Food Waste Co-Digestion Capacity Study

In 2016, California passed Senate Bill 1383 (SB 1383), an aggressive environmental policy that establishes specific targets and timelines to divert organic waste (particularly food waste) away from landfills and, thus, reduce statewide emissions of methane, a short-lived but powerful climate pollutant that is approximately 25 times more powerful than carbon dioxide (CO₂) in its warming effect on the atmosphere over a 100-year horizon.

More specifically, SB 1383 set these two primary targets:

• Divert 75 percent of organics away from landfills by 2025 (relative to 2014 levels).
• Reduce methane levels by 40 percent by 2030 (relative to 2013 levels).

Carollo Engineers and the California State Water Resources Control Board recognized that the wastewater sector has a unique opportunity to support SB 1383’s objectives through co-digestion and biogas utilization. Thus, in 2019, Carollo Engineers prepared a USEPA-funded study to project per-capita food waste in 2030 and analyze whether or not municipal water resource recovery facilities (WRRFs) in California have the capacity to co-digest these quantities as well as dewater resulting biosolids and beneficially use the additional biogas. The projections considered population growth by county and a 10 percent decrease in per-capita waste generation, on-trend with consumer behaviors since 1999.

The resulting report, Co-Digestion Capacity in California, found that up to 3.41 million short wet tons (MSWT) of food waste in 2030 is estimated to be recoverable and co-digestible at WRRFs through source-separated organics and the extraction of organics from municipal solid waste. This translates to a state-wide reduction in greenhouse gas emissions by as much as 2.4 million metric tons of CO₂-equivalent (MTCO2e) per year if the resulting biogas is used for renewable natural gas (RNG) vehicle fuel production. Also, depending on utility agreements, co-digesting the estimated 3.41 MSWT of food waste in 2030 can earn the state up to $393 million per year in new revenue streams if half of the resulting biogas is used for electricity production and the other half is used for RNG vehicle fuel production.

The report continues on to detail the ancillary processes required to accommodate co-digestion at California WRRFs, the investments required to expand those processes’ capacities to match those of existing digesters, and key factors that WRRFs must weigh out when determining if co-digestion is a technically and economically feasible option for them. Such factors include the ebbing and flowing value of revenue sources; state and local regulations on air, biogas, biosolids, and nutrient limits in plant effluent; and comprehensive planning and feasibility studies.

Click here to read the report.