Water Purifiers And Activated Carbon: Adsorb Or Adsorb?

Water has been purified with activated carbon for hundreds of years stretching back to ancient India. Most of us have seen activated carbon for sale in pet stores for cleaning water and have used a crude cousin, charcoal, to cook steaks in the backyard.
As a refined version of charcoal, activated carbon is made by super heating organic material like wood or coconut shells. This super heating drives out impurities and causes the surface area of the resulting material to become tremendous. It is this large surface area that allows this substance to be used to clean water.
For years the process of cleaning water with activated carbon in water purifiers was referred to as absorption. This term refers to what a sponge does with water and it is easy to visualize the activated carbon acting like a sponge, soaking up contaminants. However, this is not actually how the process works. The molecules inside the activated carbon are passive because they are connected to other molecules around their entire perimeter. The molecules on the surface are not as “happy” because they are exposed on one side without another carbon molecule as company. Therefore, these exposed carbon molecules are actively seeking something to “hook to” or bond with. As impurity in the water pass the activated carbon these exposed molecules bond with the impurities through a process of adsorption. When the entire surface area of the activated carbon is covered with impurities is quits adsorbing impurities.
Once the entire surface of the activated carbon is completely covered with impurities the water purifier quits working. At this point it is possible to “re-activate” the carbon by reheating it and thus driving off the impurities in the air. However, since this is a relatively tricky process and may result in some impurities being picked up from the oven it is probably best to leave this to the experts and simply replace the carbon in the water purifier.
Contact time is the primary attribute that determines the efficiency or effectiveness of water purifiers. Image a flow of water that is moving at a hundred miles per hour though a thin mat of activated carbon. In this scenario not much is going to happen because the water is not in contact with the activated carbon for a sufficient period of time. Therefore the higher the volume of water that the water purifiers is trying to clean the larger the filter should be. This is why a relatively small activated carbon water purifier works great on an ice maker in your home. Not much water is moving though the filter’s quarter inch line. This contact time constraint also indicates that it is better to place several medium sized water purifiers around the house than to install a water purifier for the whole house unless you are will to install a very large filter that will have to handle showers and baths.
Now we know that the activated carbon adsorbs rather than absorbs impurities and that contact time is the most important component in the high quality water equation. These facts indicate that it is best to add several water purifiers where needed and to change the activated carbon filters on a regular basis.