A kinetic model incorporating energy spilling for substrate removal in substrate-sufficient batch culture of activated sludge

Batch assays are currently used to study the kinetic behavior of microbial growth. However, it has been shown that the outcome of batch experiments is greatly influenced by the initial ratio of substrate concentration (S-o) t o biomass concentration (X-o). Substrate-sufficient batch culture is known to have mechanisms of spilling energy that lead to significant nongrowth-as sociated substrate consumption, and the Monod equation is no longer appropr iate. By incorporating substrate consumption associated with energy spillin g into the balance of the substrate oxidation reaction, a kinetic model for the observed specific substrate consumption rate was developed for substra te-sufficient batch culture of activated sludge, and was further verified b y experimental data. It was demonstrated that the specific substrate consum ption rate increased with the increase of the S-o/X-o ratio, and the majori ty of substrate was consumed through energy spilling at high S-o/X-o ratios . It appears that the S-o/X-o ratio is a key parameter in regulating metabo lic pathways of microorganisms.