In the process of treating electroplating wastewater, electroplating sludge will be generated, and electroplating sludge contains heavy metals and other harmful substances, which are hazardous wastes. There are more than 6,000 electroplating enterprises in Guangdong Province alone.
The amount of electroplating sludge is very huge, not only the sludge disposal cost is high, but also if the electroplating sludge is not treated properly, it will easily cause heavy metal pollution to the water environment or soil environment, so it is imperative to reduce the amount of electroplating sludge. .
Material flow analysis of electroplating enterprises
1.1 Theory of Material Flow Analysis
Material flow analysis refers to the systematic analysis of material flow and storage in a specific system within a certain temporal and spatial scope. It mainly involves the sources, paths and sinks of material flow.
The material flow analysis is based on the law of conservation of mass, and the result can reach the final material balance through the process of input, storage and output.
Material flow analysis is to reveal the flow characteristics and transformation efficiency of materials in a specific area by analyzing the process of material consumption and waste, find out the direct source of environmental pressure, and then propose corresponding solutions to reduce environmental pressure.
1.2 Material flow analysis of electroplating enterprises
The material flow of the electroplating enterprise is made based on the boundary of the electroplating enterprise. See Figure 1 for details.
(1) From the perspective of input, the inputs of the electroplating process are fresh water, electroplating chemicals (liquid), electroplating chemicals (solid) and workpieces, and the inputs of the wastewater treatment process are wastewater, wastewater treatment chemicals and fresh water.The input substances will enter into the wastewater through the electroplating process and wastewater treatment process, and part of the calcium and magnesium ions in fresh water, heavy metal ions in electroplating chemicals, grease and other impurities attached to the workpiece will enter the wastewater, a small part will be discharged through the wastewater, and most will enter the electroplating sludge.Therefore, when the total input of the electroplating process is smaller, the amount of pollutants brought in is smaller, and the total input of the wastewater treatment process is correspondingly smaller, and the amount of electroplating sludge is smaller; on the contrary, when the total amount of material input is The greater the amount, the greater the amount of pollutants brought in, and the correspondingly greater total input of the wastewater treatment process, and the greater the amount of electroplating sludge produced.
(2) From the perspective of output, the output of the electroplating process is waste water, waste gas, waste liquid, waste residue, evaporated water, finished workpieces and waste workpieces, and the output of the wastewater treatment process is sludge, standard discharge water and evaporated water.
The main pollutants finally discharged into the environment are sludge, up-to-standard discharge water and waste gas. Among them, the up-to-standard discharge water and waste gas contain very little pollutants, and most of the pollutants enter the electroplating sludge.
When the amount of wastewater output by the electroplating process is smaller, the amount of pollutants contained in the wastewater is smaller, and the amount of electroplating sludge output by the wastewater treatment process is smaller; on the contrary, when the amount of wastewater output by the electroplating process is larger, the wastewater contains The greater the amount of pollutants, the greater the amount of electroplating sludge output from the wastewater treatment process.
(3) In terms of intensity, it includes the consumption intensity of fresh water and other substances, the production intensity of wastewater and its main pollution factors, and the production intensity of electroplating sludge.
When the consumption intensity of fresh water and other substances is greater, the intensity of waste water and its main pollution factors will be greater, and accordingly the intensity of electroplating sludge will be greater; on the contrary, when the consumption intensity of fresh water and other substances is smaller, waste water and its main pollution will be generated. The smaller the factor production intensity is, the smaller the electroplating sludge production intensity is accordingly.
(4) From the point of view of efficiency, it includes the utilization efficiency of fresh water and other substances, the recycling rate, and the production rate of electroplating sludge. When the utilization efficiency of materials such as fresh water is higher and the recycling rate is higher, the production rate of electroplating sludge is lower; on the contrary, when the utilization efficiency of substances such as fresh water is lower and the recycling rate is lower, the production rate of electroplating sludge is higher. high.
Electroplating sludge reduction method
Through the material flow analysis of electroplating enterprises, it is known that the reduction of electroplating sludge should be considered from the aspects of input, output, strength and efficiency, starting from the source and the end.
(1) Source reduction: From the material flow analysis of electroplating enterprises, it can be seen that the most important thing is to do a good job in source reduction. The quantity of input and output substances in the electroplating process should be reduced, mainly from several aspects:
① Purify fresh water and reduce impurities such as calcium and magnesium ions in water;
② Save water, use one water for multiple purposes, and improve the reuse rate of industrial water;
③Strictly control the quality of electroplating raw materials and reduce the loss of electroplating raw materials
④ Improve the electroplating process and reduce the concentration of toxic and harmful substances such as heavy metals in the electroplating bath;
⑤ Reduce the electroplating liquid, in order to achieve the purpose of reducing the production of toxic and harmful substances and reducing the amount of cleaning water;
⑥ Strengthen the decontamination of the workpiece before electroplating, and reduce the amount of pollutants attached to the workpiece;
⑦Improve the success rate of electroplating and reduce the rework rate and scrap rate;
⑧ Strengthen skills training, improve the operation level of front-line employees, and reduce misoperation.
From the perspective of the practice of electroplating enterprises, the source reduction method has a small investment and good effect, but the technical requirements of the enterprise are relatively high. If the technical force of the enterprise is insufficient, it is difficult to implement these measures or the effect after implementation is very small.
(2) Terminal control: From the material flow analysis of electroplating enterprises, it can be seen that the input of wastewater treatment process mainly has two aspects:
Up to standard discharge water and electroplating sludge.
As the emission standards for electroplating pollutants become more and more stringent, the concentration of pollutants in the discharge water that meets the standards is getting lower and lower, and accordingly, the amount of toxic and harmful substances exported through the discharge water that meets the standards will become less and less, and more toxic and harmful substances will enter Electroplating sludge, and to achieve stricter discharge standards, it is necessary to increase the input of wastewater treatment chemicals, and the amount of output electroplating sludge is bound to rise.
Therefore, in order to achieve the reduction of electroplating sludge, terminal control should also be done. There are several aspects:
① Do a good job in the quality and separation of electroplating wastewater. The finer the classification, the more conducive to the treatment of wastewater, and it is beneficial to reduce the input of wastewater treatment chemicals;
② Automatic dosing to reduce artificial overdosing;
③Using high-quality wastewater treatment chemicals to reduce the amount of lime used can reduce the amount of electroplating sludge
④ Use up-to-standard wastewater instead of fresh water to configure wastewater treatment chemicals to reduce the input of fresh water;
⑤Optimize the wastewater treatment process and adopt the treatment process with less sludge production;
⑥ Adopt high-efficiency mud press to reduce the moisture content of sludge;
⑦ Adopt other sludge reduction measures in line with national and local environmental protection laws and regulations;
⑧ Improve the operation level of wastewater treatment staff and reduce misoperation.
From the practice of electroplating enterprises, the effect of the terminal control method is also relatively good, but the investment is large, and the operating cost will also increase. (3) Combined method: Combine the methods of source reduction and terminal control, and select a series of methods that are technically, environmentally and economically feasible to implement to achieve the best effect of sludge reduction.
(1) The material flow of the electroplating enterprise was made by the material flow analysis method. Through the material flow analysis, it was concluded that the electroplating sludge came from two processes, namely the electroplating process and the waste water treatment process, of which the electroplating process was the source and was the electroplating enterprise. The key point to achieve electroplating sludge reduction.
(2) The input, output, strength and efficiency were analyzed, which provided a scientific basis for the reduction of electroplating sludge.
(3) In line with the actual situation of electroplating enterprises, the reduction measures of electroplating sludge with strong operability are given in terms of source reduction and end control, which provides a direction for electroplating enterprises to achieve electroplating sludge reduction.