Characteristics of wastewater from printing and dyeing plants:

The amount of wastewater in printing and dyeing plants is relatively large, and 100 to 200 tons of water is consumed per 1 ton of textiles printed and dyed, of which 80% to 90% are discharged as wastewater. Printing and dyeing wastewater has the characteristics of large water volume, high content of organic pollutants, high alkalinity, and large changes in water quality. It is one of the difficult industrial wastewaters to treat. , sand substances, inorganic salts, etc.

Air flotation treatment of printing and dyeing wastewater:

The air flotation machine has a good treatment effect on the printing and dyeing wastewater, but if you want to achieve a good treatment effect, first, there must be enough gas to be sucked into the liquid by the aerator components. The adhesion of flocs must be solved by engineering design.

Both bubbles and flocs have a certain degree of hydrophobicity, and they tend to adsorb each other and reduce their surface energy. Under certain hydraulic conditions, the micro-bubbles with kinetic energy collide with the flocs softly. When the water film of the bubble adhesion layer touches the flocs When the particle hydrophobic group is attached, it is adhered by van der Waals force, and the more collisions, the stronger the adhesion.

Among them, the micro-bubbles with large kinetic energy collide into the grooves of the floc structure and are wrapped, and the flocs or flocs collide and grow. During the process, the free bubble nets or the flocs adhering to the bubbles are bound by adsorption bridges and become larger. The air-filled flocs can make the bubbles adhere to the flocs, and the flocs can be driven by the bubbles to rise. During the ascent, it continues to copolymerize and becomes larger due to the velocity gradient.

In order to improve the adhesion effect, several coagulants can be added at the same time. Since each coagulant has a different chemical base, it can act as a bridge in the water body and give full play to its respective advantages. Under the same environmental conditions, the treatment effect of the same dye and dyeing wastewater is obviously different as long as the pH value is different.

It has been proved by experiments that when the pH=7, the number of microbubbles per unit volume is large and the average particle size is small, and the treatment effect is good; when pH>7, the number of microbubbles decreases and the particle size increases; pH<7, and the pH value The lower it is, the smaller the number of microbubbles, the larger the particle size, and the worse the treatment effect. Therefore, appropriate coagulants can be added to the wastewater to ensure the ideal pH value of the air flotation treatment and improve the quality of the treated water.

For example:

A wool spinning enterprise discharges more than 400 tons of printing and dyeing wastewater per day. In order to eliminate pollution while developing production, the enterprise invested 600,000 yuan and built a set of wastewater treatment equipment with a daily processing capacity of 1,000 tons.

1. Wastewater quality and discharge

The enterprise's printing and dyeing wastewater mainly comes from the dyeing and finishing and strip compounding processes. The dyes used are: mordant dyes, disperse dyes, neutral dyes and detergents, yuanming powder, acetic acid, sulfuric acid and other auxiliary agents. The quality of wastewater varies greatly depending on the type of product dyeing. Generally, the water quality is PH4~9, CODCr200~400mg/l, BOD5 150~300mg/1, Cr6+ 0.100~0.160mg/l, chroma 100~200 times.

2. Processing technology

The printing and dyeing wastewater is separated from the drainage of other production links and discharged. The printing and dyeing wastewater enters the adjustment tank from the underground sewage pipe through the grille, and is lifted to the sedimentation tank by the pump. Add quantitative basic aluminum chloride [Al2(OH)2Cl0～n]m (n=1～5, m≤10). In the flotation tank, the waste water is separated from the water by the adsorption of pressurized dissolved air and the flocculation of basic aluminum chloride (flocculant), so that the flocs are floated and separated from the water, and the clean water is introduced into the advection filter tank (with coke as the filter material). ), using physical adsorption to further remove suspended solids and other harmful substances before discharge. The sludge discharged from the air flotation tank is dehydrated and pressed into a mud cake by the filter press system for storage.

3. Main process parameters

Adjustment pool: effective volume 100m3, residence time 3 hours

Sedimentation tank: effective volume 7.875m3 residence time 2.9 hours

Air flotation tank: effective volume 15m3, residence time 30-40 minutes

Filter tank: effective volume 6m3 residence time 10 minutes

4. Processing effect and operating cost

Since the project was put into operation, the equipment has been running normally, the water quality is stable, and the treatment effect is good. After the wastewater is treated, all indicators meet the national discharge standards.

The treatment cost is 0.18 yuan/ton of waste water, (among which the consumption of basic aluminum chloride is 0.138 yuan/ton of waste water). After the project is put into operation, it not only improves the environment, but also exempts sewage charges.

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