Some experiments and conclusions about the influence of pure H2 gas on the anaerobic degradation of propionate by mixed cultures

Abstract

Reaction enthalpy for propionate degradation ΔG0 is only negative when the partial pressure of hydrogen pH2 is less than 10-4 bar. This means that for pH2 more than 10-4 bar, a total anaerobic degradation of propionate is impossible for thermodynamic reasons. Therefore, with increasing pH2, the anaerobic degradation rate of propionate via acetate is inhibited. There are two ways to investigate the inhibitory effect of pH2: to keep the concentration of hydrogen consuming bacteria low or to increase the mass transfer by feeding the hydrogen at higher flow rates. The author used an extended fixed bed reactor filled with polyurethane particles as a carrier for the bacteria, aerated with pure H2 gas. The results, compared with the literature by using model equations in order to standardize the data, correspond well: The addition of pure H2 gas has no observable effects on propionate degradation. In the fixed bed reactor with immobilized bacteria, it was not possible to reach an inhibitory concentration of H2 and high process stability could be maintained.