Applications of Chemical Kinetics in Environmental Systems - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 419

Section 4.2.1) to given r = 3.6 × 10 6

θ L rRT , where the units of r are ppbv
SO 2 h − 1 and R is the universal gas constant.
6.54 2 Hurricane Katrina flooded several New Orleans homes in 2005. Contam-
inated sediments from Lake Ponchartrain remained as a cake and finally
dried out in abandoned homes once the floodwater receded. These sedi-
mentsarelikelytobesourcesofvaporsoforganiccompoundstotheindoor
air. Consider a 20 m long × 20 m wide × 5 m high room where the air flow
velocity is only 10 m/h.Assume that the emission rate of the organic vapor
from the sediment to air is 100 ng/m 2 /h.Assume also that the organic vapor
degrades in the indoor air with a first-order rate constant of 10 h − 1 and
also that the fresh air entering the room has only negligible organic vapor
in it.
(a) Perform a mass balance on the organic vapor in the room and write
the unsteady mass balance differential equation.
(b) Apply the steady-state approximation to obtain the concentration of
the organic in air.
(c) For the data given above calculate the steady-state concentration.
Express your answer in ng/m 3 .
6.55 3 A pool of pure benzene of area 0.4 m 2 exists at the bottom of a lake of
volume 1000 m 3 . The volumetric flow rate of water in the lake is 50 L/s.
If the average mass transfer coefficient ( k mt ) for the dissolution of pure
benzene into water is 0.1 m/s, determine the concentration in the outflow
from the lake after 12 h of the spill. The solubility of benzene in water is
780 mg/L. Assume that the lake is well mixed and initial concentration of
benzene is zero.
6.56 2 Estimate the volume of a bioreactor required to achieve a yield of 0.5 of E .
coli bacteriausing20 mg/Lofanactivatedsludgeintheinfluentstreamofa
continuous reactor.The desired flow rate of the sludge is 10 m 3 /d.The bac-
terium follows Monod kinetics with K s = 10 mg/L and μ max = 10 d − 1 .
The bacterial decay constant is 2 d − 1 . It is desired to maintain the bacterial
population at 5 mg/L through the day. Give the answer in m 3 .
6.57 3 Air enters a room (5 m × 5m × 8 m) at a velocity of 1 m/h and carries
a gaseous pollutant at a concentration of 10 μ g/m 3 . An open-hearth fur-
nace in the room generates the same pollutant at a rate of 24 μ g/m 2 /h. The
pollutant, however, undergoes a zeroth-order reaction in the room with a
rate constant of 1 μ g/m 3 /h.
(a) Write down the appropriate unsteady-state mass balance equation for
the pollutant in the room.
(b) Solvetheaboveequationtoobtainconcentrationasafunctionoftime.
(c) What is the pollutant concentration leaving the room 1 h after the start
of the open-hearth furnace?
6.58 1 State whether the following statements are true or false. Give brief
explanations.
1. In an enzyme reactor we have to continuously provide enzymes
externally for the reaction to proceed.
2. An organic pollutant will travel faster in a water-saturated column
filled with soil than in a column filled with sand.
3. In the lower atmosphere, smog appears when the sunlight is at its
highest intensity and VOC concentration is lowest.