Feasibility of enriched mixed cultures obtained by repeated batch transfer in continuous hydrogen fermentation

This research investigated the suitability of enriched mixed cultures (EMC) for anaerobic hydrogen fermentation in continuous operation. EMC was prepared after four successive transfers in PYG (peptone, yeast extract and galactose) medium in batch cultivation. The peak hydrogen production rate (HPR) and hydrogen yield (HY) of 770 ± 10 mL H₂/L-d and 1.05 ± 0.06 mol H₂/mol galactose_added, were attained respectively. There forward a continuously stirred tank reactor (CSTR) has been operated with the substrate concentration of 15 g/L at a hydraulic retention time (HRT) of 12 h for more than 15 days by using EMC. The performance showed that HPR and HY were fluctuated significantly during the operation and the average values were 1710 ± 250 mL H₂/L-d and 0.82 ± 0.12 mol H₂/mol galactose_added, respectively. The soluble metabolic products analysis revealed that butyrate, lactate and acetate were the dominant metabolic products with less quantity of propionic and formic acids. The microbial community structure has been determined by next generation DNA sequencing technique and revealed Clostridium sp. was the dominant microbial consortium during repeated batch transfer, whereas Sporolactobacillus sp. was the major population in continuous operation. This study demonstrates that operational mode (batch and continuous) significantly influence the microbial diversity and hydrogen production, and EMC obtained by repeated process may not be suitable for continuous hydrogen fermentation.