1, source

The four processes of printing and dyeing process should discharge the waste water. The pretreatment stage (including singeing, desizing, scouring, bleaching, mercerizing, etc.) is to discharge the desizing wastewater, the scouring wastewater, the bleaching wastewater and the mercerized wastewater, and the dyeing process discharges Dyeing wastewater, printing process discharge printing waste water and soap liquid waste water, finishing process is discharged finishing waste water. Dyeing wastewater is mixed wastewater of all kinds of wastewater above, or comprehensive wastewater other than bleaching wastewater.

2, water quality and water

Water quality of printing and dyeing wastewater varies with the type of fiber used and the processing technology, the components of the pollutants vary widely. The general printing and dyeing wastewater pH value of 6 to 10, COD of 400mg / l ~ 1000mg / l, BOD of 100 ~ 400mg / l, SS 100 ~ 200mg / l, 100 to 400 times the color. However, when the printing and dyeing process and the use of fiber types and processing technology changes, the wastewater quality will have a greater change. For example, when wastewater contains alkali-reduced wastewater generated during dyeing and printing of polyester silk, wastewater COD will increase to over 2000-3000mg / l, BOD to 800mg / l or more, pH value to 11.5-12, And the quality of waste water deteriorated with the addition of polyester simulated silk alkali dyeing wastewater. When added to the amount of alkali reduction of COD in wastewater exceeds 20% of COD in wastewater, biochemical treatment will be difficult to adapt. Different manufacturers or the same manufacturer of different production periods, wastewater quality varies, water quality will exceed the above range.

(1) desizing wastewater: smaller amount of water, but high concentrations of pollutants, which contains a variety of slurry, slurry decomposition, cellulose, starch, alkali and various additives. Desizing wastewater into alkaline, pH value of 12 or so. Sizing starch-based (cotton) desizing wastewater, the COD, BOD values ​​are high, good biodegradability; sizing polyvinyl alcohol (PVA) -based (such as polyester cotton warp) desizing wastewater, COD High and low BOD, wastewater biodegradability is poor.

(2) Scouring wastewater: Large amount of water, high concentration of pollutants, including cellulose, acid, wax, grease, alkali, surfactant, nitrogenous compounds, etc. The wastewater is strongly alkaline, .

(3) bleaching wastewater: large amount of water, but less polluting, which contains residual bleach, a small amount of acetic acid, sodium thiosulfate and so on.

(4) mercerized wastewater: high alkali content, NaOH content of 3% to 5%, most of the printing and dyeing plants are concentrated by evaporation recovery, so mercerized wastewater is rarely discharged, after repeated use of the final discharge of the effluent was still strong base Sex, BOD, COD, SS are higher.

(5) Dyeing wastewater: high water content, water quality varies according to the dye used, including slurries, dyes, auxiliaries, surfactants, etc. are generally alkaline, high chroma, COD higher than the BOD More, biodegradability is poor.

(6) Printing waste water: large amount of water, in addition to the printing process of waste water, but also including printed soaping, washing wastewater, high concentrations of pollutants, including pulp, dyes, additives, BOD / COD are more high.

(7) finishing waste water: high water content, including fiber lint, resin, oil, slurry and so on.

The characteristics of printing and dyeing wastewater can be summarized as: medium concentration, complex composition, poor biodegradability, deep color, alkaline, high pH, ​​water quality changes. Printing and dyeing industry is a large industrial wastewater discharge, the national emissions of 300 ~ 4 million m3 / d.

(8) alkali reduction Wastewater: It is generated by the process of alkali reduction of polyester. It mainly contains polyester hydrolyzate to formic acid, ethylene glycol and so on. The content of this formic acid is as high as 75%. Alkali-reducing wastewater is not only high in PH but also high in organic matter concentration. CODcr is up to 90,000 in waste water discharged by alkali reduction process. It is difficult for polymer and some dyes to be biodegraded. Such wastewater is a high-concentration organic wastewater.

3, the characteristics of printing and dyeing wastewater

(1) large chroma, high organic content, in addition to containing contaminants such as dyes and additives, but also contains a large number of slurry, the viscosity of the wastewater;

(2) COD changes up to 2000 ~ 3000mg / l and high BOD up to 2000 ~ 3000mg / l.

(3) Alkaline, such as sulfur dyes and vat dyes wastewater pH value of up to 10 or more;

(4) Large changes in water temperature and water volume, due to changes in processing varieties, production, can lead to large changes in water temperature and water.

4, the choice of treatment methods

Cotton and cotton blended printing and dyeing wastewater treatment process

(1) Mixed waste water treatment process grille - pH value adjustment - Conditioning tank - Hydrolysis acidification - Aerobic biological treatment - Physiochemical treatment

(2) Wastewater quality treatment process Scouring and desizing and other high-concentration wastewater after anaerobic or hydrolytic acidification, and then mixed with other wastewater treatment; alkali reduction of alkali by alkali recovery and reuse, and then with other wastewater Mixed processing.

Wool printing and dyeing wastewater treatment process

Grille - conditioning tank - Hydrolytic acidification - Anaerobic biological treatment Scouring waste water should be recovered lanolin, and then use anaerobic biological treatment + aerobic biological treatment, and then mixed with dyeing and finishing wastewater treatment or into urban sewage treatment plant.

Silk dyeing and finishing wastewater treatment process

Grille - Leaf conditioning tank - Hydrolytic acidification - Aerobic biological treatment Silk Spinning wastewater treatment process should be used: Grille - cold water tank (heat recovery) + conditioning tank - Anaerobic biological treatment of aerobic Biological treatment.

Reeling silk should be recycled sericin and other valuable substances before processing, treatment process: grille, grid - conditioning pool - aerobic biological treatment - sedimentation or flotation.

Dyeing and finishing waste water treatment process

According to the biological degumming wastewater, chemical degumming waste water, waste water washing water quality and the actual water quality after mixing with the dyeing and finishing wastewater, the treatment process should be used: grid + grit pH adjustment - anaerobic biological treatment - Hydrolytic acidification - Aerobic biological treatment - Physico-chemical treatment - Biofilter.

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