phosphorus To further Insoluble processing phosphorus phosphorus phosphorus treatment ig.6-6 Alternative points of chemical addition for phosphorus removal: (a) before primary sedimentation, ( b) before and/or following biological treatment, (c) following secondary treatment, and (d-f) at several locations in a process (known as"split treatment Pre-precipitation. The addition of chemicals to raw wastewater for the precipitation of phosphorus primary sedimentation facilities is termed"pre-precipitation. "The precipitated phosphate is removed with the primary sludge Tab. 6-3 Factors affecting the choice of chemical for phosphorus removal st( including transportation) 5. Reliability of chemical suppl 8. Compatibility with other treatment processes Coprecipitation. The addition of ls to form precipitates that are removed biological sludge is defined as"coprecipitation. "Chemicals can be added to(D) the effluent from primary sedimentation facilities. (2) the mixed liquor(in the activated-sludge process). or( 3) the effluent from a Postprecipitation. Postprecipitation involves the addition of chemicals to the effluent from secondary sedimentation facilities and the subsequent removal of chemical precipitates. In this process, the chemical precipitates are usually removed in separate sedimentation facilities or in effluent filters( see Fig 6-6) Phosphorus Removal Using Metal Salts and Polymers As noted above, iron or aluminum salts can be added at a variety of different points in the treatment process(s orthophosphorous, adding aluminum 6-106-10 Pre-precipitation. The addition of chemicals to raw wastewater for the precipitation of phosphorus in primary sedimentation facilities is termed "pre-precipitation." The precipitated phosphate is removed with the primary sludge. Tab. 6-3 Factors affecting the choice of chemical for phosphorus removal 1. Influent phosphorus level 2. Wastewater suspended solids 3. Alkalinity 4. Chemical cost(including transportation) 5. Reliability of chemical supply 6. Sludge handling facilities 7. Ultimate disposal methods 8. Compatibility with other treatment processes Coprecipitation. The addition of chemicals to form precipitates that are removed along with waste biological sludge is defined as "coprecipitation." Chemicals can be added to (1) the effluent from primary sedimentation facilities, (2) the mixed liquor (in the activated-sludge process), or (3) the effluent from a biological treatment process before secondary sedimentation. Postprecipitation. Postprecipitation involves the addition of chemicals to the effluent from secondary sedimentation facilities and the subsequent removal of chemical precipitates. In this process, the chemical precipitates are usually removed in separate sedimentation facilities or in effluent filters (see Fig. 6-6). Phosphorus Removal Using Metal Salts and Polymers As noted above, iron or aluminum salts can be added at a variety of different points in the treatment process (see Fig. 6-6), but because polyphosphates and organic phosphorus are less easily removed than orthophosphorus, adding aluminum or iron salts after secondary treatment (where organic phosphorus and Fig. 6-6