When it comes to electroplating wastewater, its main source is the large amount of polluted wastewater generated during the processes of electroplating cleaning, coating rinsing, and post-plating passivation. The composition of this wastewater is very complex, containing a large amount of heavy metals, purifying agents, cyanide, etc. In most cases, electroplating wastewater will undergo purification treatment through physical methods such as ion exchange and air flotation. When setting up subsequent biochemical treatment, although the pollution content in the wastewater is likely to be significantly reduced after treatment, the nature of the wastewater will change with the addition of chemicals. At this point, sample collection and water quality monitoring and analysis should be carried out. So, what’s the reason for the constant mistakes in the monitoring of electroplating wastewater? Let’s learn the relevant knowledge together with Modi below! The analysis mainly focuses on the relationship between COD and heavy metals.
Understand the Monitoring and Analysis of COD (Chemical Oxygen Demand)!
1.The influence of heavy metals on CO detection: During the daily COD monitoring process, there is a situation where the chemical oxygen demand is low at the beginning and high at the end, making it impossible to calculate the removal efficiency and reduction volume of pollutants. Why? Firstly, untreated electroplating wastewater contains a large amount of high-valent heavy metals (such as hexavalent chromium, etc.). Moreover, when monitoring COD, concentrated sulfuric acid is added to the water. Under heating conditions, the oxidizing property of the high-valent heavy metals will increase accordingly, indirectly increasing the content of oxidants. At this time, the organic matter in the wastewater will be oxidized. This led to a significant increase in COD, deviating from the true value. Therefore, when monitoring COD, it is necessary to analyze the impact of heavy metals on the measurement results! Therefore, it is necessary to carry out reduction work on the heavy metals without affecting the monitoring results, converting the heavy metals from high-valent to low-valent ones, so as to achieve the effect of reducing oxidation and minimize the impact on the monitoring results to the point where it cannot be reduced at all.
2.What impact will the complexing agent have on the COD detection results? In electroplating wastewater, there are usually a large amount of complexing agents and reducing substances, and then larger cyclic macromolecular chelates are formed and present in the capsules, which will cause the monitoring result of COD to be lower. Therefore, under the condition that complexes are present, a suitable chemical chelating agent can be selected to generate a large amount of chelates for working decomposition, and then the chemical oxygen demand in water can be monitored and analyzed by using an online COD analyzer.
Factors Affecting the Results of Heavy Metal Monitoring and Analysis!
In the process of electroplating wastewater treatment, the wastewater from each section is usually mixed together in advance before being treated. However, due to the fact that the drainage volume and time periods of each section are different, and the wastewater after mixing is not representative, this will result in the monitoring data not being able to truly reflect the discharge of heavy metals. Especially for some metals with small usage, it often happens that the concentration of heavy metals in the treated water is higher than the original concentration before treatment. In addition, heavy metals are also present in the sludge from electroplating. Some enterprises will set up subsequent biochemical work to release some of the heavy metals in the sludge, which will result in a relatively high content of heavy metals in the wastewater after biochemical treatment.
In addition, it is necessary to remind everyone that as mentioned earlier, the composition of electroplating wastewater is very complex. During the process of online water quality monitoring and analysis, the problems mentioned above are prone to occur. To avoid accidents, it is necessary for relevant staff to fully understand the characteristics of the collected wastewater and correctly collect samples. At the same time, it is necessary to increase investment in research and development and carry out the monitoring work of electroplating wastewater correctly.
