Electroplating wastewater belongs to a typical industrial wastewater stream, mainly produced in workpiece washing and post-plating passivation processes. It has considerable wastewater discharge flow and diversified pollutant components. Relevant environmental regulatory authorities implement standardized Electroplating Wastewater Monitoring to track dynamic fluctuation trends of each water quality index.
Physical treatment technologies including ion exchange and solvent extraction are widely adopted for electroplating wastewater, while biochemical follow-up treatment is adopted in relatively few projects. Such treatment methods can lower the concentrations of heavy metals and partial organic pollutants to a certain degree. Meanwhile, dosing chemical agents will change the physical and chemical properties of wastewater. As treatment schemes differ at various working stages, inconsistent test results may emerge during sampling and monitoring. This paper conducts a preliminary analysis on relevant influencing factors as follows.
1.Nterference of Heavy Metals on COD Testing Results
In routine COD detection work, many operators notice a tendency that COD readings are relatively low at early testing stages and rise in later periods. Such fluctuations will interfere with reasonable calculation of pollutant removal rates and pollution reduction evaluation indicators.
Untreated electroplating wastewater contains high concentrations of heavy metal ions. During COD digestion, concentrated sulfuric acid is added and samples are heated, which strengthens the oxidizing performance of heavy metal ions. This condition indirectly raises the equivalent oxidant content and accelerates oxidation of organic pollutants in wastewater, leading to biased test values. To weaken such interference, staff may conduct reductive pre-treatment for heavy metals under appropriate conditions that will not affect testing validity. The process converts high-valence heavy metal ions into low-valence forms to reduce their oxidizing activity and cut down test deviations to a feasible extent.
2.Effects of Complexing Agents on COD Detection
Electroplating wastewater contains various complexing agents and reducing substances, which may lead to underestimated COD readings. When such chelate compounds exist in water samples, technicians can select suitable decomplexing chemicals to break macromolecular chelate structures before formal detection, which helps improve the reliability of COD test data.
The above discussion only analyzes factors triggering deviations in COD testing. Other monitoring indicators such as ammonia nitrogen and heavy metal content also face multiple interfering factors in sampling and testing, which will be further discussed in follow-up research.
