Odor Reduction and Taste Improvement
Odors that are emitted from drinking water are most commonly caused by hydrogen sulfide released from the decay of organic matter in well water. Poor tasting water can be caused by a number of factors including organic contamination and other dissolved contaminants. Activated carbon filtration is the most commonly used method of improving the taste and odor of drinking water. Activated carbon is popular because it is inexpensive and removes a wide range of contaminents.
Activated carbon has a slight positive charge to its surface, allowing it to attract and hold negatively charged contaminants in water. The most frequently removed negative ions removed from drinking water are chlorine and chloramines, which are disinfecting agents and byproducts of disinfecting agents. Although activated carbon can remove low levels of iron and manganese, it is not effective at removing hardness causing salts (calcium chloride or magnesium chloride), arsenic, fluoride, and most dissolved metals.
Activated carbon also removes organic contamimants including VOC's (volitile organic chemicals, pesticides, herbicides, benzenes, trihalomethanes, solvents, and radon. The large surface area of activated carbon gives it high capacity to absorb contaminants as well as high kinetic activity that allows high product water flow rates.
Activated carbon can be made from anthracite coal, bituminous coal or coconut shells. Coconut shell activated carbon is generally considered to be the highest quality carbon (highest activity, lowest leachables) but is also the most expensive. Activated carbon is made in granular form, carbon block (compressed powdered carbon) and is also used to impregnate various other filtration medias.
- Granular activated carbon is loose pieces of carbon that forms a filtration bed. This filtration bed maximizes surface area so that high flow rates are possible. This high flow rate is usually accompanied by some pressure drop. Particulate filtration by granular activated carbon is limited by the larger size of the carbon pieces and can generally remove only larger particles (>100 microns)
- Carbon block is composed of compressed and bonded activated carbon powder. Carbon block filters have less pressure drop than granular activated carbon but at the expense of surface area (lower treatable flow rate). Carbon block filters also have some particulate filtration qualities but are really only useful as a "polishing filter" that is utilized after primary particulate filtration. Utilizing a carbon block filter as primary particulate filtration often leads to plugging of the filter before the activated carbon is exhausted. Some carbon block filters can filter down to 0.5 micron, which effectively removes cryptosporidium and other bacteria.
- Filters impregnated with carbon generally have the lowest pressure drop of any carbon filter. Carbon impregnated filters also have the highest particulate filtration capacity. The odor/taste/organic reducing capacity of carbon impregnated filters is limited due to the small amount of total carbon included in the media. Impregnated carbon filters also tend to be the least expensive carbon filters (also because of the small amount of activated carbon).
