The effect of temperature and carbon source on denitrification using volatile fatty acids

This study explored the effect of temperature and carbon source on the denitrification process. Batch experiments were conducted within the 10–30 °C range, using either acetic acid, propionic acid or an 1:1 mixture (by weight) of the same acids as an external carbon source. A 5 M NaNO3 solution was added to yield nitrate-nitrogen concentrations of 50, 100 and 200 mg/L, and carbon to nitrogen (C:N) ratios of 2:1 and 4:1, respectively. It was observed that denitrification was feasible under all conditions investigated, provided that the initial reactor pH was adjusted to approximately 6.5. Overall, a temperature change from 10 to 20 °C exerted a greater effect on both the specific denitrification and carbon consumption rates than a further temperature increase from 20 to 30 °C, which was also evident in the corresponding temperature coefficient values. At a given temperature, the specific denitrification rate appeared to depend on the initial nitrogen concentration, while the specific carbon consumption rate was a function of the initial carbon content. Furthermore, a C:N ratio of 2:1 was sufficient for complete denitrification at all temperatures and types of carbon investigated. During the mixed VFA experiments, acetic acid was utilized faster than propionic acid, indicating a preferential utilization pattern. Finally, substantial alkalinity recovery was also observed in all runs, in accordance with the theoretically calculated values.