Talking about the treatment method of water-based paint coating sewage

0 Introduction
With the increasingly strict national environmental protection requirements, the state's environmental pollution control is also more and more attention, water-based coatings in the paint industry market share is also increasing year by year. Water-based coatings in containers, automobiles and parts, construction machinery, furniture and many other products on the application, the resulting coating wastewater discharge is also gradually increasing, the corresponding water-based coating wastewater treatment has become a headache for many enterprises.
1 Water-based coating classification
All resin coatings that use water as a dispersant can be called water-based coatings

. Common types of water-based coatings on the market can be divided into: polyurethane type, epoxy resin type, acrylic resin type and aolic acid resin type.
1.1 hydroelesterated coatings
water-based polyurethane coatings include water-soluble, water-emulsified and water-dispersed. According to the molecular structure can be divided into line type and cross-link type, and there are single-part, two-part system. In addition to the good performance of solvent-based polyurethane coatings, water-based polyurethane coatings also have the advantages of high hardness, strong adhesion, non-corrosion resistance, solvent resistance and so on. However, the development of domestic water-based polyurethane coatings is also limited by raw materials, curing agents, cross-linking agents, etc. , therefore, the development of corresponding raw materials, additives are also the key to the development of water-based polyurethane coatings.
1.2 epoxy-type water-based coatings
Epoxy-type water-based coatings are composed of two components: one group is divided into hydrophobic epoxy dispersion (emulsion) and the other group is divided into hydrophobic amine curing agents, the key of which is the emulsification of hydrophobic epoxy resins.
1.3 Acrylic-type water-based coatings
acrylic-type water-based coatings can be broadly divided into: single-component type, high-performance type, high-curing type 3 types. It is difficult to prepare solvent-resistant acrylic raw materials into solvent-resistant water-based acrylic coatings, the focus of the current research lies in the modified acrylic raw materials, this technology is called "living polymerization", can be well controlled acrylic molecular weight and its chemical structure (monosome order, etc.) and distribution.
1.4 Aolic acid resin-type water-based coatings
aolic acid resin-type water-based coating development has undergone two stages of external emulsification and internal emulsification, currently mainly using internal emulsification method synthetic hydroolic acid resin dispersion. Internal emulsification is the polymer of the carboxyl or amino with appropriate alkali or acid, so that the polymer can be dispersed in water. Although the water-based aliclicic acid resin coating has good brushing and smoothness, but there are also the shortcomings of slow film drying, low hardness and poor corrosion resistance, need to be modified to meet these performance requirements. At present, people's water-based aliclicic acid resin change mainly includes physical and chemical modified, of which acrylic resin, silicone resin and styrene modified the effect is most significant.
2 Water-based paint coating sewage characteristics
water-based paint coating sewage volume is generally larger, and mostly to take a cycle mode, water-based paint dissolved in water if not timely separation from the water body, easy to lead to paint subsidion, circulating sink odor, sewage treatment operation site air pollution, but also affect the health of operators. Containers, host plant water-based coating sewage organic content is high, sewage COD value of up to 1000 to 30000mg/L, if not timely separation of organic matter in sewage and water, such a high COD value of sewage sent to sewage treatment station one-time treatment costs are very high. Due to the characteristics of the above coated sewage, in order to save sewage treatment costs and enable sewage to meet the environmental protection discharge requirements of the corresponding areas, coated sewage needs to be treated in a timely manner so that the water-based coating components in the sewage separated from the water.
3 Water-based paint coating sewage treatment process
the market of authentic water-based paint coating sewage treatment technology is the key to destroy the emulsification system of water-based paint sewage or a stable water-soluble system, so that water-based coatings in the form of flower particles, and then add flocculants, water in the form of flower particles of water flocculation into groups, slag separation, water can be recycled. The key to wastewater treatment of pseudo-water-based coatings on the market is to use de-adhesive to remove the viscosity of pseudo-water-based coatings before breaking the emulsion to destroy the emulsification system.
3.1 milk-breaking effect
the milk-breaking effect is also known as anti-emulsification effect, the stability system of emulsion is completely destroyed, the phenomenon of two phases of oil and water stratification occurs. The method of milk breaking is roughly divided into mechanical, physical and physical chemistry. Mechanical method is mainly the use of external forces to break the emulsion, such as ion separators. Physical method has electric deposition method, filtration method, ultrasonic milk breaking method, in which electro-deposition method is the use of high-voltage electrostation field to disperse phase aggregation, filtration method is through porous materials to achieve milk breaking, and in the process of using ultrasonic milk breaking method ultrasonic strength can not be too large, otherwise it will affect the milk breaking effect. Physicochemistry mainly reduces the stability of emulsion by changing the type of emulsion or the nature of the interface, and then achieves the effect of breaking milk.
3.2 Common treatment techniques for coated sewage
physicochemistry and biological methods for common treatment techniques. Due to the high concentration of sewage pollutants, B/C value is less than 0.3, biochemicality is poor, in the actual treatment process, often using the combination of pre-treatment and biological treatment. The common treatment process flow of coated sewage is shown in Figure 1.
4 Water-based paint treatment agent selection
4.1 Water-based paint treatment agent composition
water-based paint treatment agents generally contain additives, water-based paint separators and flocculants. Additives are divided into inorganic hybrids and organics, which mainly act as coagulation. Water-based coating separators are polymerized polymer resins that separate hard-to-separate components such as resins and pigments in coatings. The product belongs to cation-type polymer composite material, the molecular main chain with a large number of positive charge groups, with a strong milk-breaking capacity, it is with soluble molecules in hydroxyl, sulfonate-based anionic groups to produce electrical neutrality, forming easy to capture adsorption flocculation particles. The main components of flocculants are polyacrylamides with different polymerization degrees and different ion degrees, which are divided into anion type, cation type and modified sex ion type, and the type of flocculant should be selected according to the actual situation of the water body to be treated in practice. The role of flocculant is mainly to flocculate water in the form of flower particles, so as to achieve the purpose of slag separation.
4.2 Water-based coating treatment agents used
first in the laboratory to carry out small sample tests to determine the combination of water-based coating treatment agents. Generally in the customer's production line to take waste water or paint samples, back to the laboratory, after simulating the analysis of environmental conditions on the site and then provide on-site wastewater (paint) treatment program. Laboratory sample simulation test results determination standards should be based on the actual treatment requirements of customers, such as the requirements of treatment of paint residue floating or sinking, two different requirements of its water-based paint treatment agent combination scheme will also be different. Secondly, according to the laboratory sample simulation test results, the water-based coating treatment agent in the sewage field treatment process to apply the proposed scheme. For example, sewage treatment site is mostly continuous treatment, pharmaceutical also need to use metering pump continuous addition. However, some customers on-site use of intermittent treatment methods, such as the use of box treatment, a box of sewage quantitative one-time treatment, this situation when the drug needs to be added to use a one-time delivery. Finally, according to the customer's on-site treatment equipment, timely and reasonable arrangement of pharmaceutical addition points. Generally on-site for the circulating tank-type treatment system, additives and water-based paint separators are added at the inflow, flocculants are added in the reflow area. If the on-site sewage is to take the box batch treatment method, the added point of the potion is not required, but it is recommended to add stirring equipment in the box, so that the potion can be fully dispersed and function in the water body. Therefore, the water-based coating treatment agent in the actual application process needs to go through a small sample test process, on-site pharmacy debugging process before the final drug use plan can be determined.
5 Water-based coating wastewater treatment case
Water-based paint wastewater treatment involves automobiles and their components, containers and other industries, the following container company water-based coating sewage treatment as an example to illustrate, its treatment process diagram 2.
water-based paint coating sewage volume of a container company is 20m3/
d;
Figure 2 A company's water-based coating sewage treatment process
Table 1 coating wastewater treatment before and after water quality parameters
the sewage after initial treatment COD still reached about 7000mg/L, can be used back to the cycle tank, cycle can reach 6 months to 1 year. When the water quality cycle life reaches 6 months to 1 year, because the water BODY and other indicators are still too high to be discharged directly, further treatment is needed to bring the sewage index to GB838-2002IV. Specific emission standards are set out in Table 2.
Table 2 Specific Discharge Standards
The follow-up treatment process is as follows: Production of wastewater, flocculation precipitation, wastewater regulation pool, anaerobic pool, oxygen pool, contact oxidation pool, MBR membrane pool, ozone oxidation pool, discharge.
6 Auxiliary Equipment Overview
auxiliary equipment are mainly slag separation equipment and slag dehydration equipment. Slag water separation equipment for slag water separation scraping machine, divided into air floater and sedimentation separator. Waste slag dewatering equipment includes frame filter, screw stacker, centrifuge, drying equipment and so on.
the role of the water separation equipment is to separate the water-based paint residue from the water body, the water body can continue to use in the circulation tank, can also enter the sewage treatment stage, the indicators after the direct discharge.
the role of waste dewatering equipment is to reduce the water content of slag, and reduce the quality of slag, and thus reduce the cost of solid waste disposal. The waste residue produced by solvent-based coating is dangerous in the 2016 edition of the National Hazardous Waste List and must be paid to be disposed of by a professional company qualified to handle hazardous waste; Usually waste paint residue can be treated by high temperature incineration, waste paint slag is mostly burned at high temperature clean, decomposed into CO2 and other harmless gases with exhaust emissions, a small part of the residue can be used in cement production as clyceration of cement, become cement products, and ultimately achieve zero pollution.
7 Conclusion
Water-based paint coating sewage after the initial treatment of water treatment agents, and then with water treatment equipment, after bio-chemical and other processes, sewage can be treated to meet the standard discharge, waste residue generated in the process can also meet the standard treatment, and eventually reached the degree of zero pollution to the environment.
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