Impact of seeding with nitrifying bacteria on nitrification process efficiency

Seeding of nitrifying bacteria into the activated sludge process was studie d both theoretically and experimentally. A simple model was developed for p rediction of the effects of seeding of nitrifying bacteria from a separate stage into the activated sludge process. The purpose of seeding is to impro ve the treatment results and the process stability as well as to decrease t he volume requirements of the process. Pilot plant studies were carried out at the Uppsala municipal wastewater treatment plant in order to evaluate t he effects of seeding. One line was supplied with supernatant from dewateri ng of digested sludge and the nitrification process gave an activated sludg e with a high fraction of nitrifying bacteria, suitable for seeding. The ot her line was supplied with pre-precipitated wastewater and with the excess sludge from the line treating the supernatant. The experimental results sho wed that nitrification could be obtained at sludge ages that would otherwis e preclude nitrification. Performance relationships for the system develope d, based on laboratory and on-line measurements were studied and are presen ted. The studies show that seeding may decrease the necessary volume needs for a stable nitrification process and that the effects could be predicted by use of a simple model.