In wastewater treatment, chemical precipitation is used to remove phosphorus and to enhance suspended-solids removal in sedimentation processes. The most common chemicals used are aluminum hydroxide, ferric chloride, ferric sulfate and lime. In the field of wastewater treatment, chemical unit operations are usually used in conjunction with physical unit operations and biological unit processes. Such treatment is considered as means of stream upgrading by coagulation, emulsion, breaking, precipitation or neutralization. Coagulation is the process that is used to remove colloids from water by the addition of chemicals. The chemicals upset the stability of the system by neutralizing the colloid charge. The emulsion breaking is similar to coagulation. The emulsion is generally broken with a combination of acidic reagents and polyelectrolytes. The common ion effect is also useful in wastewater treatment. In this case, an unwanted salt is removed from solution by adding a second soluble salt to increase one of the ion concentrations.