Improving anaerobic digestion of lignocellulosic hydrolysate derived from hydrothermal pretreatment via applied voltages

Anaerobic digestion (AD) is an effective means to convert biomass hydrolysate to biomethane for bioenergy utilization. However, byproducts such as furfural and 5-hydroxymethylfurfural may be generated from soluble sugars during the hydrothermal pretreatment of lignocellulosic biomass, potentially inhibiting subsequent AD. Emerging electro-anaerobic digestion technology may be effective in releasing the inhibition. In this study, various voltages (0.3-1.2 V) were applied for the first time in the AD of lignocellulose hydrolysate. The results revealed that maximum chemical oxygen demand (COD) removal efficiency of 95.5 % occurred at 0.9 V, outperforming the voltage absence control by 22.5 %. Meanwhile, the most significant methane yield (336.9 NmL/g COD) and energy yield (12.1 kJ/g COD) were also achieved at 0.9 V, exceeding the control by 60.1 %. At 0.3, 0.6, and 1.2 V, AD performance outperformed that of the voltage absence, although it was not optimal due to either inadequate potential drive or excess-voltage suppression. The imposed voltage stimulated the growth of biofilm and tryptophan and humic acid secretion, enhancing the electrochemical activity. The more functionally selective electroactive bacteria Petrimonas and Sedimentobacter and archaebacteria Methanosarcina and Methanomassiliicoccus were significantly enriched under applied voltages. Efficient reciprocal metabolism among electroactive microorganisms was promoted to diversify methane production pathways.