Dual-bubble method could fit existing treatment plants
RMIT University researchers removed more than 90% of microplastics from wastewater in laboratory tests by pairing microbubbles with nanobubbles. Their study points to a way for treatment plants to raise microplastic removal without major new infrastructure.
Instead, operators could optimise existing settings such as air pressure, saturation time and bubble size. According to RMIT, that would let plants test the method inside current dissolved air flotation systems.
Lead author Associate Professor Biplob Pramanik said wastewater treatment plants are a major pathway for microplastics because the particles can slip through filtration processes. Pramanik also directs RMIT’s Water Effective Technology and Tools Research Centre.
The study examined an enhanced version of dissolved air flotation, a common water treatment process. In that process, air bubbles attach to contaminants and lift them to the surface.
Results from RMIT showed the combined bubble system outperformed setups that used only microbubbles or only nanobubbles. Microbubbles supplied the lifting force, while nanobubbles improved particle attachment and aggregation.
Biplob Pramanik and Sirajum Monira
Pramanik called the method practical for the primary stage of treatment. “Our approach is simple to implement and significantly increases the removal of microplastics during the primary stage of treatment,” he said.
Dr Sirajum Monira completed the research during her RMIT PhD studies. She found the dual-bubble approach remained highly effective under realistic wastewater conditions.
Organic matter and fats, oils and grease did not reduce performance in the tests. In some cases, Monira found those materials improved removal when combined with standard coagulants.
As a result, microplastics clumped into larger particles that were easier to remove. That matters before plastics become concentrated in sewage sludge.
By removing microplastics earlier, plants could reduce the amount entering biosolids and limit their release back into the environment. RMIT has so far demonstrated the method at laboratory scale.
Meanwhile, the team wants to work with industry partners to validate the process under real operating conditions and across different wastewater streams. Organisations interested in partnering with RMIT researchers can contact the university through the details supplied with the study.
The paper, titled “Micro-Nanobubble Integrated Dissolved Air Flotation: A High-Efficiency Strategy for Microplastic Mitigation in Wastewater”, appears in ACS ES&T Water. Sirajum Monira and Biplob Pramanik authored the study, and its DOI is 10.1021/acsestwater.6c00127.
