Greenhouse gas balance for composting operations

Area of Science:

• Environmental Science
• Waste Management
• Climate Change Mitigation

Background:

• Composting is a biological process for organic waste decomposition.
• Landfilling and anaerobic lagoons are major sources of methane (CH4), a potent greenhouse gas (GHG).
• Evaluating the net GHG impact of composting requires assessing both avoided emissions and process emissions.

Purpose of the Study:

• To evaluate the greenhouse gas (GHG) impact of composting various feedstocks.
• To quantify methane (CH4) avoidance through composting compared to landfilling or lagooning.
• To assess GHG emissions generated during the composting process itself.

Main Methods:

• Literature review focusing on methane avoidance and composting emissions.
• Calculation of methane generation potential based on volatile solids and destruction rates.
• Analysis of GHG emissions from energy use and biological activity during composting.

Main Results:

• Significant GHG (CO2 equivalent) credits are achieved by diverting organic waste from anaerobic environments.
• Composting an equal mix of manure, newsprint, and food waste can conserve ~3.1 Mg CO2 per dry Mg feedstock.
• GHG emissions during composting are highest for high-nitrogen, high-moisture materials but are minor compared to avoidance benefits.

Conclusions:

• Composting provides substantial GHG avoidance, primarily through methane reduction.
• Process emissions from composting are manageable and can be minimized with optimized feedstock mixtures.
• End-use applications of compost may offer additional carbon credits, requiring project-specific quantification.