Water and Wastewater Engineering

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WASTEWATER PLANT RESIDUALS MANAGEMENT 27-63

27-8. Using the following mass flow data from the Doubtful WWTP (Problem 27-7)

determine 

, 

. Mass flows for Doubtful WWTP in Mg/d: A  7.280,

B  7.798, D  0.390, E  8.910, F  6.940, J  4.755, K  6.422, N  9.428,

X  0.468.

27-9. The c ity of Doubtful (Problem 27-7) is considering the installation of thickening

and dewatering facilities. The revised flow diagram for Doubtful to includ

e thick-

ening and dewatering with appropriate return lines is shown in Figure P-27-9 .

Calculate a value for L in Mg/d. Assume that the appropriate values of 

given in Figure 27-4 may be used when needed and that A  7.250 Mg/d,

X  1.288 Mg/d.

27-10. Determine the surface area required for the gravity thickeners (assume that no

thickener is greater than 30.0

m in diameter) to thicken the waste activated sludge

(WAS) at Grand Rapids, Michigan, from 10,600 mg/L to 2.50% solids. The waste

activated sludge flow is 3,255 m

/d. Assume that the batch settling curves of Figure

P-27-10 apply. Use a spreadsheet program you have written to plot the data and fit

the tangent line.

27-11. Determine the surface area required for the gravity thickeners of Problem 27-10 if

710 m

/d of primary sludge is mixed with the WAS to form a sludge having 2%

solids. The final sludge is to have a solids concentration of 5%. The batch settling

curve for mixed WAS and PS in Figure P-27-10 is assumed to apply. Because of the

additional sludge, assume five thickeners will be used

. Use a spreadsheet program

you have written to plot the data and fit the tangent line.

Primary

sedimentation

Secondary

reactor

Thickening

Digestion

Dewatering

FIGURE P-27-9

Revised flowsheet for Doubtful WWTP.

27-64 WATER AND WASTEWATER ENGINEERING

27-12. Settling test data from the Little Falls WWTP are shown below. Determine the sur-

face area for a gravity thickener for 733 m

/ d of waste activated sludge. The final

sludge concentration is to be 3.6%. Use a spreadsheet program you have written to

plot the data and fit the tangent line.

Suspended solids

concentration, g/L

Initial settling

velocity, m/d

4.0 58.5

6.0 36.6

8.0 24.1

14.0 8.1

29.0 2.2

41.0 0.73

27-13. Select a pipe diameter and estimate the friction headloss for pumping 38,500 kg/d of

a thickened mixture of primary and activated sludge that has a solids concentration of

0.123 4 10 30 40 100 200200.20.3 0.4 1.0

0.1

0.2

0.3

0.4

1.0

2.0

3.0

4.0

10.0

20.0

30.0

40.0

100.0

Subsidence rate, m/d

Suspended solids concentration, kg/m

Primary sludge

WAS

Grand

Rapids, MI

Mixed activated

sludge and primary

sludge

Activated

sludge

FIGURE P-27-10

Batch settling curves.

WASTEWATER PLANT RESIDUALS MANAGEMENT 27-65

6% and a specific gravity of 1.03. The sludge is to be pumped 112 m to an anaerobic

digester. Assume a Hazen-Williams C  100 and a pumping time of 1/2 hour once

per day.

27-14. To improve the performance of the digester in Problem 27-13, it has been proposed that a

more uniform feed be employed by using a clo

ck control to operate a pump for 5 minutes

at an interval of 96 minutes. Determine the pumping flow rate and the approximate num-

ber of cycles per day. (The spreadsheet solver tool may be useful for this solution.) Use

this flow rate to select a pipe diameter and estimate the friction headloss.

27-15. Design a pretreatment lime s

tabilization system for Quirm. The daily sludge flow

rate of 112 m

i s to be treated in one batch. The primary sludge has a solids concentra-

tion of 6% and a specific gravity of 1.02. Determine the volume of tank, mixer size

(kW, rpm, turbine dia.), lime feed rate, and lime storage volume for two-week delivery.

27-16. Design a pretreatment lime stabilization system for Pseudopolis. The daily sludge

flow rate of 216 m

is to be treated in one batch. Half of the sludge volume is

primary sludge with a solids concentration of 4.3% and a specific gravity of 1.02.

The other half of the volume is WAS with a solids concentration of 1.3% and a

specific gravity of 1.005. Determine the volume of tank, mixer size (kW, rpm,

turbine dia.), lime feed rate, and li

me storage volume for two-week delivery.

27-17. In the preliminary analysis of alternatives for stabilizing the WAS sludge from

Sunset’s activated sludge plant, your boss has asked you to design an aerobic

digester. The sludge flow rate is 62.3 m

/ d. The solids concentration is 2.8%, and

the specific gravity of the sludge is 1.01. Use the following data for the design:

Winter conditions govern

T e mperature of digester contents  20  C

VSS  0.8 TSS

VSS reduction goal  40%

Influent BOD  2,600 mg/L

Fraction of influent BOD consisting of primary solid

s  0.35

S l udge concentration is 70% of the incoming thickened sludge concentration

Diffused air mixing is to be used

27-18. In the preliminary analysis of alternatives for stabilizing a mixture of primary and WAS

sludge from Knight Falls’ activated sludge plant, y

our boss has asked you to design an

aerobic digester. The sludge flow rate is 404 m

/ d. The solids concentration 2.8% and

the specific gravity of the sludge is 1.01. Use the following data for the design:

Winter conditions govern

T e mperature of digester contents  15  C

VSS  0.7 TSS

VSS reduction goal  40%

Influent BOD  1,700 mg/L

Fraction of influent BOD consisting of primary solids

 0.28

S l udge concentration is 70% of the incoming thickened sludge concentration

Diffused air mixing is to be used

27-66 WATER AND WASTEWATER ENGINEERING

27-19. In the preliminary analysis of alternatives for stabilizing the WAS sludge from

S unset’s activated sludge plant your boss has asked you to design an anaerobic

digester. Determine the volume of the digester, the flow rate of methane, and the

volume of an external tank pressurized to 350 kPa. Use the data from Problem 27-17

and the following

data for this design:

S l udge thickened to 4.0%

T e mperature of digester contents  35  C

Influent bCOD  2,600 g/m

D e sign effluent bCOD  500 g/m

D e sign safety factor  5

There will be no recycle

G a s evolves from the digester at atmospheric pressure (101.3 kPa)

27-20. In the preliminary analysis of alternatives for stabilizing the mixture of primary and

WAS sludge from Knight Falls’ activated sludge plant, your boss has asked

you to

design an anaerobic digester. Determine the volume of the digester, the flow rate of

methane, and the volume of an external tank pressurized to 350 kPa. Use the data

from Problem 27-18 and the following data for this design:

S l udge thickened to 4.0%

T e mperature of digester contents  35  C

Influent bCOD  1,700 g/m

D e sign effluent bCOD  118 g/m

D e sign safety factor  5

There will be no recycle

G a s evolves from the digester at atmospheric pressure (101.3 kPa)

27-21. Determine the dimensions of Sunset’s anaerobic digester designed in Problem 27-19.

Assume a depth of 7.5 m and a bottom slope of 1:6. Provide a floating cover. The

floating cover diameters are s

old in 1.5 m increments.

27-22. Determine the dimensions of Knight Falls’ anaerobic digester designed in Problem

27-20. Assume a depth of 10.0 m and a bottom slope of 1:3. Provide a floating cover.

The floating cover diameters are sold in 1.5 m increments.

27-23. For the sketch shown on page 27-67 in Fig

ure P-27-23 , perform a heat balance on the

digester designed in Problem 27-21. Is enough methane produced to heat the digester

in January if the mean ambient temperature is 15  C? Assume optimistic heat transfer

coefficients for the building materials and a heat exchanger efficiency of 90%. The

temperature of the sludge is 12

C.

27-24. For the sketch shown on page 27-67 in Figure P-27-24 , perform a heat balance on

the digester designed in Problem 27-22. Is enough methane produced to heat the

digester in January if the mean ambient temperature is  12  C? Assume conserva-

tive heat transfer coefficients for the building materials and a heat exchanger

efficiency

of 60%. The temperature of the sludge is 10C.

27-25. Using Table 27-20 , select a CBFP to dewater an anaerobic digester sludge. The

primary sludge has a solids concentration of 4.0% and a specific gravity of 1.04. The

WASTEWATER PLANT RESIDUALS MANAGEMENT 27-67

design sludge flow rate is 62.3 m

/ d. The plant managers wish to operate on a two-

shift basis, that is, 16 h/d to minimize labor costs.

27-26. Using Table 27-20 , select a CBFP to dewater an anaerobic digester sludge. The

sludge is primary plus WAS that has a solids concentration of 2.5% and a specific

gravity of 1.03. The design slud

ge flow rate is 404 m

/ d. The plant will operate on a

three-shift basis.

27-27. The Pomdeterra anaerobic digester produces a sludge that has a total solids concen-

tration of 3.8%. They are investigating a filter press that will yield a solids concen-

tration of 24%. If they now produce 33 m

/ d of sludge, what annual volume savings

will they achieve if they install the press? ( Hint: use the approximate method from

Chapter 15.)

27-28. Ottawa’s anaerobic digester produces 13 m

/ d of sludge with a total solids concen-

tration of 2.8%. What volume of sludge must they dispose of each year if their sand

drying beds yield a solids concentration of 35%? ( Hint: use the approximate method

from Chapter 15.)

27-29. Weed Patch’s digester pro

duces 30 m

/ mo of sludge with a total solids concentration

of 2.5%. What solids concentration must their drying facility achieve to reduce the

volume to 3 m

/ mo? ( Hint: use the approximate method from Chapter 15.)

25 mm insulating board

Dry soil

300 mm thick concrete

3.0 m

4.5 m

15C at wall

Average

12C at

wall

Dry soil

300 mm thick concrete w/insulation

Plain concrete

Digester temperature  35C

FIGURE P-27-23

Anaerobic digester.

Double insulated roof U  0.54

Dry soil

10 m

Average

9C at

wall

Air temp  12C

Dry soil

300 mm thick wall with insulation

FIGURE P-27-24

Anaerobic digester.

27-68 WATER AND WASTEWATER ENGINEERING

27-16 REFERENCES

Andrews, J. F. (1969) “Dynamic Model of the Anaerobic Digestion Process,” Journal of the Sanitary

Engineering Division, American Society of Civil Engineers, vol. 95, p. 95.

Atherton, P. C., R. Steen, G. Stenson, T. McGovern, and D. Smith (2006) “Old Town Learns New Trick,”

Water Environment & Technology, vol. 18, January, pp. 47–51.

Bechtel, T. B. (2005) “A Computational Technique for Turbulent Flow of Wastewater Slud

ge,” Water

Environment Research, vol. 77, no. 4, pp. 417–422.

Davis, M. L. and D. A. Cornwell (2008) Introduction to Environmental Engineering, McGraw-Hill,

Boston, Massachusetts, p. 510.

GLUMRB (2004) Recommended Standards for Wastewater Facilities, Great Lakes–Upper Mississippi

River Board of State and Provincial Public Health and Environmental Managers, Health Education

Services, Albany, New York, pp. 80-1–80-23.

Lawrence, A. W. and P. L. McCarty (1970) “A Unified Basis for Biological Treatment Design and

Operation,” Journal of Sanitary Engineering Division, American Society of Civil Engineers, vol. 96,

no. SA3, pp. 757–778.

Lawrence, A. W. and T. R. Milnes (1971) “Discussion Paper,” Journal of the Sanitary Engineering

Division, American Society of Civil Engineers, vol. 97, p.121.

Leffler, M. R. and P. Bizier (2009) “Refining Residuals,” Civil Engineering, American Society of Civil

Engineers, vol. 79, Janu

ary, pp. 56–63.

LaGrega, M. D., P. L. Buckingham, and J. C. Evans (2001) Hazardous Waste Management, 2nd ed.,

McGraw-Hill, Boston, Massachusetts, pp. 759–761.

LaMontagne, P. L. and I. Yeveilevich (2006) “Polymer Power,” Water Environment & Technology,

vol. 18, May, pp. 61–64.

Liptak, B. G. (1974) Environmental Engineers Handbook, Chilton Book Company, Rad nor,

Pennsylvania.

Madigan, M. T., J. M. Martinko, and J. Parker (1997) Brock Biology of Microorganisms 8th ed., Prentice-

Hall, Upper Saddle River, New Jersey.

M cCabe, W. L., J. C. Smith, and P. Harriot (200

5) Unit Opertions of Chemical Engineering, M cGraw-Hill,

Boston, Massachusetts, p.48.

M cCarty, P. L. (1964) “Anaerobic Waste Treatment Fundamentals, Part 2-Environmental Requirements

and Control,” Public Works, October, p. 123.

Metcalf & Eddy (2003) Wastewater Engineering: Treatment and Reuse, 4th ed., McGraw-Hill, Boston,

Massachusetts, pp. 983–1034, 1447–1632.

M urakami, H., H. Katayama, and H. Matsuura (2001) “Pipe Friction Headloss in Transportation of High-

Concentration Sludge for Centralized Solids Treatment,” Water Environment Research, vol. 73, no.

5, pp. 558–566.

Newhof, T. (2009) personal communication.

N FPA (1993) National Electric Code, Qunicy, Massachusetts.

N FPA (1995) Standards for Fire Protection in Wastewater Treatment and Collection Facilit

ies,

Document No. 820, Qunicy, Massachusetts.

Parker, G. F. and S. W. Miller (1982) “Response of Methane Fermentation to Continuous Addition

of Selected Industrial Toxicants,” Proceedings of the 37th Purdue Industrial Waste Conference,

Lafayette, Indiana.

Parker, G. F. and W. F. Owen (1986) “Fundamentals of Anaerobic Digestion of Wastewater Sludges,”

Journal of Environmental Engineering, American Society of Civil Engineers, vol. 112, no. 5,

pp. 867–920.

Shimp, G. F., D. M. Bond, J. Sandino, and D. W. Oerke (1995) “Biosolids Budgets,” Water Environment &

Technology, vol. 7, November, pp. 44–49.

Steel, E. W. and T. J. McGhee (1979) Water Supply and Sewerage, 5th ed., McGraw-Hill, New York,

p. 466.

WASTEWATER PLANT RESIDUALS MANAGEMENT 27-69

Task Committee (1988) “Belt Filter Press Dewatering of Wastewater Sludge,” Journal of Environmental

Engineering, American Society of Civil Engineers, Task Committee on Belt Filter Presses, vol. 114,

pp. 991–1,006.

U.S. EPA (1975) Lime Stabilized Sludge: Its Stability and Effect on Agricultural Land, U.S.

Environmental Protection Agency, EPA Pub. No. 670/2-75-012, Washington, D.C.

U.S. EPA (1979) Process Design Manual—Sludge Treatment and Disposal, U.S. Environmental

Protection Agency, EPA Pub. No. 625/1-79-011, Washington, D.C., pp. 4-1–4-74, 6-2–6-127,

14-1–14-3, 9-1–9-70.

U.S. EPA (1987) Prel

iminary Treatment Facilities—Design and Operational Considerations, U.S.

Environmental Protection Agency, EPA Pub. No. 430/09-87-007, Washington, D.C.

WEF (1994) Safety and Health in Wastewater Systems, Manual of Practice No. FD-9, Alexandria,

Virgina.

WEF (1998) Design of Municipal Wastewater Treatment Plants, 4th ed.,Water Environment Federation

Manual of Practice 8, Alexandria, Virginia, pp. 9-12–9-16, 19-1–19-61, 20-1–20-118, 21-1–21-126,

22-1–22-226.

Witzgall, R. A., G. J. Volpe, R. T. Haug, W. A. Lawson, and W. H. Kido (1998) “Digester Evaluation,”

Water Envi

ronment & Technology, vol. 10, May, pp. 59–65.

WPCF (1977) Wastewater Treatment Plant Design, Water Pollution Control Federation Manual of

Practice No. 8, pp.145–150.

28-1

28-5 CHAPTER REVIEW

28-6 PROBLEMS

28-7 REFERENCES

CLEAN WATER PLANT PROCESS SELECTION

AND INTEGRATION

28-1 INTRODUCTION

28-2 PROCESS SELECTION

28-3 SIMULATION MODELING

28-4 PROCESS INTEGRATION

If the objective of the plant is to produce clean water,

we should call it a Clean Water Plant!

Dan Wolz

Superintendent

Clean Water Plant

Wyoming, MI

It’s good to be on the cutting edge. It’s not

good to be on the bleeding edge.

Jimmy Spangler

Former Superintendent

Wastewater Division

Lansing, MI

CHAPTER

28-2 WATER AND WASTEWATER ENGINEERING

28-1 INTRODUCTION

The primary goal of municipal wastewater treatment is to protect the health, safety, and welfare

of the public. A secondary but essential goal is to protect and provide for the propagation of fish,

shellfish, and wildlife. A concomitant goal is to provide for recreation in and on the receiving

water. To achieve sustainable development, maximum beneficial reuse of the wastewater and

covery of minerals and energy in the biosolids must be considered.

Based on the results of a 1,000 plant survey, the Water Pollution Control Federation (now

the Water Environment Federation) identified four major issues that future designs must focus

on (WPCF, 1989):

• Infiltration and inflow

• Equipment breakdown

• Climatic c

onditions

• Odor

The survey revealed that even though a majority of the plants were operating below their

rated average daily flow capacity, hydraulic overload problems were significant because of infil-

tration and inflow. Equipment problems were attributed to a wide variety of issues including:

inappropriate application, inadequate design, poor manufacture, an

d inadequate maintenance

funding. Climatic issues included precipitation induced flow, restricted availability of disposal

sites for biosolids due to wet or frozen ground, and lack of equipment and plant appurtenances

necessary to deal with local weather conditions. O

dor complaints were listed as one of the most

frequent management issues encountered. The odor issues were one of the most difficult to deal

with because of their plant-wide pervasiveness and the sensitivity of people to the nature of

the odor.

28-2 PROCESS SELECTION

E xperience has taught us the following fundamental precepts in process selection:

1 . The raw wastewater quality of every community is different.

2. Raw wastewater quality is variable.

3. There is no standard treatment plant design that is applicable to all sources.

4. For every source, a num

ber of treatment process alternatives are available.

5. Site conditions often limit the types of treatment process that can be used.

6. Retrofitting and upgrading of existing plants requires creative solu tions that are not

presented in standard textbooks such as this one.

7. Pilot plant testing is highly recommended in the sele

ction of new technologies or proven

technologies for new applications.

8. Pilot plant testing requires careful planning and execu tion to obtain useful design and

operating criteria.

CLEAN WATER PLANT PROCESS SELECTION AND INTEGRATION 28-3

9. It is essential that residuals management be a feature of all designs.

10. Operator experience is invaluable in developing a design.

Evaluation of Process Options

While experts with a large body of knowledge gained from experience will often be able to screen

the universe of available processes to select a set of options for study and evaluation, the sorting

process they use is not intuitively obvious. In simplified form, the sorting process may be repre-

sented as a matrix table in which all the relevant treatment proce

sses are listed on one axis and

the factors related to process selection are listed on another axis. Each process is given a rating or

ranking for each of the factors. In addition, a weighting system may be employed to account for

greater influence of more important aspects of some of the factors than others. Some of the i

mpor-

tant factors that must be considered are listed in Tables 28-1 and 28-2 (Metcalf & Eddy, 1991).

Focus Issues. The following issues have been selected as focus issues because of their

i mportance in process selection and the major findings of the WPCF survey:

• Contaminant removal.

• Reliability.

• Process flexibility.

• Utilit

y capability.

• Cost.

• Odor control.

• Nutrient and residuals management.

• Energy management.

These factors are discussed in the following paragraphs.

Contaminant Removal. Removal of contaminants is the primary purpose of wastewater treat-

ment processes. In the United States, the regulations promulgated by the U.S. Environmental

Protection Agency set the maximum allowable contaminant levels in discharged water. Obvi-

ously, processes that cannot meet National Pollution Discharge Elimination System (NPDES)

requirements can be quickly eliminated. The NPDES is complex. The following quotation illus-

trates the complexity (WEF, 1998):

Effluent compliance standards, with pollutant limits for the maximum monthly and weekly period each

year, s tatistically dictate a d esign process reliability up to the maximu m monthly effluent restriction

92 percent of the time, and processing reliability up to the

maximum allowable weekly effluent limitation

approximately 98 percent of the time. Some regulatory agencies impose more stringent standards, defining

effluent standards in terms of the maximum daily event per year (a design reliability of approximately 99.7

percent) or in terms of not exceed

ing or falling below certain criteria at any time (one hour per year has a

design or performance reliability of approximately 99.99 percent).