Evaluation of Ultrasonic Pretreatment on Anaerobic Digestion of Different Animal Manures

This article addresses the effect of ultrasonication as a pretreatment to anaerobic digestion of four types of animal manure, including swine slurry, beef feedlot manure, dairy manure slurry, and separated dairy manure effluent. The effect of ultrasonication on soluble chemical oxygen demand (SCOD) and biochemical methane potential (BMP) were determined, and the energy efficiency of ultrasonic pretreatment was evaluated. Ultrasonic pretreatment was applied at two amplitudes (80 and 160 µmpp) and at two time settings (15 and 30 s) to each of the four manure types. The SCOD of each manure sample was determined before and after ultrasonic pretreatment. In addition, BMP trials were run on each waste with and without ultrasonic pretreatment. As part of the BMP, biogas production was measured and analyzed for methane content and cumulative methane production. Ultrasonic pretreatment of swine slurry, beef feedlot manure, dairy manure slurry, and separated dairy manure effluent increased the average SCOD up to 23%, 92%, 59%, and 33%, respectively, and the average methane yield up to 56%, 43%, 62%, and 20%, respectively. Increasing the ultrasonic amplitude and treatment time resulted in an increase in manure SCOD and methane production; the greatest methane production was obtained using the ultrasonic pretreatment at the highest power and longest treatment time. The observed greatest methane production from swine slurry, beef feedlot manure, dairy manure slurry, and separated dairy manure effluent were 394, 230, 226, and 340 mL CH4 g-1 VS, respectively. In contrast, the greatest energy efficiency was obtained with the lowest ultrasonic amplitude combined with the shortest treatment time.