A regular day at READ involves processing 20 tons of food and grease trap waste from local grocery stores and campus dining commons 鈥� waste that would otherwise end up in a landfill 鈥撎� and turning it into energy. Semi-trucks deliver food waste in plastic garbage bags, which are then separated by depackagers into an organic fraction (food) and contaminants (mostly plastic). The organics are liquified into a slurry and converted into biogas.
eHowever, this process also generates ammonia in concentrations that are too high for disposal and processing at the campus’s wastewater treatment plant, yet too low to be valuable as fertilizer. Proper disposal of this ammonia-rich digestate became costly. 鈥淲e ultimately had to pay a farmer to remove and use it,鈥� said Joe Yonkoski, UC Davis Facilities Management superintendent of thermal infrastructure and biodigester supervisor. 鈥淭his cost represented a significant portion of READ鈥檚 operating costs.鈥�
To address this challenge, Facilities Management collaborated with Harold Leverenz, PE, then a postdoctoral researcher in the UC Davis Department of Civil and Environmental Engineering. In his spare time, Dr. Leverenz conducted research in his garage with Rus Adams, PE to evaluate strategies for separating and concentrating the ammonia from waste streams, including urine, the digestate from READ and others. Research prototypes of nutrient recovery technologies were installed on campus for testing at UC Davis鈥� wastewater treatment plant. The team also founded听Advanced Environmental Methods LLC, or AEM, to explore the commercial aspects of and barriers to the implementation of nutrient recovery projects.