The process of the water softening method of water is to add appropriate chemicals to the water as needed according to the principle of the volume product, so that it reacts with calcium and magnesium ions to generate insoluble precipitates such as CaCO3 and (OH)2. Commonly used agents are lime, soda ash, caustic soda, trisodium phosphate, etc., among which lime softening is the most commonly used.
After the lime is digested. The lime milk is added to the raw water and reacts with bicarbonate under high pH conditions as follows:
Among them, CaCO3 and Mg(OH)2 are precipitates. The precipitate formed by calcium and magnesium divalent ions acts as a coagulant during the sinking process. CaCO3 has a good flocculation effect. Flocculate various sediments in the reaction tank and remove them in the sedimentation tank and filter tank. For groundwater, the turbidity of the water is generally not high, and no other suspicious agents need to be added. Among them, the pH value has a great influence on the coagulation effect. When performing lime-to-soft ratio in various places, the removal effect under different pH values should be observed through the beaker test according to the actual situation of the local water quality, while considering the economics of the drug, to determine the best pH. In the production test, Ca(OH)2 was added to adjust the aqueous solution to the lowest pH value. In this method, the pH of the water and the dosage of the agent are the keys. Usually determined in beaker test, model test and production test. In order to increase the coagulation effect, polyacrylamide can be added as a coagulant. After adding lime, the pH value of the factory water will be higher. Acid neutralization should be carried out in the factory water, adjusting the pH value of the water to meet the drinking water quality standards. In water sources in many areas, while the hardness exceeds the standard, the dissolved total solids and iron and manganese also often exceed the standard. The enhanced coagulation and lime agent method can also remove certain iron, manganese and dissolved total solids. Because of the low price and wide source of lime, it is suitable for the case where the carbonate hardness of the raw water is higher and the hardness of the non-carbonate is lower. Domestic drinking water does not require deep softening. At present, it is shown that after this method is processed, the effluent hardness index fully meets the drinking water quality standards. The lime coagulation method is cost-effective. The addition of lime can remove most of the carbonate hardness in the water, but not the non-carbonate hardness. If the non-carbonate hardness of the raw water is higher, the lime soda method can be used. As the water source is increasingly polluted, the concentration of organic matter in the general water source increases, and Cryptosporidium and other pathogenic bacteria appear in the water. The United States has conducted a lot of research on the removal of the prerequisites of disinfection by-products by the enhanced coagulation method of lime medicament, taking water samples from different places and water samples with different water qualities as the research object. The relationship between lime softening and the prerequisite for removing disinfection by-products. In order to remove natural organic matter in water, anion exchange resin can be added after lime softening treatment. This method is effective for removing organic matter and chromaticity. It can reduce the chromaticity from 17 degrees to less than 3 degrees. In general, anionic resin can Effectively remove organic matter with molecular weight above 1000, but below 1000 may not be effective.