Evaluation of Green Waste Management Impacts on GHG Emissions Alternative Daily Cover Compared with Composting

Green waste is a key component of California’s solid waste stream and so is an important target for effective waste diversion. The California Integrated Waste Management Board (CIWMB) reports that about 15 million cubic yards of organics comprised largely of green waste are diverted annually in California. The diverted organics are principally used as compost and mulch in agricultural and urban green areas. In California, one of the most popular alternative waste diversion options is the use of green waste as landfill alternative daily cover (ADC). Green waste ADC reduces the need for importing clean daily cover soil and so helps conserve limited landfill volume. However when landfilled, green waste can generate methane, an important greenhouse gas (GHG), and so may be regarded as environmentally inferior to green waste composting. This study uses GHG emissions estimated from life-cycle inventory methodology to compare green waste ADC and composting alternatives. A United States Environmental Protection Agency (USEPA) based life-cycle inventory methodology was developed that considers differences in transport, material handling, green waste emissions, capture and management, energy impacts, and carbon sequestration. The ADC analysis addresses the range of conditions at landfills particular to California landfills including the extent of gas recovery, the gas collection efficiency and methane energy recovery. This study supports the reported benefits of composting but also shows that green waste ADC can actually be more beneficial in reducing GHG emissions when compared to the composting of green waste. This result indicates the importance of site-specific environmental analysis when considering organics management options. In this study, details of the life-cycle GHG inventory analyses are provided. Results of the comparison between the two green waste management options are presented. The significance and implications of this study are discussed. INTRODUCTION Since passage of California Assembly Bill 32, regulators and stakeholders alike have been engaged in an assessment of waste management practices relative to climate control, including waste management approaches for organic waste. Recognizing the statutory context of the waste management “hierarchy” and the ongoing debate on green waste ADC diversion credit, it is important to develop a technical methodology to study and address the issue. Years earlier, California Assembly Bill 939 required a 50% diversion of solid waste from landfill disposal. Green waste, as one of the key components of the waste stream, poses an attractive target for effective waste diversion. The use of green waste as ADC constitutes diversion under state law. Just over half of all California-generated solid waste is diverted by various means. As shown in Figure 1 (CIWMB, 2006), landfill ADC is a small, but important, contributor to diversion. Green waste (GW) is the major ADC component but other viable ADC materials include auto shredder fluff and wastewater biosolids.