into biochar

Abstract

Sustainable solutions for managing faecal sludge (FS) and agricultural residues remain limited in many low-resource settings, leading to environmental contamination and loss of valuable biomass. This study addressed this problem by evaluating the slow co-pyrolysis of FS and rice husks (RH) as a strategy for producing high-quality biochar for soil improvement. Co-pyrolysis experiments were conducted at three temperatures (350 °C, 450 °C, 550 °C) and three FS:RH mixing ratios (30:70, 50:50, 70:30) in a nitrogen-purged fixed-bed reactor. The resulting biochars were analyzed for yield, BET surface area, pore volume, functional groups, and particle size distribution using BET analysis, FTIR spectroscopy and SEM imaging. The results showed that increasing temperature and balancing the feedstock ratios significantly improved physicochemical properties. The optimal condition was observed at 550 °C and a 50:50 FS–RH blend, which produced biochar with the highest BET surface area, enhanced porosity, and improved nutrient- and moisture-retention characteristics. This biochar demonstrated strong potential for soil amendment and sorption applications. Given its production cost of less than USD 1 per 10 kg, the study recommends co-pyrolysis of FS and RH at 550 °C and a 50:50 ratio as an affordable, climate-resilient, and scalable pathway for sustainable waste valorization and agricultural productivity improvement.