At present, the main traditional processes for treating electroplating wastewater and heavy metal wastewater generally include the following methods: chemical dosing sedimentation method, ion exchange method, membrane separation method, and biochemical treatment. However, these traditional treatment processes are difficult to meet the emission requirements after the standard is raised, especially the requirements for heavy metal and COD emission limits. Even if some processes can achieve the standard discharge of heavy metal wastewater, their investment and operating costs also cause great pressure on the production and operation of enterprises. The problems faced by environmental protection are more complex, and the treatment of heavy metal wastewater has become a cross disciplinary issue in environmental engineering.

Given the sparse concentration, complex composition, and strict requirements for treatment of heavy metal wastewater, traditional wastewater treatment technologies have insurmountable shortcomings, mainly manifested as: large amount of treatment agents, expensive prices, difficult to control reactions, slow reactions, unsatisfactory effects, poor water quality, unstable residues, and difficulty in recovering precious metals. Therefore, the research and development of heavy metal wastewater treatment technology has the following development directions:

(1) Development and utilization of substitute drugs that have no impact on the environment;

(2) Development and application of non-toxic and harmless new water treatment agents;

(3) Development and application of new physical processing technologies, biological processing technologies, and computer-aided application technologies;

(4) Development of water treatment technologies and agents with good efficacy and low cost;

(5) Strengthen the comprehensive application of various water treatment technologies, etc.

① Any oxidants, flocculants, or other chemicals need to be added;

② It can be treated separately or combined with other technologies to improve the biodegradability of wastewater;

③ Will not or rarely produce secondary pollution;

④ The device has a small size, occupies less land, and is easy to operate and flexible. Therefore, this method is called the clean treatment method.

The electrochemical method for treating heavy metal wastewater significantly reduces the operating cost of the system, and has a significant effect on pollutant removal and economic benefits for enterprises, providing an effective way to achieve heavy metal wastewater treatment.

Using electrolytic oxidation of iron filings, iron plates, or aluminum plates to generate Fe2 ˙ Fe3+or Al3+forms precipitates such as Fe (OH) 2, Fe (OH) 3, Al (OH) 3, etc., and removes pollutants from water through flocculation and sedimentation. The latest research direction of electrocoagulation is the pulse signal electrocoagulation with periodic commutation, which has the advantages of high-voltage pulse electrocoagulation and, due to the solubility of both electrodes, is more conducive to the flocculation between metal ions and colloids, preventing electrode passivation.

The process of applying a magnetic field to an electrolytic cell to form an electrolysis system for the electrolysis of heavy metal wastewater. The mechanism is that heavy metal wastewater is subjected to the combined action of electric and magnetic field forces during electrolysis, which complicates the ion movement trajectory and reduces concentration polarization, promotes mass transfer and electrochemical reactions in the electrolysis process, and improves electrolysis efficiency. Magnetic electrolysis technology is often combined with other electrochemical treatment processes to improve treatment efficiency.

Under the action of a direct current electric field, anions or cation exchange membranes are used to selectively permeate the anions and cations in the solution, enabling directional migration of the anions and cations, thereby achieving the separation of solutes and water in the water. It is a relatively mature membrane separation technology that can treat electroplating wastewater, metallurgical industry wastewater, and other wastewater containing copper and chromium ions. During the operation of electrodialysis, there is an electrochemical reaction between the two electrodes, which leads to the accumulation of corrosive substances and an increase in resistance, resulting in an increase in power consumption. Therefore, it is necessary to introduce a large flow of water into the electrode chamber to eliminate the corrosive substances produced by the electrode reaction. Electrodialysis can be divided into unipolar membrane electrodialysis and bipolar electrodialysis. The traditional single membrane has shortcomings such as poor electrode durability and easy occurrence of slot blockage, so the current research hotspot is bipolar membrane electrodialysis. Combining bipolar membranes with unipolar membranes is a new direction for the future development of heavy metal wastewater treatment processes.

The cathodic reduction method is used for the treatment of heavy metal wastewater. The mechanism is that the anode uses an inert electrode to electrolyze wastewater, and heavy metal ions migrate to the cathode under the action of electrostatic attraction, resulting in deposition on the surface of the cathode. This method can remove heavy metal ions from the solution and recover high-purity heavy metals from wastewater. However, the concentration of heavy metal wastewater is generally low. When using traditional two-dimensional electrode electrolysis, the current density is small, the electrolysis efficiency is low, and the power consumption is high. Therefore, the problem of mass transfer has also become a difficult point to solve, and various efficient electrochemical reactors for mass transfer have become a research focus. Fixed bed, fluidized bed, and four stage continuous flow electrochemical reactors have become research directions for the slow reduction of ordinary flat electrodes.

Also known as microelectrolysis. The mechanism is to fill the electrolytic cell with active filler. When wastewater passes through the electrolytic cell, the active filler forms a primary battery with the wastewater as the electrolyte medium. The purpose of purifying wastewater is achieved through the electrochemical reaction and flocculation on the surface of the filler. In the microelectrolysis process, the commonly used reaction materials are iron filings (cast iron filings, steel filings) or aluminum iron filings with graphite or carbon particles added. Exploring the reaction mechanism and process kinetics of composite microelectrolysis technology is currently a research focus in this field.

To meet the increasingly strict environmental requirements and achieve wastewater regeneration and heavy metal recovery, several technologies such as electrochemistry, complexation, and ultrafiltration can be integrated to treat electroplating wastewater and heavy metal wastewater. At the same time, the advantages of various technologies can be utilized to achieve the most effective removal of heavy metal ions from wastewater.

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