Sludge Disinfection, Reduction and Energy Recovery by Anaerobic Digestion with Thermal Hydrolysis Pretreatment

Abstract

The disinfection of sewage sludge has become a hot focus due to the outbreak of COVID-19, which belongs to one aspect of sludge harmless treatment. However, the threat of sludge to the environment is not only caused by harmful microbes. It is necessary to explore energy recovery and resource utilization of sludge treatment that is based on harmlessness, volume reduction and stabilization. Various advanced technologies were integrated to build an advanced anaerobic digestion system in Beijing urban area, which has achieved a good sludge treatment effect in the past three years since its construction and operation. Thermal hydrolysis can effectively inactivate harmful microorganisms, the hygienic properties of advanced anaerobic digestion products can meet the standard, and its heavy metals contents are significantly lower than the related standard limit, which have changed to more stable forms. The unit treatment capacity of digester increased to 3.6 times that of conventional anaerobic digestion due to the modification effect of thermal hydrolysis on sludge properties, saving about 68% investment in digester construction. The degradation rate of organics increased from 40% to 52%, indicating that the stability of the digestion products was further improved, the residual solids were further reduced with the volume reduction rate of sludge increased from 28% to 66%. The biogas production rate was greatly increased with the improvement of organic conversion efficiency. Even operated below capacity, the advanced anaerobic digestion system still had the capacity to output 4 089×10~4 kW·h power under the condition that deducting the heat and power consumption of the system itself from the energy recovered. The treatment and disposal process of sludge were successfully connected by the resource utilization of advanced anaerobic digestion products. The large-scale production application in Beijing has created a successful and mature engineering reference for sludge advanced anaerobic digestion.