Determination of Denitrification Kinetics on Methanol and Glycerol Using Gene Expression Biomarkers

Application of external carbon sources to enhance denitrification is required to meet increasingly stringent effluent nitrogen limits at wastewater treatment plants. The dosing strategies of these compounds depend on carbon-specific denitrification kinetic and stoichiometric coefficients. However, using traditional nitrogen depletion based biokinetic assays cannot be used to discriminate the fractional activity of multiple bacterial fractions degrading a given carbon source. Therefore, the development and application of molecular activity biomarkers to infer and distinguish between different carbon sources could be useful in this regard. In this study, the expression of functional genes coding for methanol dehydrogenase (mdh2 and mxaF) and glycerol dehydrogenase (dhaD) as potential indicators of denitrification biokinetics on methanol and glycerol, respectively, was studied. Based on long-term denitrifying reactor operation, it was shown that these gene expression based biomarkers are good surrogates for carbon-specific denitrification kinetics.