Ultrasonic Pretreatment for Anoxic-Aerobic Digestion of Activated Sludge

The ultrasonic pretreatment of activated sludge was conducted and followed by the anoxic-aerobic digestion in this study. First, an experimental program of orthogonal design was carried out to determine the most effective pretreatment conditions. The results have showed that the optimal pretreatment conditions were the ultrasonic frequency of 28 kHz, ultrasonic density of 0.15 W/mL and ultrasonic time of 10 min. After that, a reactor with a volume of 30 L was designed and specialized for the anoxic-aerobic digestion of pretreated sludge. The results have shown that the ultrasonic pretreatment can reduce the digestion time of sludge and improve the digestion efficiency. Sludge reduction could reach the discharge standard after 10 days´ digestion, 12 days shorter than that without ultrasonic pretreatment. The maximum removal rate of MLVSS was increased by 11%, up to 55.10%.