Improved biogas production from tobacco processing waste via biochar-assisted thermophilic anaerobic digestion

Tobacco processing generates large amounts of waste, which can potentially serve as feedstock for the biogas production by anaerobic digestion (AD) technology. In this study, the thermophilic AD of flue-cured tobacco leaf waste with a high solid content was conducted, and the effects of biochar on biogas production at different organic loads were evaluated. The fermentation performance and microbial community with biochar addition (BAT) and without biochar addition (WBA) were thoroughly compared to explore the biochar-mediated enhancement mechanisms. Biochar addition enhanced methane production by 1.12–1.20 fold at the tested organic loads. Fermenting a low organic load (seed sludge/feedstock ratio: 2.0) in the BAT had the highest methane yield (120.4 mL/g-volatile total solids). Biochar addition significantly shortened the lag period of methane production and increased the methane production rate with an increasing organic load. The cellulolytic and fermentative bacterial genus Hydrogenispora, polysaccharide-degrading and syntrophic acetate-oxidizing bacterial genus norank_o_MBA03, and hydrogenotrophic methanogens were crucial for thermophilic flue-cured tobacco leaf digestion. Biogas production was enhanced by Hydrogenispora and Methanoculleus enrichment. These results demonstrate effective methane production from flue-cured tobacco leaves via biochar-assisted thermophilic fermentation with a high solid content and provide a useful reference for tobacco waste treatment.