Researchers at RMIT University have developed an effective, low-cost method to trap microplastics in wastewater, utilising a dual-bubble technique to achieve elimination rates of more than 90 per cent before the pollution reaches environmental waterways.
The breakthrough process combines microbubbles and nanobubbles to optimise dissolved air flotation, a standard municipal water treatment method that lifts floating contaminants to the surface for skimming.
By upgrading the baseline process to a multi-tiered bubble system, researchers successfully bypassed standard filtration limits that normally allow microscopic plastics to slip through.
Lead author Associate Professor Biplob Pramanik, Director of RMIT’s Water Effective Technology and Tools Research Centre, noted the practical nature of the modification.
“Wastewater treatment plants are a major pathway for microplastics as they slip through filtration processes, posing risks to ecosystems and human health,” Pramanik said.
“Our approach is simple to implement and significantly increases the removal of microplastics during the primary stage of treatment.”
The system relies on a structural division of labour between the bubble types. The ultra-small nanobubbles physically alter the surface characteristics of the plastic fragments, improving structural aggregation and clumping.
Once the particles cluster together, the slightly larger microbubbles provide the vertical buoyancy required to float the clusters up to the surface.
The system thrives under realistic wastewater conditions. Dr Sirajum Monira, who completed the testing during her doctoral studies at RMIT, explained that organic materials, fats, oils, and greases did not hinder the process.
Instead, when paired with standard coagulants, these organic barriers actually helped the microplastics clump into larger, more manageable clusters.
“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,” Monira said.
The RMIT research team is now seeking industry partners to scale up the laboratory trials and test the system within active treatment infrastructure and for a variety of wastewater streams.