Influence of acidogenic headspace pressure on methane production under schematic of diversion of acidogenic off-gas to methanogenic reactor

•Maintaining headspace pressure at ∼3-6 psi enhanced hydrolysis and acidogenesis.•Headspace pressure of 3.3 psi enhanced the production of COD and soluble products.•Mixed acid fermentation prevailed in all treatments with the dominance of butyrate.•Headspace pressure of 3.3 psi enhanced the production of CH4 up to 31%.

This study investigated the effects of 12.6 psi (T1), 6.3 psi (T2), 3.3 psi (T3) and ambient (T4) headspace pressure on the metabolic pathways in the acidogenic leach bed reactor (LBR) and overall methane recovery during two-phase anaerobic digestion of food waste. Diversion of biogas from LBR enhanced COD and soluble product generation in T2, T3 and T4 whereas, high pressure (T1) resulted in comparatively higher lactate production and low protein degradation. A pressure of 3-6 psi (T2 and T3) improved the production of COD by ∼22-36%, soluble products by ∼9-43%, volatile solid reduction by ∼14-19%, and CH4 production by ∼10-31% compared with control. Besides, ∼3-6 psi headspace pressure positively influenced the composition of soluble products resulting in enhanced methane recovery adding advantage to the two-phase system. A headspace pressure of ∼3-6 psi is recommended to enhance the hydrolysis-acidogenesis; however, the actual hydrogen concentration should be considered.