Different methods of water treatment are:
Aeration
Aeration is a gas transfer process in which water is brought into contact with air for the purpose of transferring volatile substances to or from the raw water.
It is most often used to remove undesirable gases such as carbon dioxide, hydrogen sulfide, and methane. By introducing oxygen, iron and manganese can be removed as well.
Clarification
Clarification is a process to reduce or remove turbidity, silt, and sediment present in the raw water. The water could be treated with chemicals or filtered.
Deaeration
This process operates on principle of raising the water temperature to the saturation point for the existing pressure.
There are two types of deaerators:
- Steam – preferred when heated water is needed (for boilers).
- Vacuum – preferred when cold water is used.
Dealkalizing
This process as its name implies, reduces the alkalinity of feed water
Decarbonation
This process is used in smaller systems by the filtered air counter flowing through the water stream and stripping out the carbon dioxide.
Note that this method should be considered when the bicarbonate level in the feed water is in the range of 14 to 20 mg/l or higher.
Distillation
Process of boiling feed water, condensing the steam produced from the feed water, and collecting the condensate, which yields a product water being theoretically free from nonvolatile impurities.
There are three methods currently used to produce distilled water:
- Single stage distillation
- Vapor compression
- Multi-effect distillation
Filtration
There are three types of filteration:
- Deep-bed sand filtration
- Cross-flow and tangential-flow filtration
- Activated carbon filtration
Ion Exchange and Removal
Basic process where specific ions in a feed-water stream are transferred into an exchange medium called “resin” and are exchanged for different ions of equal charge.
When this process is used to treat water only for removal of hardness, it is called a “water softening”, see next section.
When this process is used to treat water for removal of ions to produce pure water, it is often referred to as “deionization” or “demineralization”.
Water softening
Water softening is a process that reduces or removes dissolved impurities that cause hardness in water. There are two methods of water softening:
- Adding lime-soda ash to the raw water method through an ion-exchange process.
- Ion exchange method which is a cation -exchange process used to remove insoluble and scale-forming iron and other multivalent cations, which are the primary causes of hardness, and to replace them with sodium ions, which do not contribute to water hardness.
Reverse Osmosis
Reverse osmosis (RO) is a water purifying process involving osmosis and ionic repulsion.
Osmosis is the passage of a solvent (water) through a semipermeable membrane until there is an equal concentration of solute molecules (impurities such as sodium chloride) on both sides of the membrane.
Reverse osmosis is the flow of solvent in the direction opposite the direction of flow of natural osmosis. If enough pressure is applied to the more concentrated solution (water), pure water is diffused through the membrane leaving behind the contaminants which are continuously flushed to drain.
Microbial control
There are two methods involved in this this process:
Chemicals: The method of disinfecting water by use of chemicals. Commonly use chemicals are chlorine and chlorine compounds, hydrogen peroxide, and acid compounds. Chemicals could be biocides, substances that kill microbes, or biostats, which prevent the further growth of microbes.
Ultraviolet radiation (UV): In line radiation process using UV light generated by mercury vapor lamps
