Environmental Engineering Reference
In-Depth Information
3.5 1 Estimate the mean ionic activity coefficients of the following aqueous
solutions:
(a) 0.001 molal KCl; (b) 0.01 molal CaCl 2 ; and (c) 0.1 molal Na 3 PO 4 .
3.6 2 Consider a total evaluative environment of volume 10 × 10 10 m 3 with
volume fractions distributed as follows: air 99.88%; water 0.11%; soil
0.00075%; sediment 0.00035%; and biota 0.00005%. Consider two
compounds benzene and DDT (a pesticide) with properties as follows:
Property
Benzene
DDT
K aw (Pa m 3 /mol)
557
2.28
K sw (L/kg)
1.1
12,700
K bw (L/kg)
6.7
77,400
The temperature is 310 K and the densities of soil and sediment are
1500 kg/m 3 while that of the biota is 1000 kg/m 3 . Determine the concen-
trations and mass of each compound in the various compartments using
the fugacity level I model. Comment on your results.
3.7 2 Confined disposal facilities (CDFs) are storage facilities for contaminated
sediments. Being exposed to air, the contaminated sediment is a source of
VOCs to the atmosphere. Consider a two-compartment evaluative environ-
ment of volume 5 × 10 5 m 3 , with the following volume fractions: air 60%
and sediment 40%. Consider benzene for which K aw = 557 Pa m 3 /mol
and K sw = 5 L/kg. If the temperature is 298 K, and the density of sedi-
ment is 1200 kg/m 3 , determine the mass fraction of benzene in air using
the fugacity level I model.
3.7 3 Mercury exists in the environment in a variety of forms. Organic mer-
cury exists predominantly as dimethyl mercury, (CH 3 ) 2 Hg which is easily
assimilated by the biota. Hence fish in the lakes of several states in the
United States are known to contain high concentrations of Hg. Dimethyl
mercury has the following properties: K aw = 0.31 (molar concentration
ratio), K sw = 7.5 L/kg, K bw = 10 L/kg. Consider an evaluative environ-
ment of 10 9 m 3 of air in contact with 10 5 m 3 of water in a lake containing
10 3 m 3 ofsedimentand10 m 3 ofbiota.Thesedimentdensityis1000 kg/m 3
and that of biota is 1500 kg/m 3 .
(a) What is the fraction accumulated by the biota in the lake? Use the
fugacity level I model.
(b) If an influent feed rate of 100 m 3 /h of air with a concentration of
0.1 mol/m 3 is assumed, calculate the fraction assimilated by the biota
using the fugacity level II model.
3.8 3 Dimethylsiloxane (DMS) is a prevalent compound in various soaps, sham-
poos, and shaving creams. It is expected to pose problems when it gets
into the natural environment through sewage and eventually distributes
to all compartments. Consider a 100 m 2 area of sewage treatment unit
that contains 10 m height of atmosphere above 1 m of a water column
at 300 K. The water contains 5% by volume of solids and 10% by vol-
ume of bioorganisms. Consider the following properties: Henry's constant
 
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