Page 267 - Soil and water contamination, 2nd edition

254 Soil and Water Contamination

3. In an 80 cm deep river, ammonium release from the bed sediment occurs at a rate of
-1
-2
-1
16 mg m d . The nitrification rate constant is 0.4 d and the denitrification rate
-1
constant is 0.8 d . If internal and external sources and sinks other than release from bed
sediments, nitrification, and denitrification can be ignored, and the above rate parameters
remain constant, the system tends to equilibrium.
-1
a. Calculate the ammonium concentration in mg l at equilibrium.
-1
b. Calculate the nitrate concentration in mg l at equilibrium.
c. Name three sources or sinks apart from direct anthropogenic sources (e.g. effluent
discharges, agriculture) which may have been overlooked.
4. In a laboratory experiment the following rate equation for the decomposition of o-xylene
-1
-1
was determined (in μg l d ):
dS 45S

dt 1000 S

a. What does S mean
- in this particular equation?
- in general?
b. In a graph plot the concentration against time (in days) given an initial o-xylene
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concentration of 1500 μg l ?
-1
c. How long does it take for the o-xylene concentration to fall to 70 μg l ?
5. A column experiment is carried out to determine the potassium adsorption characteristics
of a sediment. For this purpose, a cylinder of inert material is filled with sediment,
through which a KCl solution is percolated. The cylinder is 1 m long and 0.45 m in
-3
diameter. The sediment has a porosity of 0.32 and the bulk density is 1600 kg m .

Time Cl - K + Time Cl - K + Time Cl - K +
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-1
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(day) (mg l ) (mg l ) (day) (mg l ) (mg l ) (day) (mg l ) (mg l )
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1 15 1 11 24 5 21 135 5
2 15 1 12 33 5 22 143 12
3 15 1 13 45 6 23 142 19
4 15 1 14 50 5 24 148 21
5 15 1 15 60 6 25 146 23
6 17 1 16 65 5 26 149 22
7 16 2 17 70 6 27 147 24
8 18 3 18 90 5 28 148 26
9 20 3 19 110 5 29 150 26
10 23 4 20 125 6 30 149 25
31 150 25

a. Draw the breakthrough curves of chloride and potassium (i.e. a graph in which the
relative concentrations (= (C(t) – C(0))/(C – C(0)) are displayed as function of
max
time).
-1
b. Determine the water flow velocity in m d .
c. Assuming a linear Freundlich isotherm for K sorption, calculate the retardation factor
R and the distribution coefficient K .
f d
d. Calculate the amount of potassium that is adsorbed within the column.
The experiment is repeated to study the behaviour of nitrate.

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Soil and Water.indd 266