From Landfill to Carbon Credits: Evaluating the Life Cycle Carbon Intensity of Renewable Natural Gas (RNG) Production via Anaerobic Digestion

Abstract

Using anaerobic digestion (AD) to produce renewable natural gas (RNG) from organic waste (OW) is a hybrid solution that reduces landfilling quantities while generating energy. The federal government of Canada recently introduced Clean Fuel Regulation (CFR) and a carbon credit market as an incentive for decarbonization. Hence, RNG production not only gains revenue from its sales but enables it to gain carbon credit. So far, no studies focused on the carbon credit and RNG revenue under the CFR in the Canadian context. This study considered AD of different feedstock types in Southwestern Ontario (SWO) region and conducted life cycle CI assessment studies complying with CFR. OW from the greenhouse sector (GHW) and distillation operations (wet cake – WC) were identified as a significant source in the region. Life cycle CI assessment was conducted for GHW, WC, dairy manure (DM), sewage sludge (SS), and source-separated organics (SSO). The potential carbon credit and RNG generation for each feedstock type were calculated. SSO was estimated to provide the highest RNG sales revenue (85 CAD/t) followed by WC (72 CAD/t) and GHW (32 CAD/t). Based on the carbon credit revenue, SSO (93 CAD/t) was also ranked first while WC (20 CAD/t) was the second worst due to its high CI value. Tipping fee revenue and the feedstock prices were also incorporated when calculating the net revenue. The study provides a framework that can allow RNG production facilities in Canada for regional planning of feedstock selection to maximize revenue generation considering both life cycle CI and RNG yield under Canadian Clean Fuel Regulation (CFR). The identified carbon credit revenue can also facilitate RNG facilities to balance revenue generation with more sustainable practices to reduce their overall CI while achieving Canada’s climate goals.

Keywords: Organic waste management, Anaerobic digestion, Renewable natural gas, Clean fuel regulations, Carbon credits