Statistical optimization of methane production from brewery spent grain: Interaction effects of temperature and substrate concentration

This study evaluated the effects of thermal pretreatment of brewery spent grain (BSG) (by autoclave 121 ?C, 1.45 atm for 30 min) on methane production (CH4). Operation temperature (31?59 ?C) and substrate concentration (8.3?19.7 g BSG.L-1) factors were investigated by Response Surface Methodology (RSM) and Central Composite Design (CCD). Values ranging from 81.1 ? 2.0 to 290.1 ? 3.5 mL CH4.g- 1 TVS were obtained according to operation temperature and substrate concentration variation. The most adverse condition for methanogenesis (81.1 ? 2.0 mL CH4.g- 1 TVS) was at 59 ?C and 14 g BSG.L-1, in which there was increase in the organic matter concentration from 173.6 ? 4.94 to 3036 ? 7.78 mg.L-1) result of a higher final concentration of volatile fatty acids (VFA, 2662.7 mg.L-1). On the other hand, the optimum condition predicted by the statistical model was at 35 ?C and 18 g BSG.L-1 (289.1 mL CH4.g- 1 TVS), which showed decrease in the organic matter concentration of 78.6% and a lower final concentration of VFA (533.2 mg.L-1). Hydrogenospora and Methanosaeta were identified in this optimum CH4 production condition, where acetoclastic methanogenic pathway prevailed. The CH4 production enhancement was concomitant to acetic acid concentration decrease (from 578.9 to 135.7 mg.L-1).

Automated summary

The study demonstrated that thermal pretreatment of brewery spent grain can enhance methane production, with the optimal condition at 35℃ and 18g BSG.L-1. Methane production, organic matter concentration, and volatile fatty acid concentration showed different variations under different conditions.