HIGH PURITY OXYGEN BIOLOGICAL NUTRIENT REMOVAL (BNR)

Since 1970 there have been nearly 300 high purity oxygen (HPO) activated sludge systems constructed worldwide both in industrial and municipal applications. With an increased focus of State and Federal regulations on nutrient removal, this paper provides a technology update of the high purity oxygen process for nutrient removal. This update will include experience, and actual operating performance data, from plants operating for more than twenty years in addition to current generation design concepts for optimization of the high purity oxygen process for full biological nutrient removal (BNR).Conventional design for high purity oxygen systems for nitrogen removal has been employed for over twenty years, incorporating either single or two step design dependent on wastestream characteristics. Current generation high purity oxygen BNR design incorporates anaerobic stage(s) for biological phosphorus removal, anoxic stage(s) for denitrification, and selector technology. Further optimization, dependent on effluent permit limitations, includes multiple anoxic stages for denitrification polishing. Since biological processes for nitrification prefer neutral pH conditions, current generation design also incorporates an open stage stripping CO2 for pH elevation. Increased pH, combined with the ability to efficiently operate at high dissolved oxygen concentration and high MLSS level, provide specific economic and operational advantages of the HPO-BNR System.Operating data will be presented from several high purity oxygen nutrient removal plants and provide a comparison of current generation design approach versus effluent performance, and applicability of the HPO-BNR process as a stand alone treatment system or for efficient retrofit or conversion of existing systems.