Chemical methods


Fast and efficient process

High costs due to energy consumption. It requires the use of chemicals, as for example H2O2 as an agent to activate some of the means

Fenton reactions (H2O2 + Fe (II) sal)

Appropriate chemical method

Sludge generation


It can be applied in gaseous form, besides, it increases the volume of waste water or sludge

Short half-life (20 minutes)


There is no sludge production, bad odors are greatly reduced

Sub-product formation

Sodium Hypochlorite (NaOCl)

Starts and accelerates the breaking of azo bonds

Release of aromatic amines

Electrochemical destruction

There is no consumption of chemicals or sludge formation

Relatively high flow rate leading to a direct reduction in dye removal

Advanced oxidation processes

There is no production of sludge, consumption of few or no chemical, efficiency for recalcitrant dyes

High costs, by-product formation, technical restrictions

Biological methods

Fungal discoloration

Fungi are able to degrade dyes using the enzymes

The production of enzyme has also been manifested as unreliable

Other microbial cultures

Decolorization between 24 and 30 hours

Azo dyes under aerobic conditions are not rapidly metabolized

Adsorption with microbial biomass [14]

According to the type of dyes, there is a particular affinity with certain microbial species.

Not effective for all dyes, slow process, performance depends on external factors such as pH

Anaerobic bioremediation systems

Allows discoloration of azo dyes and

other water solubledyes

Production of methane and hydrogen sulphide

Physical methods

Adsorption on activated carbon [12]

Good removal of the wide range of dyes

High costs, ineffective with dispersed and vat type dyes, regeneration is costly and results in loss of adsorbent, it is not a destructive process

Filtration membranes [13]

Removal of all types of dyes

High concentration of sludge, inefficient for the treatment of large volumes, limited service life of the membrane, which generates high costs due to periodic replacement

Ionic exchange

Regeneration: without loss of adsorbent

Not effective for dispersed dyes, economic limitations


Effective oxidation at laboratory scale

Requires a lot of O2

Electrokinetic coagulation

Economically accessible

High production of sludge generating problems for handling and disposal


Economically attractive, regeneration is not necessary, high selectivity

May or may not require chemical modification, and it generates solid residues