Choice of Filter Material for a Mechanical Filter for Purification of Water after Liming

Abstract

The possibility of using quartz sand as a filter material for mechanical filters in the schemes of preliminary water treatment in water treatment plants with coagulation and liming at thermal power plants is considered. Comparative experiments on filtering water through quartz sand at the laboratory bench of an operating thermal power plant showed the absence of leaching of silicic acid from sand at pH = 10.0–10.2 and a filtration rate of 7 m/h. The turbidity of the filtrate is close to zero, and the quality of the water obtained after filtering through quartz sand is higher than when filtering through hydroanthracite. Hydroanthracite is characterized by relatively high abrasion and increased cost in comparison with quartz sand. Model experiments were carried out in a wide pH range when filtering water through sand, which showed the absence of a significant release of silicic acid into water. We studied the long-term interaction of water with quartz sand at pH 12, in which there is no intensive release of silicic acid compounds into water. Studies of the quality of the filtrate of mechanical filters loaded with quartz sand and hydroanthracite at a high pH of the treated water were performed. To prevent silicic acid compounds from entering clarified water, it is recommended that the first portion of the filtrate of the mechanical filters be discharged before being put into operation after a long period of inactivity. Recommendations on the use of quartz sand as a filter material in mechanical filters of the preliminary water treatment scheme at thermal power plants are presented.