Modeling the Effect of Sonication on the Anaerobic Digestion of Biosolids

Ultrasound treatment of wastewater sludge prior to anaerobic digestion disrupts the flocs and causes lysis of the bacterial cells, releasing both inter- and intracellular materials. Primary and waste-activated sludge (WAS) were treated with different ultrasonic intensities, varying sonication time and amplitude at a constant frequency. Results showed that the gas production, volatile fatty acids, ratio of soluble chemical oxygen demand to total chemical oxygen demand, and soluble protein increased, while the particulate protein and particle size of the sludge decreased, with sonication time. An empirical model was developed to determine the economic viability of ultrasound based on electrical energy input and energy obtained from enhanced methane production. It has been found that ultrasonic pretreatment is only economically viable for primary sludge at low sonication doses. The Anaerobic Digestion Model No. 1 (ADM1) was applied to the batch anaerobic digestion for sonicated and non-sonicated sludge. In almost all cases, the model successfully simulated the experimental trends.