Environment

Slow sand filter cleans 99.9 percent of nanoplastics from drinking water

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Researchers have found a biologically active slow sand filter as the most effective way to remove nanoplastics from drinking water
Researchers have found a biologically active slow sand filter as the most effective way to remove nanoplastics from drinking water
Researchers at the Swiss Federal Institute of Aquatic Science and Technology carry out water filtration testing
Eawag
A filtration column at the Swiss Federal Institute of Aquatic Science and Technology
Eawag
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Today's filtration technologies do a wonderful job of producing potable water, but the spread of plastic waste throughout the environment means there are new threats to contend with. A new study has investigated the performance of different techniques when it comes to removing nanoplastics from water, and shown that biologically active systems known as slow sand filters can remove the tiny particles with 99.9 percent efficacy.

As the even smaller sibling of already troubling microplastics, nanoparticles have come into focus as a big problem as scientists deepen our understanding of plastic pollution. Where microplastics that measure less than 5 mm (0.2 in) are notoriously difficult to track and threaten the livelihood of organisms such as marine life, it is becoming clear that nanoplastics might pose their own unique set of problems.

Measured in mere nanometers, studies have shown these tiny traces of plastic have the capacity to stunt plant growth and trigger death and swimming abnormalities in shrimp and fish. Scientists consider plastic particles measuring between 1 nanometer and 20 micrometers to be respirable, while fruit fly experiments suggest they may alter gene expression associated with stress response and oxidative damage.

While many questions remain over the effects of nanoplastics on the human body, there is no doubt that preventing them from entering at all would be the best-case scenario. To explore the possibilities in this area, scientists at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) set out to study how effectively different treatment processes can eliminate nanoplastics from drinking water.

A filtration column at the Swiss Federal Institute of Aquatic Science and Technology
Eawag

The team's experiments involved testing of three techniques; activated carbon filtration; ozonation, where ozone is chemically infused into water to treat and disinfect it; and slow sand filtration. This last technique involves an ecosystem that includes a gravel layer, sand, and a biologically active layer on the surface that includes worms and bacteria. These form a biofilm that carries out most of the decontamination.

Nanoplastic particles were tagged with the chemical element palladium and added to untreated water in considerable quantities, enabling their journey through water treatment process to be tracked with a mass spectrometer. Of the techniques studied, the team found slow sand filtration "dominated" removal of the nanoplastic particles, successfully eliminating them with an efficacy of 99.9 percent.

Based on their results, the team says that this filtration method would be effective at removing high levels of nanoplastics for extended periods of time, though the top few centimeters of sand would need to be removed to prevent clogging of the biofilm.

The research was published in the Journal of Hazardous Materials.

Source: Eawag

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6 comments
Capt_Ahab84
I believe if you have a reverse osmosis filter at home, it would essentially achieve the same result.
CarolynFarstrider
Ok, fair start. But now we have a sand column contaminated with microplastics. What do we do with that?
Karmudjun
Nice article Nick. Thanks
@Capt_Ahab84, If you have a reverse osmosis filter at home, and depending upon the quality or the system (not all RO are the same) the microparticulates can make it through. The nanoparticulates are the question and those actually rain down on rooftops with evaporated water called 'rain'. And heating microparticulates leads to the production of many nanoparticulates, so it is a rather ubiquitous contaminant. When I post against an opinion, I try to cite resources and while this one reference doesn't cover the difference in RO membranes to a nanoparticulate level, it should give you a heads up: https://www.dw.com/en/plastic-fibers-pervasive-in-tap-water-worldwide-new-study-shows/a-40370206
This is an old article - 5 years old - but it discusses how prevelant the microparticulates are and nanoparticulates are several orders of magnitude greater in number. So no, not all - and maybe not even the best RO - may not filter as well as the sand column.
Jinpa
In which pocket will Swiss hikers put their heavy sand filter water bottles as they traipse the mountain trails? Will Brita or Pur come out with heavier sand filter cartridges?
Wombat56
Something described as a SLOW sand filter is unlikely to make much bulk water purification, such as for a city.
Anechidna
@Wombat56, it's termed a slow sand filter as it doesn't operate under pressure via a pump. Generally, they run at 400ltr/hr/m2. It is the preferred means of water filtration in Europe and London UK has some 31 hectares of slow sand filter providing about a third of London's water needs. No chemicals are a big plus, chlorine comes with significant OH&S risks at treatment plants. I know people who've built their own and it beats the technologically advanced system they had installed in a new build. The cost to build was under $1k, their other system cost approximately $140/6mnths as their rainwater contains huge quantities of dust and clogs up 5 & 10-micron filters. The slow system costs zero to service, simply clean off 2mmof biofilm every six months.