Effect of nanobubble water on anaerobic methane production from lignin

Lignocellulosic biomass is abundant in the environment, which can be used as the substrate for methane production via anaerobic digestion (AD). However, the methane production efficiency from lignocellulosic biomass is relatively low, mainly due to its refractory components, of which lignin is the major barrier to bioconversion and also resists the hydrolysis of lignocellulose, thus limiting the AD process. This study compared the effects of two different gases (N(2)and CO2) nanobubble water (NBW) on methane production from lignin using mono-digestion and co-digestion with acetic acid (HAc) at four different total organic carbon (TOC) ratios of HAc to lignin (97.5%:2.5%, 95%:5%, 90%:10%, and 80%:20%). Results show that N-2-NBW is the promising NBW which can enhance methane production by 22% compared to the control. In addition, co-digestion of lignin with acetic acid reflects a higher methane production potential in comparison with the mono-digestion of lignin, achieving a much higher methane production (824-1061 mL CH4/g-TOCremoved) when lignin content was less than 20% (TOC basis) and the highest lignin reduction (43%) at the TOC ratio of HAc to lignin of 95%:5%.