Electroplating wastewater treatment equipment is a device specifically designed to handle the wastewater generated during the electroplating production process. It can effectively remove pollutants such as oils, suspended solids, heavy metals, and organic substances from the wastewater, converting it into clean water that meets discharge standards. Electroplating wastewater treatment equipment typically consists of pre-treatment, intermediate treatment, and post-treatment stages, which include physical treatment, chemical treatment, and biological treatment technologies.

The application scope of electroplating wastewater treatment equipment is very wide, covering fields such as electroplating, electronics, printing, and surface treatment. It not only effectively solves the wastewater problems arising from industrial production but also reduces environmental pollution, enhances corporate image and social responsibility. At the same time, electroplating wastewater treatment equipment can save water resources, lower production costs, and improve the economic benefits of enterprises.

Equipment introduction

At present, in China, the treatment of electroplating wastewater mainly involves classifying it into three categories: 

Chromium-containing wastewater: The hexavalent chromium is mainly treated with the method of neutralization. 

2. Cyanide-containing wastewater: Mainly treated by removing cyanide. 

3. Other wastewater: includes copper, nickel, zinc, etc. 

The sources of electroplating wastewater are generally as follows: (1) cleaning water of plated parts; (2) waste electroplating solution; (3) other wastewater, including water from flushing the workshop floor, washing the electrode plates, condensation water from ventilation equipment, as well as various electrolyte solutions and drainage caused by leakage of the electroplating tank or improper operation and management; (4) cooling water of equipment. The cooling water is not contaminated during use, except for the increase in temperature. The quality and quantity of electroplating wastewater are related to factors such as electroplating production process conditions, production load, operation management and water usage methods. The quality of electroplating wastewater is complex and the components are difficult to control. It contains heavy metal ions such as chromium, cadmium, nickel, copper, zinc, gold, silver, and cyanide, and some of them are carcinogenic, teratogenic, mutagenic toxic substances.

Source of wastewater

The sources of electroplating wastewater are generally as follows: 

Plating part cleaning water 

(2) Waste electroplating solution; 

(3) Other wastewater includes the water used for cleaning the workshop floor, washing the electrode plates, the condensate from ventilation equipment, as well as various types of solution and drainage resulting from leakage in the plating tanks or improper operation and management. 

(4) The cooling water for the equipment remains uncontaminated and its temperature only increases during use. 

(5) Metal surface treatment: Metal surface treatment involves cleaning before surface treatment, electroplating, passivation film protection, mechanical processing, and coating application, with electroplating being the main method.

Wastewater characteristics

The cleaning wastewater and the waste liquid generated during the alkaline oil removal process are all alkaline wastewater, typically containing oils and other organic compounds. 

2. The cleaning water generated during the acid washing process is usually highly acidic and contains heavy metal ions as well as a small amount of organic additives. 

3. The pre-treatment wastewater accounts for approximately 50% of the total electroplating wastewater. The wastewater contains certain salts, free acids, and organic compounds, and its components vary greatly. These variations are influenced by the type of plating, the pre-treatment process, and the management level of the factory. 

4. The rinsing water for the coating is the main source of heavy metal pollution in electroplating operations. The amount of rinsing wastewater discharged, as well as the types and concentrations of heavy metal ions, vary with factors such as the physical shape of the parts, the formula of the electroplating solution, the rinsing method, and the management level of the electroplating operation. In particular, the rinsing process has a significant impact on the concentration of heavy metals in the wastewater, directly affecting the recovery of resources and the treatment effect of the wastewater. 

5. Post-treatment of the coating mainly includes passivation after rinsing, removal of defective coatings, and other special surface treatments. During the post-treatment process, a large amount of heavy metal wastewater is also generated. Such coating post-treatment wastewater is complex and variable, and the volume is unstable. Generally, it is combined and treated with mixed wastewater or acid-base wastewater. 

6. The electroplating wastewater usually contains high concentrations of heavy metal ions and a large amount of accumulated impurities. Not only are the types of pollutants different, but also the concentrations of the main pollutants, the concentrations of other metal impurity ions, and the solution medium often have significant differences. These differences determine the diversity of treatment technologies and the particularity of processing methods for these wastewater.

Conventional methods for wastewater treatment

Currently, the physicochemical method is generally adopted for treatment. There are many treatment methods, and quite a few of them are effective, but not many can achieve overall compliance. The main source of zinc in electroplating and metal processing wastewater is the drag liquid from electroplating or acid washing. The pollutants are transferred to the washing water during the metal washing process. The acid washing process involves first immersing the metal (zinc or copper) in a strong acid to remove the surface oxide, and then immersing it in a brightening agent containing strong chromic acid for brightening treatment. This wastewater contains a large amount of hydrochloric acid, zinc, copper and other heavy metal ions, as well as organic brightening agents, etc. It is highly toxic, and some also contain carcinogenic, teratogenic, mutagenic and other highly toxic substances, which pose a great threat to human health. Therefore, electroplating wastewater must be carefully recycled and treated to eliminate or reduce its pollution to the environment. 

The electroplating wastewater treatment equipment is composed of a regulating tank, a dosing tank, a reduction tank, a neutralization reaction tank, a pH regulation tank, a flocculation tank, a inclined tube sedimentation tank, a box-type filter press, a clear water tank, an air flotation reaction, and an activated carbon filter. 

There are mainly the following several methods. 

Air flotation method 

The air flotation method involves introducing air into the water to generate tiny bubbles. Due to the adhesion between these bubbles and the fine suspended particles, they form flotation bodies. By utilizing the buoyancy of the bubbles, they rise to the surface, forming foam or sludge, thereby enabling the separation of suspended substances in the water. According to the different methods of bubble generation, it can be classified into three types: air injection flotation, dissolved air flotation, and electrolytic flotation. 

The air flotation method is a new type of solid-liquid separation technique that replaces the sedimentation method. In 1978, Shanghai Tongji University successfully applied the air flotation method to treat electroplating heavy metal wastewater. Subsequently, due to its continuous processing, compact equipment, small land occupation, and ease of automation, it has been widely used. 

The air flotation technology for solid-liquid separation is highly adaptable and can handle chromate wastewater, chromium-containing passivation wastewater, and mixed wastewater. It not only removes heavy metal hydroxides but also can eliminate other suspended solids, emulsified oil, surfactants, etc. The principle of using air flotation for treating chromate wastewater is as follows: under acidic conditions, ferrous sulfate and hexavalent chromium undergo an oxidation-reduction reaction. Then, in alkaline conditions, a flocculent is formed, and under the action of countless tiny bubbles, the flocculent floats to the surface, making the water quality clearer. 

2. Ion exchange method 

Ion exchange method mainly involves using the exchange ions in the ion exchange resin to exchange with certain ions in the electroplating wastewater, thereby removing them and purifying the wastewater. 

The application of ion exchange technology for treating electroplating wastewater in China began in the 1960s and was subject to experimental research. By the end of the 1970s, due to the urgent need to address environmental pollution issues, this technology experienced significant development. Currently, it has become one of the effective methods for treating electroplating wastewater and recovering certain metals, and it is also an important link in achieving closed-loop circulation for some electroplating wastewater. However, the investment cost of using the ion exchange method is very high, and the system design and operation management are rather complex. Generally, small and medium-sized enterprises find it difficult to adapt to it. Often, due to poor maintenance and management, the expected results cannot be achieved. Therefore, its application and promotion have been somewhat restricted. 

Currently, the ion exchange method is widely used for treating electroplating wastewater containing chromium and nickel in China. There are already relatively mature experiences in design, operation and management. After treatment, the water can meet the discharge standards and the effluent quality is good, usually allowing for recycling. The regenerant eluent after the resin exchange adsorption saturation can be adjusted by electroplating process components and purified to be reused in the plating tank, basically achieving closed-loop circulation. In addition, the ion exchange method can also be used to treat wastewater containing copper, zinc, gold, etc. 

3. Electrolysis Method 

The electrolysis method mainly involves causing the harmful substances in the wastewater to undergo oxidation and reduction reactions at the anode and cathode respectively through the electrolysis process, thereby converting them into harmless substances; or using the oxidation and reduction products of the electrodes to react chemically with the harmful substances in the wastewater, generating insoluble precipitates, which can then be separated and removed or recovered by the electrolysis reaction to obtain metals such as silver and copper. In China, the electrolysis method was used to treat electroplating chromium-containing wastewater in the 1960s, and experiments were conducted on wastewater containing silver, copper, etc. in the late 1970s to recover these metals, achieving very good results. 

The electrolytic method for treating electroplating wastewater is generally used in medium and small-sized factories. Its main features are that no treatment chemicals need to be added, the process is simple, the operation is convenient, and it occupies less production space. Moreover, due to the high purity of the recovered metals, it has excellent economic benefits for the recovery of precious metals. However, when the treatment volume is large, the electrolytic method consumes a lot of electricity and requires a large amount of iron electrodes. At the same time, the separated sludge is as difficult to dispose as that of the chemical treatment method. Therefore, it is rarely used now. 

4. Extraction Method 

The extraction method involves adding a solvent (which is insoluble in water but can dissolve certain substances in water, known as solutes or extractants) into the wastewater. This allows the solute to be fully dissolved in the solvent, thereby enabling the separation or recovery of a certain substance from the wastewater. The extraction process consists of three main steps: mixing, separation, and recovery.