Controlled carbon source addition to an alternating nitrification-denitrification wastewater treatment process including biological P removal

The paper investigates the effect of adding an external carbon source on the rate of denitrification in an alternating activated sludge process including biological P removal. Two carbon sources were examined, acetate and hydrolysate derived from biologically hydrolyzed sludge. Preliminary batch experiments performed in 5 liter bottles indicated that the denitrification rate can be instantaneously increased through the addition of either carbon source. The amount by which the rate was increased depended on the amount of carbon added. In the main experiments performed in a pilot scale alternating process, the addition of either carbon source to the anoxic zone also resulted in an instantaneous and fairly reproducible increase in the denitrification rate. Some release of phosphate associated with the carbon source addition was observed. With respect to nitrogen removal, these results indicate that external carbon source addition may serve as a suitable control variable to improve process performance.