Achieving nitrification in pure oxygen activated sludge by seeding

An innovative “seeding” approach was used to increase the nitrification capacity of a pure oxygen activated sludge plant. In this approach, waste activated sludge from a parallel air activated sludge system was used to seed nitrifiers to the pure oxygen plant to increase the apparent sludge age and achieve nitrification under the high loading in the pure oxygen system. Calculations indicate that nitrification can be achieved at a traditional sludge age of 3 days with a seeding rate of 20 percent. Full-scale tests showed that nitrification can be achieved at a seed rate of 35 percent and a traditional sludge age of 4.6 days, producing effluent ammonia below 5 mg/l. Secondary clarification remained good during the operation of the system even at the higher solids loading rates, with effluent TSS concentrations at 6 mg/l.