Waste Water Treatment Process

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Chemical precipitation

Chemical precipitation is the most common method for removing dissolved metals from wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent, causes the dissolved metals to form solid particles. Filtration can then be used to remove the particles from the mixture. How well the process works is dependent upon the kind of metal present, the concentration of the metal, and the kind of reagent used. In hydroxide precipitation, a commonly used chemical precipitation process, calcium or sodium hydroxide is used as the reagent to create solid metal hydroxides. However, it can be difficult to create hydroxides from dissolved metal particles in wastewater because many wastewater solutions contain mixed metals.

 

Physio Chemical treatment Process

Solids of the size that are visible to the naked eye can be separated either by settling under the influence of gravity or by flotation, depending on the relative densities of solids and water. They may also be easily separated by filtration. However, very fine particles of a colloidal nature (called colloids, size < 1 µm) which have high stability are significant pollutants. The reason for this stability is that these particles have electrostatic surface charges of the same sign (usually negative). This means that repulsive forces are created between them, preventing their aggregation and subsequent settling. It has therefore proved impossible to separate them by settling or flotation. It is not possible to separate these solids by filtration because they pass through any filter. However, separation by physico-chemical treatments is possible.

Biological Method

Biological methods rely upon living organisms using organic or, in some instances, inorganic substances for food. Biological treatment is more widely used than any other option where reasonably complete treatment is required. It most often serves as the secondary treatment stage to remove major portions of contamination. Other processes handle primary and tertiary treatment to complete the removal of solids and other pollutants.

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Industrial Chemistry
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