Theoretical Stoichiometry of Biological Denitrifications

Biological denitrification is a phenomenon widely present in soil, water, and wastewater treatment ecosystems. Based on McCarty's half-reaction theory, taking the fraction (fs) of electron donor coupled to cells (CαHβOεNδ) synthesis as the basic parameter, we developed new stoichiometric equations for biological denitrifications. These denitrifications are complete denitrifications of nitrate with, respectively, nitrate and ammonia as the nitrogen source, complete denitrification of nitrite and reduction of nitrate to nitrite with various kinds of organic carbon sources. Taking the concept that all electron donors in stoichiometric equations are equivalent to 1/4 moles of COD, we discussed the stoichiometric equations and relationships of biological denitrifications. Some COD-independent stoichiometric relationships and parameters for biological denitrifications are discovered. The generalized stoichiometric equations and stoichiometric relationships are discussed in detail by citing the example of CαHβOεNδ = C5H7O2N. Some empirical values of fs from previous reports are calculated by using the theoretical stoichiometric coefficients and relationships. The effects of COD/N-NO3 on the denitrification behavior and the cell yield coefficient Yx/c are also discussed here. Based on this method, the parameter of fs and the balance of electron flow besides the mass balance appear very important for the stoichiometry of bioprocesses. The new method for the stoichiometric analysis of bioprocesses may be termed electronic stoichiometry.