A dyeing and weaving company, mainly produces indigo denim. The indigo dyeing process is generally dyed by the caustic soda-safety powder reduction method. It is usually produced by a slurry dyeing combined machine. The pulping and dyeing combined machine discharges about 100m 3 of wastewater per day. The main components of the wastewater are both inorganic materials ( Such as caustic soda, insurance powder), combined with a large number of organic dyes, pulp water, penetrants, softeners, etc., the water quality is characterized by high pH, ​​high CODcr, high sulfur concentration. The design uses neutralization precipitation to recover dye-catalytic oxidation in addition to S 2- - two-stage biological contact oxidation process for the treatment of indigo wastewater.
1 design parameters
The design capacity of the wastewater treatment station is 15m 3 /h. The design wastewater quality and discharge requirements are shown in Table 1.
Water quality | pH | CODcr/ | BOD 5 / | S 2- / | Chroma/time | SS/ |
Design water quality | 10~12 | 2000 | 600 | 110 | 100 | 2000 |
Emission water quality | 6 to 9 | 100 | 30 | 1 | 20 | 30 |
2 Processing principle
2.1 Neutralization and precipitation of dyes <br> Indigo dyed yarns use a single dye for recycling. The degradation rate of indigo dye bacteria is very slow, it is not suitable to use biological treatment directly, and most of it must be removed before entering the biochemical tower. Therefore, the wastewater is neutralized to pH 6-7, and the dye is self-dissolved under the neutral or acidic conditions, and the dye is self-precipitated, and then most of the dye is removed and recycled by centrifugal filtration or precipitation, which greatly reduces the amount of dye. Subsequent biochemical treatment load.
2.2 Catalytic oxidation (aeration) in addition to low-cost sulfur <br> Under neutral or weakly acidic conditions, a small amount of catalyst (CoCl 2 ) is added, aeration, S 2- is rapidly oxidized to form SO 4 2- . With the addition of 0.2mg/L CoCl 2 and aeration for 3h, the S 2- in the wastewater can be reduced to below 3mg/L, and the remaining S 2- can be further processed by subsequent biochemical treatment to reach the standard.
2.3 Two-stage biological contact oxidation <br> Aeration in addition to S 2- wastewater, enter two sections of biological contact oxidation treatment, and use artificially selected high-efficiency mixed bacteria to hang membrane. The first section uses cinder (particle size 50~100mm) as the filler. The surface of cinder is rough, with many holes of different sizes, large surface area, strong adsorption capacity, easy to hang membrane, strong oxygenation capacity, high oxygen utilization rate, and microorganisms. Strong activity and low sludge volume. In the second stage, coke and activated carbon are used as fillers. Two layers of coke (particle size 30-40 mm) and a layer of granular activated carbon are placed in the oxidation tower. Because of its stronger adsorption, the surface biomass per unit volume of the filler is more, making it more difficult to degrade. The organic matter is further broken down completely.
Contact oxidation water retention time 3h, gas-water ratio 12～15:1, pH=6～7, CODcr<100mg/L after treatment, BOD 5 <30mg/L, S 2- <lmg/L, color <20 times .
3 treatment process
The process flow is shown in Figure 1.
The wastewater discharged from the pulping workshop is sent to the treatment station via the open channel in two ways. The wastewater containing no dye directly enters the regulating tank, and the other enters the collecting basin. It is lifted to the neutralization tank by the acid-resistant sewage pump, and hydrochloric acid is added to the pump before the pump to maintain the pH in the range of 6-7.
The neutralized wastewater gravity flows into the aeration tank in addition to S 2- . The air is sent to the sump, the neutralization tank through the pipeline and the porous pipe respectively (pre-aeration and agitation), and the aeration tank, the perforations of the adjacent gas pipes are crossed and inclined 45° downward to avoid uneven distribution of air and perforations Blocked. After addition of the acid S 2- wastewater effluent pressurized by the pump to the filter room, separated by microfiltration indigo dye. The microfiltration machine uses a PE tube filter, and the separated wastewater enters the conditioning tank.
The filtered wastewater and the pulp bleaching wastewater enter the regulating tank, and are again pre-aerated by the porous tube and then upgraded to the biological contact oxidation tank. The biological contact oxidation tank is composed of four stages: a oxidation tank, a sedimentation tank, a dioxide tank, and a second sedimentation tank. The wastewater is evenly distributed through the triangular rafts from bottom to top: one oxidation passes through three layers (1 m per layer) of cinder filler (particle size 50-100 mm), and the lower part is fully aerated with SB-600 aerator (4 pieces). A sedimentation tank passes through a layer of gravel and sand with a thickness of about 0.6 m, and is arranged in reverse grain size (grape particle size: 50 to 20 mm, sand particle size: 3 to 4 mm). The porous gas pipe is laid down, and the porous water pipe in the contact layer is backwashed. . The filler of the dioxide tank is coke (particle size 30-80 mm), 3 layers, each layer is 0.9 m; the second sedimentation tank is arranged in the same sedimentation tank. The biological contact oxidation tank has a water head difference of 1.20m, and the backwash water is returned to the adjustment tank. The bottom of the tank is provided with a drain valve.
In order to prevent the maintenance or operation from being abnormal, the special accident sewage storage tank, with a volume of 600m 3 , can be stored for 3~4d production sewage, and can be slowly withdrawn after treatment (1 sewage sludge pump) Another indigo recovery slag pool with a volume of 25m 3 ; a sludge collection tank with a volume of 35m 3 and two movable vertical mud pumps (one for one).
4 processing results
The production test run is more than half a year, and the monthly average result data of the effluent water quality monitoring is shown in Table 2.
The results of the operation show that the effluent meets the discharge water quality.
Water sample number | CODcr/(mg·L -1 ) | BOD 5 /(mg·L -1 ) | SS/(mg·L -1 ) | Sulfide / (mg·L -1 ) | Chroma/time | ||||||||||
Influent | Water | Removal rate | Influent | Water | Removal rate | Influent | Water | Removal rate /% | Influent | Water | Removal rate | Influent | Water | 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 |
5 Main economic indicators
The project will process 360m 3 of wastewater, covering an area of ​​about 500m 2 and a total investment of 580,000 yuan. Operating cost analysis:
1% old fee: depreciation period is considered according to 15a, then the depreciation fee per cubic meter of wastewater is 0.30 yuan;
2 Labor costs: a total of 4 people, the average person per month is 800 yuan, the labor cost per cubic meter of wastewater is 0.30 yuan;
3 Electricity: The electricity consumption per hour is about 24kWh, which is 1.20 yuan per cubic meter of wastewater.
4 Pharmacy fee: the total cost of acid and cobalt salt per cubic meter of wastewater is about 1.50 yuan;
5 Indigo recovery: About 20g of indigo is recovered per cubic meter, and the recovery cost per cubic meter of wastewater is 1.60 yuan per ton of indigo.
6 total operating costs per cubic meter of wastewater treatment requires 1.70 yuan.
6 Conclusion
Indigo dyeing yarn wastewater treatment process: dye recovery - oxidation desulfurization - biological treatment of organic matter, the process has the characteristics of low investment, low operating cost, convenient management, small floor space, high treatment efficiency, good effluent quality, and good Value.
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Changxing Dingqiang Textile Co., Ltd. , https://www.dingqiangtextile.com