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 (200–1,600°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 (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.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 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 biological 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 flow rate, 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 flow rates 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 absorbed 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.Carbon filters through both its grain size and by its ability to bind up organic and inorganic materials to itself through an electrical charge on its surface. This is known as Adsorption.Carbon filtration is used successfully in industry for filtering wastewater, for the removal of fine insoluables from water and to remove metals and chlorine compounds from domestic water. Carbon filtration is also used to control biological contamination in water.Activated Coal carbon has a different internal structure than coconut carbon thereby allowing for more uptakes of certain contaminants.
What is activated carbon made from?
Activated carbon can be manufactured from any organic material containing carbon. Commercial carbons are made from sawdust, wood, charcoal, peat, lignite, petroleum coke, bituminous coal, and coconut shells.Activated carbon products made from bituminous coal, coconut shell, and wood. Water Filter Corp chooses these raw materials in order to provide good activated carbon to its customers.How is activated carbon produced?The coal is pulverised to a very fine particle, about the size of talcum powder. The powdered coal is mixed with a binder to glue it back together and pressed into briquettes. These in turn are crushed and classified to the size of the desired end product.This process, called reagglomeration, creates an activated carbon that is harder and less dusty than a direct activation process.Reagglomeration also assures that the activation occurs through the granule to the core. Some direct activation processes only activate the exterior of the granule.
The sized material is heated in an oxygen void environment to avoid burning and to remove the volatile components of the coal. The carbon is activated by additional heating in a controlled environment of oxygen and steam. The activation process creates a highly porous graphitic plate structure with tremendous surface area.
How much surface area does activated carbon have?
A single pound of activated carbon has the surface area equal to 125 acres.How much does it weigh?Pure carbon weighs about 130 pounds per cubic foot. It is much denser than activated carbon. During the manufacturing process the structure is opened up, creating porosity (pore volume) inside the granule. The finished product has a density between 25 to 40 pounds per cubic foot.How much void space is in carbon?A container of carbon is roughly 20% carbon, 40% interstitial space (the volume between the carbon granules), and 40% pore volume (the volume inside the carbon granules).Another way to visualise this is: If you had a 55 gallon drum full of dry carbon, you could add 44 gallons of water to the drum before it would overflow. Therefore, 80% of the drum volume is air.What is this pore space?The pore space is the internal volume of the carbon granule. The pore space consists of all the cracks and crevices created when the coal is crushed and glued back together, and the volume between the graphite plates. The distance between the graphite plates determines whether the space is an adsorption pore or a transport pore.What is an adsorption pore?Adsorption pores are the internal volume where the graphitic plates are close together creating a higher energy. Higher energy is important to adsorption because it is the energy that holds the contaminant (the carbon adsorbs the contaminant).The volume where the graphite plates are far apart and the cracks and crevices make up the transport pores. It is important to note that all adsorption takes place in the adsorption pores and not the transport pores.
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