Analysis of the color reversal problem in printing and dyeing wastewater treatment by Polyaluminum Chloride(PAC) manufacturers.
Why is the color of the treated wastewater in the printing and dyeing industry light yellow when it is treated through biochemical treatment and added with Polymeric Aluminium Chloride(PAC) or Ferrous Sulfate (PFS) and liquid alkali? What are the general reasons for this phenomenon and what methods should be used to handle it? Below, the manufacturer of Yuxin Ring Polymeric Aluminium Chloride(PAC) will analyze with us the reasons for the yellowing of printing and dyeing wastewater after treatment, as well as the reasons for the yellowing of wastewater treated with ferrous sulfate.
Printing and dyeing wastewater generally has characteristics such as high organic content, deep chromaticity, and high alkalinity. If treated with ferrous sulfate and liquid alkali, there are two possibilities for yellowing: first, there are some inorganic metal ions in the printing and dyeing wastewater that have not been deposited, and second, the color of organic matter; For the removal of inorganic metal ions that have not been deposited, alkali adjustment and participation in sodium sulfide can be used to deposit inorganic metal ions. If the presence of organic matter in printing and dyeing wastewater causes the color to appear light yellow, it is necessary to consider high-grade oxidation or adsorption.
The original color of wastewater is yellow, but after treatment with ferrous, the color fades and then turns yellow. The reason for this may also be a phenomenon of color reversal, which is related to the use of some reactive dyes. The color appears to have been removed from the front, but then appears to be similar to the original wastewater. Therefore, most treatment processes for printing and dyeing wastewater use biochemical treatment.
Recently, I have been exposed to decolorization of wastewater from dyeing factories using ferrous, sodium hydroxide, and polyaluminum chloride. Even after treatment, some of the red color cannot be removed, with a pH value of 8. Why can’t some of the red color be removed? Are you considering changing to other agents?
The addition method of ferrous sulfate and the use of ferrous sulfate with pH value may have a poorer effect on the treatment of red and green wastewater, but as long as the reaction conditions are appropriate, the chromaticity can generally be reduced to the emission standards. The following claims are made in this situation:
1. Add sodium hydroxide to the front end and ferrous to the back end, and maintain a pH of around 9 after adding ferrous. After adding sodium hydroxide in this way, the pH can reach 12 or above, and under strong alkaline conditions, it can destroy the molecular structure of some colored groups, transforming difficult to treat colored groups into easy to treat colored groups.
Furthermore, when initially reacting with ferrous ions, the pH will be around 11. When ferrous ions have a pH above 11, their decolorization effect will be better than those with a pH of around 8, especially for some difficult to handle colored groups.
2. Replacing sodium hydroxide with lime not only reduces the cost of chemicals but also has the effect of improving treatment.