Water and Wastewater Engineering
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14-40 WATER AND WASTEWATER ENGINEERING
Manufacturer
K 1/n
A6.3 0.37
B 8.7 0.45
K is in units of (mg/g)(L/mg).
14-15 DISCUSSION QUESTIONS
14-1. A community of 70,000 has solicited proposals for a lime-soda softening plant to
treat their groundwater. Your company has proposed air stripping CO
2
as one of the
process steps. The city engineer has asked why CO
2
has to be removed as it does not
contribute to hardness. Explain.
14-2. One of the treatment alternatives for removing iron and manganese from a ground-
water is NF. To use this process, the raw water must not have any dissolved oxygen
in it. Explain why.
14-3. Explain why a GAC column cannot be designed based on the re
sults from an iso-
therm experiment to determine the Freundlich constants.
14-16 REFERENCES
AWWA (1990) Water Treatment Plant Design, 2nd ed. American Water Works Association, Denver,
Colorado, McGraw-Hill, New York, pp. 68–74.
AWWA (2004) Water Fluoridation Principles and Practices, American Water Works Association
Manual of Practice M4, Denver, Colorado.
AwwaRF (2000) Arsenic Trextability Options and Evaluation of Residuals Management Issues, Awwa
Research Foundation, Denver, Colorado.
AwwaRF (2002) Implementation of Arsenic Treatment Sys
tems-Part 1. Process Selection, Awwa
Research Foundation, Denver, Colorado.
Ball, B. R. and M. D. Edwards (1992) “Air Stripping VOCs from Groundwater: Process Design
Considerations,” Environmental Progress, vol. 11, no. 1, pp. 39–48.
Brady, R. D. (2005) “Activated Carbon Processes,” in E. E Baruth (ed.), Water Treatment Plant Design,
McGraw-Hill, New York, pp. 14.1–14.38.
Clark, R. M. and B. W Lykins (1989) Granular Activated Carbon: Design, Operation, and Cost,
Lewis
Publishers, Chelsea, Michigan.
Clifford, D. A. (1999) “Ion Exchange and Inorganic Adsorption,” in R. D. Letterman (ed.), Water Quality
and Treatment, 5th ed. American Water Works Association, McGraw-Hill, New York, pp. 9.1– 9.91.
Cook, P. (2005) “Arsenic Removal Technologies for Drinking Water Treatment,” Emerging Issues in
Water Treatment, Michigan Section of American Water Works Association Research and Technical
Practice Seminar, Lansing, Michigan, May 17.
Cook, P. (2007) Michigan Department of Environmental Quality, personal communication.
Crittenden, J. C. et al. (1987) “Design of Rapid Fixed-Bed Adsorption Tests for Nonconstant Diffusivities,”
Journal of Environmental Engineering Division, vol. 113, no. 2, pp. 243–259.
C ulp, R. L. and G. L. Culp (1971) Advanced Wastewater Treatment, Van Nostrand Reinhold, New York,
pp. 145–157.
C u
lp, R. L., G. Wesner, and G. L. Culp (1978) Handbook of Advanced Wastewater Treatment, Van
Nostrand Reinhold, New York, p. 185.
REMOVAL OF SPECIFIC CONSTITUENTS 14-41
Djebbar, Y. and R. M. Narbaitz (1995) “Mass Transfer Correlations for Air Stripping Towers,”
Environmental Progress, vol. 14, no. 3, pp. 137– 145.
Dobbs, R. A. and J. M. Cohen (1980) Carbon Adsorption Isotherms for Toxic Organics, U.S.
Environmental Protection Agency, Publication No. EPA-600/8-80-023, Cincinnati, Ohio.
Drewes, J. E., C. Bellona, M. Oedekoven, P. Xu, et al. (2005) “Rejection of Wastewater-Derived
Micropollutants in High-Pressure Membrane Applications Leading to Indirect Potable Reuse,”
Environmental Progress, vol. 24, no. 4, pp. 400–415.
Dvorak, B. I. and
M. K Maher (1999) “GAC Contactor Design for NOM Removal: Implications of EBCT
and Blending,” Journal of Environmental Engineering, vol. 125, no. 2, pp. 161–165.
D yksen, J. E. (2005) “Aeration and Air Stripping,” in E. E. Baruth (ed.), Water Treatment Plant Design,
American Water Works Association and American Society of Civil Engineers, McGraw-Hill, New
York, p. 5.1–5.24.
E ckert, J. S. (1961) “Design Techniques for Sizing Packed Towers,” Chemical Engineering Progress,
vol. 57, no. 9, pp. 54–58.
Fields, K., A. Chen, and L. Wans (2000) Arsenic Removal from Drinking Water by Iron Removal Plants,
U.S. EPA 600R00063, Washington, D.C.
Fornwalt, H. J. and R. A. Hutchins (1966) “Purifying Liquids with Activated Carbon,” in Chemical
Engineering, vol. 73, no. 8, pp. 179–184.
FR (1989) Federal Register 54 FR 22062.
Freundlich, H. (1906) “Über die Adsorption in Lösungen,” Z. Phys. Chem. A, vol. 57, pp. 385
–470.
Ghurye, G. and D. A. Clifford (2001) Laboratory Study on Oxidation of As(III) to As(V), U.S.
Environmental Protection Agency Publication EPA 600-R-01-021, Washington. D.C.
GLUMRB (2003) Recommended Standards for Water Works, Great Lakes–Upper Mississippi River
Board of State and Provincial Public Health and Environmental Managers, Health Education
Services, Albany, New York, pp. 75–77, 82.
Graham, M., I. Najm, M. Simpson, B. MacLeod et al. (2000) Optimization of Powdered Activated
Carbon Application for Geosmin and MIB Removal, American Water Works Association Research
Foundation, Denver, Colorado.
Gross, R. L. and S. G. TerMaath (1985) “Packed Tower Aeration Strips Trichloroethene from
Groundwater,” Environmental Progress, vol. 4, no. 2, pp. 119–124.
G u, B., Y. K. Ku, and G. M. Brown (2005) “Sorption and Desorption of Perchlorate and U(VI) by
Strong-Base Anion Exchange Resins,” Environmental Science and Technology, vol. 39, no. 3,
pp. 901–907.
Hand, D. W., J. C. Crittenden, J. L. Gehin, and B. W. Lykins (1986) “Design and
Evaluation of an
Air-Stripping Tower for Removing VOCs from Groundwater,” Journal of American Water Works
Association, vol. 78, no. 9, pp. 87–97.
Hand, D. W., D. R Hokanson, and J. C. Crittenden (1999) “Air Stripping and Aeration,” in R. D.
Letterman (ed.), Water Quality and Treatment, 5th ed. American Water Works Association,
McGraw-Hill, New York, pp. 5.1–5.68.
H uang, C., J. E. Van Benschoten, and J. N. Jensen (1996) “Adsorption Kinetics of MIB and Geosmin,”
Journal of American Water Works Association, vol. 88, no.4, pp. 116–128.
H ullman, R. (2009) Fate of Pharmaceuti
cals in Drinking Water Utilities, M.S. thesis, Michigan State
University.
Kavanaugh, M. C. and R. R. Trussel (1980) “Design of Aeration Towers,” Journal of American Water
Works Association, vol. 72, no. 12, pp. 684–692.
Kawamura, S. (2000) Integrated Design and Operation of Water Treatment Facilities, 2nd ed. John Wiley
& Sons, New York, pp. 523.
LaGrega, M. D., P. L. Buckingham, and J. C. Evans (2001) Hazardous Waste Management,
McGraw-Hill, Boston, Massachus
etts, pp. 463–476.
14-42 WATER AND WASTEWATER ENGINEERING
Lowery, J. D. and S. B Lowery (1988) “Radionuclides in Drinking Water,” Journal of American Water
Works Association, vol. 80, no. 7, pp. 50–64.
MWH (2005) Water Treatment: Principles and Design, John Wiley & Sons, Hoboken, New Jersey,
pp. 1194, 1220, 1222, 1330–1339, 1522–1526, 1568–1592.
Nghiem, L. D., A. I. Schäfer, and M. Elimelech (2004) “Removal of Natural Hormones by Nanofiltration
Membranes: Measurement, Modeling, and Mechanisms,” Envi
ronmental Science & Technology,
vol. 38, no. 6, pp. 1,888–1,896.
Nghiem, L. D., A. I. Schäfer, and M. Elimelech (2005) “Pharmaceutical Retention Mechanisms by
Nanofiltration Membranes,” Environmental Science & Technology, vol. 39, no. 19, pp. 7,698–7,705.
NSF (2001a) Environmental Technology Verification Report: Removal of Arsenic in Drinking Water—
Hydranautics ESPSA2-4040 Reverse Osmosis Membrane Element Module, NSF International 0120
EPADW395.
NSF (2001b) Environmental Technology Verification Report: Removal of Arsenic i
n Drinking Water—
KOCH Membrane Systems TFC-ULP4 Reverse Osmosis Membrane Module, NSF International 0125
EPADW395.
Perry, R. H. and C. H. Chilton (1973) Chemical Engineer’s Handbook, p. 18–44.
Reynolds, T. D. and P. A. Richards (1996) Unit Operations and Processes in Environmental Engineering,
PWS Publishing, Boston, Massachusetts, p. 353–355.
Rizzo, R. L. and A. R. Sheperd (1977) “Treatment of Industrial Wastewater with Activated Carbon,”
Chemical Engineering,
vol. 84, no. 1, pp. 95–100.
Rosenfeldt, E. J. and K. G. Linden (2004) “Degradation of Endocrine Disrupting Chemicals Bisphenol
A, Ethinyl Estradiol, and Estradiol During UV Photolysis and Advanced Oxidation Processes,
Environmental Science and Technology, vol. 38, pp. 5,476–5,483.
Rubel, F. (2001) Design Manual–Removal of Arsenic from Drinking Water Supplies by Ion Exchange,
U.S. EPA Draft Document, Washington, D.C.
Rubel, F. (2003) Design Manual–Removal of Arsenic from Drinking Water Supplies by Adsorptive Media,
EPA 600-R-03-019, Washington, D.C.
R ubel, F. and R. D. Woosley (1979) “The Removal of Excess Fluoride from Drinking Water by Activated
Alumina,” Journal of American Water Works Association, vol. 71, no. 1, p. 45.
S cott, G. R. (1955) “Committee Report: Aeration of Water,” Journal of American Water Works
Association, vol. 44, no. 4, p. 873
.
Sommerfeld, E. O. (1999) Iron and Manganese Removal Handbook, American Water Works Association,
Denver, Colorado.
S uffet, I. H., A. Corado, D. Chou, M. J. McGuire et al. (1996) “AWWA Taste and Odor Survey,” Journal
of American Water Works Association, vol. 88, no. 4, 168–180.
Ternes, T. A., M. Meisenheimer, D. McDowell, F. Sacher et al. (2002) “Removal of Pharmaceuticals
During Drinking Water Treatment,” Environmental Science & Technology, vol. 36, no. 17,
pp. 3,855–3,863.
Treybal, R. E (1980)
Mass Transfer Operations, 3rd ed., McGraw-Hill, New York.
Tripp, A. R. and D. A. Clifford (2006) “Ion Exchange for the Remediation of Perchlorate-Contaminated
Drinking Water,” Journal of American Water Works Association, vol. 98, no. 4, pp. 105 – 114.
U.S. EPA (1971) Process Design Manual for Carbon Adsorption, U.S. Environmental Protection
Agency.
U.S. EPA (2000) Technologies and Costs for Removal of Arsenic from Drinking Water, EPA 815R00028,
Washington, D.C.
U.S. EPA (2002) Implementation Guidance for the Arsenic Rule–Drinking Water Regulations for Arsenic
and Clarifications to Compliance and New Source Contaminants Monitor
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Environmental Protection Agency Publication EPA 816-R-03-014, Washington. D.C.
REMOVAL OF SPECIFIC CONSTITUENTS 14-43
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Technologies, U.S. Environmental Protection Agency Publication No. 816RO5004.
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15-1
15-8 MANAGEMENT OF LIQUID RESIDUALS
15-9 DISPOSAL OF SPECIFIC RESIDUAL
CONSTITUENTS
15-10 ULTIMATE DISPOSAL
15-11 CHAPTER REVIEW
15-12 PROBLEMS
15-13 DISCUSSION QUESTIONS
15-14 REFERENCES
WATER PLANT RESIDUALS MANAGEMENT
15-1 INTRODUCTION
15-2 SOLIDS COMPUTATIONS
15-3 SOLIDS PRODUCTION
AND CHARACTERISTICS
15-4 MINIMIZATION OF RESIDUALS
GENERATION
15-5 RECOVERY OF TREATMENT CHEMICALS
15-6 RESIDUALS CONVEYANCE
15-7 MANAGEMENT OF SLUDGES
15
CHAPTER
15-2 WATER AND WASTEWATER ENGINEERING
15-1 INTRODUCTION
The precipitated chemicals and other materials removed from raw water to make it potable and
palatable are termed residuals. Satisfactory treatment and disposal of water treatment plant
residuals can be the single most complex and costly operation in the plant.
Residuals withdrawn from coagu
lation and softening plants are composed largely of water,
and the residuals are often referred to as sludge. A s much as 98 percent of the sludge mass may
be water. Thus, for exam ple, 20 kg of solid chemical precipitate is accompanied by 980 kg of
water. Assuming equal densities for the precipitate and
water (a bad assumption at best), approxi-
mately 1 m
3
of sludge is produced for each 20 kg of chemicals added to the water. For even a
small plant (say 4,000 m
3
/ d) this might mean up to 800 m
3
/ y of sludge.
Water treatment plants and the residuals they produce can be broadly divided into four gen-
eral categories. First are those treatment plants that coagulate, filter, and oxidize surface water for
removal of turbidity, color, bacteria, algae, some organic compounds, and s
ometimes iron and/or
manganese. These plants generally use alum or iron salts for coagulation and produce two waste
streams. The majority of the waste produced from these plants is sedimentation basin (or clari-
fier) sludge and spent filter backwash water (SFBW). The second type of treatment plants are
those that practice softening for the removal of calcium and magnesium by the addition of lime,
sodium hydroxide, and/or soda ash. These plants produce clarifier basin sludges and SFBW. On
occasion, plants practice both coagulation and softening. Softening plant wastes c
an also contain
trace inorganic compounds such as radium that could affect their proper handling. The third type
of plants are those that are designed to specifically remove trace inorganic compounds such as
nitrate, fluoride, radium, arsenic, and so on. These plants
use processes such as ion exchange,
nanofiltration, and reverse osmosis. They produce liquid residuals ( concentrate) or solid residu-
als such as spent ion exchange resin. The fourth category of treatment plants includes those that
produce air-phase residuals
during the stripping of volatile compounds. The major types of treat-
ment plant residuals produced are shown in Table 15-1 .
Most of the coagulants and the impurities they remove settle to the bottom of the settling
basin where they become part of the sludge. These sludges are referred to as alu m, iron, or
polymeri
c sludge according to which primary coagulant is used. These wastes account for
approximately 70 percent of the water plant residuals generated in the United States. The sludges
produced in treatment plants where water softening is practiced using lime or lime and soda as
h
account for an additional 25 percent of the industry’s residuals production. It is therefore appar-
ent that most of the waste generation involves water treatment plants using coagulation or soften-
ing processes. Because 95 percent of the residuals produced are c oagulants or softening sludge,
they will be stress
ed in this chapter.
The most logical residual management program attem pts to use the following approach in
sludge disposal:
1 . Minimization of residual generation.
2. Recovery of treatment chemicals.
3. Residual treatment to reduce volume.
4. Ultimate disposal in an environmentally
safe manner.
With a short digression to explain some fundamental solids computations and to identify the sources
of water plant residuals and their production rates, this chapter is organized along these lines.
WATER PLANT RESIDUALS MANAGEMENT 15-3
15-2 SOLIDS COMPUTATIONS
Volume-Mass Relationships
Because most water treatment plant (WTP) sludges are primarily water, the volume of the sludge
is primarily a function of the water content. Thus, if the percent solids and the specific gravity
of the solids are known, one can estimate the volume of the sludge. The solid matter in water
treatment (and wastewater treatment) slud
ge is composed of fixed (mineral) solids and volatile
(organic) solids. The volume of the total mass of solids may be expressed as
M
S
s
s
V
(15-1)
where M
s
mass of solids, kg
S
s
specific gravity of solids
density of water 1,000 kg/m
3
Because the total mass is composed of fixed and volatile fractions, Equation 15-1 may be rewritten as:
M
S
M
S
M
S
s
s
f
f
v
v
(15-2)
where M
f
mass of fixed solids, kg
M
v
mass of volatile solids, kg
S
f
specific gravity of fixed solids
S
v
specific gravity of volatile solids
Solid/Liquid Residuals
1. Alum sludges
2. Iron sludges
3. Polymeric sludges
4. Softening sludges
5. Spent filter backwash water
6. Spent granular activated carbon or powdered activated carbon
7. Slow sand filter cleaning residue
8. Residuals from iron and manganese removal plants
9. Spent precoat filter med
ia
Liquid-Phase Residuals
10. Ion exchange regenerant brine
11. Waste regenerant from activated alumina
12. Nanofiltration/reverse osmosis concentrate
13. MF and UF membrane concentrate
Gas-Phase Residuals
14. Air stripping off-gases
15. Ozone off-gas
TABLE 15-1
Major water treatment plant residuals
15-4 WATER AND WASTEWATER ENGINEERING
The specific gravity of the solids may be expressed in terms of the specific gravities of the fixed
and solid fractions by solving Equation 15-2 for S
s
:
SM
SS
MS MS
ss
fv
fv vf
⎡
⎣
⎢
⎤
⎦
⎥
(15-3)
The specific gravity of sludge ( S
sl
) may be estimated by recognizing that, in a similar fashion
to the fractions of solids, the sludge is composed of solids and water so that
M
S
M
S
M
S
sl
sl
s
s
w
w
(15-4)
where M
sl
mass of sludge, kg
M
w
mass of water, kg
S
sl
specific gravity of sludge
S
w
specific gravity of water
It is customary to report solids concentrations as percent solids, where the fraction of solids ( P
s
)
is computed as
P
M
MM
s
s
sw
(15-5)
and the fraction of water ( P
w
) is computed as
P
M
MM
w
w
sw
(15-6)
Thus, it is more convenient to solve Equation 15-1 in terms of the solids fraction. If each term in
Equation 15-4 is divided by ( M
s
M
w
) with the recognition that M
sl
M
s
M
w
, then Equation
15-4 may be expressed as
1
S
P
S
P
S
sl
s
s
w
w
(15-7)
If the spec ific gravity of water is taken as 1.0000, as it can be without appreciable error, then
solving for S
sl
yields
S
S
PSP
sl
s
ssw
()( )
(15-8)
With these expressions, the volume of sludge ( V
sl
) can be calculated with the following equation:
sl
s
sl s
M
SP
()( )( )
V
(15-9)
WATER PLANT RESIDUALS MANAGEMENT 15-5
Volume Reduction Relationships
In the simplest, approximate terms, if one assumes that the mass of sludge ( M
s
), density of water
( ), and specific gravity of the sludge ( S
sl
) do not change as water is removed, the volume after
dewatering is
dewatered
(
wet
)
wet
dewatered
P
P
s
s
V
V
(15-10)
From the previous derivation of the equation for the volume of sludge, it may be noted that
the specific gravity of the sludge is a function of the percent water in the sludge ( Equation 15-8 ).
Thus, Equation 15-10 is only a rough estimation of the reduction in sludge volume. A more rigor-
ous es
timate of the resultant volume from dewatering is given by:
dewatered
PS
s
()()( )
(
wet
wet sludge
ccake filter cake
)( )P
s
V
(
wet
)
V
(15-11)
where the terms are as noted previously with subscripts added to indicate before dewatering and
after dewatering. The name given to the dewatered sludge is cake. The density of the cake is
calculated as
cake cake
()()S
(15-12)
where S
cake
specific gravity of the cake.
The specific gravity of the cake may be calculated with Equation 15-8 with appropriate substitu-
tion of the subscript cake for the subscript s l.
Example 15-1. Compare the estimate of sludge volume us ing the approximate and rigorous
forms of the equation for estim
ating the volume using the following data:
S p e cific gravity of solids 2.5
Solids fraction of wet sludge 15%
Solids fraction of dewatered sludge 25%
Volume of wet sludge 6.0 m
3
/ d
Solution:
a . Volume of dewatered sludge using Equation 15-10.
dewatered
m /dm/d()60
015
025
3 60
33
.
.
.
.
V
b. Volume of dewatered sludge using Equation 15-11.
(1) Compute the specific gravity of the sludge before dewatering and the specific grav-
ity of the cake after dewatering using Equation 15-8.
S
wet sludge
2 5
015 2 5 085
1 099
.
...
.
()( )
15-6 WATER AND WASTEWATER ENGINEERING
S
cake
2 5
025 2 5 075
1 176
.
...
.
()( )
(2) Compute the volume of dewatered sludge.
dewatered
m /d kg/m
()()( )(60 015 1 000 1
33
.., .0099
1 176 1 000 0 25
336
3
3
)
()( )()., .
.
kg/m
m /d
V
c. Comparison of volume estimates.
%%error
m /dm/d
m /d
3 60 336
336
100
33
3
..
.
()7714. %
In one year’s time the estimated volume of sludge is 1,314 m
3
b y the approximate method.
The more rigorous method yields an estimated annual sludge volume of 1,226 m
3
.
Comment. For dilute concentrations of light solids the percent error decreases to a negligible
amount. For high concentrations of heavy solids the percent error is significant.
15-3 SOLIDS PRODUCTION AND CHARACTERISTICS
In water treatment plants, sludge is most commonly produced in the following treatment processes:
presedimentation, sedimentation, and filtration (filter backwash).
Presedimentation
When surface waters are withdrawn from watercourses that contain a large quantity of suspended
materials, presedimentation prior to coagulation may be practiced. The purpose of this is to reduce
the accumulation of solids in subsequent units. The settled material generally consi
sts of fine
sand, silt, clay, and organic decomposition products.
Coagulation Sedimentation Basin
On a theoretical basis the dry mass of sludge produced from the addition of alum may be estimated
from the reaction chemistry described by Equation 6-8 in Chapter 6, which is reproduced here:
Al SO H O HCO
Al OH H O s
3243 2
32
14 6
23
()
() ()
683
22
CO H O SO
4
2
(15-13)
With a gram molecular weight of 594 for Al
2
(SO
4
)
3
· 14H
2
O, the addition of 1 mg/L of alum is
equivalent to
1
594 1 000
1 684 10
6
mg/L
g/mole mg/g
m
()(),
.
ooles/L
Noting that 1 mole/L of alum yields 2 moles/L of the aluminum precipitate and that the gram
molecular weight of the precipitate is 132.05 g/mole, then the mass of dry solids is
2 1 684 10 13205 4 446
6
()()...
moles/L g/mole 110 0 44
4
g/L or mg/L.