Coating refers to covering metal and non-metal surfaces with protective layer or decorative layer.
Coating is an important part of product surface manufacturing process, which can effectively prevent rust and corrosion, and beautify the product appearance. With the rapid development of domestic coating technology, coating has been widely used in home appliances, machine tools, machinery, electronics, automobiles, construction, aerospace and other fields.
The coating of automobile and its parts is one of the most waste water producing links in the automobile manufacturing process.
The waste water from automobile painting workshop contains pollutants such as resin, surfactant, heavy metal ion, oil, paint, pigment, organic solvent, etc., with complex composition, high CODcr value and poor biodegradability.
If not handled properly, it will cause serious pollution to the environment.
For this kind of wastewater, the traditional method is to directly coagulate the mixed wastewater, but the treatment effect is not ideal, and the quality of the effluent is not stable, so it is difficult to reach the discharge standard.
In particular, the spray paint wastewater contains a large number of water-soluble organic solvents, if the direct use of coagulation treatment effect is very poor.
At present, the main treatment methods of coating wastewater in China are physicochemical method, biological method, physicochemical biological method, etc.
Among them, physicochemical biological method is a widely used treatment process in China.
Next, I will introduce a kind of sewage treatment process of automobile painting workshop in detail.
The steps are as follows:
Preprocessing
The Phosphating Wastewater and electrophoresis wastewater discharged from the automobile coating workshop are separated by the cyclone method through the cyclone settler, and the wastewater is discharged into the comprehensive Phosphating Wastewater storage tank and electrophoresis wastewater storage tank.
The paint waste water is filtered by the wedge wire screen and discharged into the paint waste water storage tank.
The pre-treatment degreasing waste water is first removed by the wedge wire filter element, and then treated by ultrafiltration. The ultrafiltration effluent is discharged into the degreasing waste water storage tank, and the ultrafiltration concentrate is stored in the concentrated oil tank.
Each storage tank is equipped with two stainless steel submersible mixers which are installed in diagonal form. By using the push flow mixing function of the submersible mixer, each wastewater is in the flow mixing state without sedimentation.
Coagulation sedimentation
The water in each wastewater storage tank is pumped into the phosphating comprehensive wastewater storage tank for water distribution. After homogenization adjustment, the wastewater flow is 30m3 / h, calcium salt is added to 500mg / L, acid-base pH is adjusted to 10.5, coagulant 50mg / L and coagulant aid 1.0mg/l are added. After coagulation and coagulation aid, heavy metal ions, phosphates, fluorides and some organic matters in the wastewater form sedimentation and produce flocculation, which is introduced into the sedimentation tank Leave.
Biohydrolytic acidification
The outlet water of the sedimentation tank enters the biochemical treatment system after adding acid to adjust the pH value to 7.5-8 through the pH regulating tank. After hydrolysis and acidification by anaerobic bacteria, the macromolecular organics in the wastewater will be converted into micromolecular organics, and then the 160mg / L poly aluminum iron diacetate will be added to settle the suspended matters through the sedimentation tank.
Biofiltration
The precipitated water enters the biofilter for treatment, and the hydrolytic acidified water enters the Upflow Biological Aerated Filter. The wastewater flows through the filter material layer from the bottom to the top, and the bottom provides aeration. The air and water flow upward, so that the organics in the wastewater can be degraded and digested. The upflow form of the water flows through the filter layer area to the top outlet pipe, which is discharged into the discharge water tank by the outlet pipe, and the outflow water is detected by COD Discharge through drainage well.
After the above treatment, the removal rate of CODCr is more than 50% after coagulation and sedimentation, 20% after hydrolysis and acidification, 50% after biofilter, 90% after heavy metal nickel coagulation and sedimentation, and 90% after phosphate coagulation and sedimentation After sedimentation, the removal rate is more than 95%, and each index of effluent is better than the three-level discharge standard of class 2 pollutant and the high discharge standard of class 1 pollutant in the national wastewater discharge standard GB8978-1996.