Ever wondered how the water from your household water purification unit gets purified? This compact piece of technology has been humbly providing us potable water for days together without us thinking about the secret behind it. Water purifiers employ the simplest as well as the most advanced techniques in filtration: simplest being a normal filter cloth and one of the advanced techniques the removal of impurities by activated charcoal and UV light treatment. Activated charcoal is the ‘black powder’ that has been largely responsible in keeping us healthy.
The water that is supplied to our houses undergoes a preliminary treatment. The local government is responsible for this treatment. Water taken from sources such as rivers, lakes or reservoirs is not fit for direct use. This water is treated using various biological and chemical processes to remove dirt, micro-organisms and other impurities. However, some of these are left unfiltered. This water can be used for household purposes such as washing and bathing, but cannot be used for direct consumption. This is where water purifiers come into the picture.
Water purifiers employ a series of water purification techniques to remove the impurities present in the water. A simple filter cloth cartridge first removes the smallest of turbidity causing particles. The particles are as small as 100-1000 microns. Then the water passes through the activated charcoal chamber. Activated charcoal removes the majority of the odour, taste and colour imparting particles (5-50 microns) and some of the bacteria and micro-organisms that might have passed unchecked from the initial treatment.
Activated charcoal is a specially treated powder. It is derived from powdered coal which is heated (carbonised) in the absence of air to temperatures of about 700-8000 C. The powder that is obtained has extremely useful properties that attract and bond with certain compounds. Because of its powdered form, after carbonisation, the pores of the powder open up further and the surface area of activated charcoal increases. The surface area of the pores is so large that 10 grams of activated charcoal can have a surface area of a football field (5000 sq m)!
This large surface area and the ability to attract and bind with many compounds are what make activated charcoal special.
Water is chlorinated before being supplied to our houses. Sometimes excess chlorine gets added and it imparts a characteristic odour to the water. The activated charcoal chamber is responsible for removing such odour imparting compounds. Similarly, organic matter and other bacteria are trapped. This is because the activated charcoal is slightly positively charged. So when water passes over it, all these impurities are attracted to it. This process of bonding is technically known as adsorption. And because of its large surface area, adsorption goes on for thousands of litres of water.
However, the activated charcoal has its own shelf life. The positive charge on it wears off after certain litres of usage. As the number of impurities on the surface starts increasing, the area available for adsorption decreases. The efficiency of the whole process decreases further with time. To avoid this, regular maintenance of the charcoal chamber is necessary. The charcoal is replaced after purifying a certain quantity of water. The timing largely depends upon the quality of the water being supplied to the purifier. If unchecked, the charcoal might become the breeding ground for harmful bacteria which can enter our digestive system and cause problems such as dysentery. The water can be further treated with UV light to ensure the complete removal of bacteria in the water. UV treatment generally forms the last part of a water purifier.
Water purifiers provide us with a low cost safeguard against any water borne diseases. So, the next time you pass by a water purifier, take a moment to think about what all on inside it.