Cutting edge

September 28, 2001

A funnel and a piece of pipe provide the cheap, green answer to purifying water at tap point around the world

Water is one of the basic needs of all living beings. Each of us consists of about 65 per cent water and humans need at least two litres of it a day. In many regions of the world, surface and ground water are the main sources of drinking water. These water sources are often polluted by urban and industrial chemicals. Water treatment plants reduce the concentration of harmful chemicals to a safe level, while disinfection removes microbiological hazards. But when the water is supplied to users via distribution networks, additional safety problems arise.

When the distance between treatment plants and the water user is great, secondary water pollution becomes important because micro-organisms reproduce within the supply system. And because of the presence of disinfectant agents, the various harmful byproducts accumulate in treated water, many of them poisonous.

At present, this global problem is resolved by producing bottled water for cooking and drinking. The installation of different adsorption-filtering and osmotic systems at the points of use is also popular. But these approaches are expensive and they use natural resources, such as plastic for bottles and charcoal for filter cartridges.

Now there is a more economical solution. Secondary polluted water contains organic matter whose molecules exhibit surface-active properties. These molecules can be adsorbed (collected) at the air-water interface. Their surface concentration is 100-1,000 times higher than in the bulk water phase. We have used this fact to develop the Bubble-Film Extraction system for conditioning secondary polluted water. The principle of BFE is simple: air bubbles are fed into contaminated water and dissolved surface-active matter is absorbed onto the surface of the bubbles. The flow of air bubbles delivers the surface-active molecules to the water surface, which becomes covered by a thin layer of impurities.

My work has shown that the flow of bubbles can be easily and almost completely transformed into a stream of thin, flat liquid films, or membranes, inside a special device called a bubble-film extractor. This is basically a piece of pipe of a special configuration connected to a funnel. The funnel is partially immersed in the water, so that inside it the air bubbles with pollutants on their surface are transformed into a stream of thin liquid films. The lifetime of the water membranes inside the extractor allows them to be transported into a separate storage area or into the sewage system directly.

Bubble-film extractors do not require any replacement units, in contrast to filtering or adsorption systems. And the purification requires less than one unit of electricity per 1,000 litres of water purified. Special tests have shown that BFE reduces the concentration of toxins in secondary polluted tap water to a safe level.

As a result of our research, a range of handy, effective and economical devices have been constructed for the consumer market. The earliest models are intended for the purification of tap water supplied to consumers via the large water distribution networks.

Sergey Gevod is a postgraduate student in the department of inorganic chemistry, Ukrainian State Chemical Technology University, Dnepropetrovsk, Ukraine. He did this research on an Intas fellowship with European Union researchers.


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