Environmental Engineering Reference
In-Depth Information
6.6 3 On November 1, 1986, a fire in a chemical warehouse near Basel, Switzer-
land caused the release of 7000 kg of an organo-phosphate ester (pesticide)
into the river Rhine. Assuming that the river is in plug flow, determine the
concentration of the pesticide detected near Strasbourg, which is 150 km
from Basel. The relevant chemical properties of the pesticide are as fol-
lows: First-order rate constant for reaction in water = 0.2 d 1 , first-order
rate constant for reaction on sediment = 0.2 d 1 , the sediment-water par-
tition constant
200 L/kg. River Rhine has an average volumetric flow
rate of 1400 m 3 /s, a solids concentration of 10 mg/L, a resuspension rate
of 5 × 10 5 d 1 , a total cross-sectional area of 1500 m 2 , and an average
water depth of 5 m.
6.7 3 A CSTR box model can be useful in estimating pollutant deposition onto
indoor surfaces.
(a) Consider a living room of total volume V and total internal sur-
face area A onto which ozone deposition occurs. Let V d rep-
resent the deposition velocity; it is defined as the ratio of the
flux to the surface ( μ g/m 2 s) to the average concentration in air
( μ g/m 3 ). Outside air with ozone concentration C o exchanges with
the indoor air through vents at a known rate R exc . At steady state
what will be the value of V d for 75% deposition of ozone in
a room that is 5 m × 5m × 2.5 m, if R exc = 5 L/min and C o =
75 ppb? Experimental values range from 0.001 to 0.2 cm/s. What
are the possible sources of such wide distributions in experimental
values?
(b) A home near a chemical plant has a total internal volume of 300 m 3 .
The normal air exchange between the indoor and outdoor occurs at a
rateof0.1 h 1 .Anepisodicreleaseofachlorinatedcompound(1,1,1-
trichloroethane, TCA) occurred from the plant. The concentration
of TCA was 50 ppbv in the released air. If the normal background
concentration of TCA is 10 ppbv, how long will it take before the
concentration inside the room reaches a steady-state value?
6.8 3 Consider a beaker of water in equilibrium with CO 2 in the air (partial
pressure P CO 2 ). The pH of the water is made slightly alkaline so that the
dissolution of CO 2 in water is enhanced.The solution process is controlled
bydiffusionandreactioninthestagnantboundarylayerofthickness δ .CO 2
undergoes two competing reactions in water:
=
H 2 O k 1
HCO 3
H + .
(a) Dissolution in water: CO 2 +
+
k 2
HCO 3 .
(i) Obtain first the amount of CO 2 in the boundary layer at any time
t and the flux to the surface. The ratio of the two will give the
time constant for diffusion in the boundary layer.
(ii) Assume that only the two forward reactions are of importance
and write down the reaction rate equation for the dissolu-
tion/reaction of CO 2 in water. The reciprocal of the first-order
rate constant (at constant pH) is the time constant for reaction
in the boundary layer.
(b) Reaction with OH :CO 2 + OH
 
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