A group of China and US-based researchers have developed 3D printed ‘hydrocyclones’ with the potential to remove the vast majority of the harmful microplastics finding their way into drinking water reservoirs.
Using metal 3D printing, the engineers have been able to customize their cyclonic separator so that it can pick up the particles of polymers of all shapes and sizes. Given that the device has already shown an efficacy of more than 80% in filtering out microplastics sized 20µm or larger, the team says it could soon be used to do so at scale, and address what is now a “major challenge” in water treatment.
A ‘contaminant of emerging concern’
According to the researchers, microplastics, or polymer fragments sized between one and five micrometers, are fast becoming a “contaminant of emerging concern” among water management agencies. Whether they be ‘primary’ microplastics originating from things like skin care products, or those considered ‘secondary’ as they come from larger objects, both have the properties to last in the environment.
As a result, these tiny plastic particles are increasingly being consumed by wildlife, leading to fears that humans are therefore beginning to consume them as well. Although there’s currently no definitive research to prove how microplastics affect human health, some studies have warned of their potential to cause cellular death and allergic reactions, hence calls to filter them out are now growing louder.
Doing so, however, is another question, as water reclamation technologies tend to be built for removing other, better-understood contaminants. While prior approaches to tackling microplastics, involving induced agglomeration and gravitational filtration, have been trialed, the researchers point out that these aren’t being used, due to their “low removal efficiencies and high energy costs.”
Filtering out microplastics en masse
To develop an alternative water treatment process, the team has taken inspiration from the hydrocyclones used within food, chemical and plastic waste separation procedures. Given their speed, cost efficacy and load capacity, such devices represent a promising candidate for microplastic removal, thus the team sought to build on their design by making them smaller and 3D printing them.
By additive manufacturing a ‘mini-hydrocyclone,’ the engineers theorized that they could produce a device with stronger micro-scale capabilities, and through using stainless steel to do so, lend it the ability to separate polymers of varying densities.
Putting this concept into practice, the team 3D printed two different designs: one for filtering out large microplastics, and one for those broken into smaller particles. These devices were then deployed to remove nylon and low-density polyethylene (those commonly found in untreated water) from samples, with the concentration of each measured before and after mini-hydrocyclone processing.
Interestingly, by feeding microplastics through their prototypes in series, the researchers found they were able to improve their chances of removing multiple polymers, without raising feed pressure. In doing so, the team therefore developed a means of driving efficiency that doesn’t require more energy to achieve, although they admit their devices still work best when filtering out single contaminants.
Given that by their nature, treatment plants process water with varying impurities, the engineers say that moving forwards, further study is needed into the impact these could have on their device’s efficacy. That being said, the team maintain that their mini-hydrocyclones, with a 92% nylon and 70% polyethylene removal rate, could still be used at scale in future, at industrial and local wastewater facilities.
“3D printing allows a mini-hydrocyclone (MHC’s) design to be highly-customized to meet the user’s needs,” add the team in their paper. “Both single and two-stage MHC experiments proved to be effective. MHCs have the potential to effectively remove microplastic contamination from water sources while reducing energy cost, decreasing carbon footprint and lowering maintenance needs.”
3D printing in water filtration
This is far from the first time that additive manufacturing has been deployed within water filtration applications. Late last year, researchers at FabRx, University College London and Universidade de Santiago de Compostela developed a 3D printed drug removal device, designed to separate pharma agents found in water supplies.
Elsewhere, in a similar project, a University at Buffalo team have used 3D printing to create a water-purifying graphene aerogel that’s capable of removing dyes, metals and organic solvents from drinking water. With further development, these researchers say that it could be possible to scale their styrofoam-like material for industrial-scale deployment at large wastewater treatment facilities.
GE Research, meanwhile, has been awarded $14 million by DARPA to 3D print a portable device that ‘produces water out of thin air.’ While the compact system is being designed to produce enough daily water for sustaining up to 150 troops in the field, it’s thought that it could also prove vital in addressing global water scarcity.
The researchers’ findings are detailed in their paper titled “Microplastics Separation Using Stainless Steel Mini-Hydrocyclones Fabricated with Additive Manufacturing.”
The study was co-authored by Yian Sun, Lin Liu, Zeth Kleinmeyer, Gina Habil, Qinghai Yang, Lixin Zhao and Diego Rosso, who hail from the Northeast Petroleum University, University of California Irvine and the PetroChina Research Institute of Petroleum Exploration & Development.
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Featured image shows a pile of discarded plastics washed up on a beach. Image via Sören Funk, Unsplash.
