INFLUENCE OF MASS-TRANSFER LIMITATIONS ON DETERMINATION OF THE HALF SATURATION CONSTANT FOR HYDROGEN UPTAKE IN A MIXED-CULTURE CH4-PRODUCING ENRICHMENT

There is strong evidence in the literature supporting the existence of significant mass transfer limitations on the kinetics of exogenous H-2 Consumption by methanogens. The half saturation constant for H-2 uptake by a mixed-culture, CH4-producing enrichment was measured using an experimental protocol that avoided internal mass transfer limitations. The value obtained was two orders of magnitude smaller than any other previously reported. A mathematical model for acetogenic syntrophic associations was developed to check the capacity of H-2 as electron transporter between syntrophic partners. It was found that H-2 diffusion could account for the rate of transport of electrons between the syntrophic microorganisms and that formate is not a necessary intermediate. The possibility that formate may be an intermediate in this system was not ruled out. A Monod-type kinetic equation was modified to include the observed H-2 threshold effect. This modified equation was used to predict the CH4-production rate in a batch-fed digester. The results show that the external and internal H-2 pools are kinetically coupled.