Activated carbon

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Reef Keeper
Jul 5, 2003
We typically use activated carbon in three different facets of aquaculture: taking impurities out of water as it is brought into the facility; removing halogens such as ozone, chlorine, and bromine; and removing color and metabolic by-products in recirculating systems. Activated carbon is the generic term used to describe the family of carbonaceous adsorbents with an extensively-developed internal pore structure. A wide variety of activated carbon products are available, exhibiting markedly different characteristics. It is commonly made from wood, coal, lignite, and coconut shell. The material is first subjected to a heating process called carbonization, which forms a fixed carbon mass full of tiny pores. It is then activated by a second heat/steam treatment (200-1600°C) while regulating oxygen level, which creates a huge internal pore network and imparts surface chemistries that give carbon its unique filtering characteristics. Some carbons are activated with phosphoric acid, potassium hydroxide, or zinc chloride, which makes them unsuitable for use in aquaculture. When selecting an activated carbon, consider the adsorptive and physical characteristics of that carbon on the chemical to be removed from the system.

Activated carbon’s adsorptive characteristics are based on the principle that the greater the surface area, the higher the number of adsorptive sites available. The pore size and the pore size distribution are extremely important, as they affect the efficacy of the carbon in your application. The macropores (larger than 25 nm) are used as the entrance to the carbon, the mesopores (1-25 nm) for transportation, and the micropores (less than 1 nm) for adsorption. It is a generalization to say that the porosity of an activated carbon can be measured by adsorption of iodine from solution, but this measurement may not at all predict its ability to adsorb other chemicals
Activated carbon will adsorb the following from water:
Chlorine and some chloramine, many dissolved organic contaminants, trihalomethanes (THM), and phenolics, total organic carbon (TOC), oil and hydrocarbon contamination, ozone, bromic acid and total organic halogens (TOX), adsorbable organic halogens (AOX) including chloraform, biological oxygen demand (BOD), chemical oxygen demand (COD).