8.31 (a) Use the Internet to research the number of people in the world who do not have access
to an improved water supply. Then look up the Millennium Development Goals (MDGs) at the
United Nations Web site, www.un.org. MDG 7 states that by 2015 the world will decrease by
half the number of people without access to an improved water supply. Select a country in Africa
and another country in Asia or Latin America. Compare the progress of these two countries in
meeting goal 7 in terms of the number of people still not served by an improved water supply.
Solution:
8.32 What is the source of drinking water in the town where you currently live (groundwater,
surface water, reclaimed water, or a mixture)? Sketch the unit processes used to treat this water
in order of occurrence as currently practiced. What water constituent(s) does each unit process
remove?
Solution:
Students’ responses will vary.
8.33 Identify three significant water users in your town or city that could benefit from the use of
reclaimed water. What economic, social, and environmental challenges do you see that might
need to be overcome before you can implement your plan for these users to use reclaimed water?
What would you do as engineer to overcome these barriers?
Solution:
Students’ responses will vary.
8.34 A city is upgrading its water supply capacity to 81,378 m3/day, using microfiltration. The
new plant membrane system will consist of 25 arrays with 90 modules per array. The modules
have an inside diameter of 120 mm, a length of 1,200 mm, and an available surface area of 30
m2. The membranes have an outside diameter of 1.0 mm, and a length of 1,200 mm. Determine:
(a) the total surface area available for filtration, (b) the membrane flux rate in L/m2•hr, and (c)
the total number of membrane fibers required for the plant and each module.
Solution:
a)
2
2
Total 90 mod ules 30 m
f
8.35 A municipality uses a microfiltration membrane system to treat 35,000 m3/day. The
membrane system consists of nine arrays with 80 modules per array. The modules are 119 mm in
inside diameter and 1,194 mm in length, and have an available filtration surface area of 27 m2.
Determine the (a) total surface area available for filtration, and (b) membrane flux rate in
L/m2•hr and gpm/sq. ft.
Solution:
8.36 Atrazine and trichloroethylene can be removed from water by adsorption to activated
carbon. The Freundlich parameters for atrazine are K = 182 mg/g (L/mg)1/n and 1/n = 0.18.
The parameters for trichloroethylene are K = 56 mg/g (L/mg)1/n and 1/n = 0.48. What is the
adsorbed concentration of both contaminants (units of mg chemical per gram of activated
carbon) if you want the aqueous phase concentration at equilibrium to be 10 µg/L? (this problem
may require you review information presented in Chapter 3).
Solution:
8.37 A methyl tert butyl ether (MTBE) adsorption isotherm was performed on an activated
carbon at 15 ºC using 0.250-L amber bottles with an initial MTBE concentration, Co, of 150
mg/L. The isotherm data for each experimental point is summarized below. Calculate the
adsorbed-phase concentration, qe, for each isotherm point, plot the log (qe) versus log (Ce) and
determine the Freundlich isotherm parameters K and 1/n (this problem may require you review
information presented in Chapter 3).
Mass of GAC, g
MTBE equilibrium liquid–phase
concentration, Ce, mg/L
0.155
79.76
0.339
42.06
0.589
24.78
0.956
12.98
1.71
6.03
2.4
4.64
2.9
3.49
4.2
1.69
Solution:
o
e
MC
VC
placedinbottle equilibrition equilibritio
e
Mq
n
y = 0.6906x + 0.761
R
2
= 0.995
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0
Equilibrium liquid-phase concentration, mg/L
Equilibrium adsorbed-phase
concentration,mg/g
8.38 Powdered activated carbon (PAC) is to be added to a water treatment plant to remove 10
ng/L of MIB which is causing odor problems in the finished water. A standard jar test is
performed to evaluate the impact of PAC dosage on the removal of MIB. The results are shown
Figure 8.26. If 60 percent MIB removal is required, determine the dosage of PAC required and
quantity of PAC needed for 3 months (90 days) of treatment if the plant flow rate for is 40,000
m3/d.
Figure 8.26. Results from Jar Test Investigating Powdered Activated Carbon Usage at a Water
Treatment Plant.
Solution:
0
10
20
30
40
50
60
70
010 20 30 40 50 60
PAC Dosage (mg/l)
MIB Removed (%)
( )
= × ×× ×
=
3
36
Mass 44 mg PAC 1,000 L kg 40,000 m
PAC 90day
L day
m 10 mg
r equired
158,400 kg
8.39 Reverse osmosis is used to treat brackish groundwater water and requires 1 kWh of energy
per 1 m3 of treated water. In comparison, reverse osmosis of seawater requires 4 kWh of energy
per 1 m3 of treated water (this difference is because of the higher TDS concentration of
seawater). According to eGRID, the carbon dioxide equivalent emission rate is 1,324.79 lb
CO2e/MWh in Florida and 727.26 lb CO2e/MWh in California. Estimate the carbon footprint of
using reverse osmosis to desalinate 1 m3 brackish groundwater and 1 m3 sea water in Florida and
California. Ignore line losses in your estimate (you may have to go back to Chapter 2 to review
carbon footprints and eGRID).
Solution:
8.40 Fill in the rest of this table, providing the electricity requirements to treat 1 MDG of treated
water. Fill in the carbon footprint assuming the treatment plant is located in California.
According to eGRID, the carbon dioxide equivalent emission rate is 727.26 lb CO2e/MWh in
California. (you may have to review Chapter 2 for information on carbon footprints and
eGRID).
Solution:
