Achieving Wastewater Energy Recovery and Methane Abatement for the San Francisco Bay Area

California Senate Bill 1383’s directive to reduce landfilled organic waste has prompted San Francisco Bay Area municipalities to divert food waste to wastewater treatment plants for biogas production via anaerobic digestion. However, unquantified fugitive methane emissions from digester leaks could negate the net climate benefits of this policy. This thesis assesses the net greenhouse gas reductions of food waste co-digestion once empirical biogas leakage, energy displacement, and avoided landfill emissions are accounted for. Using leakage rates measured at Bay Area digesters, it finds that co-digestion with energy recovery reduces emissions relative to landfilling at or below median observed leakage but becomes a larger net source than even flared landfill gas once leakage reaches the upper range of observed facilities. Directing food waste to digestion without leakage control can therefore worsen climate outcomes. This thesis also evaluates the economics of implementing continuous leak detection and repair technologies at wastewater treatment plants, finding that recovering leaked methane is financially viable for many Bay Area facilities, particularly facilities upgrading biogas to renewable natural gas, where stacked state and federal incentives roughly double the value of recovered gas. Critically, these same incentives reward biogas production on default emissions assumptions without requiring leakage below climate-benefit thresholds, favoring throughput expansion over leakage control. This analysis motivates two policy recommendations to ensure California’s methane reduction targets are actualized: (1) that state agencies transition to performance-based carbon intensity scores in issuing compliance credits and grant awards, and (2) that the Bay Area Air District implement a comprehensive leak detection and repair program covering wastewater facilities, anchored by empirical emissions measurements.