Effect of temperature on continuous fermentative lactic acid (LA) production and bacterial community, and development of LA-producing UASB reactor

A frequently used fermentation manner in lactic acid (LA) production, batch fermentation by pure cultures, has a limited practicability: low volumetric productivity and high energy consumption. In this study, continuous LA fermentation was performed in a completely stirred tank reactor at 12 h HRT, inoculated with anaerobic digester sludge. Glucose (25 g COD/L) was used as a feedstock and temperature was increased from 35 to 60 °C. LA production significantly increased from 50 °C, which was negligible up to 45 °C, with obvious bacterial community change. At 50 and 55 °C, LA production was maximized, reaching 23 g COD/L, corresponding to 92% LA conversion efficiency. Pyrosequencing analysis showed that microbial diversity was simplified at 50–60 °C, and the sequences closely related with Bacillus coagulans became predominant, followed by Lactobacillus fermentum. An LA-producing upflow ananerobic sludge blanket reactor was successfully developed, which enhanced the productivity up to 4.8 g LA/L/h by shortening HRT to 4 h.