Plastic's resilience makes it great for product packaging, but not so great when it ends up in the ocean. Now, scientists from KTH Royal Institute of Technology in Sweden are testing a new filter system to catch tiny bits of plastic before they enter natural waterways, and quickly break them down using visible light from the Sun.
The silky smooth texture of some toothpaste or hand soaps owes a lot to plastic microbeads, and while these additives are currently being phased out, microplastics are still getting into our waterways. They've penetrated even the deepest trenches of the oceans, where they not only pollute the environment but are eaten by marine animals and slowly poison creatures all the way up the food chain.
"These plastics will start accumulating in the food chain, transferring from species to species, with direct adverse consequences to human population," says Joydeep Dutta, chair of the Functional Materials division of KTH. "Tackling plastic pollution at its source is the most effective way to reduce marine litter."
Normally, plastics break down with exposure to sunlight in a process called photocatalytic oxidation, but that can take many years. So the KTH team, along with a Swedish company called PP Polymer AB, developed a membrane that speeds it up.
That membrane is made up of nanoscale wires coated in a semiconductor material that can absorb visible light from the sun and use it to break down plastic particles. In practice, a filter system made with these membranes catches microplastics in water, and when sunlight hits the material, it exchanges electrons with the atoms in the plastic, splitting the pollutant into CO2 and water. While it's faster than the natural process, the team hasn't specified just how quickly the system works.
"The semiconductor material is able to excite the molecules and set off this process using the 40 percent of solar radiation that is visible light," says Dutta.
Tests of these systems are due to start this month that will see filters placed in wastewater pipes leading out of homes, as well as in wastewater treatment plants as a final stage after other processes have taken place.
The filter is just one part of a larger project called Cleaning Litter by Developing and Applying Innovative Methods in European Seas (CLAIM), which will run until 2021. Other systems being tested include big floating booms that will be placed in river mouths to catch larger pieces of plastic litter, and a ship-mounted system that will measure levels of plastic in the oceans.