Microplastics could be eliminated from wastewater at source

A team of researchers from the Institut national de la recherche scientifique (INRS), Quebec, Canada, have developed an electrolytic process for treating wastewater, degrading microplastics at the source.

 Microplastics are fragments of plastic less than 5mm long, often contained in toiletries or shedding from polyester clothing. They are present in virtually every corner of the Earth, and pose a particularly serious threat to marine ecosystems. High concentrations of microplastics can be carried into the environment in wastewater.

There are no established degradation methods to handle microplastics during wastewater treatment; although some techniques exist, these involve physical separation as a means of filtering the pollutant. These techniques do not degrade microplastics, which requires additional work to manage the separated fragments. So far, research into degradation of microplastics has been very limited.

The INRS researchers, led by water treatment expert Professor Patrick Drogui, decided to try degrading plastic particles through electrolytic oxidation – a process that does not require the addition of chemicals.

“Using electrodes, we generate hydroxyl radicals to attack microplastics,” Drogui said. “This process is environmentally friendly because it breaks them down into CO2 and water molecules, which are non-toxic to the ecosystem.”

Drogui and his colleagues experimented with different anode materials and other parameters such as current intensity, anode surface, electrolyte type, electrolyte concentration and reaction time. They found that the electrolytic oxidation could degrade more than 58 ± 21 per cent of microplastics in one hour. The microplastics appeared to degrade directly into gas rather than breaking into smaller particles.

Lab-based tests on water artificially contaminated with fragments of polystyrene showed a degradation efficiency as high as 89 per cent.

“This work demonstrated that [electrolytic oxidation] is a promising process for degradation of microplastics in water without production of any waste or by-products,” the researchers wrote in their Environmental Pollution report.

Drogui envisions this technology being used to treat microplastic-rich wastewater emerging from sources such as commercial laundries.

“When this commercial laundry water arrives at the wastewater treatment plant, it is mixed with large quantities of water, the pollutants are diluted and therefore more difficult to degrade,” he explained. “Conversely, by acting at the source, i.e. at the laundry, the concentration of microplastics is higher, thus more accessible for electrolytic degradation.”

Next, the researchers will move on to experimenting with degrading microplastics on water outside the artificial laboratory environment. Real commercial laundry water contains other materials that can affect the degradation process, such as carbonates and phosphates, which can trap radicals and limit degradation. If the technology is effective under these circumstances, the researchers plan to conduct a study to determine the cost of scaling up this treatment to implement in laundries.

Last week, researchers from the University of Barcelona published a study suggesting that encouraging a greater proliferation of seagrass meadows in the shallows of oceans could help trap, extract and carry marine plastic debris to shore.