Very briefly, they work in two ways:

Mechanical Filtration Like a very fine sieve to remove particulate matter and sediment. The finest of these is the 0.2 micon Ceramikx/Carbon Block cartridge which we use to make the Pearl-B and Oyster-TBC (see previous question).

Electrokinetic adsorbtion. The contaminants 'stick' to the acvtivated carbon.

Activated carbon is made by grinding bituminous coal, peat, or peanut or coconut shells and baking in controlled conditions to 540C in the absence of oxygen which bakes off the impurities.Then superheated steam at 870C activates the carbon and creates a massive network of pores that greatly increases the surface area of the carbon. This surface area is why carbon can absorb such large quantities of various compounds. This is called Granular Activate Carbon or GAC

Coconut shell carbon is, by far, the superior carbon and adsorbs the widest spectrum of chemicals the most efficiently.

Health note: This is not a problem if you or yours have a nut allergy. This carbon has been sterilised and acid washed. It is just carbon but activated to remove harmful chemicals from your drinking water.

The newest and best activated carbon technology is Coconut Shell Activated Carbon Block. This is coconut shell GAC which has been further pulverised into smaller particles, then fused and then extruded. The result is all the top chemical adsorption qualities of coconut shell activated carbon but with finer particles giving a much larger surface area and much more activated carbon in the same volume as GAC; and with smaller micron ratings and a longer service life.

An additional benefit of carbon block is that the water is distributed radially & evenly through out the media without 'Water Channeling'.

GAC is a loose media (like sand) and can suffer from 'Water Channeling" where the water keeps to the same waterways through the media. This results in some of the media not being used and leads to early depletion.At Fountain Filters we use coconut shell activated carbon block cartidges in all the water filter systems except the Pearl-M Heavy Metals filter which uses a special mixed media GAC/KDF-55 cartridge and the Pearl-B which as a special, washable, 0.2 micron cartridge