Microfilters have been around for nearly 100 years and in that time they’ve made fantastic advancements in the way we process water, air and medicine.
However, nature has a headstart on us. Roughly, a 600 million years one. What we think of as miraculous processes, such as making saltwater drinkable, has been commonplace in the animal kingdom for millennia – with thousands of species able to do it from birth.
Many creatures, from fish to mammals, are able to safely filter out tiny particles and bacteria with their bodies. They are, in effect, some of the best-engineered microfilters in existence.
So what can they tell us about designing and improving the microfilters we rely on every day?
The way fish filter saltwater is a masterclass on desalination
All living things need water to carry out their basic biological functions. For creatures that live in the ocean, however, this creates a problem. Too much salt in the body would be lethal and fresh water is in short supply.
For most fish, the solution is based around osmosis in a process known as osmoregulation.
Freshwater fish have relatively salty bodies and the water around them is less salty. Because water will always move to keep salt-levels balanced, it passes through the fish’s skin (its membrane) to naturally keep that balance. To avoid losing too much salt, freshwater fish have kidneys that excrete water quickly and have chloride cells in their gills that pump salt into the fish.
Saltwater fish have the opposite problem. Their bodies are always losing water and taking on salt. To resolve this, saltwater fish are constantly drinking water and the chloride cells in their gills help to pump out the salt.
The way fish regulate salt has been the bio-inspiration for much research in membrane technology and desalination.
Perhaps the most well-known is electrodialysis: a method of desalination that pulls salt out of the water through a membrane using an electrical charge. This method uses much less energy than traditional water distillation and is a clear example of why it’s so important to research how nature uses filtration.
How sharks use water tornados to filter water
A fish’s gills are a marvel of biological engineering. Not only do they help regulate salt levels in fish, but they can also work as microfilters of parasites and algal cells.
Of particular interest to researchers are filter-feeding animals, such as basking sharks. They feed by passing water over their gills while keeping out harmful parasites, all without causing any clogging.
For many years, how this worked was something of a mystery. After all, a traditional dead-end filter would create clogs that couldn’t be cleared by a fish.
In 2001, it was discovered that filter-feeding fish use a version of crossflow filtration with their gills. This is where the fluid is passed across a membrane rather than directly through. A process we often use in the treatment of sewage water to avoid blockages.
Yet, as one of the researchers Lauria Sanderson pointed out, this doesn’t entirely solve the mystery. Crossflow filters do eventually clog. A fish’s gills don’t.
With further research, the answer appears to be the ribbed structure inside the mouths of these fishes. When swimming along, these ribs help to create a water vortex that prevents particles from building up.
The success of this method is the perfect inspiration for improving the ways we maintain membrane filters, and researchers are already working on methods to make filtration more efficient by replicating these structures.
Introducing the Human Microfilter
It’s not just fish that come installed with inspiring microfilters. One of the most fascinating natural filters exist inside our own bones, where our blood is produced: the bone marrow.
The human body makes 200 billion red blood cells each day. These are created in the red marrow of our bones and they are vital for transporting oxygen to the tissue in our body and then taking away carbon dioxide – to replace the 200 billion red blood cells that day every day.
But how do the red blood cells go from our bones into our bloodstream? And you already know the answer: through microfiltration.
Blood vessels need to be able to constantly take in new red blood cells while still being able to efficiently carry cells around the body. To do this, the walls of the vascular cells inside the bone marrow need to be able to rearrange in order to allow in red blood cells but nothing else. A feature that would be highly prized in filtration.
Smart Separations’s own Hugo Macedo has outlined a theory during his PhD on how this mechanic in our blood could be replicated in artificial membranes to harvest red blood cells at scale to help reduce blood shortages in healthcare.
The future of microfiltration
The future of microfiltration is sustainability. Ensuring that we process liquids and gases with minimal waste and minimal energy usage.
Filtration is an integral part of many of the natural processes all around us, not just in animals but plants, trees and even some inorganic processes. These all happen without relying on fossil fuels or dedicated maintenance teams.
If we want to begin removing pollutants from the air and sea, we will need to replicate these natural filters in the technology we use.
At Smart Separations, we want to build a platform that is at the foundation of this. A ceramic microfiltration membrane that can be customised to be used with a variety of systems. To find out more, get in touch today.
