UC Santa Cruz

Organic materials decomposing in landfills generate methane, making landfills a major anthropogenic methane source in the United States. Methane has a warming effect approximately 86 times greater than carbon dioxide on a per-mass basis over a 20-year horizon. California has responded with Senate Bill 1383 (SB 1383), which requires a 75% reduction in organic waste disposal relative to 2014 levels. Composting is a major pathway for achieving this goal while producing a soil amendment that can improve soil properties and promote soil carbon storage. Yet California’s existing composting system processes only about 6.5 million metric tons (MMT) of organic material annually, compared with approximately 14.3 MMT that must be diverted, creating substantial spatial, regulatory, and infrastructure challenges.This dissertation develops statewide geospatial optimization frameworks integrating 447 waste-generating jurisdictions, approximately 200 existing composting facilities, more than 37,530 kilometers of agricultural working lands, and millions of transportation routes. I examine: (1) the spatial alignment of waste generation, processing capacity, and cropland compost demand; (2) the effects of alternative compliance structures on costs, emissions, and regional participation; and (3) the siting of additional composting infrastructure under economic, logistical, and airpermitting constraints. Results show that California’s organic waste diversion system is shaped by strong spatial differences in waste generation, processing capacity, transportation requirements, and compost end-use opportunities. These differences influence both the cost and greenhouse gas performance of diversion and create uneven compliance burdens across regions. More flexible statewide coordination can improve system efficiency by shifting diversion toward locations with lower marginal costs and better access to processing and end-use markets, while jurisdiction-level compliance promotes broader participation by requiring each jurisdiction to contribute directly to the diversion target. At the same time, substantial additional processing capacity will be needed to accommodate future diversion, and major infrastructure-siting barriers arise not only from water- and air-quality regulations, but also from the limited availability of VOC Emission Reduction Credits (ERCs). Overall, effective organic waste diversion requires coordinated planning of infrastructure, end-use markets, compliance, and environmental regulation, alongside expansion of existing, decentralized, and source-proximate processing options.