Three grades of sewage treatment water quality

Sewage treatment is divided into three levels, and the water quality effect achieved after different levels of treatment is different. It is necessary to design a reasonable treatment plan according to the needs of users.  Primary sewage treatment:   Primary sewage treatment, also known as sewage physical treatment, is a process of removing suspended solids in sewage, adjusting pH value and reducing the degree of corrosion of sewage through simple sedimentation, filtration or appropriate aeration. The treatment can be composed of screening, gravity sedimentation and flotation in series to remove most of the particulate matter with a particle size above 100 microns in the sewage.  Sieving can remove larger substances; gravity sedimentation can remove inorganic particles and cohesive organic particles with relative density greater than 1; flotation can remove particles with relative density less than 1 (oil, etc.). After primary treatment, the wastewater generally still does not meet the discharge standards.  Secondary sewage treatment:   After primary treatment, the sewage is treated in an aeration tank and a sedimentation tank with activated sludge to further purify the sewage. Biological method and flocculation method are commonly used. The biological method is to use microorganisms to treat sewage, mainly to remove the organic matter in the sewage after primary treatment; the flocculation method is to destroy the stability of the colloid by adding a flocculant, so that the colloidal particles flocculate, and the flocs are formed to cause adsorption, mainly to remove Inorganic suspended matter and colloidal particles or low-concentration organic matter in sewage after primary treatment.  Sewage after secondary treatment can generally meet the requirements for agricultural irrigation and wastewater discharge standards. However, under certain conditions, it may still cause pollution of natural water bodies. Tertiary treatment of sewage:   The tertiary treatment of sewage is also called advanced treatment: after the sewage is treated through the secondary treatment, other polluting components in the sewage (such as nitrogen, phosphorus, fine suspended matter, trace organic matter and inorganic salts, etc.) are further removed. process.