The So/Xo-dependent dissolved organic carbon distribution in substrate-sufficient batch culture of activated sludge

The ratio of initial substrate concentration (So) to initial biomass concentration (Xo) is a key parameter of batch culture of activated sludge, and this ratio determines metabolic pathways of microorganisms in batch culture. Based on a balanced dissolved organic carbon (DOC) reaction, a kinetic model was developed to describe the dependence of the DOC distribution on the So/Xo ratio in substrate-sufficient batch culture of activated sludge. The proposed model was verified very well with both experimental data and theoretical analyses. It is clearly demonstrated that the final DOC distribution is governed by the So/Xo ratio, and a considerable portion of DOC is oxidized to carbon dioxide through energy uncoupling at higher So/Xo ratios. This study for the first time quantitatively shows the DOC partition between energy spilling-associated and growth-associated metabolisms at different So/Xo ratios.