The hydraulic retention time influences the abundance of Enterobacter, Clostridium and Lactobacillus during the hydrogen production from food waste.

The influence of hydraulic retention time (HRT) on the microbial communities was evaluated in an anaerobic sequencing batch reactor (AnSBR) using organic waste from a restaurant as the substrate. The relationship among Lactobacillus, Clostridium and Bacillus as key micro-organisms on hydrogen production from organic solid waste was studied. The effect of the HRT (8-48 h) on the hydrogen production and the microbial community was evaluated. Quantitative PCR was applied to determine the abundance of bacteria (in particular, Enterobacter, Clostridium and Lactobacillus genera). An AnSBR fermentative reactor was operated for 111 cycles, with carbohydrate and organic matter removal efficiencies of 80 ± 15·42% and 22·1 ± 4·49% respectively. The highest percentage of hydrogen in the biogas (23·2 ± 11·1 %), and the specific production rate (0·42 ± 0·16 mmol H gVS d ) were obtained at an HRT of 48 h. The decrease in the HRT generated an increase in the hydrogen production rate but decreasing the content of the hydrogen in the gas. HRT significantly influence the abundance of Enterobacter, Clostridium and Lactobacillus during the hydrogen production from food waste leading the hydrogen production as well as the metabolic pathways. The microbial analysis revealed a direct relationship between the HRT and the presence of fermentative bacteria (Enterobacter, Clostridium and Lactobacillus genera). Clostridium sp. predominated at an HRT of 48 h, while Enterobacter and Lactobacillus predominated at HRTs between 8 and 24 h. SIGNIFICANCE AND IMPACT OF THE STUDY: Significance and Impact of the Study: It was demonstrated that hydrogen production using food waste was influenced by the hydraulic retention time (HRT), and closely related to changes in microbial communities together with differences in metabolic patterns (e.g. volatile fatty acids, lactate, etc.). The decrease in the HRT led to the dominance of lactic acid bacteria within the microbial community whereas the increase in HRT favoured the emergence of Clostridium bacteria and the increase in acetic and butyric acids. Statistical data analysis revealed a direct relationship existing between the HRT and the microbial community composition in fermentative bacteria. This study provides new insight into the relationship between the bioprocess operation and the microbial community to understand better and control the biohydrogen production.