Inside
the mouth of this anchovy, plankton particles are captured by the gill arch
system. Credit: Jens Hamann
Wastewater from
washing machines is considered a major source of microplastics—tiny plastic
particles that are suspected of harming human and animal health. Researchers at
the University of Bonn have now developed a filter to curb this problem. Their
invention was inspired by the gill arch system in fish.
In
initial tests, the now patent-pending filter was able to remove more than 99%
of plastic fibers from washing machine wastewater. The results have now been published in the journal npj
Emerging Contaminants.
Wastewater from a washing machine in
a four-person household produces up to 500 grams of microplastics each year,
mainly caused by textile abrasion. The household appliances are thus one of the
most important sources of the tiny particles. Microplastics currently make
their way directly into the sewage sludge of wastewater treatment plants. As
this sludge is often used as fertilizer, the fibers ultimately end up on the
fields.
Many manufacturers have thus been
searching for ways to remove microplastics from washing water to prevent them
from entering the environment. "The filter systems available
so far, however, have various disadvantages," explains Dr. Leandra Hamann
from the Institute for Organismic Biology at the University of Bonn. "Some
of them quickly become clogged, others do not offer adequate filtration."
Looking inside the mouths of fish
The scientist, alongside her
doctoral supervisor Dr. Alexander Blanke and colleagues, has thus turned to the
animal kingdom in her search for possible solutions. The team focused on fish
that can be considered true masters of filter technology—and have evolved this
filtration over hundreds of millions of years.
Some fish feed by means of
filtration; these include, for example, mackerel, sardines, and anchovies. They
swim through the water with their mouths open and sift out the plankton with
their gill arch system. "We took a closer look at the construction of this
system and used it as the model for developing a filter that can be used in
washing machines," says Blanke, who is a member of the transdisciplinary
research areas Life & Health and Sustainable Futures at the University of
Bonn.
During their evolution, these fish have developed a technique similar to cross-flow filtration. Their gill arch system is shaped like a funnel that is widest at the fish's mouth and tapers towards their gullet. The walls of the funnel are shaped by the branchial arches. These feature comb-like structures, the arches, which are themselves covered in small teeth. This creates a kind of mesh that is stretched by the branchial arches.
The
filter element in the center imitates the gill arch system of the fish. The
filter housing enables periodic cleaning and installation in washing machines.
Credit: Christian Reuß/Leandra Hamann
Self-cleaning: Plankton rolls toward the gullet
"During food intake, the water
flows through the permeable funnel wall, is filtered, and the particle-free
water is then released back into the environment via the gills," explains
Blanke. "However, the plankton is too big for this; it is held back by the
natural sieve structure. Thanks to the funnel shape, it then rolls toward the
gullet, where it is collected until the fish swallows, which empties and cleans
the system."
This principle prevents the filter
from being blocked—instead of hitting the filter head-on, the fibers roll along
it toward the gullet. The process is also highly effective, as it removes
almost all of the plankton from the water. Both are aspects that a microplastic
filter must also be able to deliver. The researchers thus replicated the gill
arch system. In doing so, they varied both the mesh size of the sieve structure
and the opening angle of the funnel.
Filter achieves high efficiency
"We have thus found a
combination of parameters that enable our filter to separate more than 99% of
the microplastics out of the water but not become blocked," says Hamann.
To achieve this, the team used not only experiments but also computer simulations.
The filter modeled on nature does not contain any elaborate mechanics and
should thus be very inexpensive to manufacture.
The microplastics that it filters
out of the washing water collect in the filter outlet and are then suctioned
away several times a minute. According to the researcher, who has now moved to
the University of Alberta in Edmonton, Canada, they could then, for example, be
pressed in the machine to remove the remaining water. The plastic pellet
created in this manner could then be removed every few dozen washes and
disposed of with general waste.
The team from the University of
Bonn and the Fraunhofer Institute for Environmental, Safety, and Energy
Technology UMSICHT has already applied for a patent for its development in
Germany; EU-wide patenting is currently underway.
The researchers now hope that manufacturers will further develop the filter and integrate it into future generations of washing machines. This would stem the spread of microplastics from textiles, at least to some extent. And that is also necessary: Analyses indicate that the particles may cause serious damage to health. They have already been found in breast milk and in the placenta—and even in the brain.
Source: Fish-inspired filter removes 99% of microplastics from washing machine wastewater
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