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Table of contents（Click to go to where you want to see）

4.1.Pretreatment-physical method (Our company’s main products and cases)
4.2.Membrane treatment technology
4.3.Chemical method
4.3.Ion exchange method
4.4.Adsorption method

5.Construction of wastewater standard system for surface treatment industry

What is metal surface treatment wastewater？

Metal surface treatment wastewater mainly comes from electroplating, anodizing, pre-treatment, and electrophoretic coating wastewater. It contains a lot of harmful substances, such as heavy metals, acid and alkali ions, and other substances.

These substances are very harmful. If they are not treated professionally, direct discharge may seriously damage the natural ecology. At the same time, it contains a large amount of nitrogen, phosphorus, and other harmful substances, which will cause eutrophication in the water body and destroy the ecological balance of the water body.

Sources and types of metal surface treatment wastewater

Corrosion protection treatment

In producing metal products, it is often necessary to perform corrosion protection treatment on the metal surface, such as galvanizing, chromium plating, nickel plating, etc. These treatments typically involve secondary processes that generate large amounts of wastewater

Electroplating wastewater

This wastewater is primarily generated during electroplating, including pre-treatment and rinsing wastewater, passivation treatment wastewater, depleting waste liquid, etc.
To learn more about electroplating wastewater treatment, please click: Electroplating Wastewater Treatment–The Complete Guide
Anodizing wastewater

This type of wastewater is generated during anodizing, oil removal, acid polishing, oxidation, electrolysis, coloring, and dyeing of aluminum and magnesium alloys.
Wastewater treatment before painting

During the surface treatment of some metal processing parts, wastewater is generated from pre-treatment before painting, such as oil removal, pickling, rust removal, surface adjustment phosphating treatment, etc.
Electrophoretic coating wastewater

Mainly, wastewater generated from the production process of water

Cleaning and decontamination

Metal surfaces often need to be cleaned and decontaminated during metal processing to remove grease, dirt, and other impurities. The cleaning process usually uses chemical cleaners or solvents, and cleaning wastewater contains pollutants such as organic matter and surfactants.

cooling and lubrication

In metal processing, water is used for cooling and lubrication to reduce processing temperature and friction and improve efficiency. Wastewater from cooling and lubrication contains metal ions, grease, and emulsifiers.

cutting and grinding

The metal-cutting and grinding process produces large amounts of wastewater, which contains metal particles, cutting fluids, grinding agents, etc.

wastewater reuse

In some metal processing companies, wastewater will be treated and reused to reduce water consumption and wastewater discharge, but the treatment process will also produce a certain amount of sewage.

The wastewater produced in these processes usually contains large amounts of heavy metal ions (such as chromium, nickel, lead, zinc, etc.), organic matter, surfactants, grease, particulate matter, and other pollutants. If this wastewater is discharged directly into the environment without treatment, it will cause serious pollution and harm to water bodies and the ecological environment.

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Hazards of metal surface treatment wastewater

Metal surface treatment wastewater contains many harmful substances, such as heavy metals, acid and alkali ions, and other substances. These substances are hazardous. Direct discharge may induce severe natural ecological damage if not professionally treated.

For example, after heavy metals enter the environment, they are difficult to decompose and will persist, accumulate, and migrate in nature for a long time, eventually causing severe harm; heavy metals can also accumulate in algae and sediment and will be broken down after being adsorbed by fish and shellfish. The balance of the original food chain has caused irreparable losses; after heavy metals enter the human body, they will cause heavy metal poisoning and endanger human health.

In addition, metal surface treatment wastewater also contains a large amount of nitrogen, phosphorus, and other harmful substances. These substances will cause many diatoms, cyanobacteria, and other algae in the water body, which significantly reduces the dissolved oxygen content and chemical oxygen consumption in the water body. A significant increase will eventually cause eutrophication of water bodies and destroy the ecological balance of water bodies.

The discharge of electroplating wastewater among global metal surface treatment wastewater is increasing yearly. The increasingly severe water shortage problem has become the focus of current attention, and the advanced treatment and reuse of metal surface treatment wastewater is highly critical in this context.

Methods of treating metal surface treatment wastewater

Preprocessing-physical method(Our company’s main products and cases)

The physical method is a pretreatment method for wastewater treatment, mainly removing large particles of insoluble suspended solids in wastewater.

According to different principles, it can be divided into filtration, gravity separation, and dissolved air flotation, among other methods to separate suspended solids in wastewater effectively. However, this method only targets insoluble solids or oily substances and does not affect soluble pollutants. Moreover, this method is only a preliminary preprocessing and needs to be combined with other methods.

Application case(Preprocessing-physical method)

Painting Wastewater Treatment Case-Painting Process Wastewater Treatment Project for An Automobile Manufacturing Company in Zhejiang

The wastewater generated during the coating production process of the enterprise has the characteristics of many types of pollutants, high concentration, complex composition, intermittent discharge of wastewater and irregular discharge time, poor biodegradability, etc. Reasonable selection of wastewater treatment methods and design of treatment processes that meet the requirements of the enterprise according to different process characteristics in accordance with local conditions can improve the treatment efficiency of wastewater, reduce treatment costs and shorten the treatment cycle.

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Case Studies-An example of a painting wastewater treatment project in an automobile manufacturing company

Although automobile painting wastewater has high water quality complexity and is difficult to treat, it is necessary to classify, collect, and pre-treat wastewater according to quality as long as the characteristics of the wastewater are understood and appropriate treatment processes are adopted.

Case Studies-Electroplating Wastewater Project of A Jiangsu Enterprise

This case introduces a wastewater treatment project of an electroplating enterprise in Jiangsu. Our factory's high-efficiency dissolved air flotation technology was used to effectively treat the electroplating wastewater, providing good conditions for subsequent wastewater treatment.

Case Studies-Nanjing Steel Project

This case study introduces how Nanjing Iron and Steel Group uses our Lamella Plate Clarifier to remove fine particles from diluted tailings, achieving good separation results and clear effluent.

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Case Studies-Changzhou Dongfeng Agricultural Machinery Production Wastewater Treatment

This case study introduces how Changzhou Dongfeng Agricultural Machinery Group uses our factory's high-efficiency dissolved air flotation to treat oily wastewater, such as machining and cutting fluids. After treatment, the removal rate of oil, grease, suspended solids, etc., in the raw water is over 90%, significantly reducing the back-end processing load.

Ultrafiltration

Ultrafiltration technology is a type of membrane treatment technology. It is a pressurized membrane separation treatment process. The application of this process requires external pressure. When the pressure conditions meet the requirements for wastewater treatment, the separated solution will flow along the ultrafiltration membrane at a specific flow rate.

The surface of the filter membrane flows. During this process, the solution's solvent and low molecular substances will pass from the high-pressure side through the ultrafiltration membrane and enter the low-pressure side. These solvents and low molecular substances passing through the ultrafiltration membrane will be discharged with the filtrate or reused. , and the solution's polymer substances, colloidal particles, and microorganisms will be intercepted by the ultrafiltration membrane and discharged in the form of concentrated liquid.

The ultrafiltration membrane has a tiny pore size and can effectively intercept macromolecular substances such as suspended solids, colloids, particles, and bacteria in wastewater. The ultrafiltration process has the advantages of relatively low energy consumption, a relatively short production cycle, and relatively low operating costs. It is significantly more effective for electrophoresis wastewater, and the filter membrane can effectively intercept paint for recycling.
reverse osmosis

Reverse osmosis is also called reverse osmosis. In the specific application process, the pressure difference is often used as the driving force to separate the solvent from the solution. At this stage, the permeation mechanism of reverse osmosis membranes has not been unanimously explained, and most experts agree more with the selective sorption-capillary flow mechanism. Under this theory, the Gibbs adsorption formula is the fundamental basis.

Due to the hydrophilicity on the membrane surface, water molecules can be adsorbed during the wastewater treatment process. When a certain pressure is applied, the pure water layer continuously flows through the reverse osmosis through the capillary tube. Membrane, thereby achieving the effect of separating macromolecular harmful substances in the solution.

The practical application of reverse osmosis technology was first used to treat heavy metal wastewater, such as nickel plating, chromium, zinc wastewater, and mixed heavy metal wastewater. Generally speaking, reverse osmosis has the advantages of no noticeable phase change, regular temperature operation, simple equipment, high efficiency, and low energy consumption. However, to achieve the ideal treatment effect, it generally needs to be completed with the help of high-pressure equipment.

In the actual treatment process, the probability of contamination on the membrane surface is relatively high. In addition, during the entire process, the membrane's stability, drug resistance, and heat resistance are relatively limited. These limitations make reverse osmosis less suitable for process applications. There is still a need to strengthen process improvement and combine it with other technologies to achieve the best treatment results.
Microfiltration

Microfiltration, also known as microporous filtration, includes dead-end and cross-flow filtration. This process mainly uses porous membranes as the filtration medium. In the wastewater treatment process, there are also specific requirements for pressure.

When the pressure is between 0.1MPa and 0.3MPa, the filter membrane is affected by pressure and can effectively intercept gravel, silt, and clay particles in the solution. At the same time, a large amount of solvents, small molecules, and a small amount of macromolecules can pass through the filter membrane to effectively filter.

This process is widely used in food and beverage, medicine and health, electronics, chemical, and other industries.

Chemical method

In the wastewater treatment of the surface treatment industry, chemical methods are mainly used to oxidize and degrade complex substances into simpler ones through chemical reactions. The harmful elements in water can be directly oxidized or reduced using redox reactions, converting them into non-toxic substances.

For example, in the treatment of chromium-containing wastewater, substances such as iron sulfide, iron powder, and sodium sulfite can be added, followed by the addition of sodium hydroxide for precipitation and separation. Electrolysis can also be used to treat or recover heavy metal ions in wastewater through electrolytic action. This method is generally applied to concentrated electroplating wastewater and can simultaneously remove multiple metal ions, achieving good purification effects. However, it is not suitable for low-concentration metal wastewater. Alternatively, when treating nitrogen-containing wastewater, the wastewater can be directed to a regulating buffer tank, where the pH value is adjusted by adding acid or alkali to meet the requirements of nitrification and denitrification. Then, the wastewater is pumped into a denitrification tank with the addition of a carbon source, ensuring that the total nitrogen content in the wastewater meets the standard requirements for discharge.

Finally, the wastewater enters an aerobic tank to remove excess carbon source.

Ion exchange method

The ion exchange method is a technique used to separate harmful substances from wastewater using ion exchange agents. In this process, the ions present in the water are replaced by ions present on the resin. The exchange resins, made of styrene and divinylbenzene containing sulfonic acid groups, have the ability to exchange hydrogen ions with various cations in water, thereby removing heavy metal ions.

This method is usually used as a supplementary treatment method and can be combined with other methods. It can also be used to treat wastewater that contains phosphorus. Ion exchange resins have a relatively stable adsorption capacity for phosphate ions. In a higher pH environment, this method can be useful in removing phosphorus from wastewater and achieving good removal efficiency. However, it still has some issues, such as poor selectivity and high regeneration costs.

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Adsorption method

The adsorption method is also widely used in the treatment of metal surface treatment wastewater.

The specific wastewater treatment process mainly utilizes the high adsorption capacity generated by the weight and pores of the adsorbent material to remove harmful substances from the wastewater.

When applying this treatment method to treat wastewater from metal surface treatment, selecting adsorbent materials with relatively unique structures is important. Modified methods are commonly used to produce adsorbent materials to achieve optimal adsorption effects. The effectiveness of the adsorption method is closely related to parameters such as pH value, temperature, and time.

Therefore, in applying this process, it is necessary to strengthen the scientific control of these parameters.

Construction of wastewater standard system for surface treatment industry

Technology and equipment standards

The surface treatment industry has formulated complete technical standards for wastewater treatment, mainly formulating reasonable methods for different wastewater quality conditions and corresponding standards for single wastewater based on the principle of branching and diversion.

This technical standard should be combined in wastewater treatment work to formulate a complete plan to Standardize governance work further and achieve good governance results. If separation treatment is not possible, some agricultural wastewater will be discharged into comprehensive wastewater tanks for centralized treatment, so comprehensive wastewater treatment standards must be included.

It is also necessary to select cost-effective process equipment according to process requirements and apply it to wastewater treatment, which can give full play to the technical level and achieve good treatment results. The production process, formulate relevant standards for this purpose, carry out wastewater treatment and reuse based on this standard, and improve resource utilization.

reuse standards

Different processes have different water requirements for wastewater treatment. When reusing, it must be treated appropriately according to these standards to ensure that it meets the needs of other processes. Water quality that is too high or too low will affect production. To this end, relevant standards should be formulated for wastewater treatment and reuse to improve resource utilization.

Resource recovery standards

Resource recovery refers to separating high-content and relatively single substances during wastewater treatment and directly using them to produce raw materials. During the wastewater treatment process, the substances that meet the requirements in the wastewater should be extracted and recycled according to the above characteristics. Use this standard to regulate wastewater treatment and resource recovery to ensure resources can be used rationally.

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