General

Technologies for treating industrial wastewaters can be divided into three categories: chemical methods, physical methods, and biological methods. Chemical methods include chemical precipitation, chemical oxidation or reduction, formation of an insoluble gas followed by stripping, and other chemical reactions that involve exchanging or sharing electrons between atoms. Physical treatment methods include sedimentation, flotation, filtering, stripping, ion exchange, adsorption, and other processes that accomplish removal of dissolved and nondissolved substances without necessarily changing their chemical structures. Biological methods are those that involve living organisms using organic or, in some instances, inorganic substances for food. In so doing, the chemical and physical characteristics of the organic and/or inorganic substance are changed.

Most substances found as pollutants in industrial wastewaters can be categorized as to whether chemical, physical, or biological treatment should be the most appropriate. For instance, dairy wastewater should most appropriately be treated by biological means, because the bulk of the pollution load from a typical dairy is organic material from whole milk, which is readily biodegradable. As a general rule, biological treatment is more economical than any other type of treatment where reasonably complete treatment is required and wherever it can be made to work successfully.

It is very often possible to make preliminary selections of candidate treatment technologies based on fundamental properties of the pollutants and experience. For instance, when candidate treatment technologies to treat wastewaters from a metal plating operation are being considered, none of the biological treatment technologies would be appropriate, since metal ions are not...