The Global View

Scientists find way to tame tiny particles out of sewage

Sewage SignHow can you tame the growing number of ultra-tiny particles that are going into consumer products and, eventually, back into the environment? How about using an ultra-tiny form of behaviour modification?

Every day, more and more products appear on shop shelves that are made with nanomaterials, ultra-tiny particles less than 1/1000th the width of a human hair. These nanoparticles offer a host of unique properties — nano-sized bits of silver, for example, act as anti-bacterials. But many worry about unintended consequences when such materials enter the waste stream and, eventually, the environment.

A team of UK researchers is proposing a novel solution that could reduce those worries: why not coat those nanoparticles with something that helps them clump together and make them easier to control?

The team’s study simulated a primary sewage treatment process to show that coating silica nanoparticles — similar to those used in ointments, toothpaste and household cleaners — with a detergent-like material made the nanoparticles clump together into the sewage sludge, the solid residue left behind after treatment. Sludge is often stored in landfills or recycled as agricultural fertiliser.

Left uncoated, the nanoparticles in the test process stayed in the water, which in sewage plants is treated and then released in the effluent stream.

As nanoparticles are simply too small to be seen using most methods, the team used neutron scattering to view the test sewage at the nano scale. The neutrons easily penetrate the sewage “soup” and scatter strongly from the nanoparticles, allowing their aggregation behaviour to be followed with time.

The researchers say their study demonstrates the potential for coating or otherwise changing the surface chemistry of nanoparticles to re-route their journey through sewage treatment plants.