An investigation of ultrasound effect on digestate solubilization and methane yield

In this study, different ultrasound power intensities of 0.05-0.21 kW/L (4.13-16.52 kW h/kg TS) were applied at a frequency of 20 kHz and for durations of 5-20 min to digestate obtained from a domestic wastewater treatment plant. The ultrasonic effect on digestate solubilization was revealed by increased levels of soluble Chemical Oxygen Demand (sCOD), soluble Total Organic Carbon (sTOC), and soluble Total Nitrogen (sTN) released into the solution. The highest material release was achieved at an ultrasonic energy intensity of 0.21 kW h/L. Furthermore, the ultrasonic effect on CH4 production was studied using the anaerobic digestion process. The application of ultrasound at 0.05-0.21 kW h/L provided 1.6-2.3-fold increase in net CH4 production. Analysis of the energetics of the system showed that only about 4 and 11% of the energy input was recovered in terms of additional CH4 production at 0.21 and 0.05 kW h/L, respectively. A comprehensive cost-benefit analysis of the system is required for making a conclusion on the feasibility of the system, and such analysis should include environmental, economic, and societal benefits of the system, among others.