For flood affected populations: purifying water—with sunlight There are some four billion cases of diarrhoea each year worldwide and about two million deaths, mainly of children under the age of five, according to the WHO. The problem is particularly serious after floods, such as in Pakistan, where the outbreak of diarrhoea has been reported from several regions, mostly due to water-borne diseases.

Science can now offer a cheap and easy way to make the dirty water available safe for drinking. The technology, known as ‘SODIS’ (Solar Water Disinfection), requires only one-litre transparent plastic (PET) bottles and sunlight! These commonly found plastic bottles allow the UV light to pass through, killing the germs and making the water drinkable. If the water is muddy, it should be filtered through a piece of cloth in order to remove the dirt particles.

One-litre bottles work best, but two-litre bottles may also be used. The bottle is placed for a minimum of six hours in sunlight and the water can then be drunk directly from it. The bottles must not be old or heavily scratched and any labels should be removed in order to allow the light to pass through unobstructed.

This easy way of purifying water was discovered by Prof Atfim Acra at the American University of Beirut in the 1980s. The Swiss Federal Institute of Aquatic Science and Technology (Eawag) in collaboration with the Department of Water and Sanitation in Developing Countries (Sandec), has already implemented projects in 33 countries. The clinical control trials demonstrating the efficacy of the process were carried out by Professor Ronan Conroy of the Royal College of Surgeons in Ireland, in collaboration with Michael Elmore-Meegan before it was recommended by WHO as a safe method for water treatment.

The disinfection process involves three different mechanisms. Firstly the solar radiation (UV-A) attacks the bacteria directly, killing them by interfering with their metabolic processes. Secondly, the UV-A radiation reacts with the oxygen dissolved in water, producing highly reactive oxygen species and peroxides that kill bacteria.

Thirdly, the infra-red light heats up the water, and if the temperature rises above 50 degrees Centigrade, then there is a three-fold increase in the rate of disinfection. For further background reading see http://en.wikipedia.org/wiki/Solar_water_disinfection and references therein.

The Government of Pakistan agencies and NGOs involved in aid distribution should distribute clean PET bottles along with instruction pamphlets so that the flood affected persons could save themselves from diarrheal diseases.

(I am grateful to Prof Naeem Jafari, Advisor Academic Affairs, Ziauddin University, Karachi, for bringing this technology to my attention).

The mysterious universe One of the greatest puzzles of our universe is that the total visible matter made up of atoms including planets, solar systems, stars, galaxies etc accounts for only four per cent of the total mass of the universe. The rest is accounted for by a mysterious force known as dark energy (72 per cent of total mass of universe) and dark matter (24 per cent of total mass of universe). Scientists are struggling to understand what these two entities, dark energy and dark matter, really are.

Dark matter, though completely invisible, is being studied by the effect of its gravitational pull on other objects. Dark energy, however, exerts no such effect and is more difficult to explore. It is the force that is pushing the galaxies apart and causing the universe to expand at an accelerating pace.

Scientists are now using a massive cluster of galaxies to serve as a huge magnifying lens to study dark energy. This cluster of galaxies (known as Abell 1689) acts as ‘cosmic lens’ and allows Nasa’s Hubble telescope to look at the galaxies lying behind this huge lens. The light coming from these rear galaxies is affected by dark energy, and the scientists can then indirectly measure how this mysterious force is contributing to the acceleration of our universe.

Exciting breakthrough in solar cell technology Solar cells have an efficiency of about 20 per cent and they are expensive to manufacture. This makes them uncompetitive as compared to other forms of energy production which use oil, gas, fuel or even nuclear energy.

A problem is that they use only a part of the light spectrum, while the remaining part of the spectrum which also produces heat is wasted. Now Nick Melosh and coworkers at Stanford University have developed an exciting new type of solar cell that makes use of the heat produced by the sun light and converts it also into electricity.

The new technology (known as “photon enhanced thermionic emission”, PETE) can work at high temperatures, unlike currently available solar cells, and its utilisation of light and heat (produced by solar radiation) can increase the efficiency of the new solar cells to above 50 per cent, making them competitive to other forms of electricity production.

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