Industrial dye degradation is any of a number of processed by which

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

s are broken down, ideally into innocuous products. Many dyes, specifically in the textile industry such as methylene blue or methyl red, are released into ecosystems through water waste. Many of these dyes can be carcinogenic. In

paper recycling The recycling of paper is the process by which waste paper is turned into new paper products. It has a number of important benefits: It saves waste paper from occupying homes of people and producing methane as it breaks down. Because paper fi ...

dyes can be removed from fibres during a

deinking Deinking is the industrial process of removing printing ink from paperfibers of recycled paper to make deinked pulp. The key in the deinking process is the ability to detach ink from the fibers. This is achieved by a combination of mechanical ac ...

stage prior to degradation.

Methods

Heterogeneous photocataylsis is one approach to the degradation of dyes. As applied to dye-containing effluents from the

textile industry The textile industry is primarily concerned with the design, production and distribution of yarn, cloth and clothing. The raw material may be natural, or synthetic using products of the chemical industry. Industry process Cotton manufacturi ...

, several approaches are standardized for removal or degradation of dyes. These include oxidation, e.g. using air or

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

, or

Fenton chemistry Fenton's reagent is a solution of hydrogen peroxide (H2O2) with ferrous iron (typically iron(II) sulfate, FeSO4) as a catalyst that is used to oxidize contaminants or waste waters as part of an advanced oxidation process. Fenton's reagent can be us ...

. One challenge is that oxidants can be indiscriminent such that large amounts of reagents can be required (see

Chemical oxygen demand In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution whic ...

). One promising approach combines oxidation with

photocatalysis In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abili ...

. Reduction is also employed, a standard reagent being

dithionite The dithionite is the oxyanion with the formula 2O4sup>2−. It is commonly encountered as the salt sodium dithionite. For historical reasons, it is sometimes called hydrosulfite, but it contains no hydrogen and is not a sulfite. The diani ...

, which traditionally affords leuco dyes. Precipitation, often coupled with

flocculation Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from pr ...

, is yet another approach, although it can produce substantial quantities of solids.

References

{{Reflist Dyes Pollution control technologies