Bioenergy Potential from Food Waste in California

Food waste makes up approximately 15% of municipal solid waste generated in the United States, and 95% is ultimately landfilled. Its bioavailable carbon and nutrient content makes it a major contributor to landfill methane... [ view full abstract ]

Food waste makes up approximately 15% of municipal solid waste generated in the United States, and 95% is ultimately landfilled. Its bioavailable carbon and nutrient content makes it a major contributor to landfill methane emissions -- because food waste biodegrades more quickly than other organic waste, 34-51% of generated methane escapes typical landfill gas capture systems. First and foremost, policy measures are necessary to ensure source-reduction through changes in consumer behavior and improved harvesting, processing, and transportation methods. However, source-reduction alone will not be a sufficient strategy. Food waste that cannot be avoided presents an important opportunity for energy recovery.

This paper presents the first detailed analysis of monthly food waste generation in California at a county level, and its potential contribution to the state’s energy production. California serves as a useful starting point for building an analysis framework that can be applied to the US or globally because of its diversity and significance in national food production (40% of US vegetables, 20% of dairy, and 70% of fruits, tree nuts, and berry production by revenue). We define food waste as organic materials wasted within the food supply chain, including organic waste generated during harvest, food processing, retail, and in eating establishments and consumers’ homes. For example, this distinction includes olive pits, but excludes olive tree branches and other woody/herbaceous crop residues. To date, no other study has quantified monthly variation in feedstock supply, which is critical for high-moisture waste that cannot be stored for long periods of time. Previous studies have used combustion and anaerobic digestion to model energy production; however, this study is the first to model facility-specific excess combustion and AD capacity, technology- and feedstock-specific methane yields, and storage and transportation impacts.

We develop and analyze a set of scenarios that rely on excess capacity at existing anaerobic digester (AD) and solid biomass combustion facilities, and alternatives that allow for new facility construction. Our findings indicate that potential monthly electricity generation using a combination of AD and combustion varies from 420 to 700 MW in scenarios allowing for new infrastructure investments, with an average of 530 MW. At least 66% of gross high moisture solids and 23% of gross low moisture solids can be treated using existing local infrastructure, and this fraction increases to 99% of high moisture solids and 55% of low moisture solids if waste can be shipped anywhere within the state. These large ranges reflect the uncertainty regarding excess capacity for FW co-digestion at WWTFs and organic WtE facilities. Uncertainty in biogas flaring practices at AD facilities can also reduce potential energy production by 10 to 40%.