Chemical phosphorus removal is a wastewater treatment method, where phosphorus is removed using salts of aluminum (e.g. alum or polyaluminum chloride), iron (e.g. ferric chloride), or calcium (e.g. lime). Phosphate forms precipitates with the metal ions and is removed together with the sludge in the separation unit (sedimentation tank, flotation tank, etc.).
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Chemical phosphorus removal Wikipedia(Text) CC BY-SA