Main features of woven fabric printing and dyeing wastewater:

Woven fabric printing and dyeing wastewater mainly includes: desizing wastewater (Desizing and bleaching), mercerizing wastewater, dyeing wastewater or printing wastewater.

Desizing wastewater:

Alkaline, PH can reach more than 12. The wastewater mainly contains starch, PVA, PA and other slurry, fiber, additives and so on. Desizing wastewater accounts for about 15%~20% of the total printing and dyeing wastewater, COD up to 20,000-30,000 mg/L, pollutants occupy more than half of the total pollutants in the wastewater of printing and dyeing plant, and PVA slurry is quite difficult to degrade.

Mercerizing wastewater:

High alkali content, alkali content reaches 3~5%. Alkali is often recovered by evaporation and concentration, and the wastewater is generally rarely discharged.

Dyeing wastewater:

Wastewater mainly contains dyes, auxiliaries, surfactants and so on. Generally alkaline, high chroma, large amount of water, poor biodegradability.

Printing wastewater:

Mainly includes washing wastewater from diluting and color matching, printing roller and screen, as well as washing and detergent wastewater generated during post-printing treatment. The wastewater mainly contains various slurries, dyes, and additives. The water volume is large and the pollutant concentration is high. The components of the finishing wastewater mainly include slurries, oils, various resins, and fiber scraps. Due to the small water volume of finishing wastewater, its impact on the overall printing and dyeing wastewater quality is relatively small.

Process design

Process design introduction

1) The use of mass distribution treatment. The high concentration desizing wastewater is pretreated first, and then mixed with other wastewater before further treatment.

2) The desizing wastewater belongs to high concentration wastewater, with high PH, high COD, high salinity and high suspended matter. In order to avoid impact on the comprehensive wastewater, the desizing wastewater is pretreated separately, which greatly reduces the overall concentration of the comprehensive wastewater.

The desizing wastewater first enters the mechanical grille to remove most of the suspended matter, and after pH adjustment, enters the pre-treatment adjustment tank. Then the pH value is fine-tuned into the hydrolysis tank, and the macromolecular organic matter that is difficult to biodegrade in the wastewater is further decomposed into small molecular organic matter pollutants that are easy to degrade through the effect of hydrolytic acidification. The effluent from the hydrolysis tank enters the anaerobic tank, in which the desizing wastewater fully contacts and transfers mass with the anaerobic sludge, degrades the organic matter in the wastewater, and the biogas generated is discharged. The anaerobic sludge and wastewater rise to the separation area through the gap of the three-phase separator, and the sludge is precipitated and concentrated in the separation area and returned to the lower part of the three-phase separator to maintain the biomass in the anaerobic reactor. The precipitated effluent is discharged out of the anaerobic tank through the pipeline and enters the comprehensive wastewater adjustment tank.

3) The comprehensive wastewater includes dyeing wastewater, printing wastewater, and desizing wastewater after pretreatment.

The comprehensive wastewater first enters the mechanical grille to remove most of the suspended matter and enters the comprehensive adjustment tank. Then it is lifted to the initial settling reaction tank by the lifting pump, and the pH value is fine-tuned. At the same time, Fe₂SO₄ and PAM are added to make the SS and some colored substances in the sewage undergo physicochemical reaction and flocculation precipitation, and most of them are removed in the initial settling tank. The supernatant of the initial sedimentation tank enters the hydrolysis tank and the anoxic aerobic tank. The macromolecular organic matter which is difficult to biodegrade in the wastewater is further decomposed into small molecular organic matter pollutants which are easy to degrade through the hydrolysis acidification of the hydrolysis tank, and the biodegradability is improved. In the anaerobic aerobic tank, most of the pollutants are degraded and the sewage quality is further purified through the action of aerobic microorganisms. After the sludge water is separated in the secondary sedimentation tank, the supernatant flows to the advanced oxidation reaction tank. Part of the sludge is returned to the activated sludge tank through the sludge return pump, and the remaining sludge is discharged to the sludge thickening tank. The effluent from the secondary sedimentation tank then passes through the advanced oxidation reaction tank. After the advanced oxidation reaction, the macromolecular organic matter that is difficult to biodegrade is further degraded. The degraded sludge is discharged by flocculation and sedimentation in the mixed sedimentation tank.