Activated Carbon

Activated Carbon

Joe ChoromanskiRipley Aquariums

Activated Carbon(Everything I thought I knew but I was WRONG!)

Joe ChoromanskiRipley Aquariums

1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal

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


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.


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.


Activated CarbonWhat got me interested in this exciting topic?


Activated CarbonWhat 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.


Activated CarbonHistory 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.


Activated CarbonHistory 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.


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


Activated CarbonWhat 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.


Activated CarbonWhat 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)


Activated Carbon Activated Carbon can be produced from a wide variety of carbonaceous raw materials including:

Bituminous CoalCoconut ShellsWoodLignite CoalPeat, Olive Pits, etc.


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.


Activated Carbon

Carbon TypeTotal Pore Volume (ml/g)Mean Pore Radius (Angstroms)Surface Area (m2/g) Coconut Shell0.5 0.610 111000-1100Peat0.6 0.711 121000-1275Bituminous Coal0.6 0.712 141000-1150Bituminous Coal0.7 0.814 16900-1050Lignite Coal0.9 1.029 32900-1050Peat1.1 1.223 26600-675Wood1.4 1.822 - 261200-1600


Activated CarbonPore Structure


Activated CarbonActivationThe raw materials are first carbonized via a controlled heating process at low temperatures (200 - 300C) 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.


Activated CarbonActivationThe carbonized materials are then activated by steam (or chemical treatment). Steam activation is carried out at high temperatures (982C) 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.


Activated CarbonRE-ActivationThe adsorptive capacity of any AC is exhausted eventually.After carbon becomes used up (pore spaces filled), it can be partially reactivated w/ high temperature steamVery expensive but is done in the municipal drinking water industry


Activated CarbonAC Production


Activated CarbonThe Three Types/Forms of ACPowderedGranularPelleted / Extruded


Activated CarbonActivated Carbon Particle Sizing

MeshU.S.(ASTME11)

AInches

Amm

BInches

Bmm

4

1/4"

6.350

0.187"

4.760

8

1/8"

3.175

0.093"

2.380

10

1/10"

2.540

0.079"

2.000

12

1/12"

2.117

0.066"

1.680

14

1/14"

1.814

0.056"

1.410

16

1/16"

1.588

0.047"

1.190

20

1/20"

1.270

0.033"

0.841

30

1/30"

0.846

0.023"

0.595

40

1/40"

0.635

0.017"

0.420


Activated CarbonMeasuring Adsorptive PropertiesMolasses Number / Decolorizing EfficiencyHigher number, better performance with large molecule contaminants


Activated CarbonMeasuring Adsorptive Properties**None are good indicators of DOC removalIodine NumberThis test measures very small poresA high number indicates good performance on small-sized contaminantsTannin ValueTastes & odors; low number goodButane Activity (formerly CCl4 )Vapor phase only


Activated CarbonChoosing the correct type of AC:

Different purification goals require different activated carbon properties.There are >150 types of carbon available


Activated CarbonChoosing 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)


Activated CarbonAQUARIUM USES FOR CARBON:Dissolved Organic Carbon RemovalChemotherapeutantsProteins (yellow color; non-ozonated systems)Organic acids, carbohydrates, hormones, etc.

Oxidant RemovalChlorine / Chloramine from drinking waterOzone byproducts


Activated CarbonDissolved Organic Carbon RemovalActivated Carbon removes organic compounds from water via physical adsorption


Activated CarbonWhat is Adsorption?Organic molecules bond to the internal pores of activated carbon


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


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.


Activated Carbon The AC surface is non-polar which makes non-polar organic molecules most readily adsorbed. Will not adsorb saltsWill not adsorb alcoholsPresence of biofilms can affect adsorption


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)


Activated Carbon Trace metals Some easily removed when in low concentrations in FWAny physical adsorption process can remove trace ions from solutionDepends on the metal (some have good adsorption potential while others do not)


Activated CarbonOxidant RemovalActivated Carbon removes oxidants (Chlorine & Chloramine) from water via reactions, not adsorption


Activated CarbonOxidant Removal Chlorine (free chlorine HOCL)

Chlorine will oxidize carbon physically (actually destroys the carbon)Chlorine can bind w/ surface oxidesChlorine can react w/ surface & breaks down to other products (chloride ions)Reaction fast; never sees pores


Activated CarbonOxidant Removal Chloramines (NH2Cl, NHCl2, & NCl3)

A little more difficult that ChlorineCatalytic oxidation and adsorptionAmmonia initially formed but quickly converts to N2Chloride ions


Activated Carbon


Activated CarbonOxidant 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


Activated CarbonWater Treatment Methods for GAC & PAC(Diagrams from Calgon Carbon Corporation / Chemviron Carbon)


Activated CarbonDOC Removal Filter Design

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


Activated CarbonPHOSPHATES??

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).


Activated CarbonPHOSPHATES??

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.


Activated CarbonSo, whats the best carbon for aquariums?

Depends on the target contaminant and many, many other variablesIn general:a coal-based carbon (bituminous, not lignite)Low ash (pH), high in macro & microporesHarder, less moisture8 x 30 to 12 x 40 meshAcid washed in HCl


Thank you!

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Activated Carbon

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