Theoretical stoichiometry of biological denitrifications

Biological denitrification is a phenomenon widely present in soil, water, a nd wastewater treatment ecosystems. Based on McCarty's half-reaction theory , taking the fraction (f(s)) of electron donor coupled to cells (CalphaHbet aOepsilonNdelta) synthesis as the basic parameter, we developed new stoichi ometric equations for biological denitrifications. These denitrifications a re complete denitrifications of nitrate with, respectively, nitrate and amm onia as the nitrogen source, complete denitrification of nitrite and reduct ion of nitrate to nitrite with various kinds of organic carbon sources. Tak ing the concept that all electron donors in stoichiometric equations are eq uivalent to 1/4 moles of COD, we discussed the stoichiometric equations and relationships of biological denitrifications. Some COD-independent stoichi ometric relationships and parameters for biological denitrifications are di scovered. The generalized stoichiometric equations and stoichiometric relat ionships are discussed in detail by citing the example of CalphaHbetaOepsil onNdelta = C5H7O2N. Some empirical values of f(s) from previous reports are calculated by using the theoretical stoichiometric coefficients and relati onships. The effects of COD/N-NO3 on the denitrification behavior and the c ell yield coefficient Yx/c are also discussed here. Based on this method, t he parameter of f(s) and the balance of electron flow besides the mass bala nce appear very important for the stoichiometry of bioprocesses. The new me thod for the stoichiometric analysis of bioprocesses may be termed electron ic stoichiometry.