Pilot-scale experiment on thermally hydrolyzed sludge liquor anaerobic digestion using a mesophilic expanded granular sludge bed reactor
A pilot process of thermal hydrolysis combined with an expanded granular sludge bed reactor (EGSB) was carried out to evaluate pretreated sludge liquor into biogas conversion, process stability, and energy input/output balance. Approximately 25% of suspended solids of sludge were liquefied into aqueous phase during thermal hydrolysis pretreatment, which resulted in chemical oxygen demand (COD) concentration of 20.0 to 35.0 g/L. A mesophilic EGSB reactor was operated for 206 days treating pretreated liquor. Under an organic loading rate of 11.0 kg COD/(m3·d) and hydraulic retention time of 60 h, COD conversion efficiency was maintained at 63%. The energy from biogas provided 80% of that demand for heating pretreatment. Dewatered sludge after thermal hydrolysis could be incinerated with municipal solid waste in an industrial-scale incinerator. Total energy production from combined biogas anaerobic digestion and sludge incineration, treating 1.0 kg raw sludge with moisture content of 82%, was 2419 kJ. The energy demand of thermal hydrolysis pretreatment was 340 kJ.