Enhanced anaerobic digestion of waste-activated sludge by thermal–alkali pretreatment: a pilot-scale study

Abstract

The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal–alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4–8 h, and the optimal alkali concentration range was 0.0125–0.015 kg NaOH/kg dry-sludge. Thermal–alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge. HIGHLIGHTS Enhanced anaerobic digestion of WAS by thermal–alkali pretreatment was studied at a pilot-scale level.; Optimal thermal temperature and retention time were confirmed for a pilot-scale study.; Energy demand can be basically met based on biogas production.;

Keywords

• alkali hydrolysis
• anaerobic digestion (ad)
• pretreatment
• thermal
• waste-activated sludge (was)