Study: Food Waste Composting Results in 39 to 84 Percent Lower Methane Emissions

A new study published in Scientific Reports examined CH₄ emissions reduction through food waste diversion.

Researchers from the University of California, Berkeley and Humboldt State University conducted a commercial-scale study of food waste composting. They discovered that this method resulted in 39 to 84 percent lower CH₄ emissions than landfilling. 

"Composting food waste presents a potential opportunity for emissions reduction, but data on whole pile, commercial-scale emissions and the associated biogeochemical drivers are lacking," researchers wrote in the report.

The study involved one windrow pile of about 15 × 4 × 2 m (length, width, height). Over a period of 80 days, the compost pile was analyzed based on state guidelines. The compost was comprised of 34.3 percent of food waste gathered from Marin County farmer’s markets and restaurant organic waste. Yard waste was used as a bulking agent.

Methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions were monitored during the composting process.

"During the initial mesophilic phase (first 3 days of composting) CH₄ emissions were low and CO₂ and N₂O emissions peaked," researchers noted. "Once the temperature exceeded 60 °C (thermophilic phase starting on day 5) CH₄ emissions increased over time up to 4.7 mg CH₄ m⁻² s⁻¹, after which they declined sharply on day 70 (during maturation phase)."

The study found that while GHG emission factors (EFs) were higher with the micrometeorological mass balance (MMB) method used during the research phase, higher resolution data was gathered. 

"Pile CH₄ emissions were higher after wetting events during the thermophilic phase of composting and at the end of the process," researchers said. "Turning served to aerate the pile and temporarily lower CH₄ emissions. Pile N₂O emissions were detected at the beginning and end of the composting process but were mostly below the method’s detection limit. The pattern in N₂O fluxes likely reflected the more optimal conditions for organic matter decomposition including lower temperatures and high substrate availability at the start of the experiment, and cool temperatures, high moisture, and low redox conditions near the end of the process."

The researchers concluded that increasing pile aeration and lowering water usage and frequency at the middle and end of the composting process has the potential to further lower methane emissions.

"We show that GHG emissions from food waste composting are lower than landfilling and suggest that future deployment of continuous measurement approaches such as the one described here can help further lower emissions and contribute to climate change mitigation," they said.