Modeling acidogenic and sulfate-reducing processes for the determination of fermentable fractions in wastewater

The biochemical acidogenic potential (BAP) of a wastewater is the maximum concentration of volatile fatty acids (VFAs) that can be measured at the end of an anaerobic fermentation test. A model was constructed to describe the acidogenic reactions occurring during BAP tests and to divide the BAP into organic fractions. The model was calibrated with a set of specific experiments highlighting the role of sulfate-reducing bacteria on acidogenic processes, which description was necessary for correct parameter identification. The model could describe acidogenic fermentation processes, with or without sulfate reduction, at 20 degrees C, for 13 wastewaters of different origin, composition, and settleability using the same optimized parameters. A simplified version of the model, without sulfate reduction, was able to describe VFA production by the adjustment of only three variables: readily fermentable organic matter (Sf), anaerobically hydrolyzable organic matter (Xf), and heterotrophic acidogenic biomass (Xha), which proved to be coherent with the experimental BAP value. The combination of the BAP test and the model developed in this study resulted in a new reliable tool to characterize wastewater under anaerobic conditions. As VFAs are the main substrates for phosphate-accumulating organisms (PAOs), the use of organic fractions VFA, Sf, Xf, and Xha in wastewater treatment plant modeling could improve the predictability and optimization of enhanced biological phosphorus removal (EBPR) processes.