What is a microplastic?
Ayus installs and maintains 4-stage water filters at home, hidden under the kitchen sink. One of the stages is an ultrafiltration membrane, and many people ask us what it does to microplastics. To answer, let us start with the definition.
A microplastic is a plastic particle smaller than 5 millimetres. It can come from larger objects that break down over time, from clothing fibres or from packaging. Microplastics are in the environment and can also turn up in water.
How big is a microplastic?
To talk about things this small we use the micrometre (µm), a thousandth of a millimetre. The 5 mm upper limit is 5000 µm. A microplastic is at least 1 µm. To give you an idea:
- 5 mm, or 5000 µm: the maximum size of a microplastic, roughly a broken grain of rice.
- 1 mm, or 1000 µm: a grain of coarse sand.
- About 70 µm: the thickness of a human hair.
- About 1 to 2 µm: the size of a bacterium.
- 1 µm: the minimum size of a microplastic.
How does a filter hold back microplastics?
A membrane filter works like a very fine sieve. Water passes through the pores; anything larger than the pores stays on the outside. There is no chemistry involved: it is a question of size.
In the Ayus filter, the third stage is an ultrafiltration membrane made of hollow fibres. The pores measure [X] µm. As a microplastic is at least 1 µm, it is held back. The same goes for bacteria and other fine particles. See the 4 stages in how it works.
What should you look for in a filter for microplastics?
As everything comes down to size, the most useful question is what pore size the filter has. A membrane filter usually states this value; a filter made only of activated carbon is designed for taste and smell, and often does not state it.
Then there is maintenance. A membrane only does its job well while it is in good condition, so the cartridges have to be changed on time. And a sediment filter before the membrane helps stop it clogging with larger particles.
Are minerals held back too?
No. The minerals in water, such as calcium and magnesium, are dissolved. They are not particles: they are ions, much smaller than the membrane’s pores. So they pass through and stay in the water you drink.
This is the main difference from reverse osmosis, which removes almost all the minerals. We compare the two in the guide reverse osmosis or ultrafiltration.
What do the other stages of the filter do?
Before the membrane, a sediment filter holds back sand, rust and dirt, and an activated carbon cartridge removes the chlorine taste and smell. That way the membrane receives water already free of large particles and lasts longer.
After the membrane, the water flows through a magnesium cartridge and on to the 3-way tap. To keep the membrane doing its job, we change the filters every [INTERVALO A CONFIRMAR]. Find out more in maintenance.
