Life Cycle Analysis of a Biorefinery for Activated Carbon and Biomethane Production

Abstract

A Life Cycle Analysis (LCA) based on ReCiPe 2016 model of a biorefinery case-study was performed. On the basis of an existing Portuguese Anaerobic Digestion plant, the proposed biorefinery hypothesized the use of (i) Maize Cob Waste (MCW) as co-substrate for Anaerobic co-Digestion (AcoD) with Organic Fraction Municipal Solid Waste (OFMSW), (ii) the use of MCW derived activated carbons (ACs) in a H2S removal unit, and (iii) the biogas upgrading to biomethane in a Pressure Swing Adsorption unit. The main aim was to compare the environmental benefits obtained from distinct uses of biogas, specifically the cogeneration of electricity/heat and biomethane production.Three biogas production configurations were considered: (i) AD of standalone hydrolysed OFMSW (hOFMSW); (ii) AcoD of hOFMSW and MCW pre-treated with H2O2 (hOFMSW+PreMCW); and (iii) AcoD of hOFMSW with non-pre-treated MCW (hOFMSW+MCW). The increase of biogas and methane yields obtained with AcoD of hOFMSW+MCW provided an overall better environmental performance than other configurations.The biogas upgrading to biomethane from AcoD of hOFMSW+MCW generated higher environmental impacts than cogeneration, due to the AC production and upgrading processes. If an optimised H2S adsorption capacity is considered, the Fossil Resource Scarcity, Mineral Resource Scarcity, and Global Warming human health impact categories decreased by 20%, 15%, and 17%, respectively, when compared to the base-case upgrading scenario. Further decreases of up to 52%, 23%, and 28% for those impact categories, respectively, are observed when the natural gas used in the OFMSW collection and transportation fleet is substituted by biomethane produced in the biorefinery.