Xử lý nước uống bắt đầu phản ứng với mức độ cao của các bệnh đường nước - chẳng hạn như kiết lỵ, thương hàn, dịch tả lây truyền qua bị nhiễm phân của thực phẩm và nước trong dân cư đô thị. Thành phố xuất hiện gần nguồn nước ngọt, thường các con sông, mà dần dần trở nên ô nhiễm. Một trong những phương pháp điều trị đầu tiên và vẫn còn hiệu quả nhất cho nước sông là lọc cát chậm. Trong quá trình này, đến nước thô được thông qua từ từ thông qua một giường. | 12 Water Treatment Drinking water treatment began in response to high levels of waterborne diseases such as dysentery typhoid and cholera transmitted through fecal contamination of food and water in urban populations. Cities arose close to freshwater sources often rivers which became progressively polluted. One of the earliest and still most effective treatments for river water is slow sand filtration. In this process incoming raw water is passed slowly through a bed of sand which builds up a layer of microorganisms on the surface. As the water passes down through this surface layer pathogens are removed and organic molecules oxidized. For over 150 years this process has been in use in treating water for the city of London. About 100 years ago this water filtration process was reinforced by the addition of chlorine as a sterilizing agent to destroy pathogens that might escape removal by filtration and also pathogens that enter the drinking water supply after treatment. From this relatively unsophisticated beginning modern drinking water treatment has developed into a well-researched area of chemical engineering. As the demand for potable water has increased treatment processes that will handle larger throughputs of water of varying quality have been required. Because of the low rate of flow through the beds of slow sand filters many hectares of filter beds would be needed to filter sufficient water for average modern cities. Some of the filter beds will be out of action at any given time as slow sand filters gradually clog up with incoming detritus and grow algal mats. They then have to be cleaned and after cleaning their filtration effectiveness is much lower. Hence more compact systems were devised that can handle large flow rates in a more controllable manner. Rapid sand filters were developed that will remove flocculated particles but lack the fine filtering capability of slow sand filters and also lack the biological processes that decontaminate water. Thus .
