An analysis of single and two stage, mesophilic and thermophilic high rate systems for anaerobic digestion of corn stalk

The feasibility of corn stalk anaerobic digestion was investigated in an upflow anaerobic solid-state (UASS) reactor with an additional anaerobic filter (AF) reactor. One single-stage (UASS) and two two-stage systems (UASS + AF) were compared at organic loading rates (OLR) of 2.5, 4.5, and 8.0 gvs L−1 d−1. The single-stage system was operated under mesophilic conditions and the two-stage systems under both mesophilic and thermophilic conditions. Independently of OLR, the mesophilic two-stage system showed higher average methane production rates (0.50 ± 0.01, 0.63 ± 0.11, and 0.67 ± 0.12 LCH4L-1d-1) than the single-stage (0.46 ± 0.02, 0.46 ± 0.06, and 0.31 ± 0.09 LCH4L-1d-1) and thermophilic two-stage (0.30 ± 0.02, 0.42 ± 0.05, and 0.66 ± 0.12 LCH4L-1d-1) systems. Respective methane yields were 84-201, 39-184, and 88-119 mL gvs−1. The observed advantage of mesophilic digestion is of particular interest, as degradation of lignocellulosic biomass is usually reported to benefit from higher temperature. The results show the general feasibility of an additional AF reactor after the UASS digestion of corn stalk under mesophilic conditions.