Carbon, sometimes called “charcoal,” is the most universally applied of all water treatment filter media. Residential water filters, from the common end-of-faucet taste enhancers to elaborate whole house systems, almost always are carbon filters or use filter carbon as one of their principal ingredients.
Filter carbon is a manufactured product, made commonly from coal, woods, and nut shells. Not all filter carbon is the same. It varies depending on the raw material and manufacturing techniques applied. Performance depends on the pore size of the carbon as well as the format produced by manufacturing. It can be used in granular form (similar to coffee grounds), powder, or tight, molded blocks. It can even be stuck to the surface of other filtering devices like pleated filters or combined in beds with other media like KDF.
Carbon made with bituminous coal is the most common and most universally used. It has average pore size, containing large and small pores, and is therefore useful in most filtering applications. Carbon will smaller pores–coconut shell carbon is the most popular–is best at dealing with contaminants like VOCs that require lots of small pores. Large pore carbon, typically made from wood or lignite coal, is best at removing colors from water.
Carbon reduces contaminants either by catalytic action, physical straining, or adsorption. For example, it acts as a catalyst to convert chlorine to harmless chloride or to break down chloramine to chlorine and ammonia. Although all carbon can perform this function, specially prepared carbon called “catalytic carbon” can do it much faster. Catalytic carbon can also be used to reduce hydrogen sulfide odors or to remove iron from well water. Most chemical reduction is done by adsorption, with the contaminant becoming trapped on the craggy surface of the carbon. Although this isn’t it’s best function, carbon can also be used to physically trap particles in granular beds or in carbon block form. Very tight carbon blocks can screen out things as small as bacteria or cysts.
In addition to removing chemicals, which is carbon’s main function, it almost always improves the taste, odor, and appearance of water.