Inexpensive solar-powered lens purifies polluted water

A university student in the US has developed an inexpensive solar lens that uses sunlight to heat and disinfect polluted water, destroying 99.9 per cent of bacteria and pathogens.
Deshawn Henry, a University at Buffalo sophomore civil engineering major, researched how to improve a six-foot-tall, self-sustaining magnifying glass.
Termed a water lens, the device uses sunlight to heat and disinfect polluted water.
Since the frame for the lens can be constructed from commonly found materials - wood, plastic sheeting and water - the lens can be built at a very low cost, offering an inexpensive method to treat water.
The device can heat a litre of water to between 54 degrees Celsius and 65 degrees Celsius in a little more than an hour, destroying 99.9 per cent of bacteria and pathogens.

"The water lens could have a huge impact in developing countries," said Henry, who performed the study under James Jensen, professor in the Department of Civil, Structural and Environmental Engineering.

"Millions of people die every year from diseases and pathogens found in unclean water, and they can't help it because that's all they have," he said.
The lens consists of a plastic sheet covered with water supported by a wooden frame. The frame holds a small container of water below the lens in line with a focal point created from a concentrated ray of sunlight.
Barring the weather, once assembled, the lens functions freely. Due to the sun's movement throughout the day, Henry needs to repeatedly shift the container to match the focal point.

Henry's research tested how altering the thickness of the plastic sheet and the volume of water over the sheet affected the efficiency of the lens.
The device was tested with plastic sheets that were 0.7, 1 and 2 millimetres thick, and water volumes of four, six and eight litres.
The study found that adding more water to the lens improved efficiency, as larger areas of water transmitted more energy from sunlight. However, thicker plastic sheets consumed more energy from light, lowering the lens' efficiency.
A plastic sheet that was too thin or excessive amounts of water could break the lens.

Henry concluded that the 0.7-millimetre sheet could efficiently heat the container while supporting eight litres of water, but any more and the sheet could potentially break.