Category | Technology | Advantages | Disadvantages |
Chemical methods | Oxidation | 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 | |
Ozonization | It can be applied in gaseous form, besides, it increases the volume of waste water or sludge | Short half-life (20 minutes) | |
Photochemicals | 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 | |
Irradiation | Effective oxidation at laboratory scale | Requires a lot of O2 | |
Electrokinetic coagulation | Economically accessible | High production of sludge generating problems for handling and disposal | |
Bioadsorbents | Economically attractive, regeneration is not necessary, high selectivity | May or may not require chemical modification, and it generates solid residues |