A new way to filter polluting nano-particles out of the water
.jpg "Purifiers cannot filter nanoparticles / PREETI SINGH")
Nano-particles are slowly infiltrating the environment. They have entered cosmetics, detergents, toothpastes, textiles—the list is long. The biggest concern is for aquatic life. Smaller than the smallest grain of dust, they are quite challenging to filter out of the water in treatment plants.
Addressing the fears of nano-particle pollution, scientists at the Natural Environment Research Council’s Centre for Ecology and Hydrology (nerc-ceh) in UK have proposed a way to stall the pollution.
Previous studies have found that nano-materials settle down at the bottom of waterbodies, making bottom-feeders, like mussels and worms, susceptible to toxicity.
Two years ago, a group from the Arizona State University studied the impact of higher concentration of titanium dioxide nano-particles on the growth rate of algae. They found that some stress genes were over expressed in response to the particles.
Helen P Jarvie and her team from nerc-ceh and King’s College, London have tried to separate the nanoparticles from the water in the municipal sewage treatment plant—the particles’ main outlet to the environment. The team experimented with silica nano-particles (which are also used for cancer treatment) by coating them with a chemical called Tween 20. This chemical is stable and relatively non-toxic and is used widely in household products such as detergents and emulsifiers.
Behaviour of both coated and un-coated particles was observed during simulated primary waste water treatment. The scientists found that while uncoated silica particles escaped with the water as usual, the coated particles underwent rapid aggregation (flocculation). In other words, they collected together to form a larger particle and, in turn, became too heavy to escape and settled down as sediment. The clean water left the treatment plant.
“Our results show that coated silica particles could be removed by sedimentation to sewage sludge whereas uncoated particles would continue to the effluent stream,” said the study that was published in the December 2009 issue of Environmental Science and Technology.
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