How do Activated Carbon (Charcoal) Filters Work – A guide

Most water or air filtration systems use activated carbon or charcoal filters of some kind. As a result, most of us have heard this term but there’s still some confusion as to what it is. So, what exactly are activated carbon or charcoal filters and how do they work? Here’s our guide.

What is activated carbon or activated charcoal?

Activated carbon and activated charcoal are essentially the same thing so in his article we’ll use them interchangeably. What activated carbon is is any piece of carbon that’s been treated with oxygen, either chemically or physically.

What’s special about it is that these oxygen treatments open up millions of tiny pores in the carbon, significantly increasing its overall surface.

How drastic is the increase? A one pound (450g) piece of activated carbon has a total surface area of around 100-125 acres or 40 hectares! Just one gram of the stuff has a surface area of almost 5,400 square feet (500 square meters).

It’s this insane square footage that’s at the core of the working principle of activated carbon filters.

carbon charcoal in water

Activated carbon filter working principle

All carbon filters, both for water and air purification, work on the same principle – adsorption. That’s adsorption with a “d” and not absorption with a “b”.

The difference between adsorption and absorption is that in the latter process (with a “b”), the foreign particles are drawn into something while with adsorption (with a “d”) the foreign particles simply adhere or stick to the surface of the adsorption agent when they are forced to pass through it.

That’s why the high surface area of activated carbon makes it such a great adsorption agent – it gives it plenty of surface for the unwanted chemical impurities to stick onto.

In other words, activated carbon filters are simply filled with lots of tiny pellets of activated carbon that have an enormous surface area. And when the water or air passes through the filter, all the unwanted particles in it get trapped on the surface of the carbon/charcoal pieces – it’s as simple as that.

Of course, because activated charcoal works by trapping particles on its surface, it does eventually run out of space and stops filtering. At that point, you simply need to change your filter.

It is possible to “reactivate” a used-up active carbon filter by heating it up to 1652 degrees Fahrenheit (900 degrees) Celsius

DIY water filter explained

Activated carbon in a DIY filter

but that will increase all the stored-up toxic elements and it requires a lot of effort. And, with carbon literally being the most plentiful element on the planet, reactivating it is just unnecessary and you can simply get a new activated carbon filter at an affordable price.

What contaminants does activated carbon adsorb?

The standard size of particles that carbon filters are good against is 0.5 to 50 micrometers. For context, one micrometer is equal to one-millionth of a meter which is one-thousandth of a millimeter (i.e. 0.001 mm) or about 0.000039 inches. It’s also called a micron and the next smaller measuring unit is the nanometer which is one-thousandth of a micrometer.

The chemicals which have particles that fit in the 0.5 to 50 micron range include:

  • Sediment
  • Chlorine
  • Volatile organic compounds (commonly abbreviated as vocs in water filters)
  • Siloxanes
  • Hydrogen sulfides
  • Most taste and odor particles in water

What activated charcoal filters are NOT good against is:

  • Salts
  • Minerals like calcium and magnesium
  • Dissolved inorganic compounds like fluoride and nitrate
  • Microbial contaminants like bacteria, viruses, spores

While activated carbon filters can’t stop everything, they are an essential part of any good and comprehensive filtration system.

Plus, if you know what’s in your water and what isn’t, and you know that the only things you need filtered fall in activated carbon’s range, you can easily use just a simple activated charcoal filter to solve your problems.

This is why before you purchase a filtration system, it’s best to test the quality of your water. This will help you to pick the type of filter that suits your needs.

Activated carbon filter design

Highly popular activated charcoal filter. See it here.

As activated carbon filters can be used for many different purposes from water and air filtration to industrial gas and biogas processing, they can have lots of different designs.

Even just activated carbon water filters can come in different shapes and sizes, however. You can get a small activated carbon filter faucet attachment for just several dollars or giant activated carbon filters suitable for both residential and commercial use.

Additionally, activated carbon filters are often incorporated into larger and more comprehensive water filtration systems such as Reverse Osmosis filter systems. These use activated carbon filters in conjunction with reverse osmosis filters, sediment filters, semi-permeable membranes and more.

This 6-stage iSpring Filter uses activated carbon together with several other mediums
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Charcoal water filter benefits

Activated carbon water filters have a lot of benefits, both when they are used on their own and in combination with other filters. If we had to sum up most of their main positives, however, we’d list these four points:

  • Activated charcoal filters improve the taste of water. Even if you know your tap water is 100% healthy, a simple activated carbon filter can still improve its flavor. A lot of people don’t like the taste of tap water as they feel it has a certain metallic taste or an unpleasant aroma. Activated carbon takes care of both these problems and it also removes any and all odors from water as well.
  • These filters are also very affordable and easy to replace. Where other and more complex water filtration systems can cost 3- or even 4-digit sums of money, activated carbon is surprisingly affordable. This also makes the fact that they eventually expire almost inconsequential as replacing them won’t affect your overall budget at all.
  • Some activated charcoal filters are also designed to actively make your water healthier and not just remove stuff from it. These filters can add important minerals such as calcium and magnesium to your water and improve its quality that way as well.
  • Activated carbon filters don’t remove any of the beneficial components in drinking water. Many other water filtration systems will remove important minerals in tap water but activated carbon doesn’t do that.

Charcoal water filter price

We mentioned the affordability of charcoal water filters above but it’s worth pointing out just how budget-friendly they are. An activated carbon faucet water filter can literally cost less than a cup of coffee and yet it can last up to 6 months or more.

Pretty much the only time you’ll see an activated charcoal water filter with a price tag in the hundreds will be when the charcoal filter is a part of a bigger water filtration system with other types of filters in it.

Side effects of charcoal water filters

Do activated carbon water filters have any drawbacks and negative side effects? Are we just tooting their horn for no reason or are they really that awesome?

As activated carbon filters don’t actively add anything to the water, unless you’ve picked one that also adds minerals to it, there’s very little in terms of side effects that can be expected from them.

Charcoal filter

Even when a charcoal water filter gets depleted, i.e. its surface area can’t adsorb any more contaminants and they start just flowing through the filter, the filter still won’t “add” the previously collected contaminants back into the water stream.

One of the few possible side cons of a charcoal water filter is that there is a likelihood that it could start harboring bacteria. This can happen if the filter isn’t replaced in time and bacteria have been given the opportunity to develop throughout the contaminants the filter has gathered.

Another possible con also stems from not replacing your filter in time and it’s that it can simply get clogged from debris. In that case, the filter will simply slow down and will barely allow any water through. Both of these problems are easily avoidable by simply replacing your activated carbon filter in time.

When to replace your carbon filter

Every charcoal filter model will indicate it’s filtering capacity and when it needs to be replaced so just keep an eye on that. Some models even come with reminders which will notify you when the filter needs replacement. If you’re not sure if it’s time to change your filter, you’ll also usually notice a change in the water’s taste after a while as the filter will no longer be doing its job properly.

How to choose a quality carbon filter

One thing to note is that because activated carbon water filters are meant for personal use, they are not subjected to as much governmental oversight and regulation as municipal water filtration systems.

As a result of that, there are some sub-par charcoal water filters on the market that should be avoided, although that’s simply because they’re not efficient and effective enough, not because they have any dangerous side effects.

The NSF International (5) does provide standards and certification for filtration systems, so look for certification when choosing your filter. This will help you to find one that’s been subject to testing and meets quality standards.

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