They say that their device can deliver safe drinking water to families in rural areas for just US$2.50 a year, including both the cost of the device and running costs. Their work was published online in Proceedings of the National Academy of Sciences last month (6 May).
The team, from the Indian Institute of Technology Madras (IITM), used a mixture of nanoparticles to form a 'nanocomposite' that releases a steady stream of silver ions that kills water-based microbes.
This technique was already known as a promising way to provide safe drinking water, but it has proved a challenge to find an effective material to enable this.
"We had to find a material that was easily available, cheap, environmentally friendly and that maintained a sustained release of silver ions that could keep its concentration in water at less than 50 parts per billion, which is the WHO permissible level for silver [nanoparticles] in water," Thalappil Pradeep, an author of the paper and a professor in IITM's chemistry department, tells SciDev.Net.
He says they chose a nanocomposite material called aluminium oxy-hydroxide-chitosan because both its structure and the diameter of the silver nanoparticles embedded in the material created optimal conditions for controlling the release of silver ions in temperatures ranging from five to 35 degrees Celsius.
Pradeep says that the silver nanoparticles are small enough to be highly active and therefore to easily release ions into the water, but large enough to be kept confined within the nanocomposite matrix, which acts as a cage to ensure limited interaction of the silver nanoparticles with water.
The nanomaterial is held in a sieve through which water is passed. The device can be reactivated — when the silver nanoparticles get coated with other impurities present in water and the release of ions stops — by boiling the device or treating it with lemon juice. Each unit is expected to last around six years.
The system can be set up in community water treatment plants. Alternatively, families can buy the device, in which case the sieve is attached to the lid of a bucket-like container.
Currently, the researchers are installing the devices in community water treatment plants in the state of West Bengal. However, they are still looking for companies that can mass-manufacture the devices for household water filtration.
Amitabha Sengupta, a former scientist at the West Bengal State Water Investigation Department, who is now retired, says that such a low-cost filter is urgently needed to bring safe drinking water to the poor due to the huge number of deaths from waterborne intestinal diseases in India.
But he adds that more work needs to be done on low-cost methods of removing chemical contaminants such as arsenic from drinking water.
Link to paper's abstract