Applications of Chemical Kinetics in Environmental Systems - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 417

6.42 2 During a routine navigational dredging of a river, a 55-gallon drum con-
taining pure benzene was excavated. A small leak was observed through
a hole 10 cm 2 area on the top of the drum. How much benzene has been
lost to the river water by diffusion during the one year the drum has been
on the bottom sediment surface? The drum has a height of 100 cm.
6.43 2 Estimate the total volume of water required to remove a 3% residual
trichloroethylene (TCE) spill from 1 m 3 of an aquifer of porosity 0.3 and
organic carbon content of 1%. The density of TCE is 1.47 g/cm 3 and its
aqueous solubility is 1100 mg/L. Assume no retention of TCE on aquifer
solids.
6.44 2 Estimate the number of pore volumes required to reduce 99% of the
porewater concentration of the following contaminants from an aquifer
with 2% organic carbon content and a porosity of 0.4: 1,2-dichloroethane,
1,4-dichlorobenzene, biphenyls, and Aroclor-1242.
6.45 3 Compare the rates of emission to air of the following pesticides applied to a
surface soil at an average concentration of 10 μ g/g each. The soil porosity
is 0.6 with a 3% water saturation and organic carbon content of 3%. The
soil density is 2 g/cm 3 and the area of application is 1 ha.Assume a surface
mass transfer coefficient of 1 cm/s. Repeat your calculation for a saturated
surface soil of 10% water saturation: (a) lindane, (b) chloropyrifos, and (c)
p , p -DDT.
6.46 3 The groundwater source in Baton Rouge is high in Fe(II). The Central
Treatment Facility uses aeration to oxidize Fe(II) and precipitate as iron
oxy-hydroxide. The reaction rate is given in Section 5.8.1 (Chapter 5). The
observed rate constant is k = 1.6 × 10 − 7 L/mol min atm at the water pH
of 6.7. The oxygen concentration in water is to be kept at its saturation
value. If the oxidation reactor is a CSTR, what residence time is required
to reduce Fe(II) by 90% in the groundwater?
6.47 3 Emissions from wastewaters in petroleum refineries are categorized into
primary and secondary. Secondary sources of emissions are generally from
wastewater ponds. Before the water reaches a pond, streams from differ-
ent unit operations are mixed in a large vessel where air emissions can
be a problem. There is little or no chemical degradation in these vessels.
The only loss mechanism is mass transfer to the vapor space. Although
no aerators are placed, there is enough turbulence to mix the water. Use
a CSTR model to assess the rate of air emissions from a vessel in which
the inlet concentration of ethyl benzene is 1 × 10 − 5 g/mL at a flow rate
of 2 L/s. The vessel cross-sectional area is 1 m 2 .
6.48 2 Determine the number of pore volumes of air required for 99% removal
of chlorobenzene from the vadose zone of an aquifer. The total volume of
the aquifer is 1 m 3 . It has a porosity of 0.6, an organic carbon fraction of
0.02, and a bulk density of 1.4 g/cm 3 . The zone is 5% water saturated and
5% saturated with chlorobenzene.
6.49 2 On a clear, calm Monday evening (January 18, 1999), a tanker truck car-
rying 22 tons of liquid anhydrous ammonia rolled over as it was making
a sharp turn outside the Farmland Industries chemical plant in Pollock,
Louisiana. The liquid ammonia escaped through a valve. Assume that it
formed a 2500-m 2 pool and turned into gas as it went into the air. Estimate