Use of nanobubble water bioaugmented anaerobically digested sludge for high-efficacy energy production from high-solids anaerobic digestion of corn straw

An increasing attention has been paid to the secure and sustainable management of agricultural wastes, especially lignocellulosic biomass. Nanobubble water (NBW) contains 10⁶–10⁸ bubbles/mL with diameter <1000 nm. Although previous studies have examined the enhancement effects of NBW on methane production from organic solid wastes, the NBW-based anaerobic digestion (AD) system is still restrained from practical application due to the large increase in AD reactor volume, generation of wastewater, and increase in energy consumption as well. In this study, NBW bioaugmentation of anaerobically digested sludge for the first time was performed for high-solids AD of corn straw. Results show that cellulase, xylanases and lignin peroxidase activities were increased by 2–55% during the NBW bioaugmentation process. Significant enrichment of hydrolytic/acidogenic bacteria and methanogenic archaea were noticed in the NBW bioaugmented sludge. This study clearly demonstrated 47% increase in methane production from high-solids AD of corn straw when O₂-NBW bioaugmented sludge was applied, achieving a net energy gain of 5138 MJ/t-volatile solids of corn straw with an energy recovery of 34%. The NBW-based high-solids AD system can provide a novel and sustainable management solution for renewable energy production from agricultural wastes, targeting the reduction of environmental pollution and energy crisis.