removal of steroid hormones by activated carbon adsorption

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.

removal of steroid hormones by activated carbon adsorption

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