Printing and dyeing wastewater treatment method
Characteristics of printing and dyeing wastewater: Textile printing and dyeing wastewater exhibits characteristi...
Printing and dyeing wastewater treatment method
Characteristics of printing and dyeing wastewater: Textile printing and dyeing wastewater exhibits characteristics of extensive water volume, high organic contaminant concentration, substantial alkalinity, and vast water quality fluctuations. It is one of the challenging industrial wastewaters to manage, comprising dyes, pulp, additives, oil agents, acids and alkalies, fiber impurities, sand substances, inorganic salts, etc.
Fundamental understanding of printing and dyeing wastewater: It features expansive wastewater volume, elevated temperature, deep color, alkalinity, and elevated organic pollutant load. Each physical, chemical, and biological method possesses its unique treatment benefits, however, they all display limitations and pose difficulty in ensuring that the wastewater treatment adheres to the designated standards.
Classification of Printing and Dyeing Wastewater
1. Water reuse wastewater: The water volume is diminished, the pollutant concentration is heightened, and it chiefly comprises pulp and its decomposition products, fiber shavings, acids, starch bases, and enzyme pollutants, with high turbidity; The wastewater is alkaline with a pH value of approximately 12. When utilizing starch slurry, both BOD and COD are high, indicating robust biodegradability; When employing synthetic slurry, COD is exceedingly high, BOD is less than 5mg/L, and the water biodegradability is feeble.
2. Boiling wastewater: With significant water quantities and enhanced pollutant concentration, it primarily contains cellulose, fruit acid, wax, oil, alkali, surfactants, nitrogen-containing compounds, etc. The wastewater displays strong alkalinity, elevated water temperature, brown color, and high COD and BOD, reaching thousands of milligrams per liter. The pollution of chemical fiber refining wastewater is relatively modest.
3. Bleaching wastewater: The water volume is considerable, the pollution is minimal, and it primarily comprises residual bleach, a small quantity of acetic acid, oxalic acid, sodium thiosulfate, etc.
4. Silk polishing wastewater: It possesses a high alkali content, with NaOH content of 3% -5%. Most printing and dyeing factories recuperate NaOH through evaporation and concentration, so silk polishing wastewater is generally seldom discharged. After repeated utilization in the process, the final discharged wastewater still retains strong alkalinity, with high BOD, COD, and SS.
5. Dyeing wastewater: The water quality is variable and occasionally contains toxic substances (such as sulfurized alkali, tartaric acid, aniline, copper sulfate, phenol, etc.) from the utilization of various dyes. It is alkaline and occasionally has a pH of 10 or above (when using sulfurized or reduced dyes). It also contains organic dyes, surfactants, etc. High chromaticity, low SS, higher COD than BOD, poor biodegradability
6. Printing wastewater: comprising pulp, high BOD and COD.
7. Sorting process wastewater: primarily comprising fiber shavings, resin, formaldehyde, oil agents, and slurry, with a small quantity of water.
8. Alkali reduction wastewater: Generated during the alkali reduction process of polyester simulated silk, primarily containing polyester hydrolysis products such as terephthalic acid and ethylene glycol, with terephthalic acid content as high as 75%. Alkali reduction wastewater not only exhibits a high pH value (generally>12), but also a high concentration of organic matter. The CODcr in the wastewater discharged from the alkali reduction process can reach up to 90000 mg/L. Polymer organic matter and some dyes are difficult to biodegrade, rendering this type of wastewater a high concentration and stubbornly resistant to degradation organic wastewater.
Printing and dyeing wastewater treatment methodologies
1. Adsorption methodology: The predominantly utilized methodology in physical treatment is adsorption, which entails blending powders or particles of porous materials like activated carbon and clay with wastewater, or permitting wastewater to traverse a filter bed composed of its granular materials, thereby enabling pollutants in the wastewater to be adsorbed onto the surface of the porous material or filtered out. The adsorption rate, BOD removal rate, and COD removal rate of activated carbon attained 93%, 92%, and 63%, respectively.
2. Coagulation methodology: There exist primarily coagulation precipitation methodology and coagulation air flotation methodology. The coagulants employed are predominantly aluminum salts or iron salts, among which basic aluminum chloride (PAC) exhibits superior bridging adsorption performance. The primary advantages of coagulation methodology are straightforward process flow, convenient operation and management, modest equipment investment, compact footprint, and high decolorization efficacy for hydrophobic dyes; The disadvantages are elevated operating costs, substantial sludge production and challenging dehydration, and subpar treatment effect on hydrophilic dyes.
3. Oxidation methodology: Ozone oxidation methodology can achieve commendable decolorization effect on most dyes, but displays poor decolorization effect on insoluble dyes such as sulfurization, reduction, and coatings. From domestic and international operational experience and outcomes, this methodology possesses good decolorization effect, but it consumes considerable electricity and presents certain difficulties in large-scale promotion and application. The oxidation methodology exhibits a high decolorization efficiency in treating printing and dyeing wastewater, but equipment investment and power consumption still necessitate further reduction.
4. Electrolysis methodology: Electrolysis exhibits a robust treatment effect on printing and dyeing wastewater containing acidic dyes, with a decolorization rate of 50% -70%, but the treatment effect is deficient for wastewater with dark colors and high CODCr.
5. Biological methodology: In the biological treatment of printing and dyeing wastewater in China, surface accelerated aeration and contact oxidation methodologies predominate. Additionally, the blast aeration activated sludge methodology, jet aeration activated sludge methodology, and biological turntable have also been implemented, and the biological fluidized bed remains in the experimental application phase. Due to the low removal rate of chromaticity by organisms, generally around 50%, physical or chemical treatment is required when the effluent chromaticity requirement is stringent.
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