Using small devices to desalinate water

Various attempts have been made to make small devices which can convert salt water into safe drinking water - something that could be a boon to people in remote areas with abundant salt water sources but no potable water.

Clear Water Solutions, a Swiss-based company, has developed a very simple method to desalinate and purify water. The device is made from solar cell plates and can produce up to 12-18 litres of fresh drinking water from about 40 litres of sea or salt water per day. The water is heated in the cell by the sun; a part of it evaporates, rises up and condenses on the cooler glass cover. Water then flows along the glass and over a separate channel into the distilled-water collector.

Another desalination device using solar power was developed by the Research Institute for Sustainable Energy based in Murdoch, Western Australia. The solar energy evaporates the sea water inside a glass covered box, condensing the humidity on the lower side of the glass cover. Desalinated water droplets condense on the internal side of the cover and are channelled in to a collector.

Water cone

MAGE Water Management, a German-based company, has come up with the idea of a simple and easy to transport desalination device, called water cone.

Mirco Richardson of MAGE said: “The principle is very simple: You have a base pan, which will take up to 3-5 litres of sea water; you pour that water into the pan, then you float the cone on top of the pan thereby creating a closed circuit system inside, which means you seal the whole system. You let the sun shine onto the cone and within minutes you have a certain evaporation-condensation process that takes place.”

Access to the drinking water is achieved by removing the cone from the pan and pouring it into a bottle. Between 1.4 and 1.6 litres of clean drinking water can be harvested in 24 hours, according to Richardson.

This may not seem a lot, “but when you compare it to… no water, then 1.5 litres of drinking water is a whole lot for every day,” he said.

Average daily water consumption for children and adults ranges between one and three litres, according to a World Health Organization (WHO) report.

Mark Silbernagel, test director at the Seawater Desalination Test Facility in Port Hueneme in California and a member of the technical advisory committee for the US-based Global Water NGO, said that while the design would definitely work to produce small quantities of potable water the amount of water produced might not be enough.

“The drawback is that 1 to 1.7 litres of water in a 24-hour period is a very small quantity of water for a person in arid regions. It would take multiple water cones to satisfy the needs of a single person,” Silbernagel said.

Germs

Meanwhile, Roya Sheikholeslami, chair of Chemical Process Engineering at the University of Edinburgh, told IRIN that the issue was: “How does one prevent biological growth in such a system? That would be a major health challenge.”

Richardson said “because you have UV radiation, it kills a lot of germs and bacteria that can possibly develop in there”. He added that the water cone also acted as a filter. “You can filter with this. If you have mercury or arsenic in the base water, we can filter that out too through evaporation-condensation.”

According to the Encyclopedia of Desalination and Water Resources (DESWARE), the quality of harvested water is very high because all the salts, inorganic and organic components and microbes remain in the base water. In sunny conditions the temperature of the water rises sufficiently to kill all pathogenic bacteria.

“There are many other systems that filter, but most filtering systems do not desalinate, so this is our little niche,” said Richardson.

Cost-effective?

The water cone system costs about 20 euros (about US$26.5) - down from 100 euros when it was first produced 6-7 years ago.

“By investing 20 euros you can have 1.5 litres of clean drinking water a day for 1.5-2 years,” Richardson said. Provided the cone is used for two years, the monthly cost is about $1.10.

During a project in Yemen in 2004, he said, fishermen took the water cones with them on fishing expeditions, allowing them to spend longer at sea and catch more fish.

However, Silbernagel said that the cost of 20 euros was high. “I would have expected something like this to be less than 10 euros. The water cone has the potential to be very inexpensive,” he said.