Seeding of Nitrifying Bacteria as a Way for Nitrification Improvement

Seeding of nitrifying bacteria into the activated sludge process may decrease the necesary volume needs for a stable nitrification process. Both theoretical and experimental studies were carried out in order to evaluate the effects of seeding. A model was developed for prediction of the effects of seeding of nitrifying bacteria from a separate stage into the activated sludge process. Seeding technology is the most effective when used at an activated sludge process with a sludge age near or below the critical sludge age for nitrification at nonseeding conditions. The nitrifying bacteria in the seeding sludge have a positive effect on the nitrification process. Experimental studies have been performed at a specially built pilot plant with two separate lines of the activated sludge process located at the Uppsala municipal wastewater treatment plant. One line was supplied with supernatant from dewatering of digested sludge and the nitrification process provided an activated sludge with a high fraction of nitrifying bacteria, suitable for seeding. The other line was supplied with pre-precipitated wastewater and with the excess sludge from the line treating the supernatant. The experimental results showed that nitrification at sludge ages that would otherwise preclude nitrification could be obtained. Performance relationships for the system developed, based on laboratory and on-line measurements were studied and are presented in the paper. The studies indicate that seeding may be advantageous for improving process performance and stability; it provides also an interesting alternative in design and operation of the activated sludge process.