Granular Activated Carbon (GAC) filters are an excellent choice for removal of chlorine, taste and odour, or organics in water. Some types will even reduce metals. There are many different variations but most are either coconut coal, wood based or bone.
What is granular activated carbon?
Coconut husks or coal is heat treated in the absence of oxygen to produce activated carbon. Granular just means the shapes produced are irregular particles in sizes ranging from 0.2 to 5mm (ideal sizes for water treatment). The treatment is designed to produce a vast structure of pores creating a massive surface area for adsorption.
How does carbon work?
Granular activated carbon works by absorbing the soluble pollutants onto its surface and holding them. Because it has such a massive surface area the amount of absorption is probably one of the greatest of any natural man made material available. Eventually all the pores are filled and the carbon will need to be replaced. As the contaminants are absorbed onto the carbon backwashing the filters is a good idea as the pollutants are held firm but the carbon can be rebeded stopping channelling.
By choosing the type of GAC coconut, coal wood etc and by treating it in suitably different ways its performance can be optimised for particular jobs. 12 x 30 coconut shell is often used in systems for dechlorination, organic colour removal and protection of RO membranes. Coal based GAC is often used for removing larger chain organic molecules or where high hardness and mechanical strength are need. If the carbon is treated with silver it acts as a natural bactericide and helps reduce bacteria although this is expensive. Acid washing carbon increases the purity, reduces the ash content and is particularly suited for ultrapure water treatment systems. Bone charcoal is phosphate rich and good at reducing natural colour, and heavy metals including lead.
Different contaminants require different contact times and different flow rates so careful attention to the flow rates and the application is important eg for chlorination using coconut based GAC at contact time of 4-6 minutes is suggested.
How Does It Work
Water flows into the valve at the top, down through the media and then up through the riser tube in the middle of the vessel. As the water travels through the media the sediment is trapped so only clean clear water flows out to service. There are timer options that can be set to automatically self clean (backwash) and wash away any of the accumulated sediment.