The basic water treatment process for surface waters consists of preliminary screening and storage, followed by coagulation and flocculation to allow the aggregation of colloidal particles. Sedimentation of the aggregated particles produces sludge and partially purified water. The purification process is completed by filtering and disinfecting the water before distribution. Some waters may require additional treatment: for example, nitrate removal, or fluoridation, or further removal of organic material by granular or powdered activated carbon. The pH may have to be adjusted to minimise plumbo-solvency in areas served with lead distribution pipes. The sludge produced in water treatment can be sent to a sewage works where it can aid primary sedimentation, or it can be dewatered and buried at a landfill site. Small quantities of water can be disinfected by solar radiation and this is useful in remote locations.
In areas of the world lacking adequate quantities of surface water or non-saline groundwater, desalination is practised, with the major processes being multistage flash distillation and reverse osmosis.
List the four commonly used desalination processes for the production of potable water.
The four processes are:
multistage flash distillation;