Making Anaerobic Digestion Work with High Strength Wastes: Lessons Learned from Pilot to Full Scale

Abstract

Codigestion of wastewater solids and food wastes has been practiced in Europe to increase gas productions in the existing anaerobic digester systems and energy generation. Although a review of the codigestion technologies and food waste sources indicate that various types of high strength wastes including food wastes can be amenable for codigestion, optimization of gas production and system performance requires a thorough analysis as well as the available waste sources within the vicinity of the host facility. The food processing waste digestion showed a 35% greater biogas generation compared to the control digester that has not received any supplemental waste. The tests also confirmed that the wastes did not cause inhibition of biologic activity under the mesophilic conditions. Benefits due to the increased biogas production by anaerobic digestion of FOG wastes at the Johnson County facility were calculated to increase the biogas generation by more than 50%. Following implementation, the overall program will reduce the treatment plant's electricity purchase costs by over $500,000 per year under average conditions utilizing the new cogeneration system. At Pinellas County, FL the payback period of the evaluated biogas cogeneration project was estimated to be from 5.5 to 7.5 years, with associated 20-year lifecycle benefits in the order of $5.5 to $9 million, depending on the cost of electricity and natural gas.