200m3 electrophoresis electroplating sewage treatment project

I. Project introduction

According to the user's introduction, the company's wastewater mainly consists of 200m3/d electrophoretic coating wastewater, and the electrophoretic coating wastewater consists of four wastewaters, all of which are intermittently discharged, as follows:
1) Degreasing and washing wastewater: high pressure flushing is about 20m3/week, degreasing waste liquid is about 380m3/month;
2) Phosphating and surface conditioning wastewater: the wastewater is about 200m3/month, and the phosphating wastewater is about 490m3/week;
3) Electrophoresis inverted tank waste liquid: high pollution wastewater, with an annual discharge of about 21m3/a.
4) Electrophoresis cleaning and painting wastewater: spray paint wastewater of 276m3/month, and electrophoresis cleaning wastewater of about 30m3/week;

The main components of the above process drainage are:

1), prewashing drainage: mainly physical impurities, such as oil, sediment, etc.;
2) Degreasing and derusting sludge: Invalid acid washing liquid and additives such as corrosion inhibitors and surfactants, and impurities such as Fe2+, Fe2O3, oil stains and sediment;
3) Washing and draining after degreasing and derusting; residual acid washing liquid and its additives, Fe2+, Ca2+, and other impurities;
4) Phosphating waste liquid: a failed phosphating solution containing phosphates of Fe, Zn and Mn and Ca2+, Mg2+, PO43-, NO3-plasma;
5) Washing and draining after phosphating, divided into two parts;
a, tap water washing drainage: residual phosphating solution and additives and impurities;
b. Pure water washing and drainage: There are very few impurities, mainly Ca2+ and Mg2+.
6) Washing and draining after electrodeposition: containing a small amount of coating particles.

Third, the processing volume and implementation standards

1. Disposal of water: According to the data provided by the user, the designed sewage treatment water volume of this project is 200m3/d.
2. Execution standard: According to the requirements of customers and local environmental protection departments, all the company's sewage discharge standards implement the secondary emission standards stipulated in the “Comprehensive Wastewater Discharge Standard of the People's Republic of China” GB8978-1996, but according to the requirements of environmental protection departments and users, heavy metal ion requirements Zero emissions, based on this requirement.

Fourth, process design

According to customer introduction and communication with customers, the company's wastewater is divided into two types, one is electrophoretic coating wastewater, the total amount is about 200m3 / d, divided into four, for independent discharge, and the pollutant content, type and pollution of each wastewater According to the water quality analysis, if the wastewater is mixed, it will increase the difficulty of treatment, and the dosage and floor space will increase. In view of this, the whole sewage treatment plant construction will adopt the method of sub-governance + comprehensive treatment, namely: The wastewater is pretreated separately to remove most of the pollutants in the wastewater and remove pollutants that interfere with each other and interfere with the treatment efficiency and effectiveness to ensure that the drainage is up to standard.

The implementation process is as follows:

Painting wastewater:
According to the user's introduction, the coating wastewater is divided into four types, which are discharged separately. The discharge time of each wastewater is different. The water quality and quantity of each discharge are different, and it cannot be treated by a single process. The comprehensive treatment method, that is, the four kinds of wastewater are separately pretreated separately, using different processes, and finally mixed with domestic wastewater with uniform water quality and water volume for comprehensive treatment. Details are as follows:

1. Degreasing cleaning wastewater:

The wastewater is divided into two types, one is from high pressure washing process, the main pollutant is oil pollution, the discharge is about 20m3/week, the petroleum content is about 487.5mg/l, and it is in the state of emulsified oil, the CODcr content is about 8875mg. /l, is weakly acidic; the second is degreasing process wastewater, the main pollutants are oil pollution and CODcr, the emission is about 380m3/month, the wastewater is alkaline, the CODcr content is about 2400mg/l, and the CODcr is mainly oily (saponification of oil) And a surfactant.
After mixing the two kinds of wastewater, the total water volume is about 480m3/month, 120m3/week, the combined discharge is 17m3/d, the comprehensive water quality CODcr is about 3480mg/l, and the PH value is weakly alkaline. According to the water quality analysis, the CODcr data in the wastewater is mainly It is caused by oil pollution, but the oil content in the wastewater is low, and it exists in the state of emulsified oil, which cannot be recovered and the recovery value is too low. In summary, the wastewater treatment process is treated by chemical reaction + air flotation process. The basic principle is: the oil composition is a hydrocarbon compound, the specific gravity is small, and the saponification reaction occurs in the case of alkali. The saponified product is insoluble in water, easy to float in water, and can be removed by air flotation. 

2. Phosphating and surface conditioning wastewater:

The wastewater is mainly derived from surface waste liquid, phosphating waste liquid and phosphating washing process. The total water volume is about 2154m3/month, 538.5m3/week, and the combined discharge is 77m3/d. The main pollutants are phosphate ion and zinc ion. And nickel ions, CODcr content is low. According to the above water quality analysis, it is determined that the basic treatment process of the wastewater is chemical reaction + precipitation process, excessive lime milk is added to the wastewater, and the pH value of the wastewater is adjusted to about 10, and the phosphate ions in the wastewater react with calcium ions to form an insoluble calcium phosphate precipitate. The zinc and nickel ions react with the hydroxide ions to form insoluble zinc hydroxide and nickel hydroxide precipitate, and then a flocculant and a coagulant are added to remove the precipitate formed by a precipitation process. However, according to the requirements of zero discharge of heavy metal ions, it is necessary to remove heavy metal ions in the wastewater in this process. After pre-treatment, the concentration of heavy metal ions in the wastewater has been reduced below the national standard, if zero discharge is required, and the investment amount and operation are also taken into account. At the cost, an adsorption aid can be added to the wastewater to adsorb the remaining heavy metal ions in the wastewater and be removed by a subsequent forced filtration process to achieve zero discharge.

3, electrophoresis inverted tank waste liquid:

The wastewater is derived from the electrodeposition tank to replace the sediment solution. The pollution level is high, the water volume is small, the discharge period is long, the total discharge per year is about 21m3/a, the wastewater is weakly acidic, the PH value is 5~6, and the CODcr content of the mixed wastewater is about 20476mg/l. The monthly discharge is equivalent to 1.75m3/month, equivalent to 60L/d per day. The CODcr content of the wastewater is high. The basic composition is mostly high molecular organic compounds, which are difficult to biodegrade. The wastewater will be treated by chemical reaction + filtration + catalytic oxidation process. The wastewater is weakly acidic and has a high suspended solid content. After adding appropriate amount of lime milk, the wastewater is adjusted to be neutral to weakly alkaline (pH 7~7.5), and a large amount of suspended matter is formed. As usual, when there is excessive suspended solids in the water, The air suspension or sedimentation is required to remove the suspended solids, but the total amount of water is small. Therefore, it is determined in the process that the filtration method is directly used to remove the suspended matter in the wastewater. The wastewater from the suspended solids is degraded by catalytic oxidation to decompose the organic compounds in the wastewater into small molecular compounds, carbon dioxide and water, thereby improving the biochemical ratio of the wastewater and creating conditions for subsequent biochemistry.

4, electrophoresis cleaning and painting wastewater:

The part of the wastewater comes from the pure water cleaning process and the topcoat cleaning process in the late stage of electrodeposition. Because of the partial coating (paint) particles, the suspended solid content is high, while the electrophoretic cleaning wastewater has a high CODcr content of about 20,000 mg/l. After mixing the two kinds of wastewater, the mixed water volume is about 99m3/week, about 14m3/d, the comprehensive wastewater PH value is about 9~10, the SS content is about 443mg/l, and the CODcr content is about 8152mg/l. The wastewater is alkaline, pollution. The degree is high. In principle, it needs to be treated by chemical reaction + filtration + catalytic oxidation process, but the amount of discharged water is very small. If the catalytic oxidation reaction process is used alone, it is necessary to increase the investment cost and operating cost. Therefore, the process design will adopt The process of combined treatment of electrophoresis inverted tank wastewater reduces the total investment and operating costs while meeting the processing requirements.

Fifth, the process implementation

According to the information provided by the user, the factory outlet (shop) is about 500m away from the construction site of the sewage treatment station, and the difference between the two places is about 2m. At present, the factory covers a relatively tight area, and there is no spare place to build a water pool. For the convenience of management and operation, this design The collection basins are all located in the newly built sewage treatment plant. Only three sewage collection wells (electrophoresis inverted tank waste water pumping sewage treatment station) are constructed in the production plant area, and four collection basins (electrophoresis wastewater) are constructed in the sewage treatment plant. The collection wells in the plant area are connected with the discharge pump, and the elevation design is used to reduce the amount of pumps to reduce investment and operating costs. The pipelines are perforated steel pipes to avoid pipeline damage.