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). [Display omitted] •Optimization of CH4 production from brewery spent grain (BSG) were examined.•Thermally pretreated BSG (121 °C, 1.45 atm for 30 min) enhanced CH4 production.•Temperature had a more significant effect on CH4 production than BSG concentration.•Hydrogenispora is the main bacterial genera involved in BSG fermentation.•Acetoclasctic methanogenesis was the dominant pathway related on BSG degradation.