Anaerobic acidogenesis of a complex wastewater: II. Kinetics of growth, inhibition, and product formation.

The kinetics of the acidogenic phase of anaerobic digestion were studied in continuous culture using a complex substrate based on beef extract. A number of different steady states was achieved covering a wide range of hydraulic retention times and product concentrations. The Monod equation failed completely to describe the growth of the acidogenic bacteria, while there was evidence of product inhibition. Therefore, two of the most commonly used inhibition models were applied, the non-competitive and the Haldane-type model. The former gave superior results, and the estimated values for the biokinetic constants were a maximum specific growth rate (mu(max)) of 32.6 day(-1), a substrate saturation constant (K(s)) of 1.77 g COD/L, an inhibition constant (K(i)) of 0.633 g/L of total volatile fatty acids, and a specific decay rate (k(d)) 1.747 day(-1). The same inhibition models were also applied to the description of the specific rate of product formation, with the noncompetitive model fitting the data slightly better. The maximum specific rate of product formation was estimated to be 125.7 g total volatile fatty acid/g biomass/day.