Waste produced at the University of California is converted into campus energy

Built using technology developed by Ruihong Zhang, professor at the University of California, Davis, the plant converts 50 tons of organic waste to 12,000 kWh of electricity each day.

By Heitor Shimizu, in Davis

Agência FAPESP – The main thrust of the research of Ruihong Zhang, professor in the Department of Biological and Agricultural Engineering at the University of California, Davis, has been in attempting to solve two important current problems at the same time: the shortage of power and the excess of waste.

Zhang and the scientists in the group she leads are studying the use of bacteria to convert organic waste, mainly food waste, into energy. She has studied the topic for nearly 20 years in search of a solution to the problem of “how to turn as much organic waste as possible into as much renewable energy as possible.”

The research stopped being basic and became applied when, in April of this year, UC Davis opened a biodigestion plant for waste, based on Zhang’s research.

The plant was named UC Davis Renewable Energy Anaerobic Digester, or READ for short. It cost $8.5 million.

Installed in the campus’ former landfill, the READ uses a technology developed by Zhang and licensed by UC Davis to CleanWorld, a company established by former students of Zhang and UC Davis alumni. In the system, microorganisms inside large, oxygen-deprived tanks feast on the organic waste produced and stored at the campus.

The system uses a fermentation process through which bacteria devour the waste and produce methane and carbon dioxide, in other words, biogas.

The plant was designed to convert 50 tons of waste into 12,000 kWh of energy each day. In addition to producing renewable energy, the READ rids UC Davis of 20,000 tons of waste each year.

The numbers are important because they underscore an advantage in the technology developed by Zhang. The idea for using anaerobic digesters to produce energy is not new, but the difference in this case lies in its efficiency. According to the researcher, the system uses a broader variety and larger quantity of waste than traditional models.

The technology, known as High Solids Anaerobic Digestion (HSAD), is able to use a broad variety of organic waste and offer more efficient digestion with higher energy production.

“It also destroys pathogens found in the waste as a result of biofertilizer production,” said the researcher who directs the Biogas Energy Project at the UC Davis Research Center. During Zhang’s research, a pilot plant was built in 2004.

Since it is installed in a former landfill, which naturally produces a large quantity of methane, the plant also combines the biogas produced by the bacteria with the methane from the former landfill. The result is the capacity to generate 5.6 million kWh per year of clean energy.

In addition, by converting the gases into energy, the plant is expected to reduce greenhouse gas emissions by 13,500 tons per year. UC Davis will earn 100% of the green energy and carbon credits and receive all of the electricity generated.

Whatever is not turned into biogas for generating renewable energy can be used as fertilizers – READ is capable of generating close to 15 million liters per year, enough to meet the demand for an estimated 600,000 m2 of farmland.

“It’s important to point out that the biodigestion system is not just important because it produces energy or fertilizers, but also because it gives us a way to manage our solid waste. It is a technology that allows us to be more economically and environmentally sustainable,” Zhang said.