Printing and dyeing wastewater is waste water produced during the process of spun sizing and sizing of fiber materials, scouring, desizing, bleaching, mercerising, printing, and dyeing. Wastewater contains naphthalene compounds, lanthanides, amines, and sulfides. , chromium, alkali, acid and other toxic and harmful substances.
Dye wastewater has high chroma, complex composition and low biodegradability. After discharge, it has a great impact on the surface water environment, especially the color destroys the landscape environment.
The direct electrolysis method that has emerged in recent years has opened up new ways for dye wastewater treatment. The electrolysis method is through the electrode reaction, in the electrolysis process, to achieve the two processes of air flotation and flocculation to remove organic matter and decolorize.
The process of electrolysis to remove dye molecules is actually an electrolysis-air flotation-flocculation process. Anion electrode reactions occur. The formation of a flocculant with high adsorption activity on the anode can effectively remove the colloidal particles and impurities in the dye wastewater. The H2 generated by the cathode can drive the floc upwards to the surface and precipitate after the reaction, which is an air flotation process. The oxidation or reduction reaction occurring at the poles can destroy the chromophoric groups of the dye molecules, turning the macromolecules into small molecules, or completely oxidizing to CO2 and HO2, and the solution color becomes colorless.
The added electrolyte is usually NaCl, which helps to decolorize the wastewater and remove COD. The reason is that when the NaCl solution is electrolyzed, chlorine is released on the anode, and Cl2 is a strong oxidant. Cl2, Na+, and O2 further generate NaClO, which is more oxidizing. Both Cl2 and NaClO are strong oxidants that can oxidize the dye molecules and cause the long bonds to lose color. In addition, after the addition of NaCl, the H2O electrolysis is accelerated, and the bubble-like floe formed by the H2 formed on the cathode moves upwards, accelerating the flotation and flocculation of the organic matter.
The electrolysis method has a better treatment effect on the dye wastewater. The removal rate of COD cr is over 90%, and the decolorization rate is 100%.