A Combination of Mechanical, Chemical, and Thermal Pretreatments of Agricultural Feedstocks Enhances Biomethane Yields in Advanced Anaerobic Digestion

Abstract Multi-step advanced anaerobic digestion (AAD) pretreatment of feedstocks increases biogas yields compared to non-pretreated feedstocks, and is key to the processing of recalcitrant lignocellulosic feedstock to make commercial biogas production more economically viable. Here, we present several low energy and eco-friendly pretreatments to commercially relevant lignocellulosic feedstocks (rye and maize), to increase biomethane yields. In this study, the impact of two heating treatments, 55 °C and at 80 °C, the addition of a bio-organic catalyst (BOC), and mechanical particle size reduction by cavitation were investigated. For both feedstocks, thermal pretreatment significantly increased both solubility and enhanced biogas yield (8.6–136.6%), with maize responding better to a temperature of 55 °C (136.6% increase) and rye to 80 °C (62% increase). The BOC addition enhanced the rye yield (14%) but decreased from maize (4%), and cavitation enhanced the biochemical methane potential (BMP) of rye (38.7%) but had an inhibitory effect on maize (10.6%). The results of this multi-process study demonstrate the efficacy of low energy pretreatments for lignocellulosic material that can be applied to existing AD plants.