Activated carbon is one of the most reliable ways to make drinking water taste, smell and test better. It comes in two main forms for water plants: granular activated carbon (GAC) and powdered activated carbon (PAC). Both are made from the same raw materials and work by adsorption. Organic molecules stick to the carbon’s internal surface. But they are used in very different ways, and choosing the wrong one costs money.

This guide explains the difference in plain terms and helps you decide which one fits your plant.

What is granular activated carbon (GAC)?

GAC is made of grains, typically 0.4 to 2.4 mm in size (sold as mesh sizes such as 8×30 or 12×40). It is packed into a fixed bed: a pressure vessel, a contactor, or a layer that replaces sand or anthracite in an existing filter. Water flows through the bed continuously.

Because the water stays in contact with the carbon for several minutes (called empty bed contact time), GAC can remove contaminants that are always present in the water, not just occasional ones.

GAC is commonly used to remove:

• Chlorine and chloramines (dechlorination before RO membranes or in point-of-use filters)
• Taste and odour compounds
• Natural organic matter that forms disinfection by-products such as trihalomethanes (THMs)
• Pesticides, solvents and other dissolved organic chemicals
• PFAS and other emerging contaminants (with suitable grades and contact time)

When the carbon is full, the bed is replaced or the carbon is reactivated and reused.

See our FM AQUA granular activated carbon for water treatment.

What is powdered activated carbon (PAC)?

PAC is a fine powder, with most particles smaller than 0.18 mm (it passes an 80 mesh sieve). Instead of sitting in a bed, it is mixed into the water as a slurry, usually at the start of treatment along with coagulants. It adsorbs contaminants for a short time, then settles out with the sludge or is caught by the filters.

PAC is used once and removed. It does not need any new equipment beyond a dosing system, so a plant can start, stop or change the dose whenever water quality changes.

PAC is commonly used for:

• Seasonal taste and odour problems, such as earthy or musty smells from algae blooms
• Short pollution events, such as a chemical spill upstream
• Pesticide peaks after heavy rain or farming seasons
• Plants that only need carbon a few weeks a year

See our powdered activated carbon (PAC).

GAC vs PAC at a glance

Which one should you choose?

Choose GAC if:

• The contaminant is present all year, such as chlorine, organic matter that forms THMs, or industrial chemicals
• You need a steady, predictable water quality
• You are protecting RO membranes or treating water at the point of use

Choose PAC if:

• The problem comes and goes, such as taste and odour during algae season
• You need a fast response without building new equipment
• You want to test whether carbon solves a problem before investing in GAC

Use both if:

Many larger plants keep PAC dosing for emergencies and seasonal peaks, and use GAC filters for the day-to-day job. The two work well together.

Does the raw material matter?

Yes. Both GAC and PAC can be made from coconut shell, coal or wood.

• Coconut shell carbon has many very small pores. It is hard, low in dust and very good at removing chlorine and small molecules. It is the usual choice for drinking water GAC.
• Coal-based carbon has a wider mix of pore sizes. It handles larger organic molecules and colour well.
• Wood-based carbon has larger pores and is often used as PAC for decolourisation.

Ask your supplier for the iodine number (a guide to small-pore capacity), particle size, hardness and ash content, and compare grades on those figures, not price alone.

How First Molecule can help

First Molecule supplies both forms for water treatment:

• FM AQUA granular activated carbon for chlorine, chloramines, THMs, taste and odour removal in drinking, municipal and industrial process water
• Powdered activated carbon (PAC) for dosing at water treatment plants
• Granular activated carbon (GAC) grades in different mesh sizes

Send us your water analysis, flow rate and the problem you want to solve, and our team will recommend the right grade. Contact us for a quote.

Frequently asked questions

Is GAC or PAC better for removing chlorine?

GAC. Chlorine is removed very quickly as water passes through a GAC bed, which is why GAC is used in front of RO membranes and in household filters.

Can PAC remove taste and odour from drinking water?

Yes. PAC is widely used for earthy and musty tastes caused by algae. The dose can be increased during the bloom season and stopped afterwards.

How long does GAC last?

It depends on the water quality, the flow and what you are removing. Chlorine removal can last a long time, while organics and THM precursors use up the carbon faster. Regular testing of the treated water shows when the bed needs replacing or reactivating.

Can I switch from PAC to GAC later?

Yes. Many plants start with PAC to deal with a problem quickly and move to GAC once they know the contaminant is a long-term issue.

Read more: activated carbon for water treatment.

Treating effluent instead of drinking water? Read our guide to activated carbon for industrial wastewater treatment.