The process got a major boost in the early 1900s with the development of carbon activation, which increased the carbon's effectiveness exponentially. Activated carbon filters are extremely effective at removing organic chemicals that can cause color, odor and taste problems in water. The raw carbon used in these systems comes from manufactured coal, as well as wood, peanut shells and coconut shells. Coconut shells are popular because they are a renewable resource, produce good tasting water and are quite effective at removing trihalomethanes (THMs).
Carbon filtration generally can be used to remove chlorine, pesticides, herbicides, industrial chemicals, THMs, polychlorinated biphenyls (PCBs) and halogenated compounds. Carbon filters remove chemicals by the process of adsorption, whereby a particle or molecule adheres to the surface of a substance, usually due to a molecular attraction. As water comes into contact with the carbon, the organics present in the water adhere to the carbon. Because the adsorption process depends on contact, the more surface area the carbon has available, the more contaminants it can adsorb. This is where the activation of the carbon comes into play.