What Parameters can Granular Activated Carbon (GAC) Remove?

DESCRIPTION OF ADSORBTION

Molecules from gas or liquid phase will be attached in a physical way to a surface, in this case the surface is from the Granular Active Carbon (GAC). The adsorption process takes place in three steps;

  • Macro transport: The movement of organic material through the macro-pore system of the active carbon (macro-pore >50nm)
  • Micro transport: The movement of organic material through the meso-pore and micro-pore system of the active carbon (micro-pore <2nm; meso-pore 2-50nm)
  • Sorption: The physical attachment of organic material on the surface of active carbon in the meso-pores and micro-pores of the active carbon

The activity level of adsorption is based on the concentration of substance in the water, the temperature and the polarity of the substance. A polar substance (a substance which is good soluble in water) cannot or is badly removed by granular active carbon, a non-polar substance can be removed totally by granular active carbon. Every kind of carbon has its own adsorption and in the water treatment business this isotherm is definite by the function of Freundlich.

The function of Freundlich:

x/m = adsorbed substance per gram active carbon

Ce = concentration difference (between before and after)

Kf, n = specific constants

Factors that influence the performance of granular active carbon in water are:

  • The type of compound to be removed. Compounds with high molecular weight and low solubility are better absorbed.
  • The concentration of the compound to be removed. The higher the concentration, the higher the carbon consumption.
  • Presence of other organic compounds which will compete for the available adsorption sites.
  • The pH of the waste stream. For example, acidic compounds are better removed at lower pH.

1. - According to this we can classify some chemicals by their probability of being efficiently adsorbed by active carbon in water:

2,4-D
Alachlor
Aldrin
Anthracene
Atrazine
Azinphos-ethyl
Bentazone
Biphenil
2,2-Bipyridine
Bis(2-Ethylhexyl)Phthalate
Bromacil
Bromodichloromethane
p-Bromophenol
Butylbenzene
Calcium Hypochloryte
Carbofuran
Chlorine
Chlorine dioxide
Chlorobenzene
4-Chloro-2-nitrotoluene
2-Chlorophenol
Chlorotoluene
Chrysene
m-Cresol
Cyanazine
Cyclohexane
DDT Lindane

Deisopropyltatrazine
Desethylatrazine
Demeton-O
Di-n-butylphthalate
Dichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
2,4-Dichlorocresol
2,5-Dichlorophenol
3,6-Dichlorophenol
2,4-Dichlorophenoxy
Dieldrin
Diethylphthalate
2,4-Dinitrocresol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Diuron
Endosulfan
Endrin
Ethylbenzene
Hezachlorobenzene
Hezachlorobutadiene
Hexane
Isodrin
Isooctane
Isoproturon
Lindane

Linuron
Malathion
MCPA
Mecoprop
Metazachlor
2-Methyl benzenamine
Methyl naphthalene
2-Methylbutane
Monuron
Napthalene
Nitrobenzene
m-Nitrophenol
o-Nitrophenol
p-Nitrophenol
Ozone
Parathion
Pentachlorophenol
Propazine
Simazine
Terbutryn
Tetrachloroethylene
Triclopyr
1,3,5-Trimethylbenzene
m-Xylene
o-Xylene
p-Xylene
2,4-Xylenol

2.- Chemicals with high probability of being adsorbed by GAC:

Aniline
Benzene
Benzyl alcohol
Benzoic acid
Bis(2-chloroethyl) ether
Bromodichloromethane
Bromoform
Carbon tetrachloride
1-Chloropropane
Chlorotoluron

Dibromo-3-chloropropane
Dibromochloromethane
1,1-Dichloroethylene
cis-1,2- Dichloroethylene
trans-1,2- Dichloroethylene
1,2-Dichloropropane
Ethylene
Hydroquinone
Methyl Isobutyl Ketone
4-Methylbenzenamine

1-Pentanol
Phenol
Phenylalanine
o-Phthalic acid
Styrene
1,1,2,2-Tetrachloroethane
Toluene
1,1,1-Trichloroethane
Trichloroethylene
Vinyl acetate

3.- Chemicals with moderate probability of being adsorbed by active carbon:

Acetic acid
Acrylamide
Chloroethane
Chloroform
1,1-Dichloroethane
1,2-Dichloroethane
1,3-Dichloropropene
Dikegulac

Dimethoate
Ethyl acetate
Ethyl ether
Freon 11
Freon 113
Freon 12
Glyphosate
Imazypur

Methionine
Methyl-tert-butyl ether
Methyl ethyl ketone
Pyridine
1,1,2-Trichloroethane
Vinyl chloride

4.- Chemicals for which adsorption with active carbon is unlikely to be effective. However it may be viable in certain cases such as for low flow or concentrations:

Acetone
Acetonitrile
Acrylonitrile
Dimethylformaldehyde
1,4-Dioxane
Isopropyl alcohol
Methyl chloride

Methylene chloride
1-Propanol
Propionitrile
Propylene
Tetrahydrofuran
Urea

Factors that influence the performance of active carbon in air:

  • Type of compound to be removed: In general compounds with a high molecular weight, lower vapor pressure/higher boiling point and high refractive index are better adsorbed.
  • Concentration: The higher the concentration, the higher the carbon consumption.
  • Temperature: The lower the temperature, the better the adsorption capacity.
  • Pressure: The higher the pressure, the better the adsorption capacity.
  • Humidity: The lower the humidity, the better the adsorption capacity.

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