There are a lot of inorganic and organic substances in the wastewater of electroplating, of which the more organic matter in the wastewater, the more oxygen consumption will be. In it, the oxygen consumed when the wastewater is oxidized with chemicals becomes chemical oxygen demand (COD). The amount of oxygen consumed by microbial oxidation is called biological oxygen demand (BDO).
Then COD production in electroplating wastewater. What is the impact of the pre-treatment process on the discharge characteristics? This chapter water quality online monitoring instrument manufacturers to understand the relevant information together with you.
In the role of the pre-treatment process, the main is to smooth the plating workpiece, oil, rust removal. Then use the polishing paste used in the polishing of the workpiece (made of grease and paraffin), which will lead to high COD in the wastewater when cleaning up the grease and paraffin.
In the past, the drugs used in the oil removal process are sodium carbonate, sodium silicate, etc., but in recent years, in order to improve the speed and quality of oil removal, while reducing the temperature of oil removal, surfactants are generally used. Most types of surfactants are combined with anionic surface activated carbon and non-ionic surface activated carbon.
However, anionic surfactants can use sulphate salts (e.g., sodium lauryl sulfate); Nonionic surfactants use the condensation products of oxyethane and certain hydrophobic compounds (such as fatty alcohol polyoxyethylene ether). These surfactants are organic, and the rust removal process uses a lot of hydrochloric acid, sulfuric acid and corrosion inhibitors. Although hydrochloric acid is not an organic matter, the CL- that makes up hydrochloric acid will increase the COD index. The Fe2+ produced by pickling steel will also increase the COD index. Frequently used corrosion inhibitors (such as hexamethyltetramine, thiourea) are also organic, and will also increase COD.
Warm reminder: Cod-8000 —COD online analyzer can be reduced to Cr (Ⅲ) in the mixed solution formed by water sample, potassium bichromate, silver sulfate (as a catalyst to oxidize the straight chain aliphatic compounds more fully) and concentrated sulfuric acid under high temperature and high pressure environment, so that the color of the mixture solution changes. The degree of change of the color of the solution corresponds to the solubility of COD (chemical oxygen demand) of the measured water sample. The instrument can directly determine the COD value of the water sample by photoelectric colorimetry.
