Precipitation is generated when a chemical reaction occurs a substances do not dissolve in the reaction solution. Understand from the word meaning is precipitate removal under the action of gravity. Suspended material in the water, this is a physical process, simple and effective, is one of an important technology for sewage treatment.
According to the nature and concentration of suspended material and flocculation properties of polyacrylamide, precipitation can be classified as natural sedimentation, flocculation, precipitation. Domain higher concentration of suspended cry of precipitation (more than 5000mg/L), and other surrounding particles influence on the settlement, between relative positions remained unchanged, sinking together formed a whole, clearly with the clarified water sludge. Secondary sedimentation tank and regional precipitation in the sludge thickener.
Flocculation is the particulate matter in the water flocculation process. After dosing of coagulants in water, including suspensions of colloidal and dispersed particles in molecular interactions generate flock and they collide together in the settlement process, the size and quality grows, settling velocity increasing. Suspended solids removal not only depends on the sedimentation rate and precipitation depth. Surface water formed alum dosing coagulants and organic suspended solids in sewage, activated sludge in sedimentation processes appear in the flocculation and sedimentation phenomena.