Sewage treatment process
1. Primary treatment
It mainly removes suspended solid pollutants in sewage, and most of the physical treatment methods can only complete the requirements of primary treatment. After the first-level treatment, BOD can generally be removed by about 30%, which does not meet the discharge standard. The primary treatment belongs to the pretreatment of the secondary treatment.
2. Secondary treatment
It mainly removes the colloidal and dissolved organic pollutants (BOD, COD) in the sewage, and the removal rate can reach more than 90%, so that the organic pollutants can meet the emission standard, and the suspended solids removal rate can reach 95%. The water effect is good.
3. Three-level processing
Further treatment of refractory organic matter, nitrogen and phosphorus, and other soluble inorganic matter that can lead to eutrophication of the water body, etc. The main methods include biological nitrogen and phosphorus removal, coagulation precipitation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis.
1. Physical method: It mainly uses physical action to separate insoluble substances in sewage, and does not change the chemical properties during the treatment process. Commonly used are gravity separation, centrifugal separation, reverse osmosis, air flotation and so on. The physical treatment of structures is relatively simple and economical, and is used in situations where the water volume of villages and towns is large, the self-purification ability is strong, and the degree of sewage treatment is not high.
2. Biological method: Use the metabolic function of microorganisms to decompose and oxidize the dissolved or colloidal organic matter in the sewage into stable inorganic substances, so that the sewage can be purified. Activated sludge method and biofilm method are commonly used. The degree of biological treatment is higher than that of physical treatment.
3. Chemical method: It is a method that uses chemical reaction to treat or recover dissolved or colloidal substances in sewage, and is mostly used in industrial wastewater. Commonly used methods include coagulation, neutralization, oxidation-reduction, and ion exchange. The chemical treatment method has good treatment effect and high cost. It is mostly used as the effluent after biochemical treatment for further treatment to improve the quality of the effluent.
Knowing each stage of the sewage treatment plant, you can clearly understand the requirements of the pipe fitting materials used in each stage. In addition, there is a lot of demand for expansion joints and waterproof casings in sewage treatment plants, and we should learn this knowledge.
