The pretreatment of water before water purification treatment, pre-preliminary processing in order to achieve good results in the water polishing to improve water quality. Because of the nature of the water has a large amount of impurities, such as sand, clay, organic compounds, microorganisms, mechanical impurities, etc., the presence of these impurities, seriously affect the water quality of the purified water and the treatment effect, and therefore must be refined before processing some impurities reduced or removed, which requires preprocessing, sometimes also called the pre-treatment.
Pretreated many ways, the main pre-Shen, coagulation, clarification, filtration and softening. After pretreatment with these methods, it is possible to make the water the suspended solids (turbidity), the chrominance, colloidal material, organic material, iron, manganese, temporary hardness, microorganism, volatile substances, dissolved gases and other impurities removed or reduced to a certain level. Pre-Shen is a large volume, low flow rate of natural sedimentation process, such as settling basin, pre-sedimentation tank. Coagulation is the use of iron salts, aluminum salts, polymers, etc. coagulant, with the impurities in the water by flocculation and bridging role precipitate large particles were formed, and then through the other devices, such as clarifiers, filtered pool, etc., to be removed. The filtering is to be processed water, flowing through the apparatus are equipped with a special filter material, such as sand filters, charcoal filter, trapping impurities in the water, removing the organic material, residual chlorine, etc.. Softened using chemicals, such as lime, soda powder, removing the bicarbonates in the water hardness; or using cation exchange resin to remove the water, calcium, magnesium, iron ions, etc., a process called softening. In addition to iron and manganese manganese sand, water divalent iron ion, manganese ion oxidation removal.