Semi-continuous l-lactate fermentation of garbage without sterile condition and analysis of the microbial structure

Abstract

In order to develop a simple l-lactate fermentation of organic wastes, acidogenic fermentation was investigated in semi-continuous culture at 55 °C with using unsterilized artificial garbage as feedstock. And, sludge from a thermophilic acidification reactor was inoculated at the start of the fermentation. The effects of pH and hydraulic retention time (HRT) on performance of l-lactate production were discussed in a series of operational conditions with regard to long-term stability. The best operational conditions for l-lactate fermentation are proposed to be 55 °C, pH 6 and HRT of 10 days to get the highest yield of lactate based on initial carbohydrate in the feedstock. The yield of 0.74 and produced l-lactate optical purity of 96.7% were obtained on these operational conditions. Another l-lactate fermentation, which were semi-continuous and batch mode operations, were conducted to present reproducibility of the fermentation. Microbial structures in the semi-continuous fermentations were analyzed with using 16S rDNA libraries, and Bacillus coagulans was shown to be the most predominant species in the l-lactate fermented cultural broth.