Model of dissolved organic carbon distribution for substrate-sufficient continuous culture.

The growth yields (Yobs) are greater under substrate-limited conditions than those under substrate-sufficient conditions in continuous cultures. This indicates that the excess substrate should cause uncoupling between anabolism and catabolism. It appears that the excess substrate could determine metabolic pathways of microorganisms, which further control dissolved organic carbon (DOC) distribution under substrate-sufficient conditions. However, how to quantitatively describe the DOC distribution remains unclear in substrate-sufficient continuous culture. Based on a balanced DOC reaction, a DOC distribution model was developed in relation to residual substrate concentration for substrate-sufficient continuous cultures. Results showed that a considerable portion of the DOC consumed was directly oxidized to carbon dioxide through energy spilling under substrate-sufficient conditions. The proposed model for the first time quantified the DOC distribution between nongrowth-associated and growth-associated metabolisms of cells. The proposed model was verified with literature data very well.