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August 26, 2020  |  Written by Kyler C. Rayden

California EPA Releases Study Indicating That Investing in Wastewater Treatment Plants’ Capacity to Process Food Waste May Save Money and the Environment

On August 25, 2020, the California Environmental Protection Agency released a new study suggesting that the state’s wastewater treatment plants (“treatment plants” or “facilities”), if operating at maximum co-digestion capacity, could process at least half of California’s landfill-bound food waste.  Such efforts could help the state meet its organic waste diversion mandate under SB 1383 and reduce CO2-equivalent by as much as 2.4 million metric tons per year.  Co-digestion is the process of adding energy-rich organic waste materials (i.e., food scraps) to anaerobic digesters to aid in the decomposition and anaerobic fermentation of the waste.  Through the co-digestion process, treatment plants may capture biogas (i.e., methane and carbon dioxide) and ethanol which may be used to produce electricity, fuel, or renewable natural gas.

There are seven wastewater treatment plants in the state that currently have, or will have by 2025, the infrastructure and processes for food waste co-digestion.  While some of these treatment plants currently have capacity to handle diverted food waste, their co-digestion capacity is limited by existing infrastructure.  According to the report, by modifying the treatment plants’ overall co-digestion capacity, these facilities could divert between 25 to 64 percent of all recoverable and digestible food waste from landfills statewide by 2030.  The estimated capital investment needed to modify these treatment plants could cost between $900 million and $1.4 billion; however, such investments could ultimately lead to an annual net benefit to the state of up to $255 million per year.  For example, the treatment plants could charge additional tipping fees, use or sell electricity generated from biogas produced in the co-digestion process, and obtain credits from the California Air Resources Board for reducing greenhouse gas emissions.

The report also provides that investments used to maximize food waste co-digestion could have major environmental benefits.  While existing co-digestion capacity may reduce up to 82,000 metric tons of CO2-equivalent greenhouse gases (GHG) per year, expanding and modifying co-digester capacity could increase that amount by almost 30 percent.  Put differently, diverting food waste from landfills to treatment plants for co-digestion could provide an estimated emissions reduction of up to approximately 2.4 metric tons of CO2- equivalent GHG per year.

Although maximizing co-digestion statewide could have economic and environmental benefits, the process of modifying the treatment plants and expanding operations, while costly, must also comply with increasingly stringent regulations governing water quality, air quality, and solids management.  For example, increasing food waste co-digestion produces increased nutrient (nitrogen) loads in discharged effluents, which treatment plants must remove to meet effluent limits set by the State Water Resources Control Board and Regional Water Quality Control Boards.  Furthermore, generating electricity via biogas combustion requires costly air pollution control equipment.  To help ease the significant costs associated with processing food waste, treatment plants may be eligible for grants and loans.

For more information, please contact Kyler Rayden at

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