2.2. Significance of Filter Sizes

So, if you go and open a catalog for filter papers, you will find a lot of papers, you have used filter papers from high school for various things. What is the definition of the filter paper that we use here? What kind of filter paper do we use? What is the characteristic of filter papers typically when you say filter paper? Predominantly you’ll say pore size. So the pore size say is in some microns. So, it will say 10 microns or it will say 1 micron you can go up 0.4 microns, 0.2 microns, 0.1 microns all of them are there. Up to about 0.7 microns you have glass fiber filters from somewhere around 0.4 or 0.1 microns and you have membrane filters and you have more specialized filters.

Filter papers are designed to trap solids while allowing liquids to pass through. The 'pore size' indicates the size of openings in the filter paper, expressed in microns (one millionth of a meter). Common pore sizes range from 10 microns to 0.1 microns. The smaller the pore size, the more particles it will trap, but it may also slow down the flow of liquid through the filter. Choosing the right pore size is crucial depending on what solids you want to retain in the filter. If you are analyzing total suspended solids, for example, a filtering paper with an appropriate pore size must be chosen to effectively separate the solids from the liquid without clogging.

Imagine using a sieve in your kitchen. A sieve with larger holes allows bigger food particles to pass through while retaining smaller pieces, similar to what filter papers do in the lab. Next time you strain pasta, think about how the holes of the strainer act like filter pores, determining which particles (food) are retained and which are allowed to pass.

So, ideally what would I want to use if I have filter papers available for 0.1 pore size. Can I use 0.1 pore size? It will stop everything bigger than 0.1 because colloids organic carbon is in the size range of 0.4, 0.2. I will definitely remove all of them. Then why do you have filter papers have 1 micron and 4 microns and 10 microns? For one is easier to make, that is one reason but they are still there in the market and people sell it for one reason. As the pore size goes down, what is the other consequence in filtration? It takes longer, it takes an enormous amount of pressure drop to push liquid through that filter.

While a filter with a pore size of 0.1 microns can trap a lot of particles, it also requires more time and effort to push liquid through due to the finer holes. Larger pore-sized filters are often easier to manufacture and faster to use, making them more practical. Therefore, when choosing a filter size, one must balance the need for particle removal with the practicality of the filtering process. This is why 1 micron filters are commonly used despite smaller options being available.

Consider trying to push water through a very fine mesh fabric. If the mesh is too fine, you may find that water barely seeps through at all. However, using a coarser mesh lets the water pass quickly, albeit with a risk of letting smaller particles through. In laboratory settings, optimizing this balance is crucial, just as it is in your kitchen when straining liquids!

So, what is the difference between 1 and 0.7 micron in terms of information lost? What is TSS? How is analysis done? How do you get m By weighing it’s a gravimetry measurement. So, if I take particles that are 1 micron versus particles that are 2 microns versus particles that are 0.7 microns or 0.5 microns. And let us say there are 10 raise to 6 particles. You calculate what is the mass contribution of all these.

The choice of filter size directly impacts the analysis of total suspended solids (TSS). Using a 1 micron filter means that some smaller particles may not be retained, potentially leading to underestimating the mass of solids in the water sample. However, calculating the contribution of these smaller particles often shows that their mass is negligible compared to larger particles. Hence, while it is useful to consider finer filters, the added complexity usually does not yield significant benefits for TSS analysis.

Think of counting grains of sand on a beach. If you only count the larger pebbles (like using a 1-micron filter), you might miss the much smaller grains (like those below 1 micron), but since there are many more larger pebbles, they contribute most of the weight you measure. Unless your study requires utmost precision in tiny grains, focusing on just the larger ones is often enough.

So, since the total suspended solids methodology is based on gravimetry. It does not really matter, below 1 micron, you are not going to get any additional information and you are also going to get you are going to waste your time by trying to push it through this thing and you are not getting any additional information. So, 1 micron is set as standard filter size for TSS because it is TSS standard filter size.

A 1 micron filter has been established as the standard for TSS measurement because it effectively balances the need to filter out sufficient particles while allowing for faster filtration. Using finer filters below this size generally does not yield significant additional data and can waste time and resources. As a result, regulations and methodologies often dictate the use of 1 micron as the standard filter size.

Just like in cooking recipes where certain measurements are standardized for ease, such as using teaspoons for dry and liquid ingredients, the 1 micron standard in water analysis helps ensure consistency and efficiency in results across various labs, preventing unnecessary complexities.

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