Coagulation and sedimentation treatment. The process in which the flocs formed in the coagulation stage are separated from the water by gravity is called sedimentation, and this process is carried out in a sedimentation tank. The water passes through a tubular mixer before entering the sedimentation tank, where the raw water is added to coagulant(one of the commonly used coagulants is drinking water grade PAC 30%). After entering the flocculation tank, the suspended solids and colloidal impurities contained in the raw water react with the coagulant to produce flocculant sedimentation. Part of the flocs settle in the flocculation tank, and the other flocs further sink during the ascent. The water finally flows into the sump in the sedimentation zone and flows to the filter tank through the pipeline.
Filter processing. Generally, a granular filter material layer with voids(such as, quartz sand) is used to trap suspended particles in water through adhesion, so as to further remover fine suspended impurities, organic matter, bacteria, viruses, etc. Then the water can be more clarified.
Disinfection processing. After filtering, the turbidity of the raw water is further reduced. At the same time, the remaining bacteria and viruses lose the protection or attachment of the turbidity, which create good conditions for disinfection. Disinfection is mainly through the oxidation of hypochlorous acid generated by the reaction of chlorine and water in the bacteria, destroying the enzyme system of the bacteria and leading to the death of the bacteria. Disinfection won’t eliminate all microorganisms, but eliminates the pathogenic microorganisms in them. But it can ensure that drinking water reaches the bacteriological indicators of drinking water. At the same time, disinfection keeps a certain amount of chlorine at the ends of urban water pipes to control bacterial growth and prevent pollution.