Long-term medium chain carboxylic acids production from liquor-making wastewater: Parameters optimization and toxicity mitigation

Medium chain carboxylic acids (MCCAs) production from waste biomass by an emerging open culture chain elongation (CE) technology is a sustainable and affordable approach for future production of renewable bioenergy. However, the toxicity of undissociated MCCAs limits MCCAs production and the stable operation of CE reactor. By utilizing expanded granular sludge bed (EGSB) as a CE reactor and Chinese liquor-making wastewater (CLMW) as feedstock, this study obtained currently highest MCCAs production rate (31.12 g COD/(L·d)) from real waste biomass with a MCCAs yield of 76.80%, and achieved a long-term and stable MCCAs production (485 days). The stable MCCAs production could be primarily attributed to the mitigation of toxic effects of undissociated MCCAs on CE bacteria due to the special structure of granule sludge. In addition, the high cell density and quick mass transfer efficiency of EGSB, the optimized operating parameters, and the efficiently shaped microbiome dominated by CE functional bacteria also contributed to the high MCCAs production. This work showed a potential for MCCAs production from CLMW and lay a foundation for scaling up MCCAs production by EGSB reactor.