With increasing environmental degradation and rapid population growth, it has become a challenge for the Government of India to supply clean drinking water to every household in India. Though the Government takes certain measures to purify water at the source of public water supply, it is still important that every household assess its needs independently and invest in a water purifier that ensures access to pure and safe drinking water.
There are several purification methods that science and technology have made possible. Let’s look at the hit parade:
What are the different methods of water purification used for home use?
Activated carbon uses the principle of adsorption to remove contaminants like chlorine and organic compounds. However, they don’t filter microbes, fluorides, nitrates, etc. from the water supply. Water softening also cannot be achieved with AC filters. In addition, heavy metals, such as mercury and lead, can only be removed with a very specific kind of activated carbon water treatment, which is typically used only in residential point-of-use filters.
Distillation is one of the oldest methods of water treatment and is still in use today, though not commonly as a home treatment method. It can effectively remove many contaminants from drinking water, including bacteria, inorganic, and many organic compounds.
It relies on evaporation to purify water. Contaminated water is heated to form steam. Inorganic compounds and large non-volatile organic molecules do not evaporate with the water and are left behind. The steam then cools and condenses to form purified water
The boiling process also kills microorganisms such as bacteria and some viruses. The effectiveness of distillation in removing organic compounds varies, depending on such chemical characteristics of the organic compound as solubility and boiling point. Organic compounds that boil at temperatures greater than the boiling point of water (some pesticides) can be effectively removed from the water.
Deionization is a method used for the removal of all ionized organic and inorganic minerals and salts from water, using a two-phase ion exchange procedure. In the first stage, the positively charged ions are removed by cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. In the second stage, negatively charged ions are removed by anion exchange for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form deionized water molecules. Living organisms, such as viruses and bacteria will not be removed by these deionization filters.
Ion exchange describes a specific chemical process in which unwanted dissolved ions in water and wastewater — like nitrate, fluoride, sulfate, and arsenic — are exchanged for other ions with a similar charge. In the exchange of cations during water treatment, positively charged ions that come into contact with the ion exchange resin are exchanged with positively charged ions available on the resin surface, usually sodium. In the anion exchange process, negatively charged ions are exchanged with negatively charged ions on the resin surface, usually chloride. Various contaminants — including nitrate, fluoride, sulfate, and arsenic — can all be removed by anion exchange.
It works great for water softening treatment as Calcium and Magnesium ions that are responsible for the hardness of water are exchanged with benign (soap-friendly) sodium ions. However, note that resins have a limited exchange capability and need to be replaced with regenerated or recharged resin.
The Reverse Osmosis technique reverses the mechanism involved in the naturally occurring process of osmosis. Water is applied at a force on a semi-permeable membrane to reverse the process and establish a reverse concentration gradient. Hence, the solvent (in this case, water) moves from a high concentration solution to a low concentration solution.
In the process, the contaminants including organic material, inorganic material, and microbes that are smaller than the nanometre-sized pores of the membrane get filtered. Reverse Osmosis ensures that more than 95% of the total dissolved solids in the water are removed. But since all the microbes are not effectively killed by RO alone, it is used in conjunction with UV (Ultraviolet) filtration that deactivates their nucleic cores.
Ozone is a powerful oxidizing agent which, when dissolved in water, produces a broad spectrum biocide that destroys all bacteria, viruses, and cysts.
As an oxidizing agent, it is 51% stronger than chlorine and has a kill rate of 3.125 times faster. Ozone owes its biocidal effectiveness to its ability to oxidize organic material in bacterial membranes, which weakens the cell wall and leads to cell rupture causing the immediate death of the cell.
Even resistant and problematic aqueous micro-organisms, such as Giardia, Cryptosporidium, Streptococcus fecalis, and E.coli are readily and rapidly inactivated by ozone. Ozone remains effective over a wide pH range.
Ozone is produced with the use of energy by subjecting oxygen (O2) to high electric voltage or to UV radiation. The required amounts of ozone can be produced at the point of use but the production requires a lot of energy and is therefore costly.