Dyes are generally synthesized through chemical reactions such as chlorination, coupling, ethylation, nitration, condensation, redox, and diazotization, and then separated and refined to obtain products. Dye production wastewater mainly comes from waste mother liquor produced in the process of dye production and synthesis, washing water during product separation and refining, and production equipment and workshop floor washing wastewater. Sewage-containing wastewater, salt-containing wastewater, naphthalene-based wastewater, and high-color wastewater are not easy to be treated in the dye industry wastewater treatment equipment.

    At present, domestic and foreign treatment methods for dye wastewater mainly include physical and chemical methods, biological methods, chemical methods, and some optimized combined processes.

    (I) Physical Chemistry Law

    Physicochemical methods are a collective term for various methods for treating wastewater by physical and chemical action, mainly including adsorption methods, extraction methods, and membrane separation methods.

    (1) Adsorption method Adsorption method is a water treatment process that uses porous solid phase substances to adsorb and separate pollutants in water. A solid substance that adsorbs and separates pollutants in water is called an adsorbent. Common adsorbents are: activated carbon, activated coal, coke, cinder, resin, wood chips, ion exchange resin, diatomaceous earth, fly ash, etc. In the treatment of dye wastewater, the dye wastewater is passed through a filter bed composed of particulate matter (that is, the adsorbent), and pollutants such as dyes and auxiliary agents in the dye wastewater are adsorbed on the surface of the adsorbent and removed. Activated carbon has a large specific surface area, and has a clear decoloring effect on dye molecules having a molecular weight of not more than 400. Activated carbon can be regenerated by heating or other methods, but the regeneration is difficult, the operating cost is high, and the activated carbon is easily lost with the waste water, which needs to be continuously replenished during the wastewater treatment process. It can be seen that the adsorption effect depends largely on the structural properties of the adsorbent and the structural properties of the pollutants. The adsorption method is more suitable for the deep treatment of low-concentration dye wastewater. The main advantages are small investment, small footprint, simple and easy method, and the adsorption method can also remove difficult biodegradable pollutants in the wastewater.

    (2) Extraction method This method uses the difference in solubility of solutes in mutually incompatible solvents, and uses one solvent to extract the solute from a solution composed of another solvent. In water treatment, the difference in solubility of organics in water and in organic solvents is mainly used, and then the extractant is separated from the pollutants. The extractant can be recycled, and the obtained pollutants can be recycled after further processing. However, the extraction method is more suitable for the treatment of small-volume wastewater, and the difficult-to-treat dye wastewater with complex components has high requirements on the extractant, and the cost will increase greatly. Therefore, the extraction method is only suitable for the treatment of a few organic wastewater. Because the extractant always has a certain solubility in water, it is inevitable that a small amount of extractant will be lost, making it difficult for the treated water to meet the discharge standard.

    (3) Membrane separation method Membrane separation technology is applied to dye wastewater, mainly through the separation, concentration and recovery of pollutants in wastewater to achieve the purpose of wastewater treatment. In the treatment of dye wastewater, more applications are ultrafiltration and reverse osmosis. The integrated reverse osmosis industrial wastewater treatment equipment was used to study the dye wastewater. At an operating pressure of 15 MPa, the effluent conductivity, COD mass concentration, and chromaticity were 23uS / cm, 10.8mg / L, and 7 (dilution multiples). ), Are in line with national emission standards. Membrane separation technology does not require the addition of chemical reagents, and does not generate new chemicals during the treatment process, avoiding secondary pollution, the process is simple and convenient, and the dye can be recovered from wastewater and recycled. However, the disadvantages of membrane separation technology are that the membrane flux will decrease with the extension of the processing process, the replacement frequency is faster, and the membrane cleaning requires a certain cost. The material of the membrane, such as acid and alkali resistance and corrosion resistance, will also be large. A degree of influence on the treatment effect