Evaluation of the continuous methane production from an enzymatic agave bagasse hydrolysate in suspended (CSTR) and granular biomass systems (UASB)

Abstract

Methane production from an enzymatic agave bagasse hydrolysate was evaluated in a continuous stirred tank reactor (CSTR) and in an upflow anaerobic sludge blanket reactor (UASB). The effect of different organic loading rates (OLRs) and hydraulic retention times (HRTs) on volumetric methane production rate (VMPR) was tested. To hydrolyze the bagasse, Cellulase 50XL, a food-grade enzyme, allowed a saccharification yield of lignocellulosic biomass similar to Celluclast 1.5L, which is used to treat lignocellulosic substrates. The UASB reactor operated at larger OLR (e.g., 20 g CODs/L-d) and shorter HRT (e.g., 30 h) than the CSTR (e.g., OLR of 7.3 g CODs/L-d and HRT of 66 h). The UASB achieved a VMPR of 4.5 ± 0.1 L CH4/L-d and COD removal of 94% while the CSTR had a VMPR of 1.92 ± 0.03 L CH4/L-d and COD removal of 88%. The better performance of the UASB than the CSTR can be explained by the high solid retention time (SRT) and the microbial community composition, which was less diverse than the CSTR’s community. Hydrogenotrophic methanogens were abundant in the UASB while acetoclastic methanogens dominated in the CSTR. The high VMPR obtained by the UASB reactor and the use of Cellulase 50XL can be advantageous features for future industrial application.