Evaluating the environmental impacts of pretreatment and nanoparticles in solid-state anaerobic digestion using life cycle assessment

Abstract

Abstract The yield of green energy from solid-state anaerobic co-digestion (SSAD) has recently been enhanced by incorporating innovative pretreatment methods and nanoparticles. However, the environmental consequences of employing new processes have not been fully examined. In this study, the environmental impacts of three high-methane-yielding scenarios including SSAD of corn stover blended with dairy manure (DM) denoted as (SYM1), calcium hydroxide-pretreated corn stover (CpCS) blended with DM (SYM2), and the CpCS blended with DM and nanoparticles (SYM3) were assessed and compared the baselines of solid state and semi-solid-state anaerobic digestion using a life cycle assessment (LCA) approach. The approach investigated the best management practices that would result in high methane yield and low environmental impact. Results of the life cycle assessment indicates the inclusion of calcium hydroxide and nanoparticle has minimal negative environmental impact. There was an environmental gain in GWP when corn stover was co-digestion with DM (SYM1) relative to DM mono-digestions (baselines) and the carbon footprint of SYM1 was less by more than 85% compared to SYM2 and SYM3. However, the large volume of untreated corn stover harnessed for SYM1 scenario resulted in over 75% fossil fuel depletion compared to the other scenarios. The surplus methane from the SYM3 (at least 2-fold of other scenarios and baselines) in conjunction with being the least with the environmental implication, makes the scenario the most attractive option for on-farm practice capable of harnessing the growing organic waste volume.