Dual-bubble approach achieves microplastic removal rates of over 90%
Using a combination of microbubbles and nanobubbles, Australian scientists have developed a method of capturing microplastics from wastewater.
By optimising existing operating conditions, including air pressure, saturation time and bubble size, the approach — developed by RMIT University researchers — is, according to RMIT, able to be adopted by wastewater treatment plants without major infrastructure changes.
An enhanced version of dissolved air flotation — a widely used water treatment process that removes contaminants by attaching them to air bubbles and lifting them to the surface — was investigated by the researchers, who found that plastic removal rates increased when microbubbles and nanobubbles were used together, outperforming systems that relied on either bubble type alone.
The lifting force needed to carry particles to the surface is provided by microbubbles, while nanobubbles made the process more effective by improving particle attachment and aggregation — increasing interactions between particles. Further, the approach was found to remain highly effective in realistic wastewater conditions.
“Organic matter and fats, oils and grease, which are typically considered barriers to treatment, did not reduce performance,” said Dr Sirajum Monira, who completed the research during her RMIT PhD studies. “In some cases, they improved it by helping microplastics clump into larger, more easily removed particles when combined with standard coagulants.
“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 added.
“Wastewater treatment plants are a major pathway for microplastics as they slip through filtration processes, posing risks to ecosystems and human health,” said Associate Professor Biplob Pramanik, lead author and director of RMIT’s Water Effective Technology and Tools Research Centre.
“Our approach is simple to implement and significantly increases the removal of microplastics during the primary stage of treatment.”
The study was published in ACS ES&T Water (doi.org/10.1021/acsestwater.6c00127).
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