Effects of yeast inoculation methods on caproic acid production and microbial community during anaerobic fermentation of Chinese cabbage waste

To provide a sufficient supply of electron donors for the synthesis of caproic acid, yeast fermentation was employed to increase ethanol production in the anaerobic fermentation of Chinese cabbage waste (CCW). The results showed that the caproic acid yield of CCW with ethanol pre-fermentation was 7750.3 mg COD/L, accounting for 50.2% of the total volatile fatty acids (TVFAs), which was 32.5% higher than that of the CCW without yeast inoculation. The synchronous fermentation of yeast and seed sludge significantly promoted the growth of butyric acid consuming bacterium Bacteroides, resulting in low yields of butyric acid and caproic acid. With yeast inoculation, substrate competition for the efficient ethanol conversion in the early stage of acidogenic fermentation inhibited the hydrolysis and acidfication. Without yeast inoculation, the rapid accumulation of TVFAs severely inhibited the growth of Bacteroidetes. In the reactor with ethanol pre-fermentation, the key microorganism for caproic acid production, Clostridium_sensu_stricto_12, was selectively enriched.