FIRST WATER - Adsorption Water Treatment




		Adsorption is the process by which molecules, colloids and particles adhere to a surface by physical action and without any chemical reaction. Carbon which has been "activated" (oxidized at high temperatures) to create millions of minute cavities is an effective and economical means of adsorbing dissolved organic and other chemicals that cannot be removed by filtration. AC filters are one of the only low-cost methods to remove low-molecular weight (<100 MW) organics and chlorine. Granular Activated Carbon (GAC) and Activated Carbon Block (ACB) are used in combination with filtration and/or disinfection to remove undesirable tastes and odors, chloramines, some pesticides and herbicides, and other chemical contaminants. They are sometimes also combined with halogen-based disinfection technologies to remove residual iodine and chlorine. Activated carbon does not remove salts. AC filters may become a breeding site for bacteria and pyrogenic materials such as certain toxins. The carbon must be sanitized or changed periodically to avoid bacterial growth. When all adsorption sites are used, the AC must be reactivated (re-charged) by a controlled heat process. This is not easily done in the field. While the target of adsorption is dissolved organics and halogens, the accumulation of suspended solids in AC beds may require frequent backwashing of the filter unless installed in combination with microfiltration and perhaps ultrafiltration.