Analysis of microbial community adaptation in mesophilic hydrogen fermentation from food waste by tagged 16S rRNA gene pyrosequencing.

Dark fermentation is an attractive process for generation of biohydrogen, which involves complex microbial processes on decomposition of organic wastes and subsequent conversion of metabolic intermediates to hydrogen. The microbes present in an upflow anaerobic sludge blanket (UASB) reactor for waste water treatment were tested for application in batch dark fermentation of food waste at varying ratios of feedstock to heat-treated microbial inoculum (F/M) of 1-8 (g TVS/g TVS). Biohydrogen yields between 0.39 and 2.68 mol H2/mol hexose were obtained, indicating that the yields were highly dependent on the starting F/M ratio. The highest H2 purity of 66% was obtained from the first 8 h of fermentation at the F/M ratio of 2, whereas the highest H2 production was obtained after 35 h of fermentation at the F/M ratio of 5. Tagged 16S rRNA gene pyrosequencing showed that the seed culture comprised largely of uncultured bacteria with various Proteobacteria, Bacteroidetes, and Firmicutes, while the starting food waste contained mainly lactic acid bacteria. Enrichment of Firmicutes, particularly Clostridia and lactic acid bacteria occurred within 8 h of the dark fermentation and the H2 producing microcosm at 35 h was dominated >80% by Clostridium spp. The major H2 producer was identified as a Clostridial strain related to Clostridium frigidicarnis. This work demonstrated the adaption of the microbial community during the dark fermentation of complex food waste and revealed the major roles of Clostridia in both substrate degradation and biohydrogen production.