How it Works
SuperSorb® CarbonPads utilize Depth Filtration to trap frying oil contaminants down to .5 micron – that’s a fraction of the size of a human hair!
Beginners Guide to Depth Filtration
All our filtration and treatment media are based on “depth filtration”, but what really is depth filtration and how does it differ from other filtration?
When referring to depth filtration we are normally comparing it to a surface filtration. The easiest way to describe a surface filter is the holes in the filter material pass from the inlet side to the outlet side. The filter will stop all particles that are bigger than the smallest hole. So, if you know the size of the smallest hole in the filter you have the filter’s rating or pore size, for example 10um, 5um or 0.5um.
When looking at what seems to be a relatively thin piece of filter media, how can we call this a depth filter? You must keep in mind that we are normally talking about particle removal with sizes much smaller than can be seen by the human eye. We can distinguish particles as small as 50um, but we are normally talking about depth filtration between 0.5 to 10um. Consider a normal piece of note pad paper (80 grams per square meter in weight) this is typically 0.1mm thick or 100 microns, so 10 times thicker than our larger, 10um particle size. Now consider typical depth filter media at 4mm thick or 4000um thick, 400 times thicker than our larger, 10um particle size.
So how does depth filtration work?
Basically, as well as stopping the very large particles on the surface we trap smaller particles within the depth. A good example is to envisage is a single row of trees planted in front of you with a 1 meter gap between them. If you kicked a football at this row of trees there is a very high probability that the ball would find a gap in the trees and pass through. Now if we added row after row of trees, still at 1-meter gaps, but staggered, to fill the gap in front, we will have added depth as well. Now take hundreds of footballs and let a strong wind blow them towards the row of trees nearly all the footballs would get stuck in the wooded area, with the wind passing through, with a reduced strength. With footballs hitting off each other there is a possibility that 1 or 2 may get through in the right conditions.
Let’s say our football has a diameter of 22cm if we scale this to 10um and our 4mm thick depth filter this means the football would need to travel 88 meters through the staggered rows of trees to escape the other side. The probability of this is very low even though the gaps set at 1m are 4.5 times larger than the ball (our particle).
Of course, we can design a range depth filter media to best retain a specific range of particle sizes and with set flow and pressure parameters can pretty much guarantee the performance we are targeting, but unlike a surface there is no measured largest hole size so no set smallest particle retention rating.
So, what are the advantages of depth filtration?
One of the main advantages is the high holding capacity of the media as we are trapping the solids within the structure rather than just on the surface. Due to the high porosity within the structure you can also maintain flowrates for longer operational life. The depth media structure can also be designed to allow larger molecular structure through, which is important when color or flavors do not want to be removed but can also hold active ingredients within its structure like activated carbon, for the specific removal of color, flavors and aromas. One of the other main advantages is the particles you want to retain are not always perfect spheres. Typical solids may be 1um in diameter, but 5um long, these could pass through a 1um rated surface filter, but would not get through a 1um depth filter, adding extra security to the process. Footballs pass through the gaps in a single row of trees The above is only scaled to 14 meters deep of what should be an equivalent of 88 meters deep of trees, but you get the idea. No footballs are getting through.
Can depth filter media be cleaned or washed? In general no. Due to the nature of the structure that traps the particles, these particles are difficult to get released or removed.
Can the depth filter media be classified to remove a given particle size like 1um or 0.5um? For a given application and specifically targeted particle size a chosen depth filter media can be used to remove this range. But the process conditions must be set-up to match that application. For example, if you double the design flow rate for that application, the depth filter media will allow this, but there is a high risk of the particle size you want to retain being pushed through. There is far more to depth filtration, but we hope this answers some of the questions that arise.
Give depth filtration a try in your kitchen! Request a free sample of our SuperSorb® CarbonPad today.