Water and Wastewater Engineering
Подождите немного. Документ загружается.
23-98 WATER AND WASTEWATER ENGINEERING
Maintenance Cleaning. Each manufac turer has a prescribed cleaning regime and frequency.
The following scenario is representative but is not to be construed as having precedence over the
manufacturer’s recommendation:
• Coarse bubble aeration to provide mechanical scouring.
• Interruption of the filtration process every 12 to 1
5 minutes for backwashing with permeate
for 30 to 60 s.
• Backwashing permeate may contain a low concentration of chlorine ( 5 mg/L).
• Approximately every two days, a strong sodium hypochlorite solution ( 100–500 mg/L)
or citric acid ( 1,000–5,000 mg/L) is us
ed to backwash for 45 minutes.
Recovery Cleaning. Maintenance cleaning is not completely effective, and the pressure drop
across the membrane will increase with time. The intention of recovery cleaning is to improve
membrane permeability to 80 percent or more of a new membranes permeability. As with mainte-
nance cleaning, the manufactu
rer’s recommendations are to be followed. The recovery chemicals
and the concentration and cleaning duration are d epend ent on the fouling material. Table 23-22
shows a typical selection of alternatives. The cleaning duration may range from 6 to 24 hours.
With proper isolation of each membrane tank, cleaning may take place in the tank (called clean
in place or CIP). In small plants the cassette is removed and placed in a staging tank.
Visit the text website at www.mhprofessional.com/wwe for supplementary materials
and a gallery of additional photos.
Suspected fouling
material
Recommended cleaning
chemical
Alteranate cleaning
chemical
Cleaning solution
concentration, mg/L
Aluminum oxide
Oxalic acid
a
Citric acid 1,000–10,000
Calcium carbonate HCl Citric acid 1,000–10,000
Ferric oxide
Oxalic acid
a
Citric acid 1,000–10,000
Organic material NaOCl H
2
0
2
500–5,000
TABLE 23-22
Recovery cleaning chemical selection chart
a
Do not use oxalic acid in hard water. It will form calcium oxalate precipitate.
A dapted from WEF, 2006b.
23-9 CHAPTER REVIEW
When you have completed studying this chapter, you should be able to do the following without
the aid of your textbook or notes:
1 . Define the following terms and abbreviations: activated sludge, mixed liquor, mixed
liquor volatile suspended solids (MLVSS), mixed liquor suspended solids (MLSS),
return sludge, RAS, wasting, waste activated sludge (WAS), m
ean cell residence time
SECONDARY TREATMENT BY SUSPENDED GROWTH BIOLOGICAL PROCESSES 23-99
(MCRT or
c
), solids retention time (SRT) or sludge age, CSTR, SBR, BNR, MF,
AOTR, SOTR, SOTE, SAE, F/M, SDNR, SVI, BPR.
2. Describe the following processes and give examples of their use: oxidation ditch, SBR,
selector, Modified Ludzack-Ettinger (MLE), Bardenpho (4-stage), A
2
/O
™
, MBR.
3. Explain why oxidation pond design criteria are often prescriptive.
4. Explain why solids retention time is referred to as the “master variable” in the design of
activated sludge systems.
5. Explain the sequence of steps in the operation of a batch reactor for carbonaceous BOD
oxidation and for denitrifi
cation.
6. List two of the major assumptions of reactor models that are rarely met in practice and
explain some methods for correcting for the faults of these assumptions.
7. Explain when it becomes important to consider using the more accurate method of
predicting sludge produ
ction.
8. Compare two systems operating at two different F/M ratios.
9. Define SVI, explain its use in the design of an activated sludge plant, and why that use
is not recommended.
W ith the aid of this text, you should be able to do the following:
10. Design a facultative oxidation pond by determining the dimensions and spe
cifying the
piping and construction features.
11. Design an oxidation ditch by determining the dimensions, required alkalinity for nitrifi-
cation, sludge production, and aeration equipment selection and placement.
12. Design a SBR by determining the dimensions, reaction time for nitrifi
cation, nitrate
removal capacity, and aeration equipment selection.
13. Design an A
2
/O
™
treatment system by determining the SRT, volume of the nitrifica-
tion tank, nitrate removal capacity, alkalinity requirements, effluent soluble phosphorus
concentration, volume and dimensions of anoxic and anaerobic reactors, and the aera-
tion system design including compressor s
izing.
23-10 PROBLEMS
23-1. Us ing the assumptions given in Example 23-1 , the rule-of-thumb values for growth
constants in the example, and the further assumption that the influent BOD
5
was reduced by 32% in the primary tank, estim ate the liquid volume of a com-
pletely mixed activated slu dge aeration tank for Perryville. The design flow rate
is 34,560 m
3
/ d and the design influent BOD
5
i s 188 mg/L. Assume an MLVSS of
2,000 mg/L.
23-2. Repeat Problem 23-1 for the town of Pea Ridge using a design flow rate of 8,450 m
3
/ d
and an influent BOD
5
of 137 mg/L.
23-100 WATER AND WASTEWATER ENGINEERING
23-3. The town of Camp Verde has been directed to upgrade its primary WWTP to a
secondary plant that can meet an effluent standard of 25.0 mg/L BOD
5
and 30 mg/L
suspended solids. They have selected a completely mixed activated sludge system
for the upgrade. The existing primary treatment plant has a flow rate of 2,506 m
3
/ d.
The effluent from the primary tank has a BOD
5
of 240 mg/L. Using the following
assumptions, estimate the required volume of the aeration tank:
1. BOD
5
of the effluent suspended solids is 70% of the allowable suspended solids
concentration.
2 . Growth constant values are estimated to be: K
s
100 mg/L BOD
5
; k
d
0.025 d
1
;
m
10 d
1
; Y 0.8 mg VSS/mg BOD5 removed.
3 . The design MLVSS is 3,000 mg/L.
23-4. Using a spreadsheet program you have written, rework Example 23-1 using the
following MLVSS concentrations instead of the 2,000 mg/L used in the example:
1,000 mg/L; 1,500 mg/L; 2,500 mg/L; and 3,000 mg/L.
23-5. Using a spreads
heet program you have written, determine the effect of MLVSS con-
centration on the effluent soluble BOD
5
( S ) using the data in Example 23-1. Assume
the volume of the aeration tank remains constant at 945 m
3
. Use the same MLVSS
values used in Problem 23-4 .
23-6. Determine the return sludge concentration ( X
r
#
) that results in the maximum return
sludge flow rate for Perryville’s proposed activated sludge plant described in
Problem 23-1 . Also estimate the mass flow rate of sludge wasting. Use the following
assumption:
MLVSS fraction of MLSS 070.
23-7. Determine the return sludge concentration ( X
r
) that results in the maximum return
sludge flow rate for Pea Ridge’s proposed activated sludge plant described in
Problem 23-2 . Also estimate the mass flow rate of sludge wasting. Use the following
assumption:
MLVSS fraction of MLSS 080.
23-8. Determine the return sludge concentration ( X
r
#
) that results in the maximum return
sludge flow rate for Camp Verde’s proposed activated sludge plant described in
Problem 23-3 . Also estimate the mass flow rate of sludge wasting. Use the following
assumption:
MLVSS fraction of MLSS 070.
23-9. Estimate the mass of sludge to be wasted
each day from the new activated sludge
plant at Perryville ( Problems 23-1 and 23-6 ).
23-10. Estimate the mass of sludge to be wasted each day from the new activated sludge
plant at Pea Ridge ( Problems 23-2 and 23-7 ).
23-11. Estimate the mass of sludge to be wasted ea
ch day from the new activated sludge
plant at Camp Verde ( Problems 23-3 and 23-8 ).
SECONDARY TREATMENT BY SUSPENDED GROWTH BIOLOGICAL PROCESSES 23-101
23-12. Estimate the mass of oxygen to be supplied (kg/d) for the new activated sludge plant
at Perryville ( Problems 23-1 , 23-6 , and 23-9 ). Assume that BOD
5
rbsCOD and
that it is 68% of the bCOD.
23-13. Estimate the mass of oxygen to be supplied (kg/d) for the new activated sludge plant
at Pea Ridge ( Problems 23-2 , 23-7 , and 23-10 ). Assume that BOD
5
rbsCOD and
that it is 68% of the bCOD.
23-14. Estimate the mass of oxygen to be supplied (kg/d) for the new activated sludge plant
at Camp Verde ( Problems 23-3 , 23-8 , and 23-11 ). Assume that BOD
5
rbsCOD and
that it is 68% of the bCOD.
23-15. Estimate the required air flow rate for the new activated sludge plant at Perryville
( Problems 23-1 , 23-6 , 23-9 , and 23-12 ). Use the following assumptions in preparing
the estimate:
Clean water correction, 0.45
Salinity correction, 0.95
Fouling factor 0.8
S ummer wastewater temperature
20 C
A t mospheric pressure 101.325 kPa
Elevation 100 m
Depth of aerator 4.5 m
Operating DO 2.0 mg/L
Percent oxygen leaving aeration tank 19%
Manufacturer ’ s SOTR 525 kg/d
Manufacturer ’ s air flow rate at standard conditions 122 m
3
/ d · aerator
23-16. Estimate the required air flow rate for the new activated sludge plant at Pea Ridge
( Problems 23-2 , 23-7 , 23-10 , and 23-13 ). Use the following assumptions in preparing
the estimate:
Clean water correction, 0.50
Salinity correction, 0.95
Fouling factor 0.9
S ummer wastewater temperature 12 C
A t
mospheric pressure 101.325 kPa
Elevation 500 m
Depth of aerator 5.6 m
Operating DO 2.0 mg/L
Percent oxygen leaving aeration tank 19%
Manufacturer ’ s SOTR 535 kg/d
Manufacturer ’ s air flow rate at standard conditions 50 m
3
/ d · aerator
23-17. Estimate the required air flow rate for the new activated sludge plant at Camp Verde
( Problems 23-3 , 23-8 , 23-11 , and 23-14 ). Use the following assumptions in preparing
the estimate:
Clean water correction, 0.70
Salinity correction, 0.95
23-102 WATER AND WASTEWATER ENGINEERING
Fouling factor 0.8
S ummer wastewater temperature 22 C
A t mospheric pressure 101.325 kPa
Elevation 2,135 m
Depth of aerator 4.5 m
Operating DO 2.0 mg/L
Percent oxygen leaving aeration tank 19%
Manufacturer ’ s SOTR 650 kg/d
Manufacturer ’ s air flow rate at standard
conditions 20 m
3
/ d · aerator
23-18. If the F/M of a 0.4380 m
3
/ s activated sludge plant is 0.200 mg/mg · d, the influent
BOD
5
after primary settling is 150 mg/L, and the MLVSS is 2,200 mg/L, what is the
volume of the aeration tank?
23-19. If the operator of the plant described in Problem 23-18 reduces wasting and allows
the MLVSS to rise to 3,000 mg/L, what is the new F/M ratio?
23-20. If a new industry increases the influent BOD
5
after settling to 180 mg/L to the plant
described in Problem 23-18 , what is the new F/M ratio? Assume that the MLVSS
remains constant at 2,200 mg/L.
23-21. Two activated sludge aeration tanks at Turkey Run are operated in series. Each tank
has the following dimensions: 7.0 m wide by 30.0 m long by 4.3 m effective liquid
depth. The plant operating parameter
s are as follows:
Flow 0.0796 m
3
/s
Soluble BOD
5
after primary settling 130 mg/L
MLVSS 1,500 mg/L
MLSS 1.40 (MLVSS)
Settled sludge volume after 30 min 230.0 mL/L
Determine the following: aeration period, F/M ratio, SVI.
23-22. Using the following assumptions, determine the solids retention time, cell wastage flow
rate, and the return sludge flow rate for the Turkey Run WWTP ( Problem 23-21 ). A
ssume:
S uspended solids in the effluent are negligible
W a stage is from the aeration tank
Yield coefficient 0.40 mg VSS/mg BOD
5
removed
D e cay rate of microorganisms 0.040 d
1
Effluent BOD
5
5.0 mg/L (soluble)
23-23. The 500-bed Lotta Hart Hospital has a small activated sludge plant to treat its waste-
water. The average daily hospital discharge is 1,500 L per day per bed, and the aver-
age soluble BOD
5
after primary settling is 500 mg/L. The aeration tank has effective
liquid dimensions of 10.0 m wide by 10.0 m long by 4.5 m deep. The plant operating
parameters are as follows:
MLVSS 2,500 mg/L
MLSS 1.20 (MLVSS)
Settled sludge volume after 30 min 200 mL/L
SECONDARY TREATMENT BY SUSPENDED GROWTH BIOLOGICAL PROCESSES 23-103
Determine the following: aeration period, F/M ratio, SVI.
23-24. Using the following assumptions, determine the solids retention time, the cell wast-
age flow rate, and the return sludge flow rate for the Lotta Hart Hospital WWTP
( Problem 23-23 ). Assume:
Allowable BOD
5
in effluent 25.0 mg/L
S uspended solids in effluent 25.0 mg/L
W a stage is from the return sludge line
Yield coefficient 0.60 mg VSS/mg BOD5 removed
D e cay rate of microorganisms 0.060 d
1
Inert fraction of suspended solids 66.67%
23-25. Rework Example 23-7 assuming that the State of Iowa rules for loading and deten-
tion time apply.
23-26. An oxidation pond having a surface area of 90,000 m
2
is loaded with a waste flow
of 500 m
3
/ d containing 180 kg of BOD
5
. The operating depth is from 0.6 to 1.6 m.
Using the Michigan rules, determine whether this design is acceptable.
23-27. Using the EPA criteria, design a controlled discharge oxidation pond for Coprolite.
Coprolite is located in a state where the average winter temperature is 16 C. The
design assumptions are as follows:
Flow rate 3,800 m
3
/ d
BOD
5
100.0 mg/L
Three cells in series
Minimum operating depth 0.6 m
23-28. Estimate the volume of an extended-aeration oxidation ditch for carbonaceous BOD
oxidation and nitrification for the city of Pasveer using the following design data:
Influent data
D e sign flow rate 8,000 m
3
/ d
bCOD 430 mg/L
NH
3
-N 25 mg/L
Total suspended solids (TSS) 250 mg/L
Biodegradable volatile suspended solids 120 mg/L
Minimum sustained temperature 10 C
pH 7.2
Alkalinity 200 mg/L as CaCO
3
Effluent discharge standards
bCOD 20 mg/L
NH
3
-N 1.0
TSS 10 mg/L
A ssume the MLSS 3,000 mg/L, MLVSS (0.9) MLSS, and typical kinetic coef-
ficients in Tables 23-13 and 23-14 apply.
23-104 WATER AND WASTEWATER ENGINEERING
23-29. Determine whether or not there is sufficient alkalinity for nitrification of the extended
aeration oxidation ditch at Pasveer ( Problem 23-27 ). Compute the mass per day of
sodium bicarbonate to add if alkalinity is required. Assume a residual of 80 mg/L as
CaCO
3
is required to maintain the pH.
23-30. Estimate the mass of sludge to be wasted each day from the extended aeration oxida-
tion ditch at Pasveer ( Problem 23-28 ).
23-31. Determine the total length of brush aerators for the extended aeration oxidation ditch
at Pasveer ( Problem 23-28 ). Use the data in Table 23-15 for the length e
stimate. Use
the following assumptions in the design:
Clean water correction, 0.50 for nitrification
Salinity correction, 0.95
S ummer wastewater temperature 20 C
Operating DO = 3.0 mg/L
23-32. Determine the oxidation ditch dimensions and select brush aerators for the extended
aeration o
xidation ditch at Pasveer ( Problems 23-28 , 23-29 , and 23-30 ). Use the data
in Tables 23-15 and 23-16 to select the aerators.
23-33. Estimate the volume of an extended-aeration oxidation ditch for carbonaceous BOD
oxidation and nitrification for the city of Brooklyn using the following design data:
Influent data
D e sign flow rate 26,500 m
3
/ d
bCOD 440 mg/L
NH
3
-N 18 mg/L
Total suspended solids (TSS) 240 mg/L
Biodegradable volatile suspended solids 190 mg/L
Minimum sustained temperature 13 C
pH 7.0
Alkalinity 120 mg/L as CaCO
3
Effluent discharge standards
bCOD 20 mg/L
NH
3
-N 1.0
TSS 10 mg/L
A ssume the MLSS 3,000 mg/L, MLVSS (0.75) MLSS, and typical kinetic coef-
ficients in Tables 23-14 and 23-5 apply.
23-34. Determine whether or not there is sufficient alkalinity for nitrification of the extended
aeration oxidation ditch at Brooklyn ( Problem 23-33 ). Compute the mass per da
y of
sodium bicarbonate to add if alkalinity is required. Assume a residual of 80 mg/L as
CaCO
3
is required to maintain the pH.
23-35. Estimate the mass of sludge to be wasted each day from the extended aeration
o xidation ditch at Brooklyn ( Problem 23-33 ).
SECONDARY TREATMENT BY SUSPENDED GROWTH BIOLOGICAL PROCESSES 23-105
23-36. Determine the total length of brush aerators for the extended aeration oxidation ditch
at Brooklyn ( Problems 23-33 , 23-34 , 23-35 ). Use the data in Table 23-15 for the
length estimate. Use the following assumptions in the design:
Clean water correction, 0.70 for nitrification
Salinity correction, 0.95
S ummer wastewater temperature 24 C
Operating DO 3.0 mg/L
23-37. Determine the oxidation ditch dimensions and select brush aerators for the extended
aeration oxidation ditch at Brooklyn ( Problems 23-33 , 23-34 , 23-35 , 23-36 ). Use the
data in Tables 23-15 and 23-16 to sele
ct the aerators.
23-38. Estimate the volume and dimensions of an SBR for the town of Bath using the
following design data:
Influent data
D e sign flow rate 4,900 m
3
/ d
bCOD 200 mg/L
rbCOD 45 mg/L
Total Kjeldahl nitrogen (TKN) 26 mg/L
NH
3
-N 23 mg/L
Total suspended solids (TSS) 170 mg/L
Volatile suspended solids (VSS) 140 mg/L
Biodegradable volatile suspended solids 65 mg/L
Minimum sustained temperature 9 C
pH 7.4
Alkalinity 300 mg/L as CaCO
3
Effluent discharge standards
bCOD 20 mg/L
NH
3
-N 1.0
TSS 10 mg/L
A ssume MLSS 2,800 mg/L, MLVSS (0.8) MLSS, NO
x
80% of TKN,
c
25 d. Also assume the cycle time and phase times used in Example 23-13.
23-39. Check the assumed react plus aerated mix time used to design the SBR for the town
of Bath using the data from Problem 23-38 .
23-40. Check the assumed anoxic fill time used to d
esign the SBR for the town of Bath
using the data from Problems 23-38 and 23-39 .
23-41. Estimate the number of jet aerators for the SBR being designed for the town of Bath
using data from Problems 23-38 , 23-39 , and 23-40. Assume that 60% of the theoreti-
cal oxygen released in denitrification is available for oxidation and that the oxygen
concentration leaving the tank is 19%. Assume the following d
ata for the jet aerators:
SBR is at sea level
0.75
0.95
23-106 WATER AND WASTEWATER ENGINEERING
F 1.0
Depth of aerator 5.0 m
T e mperature 9 C
Manufacturer’ s SOTR 1,570 kg/d at 6.0 m depth
Manufacturer’ s air flow rate at standard conditions 3,000 m
3
/ d · jet
23-42. Estimate the volume and dimensions of an SBR for the city of New Ark using the
following design data:
Influent data
D e sign flow rate 22,700 m
3
/ d
bCOD 180 mg/L
rbCOD 40 mg/L
Total Kjeldahl nitrogen (TKN) 17 mg/L
NH
3
-N 13 mg/L
Total suspended solids (TSS) 180 mg/L
Volatile suspended solids (VSS) 150 mg/L
Biodegradable volatile suspended solids 70 mg/L
Minimum sustained temperature 12
C
pH 7.1
Alkalinity 150 mg/L as CaCO
3
Effluent discharge standards
bCOD 20 mg/L
NH
3
-N 1.0
TSS 10 mg/L
A ssume MLSS 2,800 mg/L, MLVSS = (0.8) MLSS, NO
x
80% of TKN,
c
25 d. Also assume the cycle time and phase times used in Example 23-13.
23-43. Check the assumed react plus aerated mix time used to design the SBR for the city of
New Ark using the data from Problem 23-42 .
23-44. Check the assumed anoxic fill time used
to design the SBR for the city of New Ark
using the data from Problems 23-42 and 23-43 .
23-45. Estimate the number of jet aerators for the SBR being designed for the city of New
Ark using data form Problems 23-42 , 23-43 , and 23-44. Assume that 60% of the theo-
retical oxygen released in denitrification is available for oxidation and that the oxygen
concentration leaving the tank i
s 19%. Assume the following data for the jet aerators:
SBR elevation 500 m
0.65
0.95
F 1.0
Depth of aerator 5.0 m
T e mperature 12 C
Manufacturer ’ s SOTR 1,370 kg/d at 5.0 m depth
Manufacturer ’ s air flow rate at standard conditions 2,200 m
3
/ d · jet
SECONDARY TREATMENT BY SUSPENDED GROWTH BIOLOGICAL PROCESSES 23-107
23-46. Your firm has been asked to do a preliminary study of the feasibility of a new A
2
/O ™
BPR wastewater treatment plant for Pittsburgh. Begin the design of the complete-mix
BOD removal and nitrification stage. As a first step determine the SRT and volume
of tank required for nitrification using the following design data:
Influent data after primary settling
D e sign flow rate 35,500 m
3
/ d
BOD
5
200 mg/L
bCOD 320 mg/L
rbCOD 60 mg/L
Total Kjeldahl nitrogen (TKN) 45 mg/L
NH
3
-N 35 mg/L
Soluble phosphorus 7 g/m
3
Total suspended solids (TSS) 75 mg/L
Volatile suspended solids (VSS) 65 mg/L
Biodegradable volatile suspended solids 40 mg/L
Minimum sustained temperature 15 C
pH 7.0
Alkalinity 220 mg/L as CaCO
3
Effluent discharge standards
bCOD 20 mg/L
NH
3
-N 1.0 mg/L
NO
3
-N 10 mg/L
TSS 10 mg/L
Total phosphorus 2.0 mg/L
A ssume DO for aeration tank nitrification 2.0 mg/L; MLSS 3,500 mg/L,
MLVSS (0.8) MLSS, NO
x
80% of TKN, and RAS 0.54(Q).
23-47. In continuing the design of the BPR process for Pittsburgh’s new wastewater treat-
ment plant, determine the volume of the anoxic tank. Use the data provided in
Problem 23-46 .
23-48. Check the alkalinity for the BPR wastewater plant being designed for Pittsburgh. Use
the data from Problems 23-46 and 23-47. Assume an alkalinity
of 100 g/m
3
is needed
to maintain a pH of about 7.
23-49. Estimate the effluent phosphorus concentration for Pittsburgh’s new BPR wastewater
treatment plant. Use the data and assumptions from Problems 23-46 through 23-48.
In addition, assume the following:
• 9.5 g rbCOD/g P is removed by BPR
• rbCOD/nitrate ratio is 6.6 g rbCOD/g NO
3
-N
• Phosphorus content of heterotrophic bacteria is 0.02 g P/g biomass
• No NO
3
-N in influent
23-50. As part of a preliminary design, estimate the required blower power for the complete-
mix BOD removal and nitrification stage for Pittsburgh’s new BPR wastewater