Pilot-scale operation of enhanced anaerobic digestion of nutrient-deficient municipal sludge by ultrasonic pretreatment and co-digestion of kitchen garbage

A pilot-scale study was carried out to evaluate the in situ anaerobic digestion of nutrient-deficient activated sludge (AS) from southern China. A single and two-stage system were compared and the performance of ultrasound pretreatment and co-digestion with kitchen garbage was evaluated by comparing volatile solids removal and biogas production. The results showed that two-stage systems performed better than single-stage systems at high feeding concentration and short retention time. Ultrasonic pretreatment significantly enhanced sludge solubilization though cell lysis and subsequently increased biogas yields. Mixture with kitchen garbage resulted in substantial volatile solids reductions in both single and two-stage systems of up to 47% as well as significant increases in biogas yields. Processes including digestion, dewatering, drying and incineration of this type of sludge were proposed, and mass balance calculation showed that these processes were feasible and had the potential to provide environmental and economic benefits for wastewater treatment plants in southern China.