Biogas production, waste stabilization efficiency, and hygienization potential of a mesophilic anaerobic plug flow reactor processing swine manure and corn stover

Swine manure and corn stover are abundant agricultural wastes which contribute to greenhouse gas (GHG) emissions, nutrient runoff leading to eutrophication, and a biosafety risk with respect to improper swine manure handling. Anaerobic co-digestion (AcoD) of swine manure and corn stover can mitigate these negative impacts while producing biogas as a renewable energy source. Semi-continuous mesophilic plug flow reactor (PFR operation) was studied during a step-wise increase in organic loading rate (OLR) over the range of 0.25–4.7 kg volatile solids added (VS) m−3 d−1, which corresponded to total solids content (TS) of 1.5–9.0%. Process stability was observed at all OLR, with the highest total biogas yield and methane content of 0.674 ± 0.06 m−3 kg−1 and 62%, respectively, at 0.25 kg m−3 d−1. As OLR and TS increased, VS reduction decreased and volatile fatty acids (VFA) increased due to shorter hydraulic retention times (HRT). Hygienization potential was assayed using fecal indicator bacteria (FIB), with some groups being reduced (E. coli, fecal coliforms) and others not (Clostridia spp., fecal enterococci). Lignocellulolytic enzyme activity trended upward as OLR was increased, highlighting changes in microbial activity in response to feeding rate.