Optimization of integrated compost-dewatering and pyrolysis for sustainable faecal sludge management: enhancing pathogen inactivation and biochar production
摘要
Conventional methods for faecal sludge management, such as lime addition and anaerobic digestion, often face limitations such as pathogen regrowth and odour emission. This study addresses these gaps by exploring an integrated compost-dewatering and pyrolysis approach to transform faecal sludge into a sustainable and hygienic resource. Aerobic compost dewatering and slow pyrolysis (350 °C, 450 °C) were used to treat pre-sanitised faecal sludge. Key parameters such as temperature, pH, lactic acid bacteria, faecal coliforms, odour, and biochar properties were analysed comprehensively over a 50-day period. The addition of biochar to the faecal sludge composting reactors was evaluated at various levels in Reactor 1 (5% biochar), Reactor 2 (10% biochar), and Reactor 3 (15% biochar). A non-biochar amended compost reactor served as a control. The key results include a peak thermophilic temperature of 66 °C in reactor 3, indicating enhanced composting efficiency. Lactic acid bacteria plate count analysis confirmed the continuous presence of lactic acid bacteria in the reactors, which supports active pathogen inactivation. Lactic acid bacteria concentrations were recorded as 7.4 × 108 CFU/100 mL in reactor 1, 7.6 × 108 CFU/100 mL in reactor 2 and 6.9 × 108 CFU/100 mL in reactor 3. Biochar supplementation contributed to facilitating the thermophilic phase of composting and reduced total carbon levels most effectively in Reactor 1. Coliform bacterial enumeration analyses of the final compost and biochar revealed complete pathogen elimination. In contrast, coliform bacteria were detected in the control reactor during compost-dewatering process. The biochar produced from the compost via pyrolysis at 350 °C and 450 °C presented alkaline pH values (10–11), with a higher pH in the biochar produced at 450 °C. Elemental analysis revealed a carbon concentration of 69.3% at 350 °C and 48.8% at 450 °C in reactor 1, which decreased the hydrogen and nitrogen contents as the temperature increased. The compost-dewatering and pyrolysis process achieved complete pathogen inactivation and mitigated odour emissions, providing a safe and hygienic solution for faecal sludge recycling.