The laboratory-scale study demonstrates a practical way to improve the capture of plastic particles before they enter the environment.
The research builds on dissolved air flotation, a widely used treatment technique already employed in wastewater facilities.
Rather than requiring new infrastructure, the method improves performance by optimising operating conditions such as air pressure, saturation time and bubble size, making it a potentially cost-effective upgrade for existing plants.
The findings suggest wastewater operators could significantly reduce the release of microplastics into waterways while also limiting the amount of plastic contamination entering sewage sludge and biosolids.
The research team is now seeking industry partners to validate the technology in full-scale wastewater treatment operations.
Combining two bubble types boosts performance
Dissolved air flotation is commonly used to remove suspended contaminants by attaching them to air bubbles that float to the water’s surface, where they can be separated.
The RMIT team enhanced this process by combining microbubbles with nanobubbles rather than relying on a single bubble type.
Testing showed the dual-bubble system consistently outperformed conventional approaches, achieving microplastic removal rates exceeding 90%.
Each bubble type plays a different role during treatment. Microbubbles provide the buoyancy needed to lift contaminants, while nanobubbles increase the likelihood that microplastic particles will attach to the bubbles and cluster together.
This combination improves the efficiency of particle separation during the primary stage of wastewater treatment.
Effective under realistic wastewater conditions
The researchers also assessed how the system performed in wastewater containing organic matter as well as fats, oils and grease, conditions that often complicate treatment processes.
Instead of reducing efficiency, these materials did not hinder the removal process. In some cases, they enhanced performance by helping microplastics form larger clusters when used alongside standard coagulants, making the particles easier to remove.
Capturing microplastics earlier in the treatment process also reduces the concentration of plastic particles in sewage sludge.
This could help minimise contamination in biosolids that are later reused, reducing another pathway through which microplastics can return to the environment.
Pathway to industry adoption
One of the key advantages of the approach is its compatibility with existing wastewater treatment infrastructure.
Because the improvement relies on optimising operational parameters rather than installing entirely new systems, implementation could be relatively straightforward for treatment facilities.
Having successfully demonstrated the technology at laboratory scale, the RMIT research team is now looking to work with industry partners to test the dual-bubble process under real-world operating conditions across different wastewater streams.
If successful at commercial scale, the technology could provide wastewater treatment plants with a practical and scalable tool to curb microplastics pollution before it reaches rivers, oceans and agricultural environments.
