Department of Civil Engineering-I.I.T. Delhi

CEL 795: Water and Wastewater Treatment Processes

HW 5 Solution

Q1: For the following information, determine Langmuir and Freundlich model constants? Also

plot Q of these models with equilibrium adsorbate concentration ranging from 0 to 10 mg/L?

Compare these two models and comment on their suitability in describing the observation?

[20 points]

Solution: See class example; See which model describe the data well in graph paper.

Q2: For the following information, determine Langmuir model constants and adsorption

capacity of alumina for initial anthracene concentration equal to 0.000811 moles/L? Also plot Q

vs. C (t) for C (t): 0 to 10 moles/L and comment on it.

Solution:

Q=Qmax*KC/[1+KC]

so Qmax*K=22; K=375 L/mol; Qmax=22/375 (mol/kg)

C[0]=0.000822 mol/L; Ceff=?

Q=[C0-Ceff]*V/[XV]

say 1 kg alumina was used in 1 liter sample.

Q=[C0-Ceff] (mol/kg) = 22Ceff/[1+375Ceff]

solve for Ceff; calculate % removal now;

adsorption capacity of alumina = Q=[C0-Ceff]*V/[XV]= [C0-Ceff] (mol/kg)

Q3. What is the difference between Langmuir and Freundlich adsorption isotherm

mechanisms?

Solution: See lecture notes

Q4. Untreated drinking water has 0.02 mg/L of geosmin, which gives earthy odor. How much

removal can be achieved by adding 10 mg/L powdered activated carbon (PAC) in water?

Assume geosmin adsorption on PAC is defined by Freundlich adsorption

Qeq = Kf (Ceq)1/n

where Qeq is mass of geosmin adsorbed on PAC (µg) per mg of PAC; Ceq is

concentraton of dissolved geosmin in water (µg/L), and Kf= 0.5 (µg/mg)(L/ µg)(1/n)

and

(1/n)=1.08.

Solution:

See approach used in Q2; here X=10 mg/L is given; reactor volume =1 liter;

C0=0.02 mg/L

Ceff=?

determine Ceff and then calculate % removal

Q5. How does adsorption happen? Differentiate between competitive and cooperation

adsorption?

Solution:

See lecture notes; in competitive adsorption-two ions compete for same adsorption sites and one ion

might not get completely adsorbed on sites (ex: reduction in adsorption of arsenate ions due to

sulphate ions on iron oxide sites);

in cooperation adsorption-one ion cooperate with other ion and increase its adsorption on adsorbent

(ex: Calcium ions increase adsorption of arsenate ions on iron oxide sites)

Q6. What is the difference between Langmuir and Freundlich adsorption isotherm mechanisms? What

do these models indicate about adsorption capacities of adsorbent? Can these models provide

information on homogeneity or heterogeneity of adsorption sites?

Solution: See lecture notes

Q7. How does drawing a breakthrough curve help in deciding time for changing of activated

carbon packed in activated carbon-based absorber?

Solution:

See lecture notes

Q8. Draw a breakthrough curve and label all important information one can obtain from this

curve. Can this curve be used in setting time for changing adsorbent in absorber?

Solution: See lecture notes