Effect of the type of the external carbon source on denitrification kinetics of wastewater

The effective denitrification in conventional wastewater treatment plants (WWTPs) requires maintaining the concentration of organic carbon compounds on the sufficient level in the biological reactor. There are many so-called external carbon sources used for this purpose. In this paper, the effect of addition of various external carbon sources on denitrification kinetics was described. The tests were performed with the use of real municipal wastewater from the full-scale WWTP in Zgierz (Poland). Three external carbon sources were selected, that is, acetic acid and two yet untested commercial compounds being the mixtures of various organic and some inorganic substances. One of the commercial carbon sources was glycerine-based, while the second one alcohol-based. Apart from organic carbon both commercial carbon sources contained nitrogen and phosphorus at relatively high amounts and in the case of one of them it exceeded 1,000 mg NH4+-N L-1. This compound had the lowest potential of denitrification equal to 0.102 mg NO3--N mg COD-1. Although the ratios of nitrogen to chemical oxygen demand (COD) of both commercial compounds did not exceed 2.5%, which indicated that the denitrification potential of these carbon sources should not be decreased, lower rates of denitrification were observed in the tests with the use of them. When acetic acid was the external carbon source, denitrification was the fastest and its rate increased from two-to three-fold in comparison with the commercial carbon sources tested. These experiments indicated that heretofore assumed critical values of nitrogen to COD ratio for external carbon sources should be verified.