[KATHMANDU] A nanomembrane filter that uses inexpensive fly ash waste, a byproduct of thermal power plants, could offer an environment-friendly option to treat water, says a new study. 

Developed by a team of scientists from Nepal’s Tribhuvan University and South Korea’s Chonbuk National University and Hanyang University the nanomembrane filter is made of fly ash and polyurethane and is coated with silver nanoparticles.

Their tests show that the filter can adsorb arsenic and dyes; and kill disease-causing microorganisms, according to a report published in the Journal of Hazardous Materials on 15 January. The spider-web-like membrane captures particles and microorganisms bigger than its pores, resulting in better purification of water than conventional filters.

The technique offers new ways to use one polluting waste material to control other pollutants in scalable and inexpensive ways, the report says. Researchers are working on ways to improve the adsorption capacity and regenerative ability of these membranes for commercial water and air filters.

“The formation of spider-web-like nanonets not only increases the surface area of the membrane but also reduces the pore size,” lead author Hem Raj Pant of the Institute of Engineering, Kathmandu, explained to SciDev.Net. As a result, impure water takes longer to pass through the filter and that traps impurities, he said.

Silver nanoparticles added to the membrane give it antibacterial properties, but the paper does not mention any water quality analysis, says Prakash Amatya, technical advisor at Handmade Water, a non-profit that treats waste water from dyeing units In Kathmandu.

Amatya also says that the paper sheds no light on how the toxic heavy metal compounds in the fly ash can be safely and cost-effectively prevented from leeching into water. “The findings seem promising but they still need to be tested to gauge water quality.”

According to a 2012 report of Nepal’s Central Bureau of Statistics, less than half of Nepal's urban households use water purification technologies, while the number is even lower at 13 per cent in Nepal's rural areas.

Arinita Maskey Shrestha, water, sanitation and hygiene specialist at UNICEF, Kathmandu, described Pant’s study as “interesting”, but was uncertain about its suitability in Nepal that is classified among the world’s least developed countries. “In Nepal, various water treatment technologies have been rejected due to the complexity of day-to-day maintenance and high installation costs,” he said.

Most Nepalis prefer simple water purification methods such as boiling to meet their drinking water requirements.