Top: A new ammonia distillation system installed at the UC Davis READ facility includes a large cylindrical scrubber column located between tanks (above, center). Photos by Anjie Cook, courtesy UC Davis
The University of California Davis (UC Davis) constructed a pilot-scale, on-campus food waste digester in 2002. Known as the Renewable Energy Anaerobic Digester (READ), the design was developed and patented by Ruihong Zhang, a professor in the university’s Department of Biological and Agricultural Engineering. Recently, UC Davis received a $4.77 million grant from CalRecycle to upgrade READ, which receives 20 tons/day of food waste from customers including local grocery stores and the campus dining commons. With the improvements the grant provides, “the READ facility becomes an important part of UC Davis’ strategy to eliminate the use of fossil fuels from its operations and fight climate change,” according to an article written by the university’s Finance, Operations and Administration (FAO) Communications office. Electricity generated from the biogas will feed into the campus grid and be allocated to power the campus’ electrified buses.
Food waste is tipped in an off-loading zone where it will be processed in the depackager (on left).
For many years, READ was owned and operated by CleanWorld, a digester developer that acquired the license for the technology from Zhang. In 2017, UC Davis “inherited” READ from CleanWorld. At the time, only two of the three digester tanks were in working condition. Funds from the CalRecycle grant are paying for a replacement digestion tank, enabling READ to operate at full capacity and provide redundancy in the event issues arise with the other tanks, reports the FAO Communications article. Incoming food waste is processed through a new depackager, with the slurry fed into the digester. The unit enables READ to handle more types of waste, boosting its capacity from 5,400 to 11,500 tons annually.
Another innovation being installed at the facility is an ammonia distillation system. High ammonia concentrations in the digestate prevent it from being discharged to the campus wastewater treatment plant (WWTP). The levels are too low, however, to be valuable as a fertilizer. “We ultimately had to pay a farmer to remove and use it,” said Joe Yonkoski, UC Davis Facilities Management superintendent in a separate FAO Communications article. “This cost represented a significant portion of READ’s operating costs.” The new system processes the ammonia-rich digestate, separating it into nearly ammonia-free digestate that can be processed at the campus WWTP, and concentrated ammonia, a commodity that is being purchased by California Safe Soil as an ingredient in the formulation of a certified organic fertilizer.
