Efficient continuous biogas production using lignocellulosic hydrolysates as substrate: A semi-pilot scale long-term study

Traditional solid-state biogas production from lignocellulosic biomass has some issues such as relatively low methane yield, instability of fermentation system, etc., and these might be solved by changing solid-state mode to completely liquid-state mode using lignocellulosic hydrolysates as substrate for biogas production. However, the potential and possibility of this new technology for industrial application is still unclear. In this study, semi-pilot scale long-term biogas production using various lignocellulosic hydrolysates (acid hydrolysates of bagasse, rice straw, and corncob) as substrate was carried out in a 100 L up-flow anaerobic bioreactor (internal circulation reactor, IC) for 76 days. During operation, biogas was generated almost immediately when the substrate was pumped into bioreactor and the start-up can be finished in short period. Throughout the fermentation process, most COD (>85%) of lignocellulosic hydrolysates was utilized for biogas production. High biogas yield (0.549 ± 0.058 m3/kg COD consumption), methane yield (0.381 ± 0.043 m3/kg COD consumption) and CH4 content in biogas (69.6 ± 5.6%) can be obtained respectively when the fermentation system was stable. Variations of inlet pH value and types of lignocellulosic hydrolysate showed little influence on the operation performance of this fermentation system. Overall, the fermentation scale, operation period, COD removal, biogas yield, CH4 content in biogas, and operation performance with various inlet pH value and different kinds of substrate shows that this technology has great potential and possibility of industrialization.