Table 4.
Some physical treatments used in the removal of dyes.
| Treatment | Dye | Colour Removal | Parameters Influencing Treatment | Advantages | Disadvantages | References |
|---|---|---|---|---|---|---|
| Adsorption (activated carbon—adsorbent materials) | Light Green SF. | Associated with operating parameters. | Contact time, absorbent particle size, absorbent concentration, pH. | Between 75% and 86% of adsorption took place in the first 2 h. | Desorption processes are required to remove the dye, relatively high operating costs. | [129] |
| Violet Cristal. | Between 72.2% and 97.8%. * | pH, adsorbent material, adsorption temperature, adsorbent surface area. | High adsorption capacity. | High temperatures (70 °C) are required, which increases operating costs. | [146] | |
| Nanofiltration (composite membrane) | Congo Red, Methyl Blue, Sunset Yellow and Neutral Red. | Between 80.6% and 99.8%. * | Membrane composition and molecular weight cut-off, feed flow and dye loading. | High efficiency and possible dye reuse. | Membrane dye adsorption, high cost and required membrane cleaning procedures. | [147] |
| Flotation | Red 3BS, Navy SG, and Yellow S3R | Not specified | Agitation, type of gas sparger, range of pore | Efficient separation method for the removal of oil, dissolved ions, grease, biomolecules and solids suspended in water. | Pretreatments with coagulants or biosurfactants are required for dye removal. | [148] |
| Irradiation | Methylene Blue, Reactive Red KE-3B, Reactive Orange XBR. | Between 31.0 and 85.0%. * | Composition, hydrophilicity and porosity of the membrane, pH and salts, structure of the chromophore, irradiation time. | Degradation under visible light irradiation. | Use toxic solvents. The presence of salts decreases colour removal. | [149] |
* Depends on the type of treatment and the type of dye.