Kinetics of syntrophic acetogenesis in a saline medium

Background: The anaerobic degradation kinetics of volatile fatty acids (VFA) in a saline (24g NaCl dm^-3) and mesophilic (37 °C) medium was studied under batch test conditions. The acetate production kinetics without inhibition by propionic, butyric and valeric acids was determined. The inhibition of acetate production during syntrophic acetogenesis by VFA and pH was studied. The acetogenesis without inhibition was modelled using a Monod equation. The pH inhibition was represented by a Michaelis pH function, while the inhibition by acetic acid (HAc) was represented by a non-competitive model. Results: The specific maximum degradation rate and saturation constant (k_max,VFA, Ks,_max) values were (5.89, 15.95), (7.97, 25.99) and (7.75 g VFA g^-1 volatile suspended solids day^-1, 11.52 mg VFA dm^-3) for propionic, butyric and valeric acids respectively, with maximum velocity at pH 7. The inhibition constants (KI,HA_c) were 1295, 671 and 572 mg HAc dm-3 for propionic, butyric and valeric acids respectively. Conclusion: VFA and pH can be inhibitory for acetogenesis under these conditions.