Activated Carbon: Water Treatment Methods and Principles

Activated carbon filtration is made from materials such as wood, wood chips, fruit pits, coconut shells, coal, or petroleum residue through high-temperature dry distillation and carbonization. After production, it needs to be activated with hot air or steam. Its main function is to remove chlorine, chloramine, and other soluble organic substances with molecular weights between 60 and 300 Daltons. Activated carbon has a granular surface and a porous interior, containing numerous capillaries approximately 10 nm to 1 Å in size. One gram of activated carbon has an internal surface area of 700-1400 m², and the adsorption occurs on the inner surfaces of these capillaries and the surface of the particles. Factors affecting the ability of activated carbon to remove organic matter include its surface area, pore size, and the molecular weight and polarity of the organic matter being removed. It primarily relies on physical adsorption to remove impurities. Once the adsorption capacity reaches saturation, excess impurities will fall and pollute downstream water. Therefore, it is necessary to periodically remove the adsorbed impurities using backflushing.

If the adsorption capacity of this type of activated carbon filter significantly decreases, it must be replaced. Measuring the TOC concentration difference (or bacterial count difference) between the influent and effluent is one of the bases for considering replacing activated carbon. Some reverse osmosis membranes are not very tolerant to chlorine, so activated carbon treatment is required before reverse osmosis to ensure that chlorine can be effectively adsorbed by the activated carbon. However, bacteria adsorbed on the pores of activated carbon can easily multiply and grow. At the same time, activated carbon has limited effectiveness in removing larger organic molecules, so a reverse osmosis membrane must be used to reinforce it.