Metabolic modeling of the substrate competition among multiple VFAs for PHA production by mixed microbial cultures

Mixed microbial cultures (MMCs) are an effective method for polyhydroxyalkanoates (PHA) production. There are several models established to describe the metabolism of this process. Substrate competition was commonly found in the uptake of multiple volatile fatty acids (VFAs), thus this behavior should be considered in process modeling. In this study, a metabolic model is developed to describe for the first time the substrate competition among four commonly used VFAs (acetate, propionate, butyrate and valerate) in PHA production by MMCs. An inhibition parameter was introduced to describe the inhibition of butyrate and valerate on the uptake of acetate and propionate. The modeled results showed good agreement with experimental data within 95% confidence interval. This model enhanced the understanding of the metabolism of substrate uptake in PHA production, providing a successful approach to predict PHA composition and optimize the process efficiency when four competing VFAs are supplied.