Food waste co-digestion in Germany and the United States: From lab to full-scale systems

Using food waste (FW) as a co-substrate in anaerobic digestion (AD) results in increased energy production, decreases in greenhouse gas emissions, and recycles the FW nutrients back to the land for producing crops. This research investigated food waste AD systems in the United States (US) and Germany (DE) that co-digested FW with dairy manure at the lab and full-scale. In DE, the post-consumer FW had 32-49% more CH4 potential (477-499 mL(CH4)/gvs) than maize and grass silage (368 and 331 mL(CH4)/g(VS)) and solid and liquid manure (243 and 91 mL(CH4)/gvs). Methane production in the full-scale DE system with 66% FW (by volume) was 882 m(CH4)(3)/d, which was 37% higher than the laboratory results due to the 86-day retention and 42 degrees C AD conditions in the field. The pre-consumer FW in the US had a similar CH4 potential (264-553 mL(CH4)/g(VS)), but due to the lack of heating in the full-scale system, 62% less CH4 was produced than the lab-based potential. While DE requires pasteurization of FW for AD and bans FW bans to landfills, the US does not have specific requirements for FW treatment in AD or federal FW landfill policies, with a few forthcoming FW bans in some municipalities and states. As FW diversion and utilization in AD systems is expected to grow, it is important to understand the effect of FW in biogas production and nutrient content, comparisons between lab and field-scale results, and the effect of policy on FW utilization.