Environmental water-based ink and its wastewater treatment (below)

3 Wastewater Treatment Process Overview

During the production and application of water-based inks, a certain amount of waste water will be generated due to the cleaning of the equipment. The ever-changing water-based ink color causes the chemical composition of its waste water to be quite complex. It has high COD, high chroma, and is difficult to biodegrade. Once it enters the water, it will cause serious pollution to the water environment. Wastewater treatment processes have a very close relationship with the type and characteristics of aqueous inks. The current research and application of aqueous ink wastewater treatment mainly include the following processes.

3.1 Chemical coagulation process [5]

Zhang Tao and others used chemical coagulation technology to test the water-based ink wastewater from a water-based ink manufacturer in Xi'an. Through the selection of commonly used flocculants FeSO4·7H2O, FeCl3·6H2O, PAC, PFC, PAFC and coagulants cationic polyacrylamide, polyacrylamide, chitosan, polydicyandiamide and pH adjustment, and dosage selection . The optimum conditions of the coagulation process at room temperature were obtained: FeCl3·6H2O was selected as the optimal flocculant, the dosage was 80 mg/L, the optimal coagulation pH was 4.0, and the best coagulant aid was shell The amount of polysaccharides was 0.8 mg/L. After treatment, the COD of raw water decreased from 5 638.2 mg/L to 634.5 mg/L, the removal rate reached 87%, and the chroma decreased from 240 to 10 times, with a removal rate of 99%. A good test result was obtained.

3.2 Iron filings micro-electrolysis process [6]

Zhang Tao and others also adopted the iron filing micro-electrolysis process to test the water-based ink waste water of the same water-based ink manufacturer. After raw water was first adjusted to pH with HCl, it was subjected to sedimentation and pretreatment. The COD was reduced from 6 000 to 8 000 mg/L to 800 to 1000 mg/L, and the chroma decreased from opaque to 160 times. The effluent was then neutralized by microelectrolysis and lime milk. Through the static and dynamic tests on the main micro-electrolytic process parameters: pH value, iron content, coke amount, and reaction time, the optimum conditions for micro-electrolysis were obtained: pH 4.0, iron scrap amount 10%, and coke content as filler The amount was 16.67% and the reaction time was 60 min. The COD of the wastewater is removed again by 50% and the color is removed by 90%. After two-stage treatment of raw water by sedimentation pretreatment and iron chips micro-electrolysis, the removal rate of COD reached 85%, and the removal rate of color was 95%, which had a good effect.

3.3 Combined flotation-contact oxidation process [7]

The printing wastewater treatment project of a carton packaging enterprise in Guangzhou indicated that the combined treatment of flotation and contact oxidation can achieve a better result in the integrated treatment of aqueous printing ink wastewater, canteen sewage, and domestic sewage. The water-based ink wastewater is coagulated and floated after separating large suspended solids. After solid-liquid separation, it is mixed with canteen sewage and domestic sewage. After anaerobic adjustment, the secondary biological contact oxidation aeration causes the effluent CODcr to reach 67 mg. L, color less than 10 times. Ink wastewater wastewater CODcr up to 182 000 mg/L, color 4000 times, through the flocculating agent basic aluminum chloride and coagulant caustic soda and polyacrylamide to make wastewater after flocculation bloom, COD removal rate can be achieved 47.6%. Daily 20 tons of air-floated wastewater is mixed with 100 tons of daily canteen wastewater and domestic wastewater (COD < 366 mg/L), followed by anaerobic preconditioning followed by secondary biological contact oxidation . The biological contact oxidation zone A stays for 2.8 hours and the B stay stays for 3.3 hours. This process combination has the characteristics of stable treatment effect and impact resistance. Due to the incorporation of domestic sewage, the biodegradability of the mixed wastewater is improved, and the secondary biological contact oxidation is more conducive to the change of pollutant loads, impact resistance, and ease of operation and adjustment.

3.4 Coagulation gas flotation-microelectrolysis-SBR process [8]

The treatment engineering practice of an aqueous environment ink and binder mixed wastewater of a carton packaging company by an environmental engineering company in Qingdao indicates that the CODcr of the raw water is 2805.5 mg/L, and the chroma is 1 562.5 times. After removal of oil by precipitation, CODcr removal rate It reached 20.4% and the color removal rate reached 10%. After coagulation and air flotation treatment, the COD cr removal rate reached 74.6% and the color removal rate reached 83.9%. Then, micro-electrolysis resulted in a COD removal rate of 28.6% and a color removal rate of 66%, which improved the biodegradability and significant decolorization of the wastewater. Finally, a SBR with a volume of 140 m3, a volume load of BO D5 of 0.18 kg/m3 and a charge/discharge rate of 30% was used to achieve a COD removal rate of 82.2% and a color removal rate of 60%. The final effluent CO D cr reached 71.9 mg/L, the removal rate was 97.4%, the chroma was 30.7 times, and the removal rate was 98%. The treatment effect of this project is obvious. Although the removal of COD and color relies mainly on coagulation and air flotation, due to the adoption of the micro-electrolysis process, the biodegradability of the wastewater is improved, thus ensuring the stable operation of the SBR process unit.

3.5 Chemical Oxidation - Coagulation Process [9]

Yang Hao and others used chemical oxidation-coagulation process to test the wastewater of carton packaging companies. The composition of wastewater mainly includes aqueous ink, starch and surfactants. Selective tests using oxidative decolorants KMnO4, H2O2, NaClO, activated carbon; screening tests and dosages of flocculants: Y-13, FSH 7, FCH 3, FO4248, AN910SH, and pH adjustment tests. The results are as follows: Under the optimal experimental conditions for the raw water adding the best oxidizer NaClO 15 g/L, the best coagulant FCH 3 0.2 g/L, and the pH adjusted to 8.5, the CODcr removal rate reached 94%, and the color removal efficiency reached 100%.

3.6 Ultrafiltration Technology

Studies have shown [10] that after the wastewater passes through the three groups of ultrafiltration modules, the COD removal rate reaches 92%, the solid content in the concentrate reaches 99 g/L (about 10%), and the turbidity of the permeable liquid ranges from 0.13 to 0.4 NTU. . However, the removal rate of COD is closely related to the amount of soluble contaminants. Soluble contaminants cannot be removed by ultrafiltration.

4 Conclusion

(1) The development and application of water-based ink has a very significant role in reducing atmospheric environmental pollution; at the same time, it is also very effective in reducing residual toxic substances on the surface of printed matter and ensuring food hygiene and safety; using water-based ink is conducive to improving the safety of working environment. , safeguarding the health of contact operators, reducing resource consumption and reducing environmental protection costs, therefore, has a wide range of application prospects in China.

(2) The simple biological treatment process cannot meet the requirements for the treatment of aqueous ink wastewater, and physical, chemical and biological comprehensive treatment processes must be used. Coagulation process as the main method of pretreatment of aqueous ink wastewater is more efficient and reliable for removing COD and color. To improve the biodegradability of wastewater, methods such as micro-electrolysis, chemical oxidation, and anaerobic biological treatment have all been adopted. After that, aerobic biological treatment is performed with better results.

Source: Shanghai Chemical Industry Author: Cai Yanxing, Zhang family