RMIT researchers develop dual-bubble method to remove 90% of microplastics

RMIT researchers develop dual-bubble method to remove 90% of microplastics

Researchers at RMIT University have developed a wastewater treatment method that removes more than 90% of microplastics by utilizing a combination of microbubbles and nanobubbles. The approach, which has been successfully demonstrated at a laboratory scale, aims to stop plastic particles from entering waterways, oceans, and agricultural environments.

The system builds upon dissolved air flotation, a common treatment process where air bubbles attach to contaminants and lift them to the water's surface for separation. According to the researchers, integrating both micro- and nanobubbles results in significantly higher removal rates compared to systems that rely on a single bubble type.

Each bubble type serves a distinct purpose in the process. Microbubbles provide the buoyancy and lifting force necessary to carry particles to the surface. Meanwhile, nanobubbles increase the likelihood that microplastic particles will attach and aggregate by increasing interactions between particles.

The method is designed for easy integration into existing facilities. RMIT stated the dual-bubble approach can be adopted by wastewater treatment plants without major infrastructure changes by optimizing current operating conditions, such as bubble size, saturation time, and air pressure.

"Wastewater treatment plants are a major pathway for microplastics as they slip through filtration processes, posing risks to ecosystems and human health,"

Biplob Pramanik, Associate Professor and director of RMIT’s Water Effective Technology and Tools Research Centre, via RMIT

Pramanik added that the approach is simple to implement and increases the removal of microplastics during the primary stage of treatment.

Testing indicated that the system remains effective under realistic wastewater conditions. Dr Sirajum Monira, who completed the research during her RMIT PhD studies, noted that substances typically viewed as barriers to treatment—such as fats, oils, grease, and organic matter—did not reduce performance.

In some instances, these materials actually improved the process. When combined with standard coagulants, they helped microplastics clump into larger particles that are more easily removed.

Capturing these plastics early in the treatment cycle also prevents them from becoming concentrated in sewage sludge. Monira stated that reducing the amount of plastic entering biosolids helps minimize the release of pollutants back into the environment.

"By capturing the microplastics before they become concentrated in sewage sludge, we can reduce the amount entering biosolids and ultimately minimise their release back into the environment,"

Sirajum Monira, Researcher, via RMIT

The study, titled Micro-Nanobubble Integrated Dissolved Air Flotation: A High-Efficiency Strategy for Microplastic Mitigation in Wastewater, was published in the journal ACS ES&T Water.

The research team is now seeking industry partners to validate the dual-bubble process. The next phase involves testing the technology under real operating conditions across a variety of wastewater streams to ensure it is scalable for full-scale wastewater treatment operations.