UC Merced

The growing need for sustainable municipal solid waste treatment and energy production has driven the development of new waste management methods like co-digestion. Anaerobic co-digestion of food waste (FW) and wastewater solids (WWS) has been implemented at a few wastewater treatments plants to efficiently treat organic wastes and produce methane-rich biogas as an energy source. Yosemite National Park has an opportunity to design a new co-digestion facility with an upcoming upgrade to their local wastewater treatment plant in El Portal, California. The Park annually produces approximately 5 million tons of primary WWS and 1 million tons of FW waste, with a volatile solid ratio of 70:30 FW to WWS, or 70% FW. Diverted FW is currently sent to the Mariposa County landfill’s compost facility. To measure the possible increase in biogas production associated with FW addition to WWS, a biochemical methane potential (BMP) test was done over 35 days under mesophilic conditions with treatment mixing ratios ranging from 0% to 100% FW on a volatile solids basis. Calculated annual methane production increased 3.25 times from 0% FW scenario (WWS only) versus a 70% FW scenario, translating to a potential increase in methane production at the wastewater treatment plant of 28,000 to 91,000 m3/yr. Results showed that if the wastewater treatment plant also implemented combined heat and power to combust the increased biogas from 70% FW co-digestion, potentially 920,000 kWh/yr could be produced to cover all electricity and heating needs. This research demonstrates that Yosemite National Park could combine FW and WWS to sustainably manage their organic waste in line with their Zero Landfill Initiative, as well as produce enough energy to fully power the El Portal wastewater treatment plant.