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8/10/2019 Removal of Steroid Hormones by Activated Carbon Adsorption
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REMOVAL OF STEROID
HORMONES BY
ACTIVATED CARBON
ADSORPTION -
KINETIC AND
THERMODYNAMICSTUDIES
by: Augustine O. Ifelebuegu
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EndocrineDisrupting Chemicals
- are substances that alter the hormonal system.
- 17beta-estradiol(E2) and 17alpha-
ethinylestradiol(EE2) are examples of EDC.
- usually found as discharged to the environment
through effluent from wastewater treatment.
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Granular Activated Carbon
- usually used in the treatment of potable water.
- can remove E2 and EE2 steroid hormones by
adsorption.
Parameters such as pH, temperature, and weight of
adsorbent (GAC) are deliberated using adsorption
isotherm, pseudo first and second order kinetics,
Gibbs free energy, enthalpy and entropywere used.
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Effects of pH (4, 5, 6, 8 and 10)
- Percentage efficiency was better in the acidic and
neutral pH ranges.
- Negative carbon particles reduce the sorption
process by electrostatic repulsion.
- Higher pH results in the production of aquacomplexes which reduces the adsorption capacities
of the activated carbon.
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Effect of varying adsorbent dose
- The adsorption rate of E2 and EE2 increased
initially up to a certain level and remained constant
afterwards.
- The initial increase is attributed to the greater
availability of the surface area and increased
adsorption site at higher concentrations of the
adsorbents.
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Pseudo 1stand 2ndorder
= 1( )(1)
= 2( )
2(2)
where: t is contact time in (min)
k1is pseudo 1storder adsorption rate constant,
(min-1
)qe, q are the amount of the adsorbate at equilibrium
time
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Pseudo first order kinetics can be obtained by:
= (3)
while,1
1
= (4)
will give the k for the pseudo second order
kinetics
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Intra-particle diffusion kinetics
= 1/2 + C(5)
- Non of the plots for E2 and EE2 passed through
the origin.
- There are two sections on the plot which show
some fit (the initial and the last sections).
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- The initial part may be considered as the faster
adsorption stage and can be attributed to the
boundary layer diffusion of E2 and EE2 on the
external surface of the activated carbon.
- The last stage shows decrease as a result of lower
adsorbate concentration.
- The middle stage (curved part) is where the intra-
particle diffusion kinetics is controlled.
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Effects of Temperature
- sorption process showed increase with increasing
temperature.
= (6)
= (7)
= (8)
where: R is gas constant
T is temperature (K)
=
is the quantity of the adsorbate that
adsorbed onto the adsorbent (L/g)
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- Enthalpy indicates chemical nature of the sorption
process.
- Increase in temperature increases the sorption
capacity.
- Positive entropy suggest an increased randomness
after the adsorption process.
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Adsorption Isotherms
=
1+ (9)
= ()(
)(10)
where: qeis the amount of adsorbate adsorbed per
unit mass of adsorbent (mg/g)
Ceis equilibrium concentration
qm, b, kf, n are emperical constants
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Langmuir equations:
- qmcorresponds to the surface
concentration.
- b relates to the energy of adsorption.
Freundlich equations:
- kf estimation of the adsorption capacity.
- 1/n measure of strength of adsorption.
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- Based on the data, there was no perfect fit of the
experimental data to any of the models.
- Langmuir isotherm model obtain better fits
- Adsorption of E2 and EE2 occurs in localized sites.
- Freundlich isotherm model showed fairly good fit.
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- Organics present in the water may have effects in
isotherm models.
- Freundlich isotherm, n is below unity the adsorption
process is chemical process.