Carbon Filtration

Activated carbon (AC) is a natural material derived from bituminous coal, lignite, wood, coconut shell, and other sources. Coconut shell based carbon is generally known to be best, because it is known to be more effective, the cost is often about one fifth more than wood or bituminous charcoal, and it is a renewable resource. Charcoal is able to remove impurities from water by absorbing the volatile organic chemicals, there by improving the taste and odor of the water. Activated Carbon is produced in three major forms - block, granulated, and powdered form. When activated by steam and other means, each form can perform different adsorption properties. Various blends of carbon can be used to achieve specific water quality - contaminants and smell reduction, and improved taste.

When flow conditions are suitable over the surface of any Activated Carbon form, some dissolved chemicals in water flowing over the carbon surface adhere to the carbon in a thin film while the water passes on. Called absorption, this process is an effective method in removing some chlorine and it's by-products (TTHM's) and volatile organic compounds (carbon based VOC's). However, carbon filtration alone does not remove many hazardous chemicals such as arsenic, fluorides, some heavy metals, and nitrates.

The most widely used forms of activated carbon used in the treatment of drinking water are granular activated carbon (GAC), extruded solid carbon block (CB) and powdered activated carbon (PAC).

Granulated Activated Carbon (GAC) has a tremendous surface area resulting from its porous structure. GAC filters degree of effectiveness depends on the flow rate of the water and contact time with the water. However, if not regularly replaced, these filters will begin a process called channeling, whereas buildup of contaminants on the surface of the carbon causes water passing through to take "the path of least resistance" through a filter. Eventually, this leads to dumping, a sudden change in your water pressure releasing the trapped contaminants into your glass.

Carbon Block (CB) filtration water is taken through pores in heavy arranged carbon block. While Carbon Block filters remove Particulate Lead (not dissolved Lead) and Cysts, they do not remove metal substances such as in hard water, and are generally more expensive than other Carbon filter types.

Powdered Activated Carbon (PAC) is mainly used in municipal wastewater and drinking water treatment. The carbon powder is mixed in sediment tanks to produce a slurry that filters contaminants when the water slowly seeps through the treatment tanks. PAC is not ideal for home water filtration systems because of its smaller size for 2 reasons, (1) PAC cannot typically be used in pressurized filtration, and (2) unless a very fine membrane is used, much of the powder is washed out of the filter.

Problems with Carbon-Only Water Filters

Carbon water filters are generally poor at removing heavy metal substances from water like iron, manganese, and hydrogen sulfate. In addition, carbon water filters also may not be able to remove inorganic contaminates such as arsenic, asbestos, barium, beryllium, chromium, copper, fluoride, mercury, nickel, nitrates, sulfate, and the like.

No form of carbon filter removes bacteria. In fact under quite normal operating condition all carbon forms become perfect breeding grounds for bacteria, including pathogenic bacteria. Silver is often used as an additive to prevent bacterial growth. However, this is often applied in a spray over a small percent of the carbon granules. Therefore, the remaining uncoated granules are still subject of bacterial growth.