Developed by researcher Yang Liu and colleagues at Hong Kong Polytechnic University, the method uses bacterial biofilms – a sticky substance created by micro-organisms – to trap microplastic particles. The biofilm is then processed and dispersed, releasing the plastic for processing and recycling.
Microplastics pose a major risk to food chains and human health. Smaller than 5mm in diameter, they enter the environment from a number of sources, including breakdown of larger plastic pieces, washing of synthetic clothes, breakdown of car tyres and plastic waste directly from industry.
“They are not easily bio-degradable,” said Liu. “They retain in the ecosystems for prolonged durations. This results in the uptake of microplastics by organisms, leading to transfer and retention of microplastics down the food chain.
“Due to their huge surface area and adsorption capacity, microplastics can adsorb toxic pollutants, such as pesticides, heavy metals, and drug residues at high concentrations. This leads to biological and chemical toxicity to organisms in the ecosystems and humans… Microplastics are also difficult to remove in wastewater plants, resulting in their undesired release into the environment.”
Liu and colleagues used the bacterium Pseudomonas aeruginosa to capture microplastics in a bioreactor. This species of bacterium is found in all environments and has previously been shown to colonise microplastics in the environment.
P. aeruginosa biofilms caused the microplastics to aggregate together, eventually causing them to sink. This made the microplastics more convenient to collect, Liu said.
Once the microplastics were captured by the biofilms and had sunk to the bottom of the reactor, the researchers used a biofilm-dispersal gene, which caused the biofilm to release the microplastics. The plastics could then be recovered for recycling.
Next, the researchers plan to move the proof-of-concept from the lab to an environmental setting. “We next plan to isolate and identify natural pro-biofilm forming bacterial isolates, either from the sewage or from aquatic environments, where they display heightened abilities to colonise and form biofilms on microplastics,” said Liu.
The researchers hope the technique will eventually be used in wastewater treatment plants, stopping microplastics from escaping into the oceans. They also have to find natural compounds to stimulate biofilm dispersal of the pro-biofilm forming bacterial isolates.
The technique will be discussed by Liu today (28 April) at the Microbiology Society's Annual Conference.
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