There are two principal mechanisms by which activated carbon removes contaminants from water; absorption, and catalytic reduction. Organic compounds are removed by absorption and residual disinfectants such as chlorine and chloramines are removed by catalytic reduction.
Activated carbon adsorption proceeds through 3 basic steps
1. Substances adsorb to the exterior of the carbon granules
2. Substances move into the carbon pores
3. Substances adsorb to the interior walls of the carbon
Activated carbon filtration is very common in a number of home water treatment systems. It can be used as a standalone filter to reduce or eliminate bad taste and odour, chlorine, and many organic contaminants in municipal (pre-treated or chlorinated) water supplies to produce a significantly improved drinking water. It is also very commonly used as a pre-treatment as part of a reverse osmosis system to reduce many organic contaminants, chlorine, and other items that could foul the reverse osmosis membrane. 0.5 micron carbon block filters are commonly used to remove cysts such as giardia and cryptosporidium.
Activated carbon filters remove/reduce many volatile organic chemicals (VOC), pesticides and herbicides, as well as chlorine, benzene, trihalomethane (THM) compounds, radon, solvents and hundreds of other man-made chemicals found in tap water. Some activated carbon filters are moderately effective at removing some, but not all, heavy metals. In addition, densely compacted carbon block filters mechanically remove particles down to 0.5 micron, including Giardia and Cryptosporidium, turbidity and particulates.
Although some iron, manganese, and hydrogen sulphide will be removed by these higher quality activated carbon filters, a manganese greensand iron reduction filter is generally preferred to remove these contaminants as the effectiveness of carbon filter against iron and manganese is generally short-lived if the contaminant concentration is high.
Threats
Tastes and odours in drinking-water may be indicative of some form of pollution. An unusual taste or odour might be an indication of the presence of potentially harmful substances. The taste and odour of drinking-water should not be offensive to the consumer
Mouldy, musty, earthy, grassy or fishy taste or odour although harmless, it can affect the taste and smell of your drinking water even at very low concentrations.
Organic susbstances can react with chlorine to produce undesirable levels of chlorination by-products, including tri-halomethanes. Most metals readily form complexes with humic substances in water, which can greatly increase their solubility.
Brown, red, orange or yellow water is usually caused by iron rust. While unpleasant and potentially damaging to clothes and fixtures, iron in drinking water is not a human health concern.
Activated carbon is a highly effective tool in water filters because it has enormous surface area and is highly porous - one pound of activated carbon has the surface area of more than 100 acres.