Chemical Treatment Of Printing And Dyeing Wastewater

Coagulation method

There are mainly mixed sediment method and mixed air floatation method, the mixers used are mostly aluminum salt or iron salt, among which basic aluminum chloride (PAC) has a better bridging adsorption performance, and ferrous sulfate price is the lowest.

The use of polymer mixers abroad is increasing, and has the potential to replace inorganic mixers, but due to the price in China, the use of polymer mixers is still rare.

It is reported that the weak anion polymer suspect agent is the most widely used, if used in combination with aluminum sulfate, it can play a better effect.

The main advantages of the doubting method are simple process flow, convenient operation and management, low equipment investment, less floor space and high decolorization efficiency for hydrophobic dyes.

The disadvantages are high operating cost, large amount of sludge and difficult dehydration, poor effect on hydrophilic dye treatment.

oxidation

Ozone oxidation has been widely used in foreign countries. Zima S.V. et al. summarized the mathematical model of ozone decolorization of printing and dyeing wastewater.

The results showed that the decolorization rate of pale brown dye wastewater reached 80% when the ozone dosage was 0.886gO3/g.

The study also found that the amount of ozone required for continuous operation was higher than that required for intermittent operation, and the installation of baffles in the reactor could reduce the amount of ozone by 16.7%.

Therefore, the use of ozone oxidation decolorization, should be designed as an intermittent operation of the reactor, and can be considered in the installation of baffles.

Ozone oxidation has a good decolorization effect on most dyes, but has a poor decolorization effect on water-insoluble dyes such as vulcanization, reduction and coating.

From the domestic and foreign operation experience and results, the decolorization effect of this method is good, but it consumes a lot of power, so it is difficult to popularize and apply it on a large scale.

Photooxidation treatment of dyeing wastewater decolorization efficiency is higher, but the equipment investment and power consumption still need to be further reduced.

Electrolytic process

Electrolysis has a good treatment effect on dyeing wastewater containing acid dyes, the decolorization rate is 50%~70%, but it has a poor treatment effect on wastewater with dark color and high CODcr.

Studies on the electrochemical properties of dyes showed that the order of CODcr removal rate of various dyes in electrolysis treatment was as follows: sulfide dyes, VAT dyes & GT;

Acid dyestuff, reactive dyestuff & GT;

Neutral dyestuff, direct dyestuff & GT;

Cationic dyes, this method is being popularized.