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Chemical Precipitation

Physics and Chemistry of Water

  1. Bradley A. Striebig

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.pc101

Water Encyclopedia

Water Encyclopedia

How to Cite

Striebig, B. A. 2005. Chemical Precipitation. Water Encyclopedia. 4:586–589.

Author Information

  1. Gonzaga University, Spokane, Washington

Publication History

  1. Published Online: 15 JUL 2005

Abstract

Chemical precipitation is the removal of dissolved and suspended solids from aqueous solutions through chemical means. Chemical precipitation includes the removal of dissolved solids by altering the aqueous chemistry to make the dissolved solids less soluble. It also includes removing suspended solids by increasing their size in a process referred to as chemical flocculation. Chemical precipitation processes are utilized in water and wastewater treatment due to their effectiveness for pollutant removal with relatively low capital investment. Chemical precipitation processes can also process very toxic wastewaters. The focus of chemical precipitation for municipal wastewater treatment is to remove the cell mass or suspended solids prior to and after biological treatment. Industrial process water and recycled wastewater use chemical precipitation to remove hardness and dissolved salts from water. The solubility product constant, or solubility product, is an equilibrium constant that describes the reaction by which ions dissolve and solids precipitate. Chemical precipitation by coagulation and flocculation enhances the removal of suspended solids and BOD. These processes are widely used to improve the performance of primary clarifiers, in basic physical–chemical processing of industrial wastewaters, for phosphorus removal, and for heavy metal removal.

Keywords:

  • suspended particles;
  • solubility;
  • solubility product;
  • coagulation;
  • flocculation;
  • wastewater solids;
  • sludge;
  • activity coefficient