Volatile fatty acids production from Brassica chinensis waste and analysis of the associated microbial community

In this study, Brassica chinensis waste (BCW) was selected as a raw material for anaerobic fermentative production of volatile fatty acids (VFA). The effects of stacking time, initial pH, inoculum dose, and temperature on VFA yield as well as the evolution of the microbial community structure were assessed. The results showed that stacking time had a significant impact on the VFA yield. When BCW was stacked for 3 days, VFA yield was highest and reached up to 187.79 mgCOD/gVS. VFA production was inhibited under both acidic and alkaline conditions. VFA/SCOD (soluble chemical oxygen demand (SCOD)) reached a maximum of 79.16% when the inoculum dose was 2 gTS/L (g total solids [TS] of the sludge/L of the BCW). At 35 °C, the concentration of ammonia nitrogen reached a maximum of 405 mg/L in a relatively short time, and the rapid decrease in SCOD demonstrated that soluble organic matter was rapidly consumed. Firmicutes were the dominant microorganisms at an abundance of 84.75%, followed by Proteobacteria at 11.32%; these are known to participate in the acid production step of hydrolysis in anaerobic fermentation. This study provides an eco-friendly strategy to use BCW to produce VFA by anaerobic fermentation.