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Water Filters: Ancient yet Advanced Technology
Human blood contains 95% water and overall human body contains 55 to 60% water. Our life begins with water and revolves around water. The water is our life line and we need that line to be as pure as possible. The water we get from rains, rivers, lakes and ponds is not always pure and clean. If we are visiting countryside , then those brooks and streams give us sense of being clean but that water too needs cleaning , meaning filtering. The water filter that mankind has been using from ancient time and is still using is natural filter which is a ‘well’. The water collected in to the well gets filtered through layers of soil and becomes fairly clean. The principle of water filtration is simple and the same principle is applied to commercial and domestic water filtration. The water filtration involves physical removal of unwanted constituents of natural water to make it pure drinking water. The natural water can be ground water, water from reservoirs like lakes and ponds or rain water. There are many industrial processes and applications which require 100 % pure water and for that advanced water purification, methods such as ion exchange, reverse osmosis and distillation are used. For our daily use, we need water which is free from any suspended matter and microbial contamination. The simplest form of water filter is cloth filter. The water is passed through thick cloth having very tight weaves. This makes water modestly clean. This method can be used even when one is on outdoor trips and camping. Next is sand filter. The sand filter unit is made up of two pots, one fitting on top of another. The top pot is less than half filled with layers of small stones, pebbles, coarse sand and then fine sand as top layer. This pot has small hole at bottom. The top pot is filled by slowly pouring plain water, and after sometime the clean water is collected into the bottom pot. The commercial and municipal water cleaning plants also use this method. The difference is that they have huge ponds instead of pots. The chemicals like Alum are added to water to be filtered. Alum forms floccules and impurities get trapped into these floccules and are removed easily by filtration. The care has to be taken to avoid formation of channels in the sand layers; otherwise most of the water will pass through these channels without getting filtered. The purity of the final water depends upon the fineness of the sand and proper packing of various layers. These sand filters require periodical cleaning of sand and pebbles. Ceramic candles are very good and reliable medium for water filtration. These candles have very small porosity and un-dissolved impurities from water get filtered out. For some time now, activated charcoal filters are used for water filtration and purification. Activated charcoal is a natural product produced by controlled burning of wood and mainly coconut husk. This activated charcoal has very small particle size. This makes effective surface area, very large. The charcoal has unique property of surface adsorption. Adsorption is surface phenomenon. The impurities from water get stuck to the surface of charcoal producing pure water. For domestic use granular charcoal filters are used. This filter too needs periodical cleaning and replacement of activated charcoal filter candles. The best process for water purification is reverse osmosis. This process is not exactly filtration process in conventional sense, but can be considered as filtration on ‘Ion’ level. This method is an extension of ion exchange method. In ion exchange, the positive and negative ions dissolved in water are removed in two columns of cationic and anionic resins. In reverses osmosis, the membranes with selective permeability are used. The water to be purified passes over these membranes and the ions such as sodium, potassium and calcium in water get removed. This process can be considered as ‘ionic filtration’, and is used commercially. These reverse osmosis filtration units are available for domestic use as well. Now a day, ‘Point of Use filters’ are also available which can be fitted to faucet for drinking water. Whatever method one chooses to use , one has to be sure that water used for every purpose is clean and one should remain healthy.
