Views: 562 Author: Site Editor Publish Time: 2024-12-06 Origin: Site
The wastewater generated in the textile printing and dyeing process is a kind of industrial wastewater that is difficult to treat. Its water quality varies considerably, its composition is particularly complex, and its organic matter content is high.
After the biochemical treatment of printing and dyeing wastewater, the coagulation and sedimentation process is used as the primary deep treatment method. The coagulation and sedimentation process has specific effects on removing conventional pollutants such as COD, total nitrogen, ammonia nitrogen, and chromaticity.
Recently, with the development of printing and dyeing industry technology, PVA materials, surfactants, artificial fibers, grease, etc., Appear in large quantities in printing and dyeing wastewater, and these new pollutants cannot be effectively removed by coagulation and sedimentation technology, making it difficult for the effluent to meet the discharge standards.
Therefore, the industry's current focus is to seek a more stable and efficient deep treatment technology to solve the printing and dyeing of wastewater.
The wastewater treatment project of Zhejiang X Textile Printing and Dyeing Company uses coagulation and sedimentation technology for deep treatment. In recent years, the leading indicators of effluent have exceeded the direct discharge limit of the "Emission Standard of Water Pollutants for Textile Dyeing and Finishing Industry" (GB 4287-2012).
Based on this problem, Wuxi Yosun Environmental plans to improve the current deep treatment process to ensure the effluent meets the standard.
A shallow flotation process is used to treat suspended solids with a density close to that of water that is difficult to precipitate. Its principle is that many fine bubbles attached to the suspended particles separate water and suspended solids. This process has a perfect treatment effect on removing grease, fiber, soluble impurities, and surfactants in printing and dyeing wastewater.
Ozone oxidation technology can convert macromolecular chromophores into small molecule, and has many advantage,s including decolorization, disinfection, dirt removal, and enhanced biodegradability of wastewater. Therefore, most companies apply this technology to industrial wastewater treatment.
BAF treats wastewater based on biological oxidation degradation and filtration functions, and theflowingt water quality is relatively high. We are considering transforming the original coagulation and sedimentation process into a "shallow flotation-ozone-BAF" combined process. We we are setting up a pilot test project to test whether the wastewater deep treatment process technology is feasible and optimize its test conditions.
Since our company's products are mainly solid-liquid separation equipment such as flotation and sedimentation tanks, this case will focus on tapplyingshallow flotation in this case.
The designed water volume of the project is 50 m3/d, and the inlet water is the effluent of the secondary sedimentation tank. The effluent is directly discharged by the national "Water Pollution Emission Standard for Textile Dyeing and Finishing Industry" (GB 4287-2012).
The water quality indicators of the wastewater treatment project design inlet and outlet water are shown in Table 1. Since the pH, SS, ammonia nitrogen, total nitrogen, total phosphorus, BOD, etc., of the inlet water quality have fully met the standards, the subsequent effluent water quality analysis is mainly based on COD and chromaticity.
| Project | Water Intake | Water outlet |
| pH | 7 ~ 8 | 6 ~ 9 |
| COD/(mg/L) | ≤ 200 | ≤ 80 |
| SS /( mg /L) | ≤ 50 | ≤ 50 |
| Chroma (times) | ≤ 100 | ≤ 50 |
| Ammonia nitrogen/(mg/L) | ≤ 5 | ≤ 10 |
| BOD5 /( mg /L) | ≤ 20 | ≤ 20 |
| Total nitrogen/(mg/L) | ≤ 15 | ≤ 15 |
| Total phosphorus/(mg/L) | ≤ 0.5 | ≤ 0.5 |
Table 1 Design inlet and outlet indicators of wastewater treatment projects
Figure 1 Shallow air flotation - ozone - BAF process flow
The shallow flotation-ozone-BAF combined process is shown in Figure 1. First, the height of the pump is raised to pump the effluent from the secondary sedimentation tank to the shallow flotation tank, mainly to remove grease, surfactants, soluble impurities, etc.; the sludge from the flotation tank is discharged to the sludge thickening tank and then enters the dehydrator for dehydration treatment. The dehydrated water returns to the regulating tank, and the dehydrated sludge is transported out as solid waste disposal.
The flotation effluent is sent to the ozone contact tank mainly for decolorization and biodegradability improvement. After ozone oxidation, the effluent is pumped into the BAF for treatment, mainly for effluent filtration and biological oxidation and degradation of organic matter. Finally, it flows into the transparent water tank through the BAF high-level effluent weir. The BAF biological filler layer is washed regularly with the water stored in the transparent tank. The backwash wastewater formed is discharged to the biochemical section for circulation treatment. The excess water in the clear water tank overflows and is discharged. The effluent from the transparent water tank is collected, and the relevant indicators are measured.
(1) Shallow flotation tank
A circular flotation tank with a carbon steel anti-corrosion structure is designed with a diameter of 2m and a height of 1m. The reflux pressurized dissolved air flotation method is used, and the reflux ratio is 30%. It has a pressurized container water pump, a dissolved air releaser, and a matching scraper. The equipment motor is designed according to explosion-proof standards. The residence time in the pH adjustment, coagulation, and flocculation zones is 10, 2, and 10 minutes, respectively. The poly ferric, decolorizing agent and PAMdosage are 1000-1500 mg/L, 150 mg/L, and four mg/L, respectively.
(2) Ozone reactor
Design dimensions: 1.2 m in diameter, 7 m in height. The ozone catalytic reaction zone is filled with 4-6 mm Mn-Cu-06 high-efficiency catalytic filler, equipped with an ozone generator, hydraulic retention time of 3 h, and ozone dosage of 20-45 mg/L.
(3) BAF
The design dimensions of the BAF are 2 m in length, 2 m in width, 3 m in height, and 0.5 m in pebble height. The aerated biological filter reaction zone is filled with 4-6 mm ordinary ceramsite, the filler layer height is 2 m, the air-water ratio is 3:1, the porosity is 0.5, the hydraulic retention time is two h, and it is equipped with a fan. The backwash frequency is once every 48 hours, and the backwash time is one hour.
To verify the stability of the shallow flotation-ozone-BAF combined process in removing conventional pollutants, the combined process was operated continuously for 60 days, and the COD and chromaticity of the pilot test effluent were tested daily. The COD and chromaticity changes of the BAF effluent during the stable operation stage are shown in Figure 2.
Figure 2. Changes in COD and chromaticity of BAF effluent during stable operation
Figure 2 shows that under the designed conditions, the shallow flotation-ozone-BAF combined process operated continuously and stably for 60 days, and the flowing water quality reached the direct discharge standard of the National "Textile Dyeing and Finishing Industry Water Pollution Discharge Standard" (GB4287-2012) and met the design requirements. The effluent COD was ≤80 mg/L, and the chromaticity was ≤50. After the combined process, the average COD removal rate in the wastewater reached 65%, and the average chromaticity removal rate reached 80%.
To further study the degradation law of organic matter, GC-MS tests were carried out on the effluent of the secondary sedimentation tank and the effluent of the BAF. The total ion spectra of organic matter in the GC-MS test are shown in Figures 3, 4, and 5, the organic matter content analyzed by the database is shown in Table 2, and the organic matter content of each process wastewater is shown in Figure 6.
Figure 3 Total ion current of organic matter in secondary sedimentation effluent
Figure 4 Total ion current of organic matter in flotation water
Figure 5 Total ion current of organic matter in BAF effluent
Figure 6 Organic matter content of wastewater from each process
| Ingredient Name | Second sedimentation content/% | Air flotation content/% | BAF content/% |
| 1,2-Dichloroethane | 31.1 | 31.1 | 19.1 |
| 2,2-Dichlorodiethyl ether | 18.4 | 5.5 | 5.7 |
| Decane | / | 6.9 | 1.2 |
| 1,4-Dichlorobenzene | 3.6 | 2.2 | 0.5 |
| 2-Bromo-4,6-difluoroaniline | 6.2 | 2.5 | 0.4 |
| n-Dodecane | / | 8.8 | 2.3 |
| 1 - Methylnaphthalene | 12.2 | 16.1 | 9.9 |
| Biphenyl | 26.8 | 25.5 | 12.71 |
| Tributyl phosphate | / | 1.6 | 0.6 |
Table 2 Composition and content of wastewater from each process
GC-MS results showed that there were six organic substances in the effluent of the secondary sedimentation tank, including three alkanes, one aniline, and two halogenated alkanes; there were nine organic substances in the effluent of the flotation system, including four alkanes, one aniline, two halogenated alkanes, one ether, and one ester; there were nine organic substances in the effluent of the ozone system, including four alkanes, one aniline, two halogenated alkanes, one ether, and one ester; there were seven organic substances in the effluent of the BAF system, including four alkanes, two halogenated alkanes, and one ether.
From the effluent of the secondary sedimentation tank to the effluent of the flotation system, the contents of the three organic substances decreased significantly, the content of 2,2-dichlorodiethyl ether decreased from 18.4% to 5.5%, and the content of 1,4-dichlorobenzene decreased from 3.6% to 2. 2%. The content of 2-bromo-4,6-difluoroaniline decreased from 6.2% to 2.5%, indicating that the flotation process has a significant removal effect on aniline, ether and halogenated alkanes.
From the flotation effluent to the BAF effluent, the contents of 8 organic substances decreased significantly, the content of 1,2-dichloroethane decreased from 31.1% to 19.1%, the content of decane decreased from 6.8% to 1.2%, the content of 1,4-dichlorobenzene decreased from 2.2% to 0.5%, the content of 2-bromo-4,6-difluoroaniline decreased from 2.5% to 0.4%, the content of n-dodecane decreased from 8.8% to 2.3%, and the content of methylnaphthalene decreased from 16.1% to 9. 9%, biphenyl content decreased from 25.5% to 12.7%, and tributyl phosphate content decreased from 1.6% to 0.6%.
The above organic matter contents were significantly reduced, indicating that ozone and BAF have relatively sound removal effects on alkanes, halogenated alkanes, esters, aniline, etc. In summary, the shallow flotation-ozone-BAF processsignificantly removesn refractory organic matter, especially the ozone-BAF proces, whichs, which has the most apparent removal effect.
(1) Use the shallow air flotation-ozone-BAF combined process to deeply treat the effluent from the secondary sedimentation tank of printing and dyeing wastewater. Under the conditions of polyiron dosage of 1350 mg/L, decolorizing agent dosage of 120 mg/L, and ozone dosage of 40 mg/L, the average total removal rates of COD and chroma are 65% and 80% respectively. All effluent indicators are lower than the emission limits of the "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry" (GB 4287-2012).
(2) GCMS - The analysis results show that the main organic components of the secondary sedimentation tank effluent and air flotation effluent of printing and dyeing wastewater are complex, and the content of each organic matter is relatively high. After the shallow air flotation-ozone-BAF combined process treatment, the types of organic matter are reduced, and the organic matter types are reduced. The concentration was significantly reduced, especially esters, alkanes and anilines in the effluent, indicating that the shallow air flotation-ozone-BAF combined process has a certain removal effect on refractory organic matter.
