Sewage primary treatment:
Sewage primary treatment, also known as sewage physical treatment, through simple sedimentation, filtration or appropriate aeration to remove suspended solids in the sewage, adjust the pH and reduce the degree of sewage decay process. The treatment may consist of screening, gravity settling and flotation in tandem to remove most of the particulate matter in the sewage with a particle size of 100 microns or more.
Screening can remove larger substances; gravity precipitation can remove inorganic particles and relative density greater than 1 of the cohesive organic particles; flotation can remove the relative density of less than 1 of the particulate matter (oil, etc.). Wastewater after primary treatment generally still do not meet the discharge standards.
Secondary sewage treatment:
Sewage after primary treatment, and then through the aeration tank with activated sludge and sedimentation tanks, so that the sewage further purification process. Commonly used biological method and flocculation method. Biological method is the use of microorganisms to deal with sewage, mainly to remove organic matter in the primary treatment of sewage; flocculation method is through the addition of flocculants to destabilize the colloid, so that the colloidal particles flocculation, flocculation and adsorption occurs, is mainly to remove the primary treatment of sewage after the inorganic suspended solids and colloidal particulate matter or low concentration of organic matter.
The sewage after secondary treatment can generally meet the requirements of agricultural irrigation and wastewater discharge standards. However, it may still cause pollution of natural water bodies under certain conditions.
Tertiary treatment of sewage:
Tertiary treatment of sewage, also known as deep treatment: sewage after secondary treatment, further removal of other pollutants in the sewage (such as; nitrogen, phosphorus, fine suspended solids, trace organic matter and inorganic salts, etc.) of the treatment process.