Most treatment plants use chemical coagulation and rapid gravity filtration to remove suspended particulate matters in the raw water. For chemical coagulation, correct doses of suitable coagulants and coagulant-aids are added to the raw water to combine or 'flocculate' the colloidal and larger particles of suspended matter. This causes the suspended matter to settle more readily and then be removed in the sedimentation tank.
Aluminium sulphate is the main coagulant. In most cases, hydrated lime is also added to adjust the pH of the raw water for the best flocculation results. Polyelectrolyte is used as a coagulant aid.
The water is then passed through rapid gravity sand filters which remove the finer particles of suspended matter. At Choa Chu Kang, Chestnut Avenue and Lower Seletar Waterworks, the suspended particles are removed by membrane filtration.
The filtered water, on its way to the clear water tank, where it is temporarily stored, is disinfected with either chlorine or ozone to get rid of harmful bacteria and viruses. Ozonated water such as at Choa Chu Kang, Chestnut Avenue and Woodleigh Waterworks is further treated with Biological Activated Carbon (BAC) to enhance removal of dissolved organics and improve taste and odour in the treated water.
Fluoridation is a requirement by the Ministry of Health and has been a practice since 1957. Sodium silicofluoride is added in our water treatment to prevent dental cavities.
Ammonia is added to the treated water to form chloramines, a more stable chlorine residual.
Please click here for water treatment process
video.
