Activated Carbon

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Activated Carbon

• Joe Choromanski
• Ripley Aquariums

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Activated Carbon

• (Everything I thought I knew but I was WRONG!)
• Joe Choromanski
• Ripley Aquariums

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Activated Carbon

• The use of activated carbon in marine
  aquariums has historically generated fierce
  debate.

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Activated Carbon

• Some aquarists believe that activated carbon
  is a miraculous, if not mysterious, magical
  potion used to cure all things in the aquatic
  environment.

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Activated Carbon

• Other aquarists feel that activated carbon is
  the devil incarnate, sucking the life force of
  trace elements, essential amino acids and other
  nutrients out of the aquarium.

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Activated Carbon

• What got me interested in this exciting topic?

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Activated Carbon

• What got me interested in this exciting topic?
• Charcoal-mellowing refers to a process used to
  make Tennessee whiskey, such as Jack Daniel's.
  The process involves slowly dripping the newly
  made whiskey through giant containers hard-packed
  with 10 feet of sugar maple charcoal. The process
  takes ten days, and during this time the whiskey
  absorbs the essence of the charcoal, refining the
  spirit and giving it a unique flavor and aroma.

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Activated Carbon

• History of Activated Carbon
• First described used over 3500 years ago for
  medicinal purposes (1550 B.C. in an ancient
  Egyptian papyrus and later by Hippocrates and
  Pliny the Elder)
• In the 18th century, crude carbons made from
  blood, wood and animals were used for the
  purification of liquids.

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Activated Carbon

• History of Activated Carbon
• In the 19th century, crude AC made from bone char
  (powder) was used to de-colorize sugar (mostly
  calcium phosphate with only a small of carbon).
• Early 20th century, processes were developed to
  steam activated powdered char for taste and odor
  removal in water.

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Activated Carbon

• History of Activated Carbon
• Granular Activated Carbon with industrial level
  steam activation was developed as a consequence
  of WWI, for use in gas masks

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Activated Carbon

• What is Activated Carbon?
• Activated Carbon is a crude form of graphite and
  generic term used to describe a family of
  carbonaceous adsorbents possessing a highly
  crystalline form and extensively developed
  internal pore structure.

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Activated Carbon

• What is Activated Carbon?
• This unique structure of Activated Carbon
  produces a very large surface area
• 1 lb. of Granular Activated Carbon produces a
  surface area of 125 acres (1 kg 1,000,000
  meters2 1000 m2/g)

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Activated Carbon

• Activated Carbon can be produced from a wide
  variety of carbonaceous raw materials including
• Bituminous Coal
• Coconut Shells
• Wood
• Lignite Coal
• Peat, Olive Pits, etc.

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Activated Carbon

• The choice of raw material has a large
  influence on the characteristics and performance
  of the AC, each producing an AC with differing
  surface areas, total pore volume, pore radius and
  pore volume distribution.

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Activated Carbon

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Activated Carbon

• Pore Structure

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Activated Carbon

• Activation
• The raw materials are first carbonized via a
  controlled heating process at low temperatures
  (200 - 300?C) in an oxygen-lean environment which
  keeps the material from burning. This process
  converts the raw material into a disordered
  carbon structure full of tiny pores.

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Activated Carbon

• Activation
• The carbonized materials are then activated by
  steam (or chemical treatment). Steam activation
  is carried out at high temperatures (982?C) and
  the carbonized materials react with the steam to
  form carbon monoxide and hydrogen which exit as
  gases leaving behind a highly porous activated
  carbon material.

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Activated Carbon

• RE-Activation
• The adsorptive capacity of any AC is exhausted
  eventually.
• After carbon becomes used up (pore spaces
  filled), it can be partially reactivated w/ high
  temperature steam
• Very expensive but is done in the municipal
  drinking water industry

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Activated Carbon

• AC Production

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Activated Carbon

• The Three Types/Forms of AC

Powdered
Granular
Pelleted / Extruded
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Activated Carbon

• Activated Carbon Particle Sizing

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Activated Carbon

• Measuring Adsorptive Properties
• Molasses Number / Decolorizing Efficiency
• Higher number, better performance with large
  molecule contaminants

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Activated Carbon

• Measuring Adsorptive Properties
• None are good indicators of DOC removal
• Iodine Number
• This test measures very small pores
• A high number indicates good performance on
  small-sized contaminants
• Tannin Value
• Tastes odors low number good
• Butane Activity (formerly CCl4 )
• Vapor phase only

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Activated Carbon

• Choosing the correct type of AC
• Different purification goals require different
  activated carbon properties.
• There are gt150 types of carbon available

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Activated Carbon

• Choosing the correct type of AC
• There are no valid theories that allow selection
  of the best activated carbon in any single case
  without experimentation (Johnson et al., 1964)
• It should be mentioned that the mechanisms by
  which activated carbon removes organic matter
  from water are unclear (Spotte, 1984)

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Activated Carbon

• AQUARIUM USES FOR CARBON
• Dissolved Organic Carbon Removal
• Chemotherapeutants
• Proteins (yellow color non-ozonated systems)
• Organic acids, carbohydrates, hormones, etc.
• Oxidant Removal
• Chlorine / Chloramine from drinking water
• Ozone byproducts

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Activated Carbon

• Dissolved Organic Carbon Removal
• Activated Carbon removes organic compounds from
  water via physical adsorption

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Activated Carbon

• What is Adsorption?
• Organic molecules bond to the internal pores of
  activated carbon

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Activated Carbon

• What is Adsorption?
• Adsorbates are held on the activated carbon pore
  wall surface by weak electrostatic forces (van
  der Waals forces)

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Activated Carbon

• Adsorption is a fight against solubility
• (Sigworth and Smith. 1972. Adsorption of
  Inorganic Compounds by Activated Carbon. JAWWA,
  64(6)386-391)
• The more soluble a substance, the less likely it
  is to be adsorbed.
• Variables such as temperature, adsorbate
  concentration (lower better) and pH affect both
  solubility of the adsorbate and the adsorption by
  the activated carbon.

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Activated Carbon

• The AC surface is non-polar which makes
  non-polar organic molecules most readily
  adsorbed.
• Will not adsorb salts
• Will not adsorb alcohols
• Presence of biofilms can affect adsorption

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Activated Carbon

• What about therapeutic Copper?
• Not known how copper is removed by carbon, but it
  is (can be measured).
• Cu has been classified as an element of low or
  unknown adsorption potential (Sigwood Smith,
  1972).
• Possibly more easily removed when complexed with
  other substances (Sigwood Smith, 1972 Keslar,
  2002)

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Activated Carbon

• Trace metals
• Some easily removed when in low concentrations in
  FW
• Any physical adsorption process can remove trace
  ions from solution
• Depends on the metal (some have good adsorption
  potential while others do not)

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Activated Carbon

• Oxidant Removal
• Activated Carbon removes oxidants (Chlorine
  Chloramine) from water via reactions, not
  adsorption

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Activated Carbon

• Oxidant Removal Chlorine (free chlorine HOCL)
• Chlorine will oxidize carbon physically (actually
  destroys the carbon)
• Chlorine can bind w/ surface oxides
• Chlorine can react w/ surface breaks down to
  other products (chloride ions)
• Reaction fast never sees pores

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Activated Carbon

• Oxidant Removal Chloramines (NH2Cl, NHCl2,
  NCl3)
• A little more difficult that Chlorine
• Catalytic oxidation and adsorption
• Ammonia initially formed but quickly converts to
  N2
• Chloride ions

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Activated Carbon
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Activated Carbon

• Oxidant Removal Filter Design
• Smaller particles or powders best (high SA)
• Must balance high SA desired with filter vessel
  particle retention ability during filtration and
  backwash

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Activated Carbon

• Water Treatment Methods for GAC PAC
• (Diagrams from Calgon Carbon Corporation /
  Chemviron Carbon)

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Activated Carbon

• DOC Removal Filter Design
• Should follow biological and mechanical
  filtration systems.
• Should precede disinfection (except when used to
  reduce oxidants in mixed systems)

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Activated Carbon

• PHOSPHATES??
• Many aquarists (especially hobbyists) believe
  carbon contributes phosphates to their tanks from
  carbon acid washing during production with
  phosphoric acid.
• MYTH No commercial carbons are washed with
  phosphoric acid only HCl and only in certain
  applications (adds cost).

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Activated Carbon

• PHOSPHATES??
• MYTH No commercial carbons are washed with
  phosphoric acid only HCl and only in certain
  applications (adds cost).
• Carbons are acid washed to REMOVE any remaining
  phosphorus from carbon (raw materials used do
  contain phosphorous)
• Can test carbon for P or pH before using.

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Activated Carbon

• So, whats the best carbon for aquariums?
• Depends on the target contaminant and many, many
  other variables
• In general
• a coal-based carbon (bituminous, not lignite)
• Low ash (pH), high in macro micropores
• Harder, less moisture
• 8 x 30 to 12 x 40 mesh
• Acid washed in HCl

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Thank you!