Effects of pH and temperature on products and bacterial community in l-lactate batch fermentation of garbage under unsterile condition

Acidogenesis fermentation of artificial garbage without sterile condition was conducted in batch mode to investigate effects of cultivation pH (5.5, 6.0, 6.5) and temperature (45, 50, 55 °C). Bacteria exiting natively in the garbage were utilized in this study; in turn, no specific seed was inoculated. The results indicated that only one set of operational conditions (pH 5.5 and 55 °C) led to l-lactate fermentation. Obtained yield of lactate based on initial carbohydrate was around 0.5 and optical purity of l-lactate was around 99%. In this study, three typical cases, which were l-lactate, racemic lactate and butyrate fermentation, were observed depended on sets of cultivation pH and temperature. Microbial structures of typical cases were also identified with using 16S rDNA libraries. The analysis indicated that Bacillus coagulans produced l-lactate. Lactobacillus amylolyticus, which produces racemic lactate, and Clostridium thermopalmarium, which produces butyrate, were also detected on each typical sample. L. amylolyticus and C. thermopalmarium would be eliminated by setting cultivation temperature of 55 °C and above, and pH 5.5 and below, respectively. From a series of this study, operational conditions of pH 5.5 and temperature of 55 °C would be potentially suitable for l-lactate fermentation of garbage with view of efficiency and stability of its production.