(507a) TEA and LCA of Renewable Natural Gas: Upgrading Biogas from Anaerobic Co-Digestion of Prairie Grass with Hydroxycinnamic Co-Products

Anaerobic digestion (AD) is a biological process where organic material is broken down by microorganisms to form biogas. Biogas can be burned for heat, electricity, or upgraded further using various separating technologies to form a stream composed of methane known as renewable natural gas (RNG). RNG is injected into the natural gas pipeline for general consumption. In this study, prairie grass and manure are co-digested together on a farm-site.

This study hopes to determine if hydroxycinnamic acids (HCAs) are a potential co-product for RNG. HCAs are acids derived from chemically pretreating biomass. In a previous study HCAs derived from corn stover were determined to lower the price of ethanol by $0.26/L. A previous laboratory study created a process of pretreating prairie grass in a KOH solution. The biomass co-digested with manure was found to increase the amount of methane within the biogas stream.

This study utilizes a techno-economic analysis (TEA) to determine if HCAs are a viable co-product for RNG. This process model was created in BioSTEAM to determine a minimum fuel selling price (MFSP) of RNG with HCAs as a co-product. A life cycle assessment (LCA) was also completed in openLCA to determine the effects this process has on the environment. Sensitivity and uncertainty analyses were also considered to find the MFSP and greenhouse gas (GHG) emissions of RNG under different process adaptations.