Dark and acidic conditions for fermentative hydrogen production

Bacterial consortium capable of producing hydrogen in low pH (LpH) range of 3.3-4.3 is reported in this study. This operational pH is two full units below that of previously reported hydrogen producing organisms. Low pH inocula were derived from a batch biohydrogen reactor inoculated with heat treated compost (∼120 °C, 2 h), which was allowed to accumulate biogas to reach three atmospheres of equivalent headspace pressure and system pH of 3.0. Acclimation effect had positive influence on H₂ production and LpH inocula were passed sequentially into more than 15 generations to achieve consistent conversion efficiency and hydrogen composition, further tested in 23 other culture cycles. With hydrogen composition in the headspace ranging from 50% to 60%, conversion efficiency of ∼43% achieved in LpH systems is comparable to that of other buffered systems. Feasibility of hydrogen production in LpH systems is demonstrated in unbuffered reactors under intermittent pressure release conditions and in absence of initial pH adjustment and stirring. Conversion efficiencies, however, decreased by ∼1-fold for each 3 °C drop below the optimum temperature of 22 °C.