Estimation of biokinetic parameters in the acid fermentation of primary sludge using an anaerobic baffled reactor

Abstract

Biokinetic models of anaerobic baffled reactor (ABR) type-acid fermentation with a short hydraulic retention time (HRT) of four days were proposed for obtaining high concentrations of volatile fatty acids (VFAs) as the external carbon source by inhibiting methanogenesis based on the dynamic microbial growth rate. The model equations reflect the biochemical processes of complex organic matter of primary sludge and consider the hydrolysis products as the limiting substrates for cell growth and product formation according to several biokinetic models. The substrate concentration, biomass concentration, hydraulic retention time, and pH were considered to describe the biokinetic models. We considered the effect of pH on the hydrolysis biokinetics of organic matter as an inhibitor factor. A more accurate model simulation was possible using the nonlinear least-squares method to minimize assumptions. By using various growth biokinetic equations, the biokinetic parameters of the maximum specific growth rate, microorganism decay rate, half-saturation constant, substrate hydrolysis rate coefficient, biomass yield coefficient, and hydrolyzed substrate transport rate coefficient have been completely estimated. A statistical method was proposed to calibrate the model directly from the experiment data obtained even at an unsteady state. Among the various biokinetic models, Ming's model provided the best fit with the measured data. In addition, the effect of the biokinetic parameters was also discussed to allow us to calculate the trends of the process variables as a function of the design variables.