Mechanistic investigations in ultrasonic pretreatment and anaerobic digestion of landfill leachates

Abstract

This study has attempted to gain mechanistic insight into ultrasound assisted pretreatment of landfill leachate (prior to anaerobic digestion) by coupling experimental results with simulations of cavitation bubble dynamics. Essentially, individual roles of physical and chemical effects induced by sonication in the process have been identified. Changes in properties of leachate (such as sCOD, tCOD, NH3-N and acetate concentrations) subjected to sonication at different power levels have been studied. Sonication generated intense microconvection in system that caused faster disintegration and solubilization of biosolids. However, for high power input, where transient cavitation occurred in solution, degradation of organic matter by oxidizing radicals generated by cavitation bubbles occurred that reduced sCOD value resulting in low biogas yield in anaerobic digestion. Sonication at low to moderate power input, where stable cavitation prevailed, caused disintegration and solubilization, but not degradation, of biosolids resulting in higher sCOD value and biogas yield.