Enhanced biological phosphorus removal systems

The PAC activated slndge system is a modified activated sludge process. PAC is added to the aeration tank where it is mixed with the biological solids. The mixed liquor solids are settled and separated from the treated effluent in a gravity clarifier. Polyelectrolyte will normally be added prior to the clarification step to enhance solids-liquid separation. If phosphorus removal is necessary, alum is often added at this point. Even with polyelectrolyte addition, tertiary filtration is normally required to reduce the level of effluent suspended solids. The clarifier nnderflow solids are continuously returned to the aeration tank. A portion of the carbon-biomass mixture is wasted periodically to maintain the desired solids inventory in the system. 

Jing, S.R., Benefield, L.D. and Hill, W.E. (1992) Observations relating to enhanced phosphorus removal in biological systems. Water Research 25, 21 3-223. 

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