Anaerobic digestion system set to be commercially available

The technology was invented at the University of California, Davis and is now licensed to Clean World Partners, a Sacramento-based start-up.

Anaerobic digestion relies on bacteria to break down biodegradable waste material in the absence of oxygen. While anaerobic digestion is not a new technology in itself, operational and material-handling limitations had prevented its commercial adoption.

Unlike most other digesters that primarily treat liquid waste, such as manure from dairy farms and municipal wastewater, the UC Davis high-rate digester technology can convert both liquid and solid waste, including food waste, yard waste, plant residues, paper and cardboard.

The researchers also sought to overcome two key barriers to the widespread use of anaerobic digesters: time and money. The new technology makes such waste-conversion systems replicable, with many components prefabricated; this reduces the time it takes to build them. For example, the Clean World Partners system at ARP went from bare ground to energy production within 90 days and cost about $2m to $3m (£1.2m to £1.8m).

The anaerobic digestion system is located at American River Packaging. It will convert 7.5 tons per day of food waste from regional food producers, including Campbell’s Soup Company, and a half ton each day of unrecyclable corrugated material from ARP into natural gas. The system will generate roughly 1,300kWh of renewable energy per day, meeting about 37 per cent of ARP’s electricity needs and preventing an estimated 2,900 tons of waste from entering landfills each year.

Ruihong Zhang, a UC Davis professor of biological and agricultural engineering, has been working on her anaerobic digester technology for the past decade, bringing it from the laboratory to the pilot stage in 2006.

‘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,’ said Zhang.