Anaerobic Co-Digestion to Enhance Waste Management Sustainability at Yosemite National Park

This study evaluated the co-digestion of domestic wastewater solids (WWS) and food waste (FW) at the bench-scale for Yosemite National Park, California, which operates a 1900 m³/d wastewater treatment plant in El Portal, California. A 35-day biochemical methane potential test was performed on varying amounts of FW as a percentage of total waste (WWS plus FW) on a volatile solids basis (%FW). Specific methane yield and volumetric methane yield increased substantially with increasing %FW. A higher %FW was also associated with slower degradation kinetics but higher methane content in biogas. The 75 %FW treatment had relatively rapid kinetics, a high cumulative specific methane yield (453 mL CH₄/g VS), and an elevated methane content in biogas, and is suggested as an upper limit %FW mixture for full-scale co-digestion. This, coincidently, is near the estimated ratio of WWS and FW production at the Park (70 %FW). Co-digesting the Park’s feedstock of FW with WWS in existing anaerobic digestion facilities could increase methane production five-fold. Combusting this methane in a combined heat and power system would produce about twice the energy needed to heat anaerobic digestors and power the treatment plant.