Page 274 of AES Mastercatalog by Aquatic Eco-Systems

mechanical filtration tech talk tech talk 42 activated carbon in aquaculture against pressure drop as this will affect energy cost careful consideration of particle size can provide significant operating benefits activated carbon will adsorb the following from water chlorine and some chloramines 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 chloroform colors pesticides odors and more activated carbon will also reduce biochemical oxygen demand bod and chemical oxygen demand cod it is important to be able to measure the contaminant that the carbon needs to adsorb in order to know when the saturation capacity of the carbon is reached particle size water flowrate carbon bed depth and in recirculating systems the number of passes through the bed must be optimized for every system design typically for a single pass system a deep bed with very slow flowrates would be required so that removal of dissolved organics can take place in the top portion of the bed change the carbon before it becomes saturated if the carbon is not replaced it could desorb what it has already removed this can cause a nasty toxic release always backwash the filter before use in backwashing a bed expansion of at least 25 percent should be used to remove any carbon dust if it is absolutely necessary to remove a contaminant from the water use a series of activated carbon filters and do water sampling after the first filter the second filter will act as guard bed carbon like all surfaces in recirculating aquaculture will support bacteria that consume some of the adsorbed organics and if left too long can slime over the surfaces ozone and chloramines oxidize the carbon s surface and they do not accumulate in the carbon structure 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 they are commonly made from wood coal lignite and coconut shell in activated carbon s manufacture 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 200­1,600°c while regulating oxygen level which creates an even larger 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 characteristics of that carbon on the chemicals to be removed 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 the macropores larger than 25 nm are used as the entrance to the carbon the mesopores 1­25 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 the finer the particle size of an activated carbon the better the access to the surface area and the faster the rate of adsorption small pore size must be weighed waterlife design group project for the tampa bay rays baseball stadium order online aquaticeco.com order by phone 877-347-4788 tech support 407-598-1401 271

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