GHG impacts of food waste AD and sludge AD: PRESENTATION ONLY
Harrison, D., and Theodoulou, M., Suez Water Technologies and Solutions
(free)
ABSTRACT
Utilizing Anaerobic Digestion (AD) for the treatment of organic materials is a widely-accepted practice, in fact, across Canada, 55% of sewage sludge in municipal wastewater treatment plants (WWTP) are treated with AD (CBA 2013). Digestion of Biosolids and Organic Waste is common practice in the UK although true co-digestion is challenged by regulation and financial support in the UK. Co-digesting food waste with sewage sludge within the existing infrastructure at WWTPs is viable technically, however, few examples exist where plant owners utilize the digester assets to their maximum efficiency. Efforts to implement co-digestion often come with a goal of achieving energy neutrality within the WWTP, however, there is another significant environmental benefit to implementing co-digestion: Greenhouse Gas (GHG) Emission reductions.
When co-digestion is implemented there are two sources of GHG emissions which can be impacted: 1) the emissions created from the generation of energy; and 2) the emissions from the landfilling of waste.
With respect to energy generation, the simplest shown impact is the offsetting of fossil fuel natural gas with renewable natural gas (RNG), which can be produced from the biogas generated in AD. To summarize the impact, utilizing the calculation guidelines in the IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2006), the reduction in GHG emissions for every m3 of fossil fuel natural gas (NG) offset by RNG is 0.002001 TCO2eq/m3 NG.
The emissions reduced from diverting waste from landfill are associated with removing material that would have broken down in the landfill, releasing methane into the atmosphere (which carries approximately a 25 times GHG factor to CO2). By diverting organic waste streams from going to landfill, and subsequently processing it, such to be suitable for AD, and then using it as a feedstock, a GHG emission reduction of up to 2.245 TCO2eq/T waste diverted. This impact is calculated based on the IPCC guidelines (IPCC Waste, 2006) for GHG emissions associated with waste management.
The positive environmental impacts need to come with economic benefits to achieve more substantial implementation of co-digestion. A number of case studies will be presented to highlight the benefits and challenges of co-digestion.
KEYWORDS
Advanced Anaerobic Digestion, Biogas, Biosolids, Co-Digestion, Energy Neutral, Hydrolysis, Sludge, Wastewater Treatment
