Mechanical filter
Mechanical filter (Multi-media filter) consist of several layers of different media. The media are loaded by density, the most dense in the bottom of the tank, the least dense on top. This produces a filter with excellent flow rate and relatively easy backwash properties that will filter down to ten microns.
Filter media
carbon manganese quartz resin
Ion exchange
Ion exchange is a reversible chemical process of exchanging hard water ions for soft water ions. Calcium and magnesium are the hardness ions, sodium can be considered the "softness" ions and they are exchanged to create soft water. Ion exchange effectively removes more than 90 percent of barium, cadmium, chromium, silver, radium, nitrites, selenium, arsenic, and nitrate.
Process of ion exchange
Ion exchange units can be used to remove any charged (ionic) substance from water, but are usually used to remove hardness and nitrate from groundwater.
Groundwater dissolves rocks and minerals releasing calcium and magnesium ions that cause water to be hard. These dissolved ions give hard water its characteristics. Water hardness ordinarily is expressed in grains of hardness per gallon (gpg) of water. Water impurities can also be measured in either parts per million (ppm) or milligrams per liter (mg/l). One gpg is equal to 17 ppm (mg/l).
Softeners offer: 1) cleaner, softer feeling clothes; 2) longer life of appliances including washing machine, dishwasher, and water heater; 3) less use of household cleaning products, such as detergents, as well as personal cleanliness products, like shampoo; 4) reduction of water spotting.
Water softener
Calcium (Ca2+) and magnesium (Mg2+) ions that cause water hardness can be removed fairly easily by using an ion exchange procedure. Water softeners are cation exchange devices. Cations refer to positively charged ions. Cation exchange involves the replacement of the hardness ions with a nonhardness ion. Water softeners usually use sodium (Na+) as the exchange ion. Sodium ions are supplied from dissolved sodium chloride salt, also called brine. In the ion exchange process, sodium ions are used to coat an exchange medium in the softener. The exchange medium can be natural "zeolites" or synthetic resin beads that resemble wet sand.
As hard water passes through a softener, the calcium and magnesium trade places with sodium ions. Sodium ions are held loosely and are easily replaced by calcium and magnesium ions. During this process free sodium ions are released to the water.
Softening Process
NaZeolite + Ca2 --> CaZeolite + Na+
and
NaZeolite + Mg2+ --> MgZeolite + Na+
After softening a large quantity of hard water the exchange medium becomes coated with calcium and magnesium ions. When this occurs, the exchange medium must be recharged or regenerated. To recharge the softener with sodium ions, a softener is backflushed with a salt brine solution. During a backflush the brine solution replaces the calcium and magnesium ions on the exchange medium with sodium ions from the salt solution.
Recharging Process
NaC1 + CaZeolite --> NaZeolite + CaC1
and
NaC1 + MgZeolite --> NaZeolite + MgC1
The time between recharging cycles depends on the hardness of the water, the amount of water used, the size of the unit, and the capacity of the exchange media to remove hardness.
process of water softening |
