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What Is the Difference Between GAC Carbon And Carbon Block Filter?

GAC vs Carbon Block Drinking Water Filters

There are 2 main type of carbon filters on the market, GAC and Carbon Block. Let's compare them.

Both GAC-Granular Activated Carbon and Carbon Block filters (which are sometimes also activated) are carbon type filters that remove particles from water. In this post we will focus on drinking water. 

What are the carbon filters?

As with all water filters, carbon filters are designed to filter out or change a chemistry of specific contaminants from drinking water based on particle size or its ion charge. 

Ancient Egyptians discovered the detoxifying effects of carbon thousands of years ago. The removal of contaminants from water using carbon is still practised today and of course improved, , creating a better tasting and smelling food and beverage. 

How do activated carbon blocks and GAC filters work?

One way a carbon filter removes contaminants by adsorption. As a sponge absorbs water, carbon filters absorb pollutants. Particles adhere to a surface through adsorption, just like Velcro. As a carbon with a clean surface, it is oleophilic, which means "oil-loving" it has a strong attraction with organic compounds and other non-polar contaminants. Organic chemicals link or attach to the surface of the carbon filter by van der Waals forces allowing clean water to pass through a carbon filter.

Another way a carbon filter works, especially on liquid gases such as Chlorine, is through a chemical reaction rather than adhesion of particles to carbon particles. If the carbon is activated, a
ctivated catalytic (more reactive) carbon chemically alters the chlorine molecules, converting them into chloride (negatively charged ionic form of chlorine). Chlorine, chloride, chloramine all get removed from activated carbons, whether granulated or block. 

Furthermore, activate carbon reduces bad tastes, odours, and other particles in drinking water because they are highly porous and have a large surface area. As drinking water moves through a carbon filter, contaminants adhere to carbon. This is called adsorption and it has a finite amount of space. You can tell when carbon filter is ready to be replaced because water volume will drop.

What's the difference between microns on carbon filters?

The diameter of the pores are measured in microns which then are labeled on individual filters. The smaller the micron size, the finer the filtration. Typical residential carbon filters for drinking water come in 1, 5, 10 microns. The use of different microns depends on what it is you'd like to remove and what other filters or membranes your system has. Typically there will be a sediment filter that is 1 or 5 microns, 1-2 carbon blocks and GAC that will be 1-10 micron, possibly a UV light (best for well water) and a RO membrane that removes .0001 micron particles.

A carbon block filter having a 1 µ diameter and 1 gpm flow rate can filter Lead, cyst, chlorine, taste, colour, odour, and VOC reduction. It has a chlorine reduction capacity above 2,500 gals. While GAC, having a larger diameter, can de-chlorination ability below 2500 gallons.

Do Carbon filters require high or low water pressure to work best?

Carbon filters do not require high pressure to remove contaminants.  If effectiveness, longevity and costs are of concern, choose to filter your residential water with a reverse osmosis water purifier that has at least 2 activated carbons with different micron sizes. 

Is a charcoal filter and carbon filter the same?

A carbon filter is also called a charcoal filter. All modern carbon filters such as KX Matrikx Pb1 Carbon Block, KX Matrikx CTO Plus or KX Marikx CTO, are made of coconut based activated carbon. Coconut shells are a renewable resource made of high-grade carbon and are ideal for filtration due to their high percentage of micro-pores on their surface, nearly 50% more than coal, making them the most promising option for removing a wide variety of contaminations. 

What exactly is activated carbon, and how does it filter water?

Activated charcoal is created when coconut charcoal is heated to a very high temperatures. The elements and compounds then bound with the carbon atoms are removed and all the binding sites for carbon are “free” for binding with incoming molecules and atoms. This makes activated charcoal much more porous than ordinary charcoal, vastly increasing its surface area. In fact, a teaspoon of activated charcoal contains about the surface area of a football field because of its porosity. Activated carbon filters are sold as granular activated carbon (GAC), carbon blocks, and radial carbon filters. 

Chlorine and ammonia are used to disinfect water at treatment plants in US and the byproduct of that process is chloramine. In order to remove any traces of these chemicals and restore drinking water to a safe and healthy state, carbon filters are used which then improve taste and smell of water.

What is the difference between the GAC carbon filter and Carbon Block?

Granular activated carbon filters

Granular activated carbon filters are made using carbon that has been ground up and is held together loosely inside a cartridge or other container. GAC filters are composed of loose granules of activated carbon. Because they have loose granules, more water passes through. GAC filters are great for low pressure applications, 40 psi and less and when you require higher flow rate.

 

Carbon block filters

A carbon block filters are made by grinding activated carbon into a fine powder. This powder is then mixed with a food-grade binder, and the mixture is then heated up to "activate" and compressed into a solid block. Finer particles mean more surface area for contaminants to adhere to. Carbon block filters are great for high pressure 60 psi and above where lower flow rate is acceptable. Flow restrictor, wider diameter water lines or pump may be used to control flow rate.  

What type of contaminants do carbons remove?

Generally, organic compounds and volatile organic compounds, THMs, pesticides, herbicides, and chlorine can be removed using both forms of activated carbon filter types. These activated carbon filters can also help to improve taste and odour. Although carbon filters effectively reduce dissolved solids, heavy metals, and fluoride, they cannot remove mineral salts (calcium, potassium etc), only reverse osmosis membrane or distillation of water can. 

You can find NSF certification on carbon filters to know precisely what it can remove. Carbon filters effectively remove chlorine and unpleasant tastes and odours, although some are also certified to remove other contaminants:

Atrazine, Benzene, Herbicides, Carbon Tetrachloride, Chlorine, Pesticides, Radon, VOCs, THMs: Trichloroethylene, Trichlorobenzene, Trihalomethane, Toluene, 2,4-D, Unnatural Taste and Odors, Chlorine, Organic Chemicals, Chloramines, Bad Taste, Odors. 

How are carbons used?

Carbon filters can be used individually or as part of a filtration system and at a point-of-entry (POE) to supply filtered water to the entire property or as a point-of-use (POU) to purify water at a specific location such as a sink.

A carbon filter should be installed before a water softener if you use it to soften municipal water. 

Have questions or aren't sure what carbons you should buy for your system or application? Send us an email and we can recommend the best solution for your needs.


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