c. From Eq. (2.56), the methanogenic reaction occurring is:
43. From Eq. (2.41):
Alk ¼CBCA
Given that the concentrations of base cations are assumed
negligible, the above equation can be written:
a. If plants take up half of the nitric acid:
b. When the water acquires 210
4
mol/liter of Ca
2þ
from mineral
weathering, the alkalinity will increase (i.e., become less negative):
e53CHAPTER 2 SOLUTIONS
c. If the remaining nitrate is denitrified and half the sulfate is reduced
to sulfide, which is not considered further, then the new Alk can be
estimated as:
44. The peak concentration in the stream can be estimated using
Eq. (2.12). First estimate the pseudo-first-order decay rate due to
base-catalyzed hydrolysis using Eq. (2.89):
Next, estimate the stream area using Eq. (2.4):
Then use Eq (2.12) to estimate C
max
:
45. a. The flux of NO3can be estimated using Fick’s first law (Eq. 1.3):
e54 SOLUTIONS MANUAL ONLINE
b. Assuming that the thin film model is appropriate for a lake, the
gas exchange coefficient for benzene can be estimated from
Eq. (2.32):
46. a. The pesticide concentration at a point 1.3 km downstream 1 hr
after the spill can be estimated using Eq. (2.12). First use Eq. (2.3a)
to estimate travel time:
Then use Eq. (2.12):
47. a. Given that the rate of decrease of 0.07 ppm/day seems to be
constant for several days, O
2
consumption by bacteria is
b. The benthic oxygen demand is the difference between the total rate
e55CHAPTER 2 SOLUTIONS
48. The total mass of methylmercury in the lake can be described as:
Given the mass of fish and the water volume:
Therefore:
Half the methylmercury in the lake is in fish tissue.
49. The approximate age of the charcoal layer can be estimated from
Eq. (2.25):
50. a. First, estimate the river velocity from Eq. (2.4):
Second, estimate the travel times to the municipal water intakes
using Eq. (2.3a):
e56 SOLUTIONS MANUAL ONLINE
Third, estimate the rate of photolysis using Eq. (1.21):
Peak concentrations of malathion can then be estimated using
Eq. (2.12):
b. Without photolysis (i.e., ignoring the e
kt
term), C
max,1km
¼
0.87 kg/m
3
and C
max,15km
¼0.22 kg/m
3
.
c. At pH 9, the concentration of OH
is 10
5
M. Setting the photolysis
rate equal to a pseudo-first-order rate for base-catalyzed
hydrolysis gives:
51. a. To estimate when the maximum concentration of dye will appear
b. Use Eq. (2.7) to estimate the longitudinal dispersion coefficient:
e57CHAPTER 2 SOLUTIONS
c. The dye concentration at point B at this time can be estimated from
Eq. (2.12):
d. The advective flux of the dye can be estimated from Eq. (1.2a):
52. The following problems are solved based on the information in
Section 2.4.3, Half-Reactions and Oxidation States.
53. a. Given that this is pure water and there are no strong acids or bases
b. CT¼3104Mþ104M¼4104M
c. The presence of nitric acid will affect the alkalinity:
54. 0.001 MC
6
H
12
O
6
is equivalent to 0.006 MCH
2
O. The CH
2
O will
e58 SOLUTIONS MANUAL ONLINE
55. To estimate the concentration of TeCB in rainbow trout, a BCF must be
estimated. In Table 2.9, the first regression equation uses log K
ow
and
was derived in part based on rainbow trout:
56. a. The rate of hydrolysis for the substituted phenyl acetate can be
estimated from Eq. (2.89) as:
b. First estimate the cross-sectional area of the river from Eq. (2.4):
e59CHAPTER 2 SOLUTIONS
57. a. At a pH of 8, the bicarbonate ion dominates. Use Eq. (2.43) to
estimate the concentration of H2CO3:
e60 SOLUTIONS MANUAL ONLINE
58. a. First calculate the total moles of inorganic carbon in the air, using
Eq. (1.25) to convert PCO2to a concentration and then multiplying
b. Using Eq. (2.43):
c. First calculate C
T
for the water. Ignoring carbonate ion, given the pH:
d. Assuming the dry weight of the dog is predominantly CH
2
O,
estimate the moles of CO
2
produced during mineralization:
e61CHAPTER 2 SOLUTIONS
e. To counteract the CO
2
effect, the alkalinity must be increased.
Using the Deffeyes diagram (Fig. 2.20), a C
T
value of 6.1 10
4
M
f. The Epsilon III system as described has an inadequate amount of
inorganic carbon to make the system resistant to disturbances. The
59. a. First, estimate the concentration of toluene above the spill, using
Eq. (2.38). Assume a temperature of 25 C in the air duct:
e62 SOLUTIONS MANUAL ONLINE
b. If the blower is turned up to increase the air velocity to 2 m/sec, the
gas exchange coefficient will increase (Eq. 2.36 (or Eq. 2.35)):
Thus, the concentration of toluene far downstream of the glue
spill under this blower rate is actually the same as under the
previous blower rate:
c. The gas exchange coefficient can be estimated as the ratio of the
60. a. Given an approximate PCO2in the atmosphere of 10
3.4
atm, use
Eqs. (2.42) and (2.43); at a pH of 5.2, [CO32] can be neglected.
e63CHAPTER 2 SOLUTIONS
b. The fermentation of sugar to ethanol can be qualitatively
represented as:
c. First determine the moles of CO
2
produced per mole of ethanol
produced by considering the oxidation states of carbon in the
fermentation reaction. In CH
2
O, carbon is in the (0) oxidation state.
In CO
2
, carbon is in the (þIV) oxidation state. In ethanol:
61. a. Reduction of Fe (þIII) to Fe (þII) requires 1 eq electrons per mole of
iron reduced. The oxidation of CH
O yields 4 eq of electrons per
e64 SOLUTIONS MANUAL ONLINE
b. From the fourth equation in Table 2.6:
c. Assume a molecular diffusion coefficient of 10
5
cm
2
/sec. Using
Fick’s first law in Eq. (1.3):
62. a. From inspection of the Deffeyes diagram in Fig. 2.20, one can
conclude that pH 4 will be reached when Alk is 10
4
eq/liter; pH
is essentially independent of C
in this pH range. (This conclusion
e65CHAPTER 2 SOLUTIONS
b. First calculate the mass of added acid per depth:
c. At the sediment-water interface, given the lake volume of
d.
2
e. The partial pressure of H
2
S in air at equilibrium with aqueous H
2
S
is:
e66 SOLUTIONS MANUAL ONLINE