[Nitrifiers accumulation with reject water and bio-augmentation for nitrification of sewage at short SRT]

Sequencing batch reactor, treating simulated municipal wastewater for N removal and operated at near the minimum SRT (solids retention time) for nitrification (in reactor 2), was seeded daily with nitrifying biomass accumulated with reject water (in reactor 1) came from Xi' an Dengjiacun wastewater treatment plant. Comparison of the nitrification ability, the characteristics of the activated sludge before seeding and after seeding was made. The experiment result shows that, the maximum nitrification rate of the activated sludge in the reactor 1 reached 81.4 mg/(L x h). The effluent concentration of NH4+ -N of the reactor 2 decreased at a rate of 0.992 mg/(L x d) (R2 = 0.903), and the maximum nitrification rate increased 1.36 times. Once seeding was terminated, the effluent concentration of NH4+ -N increased at a rate of 1.956 mg/(L x d) (R2 = 0.999), and nitrification caused by seeding was not completely disappeared after seeding was stopped for 34 d. The amount and varieties of protozoa and the value of SVI in the reactor seeded with nitrifiers increased during the initial time of seeding, but were recovered when the reactor 2 reached stable state.