Indigo dyeing wastewater treatment process design

A dyeing and weaving company, mainly produces indigo denim. Indigo dyeing process generally uses caustic soda-insurant powder reduction stabilizing body dyeing method for multiple dyeing, commonly used in pulp dyeing and compounding machines for production. The dyeing and dyeing compounder discharges about 100m 3 of wastewater per day, and the main components of wastewater are both inorganic materials (such as Caustic soda and insurance powder), together with a large amount of organic dyes, slurry, penetrants, softeners, etc., characterized by high pH, ​​high CODcr, and low sulfur concentration. The indigo wastewater was treated by the process of neutralizing precipitate recovery dyes-catalytic oxidation and S2--secondary biological contact oxidation.

1 design parameters

The design capacity of the wastewater treatment station is 15m3/h. Design wastewater quality and discharge requirements are shown in Table 1.

Table 1 Design Wastewater Quality and Emission Requirements

Water quality

pH

CODcr/
(mg·L-1)

BOD5/
(mg·L-1)

S2-/
(mg·L-1)

Chroma / times

SS/
(mg·L-1)

Design water quality

10 to 12

2000

600

110

100

2000

Discharge water quality

6 to 9

100

30

1

20

30

2 processing principle

2.1 Neutralization recovery dyes Indigo dyed yarn uses a single dye, which is conducive to recycling. The degradation rate of indigo dye bacteria is very slow, and it is not appropriate to use biological treatment directly, and most of them must be removed before entering the biochemical tower. Therefore, the wastewater is neutralized to a pH of 6 to 7, and the dye is insolubilized in neutral or acidic conditions, so that the dye is precipitated by itself, and then most of the dye is removed and recycled by centrifugal filtration or precipitation. Follow-up biochemical processing load.
2.2 Catalytic Oxidation (Aeration) In addition to low-sulfur sulphur, a small amount of catalyst (CoCl2) is added under neutral or weakly acidic conditions to aerate and S2- is rapidly oxidized to form SO42-. With the addition of 0.2mg/L CoCl2, aeration for 3h, the S2- in the wastewater can be reduced to below 3mg/L, and the remaining S2- can be further processed by subsequent biochemical treatment until reaching the standard.
2.3 Two-stage biological contact oxidation Oxidation and aeration In addition to the S2- wastewater, it enters two-stage bio-contact oxidation treatment and uses an artificially-selected high-performance predominant mixed bacterial group to form a membrane. The first stage uses coal slag (particle size 50-100mm) as filler. The surface of the coal slag is rough, with many holes of different sizes, large surface area, strong adsorption capacity, easy to form a membrane, strong oxygenation ability, high oxygen utilization rate, and microorganisms. Strong activity, less sludge. The second stage uses coke and activated carbon as the fillers. Two layers of coke (particle size 30-40mm) and a layer of granular activated carbon are placed in the oxidation tower. Because of its stronger adsorption, the biomass per unit volume of filler surface is more, making it more difficult to degrade. Organic matter is further decomposed completely.
The contacted oxidative hydraulic retention time was 3 h, gas-water ratio 12-15:1, pH = 6-7, CODcr<100mg/L, BOD5<30mg/L, S2-<lmg/L, chroma<20 times after treatment.

3 Treatment process

The schematic diagram of the process flow is shown in Figure 1.

The waste water discharged from the pulping and dyeing workshop is sent to the treatment station by two channels in the open channel, and the waste water containing no dye directly enters the conditioning tank, and the other enters the collection tank. The acid-resistant sewage pump was lifted to the neutralization tank, and hydrochloric acid was added before the pump to maintain the pH in the range of 6 to 7.
The neutralized wastewater gravity flows into the aeration tank except S2-. Air is sent to collection basins, neutralization pools (for aeration and agitating) and aeration tanks through pipelines and porous tubes respectively. The adjacent tubes have intersecting holes and are inclined at an angle of 45° to avoid uneven distribution of gas and pores. Blocked. In addition to the S2-after the wastewater by acid-resistant sewage pump sent to the filter room, the indigo dye separation by microfiltration. The microfiltration machine uses a PE tube filter, and the separated waste water enters a conditioning tank.
The filtered waste water and slurry bleaching wastewater enter the conditioning tank and are once again aerated by the porous tube and then raised to a biological contact oxidation tank. The biological contact oxidation tank consists of four sections: an oxidation tank, a sedimentation tank, a dioxide tank, and a second sedimentation tank. The wastewater is distributed evenly from the bottom of the triangle by pouring water over the triangle: one oxidation through 3 layers (1m per layer) of cinder packing (particle size 50-100mm), and the lower part is fully aerated with SB-600 aerator (4 pieces). A sedimentation tank is passed through a contact layer of gravel and sand of about 0.6m thickness, anti-particle size arrangement (particle size of gravel 50~20mm, sand size 3~4mm), porous air pipe under the cloth, and porous water pipe backwash in contact layer . The filler for the dioxidizing tank is coke (particle size 30-80mm), 3 layers, each layer 0.9m; the second sedimentation tank is arranged with the same sedimentation tank. The contact head of the biological contact oxidation tank is 1.20m in water head and the backwash water flows back to the regulating tank. A drain valve is provided at the bottom of the tank.
To ensure that the maintenance or operation is not normal does not affect the production, the special accident sewage reservoir, the volume of 600m3, for 3 ~ 4d production sewage storage, after the treatment can be slowly drawn back (preparation of sewage sludge pump 1); Another indigo-recovery slag pool, volume 25m3; sludge collection tank, volume 35m3, and equipped with active vertical mud pump 2 (one with a preparation).

4 processing results

More than six months of productive trial operation, see Table 2 for monthly average results of effluent quality monitoring.
The results of the operation showed that the effluent meets the discharge quality.

Table 2 Average monthly test results

Water sample number

CODcr/(mg·L-1)

BOD5/(mg·L-1)

SS/(mg·L-1)

Sulfide/(mg·L-1)

Chroma / times

Into the water

Outflow

Removal rate
/%

Into the water

Outflow

Removal rate
/%

Into the water

Outflow

Removal rate/%

Into the water

Outflow

Removal rate
/%

Into the water

Outflow

Removal rate
/%

1

1762

62

96.5

356

20

94.4

1105

8

99.3

138

0.3

99.8

116

9

92.2

2

1405

53

96.2

310

16

94.8

1415

11

99.2

106

0.23

99.8

85

7

91.8

3

1530

55

96.4

384

twenty one

94.5

1216

8.5

99.3

110

0.24

99.7

98

8

91.8

4

1624

60

96.3

366

20

94.5

630

7.5

98.8

102

0.26

99.7

90

8

91.1

5

1843

76

95.9

344

18

94.7

864

8

99.1

98

0.18

99.8

82

7

91.5

6

1385

58

95.8

324

16

95.1

1326

9.5

99.3

97

0.14

99.9

104

8

92.3

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