Comparison of methanol, ethanol, and methane as electron donors for denitrification

The results of denitrification assays using three electron donor sources-methanol, ethanol, and methane-are presented and discussed based on the apparent kinetic parameters estimated from the experimental data. The research was carried out in batch reactors fed with synthetic wastewater simulating nitrified effluents from domestic sewage treatment plants. The most effective electron donor was ethanol, which completely removed nitrite and nitrate in 50 min. The same efficiency was achieved by feeding the reactors with methanol and methane for 120 and 315 min, respectively. The kinetic model of two reactions in series, having nitrite as the intermediate compound, adequately represented the denitrification process in the reactors fed with methanol and ethanol. To apply this model, the conversions of nitrate-to-nitrite and of nitrite-to-molecular nitrogen were represented, respectively, by first- and zero-order equations. In both the methanol and ethanol experiments, nitrite conversion was the limiting step in the overall process. The model of two reactions in series could not be fit to the data from the methane fed reactor, probably due to the significant interference of the mass transfer phenomena on the overall process. However, a good fit was achieved with a simple model expressing the conversion of nitrate directly into molecular nitrogen.