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