Engineered heat treated methanogenic granules: A promising biotechnological approach for extreme thermophilic biohydrogen production

In the present study, two granular systems were compared in terms of hydrogen production rate, stability and bacterial diversity under extreme thermophilic conditions (70 °C). Two EGSB reactors were individually inoculated with heat treated methanogenic granules (HTG) and HTG amended with enrichment culture with high capacity of hydrogen production (engineered heat treated methanogenic granules – EHTG), respectively. The reactor inoculated with EHTG (REHTG) attained a maximum production rate of 2.7 l H2 l−1day−1 in steady state. In comparison, the RHTG containing the HTG granules was very unstable, with low hydrogen productions and only two peaks of hydrogen (0.8 and 1.5 l H2 l−1day−1). The presence of active hydrogen producers in the REHTG system during the reactor start-up resulted in the development of an efficient H2-producing bacterial community. The results showed that “engineered inocula” where known hydrogen producers are co-inoculated with HTG is an efficient way to start up biohydrogen-producing reactors.