Strategies of co-cultures and bioaugmentation by Bacillus amyloliquefaciens, Clostridium bifermentans, Enterobacter muelleri, and E. tabaci for increasing the production of hydrogen from raw glycerol

Abstract

The recovery of glycerol generated by the biodiesel industry was investigated to increase hydrogen production by different strategies by Bacillus amyloliquefaciens (BA), Clostridium bifermentans (CB), Enterobacter muelleri (EM) and E. tabaci (ET) singly, in co-culture and bioaugmentation of the microbial consortium (MC) at different amounts of inoculum (1X and 2X) in batch reactors containing raw glycerol. The inoculum concentrations provided changes in metabolic bioconversion. MC + BA bioaugmentation (2X) showed higher efficiency in converting glycerol (85%) and a high H2 yield (2.21 mol H2 mol−1 glycerol). BA and ET alone (1X) showed high substrate consumption and 0.92 and 0.89 mol H2 mol−1 glycerol, respectively. The cumulative production of H2 was 24% higher for the co-culture BA + CB + ET, but the consumption of glycerol and the yield of H2 were similar to those obtained by monoculture systems. In addition, the favoring of the oxidative metabolic pathway was highlighted, with ethanol generation and reduced concentration of acetic, butyric, and propionic acid for BA, EM, and ET (1X). The bioaugmentation assays (1X) highlighted the reductive pathway with high concentrations of 1,3-propanediol. Both metabolic pathways were used in co-culture. The possibility of valuing residual glycerol in the production of H2 and by-products of economic value using bioaugmentation or isolated microorganisms may be promising.