The laboratory-scale horizontal acidogenic bioreactor was conducted in semi-anaerobic and strict anaerobic conditions using Napier grass (Pennisetum purpureum) as the sole substrate to determine the effects of micro-aeration on organic acids yield. During semi-anaerobic condition, total volatile fatty acids (VFAs) yield was significantly higher (α=0.05) i.e. 3,524±191, and 2,831±89 mg/L for the micro-aerated, and anaerobic conditions, respectively. The biomethane production was effectively suppressed during micro-aeration as a result of methanogenesis inhibition by the controlled oxygenation. Improved hydrolysis by facultative organisms was evidenced by the elevated soluble chemical oxygen demand concentration which was readily available for organic acid production. Hemicellulose in the biomass was efficiently degraded at 10.0% during micro-aerated period, while other constituents i.e. cellulose and lignin remained in the digestate. Potential use of these co-products of VFA-rich liquor and pretreated solid digestate for higher biofuels or valuable biochemical compounds was discussed in the context of the bio-circulargreen economy model.
