How San Jose found a way to turn food waste into electricity and compost

San Jose, California had opened a facility in 2013 that was designed to process 90,000 tons of organic waste annually and generate 1.6 megawatts of electricity. So instead of sending all that material to landfills, the plant used a process that produces biogas for power generation and turns the rest of the solid material into compost.

San Jose's Landmark Waste-to-Energy Initiative

The facility uses dry-fermentation anaerobic digestion, in which microorganisms break down organic matter without oxygen. The process produces methane-rich biogas that can be used to generate electricity, this gives discarded food and other organic material another way to be used.

When the plant began commercial operations, it was described as the world’s largest commercial dry-fermentation anaerobic digestion facility. Its design brought together organic waste processing, electricity generation and compost production at one site.

How the Plant Works

The facility uses 16 digesters to process food scraps and other organic material. Inside the digesters microorganisms break down the waste and produce biogas which is captured and used as fuel.

The gas powers a combined heat and power system that generates electricity for nearby recycling operations. Excess electricity can also be supplied to the grid.

The plant was designed to process up to 90,000 tons of organic waste each year, with an electricity generation capacity of 1.6 megawatts.

The process also produces solid material that is composted on-site. The resulting compost can be used as a soil amendment, allowing the facility to recover useful material as well as energy.

Advancing Toward Zero Waste

The facility was part of San Jose’s effort to divert waste from landfills through recycling, composting and other waste management methods.

The US Environmental Protection Agency (EPA), in its 2015 progress report reported that San Jose was diverting about 74% of its waste from landfills through reuse, recycling, composting and anaerobic digestion. The city’s goal at the time was to achieve zero waste by 2022.

Organic waste can produce methane when decomposes in landfills. By processing organic material and capturing the biogas generated during digestion, the San Jose facility was designed to help reduce emissions associated with landfilled food waste. It does not eliminate all methane emissions.

How the Facility Turns Leftover Waste Into Compost

The facility combines two processes to use organic waste. Anaerobic digestion produces biogas that can fuel electricity generation while composting turns the remaining solid material into a soil amendment.

The project was developed via a partnership between the City of San Jose and Zero Waste Energy Development. Its 90,000 ton annual processing capacity and 1.6 megawatt electricity generation capacity made it a notable part of the city’s waste management efforts.

Kerrie Romanow, City of San Jose Environmental Services Department Director at that time said, “As the capital of Silicon Valley, this type of leading edge project propels the City as a leader in diverting waste from landfill and converting it to usable, clean energy,” as quoted by Zero Waste.