Roughly one-third of food produced for human consumption is wasted, according to a report requested by the United Nations. That amounts to about 1.3 billion tons per year. UC Davis scientist Ruihong Zhang hopes to put a dent in this appalling statistic with her system for converting food waste (along with plant residues, yard waste and paper products) into usable energy.
Zhang’s system relies on anaerobic digestion. In the absence of oxygen, naturally occurring microorganisms, bacteria and methanogens break down biodegradable materials and convert them to biogas and fertilizer. The biogas can power homes and businesses, and the fertilizer can provide nutrients to gardens and crops. With a unique two-stage process, her anaerobic phased solids system is capable of handling higher percentages of solid waste than other models. Multiple sequentially loaded batch dispensers make up the first stage, and a high-rate biofilms digester follows. The two-stage model ensures high system stability, even gas production, and rapid hydrolysis.
Research on the system began a decade ago, but the real test came when Zhang put the technology into action during a pilot project the at the UC Davis campus. The anaerobic phased digester system was operational for 10 consecutive months with successful results.
In April, the first commercial application was unveiled by Clean World Partners, a Sacramento-based startup that licensed the technology. The biodigester is operational at American River Packaging, and it will convert 7.5 tons of food waste and 5 tons of unrecyclable corrugated material into natural gas daily, creating 1,300 kilowatt-hours of renewable energy each day.
“This kind of project and technology is actually changing how societies treat and view waste as a resource, which, overall, leads to a better world, a cleaner environment and new jobs,” said Zhang.
Anaerobic digestion captures 100 percent of the harmful greenhouse gases that would have otherwise seeped into the environment during the breakdown of organic waste. If hospitals, schools, and other businesses catch on, landfill volumes could be reduced while producing renewable energy at the same time. Zhang’s system is likely to appeal to investors due to its improved design—it takes half the time that other digesters would use, and many components are prefabricated, reducing cost and build time.
“I applaud Professor Zhang for this tremendous accomplishment,” said UC Davis Chancellor Linda P.B. Katehi. “Scientists like Professor Zhang are helping UC Davis address the most pressing global problems of our time. Her work brings us a giant step closer to the sustainable future we all hope for.”
Funding for Zhang’s biodigester research came from the Department of Energy’s Community Renewable Energy Development project, the California Energy Commission’s Public Interest Energy Research program, and CalRecycle.
Anaerobic digestion facilities are cropping up in other U.S. states such as Massachusetts and Oregon. Northern Ireland is taking advantage of similar systems, and the United Kingdom recently introduced a feed-in-tariff system to encourage installation of anaerobic digestion technology.