Methods for Purification of Water
Purification of water is a process of removing undesirable chemicals, materials and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacology, chemical and industrial applications. According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply, 88% of the 4 billion annual cases of diarrheal disease are attributed diarrheal diseases each year. The WHO estimates that 94% of these diarrheal cases are preventable through modifications to the environment, including access to safe water. Simple techniques for treating water at home, such as chlorination, filters and solar disinfection and storing it in safe containers could save a huge number of lives each year.
a) Storage: The method for purification of water is storage. Water flowing from any source may contain dust, dirty substance and other unwanted wastes. The water coming from the sources like rivers, springs, streams etc. may be collected in reservoirs where the heavy dust and wastes get settled at the bottom and light one remains floating. This helps to purify water in a large scale. During storage exposure of UV rays from sunlight kills the germs. If the water is stored for 5-6 days about 90% of bacteria are destroyed in the lack of food. During storage aeration process also occurs contributing to purify the water.
|Filtration process is also the method of purification of water. Water can be purified by applying the filtration process in domestic scale or commercial scale. For domestic purpose, we can use traditional filter or modern commercial filter but for large scale we have to apply slow sand filter or rapid sand filter. During filtration, the minute insoluble particles as well as bacteria are also separated and the filtrate water becomes pure, safe for drinking.
c) Boiling: Boiling is the simplest way for purification of water. It disinfects drinking water from the disease-causing microorganisms such as E. coli, Cryptosporidium and Giardia Lamblia, which are mostly present in lakes and rivers. According to the Wilderness Medical Society, water temperatures above 70 degree Celsius kill all pathogens within 30 minutes and above 85 degree Celsius within a few minutes. It is also observed that a water temperature at 100 degree Celsius kills almost all the microbes, including the enteropathogens (pathogens that cause diseases in the intestine). However, some fungal pathogens such as Clostridium botulinum and other their spores get killed only at 118 degree Celsius. To be on the safer side, it is recommended to boil water for a few minutes for drinking. For cooking, cleaning and bathing purposes, we can use water from water heaters.
d) Distillation: Distillation process can also be taken as the method of purification of water. It involves boiling the water to produce water vapour. The vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vaporized, they remain in the boiling solution. Even distillation does not completely purify water, because of contaminants with similar boiling points and droplets of un-vaporized liquid carried with the steam. However, 99.9% pure water can be obtained by distillation.
e) Chemical Method: Purification of water can be done by the use of different chemicals. Chemically treated water is good for drinking as harmful germs/ micro-organisms are killed by the action of chemicals. While purifying water from chemical process, chemicals like chlorine, potassium permanganate, bleaching powder, etc. can be added in the drinking water. But it is difficult to purify if it contains dirt or bad smell. Spring water and well water can be purified by using potassium permanganate but it is not widely used.
f) Ozone: The process of ozonation is also the best way for purification of water. It is a relatively unstable molecule “free radical” of oxygen which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoan that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a “cold” electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of relatively fewer dangerous by-products (in comparison to chlorination) and the lack of taste and odour produced by ozonation.
g) Reverse Osmosis: Reverse Osmosis is the mechanical method for purification of water. Mechanical pressure is applied to an impure solution to force pure water through a semi-permeable membrane. Reverse osmosis is theoretically the most through method of large scale water purification available, although perfect semi-permeable membranes are difficult to create. Unless membranes are well-maintained, algae and other life forms can colonize the membranes.
h) SODIS: The natural way for purification of water is SODIS method. Solar water disinfection – the SODIS method – is a simple procedure to disinfect drinking water. Contaminated water is filled in a transparent PET – bottle or glass bottle and exposed to the sun for 6 hours. During this time, the UV – radiation of the sun kills diarrhea generating pathogens. The SODIS- method helps to prevent diarrhea and thereby is saving lives of people. This is urgently necessary as still more than 4000 children die every day from the consequences of diarrhea.