Activated carbon is the polishing step in many water systems. Its huge internal surface area adsorbs dissolved organics, colour, odour and chlorine that coagulation and filtration leave behind. It is used in drinking-water plants, RO pre-treatment, STP reuse systems and ETP polishing.
Granular or powdered?
- Granular activated carbon (GAC) is packed into a filter vessel that water flows through. It suits continuous treatment, such as removing chlorine before an RO or polishing reuse water. The bed is replaced or regenerated when it is exhausted.
- Powdered activated carbon is dosed into the water as a slurry and removed with the sludge in the clarifier. It suits seasonal or occasional problems, such as taste and odour episodes, or colour spikes in effluent.
What it removes well, and what it doesn't
Activated carbon is good at adsorbing organic compounds, colour, odour-causing compounds and free chlorine. It does little for dissolved salts, hardness or most metals, which need ion exchange, RO or precipitation instead.
How to compare carbons
- Iodine number: a common indicator of adsorption capacity for small molecules. Higher is generally more capacity.
- Particle size (mesh): affects pressure drop in a filter and how fast adsorption happens.
- Raw material: coconut-shell carbons are widely used for water treatment in South India.
- Moisture and ash content: listed on the specification sheet.
The best test is a trial on your own water, because performance depends on what you are trying to remove.
Protecting RO membranes
Many RO systems use a carbon filter to remove chlorine, which damages most polyamide membranes. Check chlorine after the carbon filter regularly: once the carbon is exhausted, chlorine breaks through. Some plants use sodium metabisulphite instead of, or as a backup to, carbon. See RO Antiscalants for other RO protection.
Buying activated carbon
We supply granular and powdered activated carbon for water and effluent treatment, with specification sheets and safety data sheets.