Scientists cook up novel way to remove microplastics

Image: Prateek Nuti from Pexels

Did you know food-grade plants such as okra, aloe, cactus and psyllium can be used to clean water and wastewater? New research has found a way of using these plant extracts to remove microplastics.

The health effects of ingesting microplastics — tiny pieces of plastic 5mm or smaller — are currently unclear, but studies suggest people unintentionally consume tens of thousands of these particles every year.

In the typical wastewater treatment process, microplastics are removed from water in two steps. First, those that float are simply skimmed off the top of the water. However, this step only removes a fraction of the total microplastics. The rest must be removed by adding flocculants - which are sticky chemicals that attract microplastics and form large clumps. The clumps then sink to the bottom of the water tank and can be separated from the main body of fluid.

“Microplastics by themselves may not be much of a health hazard, but anything they get into or any type of toxic substance that gets attached to these plastics could go inside our bodies and cause problems.”

Rajani Srinivasan, Tarleton State University

Srinivasan and her team from Tarleton State University, Texas, US, have been investigating nontoxic ways to tackle the issue. Previously, Srinivasan studied the use of food-grade plant extracts as nontoxic flocculants to remove textile-based pollutants from wastewater.

“I was working with the removal of microorganisms and things like that, and I thought, ‘Why not try microplastics?’” said Srinivasan.

Inspired, the team of undergraduate and Master’s students tested polysaccharide extracts from fenugreek, cactus, aloe vera, okra, tamarind and psyllium — all of which are food-grade materials — as flocculants to capture microplastics.

They tested compounds from the individual plants, as well as in different combinations. To do this, they added these extracts to various microplastic-containing water sources. Then, they examined microscope images of the flocculant clumps before and after treatment and counted the microplastics to determine how many particles had been removed.

Plants work best

In their experiments, the researchers found polysaccharides from okra paired with those from fenugreek could best remove microplastics from ocean water, whereas polysaccharides from okra paired with those from tamarind worked best for freshwater samples. Overall, the plant-based polysaccharides worked better than, or as well as, the traditional flocculant polyacrylamide, depending on the combination of extracts and water source.

Importantly, the plant-based flocculants can be implemented in existing water treatment processes. “The whole treatment method with the nontoxic materials uses the same infrastructure,” says Srinivasan. “We don’t have to build something new to incorporate these materials for water treatment purposes.”

Looking forward, she and her team will continue tailoring the ratios and combinations of plant-based flocculants to optimize removal of different microplastic types from a variety of water sources, such as ocean water, estuary water, freshwater and groundwater.

They also plan to scale up their nontoxic microplastics removal process in field studies outside of the lab.

Ultimately, they hope to commercialise this new, plant-based method so that microplastics can be removed from water on an industrial scale — enabling cleaner and safer water for everyone to drink.

The researchers acknowledge support and funding from the National Science Foundation, Tarleton State University and the High Plains Water Development District in Lubbock, Texas.