Impact of lignocellulosic-waste intermediates on hydrolysis and methanogenesis under thermophilic and mesophilic conditions

• Furfural, HMF, vanillin and humic acid were chosen as potential inhibitors.
• Various thermophilic and mesophilic batch tests were done during SMA and CMP tests.
• Furfural and HMF fully inhibited the SMA assays at 2.0 g/L under both conditions.
• Vanillin and humic did not inhibit the SMA assays at 2.0 g/L under both conditions.
• Propionate accumulation was found in the thermophilic CMP tests for furfural and HMF.

Intermediates of anaerobic conversion processes have been identified to inhibit methanogenic biomass and to decrease process performance. The used concentrations of model intermediates furfural, 5-hydroxymethylfurfural (HMF) and vanillin, as well as the recalcitrant humic acid were 0.4, 0.8 and 2.0 g/L. These compounds were used to determine their impact on methanogenesis by specific methanogenic activity (SMA) assays and hydrolysis by cumulative methane production (CMP) tests under thermophilic and mesophilic conditions at a concentrations of 0.8 g/L, using lignocellulosic biomass as the substrate.HMF showed inhibitory effects at a concentration of 0.8 g/L under thermophilic conditions during SMA tests. HMF and furfural completely inhibited the methanogenic activity at 2.0 g/L under both thermophilic and mesophilic conditions. The inhibitory effect was absent with vanillin and humic acid at concentrations ⩽2.0 g/L and 0.8 g/L, during SMA and CMP tests, respectively. The thermophilic microbial consortia were found to be more sensitive to increased concentrations of the intermediates than mesophilic consortia, determined by the methane production rates and quantity in CMP tests.