Effects of pretreatments on thermophilic aerobic digestion

In order to enhance the degradation efficiency of waste activated sludge (WAS) in thermophilic aerobic digestion (TAD), various pretreatment methods were investigated for the decomposition of WAS, including ultrasonic, thermal, alkaline, and mechanical treatments. Thermophilic aerobic digestion experiments using pretreated WAS were conducted to investigate the effects of the pretreatments on degradation efficiency in TAD. The pretreatment methods enhanced the degradation efficiency in the TAD process and thermal and mechanical pretreatments had the best efficacy from the viewpoint of solid particle decomposition. Based on the efficiencies of solid particle decomposition, the order of pretreatment efficacy was as follows: mechanical treatment > thermal treatment > alkaline treatment > ultrasonic treatment. Based on total suspended solids reduction and released compounds decomposition, the order of TAD efficacy was as follows: TAD with thermal pretreatment > TAD with mechanical pretreatment > TAD with alkaline pretreatment > TAD with ultrasonic pretreatment > control TAD (without pretreatment). Because the thermal process consumes a large amount of energy, mechanical pretreatment is considered the most practical pretreatment for the TAD process.