Carbon Block vs. Granular Activated Carbon – What’s the Difference?

Activated carbon (also charcoal) is one of the most widely used filtration methods. It’s so effective that it’s used with almost all types of filtration systems. For an in-depth look into activated carbon, check out this article.

Activated carbon comes in two forms – activated carbon block (ACB) and granular activated carbon (GAC). Both are made from ground up carbon but have different filtering capacities. Here’s a quick comparison of carbon block and granular activated carbon.

What is Carbon Block?

Carbon block is by first grinding carbon into a fine powder. This is then combined with a food-grade binder. The mixture is then heated up and compressed into a solid block. As such, this type of carbon filter has a larger surface area than GAC, because it contains more carbon particles. Because of this, it’s ability to adsorb particles is higher and the contaminant removal is more efficient. Because of these features, carbon block filters can last longer than a GAC filter. However, water takes time to flow through compressed carbon block filters which can reduce the flow rate.

What is Granular Activated Carbon?

GAC is made up of lots of loose pellets of carbon, held together in the filter housing. It has a lower surface area than ACB, which results in less contaminant removal. Another point to note is that because water flows swiftly through the granules, there isn’t enough contact time between the filter and the water. This reduces the absorbability of the filter but maintains water flow. This is why GAC is popular for shower water filters as have better flow rates. As such, GAC is less effective than ACB in contaminant removal, but may be more suitable depending on the purpose of the filter.  

What Do CB and GAC Remove?

Carbon block tends to remove a wider range of contaminants in water, including volatile organic compounds (VOCs), sediment, chlorine, rust, lead, mercury and sometimes even biological contaminants like bacteria, viruses, cysts and spores.

Granular Activated Carbon on the hand is good at reducing the taste and smell of chlorine, as well as a variety of other particles in the water. While they do target all the same contaminants as a carbon block filter, their efficiency is lower.

Differences Between Carbon Block and Granular Activated Carbon

So, while they’re made of the same stuff, these two configurations of carbon work in different ways. Here’s a quick rundown of their differences.

  • Physical – Carbon block is made up of compressed carbon while GAC is made up of loose carbon granules. Carbon block particles can be up to 20 times smaller than GAC granules.
  • Contaminant Removal – ACB removes a wider range of contaminants because of the longer contact time with water. GAC is less effective and has lower filtration capacity.
  • Water Flow – Carbon block can slow down the filtration as water needs to squeeze through the block. With GAC, water runs through much faster resulting in higher flow rates.
  • Versatility – Both configurations are commonly used in a variety of filtration types, but carbon block tends to suit smaller devices like faucet filters and filter pitchers, because they’re more efficient.
  • Replacements – Both ACB and GAC need to be replaced regularly, as per the manufacturer’s instructions, as an overused activated carbon filter can harbor bacteria. However, because GAC adsorbs at a lower rate than ACB, GAC filters tend to last longer.

Which to Choose?

If you have to choose between the two, the deciding factor will be whether you want enhanced purification or a faster flow rate. For shower water filters, choose GAC. For faucet, countertop and pitcher filters, ACB is more suitable.

More comprehensive water filtration solutions, like under-sink or whole house filters, typically have several stages in their filtration process. These tend to use both GAC and ACB in conjunction.

Carbon block gac filter

Express Water 3-stage Whole House Filter uses both ACB and GAC. Check Price Here.

Overall, while ACB is, without doubt, the more effective and efficient type of activated carbon filter, GAC has its benefits as well. When used together, they remove an impressive range of impurities.

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