Extractive fermentation as a strategy to increase the co-production of H2 and carboxylates in dark fermentation

Ion exchange resins were used to remove carboxylates from a dark fermentation batch reactor to enhance hydrogen (H2) and carboxylate production. Three anion exchange resins were tested. The A110 resin (macroporous, primary amine functionalized) was selected as suitable for carboxylates removal due to its total exchange capacity (1.25 +/- 0.12 mmol/g) and affinity towards butyrate. The extractive fermentation system included a column packed with the A110 resin which was connected to a batch-stirred tank H2 reactor. This setup achieved 3762.9 +/- 229.1 NmL H2/L of total accumulated H2 volume, equivalent to a 15.2 % increase compared with the control experiment (3288.6 +/- 279.0 NmL H2/L). Also, the molar yields of acetate (0.81 +/- 0.11 mol/mol hexose) and butyrate (1.01 +/- 0.21 mol/mol hexose) increased by 62.7 % and 71.3 %, respectively. The extractive fermentation system could dampen the inhibitory processes by product accumulation and possibly favor a change in the metabolism of dark fermentation microbial communities that enhanced the production of butyrate and H2 from lactate and acetate. Future studies might guarantee molecular analysis of the microbial communities in extractive fermentation as well testing different extraction systems.