Sunday, November 29, 2009

Fate of Silica Nanoparticles in Public Sewage Systems Sought by Scientists


Figure: Identifying and managing silica nanoparticles through the sewage system
Credit:  The Centre for Ecology & Hydrology, Dr Helen Jarvie, UK

A new understanding about nanoparticle behaviour in sewage treatment plants could improve the environmental management of nanoparticle wastes from foods, cosmetics, medicines, cleaning and personal care products, say British researchers.

Experts believe some nanoparticles may have harmful effects on the environment or human health, and research is currently being directed at understanding the issues involved. Scientists from the Centre for Ecology & Hydrology (CEH) and the Science and Technology Facilities Council's Isis Neutron Source, along with colleagues from King's College London and Oxford University, studied how certain nanoparticles behave in wastewater and have now identified a way to potentially help remove them during primary sewage treatment.

The scientists examined silica nanoparticles, over one million tons of which are used in the manufacture of consumer products each year, with a large proportion of these subsequently washed down drains into sewage systems. This makes sewage treatment plants a major gateway for nanoparticles entering the aquatic environment. 

The new study, details of which are published in Environmental Science and Technology, simulated primary sewage treatment to show that coating silica nanoparticles with a detergent-like material (called a surfactant) made the nanoparticles interact with components of the sewage to form a solid sludge. This sludge can be separated from the wastewater and disposed of. In contrast, uncoated nanoparticles stayed dispersed in the wastewater and were therefore likely to continue through the effluent stream and potentially on into the environment.

Dr Helen Jarvie from CEH, the lead author of the study, said the research proved that the surface chemistry of nanoparticles influenced their likely removal during primary sewage treatment. "By adding a coating which modifies that surface chemistry, it may be possible to re-route their journey through sewage treatment plants," she explained. 
Helen Jarvie and Steve King preparing
the sewage sample for their experiment. 

Credit: Centre for Ecology & Hydrology

The scientists used the ISIS Neutron Source to view the sewage at the nanometer scale. Nanoparticles are too small to be seen by the human eye but the ISIS Neutron Source, acting like a giant microscope, allows scientists to study objects 1,000 times thinner than a human hair. The neutrons easily penetrate the sewage and scatter strongly from the nanoparticles, allowing the aggregation behaviour of the nanoparticles to be measured through time.

Dr Steve King from the ISIS Neutron Source said the research showed that primary sewage treatment may not be effective at removing some nanoparticles. "However," he added, "we now know where those nanoparticles may go and how we might deal with them."  Further work is now planned to examine the behaviour of a wider range of nanoparticles, with different classes of surfactants, in wastewaters.

Additional information: 
The Centre for Ecology & Hydrology issued a press release for this story.
The research is published in the November 2009 issue of Environmental Science and Technology and is available online (external link). The full title is 'Fate of Silica Nanoparticles in Simulated Primary Wastewater Treatment' by Helen P Jarvie, Hisham Al-Obaidi, Stephen M King, Michael J Bowes, M Jayne Lawrence, Alex F Drake, Mark A Green and Peter J Dobson.
Related CEH links: 


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