Municipal Nutrient Removal Technologies
Reference Document
Volume 2 — Appendices

-------

-------
September 2008
Municipal Nutrient Removal Technologies Reference Document
Appendix A: Case Studies
Appendix A provides detailed case studies with information from nine wastewater treatment
facilities selected for their excellent performance and varying technologies. Two facilities
were chosen because of their denitrification technologies, two were chosen because of their
phosphorus removal technologies, and an additional five facilities were included because of
both nitrogen and phosphorus removal technologies.
Denitrification
•	Central Johnston County, North Carolina
•	Lee County, Florida
Phosphorus removal
•	Kalispell, Montana (biological phosphorus)
•	Clark County, Nevada (biological phosphorus and chemical phosphorus)
Nitrogen and phosphorus removal
•	Kelowna, British Columbia (biological nitrogen and phosphorus)
•	Marshall Street in Clearwater, Florida (biological N and chemical phosphorus)
•	Noman Cole in Fairfax County, Virginia (biological nitrogen and chemical
phosphorus)
•	North Cary, North Carolina (biological nitrogen and phosphorus)
•	Western Branch in Upper Marlboro, Maryland (three separate activated-sludge
systems operated in series)
Appendix A: Case Studies
A-l

-------
Acknowledgements
EPA and the authors would like to acknowledge the commitment, ingenuity and leadership
demonstrated by the owners and personnel at the plants represented by the data reported in
this document. The case studies in this document represent significant accomplishments
made by the leaders of the facilities and their dedicated personnel. EPA recognizes their
cooperation and assistance in providing information on their facilities. Permit compliance
was achieved under all conditions, even under tropical storm conditions in North Carolina
and under an extreme heat wave in Nevada. Some plants (Fairfax County, Virginia, and
Clark County, Nevada), recognized as environmental leaders in their regions, are providing
levels of treatment that go beyond their permit requirements. Central Johnston County, North
Carolina, retrofitted an existing aeration system for biological phosphorus removal and
nitrogen removal and developed the denitrification sludge blanket; Kelowna, British
Columbia, and Lee County, Florida, made similar modifications. Kalispell, Montana,
developed ways to minimize recycle loads from its sludge-handling processes while
producing the lowest phosphorus concentration achieved entirely by a biological process.
Clark County, Nevada, has a Process Today's Sludge Today policy. Clearwater, Florida,
developed a control strategy for nitrogen removal on the basis of three sensors, producing a
low nitrogen concentration in the effluent. Kalispell, Montana, is a good example of sound
technical analysis carried out daily by the plant personnel in optimizing the phosphorus
removal with the best reliability.

-------
Central Johnston County Wastewater Treatment
Plant
Smithfield, North Carolina
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Central Johnston County Wastewater Treatment Plant (WWTP) is in Smithfield, North
Carolina. The facility is designed for a capacity of 7 million gallons per day (MGD), and it
processed an average of 4.12 MGD during the evaluation period, October 2005 to September
2006.
The plant was selected as a case study because it achieves a high level of biological nitrogen
and phosphorus removal through a unique plug-flow, activated-sludge (AS) process
retrofitted to the existing facility, followed by a new stand-alone denitrification filter process.
The relevant National Pollutant Discharge Elimination System (NPDES) permit limits for the
facility are shown in Table 1.
Table 1. NPDES permit limits
Parameter
Annual
loading (lb)
Quarterly
(mg/L)
Monthly average
(mg/L)
Weekly average
(mg/L)
BODs, 4/1-10/31


5
7.5
BODs, 11/1-3/31


10
15
TSS


30
45
Ammonia-Nitrogen,
4/1-10/31


2
6
Ammonia-N
11/1-3/31


4
12
Total phosphorus

2
1
-
Total nitrogen
56,200a



Notes:
BOD5 = biochemical oxygen demand
mg/L = milligrams per liter
P = phosphorus
TSS = total suspended solids
a Equivalent to 3.7 mg/L at 5 MGD
Appendix A
Central Johnston County, NC • Wastewater Treatment Plant -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Plant Process
The plant layout is shown in Figure 1, and the process schematic is shown in Figure 2. After
bar screens, wastewater flows first to anoxic basin 5, then to aerobic basin 4 or 6. The flow
then goes to aerobic basin 1, 2, or 3 before secondary clarification and going through the
denitrifying filters. Following ultraviolet disinfection, the water is discharged to the Neuse
River. Biosolids are aerobically digested, dewatered, and hauled to a landfill.
Basis of Design and Actual Flow
Flow
The design flow for the facility is 7 MGD. The average flow for the study period was 4.12
MGD, while the maximum month flow during the study period was 5.17 MGD during June
2006. The maximum month flow occurred when Tropical Storm Alberto subjected North
Carolina to very heavy rains.
Loadings
Plant loadings were as follows:
Anoxic basin 5: 1 million gallons (MG), or 4.8 hours
Aerobic basin-large: 1 MG, or 4.8 hours
Aerobic basin-small, 1 and 2: 0.55 MG, or 1.9 hours
Aerobic basin-small, 3: 0.34 MG, or 1.2 hours
Total hydraulic retention time (HRT): 11.5 hours
Internal recirculation rate: 8,000-12,000 gallons per minute (gpm), or four times the
influent flow rate
Secondary clarifier: 6.7 hours, or 412 gallons per day per square foot (gpd/ft2)
Denitrification filter, hydraulic loading rate: 3 gpm/ft2
Plant influent and effluent average results for the period October 2005 to September 2006 are
shown in Table 3.
Table 4 presents plant monthly averages for process parameters.
2 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
I
§
§>
s
I
I
I
£
§
St
s
ar
05
s>
aj
§
Es
Top Of &*rm
Reuse Water
Pump Slat-on
Matenng vautt
UV Confection System
Cascaa
Ae^atcK
RAS Pump
Station Mo3
Rauae Water
StotaoeTank
Methanol
~
Pump Stabon
PeaMy
SfaCOfXMUY
Clariter
No5
DenitnfiCBtion
Ftftens
gludoe IVytng Berts
Lab and
Maintenance
Building
> f Reuse Sy«5em
Chemical/Etectncal Bulking
Filter influent
Pump Station
Digester/
Blower
BuiKJmg No 2
Chemical Feed
Facilities
So60»
Storage
Operations Budding
/
Srriids Transfer
Pump Station
Nation Be«n*
Not. 2 and 3
RAS Pump Station No
Arw*>C
Basin
fcattwoo
Standby
Secondary
Influent
Pump
Station
Anoxic
8afen
Efftuaot
|9oxH
Reoatm
Tank*
influent
Distribution
Bo*
Screening Facility
RAS Pump
Station No.2
Blower Budding
No. 1
Figure 1. Central Johnston County WWTP layout.
«*s

-------
Nutrient Removal Technology Assessment Case Study
September 2008
NRCY
Influent
Pump
Station
Bas»n
NRCV i
Fill* Backwash
Reclaim Tanks
RAS
Anoxic
Basin
RAS Pump
Cascade
Contact/
Storage
Tank
Structure
FBWR
FBWR
Aerobic
Digester/Solids
Storage Tank
To Dewatering
Facilities and
Disposal at
Sanitary Landfill
Plant Effluent
to Neuse River
LEGEND:
RAS
Sludge
Pumps
Drying Beds
(backup
dewatering)
Truck Hauling
to Sanitary
* Landfill
(Backup)
WAS Waste Activated
Sludge
Filter Backwash
Distribution System
FBWR
Flow
NRCY Nitrified Recycle
Figure 2-4
Figure 2. Central Johnston County WWTP process schematic.
4 - Central Johnston County. NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 3. Influent and effluent averages
Parameter
Average
Max
month
Max
month vs.
avg.
Max
week
Sample
method/frequency
Flow (MGD)
4.12
5.17
25%
6.2
--
Influent TP (mg/L)
5.8
8.5
46%
13.6
Weekly/composite
Effluent TP (mg/L)
0.26
0.64
140%
1.01
Weekly/composite
Influent BOD (mg/L)
320
386
20%
497
Daily/composite
Effluent BOD (mg/L)
3
4.59
32%
5.2
Daily/composite
Influent TSS (mg/L)
328
419
27%
564
Daily/composite
Effluent TSS (mg/L)
1.21
1.47
13%
1.8
Daily/composite
Influent NH4-N (mg/L)
28
34.4
27%
37.4
Daily/composite
Effluent NH4-N (mg/L)
0.44
0.54
22%
0.86
Daily/composite
Influent TN (mg/L)
31.2
42.7
37%
63.1
Daily/composite
Effluent TN (mg/L)
2.14
2.77
30%
3.13
Daily/composite
Notes:
BOD = biochemical oxygen demand
mg/L = milligrams per liter
NH4-N = ammonia measured as nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
Appendix A
Central Johnston County, NC • Wastewater Treatment Plant - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 4. Monthly averages for plant process parameters

MLSS
Sludge age
HRT
Temperature
Month
(mg/L)
(d)
(hr)
(°C)
Oct 2005
2,527
8.1
23.1
23
Nov 2005
2,445
7.9
13.9
19
Dec 2005
2,650
8.5
15.9
17
Jan 2006
2,686
8.6
15.1
16
Feb 2006
2,452
7.9
16.4
14
Mar 2006
2,643
8.5
23.6
16
Apr 2006
2,679
8.6
27.9
18
May 2006
2,417
7.8
23.5
20
June 2006
2,300
7.4
19.4
24
July 2006
2,378
7.6
23
26
Aug 2006
2,448
7.9
25.1
27
Sep 2006
2,574
8.3
21.6
25
Notes:
HRT = hydraulic retention time
MLSS = mixed liquor suspended solids
Performance Data
Figures 3 and 4 present reliability data for removal of total phosphorus (TP). The removal is
good, with the effluent TP averaging 0.26 mg/L and a medium coefficient of variation (COV)
of 62 percent.
6 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Johnston County, NC
Monthly Average Frequency Curves for Total Phosphorus
100
a
Mean = 0.26 mg/L
Std. Dev. = 0.164 mg/L
C.O.V. = 62%
0.01
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent	x Final Effluent
Figure 3. Monthly average frequency curves for TP.
100
D)
E
o
J=
Q.

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Johnston County, NC
Monthly Average Frequency Curves for Ammonia-N
: Mean = 0.44 mg/L
Std. Dev. = 0.055 mg/L
C.O.V. =12%
0.05 0.1 0.5 1 2
5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent Ammonia-N
x Final Effluent Ammonia-N
Figure 5. Monthly average frequency curves for ammonia nitrogen.
100
10
Johnston County, NC
Weekly Average Frequency Curves for Ammonia-N
~ ~ ~ ~
»~~~~
0.1
Mean = 0.44 mg/L
Std. Dev. = 0105 mg/L
C.O.V. =24%
0.05 0.1 0.5 1 2
5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent Ammonia-N
x Final Effluent Ammonia-N
Figure 6. Weekly average frequency curves for ammonia nitrogen.
Figures 7 and 8 present reliability data for removal of total nitrogen (TN). Between the
anoxic portion of the AS system and the denitrification filter, the plant gives outstanding TN
removal, with effluent TN of 2.14 mg/L and a COV of 1 percent.
8 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Johnston County, NC
Monthly Average Frequ
ency Curve
s for Total Nitrogen


• ~
~ ~ ~
















Std. Dev. = 0.36 mg/L


O.U. V. — 1 u /o



0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent TN	x Final Effluent TN
Figure 7. Monthly average frequency curves for TN.
Johnston County, NC
Weekly Average Frequency Curves for Total Nitrogen
100
~ ~ ~ ~'
_l
O)
E
c
o
O)
O
L_
4-"
Mean = 2.14 mg/L
Std. Dev. = 0.48 mg/L
C.O.V. =23%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
~ Raw Influent TN	x Final Effluent TN
Figure 8. Weekly average frequency curve for TN.
Appendix A	Central Johnston County, NC • Wastewater Treatment Plant - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Reliability Factors
This facility is unique in two areas: (1) biological phosphorus removal and nitrogen removal
in a plug-flow, AS process and (2) separate-stage denitrification filters. The results are
excellent. The plant achieves a phosphorus mean concentration of 0.26 mg/L with a COV of
62 percent without any chemical addition and a TN concentration of 2.14 mg/L with a COV
of only 16 percent. The key factors for this exceptional performance are briefly discussed
below.
In terms of wastewater characteristics, the BOD-to-TP ratio is high, with an average value of
55.1. This means that no additional food is required to support anaerobic phosphorus release.
The BOD-to-TN ratio is high at 10, when 5 or greater would be recommended.
The plant uses a plug-flow, AS process with anoxic and aerobic basins in series. This was a
retrofit design that the plant personnel implemented. Some unique features of this process are
an anoxic basin with a long detention time, followed by a two-stage aerobic stage in series
and, at the same time, the flexibility of operating parallel trains, such as during high-flow
periods. The base mode of operation includes a long detention time at the anoxic basin (1
MG in basin 5), followed by an equal-size first aerobic basin (1 MG, basin 4 or 6) and then a
smaller basin (either basin 3 or basins 1 and 2 combined). The internal recirculation from
aerobic zone to the anoxic zone in the head area is up to four times the influent flow rate.
A unique operational strategy developed at the plant calls for a low return activated-sludge
(RAS) flow rate and a deep sludge blanket in the clarifiers. The clarifiers are operated with
3 to 4 feet of blanket, while RAS is maintained at only 10 to 25 percent of the flow rate. In
addition, the controlling parameter is mixed-liquor suspended solids (MLSS), ranging
between 1,700 mg/L in summer and 2,400 mg/L in winter. There is no separate tank for
volatile fatty acid generation. This practice has proven to provide full nitrification and a
significant degree of denitrification in the retrofitted AS process. The average nitrate-
nitrogen in the secondary effluent was 4 to 8 mg/L, leaving the denitrification filter to polish
the effluent.
The plant uses denitrification filters manufactured by Leopold with a down-flow pattern and
an automated system to control the methanol feed. The package includes a nitrate probe by
Hach and a dosage-control algorithm by Leopold. The process is economical and efficient in
denitrification. This is a compact process with a small footprint.
Another unique feature of this plant is that there is no primary settling and therefore all
sludge produced is aerobic sludge. The sludge is pumped to the dewatering facility 5 miles
away for dewatering with a cationic polymer. The filtrate is returned to the head of the plant
for further processing.
10 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Recycle loads are minimal because only aerobic digestion occurs on-site.
Wet-weather flows are managed with a normal mode of operation. The plant operated
normally during a tropical storm in June 2006, when the flow increased from less than
4 MGD to more than 10.5 MGD in 3 days. Under extreme conditions such as a hurricane, the
plant would shut down part of the aeration basin and protect the sludge inventory.
Cost Factors
Capital Costs
The main upgrades of the plant for biological nutrient removal (BNR) were implemented in
2000, when the existing aeration basins were reconfigured to allow an anoxic/anaerobic/
aerobic series, and in 2005, when denitrifying filters were installed. The total cost for those
upgrades, which were largely done by plant personnel, was $3.76 million. The components
were updated to a total of $4,056 million in 2007 dollars using the Engineering News-Record
Capital Cost Index (ENR CCI) index (USDA 2007).
It was assumed that 50 percent of the 2000 upgrade and 12 percent of the 2005 upgrade could
be attributed to phosphorus removal, while 50 percent of the 2000 upgrade and 88 percent of
the 2005 upgrade could be attributed to nitrogen removal. This attribution of the 2005
upgrade was based on the bulk of those capital improvements being for the denitrifying filter.
The capital expenditure in 2007 dollars that could be attributed to phosphorus removal was
$889,000. The annualized capital charge (20 years at 6 percent) was $77,500 for phosphorus
removal.
The capital expenditure in 2007 dollars that could be attributed to nitrogen removal was
$2.4 million. The annualized capital charge (20 years at 6 percent) was $210,000 for nitrogen
removal.
The total capital attributed to BNR in 2007 dollars was $4,056 million. For the 7-MGD
facility, the capital expenditure for BNR was $0.58/gpd capacity.
Operation and Maintenance Costs
The plant uses biological phosphorus removal to achieve the limit, while using methanol
addition to complete the nitrogen removal. This means that the costs for phosphorus removal
are all electrical, while the costs for nitrogen removal are electrical plus methanol. A
summary of the electrical calculations is provided in an attachment at the end of this case
study. The total electrical usage for phosphorus removal, assumed to be 30 percent of the
total used, was 1,842,000 kilowatt-hours per year (kWh/yr). When the average electrical rate
of $0.056/kWh was applied, the cost for phosphorus removal was $103,000 for the year. The
total electrical usage for nitrogen removal was 4,170,000 kWh/yr, or $233,000.
Appendix A
Central Johnston County, NC • Wastewater Treatment Plant -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The plant adds methanol at the rate of 83.1 gpd, at a cost of $1.75/gallon. This is equivalent
to $53,000/yr for nitrogen removal.
Because of the methanol addition, an incremental amount of sludge is generated. The volume
of methanol added is equivalent to 547 lb/day after accounting for the density of methanol,
which is 0.79 g/cm3. The chemical oxygen demand (COD) of the methanol is 1.5 lb COD/lb
methanol, and the yield of volatile suspended solids (VSS) on methanol was assumed to be
0.4 lb VSS/lb COD (McCarty et al. 1969). The plant generated 328 lb sludge/day from
methanol addition, or 59.9 ton sludge/yr. Assuming $200/ton for sludge disposal, the
incremental amount for sludge addition attributed to nitrogen removal is $12,000.
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 69,900 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal is $1.48, while the unit capital cost is
$0.73/lb of phosphorus removed.
During the same period, the plant removed 619,000 lb of TN. With the results above, the unit
O&M cost for TN removal is $0.49, while the capital cost is $0.49/lb of TN removed.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the unit capital and unit O&M costs. Thus, the life-cycle
cost for phosphorus removal is $2.21/lb phosphorus removed, the life-cycle cost for ammonia
nitrogen removal is $1.02/lb nitrogen removed, and the life-cycle cost for TN removal is
$0.98/lb TN removed.
Cost-Effectiveness of the Denitrification Filter
The cost-effectiveness of the denitrification filter was evaluated separately for this plant.
From filter influent and effluent data collected during a filter stress test in 2007, the filter on
the average removes 3.5 mg/L nitrate-nitrogen. At a flow rate of 4.12 MGD, the filter
removed 43,900 lb of nitrate-nitrogen during a year. Using the costs established above—
$53,000 for methanol for the year and $12,000 for additional sludge disposal costs from
methanol addition—the O&M cost per pound of nitrate removed in the denitrification filters
is $65,000/43,900 = $1.48/lb nitrate-nitrogen removed.
Assessment of Magnitude of Costs and Main Factors
The life-cycle costs for phosphorus removal and full nitrification are extremely low,
considering the phosphorus reduction level the plant has achieved. The main factors
contributing to this achievement are the maximum use of existing facilities, good biological
phosphorus removal, and efficient control with automation and many online sensors.
12 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Assessment of magnitude of costs and main cost factors: The magnitude of cost at this
facility is very low, mainly because of the availability of existing facilities and the original
operating strategies of the plant personnel in maximizing both nitrogen and phosphorus
removal at the retrofitted AS process. The new denitrification filters, therefore, use a minimal
amount of methanol. In addition, no chemical is used to remove phosphorus. These factors
make both the capital cost and O&M costs of this plant very low.
Discussion
Reliability factors: The plant achieves excellent performance at the mean concentration of
2.14 mg/L of TN with a COV of 16 percent. This is mainly because the plant has two
separate-stage denitrification processes with an external carbon source at the second stage, or
dentrification filter. Operational strategies developed by the plant personnel achieved a
significant amount of denitrification in the AS process, followed by a separate-stage
polishing with an automated feed strategy using an online nitrate probe. For phosphorus
removal, the mean concentration of 0.26 mg/L is excellent, while the COV is moderate at
62 percent. This low a level is remarkable for an entirely biological phosphorus removal
process. Note that the denitrification filter by Leopold uses a down-flow process and
therefore removes suspended solids concurrently with nitrogen removal.
Cost factors: Three key factors are identified in achieving a high level of BNR at a low cost
at this facility: (1) the maximum use of an existing AS process with minimal retrofit costs;
(2) development of an original operating strategy to maximize BNR in the retrofitted AS
process; and (3) a separate-stage denitrification with minimal methanol feeding. This
combination of biological phosphorus removal and a down-flow denitrification filter in series
resulted in a reliable, low-cost solution for both nitrogen and phosphorus removal.
Summary
This facility removes both nitrogen and phosphorus exceptionally well and reliably. The two-
stage biological processes in series offer the highest efficiency in nutrient removal at
minimum costs. The source of wastewater is typical residential customers in the suburb of a
large metropolitan area. The BOD-to-TP ratio averages 55.1. The retrofitted AS process
consists of an anoxic stage with a 4.8-hour residence time, followed by an aerobic stage in
two tanks with a residence time of 11.5 hours. The operating strategy developed at this
facility is unique because the sludge blanket at the clarifiers is 3 to 4 feet deep and the RAS
flow rate is maintained at a low (10-25 percent) portion of the plant flow. The second-stage
denitrification filters then remove the remaining nitrogen with a methanol feed.
The design and operation result in a high level of removal—an effluent TN concentration of
2.14 mg/L with a COV of only 19 percent and an effluent TP concentration of 0.26 mg/L
with a COV of 62 percent.
Appendix A
Central Johnston County, NC • Wastewater Treatment Plant -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The costs of removal were very low for both capital and O&M. The life-cycle cost for
removal of TP was $2.21/lb of TP removed, while the life-cycle cost for TN removal was
$0.98/lb of TN removed, including the cost for methanol. The capital cost for the flow
capacity was low at $0.58/gpd capacity.
Acknowledgments
The authors are grateful for the significant assistance and guidance provided by Haywood
Phthisic, III, director of Utilities in Johnston County, North Carolina. This case study would
not have been possible without Mr. Phthisic's prompt response, with well-deserved pride in
the facility and its operation. Thanks are extended to Johnston County for participating in this
case study for the U.S. Environmental Protection Agency.
References and Bibliography
McCarty, P., L. Beck, and P. St. Amant. 1969. Biological denitrification of wastewater by
addition of organic materials. In Proceedings of the 24th Purdue Industrial Waste
Conference, Lafayette, IN.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
14 - Central Johnston County, NC • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Attachment: Electrical Cost Calculation
Electrical
Anoxic/Anaerobic Mixers
HP Number
Power
draw
(kW)
kWh/day
kWh
draw/day
kWh
%P
%N
For P
For N
10
15
15
3
1
1
22.38
11.19
11.19
24
24
24
537.12
268.56
268.56
196,048.8
98,024.4
98,024.4
70
70
70
30
30
30
137234.2
68617.08
68617.08
58,814.64
29,407.32
29,407.32
Blowers
150
100
2
2
223.8
149.2
24
24
5,371.2
3,580.8
1,960,488
1,306,992
30
30
70
70
588146.4
392097.6
1,372,342
914,894.4
Filter Pumps
150
3
335.7
24
8,056.8
2,940,732
20
60
588146.4
1,764,439
Total Draw




6,600,310


1,842,859
4,169,304
Methanol
83.1
1.75
145.425
53,080.125
gal/day
cost/gal
cost/day
cost/yr







Appendix A
Central Johnston County, NC • Wastewater Treatment Plant -15

-------

-------
Fiesta Village Advanced Wastewater Treatment
Plant
Lee County, Florida
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
This plant was selected as a case study because it is a good example of the use of the
denitrification filter process. The plant consists of an extended air oxidation ditch process
followed by denitrification filters with methanol feed. Phosphorus removal is achieved with
alum feed to the secondary effluent. Nitrogen and phosphorus are being removed
successfully down to 3 and 0.1 milligrams per liter (mg/L), respectively.
The Fiesta Village Advanced Wastewater Treatment Plant is in Lee County, Florida. It is
permitted for 5 million gallons per day (MGD) capacity, and in 2006 it processed an average
of 3.16 MGD. The plant is designed to send 2.0 MGD (annual average) into a slow-rate,
public-access reuse system for irrigation of golf courses and residential developments. It has
the potential for future reuse expansion to 3.158 MGD. Any water not reused, including
stormwater flow, is permitted for a surface water discharge to the Caloosahatchee River.
The relevant National Pollutant Discharge Elimination System (NPDES) permit limits for the
facility are shown in Tables 1 and 2.
Table 1. NPDES permit limits
Parameter (mg/L
Annual
Monthly

Daily
unless stated)
average
average
Weekly average
maximum
BOD5
20
25
40
60
TSS
20
30
45
60
Total nitrogen
3
3
4.5
6
Total phosphorus
0.5
0.5
0.75
1
Notes:
BOD = biochemical oxygen demand.; TSS = total suspended solids
Table 2. Reuse water permit limits
Parameter (mg/L
unless stated)
Annual
average
Monthly
average
Weekly average
Daily
maximum
BODs
20
30
45
60
TSS



5
Residual chlorine



1 (minimum)
Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Treatment Processes
Figures 1 and 2 present the plant layout and process flow for the Fiesta Village Facility. The
plant is an extended-aeration oxidation ditch facility, and the treatment process includes an
odor control system, primary bar manual/mechanical screening, aerated grit removal, two
oxidation ditches, two clarifiers, two aerobic digesters, three screw lift pumps, four
denitrification filters, dual chlorine contact chambers, effluent transfer pumping station,
chemical feed equipment, sulfur dioxide dechlorination, post-re-aeration, a reuse storage
tank, and a high-service reuse/effluent pump station.
Basis of Design and Actual Flow
The design flow for the facility is 5 MGD. The average flow for the study period was
3.16 MGD, while the maximum month flow during the study period was 4.14 MGD during
July 2006. The peak day flow recorded was 5.78 MGD.
Design loadings:
Biochemical oxygen demand (BOD): 240 mg/L
Total suspended solids (TSS): 268 mg/L
Total Kjeldahl nitrogen (TKN): 37 mg/L
Total nitrogen (TN): 38.2 mg/L
Total phosphorus (TP): 7.3 mg/L
Alkalinity: 284 mg/L as calcium carbonate (CaCOs)
Oxidation ditch—437 ft long x 80 ft wide x 12 ft deep, or 3 million gallons (MG), each
Anoxic zone: one aerator turned off, or 25 percent by volume
Aerators: 60 hp, four each per oxidation ditch
Hydraulic retention time (HRT): 28.8 hours
Mixed liquor suspended solids (MLSS): 3,500 mg/L
Mixed liquor volatile suspended solids (MLVSS): 2,500 mg/L
Mean cell residence time: 30 days
Food to microorganism ratio: 0.1:0.4 lb BOD/lb MLVSS
Waste activated sludge (WAS): 0.06 MGD, each, or 6,500 lb/day, each
Dissolved oxygen (DO): 0.5-2.0 mg/L in aerobic zone and 0.1-0.5 mg/L in anoxic
zone
Secondary clarifiers—diameter of 90 ft (each, and there are two)
Volume: 0.665 MG (each)
Surface area: 5,538 ft2 (each) and surface loading rate = 600-1,200 gpd/ft2
Blanket depth: less than 3 ft
Return activated sludge (RAS)—rate at 100 percent of plant influent, or 3.5 MGD (3 each)
Denitrification filter—10 ft x 40 ft, 4 cells each
Hydraulic loading rate: 2.2 gpm/ft2 at design
2 - Lee County, FL • Advanced Wastewater Treatment Plant
Appendix A

-------
f
§
B.
Is
m
9
§
S3
r-<
d.
1
o
Q>
&>
to
TREATMENT PROCESS FLOW DIAGRAM
FIESTA VILLAGE ADVANCED WASTEWATER TREATMENT PLANT
CHEMICAL
FEED POINT
i
\ v
II
, \
k 1


BAR SCREEN
rrOOOOq-
AERATtD
GRiTTANK
INFLUENT

OXIDATION
DITCH
J_L
O:
CLARIFIER
T
PUMPS •


RECYCLE
SLUDGE
WASTE
SLUDGE
m
RECYCLE SLUDGE
TO WASTE SLUDGE DISPOSAL
DENITRIFICATION
FILTERS
BACKWASH AND AERATION BASIN
CHLORINE
CONTACT
E=FLUENT
PUMPING
STATION
i-Asir,
BACKV/ASH
VVAI i ;!
DIFFUSED Aifl
BACKWASH
GOLF COURSE IRRIGATION OR DISCHARGE TO RIVER
FOR PLANT REUSE
SCREW LIFT PUMPS
DRAIN
0)
Hgure 1. Treatment process flow diagram Fiesta Village Advanced Wastewater Treatment Plant.
I
§2
1
e*s

-------
t-1
T>
ft!
O
§
ST
ia.
cs.
1
1
ex.
aT
0}
i
&
§
<¦*+
*2
t3
FIE5TA VILLAGE APVANCI
'ATER TREATMENT PLANT
SCREW LIFT PUMPS LABORATORY AND ADMINISTRATION BUILDINGS
DENITRIFICATION FILTERS
BLOWER ROOM
MUDWELL
CLAfllFlER TANKS
BACKWASH BASlN
SLUDGE BASIN
ENTRANCE
METHANOL
STORAGE
TANKS
RETENTION
POND
TANK	ALUM TANK
CHLORINE FACILITIES
OXIDATION DITCHES
EXISTING THICKENER \ imfwENT STRUCTURE
HYDRO-PNEUMATIC TANK
STORAGE GARAGE
CHLORINE CONTACT BASIN
EFFLUENT PUMP
FLORIDA POWER AND LIGHT 8LDG
Figure 2. Site plan Fiesta Village Advanced Wastewater Treatment Plant.
t
§
&
*
c/>
CD
~o
CD
3
a-
cd
ro
o
o
CO

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Aerobic Digestion
-	Diameter: 39 ft, 16 ft deep
-	Volume: 0.143 MG, 2 each
-	Disc diffusers
-	Loading rate: 0.01-0.02 lb VSS/ ft3 day
-	DO: 1-3 mg/L
-	Sludge age: 5-40 days
-	Digester temperature: less than 30 degrees Celsius (°C)
Plant Parameters
Overall plant influent and effluent average results for the period January 2006 to December
2006 are shown in Table 3.
Table 3. Fiesta Village influent and effluent averages
Parameter (mg/L
unless stated)
Average
value
Maximum
month
Max
month vs.
ave.
Maximum
week
Sample
method/frequency
Flow (MGD)
3.16
4.14
31%
4.26

Influent TP
3.85
4.58
18%
-
Monthly/composite
Effluent TP
0.102
0.19
85%
0.39
Daily/composite
Influent BOD
134
167
24%
179
Daily/composite
Effluent BOD
1.37
2.95
116%
5.2
Daily/composite
Influent TSS
199
261
31%
348
Daily/composite
Effluent TSS
0.72
1.17
61%
1.48
Daily/composite
Influent NH4-N
27.2
34.5
27%
-
Monthly/composite
Effluent NH4-N
0.13
0.2
50%
0.28
Daily/composite
Secondary
Effluent NO3-N
2.9a
3.0a
7%
3.9a
Daily/composite
Influent TN
33.2
50.6
53%
-
Monthly/composite
Effluent TN
1.71
2.61
53%
3.90
Daily/composite
Notes:
BOD = biochemical oxygen demand
Max month vs. average = (max month - average)/average x 100
NH4-N = ammonia measured as nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
a Jan-April 2007
Table 4 presents plant monthly averages for the process parameters, as available.
Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 4. Monthly averages for plant process parameters
Month
MLSS
(mg/L)
Sludge age
(d)
HRT
(hr)
Temperature
(°C)
Jan 2006
3,578
37
48
--
Feb 2006
3,807
39
44
--
Mar 2006
4,085
35
46
--
Apr 2006
3,845
24
50
--
May 2006
3,510
33
55
--
June 2006
3,564
28
47
--
July 2006
3,571
32
35
30.4
Aug 2006
3,480
36
44
--
Sept 2006
3,495
34
39
--
Oct 2006
3,509
37
49
--
Nov 2006
3,775
59
49
--
Dec 2006
4,204
41
50
--
Performance Data
Figure 4 presents reliability data for the removal of TP. The removal is good, with an effluent
TP average of 0.1 mg/L and a medium coefficient of variation (COV) of 35 percent.
100
3
O
-C
Q_
TO
° 0.1
0.01
Figure 4. Monthly average frequency curves for TP.
Fiesta Village WWTP, Lee Co., FL
Monthlv Averaae Freauencv Curves
for Total PhosDhorus


















	~ ~ ' '













* Mean = 0.102 mg/L
- Std. Dev. - 0.035 mg/L 	


	— oO /o 	



0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
« Raw Influent	x Final Effluent
6 - Lee County, FL • Advanced Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Figure 5 presents reliability data for ammonia nitrogen removal. The removal of ammonia
nitrogen is very good, with a mean effluent of 0.134 mg/L and a low COV of 40 percent.
Fiesta Village WWTP Lee Co., FL








~ ~
» ~ ~ ~
















= Mean = 0.134mg/L =


Std. Dev. - 0.054 mg/L


	C.O.V. = 40% —


¦	X	








0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 989999.5 99.999.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N
* Final Effluent - Ammonia N
Figure 5. Monthly average frequency curves for ammonia nitrogen.
Figure 6 present reliability data for removal of TN. Nitrogen is removed in two steps at this
facility. The oxidation ditch takes nitrate-nitrogen down to an average of 3 mg/L, and then
the denitrification filter takes it down to an annual average of 1.45 mg/L. at a COV of 28
percent.
Fiesta Village WWTP Lee Co., FL
Monthly Average Freq
uency Cun/
es for Nitrogen


	~	

~ ~
~	
~ ~ ~ •




















¦	X	

Mean = 1.7 I mg/L


	Std. Dev. - 0.48 mg/L -\


C.O.V. = 28%
	1—i	1—i	1	1	1	1	1	1—
	1	1	1	
	i	i	i	i	i	i	i	i	
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99-5 99.999.95
Percent Less Than or Equal To
~ Raw Influent - Total N	x Final Effluent - Total N
¦ Secondary Effluent N03-N
Figure 6. Monthly average frequency curves for nitrogen.
Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Reliability Factors
This facility is unique in three ways: separate-stage denitrification using methanol; alum feed
to the oxidation ditch effluent prior to the secondary clarifiers for chemical phosphorus
removal; and filtration of effluent with the same denitrification filters. The facility is also
unusual in that it has no primary settling and thus all sludge generated is kept aerobic before
it is disposed of off-site at another county facility.
The results are excellent. The plant achieved a TN concentration of 1.71 mg/L with a COV of
28 percent and a total phosphorus (TP) concentration of 0.1 mg/L with a COV of 35 percent.
The key factors contributing to this performance are described below.
The key reason for excellent denitrification is the use of two processes in series—the first in
the oxidation ditch for most of the removal, followed by polishing at the denitrification filter.
The oxidation ditch is operated with the target nitrate-nitrogen concentration of 3.0 to
3.5 mg/L and ammonia nitrogen at 0.2 mg/L in the secondary effluent. This target removal is
accomplished under the current loading conditions by turning one of four brush aerators off
during the day and two off during the night, thereby maintaining 25 percent and then
50 percent of the volume, respectively, as an anoxic zone. The DO concentration in the
oxidation ditch is adjusted using the remaining brush aerators. The oxidation ditch is
operated with a long SRT (30-40 days) and HRT (20-30 hours). In addition, another unique
operating plan includes the denitrification blanket in the clarifiers. The sludge blanket depth
is maintained at between 2.5 and 3.5 feet.
The denitrification filters then brings the nitrate-nitrogen to below 2 mg/L, with a low
methanol feed rate of 129 lb per day. The methanol-to-nitrate-nitrogen ratio averaged
1.9 pounds of methanol per pound of nitrate present, or 2.4 lb per pound of nitrate removed.
The plant measures nitrate-nitrogen in the effluent in adjusting the methanol feed rate, which
is steady year-round.
Alum was fed at the average dosage of 8.9 mg/L as aluminum, or at the aluminum-to-TP
ratio of 2.31, in achieving a low concentration of 0.1 mg/L for the year.
Recycle loads are minimal at this facility because aerobically digested sludge is hauled away
to another facility for final sludge processing.
During wet-weather periods, a normal mode of operation is maintained. Under extreme peak
flow conditions, the clarifiers are protected from surges by shutting off a number of brush
aerators.
8 - Lee County, FL • Advanced Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Costs
Capital Costs
The main upgrades of the plant for biological nitrogen removal (BNR) occurred in 1984,
when Phase 1, consisting of the east oxidation ditch, east clarifier, denitrifying filter, and
major structures for the west ditch and west clarifier were installed; in 1986, when Phase 2
improvements were installed; and in 2002, when equipment for the west oxidation ditch and
west clarifier was installed. Table 5 presents the costs for those improvements (Voorhees et
al. 1987; TKW Online 2007), along with capital cost updates based on the Engineering
News-Record Capital Cost Index (ENR CCI). The ENR CCI, compiled by McGraw-Hill,
provides a means of updating historical costs to account for inflation, thereby allowing
comparison of costs on an equal basis. From a Web site provided by the U.S. Department of
Agriculture (USDA 2007), the ENR index for 1984 was 4,146; for 1986, 4,295; for 2002,
6,538; and for May 2007, 7,942.
Table 5. Plant improvement costs

Year
Original cost
2007 cost
%P
%N
%other
P cost
N cost
Phase 1
1984
$6,505,833
$12,462,452
2%
50%
48%
$249,249
$6,231,226
Denite Filter
1984
$930,059
$1,781,604
12%
88%
0%
$213,792
$1,567,811
Controls
1984
$441,323
$845,390
2%
50%
48%
$16,908
$422,695
Phase 2
1986
$1,200,000
$2,218,952
0%
50%
50%
$0
$1,109,476
Phase 3
2002
$6,800,000
$8,260,263
0%
50%
50%
$0
$4,130,132
TOTAL


$25,568,661
--
--
--
$479,949
$13,461,340
The table also shows the percentage of capital cost for each unit that was attributed to
phosphorus or nitrogen removal; the rest of the capital cost was attributed to other treatment,
particularly biochemical oxygen demand (BOD) and total suspended solids (TSS) removal
and disinfection. Because the plant is not doing biological phosphorus removal, it was
assumed that only 2 percent of the Phase 1 cost plus 2 percent of the cost of controls could be
attributed to phosphorus removal for the alum addition system. Because the denitrification
filters remove solids, including aluminum phosphate precipitate, it was assumed that 12
percent of that cost could be attributed to phosphorus.
On the basis of DO usage, it was assumed that 50 percent of the cost of Phases 1, 2, and 3
could be attributed to nitrogen removal. It was assumed that 88 percent of the cost of the
denitrification filters could be attributed to nitrogen removal. To be consistent with other case
studies in this document, it was assumed that 50 percent of the control costs could be
attributed to nitrogen removal.
Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The above analysis resulted in a total of $480,000 in capital attributed to phosphorus removal
and $13,461,000 attributed to nitrogen removal, in 2007 dollars. The annualized capital
charge for phosphorus removal (20 years at 6 percent) was $42,000. The annualized capital
charge for nitrogen removal was $1,174,000.
The total capital attributed to nutrient removal, in 2007 dollars, was $13.9 million. For the
5-MGD facility, this means the capital expenditure per gallon of treatment capacity was
$2.79.
Operation and Maintenance Costs
The plant uses chemical phosphorus removal and BNR, with extensive use of alum for the
former and methanol as a supplemental carbon source for the latter. This means that the cost
for phosphorus removal is essentially all for chemicals and for the disposal of the resulting
sludge, while the cost for nitrogen removal is electrical (for the aeration basins), chemical
(for the methanol), and for the disposal of the extra sludge resulting from methanol addition.
A summary of the electrical calculations is provided in the Attachment. It was assumed that
some of the electricity for the blowers could be attributed to phosphorus removal, to account
for mixing alum in the ditch. The total electrical usage for nitrogen removal was 1,911,000
kilowatt-hours (kWh). When the average electrical rate of $0.12/kWh (including demand
charges) was applied, the cost of electricity for nitrogen removal was $229,000.
Alum is applied for both phosphorus removal and TSS reduction to meet the permit
requirements for water reuse. The average amount of alum applied over the period was
151 gallons/MG of flow; assuming $0.66/gallon, the cost of alum was $115,400. It was
assumed that 30 percent of the alum cost was attributed to phosphorus removal, bringing the
chemical cost for phosphorus removal to $34,600.
Methanol is applied at the denitrification filter to promote nitrate removal. The total amount
of methanol added over the study period was 47,000 lb. Assuming a cost of $0.27/lb (cost of
methanol for another case study plant), the chemical cost for nitrogen removal was $12,500.
The alum added (8.9 mg/L as Al) was assumed to entirely convert to aluminum hydroxide
sludge; at the average flow of 3.16 MGD, this was 677 lb of aluminum sludge per day, or
124 dry tons/year. The plant trucks its sludge at an average cost of $0.048/gallon. Assuming
a concentration of 2 percent solids, the 124 dry tons of alum sludge is equivalent to
1,486,000 gallons of sludge. Assuming 30 percent of the sludge is associated with
phosphorus removal, the cost for phosphorus sludge disposal was $21,700.
The 47,000 lb/yr of methanol has a chemical oxygen demand (COD) of 1.5 lb COD/lb
methanol, or 70,750 lb COD/yr. The typical yield of volatile suspended solids (VSS) on
methanol is 0.4 lb VSS/lb COD, giving 28,300 lb sludge/yr, or 14.2 tons sludge/yr from
10 - Lee County, FL • Advanced Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
methanol addition. At a solids concentration of 2 percent, this means an additional 708 tons,
or 170,000 gal/yr, of liquid sludge to haul to other Lee County plants for treatment and
disposal. The total hauled during 2006 was 7,520,000 gallons, meaning the methanol sludge
was approximately 2.2 percent of the total. At the plant's average disposal charge of
4.9 cents/gallon, the total cost for nitrogen removal sludge was $8,300.
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 36,100 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal is $1.77, while the unit capital cost is
$1.16/lb of phosphorus removed. If the plant were operating at full capacity (5 MGD), the
unit O&M cost for phosphorus removal would be $1.34, with the unit capital cost $0.73/lb of
phosphorus removed.
During the evaluation period, the plant removed 303,000 lb of TN. With the results above,
the unit O&M cost for nitrogen removal is $0.91, while the capital cost is $3.87/lb of TN
removed. If the plant were operating at full capacity, the unit O&M and capital costs would
be $0.57 and $2.45, respectively, per pound of TN removed.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the unit capital and unit O&M costs. Thus, the life-cycle
cost for phosphorus removal is $2.93/lb of phosphorus removed, the life-cycle cost for TN
removal is $4.78/lb of TN removed, and the life-cycle cost for ammonia nitrogen removal is
$5.57/lb of nitrogen removed. For full-capacity operations, the costs would be $2.07/lb for
phosphorus, $3.02/lb for TN, and $3.52/lb for ammonia nitrogen.
Assessment of magnitude of costs: The capital cost of $2.79 per gpd capacity is on the high
side, but the O&M costs are moderate because of the low electrical costs but high chemical
costs.
Discussion
Reliability factors. The performance has been very reliable in nitrogen and phosphorus
removal. Nitrogen removal was achieved very reliably by having two processes in series for
denitrification. Most of the removal was accomplished by the optimal use of the oxidation
ditch system, where denitrification was achieved in anoxic zones of various sizes, as well as
in the denitrifying sludge blanket in the clarifiers. The polishing of nitrate was accomplished
at the denitrification filters with minimal dosage of methanol. Phosphorus removal was
accomplished by alum addition before the secondary clarifiers, followed by the same
denitrification filters, making the process both efficient and reliable.
Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant 11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Cost factors'. Costs for both methanol and alum are low because of the optimal use of the
existing facilities. Costs are also low because sludge is not processed on-site.
Summary
The Fiesta Village facility is an advanced wastewater treatment plant with an oxidation ditch
followed by secondary clarifiers and four dedicated denitrification filters. The performance
was highly efficient and reliable for the year studied. Nitrogen removal was achieved
biologically to the mean concentration of 1.44 mg/L with a COV of 27 percent. Many factors
contributed to this high result, including maximum use of the oxidation ditch for
denitrification, thereby reducing the load to the denitrifcation filters. The personnel at the
facility are credited for developing daily operating procedures for the control parameters and
implementing them consistently. Using denitrifying blankets in the clarifiers and maintaining
flexible anoxic zones in the oxidation ditch are two unique features of the operation in
achieving effluent nitrate-nitrogen concentration of 3 mg/L as a monthly average. The
methanol usage was minimal at the average dosage of 1.9 lb per pound of nitrate applied,
compared to 3 lb in the literature.
Acknowledgments
The authors of this report acknowledge with gratitude the significant assistance and guidance
provided by Tom Hill, Lee County utilities deputy director; Dennis Lang, chief operator at
the Fiesta Village Facility; and Jon Meyer, Utilities Operations Manager. This report would
not have been possible without their prompt response with well-deserved pride in their
facility and operation. EPA acknowledges Lee County, Florida, for its participation in this
case study.
References and Bibliography
TKW Online. 2007. http://www.tkwonline.com/enviromental.html. Accessed July 15, 2007.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
Voorhees, J.R., W.G. Mendez, and E.S. Savage. 1987. Produce an AWT Effluent for Florida
Waters, Environmental Engineering Proceedings (EEDiv) ASCE, Orlando, Florida,
July 1987.
WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers).
1998. Design of Municipal Wastewater Treatment Plants. Manual of Practice No.8,
Figure 11.7, Net sludge production versus solids retention time.
12 - Lee County. FL • Advanced Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Attachment: Electrical and Chemical Costs
Electrical







for P
for N
Hp
Number
kW
Power draw
hours/day
kWh
draw/day
kWh
draw/year
%P
%N


Aerator
60
8
358.08
24
8593.92
3136781
2
50
62735.6
1568390.4
RAS pump
30
3
67.14
24
1611.36
588146.4
0
50
0
294073.2
WAS pump
7.5
2
11.19
24
268.56
98024.4
0
50
0
49012.2
Total draw




3822952


62735.6
1911475.8
Alum cost
% for P removal
Alum cost for P
Methanol cost
$115,338
30
$34,616
$12,735
(all for N
removal







Appendix A
Lee County, FL • Advanced Wastewater Treatment Plant -13

-------

-------
Kalispell Advanced Wastewater Treatment
Kalispell, Montana
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Kalispell Wastewater Treatment Plant (WWTP) is an advanced wastewater treatment
facility in Kalispell, Montana. Kalispell is in the northwestern part of the state, near Glacier
National Park. The area is subjected to extreme weather conditions, with temperatures
ranging from 95 degrees Fahrenheit (°F) in the summer to -30 °F in the winter.
This facility was selected as a case study because of good biological phosphorus removal and
nitrification using a modified University of Cape Town (UCT) process with the fermenter
technology in a cold region.
The facility began operating in October 1992 to protect Flathead Lake, the largest freshwater
lake west of the Mississippi River. The plant has received a national first place and two
Region 8 first place Operations and Maintenance Excellence Awards from the U.S.
Environmental Protection Agency (EPA), a Commendation of Excellence Award from the
Flathead Basin Commission, and a System of the Year Award from Montana Rural Water
Systems. In addition, the processes for nitrogen removal was designed and implemented as a
voluntary initiative.
Kalispell has experienced a significant increase in population since the facility was
constructed. The city plans to expand the plant over the next several years to accommodate
growth. The expansion will add to or replace some units and modify others to continue the
concept of treatment without using chemicals. The plant is designed with expansion planned
for the flows and loads shown in Table 1.
Table 1. Design flow and loads

Flow
BOD5
TSS
TKN
TP
Year
(MGD)
(mg/L)
(mg/L)
(mg/L)
(mg/L)
2000
2.5
216
259
25
4.5-6.5
2008
3.0
216
260
25
4.5-6.5
Notes:
BOD5 = biochemical oxygen demand
MGD = million gallons per day
TKN = total Kjeldahl nitrogen
TSS = total suspended solids
TP = total phosphorus
Appendix A
Kalispell, MT • Advanced Wastewater Treatment -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The National Pollutant Discharge Elimination System (NPDES) permit limits for the plant
are shown in Table 2.
Table 2. NPDES permit limits

7-day average
30-day average
Parameter
(mg/L)
(mg/L)
BODs
15
10
TSS
15
10
Total P
--
1.0
Ammonia nitrogen
-
1.4 (sufficient to meet stream limits)
Treatment Processes
Wastewater treatment at the Kalispell WWTP begins with flow entering the plant through a
36-inch-diameter pipe from the city's system. The influent flows through the headworks and
is pumped to two rectangular primary clarifiers by five low-head lift pumps. Primary clarifier
effluent then flows into the bioreactor, which consists of 11 tanks in series. During periods of
high flow, primary effluent is directed to the equalization basin. Flow from the equalization
basin is then returned to the primary clarifiers during periods of lower influent flow.
The system at Kalispell is unique because it is based on the modified UCT process with
additional flexibility provided by swing zones that can be operated in several different
modes. Four zones (anaerobic, first and second anoxic, and aerobic) are created for solids
and nutrient removal. Depending on the chemistry and biology, the plant personnel can
determine the optimum number of anaerobic zones and, thus, the subsequent anoxic zones.
Bioreactor effluent flows to two circular, center-drive secondary clarifiers and then through
an effluent deep-bed sand filter, with an up-flow, continuous backwash design. The filtered
effluent then flows through an ultraviolet disinfection system and is re-aerated before it is
discharged to Ashley Creek.
The solids process train in the plant starts with the primary sludge that is removed from the
primary clarifiers by two primary sludge pumps to the completely mixed fermenter. Primary
sludge is pumped to the fermenter at timed intervals—typically at 4.8 minutes per hour. The
target solids concentration in the fermenter is 12,000 milligrams per liter (mg/L). Waste
fermented sludge flows to the gravity thickener; two pumps return the fermenter supernatant
to the bioreactor. The fermenter has a volume of 118,000 gallons, a hydraulic retention time
of 7 to 21 hours, and a mixing power of 0.06 horsepower (HP) per 1,000 gallons. The solids
retention time (SRT) is designed to be 4 to 5 days.
2 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Sludge from the gravity thickener is pumped to the primary digester and then to the two
secondary digesters. Digested primary sludge is pumped to two belt filter presses. Secondary
sludge is pumped as return activated sludge (RAS) to the bioreactor. The RAS is pumped by
two RAS pumps to two dissolved air flotation (DAF) thickeners. DAF filtrate is wasted back
to the bioreactor, and the thickened sludge from the DAF is pumped via two DAF float
pumps to two belt filter presses, where it is mixed with digested primary sludge just before
the presses. The DAF sludge is not anaerobically digested to avoid re-release of accumulated
phosphorus. The belt press cake is trucked to a composting operation. Digester supernatant
and the filtrate from belt press are returned to the headworks.
Figure 1 shows the overall process flow diagram. Figure 2 shows details of the biological
reactor and how RAS can be directed to one of three cells depending on operating conditions.
The fermenter supernatant also can be directed to any of the first three cells as conditions
warrant.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment - 3

-------
>?
Ha

5a.
ea,
1
C/3
i;
3
t
3
s,
n"
KalispelVs
Advanced WWTP
Equalization
Basin
Pnmar>
C'liUifscf
BAR
SCREEN
GRlI
REMOVAL
LIFT
PUMPS
Primary
Clariiicf
Bioreactor
11 Cells in Series Flow
Nutrient removal
BURIAL IN
LANDFILL
Digester
Facility
kiMx Primary
ASHLEY CREEK
y:/<
rural
C'Urtfkr
Ultraviolet
Light
Disinfection

C larificT
Solids
Return Activated Sludge
VI-AS
Scum
Primary *'
Diopciit -1
I xchangc
rermenter
i
Dissolved
Air
Flotation
Units
Glacier
Gold
C ompost
Belt
Filter
Presses
ScsndB)
!W*r
Gravity
Thickener
Figure 1. Kalispell's advanced WWTP.

-------
f
§
B.
I
[6

ES.
1
r>
n>
Q,
as-
ANAER 1»t. AMOX 2nd ANOX.
AERQ0IC
WASTE ACTIVATED SLUDGE
to sludge Handling
raw
INFLUENT
3.1
FLOW
equalization
BASIN
ANAEROBIC
RECYCLE
MO OK Qt
luent	—i. .—I	(to or. ot |	p
\/ © © © © ©
DENITRlFtCATION RECYCLE
30 0% O
PRIMARY SLUDGE FERMENTER
I
r m
i	iii
i.
©

®
VtV.'.
	LI	L| — 1 .
© © ©I
%^v*v.v4»%yyA%v«*.|.v.v.*.v.vl
ALUM SOLUTION
(Standby only)
CTj
I	|_ |	RETURN ACTIVATED SLUDOE |BO-IOOttQ?|	^
SECONDARY
CLAfllflERS l?l
BtOREACTOR SRT |5?5 dot«
MLSS ?,500-3,500 m
-------
Nutrient Removal Technology Assessment Case Study
September 2008
Plant Parameters
Overall plant influent and effluent average results for the period July 2005 through June 2006
are shown in Table 3.
Table 3. Influent and effluent averages
Parameter
(mg/L unless
stated)
Average
Maximum
month
Max
month vs.
avg.
Maximum
week
Sample
method/frequency
Flow (MGD)
2.95
3.45
17%
4.04
--
Influent TP
4.11
4.88
19%
5.2
Composite/weekly
Effluent TP
0.12
0.15
25%
0.31
Composite/weekly
Influent BOD
226.36
282
25%
428
Composite/weekly
Effluent BOD
< 4
< 4
0%
5.8
Composite/weekly
Influent TSS
225.17
326
45%
680
Composite/weekly
Effluent TSS
1.21
2.9
140%
4.1
Composite/weekly
Influent NH4-N
24.35
29.4
21%
--
Grab/monthly
Effluent NH4-N
< 0.07
< 0.07
0%
--
Grab/monthly
Influent TKN
39.28
47
20%
--
Grab/monthly
Effluent TKN
0.63
1.26
100%
--
Grab/monthly
Influent TN
39.6
48.0
21%
--
Grab/monthly
Effluent TN
10.6
19.9
86%
--
Grab/monthly
Notes:
BOD = biochemical oxygen demand
Max month vs. average = (max month - average)/average x 100
MGD = million gallons per day
NH4-N = ammonia measured as nitrogen
TKN = total Kjeldahl nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
6 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 4 presents plant monthly averages for process parameters.
Table 4. Monthly averages for plant process parameters

MLSS
Sludge age
HRT
Water temp
Month
(mg/L)
(d)
(hrs)
(°C)
July 2005
2,586
10
13
18.9
Aug.2005
2,517
8
14
20
Sept 2005
2,625
11
13
18.6
Oct 2005
2,659
12
14
17.1
Nov 2005
2,637
10
15
14.9
Dec 2005
2,808
11
15
12.1
Jan 2006
2,744
10
12
11.4
Feb 2006
2,757
9
13
10.8
Mar 2006
2,657
9
14
10.9
Apr 2006
2,568
9
11
12.3
May 2006
2,536
9
13
14.8
June 2006
2,529
9
11
16.7
Notes:
HRT = hydraulic retention time
MLSS = mixed liquor suspended solids
Performance Data
This section provides information about the operational performance of nutrient removal at
the plant. Figures 3 and 4 present reliability plots for monthly average and weekly average
phosphorus. For the monthly average data, the facility has a very low coefficient of variation
(COV) of 19 percent, with standard deviation of 0.023 mg/L and a mean of 0.121 mg/L for
the 12-month period. The COV is defined as the standard deviation divided by the mean, and
it is a measure of a system's reliability. The lower the COV, the less the data are spread and
the higher the reliability. Variation is slightly higher on a weekly basis, with a COV of
41 percent. Overall, the facility is highly reliable at removing phosphorus. This is remarkable
in comparison to many other facilities, which have reported poor reliability for biological
phosphorus removal.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Kalispell, MT
Monthly Average Frequency Curves for Total Phosphorus





















































	 Mean = 0.121 rriy/L 	


	 Std. Dev. = U.U23 mg/L	






II III II III
I I I
i i 	
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent	* Final Effluent
Figure 3. Monthly average frequency curves for TP.
Kalispell, MT
Weekly Average Frequency Curves for Total Phosphorus
100.00
10.00

u>
E


-------
September 2008
Nutrient Removal Technology Assessment Case Study
Figure 5 presents the reliability plot for monthly average ammonia nitrogen. The facility
reports only a monthly result for nitrogen compounds, which precludes generating a
reliability plot for weekly data. For the period of July 2005 to June 2006, the plant routinely
produced effluent ammonia nitrogen below a detection level of 0.07 mg/L. This is
remarkable for a cold-region operation with an average water temperature of 8 degrees
Celsius (°C) on cold days. The plant's successful operating strategy has been to maintain
sufficient biomass during the winter, i.e., 2,700 parts per million (ppm) of mixed liquor
suspended solids (MLSS) vs. 2,500 ppm in the summer. The higher biomass in winter allows
the process to overcome the greatly slowed growth of nitrifiers under cold conditions.
Kalispell, MT
Monthly Average Frequency Curves for Ammonia Nitrogen








>	~	
































	Mean < 0.07 mg/L —


* *	Std. Dev. = 0.00 mg/L —






II III II III
I I I
i i 	
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent	* Final Effluent
Figure 5. Monthly average frequency curves for ammonia nitrogen.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Figure 6 presents the reliability plot for monthly TN. The plant personnel set a design goal of
900 lb/day as TN (36 mg/L at 3 million gallons per day [MGD]), but this is not a permit
limit. For the period of July 2005 to June 2006, the plant produced an effluent with an
average TN of 10 mg/L, with more than 90 percent of that in the form of nitrate.
Kalispell, MT
Monthly Average Frequency Curves for Total Nitrogen (Goal)
100
O
E
E
< 0.1
0.05 0.1 0.5 1 2	5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent X Final Effluent
Figure 6. Monthly average frequency curves for TN (goal).
Reliability Factors
The plant has a permit limit for phosphorus of 1 ppm year-round monthly average; for
ammonia nitrogen, it has a permit limit of 1.4 ppm monthly average to meet all stream
requirements. However, the plant has an operational policy to achieve the maximum nutrient
reduction without needing to add chemicals to precipitate phosphate or to support
denitrification.
The key factor in the facility's success is generating sufficient volatile fatty acids (VFAs).
The plant routinely meets its target of 18 mg/L VFAs at 20 °C and 13 mg/L VFAs at 13 °C in
the anaerobic zones. This means that the VFA-to-total phosphorus (TP) ratio ranges
seasonally between 1.5 and 6. The yearly average ratio is 3.5. The plant uses a two-stage
fermenter to generate VFAs from primary sludge and produces around 200 mg/L VFAs in
winter and 450 mg/L VFAs in summer under the sludge age of 4 to 5 days and an HRT of 7
to 21 hours. Unique design allows separate control of the SRT and HRT at this facility.
Thickened fermented sludge is transferred to the anaerobic digesters, while the supernatant is
pumped to the first anaerobic cell in the biological nutrient removal (BNR) system (Emrick
10 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
and Abraham 2002; Natvik et al. 2003). The result is that the plant obtains effluent TP
concentrations averaging 0.12 mg/L over the year with a low COV.
Another factor in the facility's success is that the plant personnel monitor each cell in the
biological reactor for nutrient concentration, pH, and suspended solids and take actions as
needed. Personnel do the monitoring by daily analyzing grab and composite samples rather
than by using online sensors. The hands-on approach and daily attention to system
performance prevent problems from becoming uncontrolled, while giving the operators a
stake in the plant performance rather depending on the computer. Adjustments that can be
made include solids wasting rate, recycle points, and which cells are aerobic or anoxic.
The flexibility in the process design is another valuable feature at Kalispell because the plant
personnel can change the effective volumes of the anaerobic, anoxic, and aerobic zones by
independently adjusting the conditions in each reactor cell as conditions warrant. The
bioreactor is optimized for SRT and HRT at varying temperatures.
Another important operating practice is that of not maintaining sludge blankets in the
secondary clarifiers (No Blanket Policy). This has helped the plant to achieve healthy biology
with sufficient sludge age and excellent phosphorus removal because maintaining an
inventory of sludge that has accumulated phosphorous maintains the chance that some of that
phosphorous will eventually be released. In the summer the sludge age is maintained at
between 8 and 10 days with an MLSS of 2,500 ppm. In winter the MLSS is increased to
2,700 ppm to ensure full nitrification under cold weather conditions.
Although this facility nitrified fully down to the detection limit (0.07 mg/L), the
denitrification was not required and therefore was not practiced. The COV for ammonia
nitrogen was 0 percent at the mean concentration of 0.07 mg/L as nitrogen. The COV was
31 percent at the mean concentration of TN of 10.6 mg/L.
Recycle loads were kept low at this facility. Secondary sludge was kept aerobic until
dewatering, and the digester supernatant was kept at a minimum. The results were that the
ortho-phosphorus returning to the headworks was measured at 6 percent of the influent TP
load.
Wet-weather flows were managed through the equalization basin, which can store
12.5 percent of the influent flow. No special mode of operation was required at this facility.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Costs
Capital Costs
The plant was upgraded for BNR in 1992, when the system was set up as an 11-cell modified
UCT with swing zones. The modifications for BNR were part of an overall upgrade program
that cost a total of $13.5 million—$9.94 million in construction costs and $3.56 million in
indirect costs. The elements involved in BNR that were included in the 1992 expansion are
shown in Attachment 1. They included additional tanks, tank coatings, a supervisory control
and data acquisition (SCADA) system, mixers, pumps, blowers, a fermenter, and a secondary
sludge thickener. As shown in Attachment 1, these costs were attributed to removal of
phosphorus, removal of nitrogen, or removal of non-nutrients, specifically biochemical
oxygen demand (BOD). For units where the purpose could be fixed on one nutrient (e.g., a
fermenter, which is only for phosphorus removal), the cost was attributed entirely to that
nutrient. For the anoxic zone mixers, the cost was evenly divided between nitrogen and BOD
removal because they are removed equally in those zones during denitrification. For the
aeration zones and where units could not be specified for nutrients, the distribution was
12 percent for phosphorus, 48 percent for nitrogen, and 40 percent for BOD, which is the
ratio at which those three removal processes take up oxygen on a molar basis during aeration.
The total of the construction costs for the BNR units was $4.2 million. Because the total
indirect costs on the $9.9 million construction were $3.56 million, the indirect costs
attributed to BNR were $1.51 million by ratio. These costs were allocated to phosphorus,
nitrogen, and BOD removal using the 12/48/40 formula, resulting in $749,000 for
phosphorus removal, $2.71 million for nitrogen removal, and $2.26 million for BOD
removal, all in 1992 dollars.
These capital cost results were updated to 2007 dollars using the Engineering News-Record s
Construction Cost Index (ENR CCI). The ENR CCI, compiled by McGraw-Hill, provides a
means of updating historical costs to account for inflation, thereby allowing comparison of
costs on an equal basis. From a Web site provided by the U.S. Department of Agriculture,
the ENR index for 1992 was 4,985, while the ENR index for May 2007 was 7,942 (USDA
2007). Multiplying the above results by the ratio 7,942/4,985 obtained the result of
$1.19 million for phosphorus removal, $4.31 million for nitrogen removal, and $3.60 million
for BOD removal in 2007 dollars.
These results were annualized using the interest rate formula for determining a set of annual
payments for a present value, given an interest rate and payback period. For this and all other
case studies for this document, a 6 percent interest rate and 20-year payback was assumed,
resulting in a multiplication factor of 0.0872. The annualized capital cost for phosphorus
removal was thus $101,500, while the annualized capital cost for nitrogen removal was
$376,000. This annualized capital cost for nitrogen removal was used for later unit cost
estimates for TN.
12 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
As shown in Attachment 1, the total capital charge for the BNR removal system was
$5.7 million in 1992 dollars, which updated to $9.1 million in 2007 dollars. For this 3-MGD
facility, the total capital cost for BNR removal was $3.03/gallon of treatment capacity.
Operation and Maintenance Costs
In all case studies prepared for this document, the O&M costs considered were for electricity,
chemicals, and sludge disposal. Labor costs for operation and maintenance were specifically
excluded for three reasons:
1.	Labor costs are highly sensitive to local conditions, such as the prevailing wage rate,
the relative strength of the local economy, the presence of unions, and other factors;
thus, they would only confound comparison of the inherent cost of various
technologies.
2.	For most processes, the incremental extra labor involved in carrying out nutrient
removal is recognized but not significant in view of the automatic controls and
SCADA system that accompany most upgrades.
3.	Most facilities were unable to break down which extra personnel were employed
because of nutrient removal and related overtime costs, making labor cost
development difficult.
The Kalispell plant uses an entirely biological process to achieve both nitrogen and
phosphorus limits; therefore, the only significant operating cost is electrical use for mixers,
pumps, and operating the fermenter. Attachment 2 shows a summary of the power use
calculations. The power use attributed to phosphorus removal was 389,000 kilowatt-hours
(kWh); using the average electrical rate of $0.045/kWh (which included all demand charges),
the electrical cost for phosphorus removal was $17,500. The power usage attributed to
nitrogen removal was 1,077,000 kWh, and at the average electrical rate, the electrical cost for
nitrogen removal was $48,500.
Unit Costs for Nitrogen and Phosphorus Removal
In the evaluation period, the plant removed 35,700 lb of phosphorus. With the results above,
the unit O&M cost for phosphorus removal was $0.49/lb, while the annualized unit capital
cost for phosphorus removal was $2.84.
In the evaluation period, the plant removed 258,000 lb of TN. With the results above, the unit
O&M cost for TN removal was $0.19/lb of TN, while the annualized unit capital cost for TN
removal was $1.46.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the annualized unit capital and unit O&M costs. Thus, the
life-cycle cost for phosphorus removal was $3.33/lb and the life-cycle cost for TN removal
was $1.64/lb.
Assessment of magnitude of costs: The capital cost of $3.03/gpd capacity is relatively high,
but the O&M costs are very low. One of the key factors is that chemicals are not used for
nutrient removal, saving both those costs and costs that would be attributed to additional
sludge generation.
Summary
The Kalispell Advanced WWTP has proven to successfully provide enhanced biological
phosphorus removal in a cold-climate region of the United States. The reliability of the
facility is good, with a mean effluent concentration of 0.12 mg/L as TP and a COV of
19 percent monthly average, or a COV of 41 percent weekly average. Ammonia nitrogen
removal reliability is outstanding, with a mean concentration at or below the detection limit
of 0.07 mg/L and a COV of 0 percent on a monthly average basis.
Reliability factors include a science-based control strategy, in-house generation of sufficient
VFAs in the fermenter, and diligent monitoring and timely control of key process parameters
by plant personnel. Removal costs for both phosphorus and nitrogen were shown to be
reasonable, with O&M costs for both being largely driven by electricity usage and relatively
low capital costs.
Acknowledgments
The authors of this report are grateful to Joni Emrick, water resource manager, and Curt
Konecky of the Kalispell Advanced WWTP for their guidance and assistance in preparing
this case study. This case study report would not have been possible without their prompt
response with well-deserved pride in the facility and its operation. The authors also wish to
thank the city of Kalispell for its participation.
References and Bibliography
Emrick, J., and K.Abraham. 2002. Long-term BNR Operations—Cold in Montana! In
Proceedings of the Water Environment Federation 75th Annual Technical Exhibition
& Conference, Chicago, IL, September 28-October 2, 2002.
Natvik, O., B. Dawson, J. Emrick, and S. Murphy. 2003. BNR "Then" and "Now"—A Case
Study—Kalispell Advanced Wastewater Treatment Plant. In Proceedings of the
14 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Water Environment Federation 76th Annual Technical Exhibition & Conference,
Los Angeles, California, October 11-15, 2003.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
Appendix A
Kalispell, MT • Advanced Wastewater Treatment -15

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Attachment 1: Capital Costs


%P
%N
%BOD
$P
$N
$BOD
Tanks
$1,300,000
12%
48%
40%
$156,000
$624,000
$520,000
Tank coats
$75,000
12%
48%
40%
$9,000
$36,000
$30,000
SCADA
$1,000,000
12%
48%
40%
$120,000
$480,000
$400,000
Mixers
$43,000
0%
50%
50%
$0
$21,500
$21,500
Ret/Sup pumps
$175,000
12%
48%
40%
$21,000
$84,000
$70,000
Blowers
$155,000
0%
50%
50%
$0
$77,500
$77,500
Fermenter
$45,000
100%
0%
0%
$45,000
$0
$0
Thickener
$35,000
100%
0%
0%
$35,000
$0
$0
Primary sludge pump
$80,000
10%
50%
40%
$8,000
$40,000
$32,000
Piping
$500,000
12%
48%
40%
$60,000
$240,000
$200,000
Site work
$800,000
12%
48%
40%
$96,000
$384,000
$320,000
Total
$4,208,000



$550,000
$1,987,000
$1,671,000








Indirects
$1,505,526
12%
48%
40%
$180,663
$722,653
$602,211
Total capital
$5,713,526



$730,663
$2,709,653
$2,273,211








Updated to 2007
$9,102,673



$1,164,078
$4,316,963
$3,621,633
Annualized




$101,508
$376,439
$315,806
Updating factors







1992 ENRCCI
4,985






May 2007 ENRCCI
7,942






A/P (6%, 20 years)
0.0872






16 - Kalispell, MT • Advanced Wastewater Treatment
Appendix A

-------
t
§
n.
Attachment 2: Electrical Costs
Horsepower
Volts
Amps
VA
Number
kW
Power draw
hours/day
kWh
draw/day
kWh
draw/year
%P
%N
For P
For N
Mixers












3
460
4
1,840
5
9.2
24
220.8
80,592
12%
48%
9,671.04
38,684.16
7.5
460
10
4,600
4
18.4
24
441.6
161,184
12%
48%
19,342.08
77,368.32
Ret Pumps
10
460
5.82
2,677.2
1
2.6772
24
64.2528
23,452.27
12%
48%
2,814.273
11,257.09
4
460
6.7
3,082
1
3.082
24
73.968
26,998.32
12%
48%
3,239.798
12,959.19
Blowers












200
460
220
101,200
2
202.4
24
4,857.6
1,773,024
0%
50%
0
886,512
Super Pumps
7.5
460
9.7
4,462
2
8.924
24
214.176
78,174.24
12%
48%
9,380.909
37,523.64
Fermenter












5
460
6.8
3,128
2
6.256
24
150.144
54,802.56
100%
0%
54,802.56
0
15
460
27
12,420
2
24.84
24
596.16
217,598.4
100%
0%
217,598.4
0
10
460
14
6,440
1
6.44
24
154.56
56,414.4
100%
0%
56,414.4
0
Gravity Thickener
2 460
3.1
1,426
1
1.426
24
34.224
12,491.76
100%
0%
12,491.76
0
Primary Clarifie
5
5r Sludge
460
3ump
6.8
3,128
1
3.128
24
75.072
kWh/yr
27,401.28
2,512,133
12%
48%
3,288.154
389,043.4
13,152.61
1,077,457







Rate
0.045
$/kWh

P
N







Totals
113,046

$/yr
17,506.95
48,485.57
&
§
1
0
CD
C/5
05
1
a3
&
§

-------

-------
Clark County Water Reclamation Facility
Las Vegas, Nevada
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Clark County Water Reclamation Facility (WRF) is in Las Vegas, Nevada. This facility
was selected as a case study because of the anoxic/oxic (A/O) process for biological
phosphorus removal with alum feed.
Originally commissioned in 1956, the facility was enhanced with biological nutrient removal
(BNR) in 1995 during an 88-million gallon per day (MGD) expansion. The plant has
obtained a very high level of phosphorus removal following a series of facility upgrades.
With the expansion, the facility essentially operates as two plants—the Advanced Waste
Treatment Plant (AWT) and the Central Plant (CP)—with separate discharges available. The
expansion allowed the plant to gain nitrification capabilities for the entire plant flow, in both
the CP and the AWT. Although the facility initially used and still uses chemical treatment to
meet standards, it has also implemented the A/O process to provide biological phosphorus
removal. The facility is designed for an average flow of 100 MGD and averaged 95 MGD
during the 2006 calendar year.
The relevant National Pollutant Discharge Elimination System (NPDES) permit limits are
listed in Table 1.
Table 1. Clark County WRF NPDES permit limits
Parameter
30-day avg.
(mg/L)
7-day avg.
(mg/L)
30-day avg.
(lb/day)
Daily wasteload
allocation (lb/day)
BOD
30
45
37,530
--
TSS
30
45
37,530
--
TP
--
--
--
173
Total NH4-N
--
--
--
502
Notes:
BOD = biochemical oxygen demand
NH4-N = ammonia measured as nitrogen
P = phosphorus
TSS = total suspended solids
Appendix A
Clark County, NV • Water Reclamation Facility -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The wasteload allocation is an arrangement in which the Nevada Division of Environmental
Protection set an overall load on the Las Vegas Wash from Clark County, the city of Las
Vegas, and Henderson, Nevada. The allocations for Clark County translate into 0.21
milligrams per liter (mg/L) total phosphorus (TP) and 0.6 mg/L for ammonia nitrogen at 100
MGD.
Basis of Design and Flow Schematic
Primary settling tanks: 818 gallons per day per square foot (gpd/ft2) at annual average flow
and 1,309 gpd/ft2 at peak hour
Activated sludge: nine basins
Hydraulic capacity per basin	10 MGD
Total volume per basin	2.13 MG
Hydraulic retention time	5.1 hours
Sludge age	5-9 days
Secondary clarifier: 710 gpd/ft2 at annual average flow
A flow sheet for the CP is presented in Figure 1 for the entire facility. The main difference
between the AWT and the CP is that the AWT employs tertiary clarifiers in advance of the
tertiary filters, as shown in Figure 2. In both plants, influent is treated in the primary settling
tanks with ferric chloride added as enhancement, then through A/O biological reactors. The
A/O process provides biological phosphorus removal and nitrification, along with some
degree of denitrification. From there, the wastewater is dosed with alum for additional
phosphorus removal and then treated in a tertiary clarifier/filter combination in the AWT or
in just a tertiary filter in the CP. When the clarifiers were first installed in the 1980s, filter
technology was such that they needed protection from high solids that would make operation
and maintenance (O&M) difficult; the CP uses an air-water, scour-backwash system so that
such protection is not vital to continued good operation. The effluent is filtered and
disinfected by ultraviolet (UV) radiation and then either sent to reclaimed water customers or
discharged to the Las Vegas Wash and the Lake Meade Wetlands.
The secondary sludge is thickened by dissolved air flotation (DAF). The primary sludge is
thickened to 5 percent solids in the settling tanks and then sent to the same holding tank with
the thickened secondary sludge. They are dewatered together by belt filter press for
landfilling.
2 - Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Primary
Treatment
BPR
Activated
Sludge

DAFT
CPT Tertiary
Facility
AWT Tertiary
Facility
Liquid
Solid
Recycle
Dewatering
Figure 1. Plant flow schematic.
Alum
8-13 mg/L
Backwash
Excess Flows
AWT
Secondary
EfflU5nr>
CENTRAL
PLANT
rrl
Floe
Basin
Tertiary Clarifiers


Gravity Thickener
4	


Filters
(no air scour)
Sludge
To Headworks
Backwash Clarifier
EQ
Basin
Sludge
Filters
(with air scour)
^To Headworks
U V.


w
Discharge to
east side of Las
Vegas Wash
Discharge to
west side of Las
Vegas Wash
Alum
4-10 mg/L
Figure 2. Tertiary processes.
Appendix A
Clark County, NV • Water Reclamation Facility - 3

-------
Nutrient Removal Technology Assessment Case Study	September 2008
Influent Flow 110 MGD
Influent Suspended Solids 299 mg/L
Influent Biochemical Oxygen Demand 294 mg/L
Bar
Screen
Screenings
Holding
Bin
Grit Removal
I Tank
To
Landfill
Ferric Chloride
Polymer
Primary
Settling Tanks
Thickened
Sludge Holding
Tank
Aeration
Basins
Return
Activated
Sludge
Ferric Chloride
Polymer
Dissolved Air
Flotation
Thickener
Secondary
Settling Tanks
Filter
Press
Waste
Activated
Sludge
Sludge
Cake
To
Landfill
Dual Media
Filters
Ultraviolet
Light Disinfection
Sodium
Hypochlorite
To Reclaimed
Water Customers
Discharge to Las Vegas Wash and Lake Mead Wetlands
Figure 3. Clark County WRF CP flowsheet schematic.
4 - Clark County. NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Plant Data
Table 2 presents average plant data for the 2006 calendar year. The data show outstanding
removal of nutrients, biochemical oxygen demand (BOD), and suspended solids. The facility
easily meets all of its permit limits.
Table 2. 2006 average CP water quality data
Parameter
Average
Max
month
Max month
vs. avg.
Max
week
Sample method/
frequency
Flow (MGD)
98
101.4
3.5%
102.3
--
Influent TP (mg/L)
5.8
7.0
20%
7.5
Daily/composite
Effluent TP (mg/L)
0.1
0.17
73%
0.41
Daily/composite
Influent BOD (mg/L)
357
390
9%
445
Daily/composite
Effluent BOD (mg/L)
< 2
4.75
137%
7
Daily/composite
Influent TSS (mg/L)
366
413
13%
456
Daily/composite
Effluent TSS (mg/L)
< 5
10
100%
21
Daily/composite
Influent NH4-N (mg/L)
26.8
28.8
7%
30
Daily/composite
Effluent NH4-N (mg/L)
0.08
0.31
300%
1.22
Daily/composite
Influent TKN (mg/L)
46
53
14%
75
Daily/composite
Effluent TKN (mg/L)
0.69
1.02
47%
2.3
Daily/composite
Influent N03/N02 (mg/L)
0.18
0.46
155%
0.8
Daily/composite
Effluent NO3/NO2 (mg/L)
15.3
16.4
7%
16.5
Daily/composite
Influent TN (mg/L)
30.3
34.5
14%
37.6
--
Effluent TN (mg/L)
15.2
16.6
7%
16.7
--
Notes:
BOD = biochemical oxygen demand
NH4-N = ammonia measured as nitrogen
NO3/NO2 = nitrate + nitrite
TKN = total Kjeldahl nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
Appendix A
Clark County, NV • Water Reclamation Facility - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 3 presents plant monthly average plant process parameters.
Table 3. CP monthly average plant process parameters

MLSS
Sludge age
HRT
Temperature
Month
(mg/L)
(d)
(hr)
(°C)
Jan 2006
2,902
9
5.43
20
Feb 2006
3,422
9
5.45
20
Mar 2006
3,684
8
5.31
24
Apr 2006
3,732
7
5.10
26
May 2006
3,147
6
5.06
28
June 2006
3,499
5
5.82
29
July 2006
3,166
5
5.73
29
Aug 2006
3,057
5
5.80
29
Sept 2006
2,425
6
6.32
28
Oct 2006
2,441
7
6.31
26
Nov 2006
2,760
8
6.42
24
Dec 2006
2,535
8
6.49
20
Notes:
HRT = hydraulic retention time
MLSS = mixed liquor suspended solids
Performance Data
Figures 4 and 5 present reliability plots for weekly average and monthly average TP. The
plant operation provides outstanding performance in TP removal: the average effluent
concentration is under 0.1 mg/L and the coefficient of variation (COV) is low at 30 percent.
This means that the data have a low standard deviation relative to the mean and, therefore,
that the plant will routinely produce effluent with TP below 0.2 mg/L through the course of
the year.
6 - Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
100
Clark Co. NV Water Reclamation Plant
Weekly Average Frequency Curves for Total Phosphorus
10
oi
E
o
.c
S
o
0.01
: CP Mean = 0.1 mg/L
; Std. Dev. = 0.042 mg/L
COV = 43%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent
A Final Effluent
Figure 4. Weekly average frequency curves for TP.
Clark Co. Water Reclamation Plant - Las Vegas, NV
Monthly Average Frequency Curves for Total Phosphorus
100
10
O)
£

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Figures 6 and 7 present reliability plots for the weekly average and monthly average total
nitrogen (TN) for the facility. TN removal is not required under the permit, and therefore it is
limited. The effluent TN averages 15.2 mg/L with a standard deviation of 0.6 mg/L.
Clark Co. Nevada Water Reclamation Facility
Weekly Average Frequency Curves for Nitrogen








~~~
~ ~ 		








M 'x m"¦		



















Std. Dev. = 0.67 mg/L


COV = 4%


















II III II III
i i i
i i 	
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - TKN	* Final Effluent - Total N
Figure 6. Weekly average frequency curves for nitrogen.
8 - Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
100
Clark Co. Water Reclamation Facility
Monthly Average Frequency Curves for Nitrogen
~ ~ ~ ~
~ ~~~~~:
10
oi
E
oi
o
: Mean =15.2 mg/L
: Std. Dev. = 0.6 mg/L
:COV = 4%
0.1
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 9999.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - TKN
x Final Effluent - Total N
Figure 7. Monthly average frequency curves for nitrogen.
Figures 8 and 9 present reliability plots for weekly average and monthly average ammonia
nitrogen for the plant. Ammonia is routinely removed to near the detection level in the plant,
with a mean of 0.05 mg/L and a very low COV of 22 percent.
Appendix A
Clark County, NV • Water Reclamation Facility - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Clark Co. Nevada Water Reclamation Facility
Weekly Average Frequency Curves for Ammonia Nitrogen
100
» ~ ~ ~ 		1
>~~ ~ ~—~—~
0.1
0.01
* *
~ Mean = 0.049 mg/L
Std. Dev. = 0.023 mg/L
" COV =49%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N X Final Effluent - Ammonia N
Figure 8. Weekly average frequency curves for ammonia nitrogen.
100
10
Ol
E
ai
o
0.1
0.01
Clark Co. Water Reclamation Facility
Monthly Average Frequency Curves for Ammonia Nitrogen
: CP Mean =0.048 mg/L
- Std. Dev. = 0.011 mg/L
COV = 22%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 9899 99.5 99.9 99.95
Percent Less Than or Equal To
« Raw Influent - Ammonia-N	x Final Effluent - Ammonia N
Figure 9. Monthly average frequency curves for ammonia nitrogen.
10 Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Reliability Factors
Several factors have contributed to efficient and reliable operation at this facility. The
effluent concentration was low at 0.09 mg/L in TP with a COV of 30 percent and 0.05 mg/L
in ammonia nitrogen with a COV of 22 percent.
One key is the wastewater characteristics and in-plant generation of volatile fatty acids
(VFAs). The BOD-to-TP ratio averaged 29.8 for the year and ranged from an average 26.5 to
34.2 monthly. Furthermore, this facility generated additional VFAs by operating primary
settling tanks as fermenters. Typical operating parameters included thickening the primary
sludge to 5 percent total solids, thereby generating enough VFAs to maintain 35 to 45 mg/L
of VFA in the primary effluent. Thickening primary sludge to 6 percent total solids was
found excessive and detrimental to both odor-control and clarification purposes.
The biological process was originally a conventional process, which was later converted to
an A/O process by adding aeration controls to ensure sufficient dissolved oxygen (DO) in the
aerobic zones. The DO set point is 2.4 mg/L to meet an instantaneous minimum DO of
2.0 mg/L. The optimal sludge age ranged from 5 days in summer at 29 degrees Celsius (°C)
to 9 days in winter at 20 °C. The average secondary effluent concentration showed an
average of 0.7 mg/L as TP, 0.1 mg/L ammonia nitrogen, and 15 mg/L in TN, with a return
activated sludge (RAS) flow ranging from 45 to 60 percent. The clarifiers are operated with a
minimal blanket (less than 6 inches) to prevent secondary release of phosphorus. Secondary
release of phosphorus is of concern at this plant because of the generally high temperatures
increasing biological activity.
Another factor is the successful polishing of the biological process effluent for phosphorus
by the tertiary clarifiers and filters. The AWT has a tertiary clarifier ahead of tertiary filters
and performs better than the CP when the biological phosphorus removal process is upset and
carries elevated levels of suspended solids. The tertiary clarifier acts as an added line of
defense for the filters and maintains steady effluent quality ahead of the filters. At the AWT,
alum addition can go up to 15-16 mg/L without a having an adverse effect on the filters. The
CP, however, does not have a tertiary clarifier, and the alum dosage is limited to 10-12 mg/L
before the filters become blinded by solids. Note that filters at the CP have an air-water
backwash capability and therefore work well under these operating conditions.
Another key to successful removal of phosphorus is having multiple chemical feeding points.
Ferric chloride is fed to the primary settling tanks with the primary purpose of removing
suspended solids and a resulting side benefit of removing some phosphorus. The dosage of
ferric chloride averages 10-12 mg/L. Alum is added as described above to polish residual
phosphorus ahead of the tertiary filters.
Appendix A
Clark County, NV • Water Reclamation Facility 11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Another key to successful phosphorus removal is minimal recycle of in-plant phosphorus
loads. Waste activated sludge (WAS) is thickened in a dissolved air floatation (DAF)
process, and the combined primary sludge (0.7 MGD) and WAS sludge (1.15 MGD) are
dewatered daily at the belt filter press with ferric chloride and polymer addition. This
operation minimizes the release of phosphorus and prevents odor generation. The key
operational activity here is the daily dewatering of all sludge. Reduction in odors is also
aided by processing the sludge daily, which is accomplished by plant personnel working two
10-hour shifts and processing all sludge generated at the plant. This practice ensures a
minimal amount of odor generation at the plant and the minimum recycle of phosphorus
loadings back to the treatment processes. The TP in the filtrate from dewatering ranges
between 100 and 300 mg/L. The TP in the recycle flows is in the range of 20 to 25 percent of
the influent total.
The final line of defense is the tertiary filters. They were designed to operate at 5 gpm/ft2
during dry-weather peak flows and have performed well. The maintenance dosage of alum is
fed into tertiary filters to prevent secondary release from biological solids. They average
6 mg/L at the AWT and 4 mg/L at the CP. The long-term average soluble phosphorus leaving
the filters is less than 0.02 mg/L.
A benefit of having biological phosphorus removal followed by chemical polishing is
reduction in chemical sludge. Over the years, the plant has observed a decrease in total
sludge production. In 1997 the average sludge production was approximately 600 wet tons
per day. In 2007 even with increased flows, the sludge production is approximately 400 wet
tons per day.
Another key in the successful operation of the plant was automating the process monitoring
and controls. Two distinct functions are automated at this plant. One is that the decisions on
WAS from nine separate trains are made and carried out by a program developed in-house
using a mixed liquor suspended solids (MLSS) probe. The other is automatic blower control
in the aerobic zones. The head section of the aerobic zone receives the maximum supply of
air, while the latter section of the zone is controlled by a program with a set point of 2.4
mg/L DO using multiple probes.
The blowers are a key part of the process and require redundancy. The operating philosophy
is to provide a minimum of 0.5 mg/L DO at all times, even during the peak hot period of the
day. The plant experienced a DO deficit during a week of air temperatures at 113 degrees
Fahrenheit (°F) (45 °C), which was detrimental to the biological treatment process.
Another key is good redundancy, achieved by running nine separate treatment processes in
parallel. If one train experiences an upset condition, operators can supply good seed MLSS
from one of the other trains.
12 - Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Alternative Processes Considered
Because the plant is almost at capacity (100 MGD versus 110 MGD), expansion plans are
being pursued. For the AWT, a pilot program is underway for membrane filtration of
secondary effluent. Three different membranes are being evaluated concurrently. If the
evaluations are successful, the membrane filter could replace both the tertiary clarifier and
the dual media filters.
Costs
Capital Costs
The plant has undergone a number of upgrades and renovations since the original
commissioning of the AWT in 1982. Those total costs were updated to 2007 dollars using the
Engineering News-Record Construction Cost Index for construction costs and the Consumer
Price Index for the applicable years (USDA 2007). The resulting capital costs, the attributed
percentages for phosphorus and nitrogen removal, and the resulting total capital costs are
shown in Table 4.
Table 4. Upgrade capital costs and resulting phosphorus and nitrogen removal
Capital
Year
Amount
Updated cost
%P
%N
P removal
N removal
AWT Des
1982
$2,800,000
$5,956,103
50%
0%
$2,978,051
$0
AWT Const
1982
$28,000,000
$58,137,516
50%
0%
$29,068,758
$0
CP Expan Design
1994
$2,000,000
$2,770,875
12%
48%
$332,505
$1,330,020
CP Expan Const
1994
$29,000,000
$42,588,388
12%
48%
$5,110,607
$20,442,426
CP Filters Design
2002
$4,200,000
$4,794,056
50%
0%
$2,397,028
$0
CP Filters Const
2002
$27,600,000
$33,526,950
50%
0%
$16,763,475
$0
Central Plant S.
Sec. Design
2003
$3,790,000
$4,230,603
12%
48%
$507,672
$2,030,689
Central Plant S.
Sec. Const
2003
$39„304,293
$46,625,048
12%
48%
$5,595,006
$22,380,023
Central Plant S.
Sec. Design
2005
$1,901,098
$1,998,417
12%
48%
$239,810
$959,240
Central Plant S.
Sec. Const
2005
$19,218,993
$20,499,227
12%
48%
$2,459,907
$9,839,629
TOTAL

$157,814,384
$221,000,000
--
--
$65,452,819
$56,982,027
The capital expenditure in 2007 dollars that could be attributed to phosphorus removal was
$65.4 million. The annualized capital charge (20 years at 6 percent) was $5.71 million for
phosphorus removal.
Appendix A
Clark County, NV • Water Reclamation Facility -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The capital expenditure in 2007 dollars that could be attributed to TN removal was
$57 million. The annualized capital charge (20 years at 6 percent) was $4.97 million for TN
removal. This same expenditure could be attributed to ammonia nitrogen removal.
The total capital attributed to BNR in 2007 dollars was $221 million. For the 110-MGD
facility, the capital expenditure per gallon of BNR treatment capacity was $2.01.
Operation and Maintenance Costs
The Clark County plant uses a combination of biological and chemical phosphorus removal
to achieve the limit. This means that costs for phosphorus removal are distributed among
primary treatment (adding ferric chloride), secondary treatment (aeration basins, mixers, and
pumps), tertiary treatment (chemical addition and filtration), solids dewatering, and
laboratory testing. Costs for each of those components of wastewater treatment are shown in
Table 5, with the percentages of the costs that were attributed to TP and TN removal and the
final values.
Table 5. Component costs and resulting phosphorus and nitrogen removal
Component
Total op. costs
% for P
% for N
P O&M
N O&M
Primary
$1,877,685
12%
48%
$225,322
$901,289
Secondary
$5,829,302
12%
48%
$699,516
$2,798,065
Tertiary
$3,967,135
12%
0%
$476,056
$0
Solids dewatering
$3,957,135
50%
0%
$1,450,019
$0
Lab
$1,529,827
10%
10%
$152,983
$152,983
Other
$3,875,144
0%
0%
$0
$0
TOTAL
$19,979,131
-
-
$3,003,896
$3,852,337
Unit Costs for Nitrogen and Phosphorus Removal
In 2006 the plant removed 1,663,000 lb of phosphorus. With the results shown in Tables 3
and 4, the unit O&M cost for phosphorus removal is $1.81/lb, and the unit capital cost is
$3.43/lb of phosphorus removed.
In 2006 the plant removed 8,994,000 lb of nitrogen. With the results shown in Tables 3 and
4, the unit O&M cost for nitrogen removal is $0.43/lb and the capital cost is $0.55/lb of TN
removed.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the unit capital and unit O&M costs. Thus, the life-cycle
cost for phosphorus removal is $5.24/lb phosphorus removed and while the life-cycle cost for
nitrogen removal is $0.98/lb nitrogen removed.
14 - Clark County, NV • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Assessment of Magnitude of Costs and Main Factors
The life-cycle costs for phosphorus removal and full nitrification are on the high side, for
achieving an extremely low level of phosphorus and ammonia nitrogen by upgrading existing
facilities.
Discussion
Reliability factors. Three major factors contribute to a reliable performance in phosphorus
removal and nitrification: (1) multiple chemical feeds to the system, (2) good biological
phosphorus removal with in-plant VFA generation and full nitrification, and (3) good tertiary
filters in suspended solids removal. This combination of chemical, biological, and physical
processes in series provides a reliable operation with exceptionally low concentrations of
phosphorus at 0.09 mg/L with a low COV of 30 percent, while the ammonia nitrogen
concentration is at 0.05 mg/L with an even lower COV of 22 percent average monthly.
Cost factors'. This plant is an example of exceeding the original design capacity with retrofit
upgrades, which results in significant cost savings. The capital cost for phosphorus removal
and complete nitrification is estimated to be low at $2.01/gpd capacity. The unit costs for
capital and O&M were $5.43/lb of phosphorus removed and $1.38/lb of nitrogen removed.
The unit costs for O&M were $ 1.84/lb of phosphorus removed and $0.51/lb of nitrogen
removed.
Summary
The Clark County plant operation has been successful in reducing effluent phosphorus to the
limit of technologies at the existing plant using a combination of biological and chemical
treatment processes in series with good reliability. The plant is almost at capacity and yet has
produced effluent far below the discharge limits. The mean TP concentration was 0.099
mg/L for the year with a COV of less than 30 percent, at either the AWT or CP. The
technique of using several different technologies in series to achieve the treatment objective
works, especially when operation is done with computer control and the system has been
designed with a reasonable amount of robustness to allow for repairs and routine
maintenance. The instrumentation technician on staff is a unique and valuable member of the
team at this facility. The costs of operation are also reasonable: life-cycle costs are $5.24/lb
and $0.98/lb for phosphorus and nitrogen removal, respectively.
Acknowledgments
The authors are grateful for the significant assistance and guidance provided by Dr. Douglas
Druiy, deputy general manager, and Danielle Fife at the Clark County WRF. This case study
Appendix A
Clark County. NV • Water Reclamation Facility -15

-------
Nutrient Removal Technology Assessment Case Study
September 2008
would not have been possible without their prompt response with well-deserved pride in their
facility and its operation. EPA thanks Clark County for participating in this case study.
References and Bibliography
Druiy, D. 2005. Phosphorus—How Low Can You Go? In Proceedings of the Water
Environment Federation, 78th Annual Conference, Washington, DC, October 29-
November 2, 2005, pp 1125-1134.
Druiy, D. 2006. Clark County, NV—Using BPR with Chemical Polishing to Achieve TP
<0.1 mg/L at a 100-MGD Plant. In Proceedings of the Water Environment
Federation, 79th Annual Conference, Dallas, TX, October 21-25, 2006.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
16 Clark County, NV • Water Reclamation Facility
Appendix A

-------
Kelowna Wastewater Treatment Plant
Kelowna, British Columbia, Canada
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Kelowna Wastewater Treatment Plant (WWTP) is in the province of British Columbia in
western Canada. This plant was selected as a case study because of its cold-weather
biological nutrient removal (BNR) with a five-stage Bardenpho process, which has been
retrofitted into a new, three-stage Westbank process.
A BNR process, as depicted in Figure 1, was commissioned in 1982 and was operated
successfully through the 1980s. Optimization was ongoing, and an understanding of the BNR
removal mechanisms and pathways was developed, tested, and documented in Kelowna and
through other worldwide research programs.
Stcrm Onflow
fttmary Effluent
Vf=A

Aerobic
Aerobic
6Q Intend Recyde
Figure 1. Kelowna five-stage Bardenpho process.
The Canadian Ministry of Environment (MOE) permit requirements, shown in Table 1,
include biochemical oxygen demand (BOD5)-total, total suspended solids (TSS), total
nitrogen (TN), and total phosphorus (TP) limits. The plant's overall performance is shown in
Table 2.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 1. Permit requirements for effluent quality

Daily limits
MOE permit requirements
(mg/L)
BOD5-total
8
TSS
7
TN
6
TP

Maximum
2.0
99th percentile
90th percentile
1.5
1.0
Annual average (added in 1988)
0.25
Table 2. Influent and effluent averages
Parameter
(mg/L unless
stated)
Average
Maximum
month
Max month
vs. avg.
Maximum
week
Sample
method/frequency
Flow (MGD)
8.5
8.8
3.4%
8.9
--
Influent TP
6.0
7.4
23%
9.1
Composite/weekly
Effluent TP
0.14
0.20
42%
0.25
Composite/weekly
Influent COD
626
747
19%
910
Composite/weekly
Effluent COD
32
36
10%
38
Composite/weekly
Effluent BOD
2.5
3.8
48%
5.7
Composite/weekly
Influent TSS
389
472
21%
532
Composite/weekly
Effluent TSS
1.2
1.6
42%
2.4
Composite/weekly
Influent NH4-N
21.3
23.1
8.3%
27.6
Grab/monthly
Effluent NH4-N
0.57
1.0
76%
1.13
Grab/monthly
Influent TKN
28.8
33
14%
38.4
Grab/monthly
Effluent TKN
2.0
2.98
49%
3.5
Grab/monthly
Influent TN
28.8
33
14%
38.4
Grab/monthly
Effluent TN
4.38
4.9
12%
5.84
Grab/monthly
Notes:
BOD = biochemical oxygen demand
COD = chemical oxygen demand
Max month vs. average = (max month - average) / average x 100
MGD = million gallons per day
NH4-N = ammonia measured as nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
2 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Treatment Processes
As the load on the facility increased, it became clear that the five-stage process with a
22-hour hydraulic retention time (HRT) design far exceeded the HRT necessary to meet
effluent discharge requirements for both TP (0.25 milligrams per liter [mg/L]) and TN (6.0
mg/L). Process developments led to implementing a high-rate BNR process that was initially
tested at the Kelowna facility. The first full-scale implementation was at the Westbank
WWTP 20 miles southwest of the Kelowna plant. Details of the basis for plant design are
provided in Attachment 1.
Figure 2 depicts a shorter HRT process, and in 1994 the Kelowna facility was retrofitted in
this mode of operation. In effect, the last two stages (anoxic and aerobic) were bypassed and
made redundant. Later, the bypassed modules were retrofitted as two additional, smaller
Westbank-type modules.
Pimped S'fPCES
Ptlmcry Effluant
VFA.
n
Anoerct^c ¦
Anctfc
£ercfcrfc
6Q interned Recv/cle
Figure 2. The Westbank three-stage process.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 3

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The Kelowna VVVVTP layout, as depicted in Figure 3, was implemented with the following
process elements:
The liquid train includes
Screening
Grit removal
Primary sedimentation
Three-stage Westbank BNR
configuration
Secondaiy clarifiers
Dual media filters
UV disinfection
Flow and load equalization
The solids train includes
•	Primary sludge fermenter
•	Air flotation for waste activated
sludge (WAS) thickening
•	Centrifuge
•	Hauling to compost facility
LIQUID STREAM
SCREENING GRIT REMOVAL PRIMARY
SEDIMENTATION
L-J
BIOREACTOR
r
SECONDARY
CLARIFICATION
FILTRATION UV DISINFI
rL
'—i

SOLIDS STREAM
DEWATERING

FERMENTER STORAGE
Figure 3. Kelowna WWTP 2005 configuration.
n
1
f
U^u
STORAGE THICKENER
COMPOSTING
4 - Kelowna. British Columbia. Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
The Westbank process configuration employs a step-feed strategy for distributing primary
effluent and fermenter supernatant (volatile fatty acids [VFA]-enriched) to the specific areas
in the process where they are required. The logic described in the sections below was
applied.
Return Sludge and Pre-anoxic Zone
The Kelowna secondary clarifier design included sidewall depths of 4 meters (m) or greater.
Additionally, the original secondary clarifiers in Kelowna were designed with side-outlet
stilling wells to reduce turbulence under the center inlet well. Floor sloping enabled sludge
and helical scrapers to convey sludge to the center of the clarifier for collection and return to
the bioreactor.
Typical return activated sludge (RAS) rates of 75 percent of the influent flow (Q) maintained
sludge blankets of 0.5 to 0.75 m, which, when concentrated to three times the mixed liquor
suspended solids (MLSS) concentrations, demonstrated significant denitrification potential.
Nitrate reductions in the RAS blanket of up to 6 mg/L have not caused rising sludge
concerns; thus, the Kelowna secondary clarifiers have been operated since 1982 as anoxic
denitrification zones and included in the overall process strategy.
With control of nitrates in the return sludge stream within the clarifier, there is minimal
potential for nitrate return to the anaerobic zone. As an added protection, the original five-
stage design included a small pre-anoxic zone for denitrification of any residual RAS nitrates
before entering the anaerobic zone.
Given the limited potential for nitrate recycle in the return sludge, the amount of primary
effluent required for RAS denitrification is greatly reduced. Plant personnel therefore
developed plans to step-feed primary effluent to both the anaerobic zone (to stimulate
phosphorus release) and the anoxic zones (to stimulate denitrification).
As a result of step-feeding the primary effluent to the main anoxic zone, the suspended solids
concentration increases significantly in the pre-anoxic and anaerobic zones. With 50 percent
primary effluent diversion, the suspended solids concentration is approximately 50 percent
higher than MLSS concentrations in the aerobic zones.
With only a small amount of primary effluent added to the RAS entering the pre-anoxic zone,
a very high denitrification rate ensures that no nitrate breaks through to the anaerobic zone.
The sizing of the pre-anoxic zone in Kelowna is less than 1 percent of bioreactor volume.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Anaerobic Zone
It has been well documented that the anaerobic zone requires consistent and sufficient VFA
loadings to stimulate phosphorus release and uptake. The amount of VFA required has been
documented as 4-8 kg VFA/kg soluble phosphorus removed.
At the Kelowna facility, a primary sludge fermenter was included in the original Bardenpho
design, and it had a proven track record of consistent VFA production in the range required
for good phosphorus removal. Therefore, the VFA-rich fermenter supernatant is discharged
directly to the anaerobic zone, ensuring a steady feed of VFA to the phosphorus
accumulation organisms (PAO).
It was established that with the side-stream VFA addition, the process performed better when
the HRT of the anaerobic zones was reduced from 3 hours to 1 hour. This might have been
the result of reduction of secondary release of phosphorus in the larger anaerobic cells.
With a Westbank configuration, the primary effluent step-feed to the anoxic zone is adjusted
to complete two tasks:
•	Primary effluent containing some VFA is added to the anaerobic zone along with the
supernatant from the side-stream, primary-sludge fermenter. The combination of the
two meets the total VFA requirements of the process.
•	Primary effluent is step-fed to the anoxic zone to complete denitrification.
Under normal operating conditions, a portion of the primary effluent (approximately
50 percent) is required in the anoxic zone to complete denitrification, and the remainder is
fed through the pre-anoxic zone to the anaerobic zone.
Anoxic Zone
The main anoxic zone requires a variable chemical oxygen demand (COD) load to control
the denitrification process. Therefore, a portion of the primary effluent is pumped directly to
the anoxic zone to stimulate denitrification. Using this technique, denitrification rates in the
anoxic zone are greatly increased, the anoxic zones are reduced to 16-21 percent of
bioreactor volume, and the amount of primary effluent step-feed to the anoxic zone is
controlled.
Control of the denitrification rate can be achieved by monitoring the oxidation-reduction
potential (ORP) at the end of the anoxic zone 24 hours a day. This information can be fed
into the computer system and sufficient primary effluent diverted to the anoxic zone to meet
the nitrate load from the nitrified internal recycle flow.
6 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Aerobic Zone
The remaining volume (up to 75 percent) of the bioreactor is allocated for nitrification. This
zone is sized on the basis of the nitrifier growth rate of the activated sludge during the coldest
anticipated wastewater temperatures, and it controls the solids retention time (SRT) in the
bioreactor.
One advantage of a step-fed configuration is the decrease in anaerobic and anoxic zone
HRT—approximately 25 percent of the bioreactor. The reduced un-aerated fraction results in
reducing the un-aerated decay rates for nitrifying bacteria. With shorter time spent under
anoxic conditions, the net nitrifier growth rate increases. This is one reason for the reduced
SRT normally used by plant operators in the Westbank configuration.
Table 3 provides a 2005 monthly summary of bioreactor operating parameters for HRT,
SRT, temperature, MLSS, and percentage of bioreactor volume in service. Throughout 2005,
one of the small modules was not required. In addition, the highest monthly MLSS was
2,803 mg/L, or approximately 80 percent of the design MLSS. It could be expected that an
additional 20 percent load could be treated using the three operational bioreactors.
Table 3. Bioreactor o
serating parameters
Month
HRT
(hr)
SRT
(days)
Temp
(°C)
MLSS
(mg/L)
Bioreactor
in service
Jan 2005
11.1
8.9
13.1
2,562
84%
Feb 2005
11.1
8.8
13.0
2,761
84%
Mar 2005
11.4
8.2
13.8
2,803
84%
Apr 2005
11.6
8.1
15.6
2,486
84%
May 2005
11.3
8.0
18.1
2,238
84%
Jun 2005
10.9
6.7
19.4
2,414
84%
Jul 2005
10.9
6.0
21.1
2,301
84%
Aug 2005
10.8
5.8
22.0
1,992
84%
Sept 2005
10.9
6.0
20.9
1,901
84%
Oct 2005
11.1
7.0
19.3
2,142
84%
Nov 2005
11.5
7.4
16.8
2,451
84%
Dec 2005
11.5
7.5
14.3
2,899
84%
Internal Nitrified Recycle Rates
Depending on the desired effluent nitrate concentration, the aerobic/anoxic configuration
commonly uses four to six times the Q for internal recycle flows. With controlled primary
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
effluent diversion to the anoxic zone, effluent nitrate concentrations in the 3.0 to 4.5 mg/L
range can consistently be achieved.
The dissolved oxygen (DO) concentration in the aerobic zone can be reduced to between
1.0 to 2.0 mg/L with little impact on nitrifier growth rate, which is maximized at DO
concentrations of 2.0 mg/L.
Three important advantages of reduced DO have assisted Kelowna operations:
•	Reduced recycle of DO to the anoxic zone requires less primary effluent to initiate
and complete denitrification.
•	Reduced DO concentrations have reduced the endogenous release of nutrients.
•	Reduced DO has reduced the proliferation of foam-producing organisms.
Supplemental Alum and Lime Addition
The Kelowna facility is equipped with a supplemental alum dosing system that is automated
with an online analyzer. This system has been provided to help the biological phosphorus
removal system achieve an annual average TP of 0.25 mg/L. The alum can be used if
equipment maintenance or process issues disrupt effective phosphorus removals. As shown
in Table 4, alum additions in 2005 were limited to 5 days.
The 1994 expansion included a lime system for controlling dissolved phosphorus in the
centrifuge centrate return stream. The option of adding lime was terminated in March 2005
because of the strong bio-phosphorus removal performance in the bioreactor.
Table 4. Supplemental alum usage

Alum
2005
(Ib/d)
6/29/2005
500
6/30/2005
500
12/20/2005
150
12/21/2005
150
12/21/2005
200
Metals and Other Cations in Activated Sludge
Under normal operating conditions, the heavy-metal load to the Kelowna sewer system is
typical of domestic sewage only. On rare occasions, however, discharges have disrupted both
nitrogen and phosphorus removal. Throughout 2005, there were no such occasions, and
8 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 5 shows typical metal concentrations found in the BNR sludge. With these
concentrations of heavy metals, it could be expected that the nitrifier growth rate would be
normal.
Table 5. Metals and other cations in activated sludge
Metal/Cation
Unit
Value
Aluminum
Mg/g
6,914
Antimony
Mg/g
1.7
Arsenic
Mg/g
1.9
Barium
Mg/g
236
Beryllium
Mg/g
0.11
Bismuth
Mg/g
12.27
Cadmium
Mg/g
1.40
Calcium
%
1.16
Chromium
Mg/g
17.77
Cobalt
Mg/g
3.41
Copper
Mg/g
768
Iron
Mg/g
4,085
Lead
Mg/g
16.85
Lithium
Mg/g
2.37
Magnesium
%
1.08
Metal/Cation
Unit
Value
Manganese
Mg/g
96.5
Mercury
Mg/g
0.90
Molybdenum
Mg/g
6.88
Nickel
Mg/g
16.47
Phosphorus
%
3.9
Potassium
%
1.54
Selenium
Mg/g
4.34
Silver
Mg/g
11.07
Sodium
Mg/g
2,446
Strontium
Mg/g
122.8
Thallium
Mg/g
0.309
Tin
Mg/g
3.78
Vanadium
Mg/g
7.18
Zinc
Mg/g
288
Zirconium
Mg/g
29.7
I/FA Sources—Fermenter, Influent Sewage, Centrifuge
The primary sludge fermenter returns the overflow (supernatant) directly to the anaerobic
zone of the bioreactor. Table 6 identifies the flows and concentrations of various parameters.
As the data show, a significant amount of VFA is produced in the fermenter supernatant
stream.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 6. Fermenter supernatant return to anaerobic zone
Month
Flow
(mL/d)
SRT
(d)
Solids
(%)
Ammonia
(mg/L)
Soluble
phosphorus
(mg/L)
Soluble
COD
(mg/L)
Suspended
solids
(mg/L)
Total
VFA
(mg/L)
VFA
(kg/d)
Jan 2005
1.56
5.3
6.9%
18.7
5.62
358
142
116
181
Feb 2005
1.56
5.5
6.5%
18.1
6.39
407
170
131
204
Mar 2005
1.56
5.4
6.6%
18.6
7.06
427
169
140
218
Apr 2005
1.55
5.6
5.6%
19.5
7.68
538
180
196
305
May 2005
1.55
4.7
6.4%
15.8
7.61
632
166
225
351
Jun 2005
1.55
3.2
5.7%
15.7
6.95
583
190
236
368
Jul 2005
1.55
3.4
6.2%
14.4
7.85
640
212
254
393
Aug 2005
1.55
2.7
6.7%
16.4
7.16
611
208
242
375
Sept 2005
1.55
2.7
6.5%
16.5
6.82
575
227
229
355
Oct 2005
1.55
3.2
5.8%
18.6
7.43
582
232
222
344
Nov 2005
1.55
4.6
5.5%
19.3
7.92
603
198
216
334
Dec 2005
1.55
5.8
5.6%
20.5
7.85
614
260
227
351
Samples of the fermenter supernatant are sent off-site monthly for analysis in a gas
chromatography (GC) analyzer to determine the concentration of various fractions of VFA.
Table 7 lists the various fractional concentrations. The most desirable fraction for favoring
the growth of PAOs is a combination of acetic and propionic acids stimulating phosphorus
release/uptake. As the data show, these two acids are the most prevalent form of VFA in the
fermenter supernatant.
Table 7. Fermenter VFA fractions
Month
Acetic
(mg/L)
Propionic
(mg/L)
Isobutyric
(mg/L)
Butyric
(mg/L)
Isovaleric
(mg/L)
Valeric
(mg/L)
Jan 2005
55.5
37.0
2.4
9.9
1.9
2.4
Feb 2005
65
26.1
2.2
9.7
2.1
2.6
Mar 2005
109
26.2
1.9
9
3.1
3.3
Apr 2005
154
57.8
1
26.8
1
9.9
May 2005
137
123
1.7
26.5
1.9
12.5
Jun 2005
121
64.5
2.6
21.2
1.1
6.3
Jul 2005
178
155
1.7
32
2
18.3
Aug 2005
209
105
3.8
24.9
3.4
9.3
Sept 2005
124
104
4.8
16.8
3.7
7.4
Oct 2005
165
105
1.9
2.7
1.7
9
Nov 2005
97
122
1
27.3
1
10
Dec 2005
122
130
3
33.3
2.7
14.6
10 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
VFAs are also found in the influent sewage and centrifuge centrate. Only a limited amount of
sampling has been performed on these two sources. Table 8 lists the available data on
influent, primary effluent, and centrifuge centrate VFA concentrations.
Given the limited number of samples, an estimate of the sources of VFA that feed the
Kelowna anaerobic zone is as follows:
•	Primary sludge fermenter	Average 315 kg/d
•	50 percent of primary effluent Average 252 kg/d
Table 8. Other VFA sources
Date
Centrifuge
centrate
(mg/L)
Primary
effluent
(mg/L)
Influent
sewage
(mg/L)
Flow
rate
VFA
(kg/d)
May 8, 2007
401


est. 130 m3/d
52
May 10, 2007
285


est. 130 m3/d
37
May 15, 2007
415


est. 130 m3/d
54
June 8, 2006
281


est. 130 m3/d
37
June 15, 2006
215


est. 130 m3/d
28
June 22, 2006
281


est. 130 m3/d
37
May 8, 2007

15

est. 36 ML/d
540
May 10, 2007

20

est. 36 ML/d
720
May 8, 2007


8
est. 32 ML/d
256
Centrifuge
The primary fermented and thickened waste activated sludge are combined at the centrifuge
for dewatering and off-site composting. The key operating parameters for the centrifuge are
included in Table 9. The first four months of 2005 included lime addition to the centrate to a
level that saw the pH rise above 9.0. This effectively precipitated most of the soluble
phosphorus to low levels. In May 2005 the operations staff stopped adding lime to the
centrate because the bio-phosphorus removal efficiencies in the bioreactor were such that the
return phosphorus load was effectively removed biologically and the assistance provided by
lime addition was not required.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 9. Centrifuge centrate return to plant influent
Flow
Flow
(m3/d)
Ammonia
(mg/L)
TP
(mg/L)
Soluble P
(mg/L)
TKN
(mg/L)
Soluble COD
(mg/L)
TSS
(mg/L)
Jan 2005
133.7
14.3
118
11
43
318
1,105
Feb 2005
113.6
15.3
70
23
46
376
1,115
Mar 2005
124.5
15.3
160
55
68
452
861
Apr 2005
117.3
17.5
91
47
54
522
1,045
May 2005
118.7
16.7
225
173
63
827
270
Jun 2005
128.8
23.1
235
159
54
667
320
Jul 2005
143.6
28.5
165
161
60
783
1,001
Aug 2005
124.5
22.4
200
164
55
726
520
Sept 2005
118.7
23.5
235
148
61
599
1,135
Oct 2005
128.5
17.6
200
96
95
632
1,084
Nov 2005
123.8
20.9
173
118
66
779
854
Dec 2005
135.3
21.4
170
84
95
593
939
Performance Data for Nitrogen Removal
Overall plant influent and final filtered effluent average results for the 2005 calendar year are
shown in Table 10. The operators at the Kelowna facility have found that to maximize
biological phosphorus removal, the SRT needs to be just enough to complete nitrification.
If a small amount of ammonia remains in the effluent (0.2-0.5 mg/L), biological phosphorus
removal appears to work at top efficiency. Table 10 shows the monthly averages in 2005,
achieved as a result of this strategy. Tables 11 and 12 show the nitrogen concentrations at
various stages in the process.
12 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 10. Nitrogen removal
Month
Influent
flow
(ML/d)
Influent
TKN
(mg/L)
Effluent
TN
(mg/L)
Nitrogen
removal
(%)
Effluent
nitrates
(mg/L)
Effluent
ammonia
(mg/L)
Jan 2005
33.2
30.6
4.64
84.8
2.10
0.85
Feb 2005
32.1
30.5
4.90
83.9
1.93
1.01
Mar 2005
31.5
27.0
4.40
83.7
2.20
0.51
Apr 2005
30.8
32.5
4.49
86.1
2.65
0.48
May 2005
32.3
24.0
4.12
81.3
2.21
0.51
Jun 2005
32.8
24.7
3.21
87.0
1.99
0.07
Jul 2005
33.0
27.0
3.53
86.9
2.08
0.44
Aug 2005
33.5
33.0
4.39
86.6
2.53
0.40
Sept 2005
33.4
27.5
4.45
83.8
2.80
0.52
Oct 2005
32.3
27.8
4.89
82.4
2.67
0.50
Nov 2005
31.2
30.7
4.66
84.8
2.45
0.67
Dec 2005
31.9
31.1
4.78
84.6
2.18
0.96
Table 11. Nitrate profile—annual average of grab samples taken at 8:00 a.m. (mg/L)
Anaerobic
End
25%
50%
End
Secondary
Return
Filter
zone
Anoxic
aerobic
Aerobic
aerobic
clarifier
sludge
effluent
0.02
0.2
1.1
1.9
2.8
2.5
0.13
2.6
Table 12. Ammonia profile—annual average of c
Primary
effluent
Anaerobic
Zone
End
anoxic
25%
aerobic
50%
aerobic
End
aerobic
Secondary
clarifier
Return
sludge
Filter
effluent
19.44
9.6
3.19
2.12
1.31
0.05
0.29
0.26
0.23
rab samples taken at 8:00 a.m. (mg/L)
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Figures 4 and 5 show monthly frequency curves for effluent TN and ammonia.
Kelowna, BC
Monthly Average Frequency Curves for Total Nitrogen








~ ~























Mean - 4.38 mq/L
Std. Dev. = 0.51 mg/L









0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent TN	x Final Effluent TN
Figure 4. Monthly frequency curves for effluent TN.
Kelowna, BC
Monthly Average Frequency Curves for Ammonia-N





























	








Std. Dev. = u.^b mg/L


C.O.V. =45%



0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent Ammonia-N	x Final Effluent Ammonia-N
Figure 5. Monthly frequency curves effluent ammonia.
14 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Performance Data for Phosphorus Removal
Overall plant influent and final filtered effluent average results for the 2005 calendar year are
shown in Table 14. As the data show, biological removal of soluble phosphorus is operating
at near maximum capability.
Table 14. Phosphorus removal
Date
Influent flow
(ML/d)
Influent
TP
(mg/L)
Effluent
TP
(mg/L)
Phosphorus
removal
(%)
Effluent
soluble P
(mg/L)
Jan 2005
33.2
5.9
0.13
97.8%
0.04
Feb 2005
32.1
5.95
0.16
97.3%
0.04
Mar 2005
31.5
5.5
0.16
97.1%
0.04
Apr 2005
30.8
7.35
0.13
98.2%
0.04
May 2005
32.3
5.67
0.19
96.6%
0.05
Jun 2005
32.8
5.4
0.11
97.9%
0.03
Jul 2005
33.0
6.05
0.12
98.0%
0.03
Aug 2005
33.5
6.1
0.10
98.3%
0.03
Sept 2005
33.4
6.3
0.10
98.4%
0.02
Oct 2005
32.3
6.35
0.12
98.1%
0.02
Nov 2005
31.2
5.03
0.13
97.4%
0.02
Dec 2005
31.9
6.15
0.21
96.5%
0.06
Table 15 shows the soluble phosphorus concentrations at various stages in the process.
Table 15. Ortho-phosphorus profile—annual average of grab samples taken at
8:00 a.m. (mg/L)
Primary
Effluent
Anaerobic
zone
End
anoxic
25%
aerobic
cell
50%
aerobic
End
aerobic
Secondary
clarifier
Return
sludge
Filter
effluent
4.26
14.9
2.54
0.18
0.01
0.01
0.02
1.91
0.03
The soluble phosphorus load to the aerobic zone is quite low because of the moderate release
of phosphorus in the anaerobic zone and the significant phosphorus uptake in the anoxic zone
for most of the year.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -15

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Kelowna, BC
Monthly Average Frequency Curves for Total Phosphorus
Mean = 0.139 mg/L
Std. Dev. = 0.03 mg/L
C.O.V. = 21%
0 01 -I	1	1	1	1	1	1	1	1	1	1		1	1	1		1	1	1	1	1	1	1	1	
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
~ Raw Influent	x Final Effluent
Figure 6. Monthly average frequency curves for TP.
Reliability Factors
The Kelowna plant has achieved a high degree of reliability in the biological removal of
nitrogen and phosphorus in a cold climate. The mean effluent concentrations were 0.14 mg/L
in TP with a low coefficient of variation (COV) of 21 percent and 4.38 mg/L in TN with a
low COV of 12 percent.
The key operating principles applied at the Kelowna site include the following:
•	Anaerobic zone sizing was reduced from 3 hours to 1 hour for optimal operation
when a primary sludge fermenter was used to produce a constant, side-stream VFA
source.
•	Secondary clarifiers with a bottom-central draw-off are used to significantly reduce
nitrates in the return sludge.
•	The secondary clarifier RAS rate is adjusted to remove nitrates and prevent excessive
phosphorus release.
•	A small pre-anoxic zone for final denitrification of RAS before entering the anaerobic
zone prevents excessive phosphorus release before the anaerobic zone.
•	When a portion of the primary effluent was introduced directly to the anoxic zone,
rapid denitrification occurred and anoxic zone sizing could be reduced.
16 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
•	Simultaneous nitrification/denitrification occurred when submerged turbine aerators
were used, thereby improving the overall nitrate removal.
•	DO in the range of 1.0 to 2.0 mg/L produced the best combined TN and TP removals.
•	Sufficient SRT is maintained to just achieve full nitrification. A small amount of
ammonia in the effluent is acceptable.
•	Online effluent monitoring of nutrients provides valuable information to the plant
operators.
If there is a soluble phosphorus breakthrough to the effluent, the online effluent
analyzer that collects and analyzes samples every 15 minutes for ammonia, nitrates,
and ortho-phosphorus provides a signal to the process computer, which can
automatically turn the supplemental alum-dosing upstream of the secondary clarifiers
on or off.
•	Flow and load equalization volume equivalent to 7.5 percent of daily flow helps to
stabilize the nutrient removal processes.
•	With a 6Q recycle, the fourth and fifth stages in the five-stage Bardenpho mode were
not required to meet TN and TP permit requirements.
•	Computer control systems monitor, operate, and alarm all equipment on-site. This
provides 24-hour-a-day, consistent process control.
•	The anoxic zone is removing significant amounts of dissolved phosphorus. This
appears to be stimulated by the addition of primary effluent and the higher
denitrification rates.
•	Recycle loads from dewatering were minimized by maintaining separate processes for
secondary sludge and primary sludge. No sludge digestion was practiced in Kelowna.
The total recycle loads from dewatering were only 13 percent in TP and 0.1 percent in
TN.
•	Wet-weather flows were managed under the normal mode of operation, using the
equalization basin. The sewer system was separated, and the seasonal variation in
flow was not very high. The maximum month flow was 10 percent higher than the
average flow. The total basin equalization capacity was 7.5 percent of the design
average flow.
All these operating principles have been put into effect because of the flexibility of process
layout, the built-in swing zones, and the leadership of the plant personnel in research and
process optimization.
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -17

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Costs
Treatment Plant Expansions
This section provides a design summary of the Kelowna facility expansions, from the 1980
expansion and Bardenpho upgrade (from conventional, high-rate activated sludge) through
two additional upgrades to the Westbank process—each with higher loadings than the
original Bardenpho bioreactor.
Expansion of 1969 Kelowna WWTP
The Kelowna WWTP was converted in 1980 from secondary treatment to nutrient removal.
The following facilities from the previous 1969 expansion were incorporated into the design:
•	Two influent comminutors
•	Two grit channels
•	Raw sewage lift station
•	Three primary clarifiers
•	Short HRT activated-sludge process (converted to flow equalization)
•	Two secondary clarifiers (converted to sludge fermenters in Phase 2)
•	Sludge thickener
1980 Five-stage Bardenpho
The 1980 Bardenpho five-stage design made the Kelowna WWTP the first full-scale facility
designed for nutrient removal in North America. The unique and highly flexible bioreactor
had two trains, each with 22 cells for anaerobic, anoxic, and aerobic service. Of the 22 cells,
17 were swing zones with either anoxic or aerobic configurations. This design enabled
complete flexibility in operating the nitrifying and denitrifying components of the process.
The original design was commissioned with a high priority on reliability. Consequently, a
very conservative HRT/SRT was used to ensure complete nitrification and denitrification to
facilitate a TN below 6.0 mg/L. Through extended optimization, it became clear that the long
HRT/SRT was not necessary to achieve the required effluent nitrogen standards.
The preexisting sludge thickener was put into service for primary sludge only with
supernatant returning to the influent works. Thus it provided sufficient rapidly degradable
COD to stimulate phosphorus removal and denitrification. Through extended optimization, it
became clear that the on-site thickener (later called a fermenter) was producing sufficient
VFA to reduce the anaerobic zone from three cells to a single cell.
The capital cost for the 1980 conversion to the Bardenpho configuration was 12.5 million
Canadian dollars (CDN$).
18 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Westbank Process Configuration
On the basis of the full-scale operation of the five-stage process, a more compact process was
developed and initially tested at Kelowna. Then a full-scale version was designed and
constructed at the Westbank WWTP site across the lake from Kelowna.
The Westbank configuration uses a step-feed primary effluent strategy to split the primary
effluent (COD) for denitrification in the anoxic zones. It also ensures anaerobic conditions
for phosphorus release in the anaerobic zone.
Using a primary sludge fermenter with direct discharge to the anaerobic zone provides a
consistent VFA source, and primary effluent is added to the anaerobic zone only if additional
VFA load to the anaerobic zone is required.
The high-rate Westbank process was implemented in two phases. The first phase involved
breaking up the five-stage process into two intermediate-sized bioreactors and two smaller
bioreactors. The second phase added more capacity upstream and downstream to the original
bioreactor.
The objective of the second-phase expansion was to fully develop the capacity of the original
bioreactor with the new high-rate process. The plant was again re-rated upward to an average
dry weather flow of 10.6 million gallons per day (MGD) (40 ML/d).
The principal change to the process involved a controlled diversion of primary effluent to
enhance the denitrification rate in the main anoxic zone. The addition of primary effluent
directly to the anoxic zone allowed smaller anoxic zones and facilitated adjustment to the
denitrification rate. Combined with the smaller anaerobic zone previously developed in the
1980s, the aerobic fraction of the process was increased from 55 percent to 71 percent.
The capital cost of the 1992 Phase 2 conversion was approximately CDNS6.2 million. The
capital cost of the 1994 Phase 3 conversion was approximately CDNS20.75 million.
Canadian-U.S. Dollar Exchange
To calculate the capital and operation and maintenance (O&M) costs in U.S. dollars,
Canadian-to-U.S. dollar exchange rate values were required. Table 16 presents the average
Canadian-to-U.S. dollar exchange rates in the 3 years that capital improvements were made,
along with the current exchange rate for calculating O&M costs (Oanda Corporation 2007).
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant -19

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 16. Average Canadian to U.S. dollar
exchange rate value
Year
1 Canadian $ = x U.S. $
1980
0.86
1992
0.83
1994
0.73
2007
0.94
Table 17 presents the assumed split of the capital cost among phosphorus removal, nitrogen
removal, and other, which is BOD removal. It was assumed that 12 percent of the upgrades
could be attributed to phosphorus removal, while 48 percent of the upgrades could be
attributed to nitrogen removal. The balance of the upgrades could be attributed to BOD
removal or other activities required by permit (e.g., filters for suspended solids). This meant
that the capital expenditure in 2007 dollars that could be attributed to phosphorus removal
was US$6.8 million. The annualized capital charge (20 years at 6 percent) was US$595,000
for phosphorus removal.
Table 17. Split of ca
jital cost between phosphorus, nitroc
en, and other
Capital
year
CDN$
US$
US$ present
worth
%
other
%P
%N
Phosphorus
Nitrogen
1980
$12,500,000
$10,750,000
$26,375,193
40%
12%
48%
$3,165,023
$12,660,093
1992
$6,200,000
$5,146,000
$8,198,502
40%
12%
48%
$983,820
$3,935,281
1994
$20,750,000
$15,147,500
$22,245,090
40%
12%
48%
$2,669,411
$10,677,643
Totals
$39,450,000
$31,043,500
$56,818,785



$6,818,254
$27,273,017
The capital expenditure in 2007 dollars that could be attributed to nitrogen removal was
US$27.2 million. The annualized capital charge (20 years at 6 percent) was US$2.38 million,
for nitrogen removal. This same expenditure could be attributed to ammonia nitrogen
removal.
The total capital attributed to BNR in 2007 dollars was US$34 million. For the 10.6 MGD
(40 ML/day) facility, this means the capital expenditure per gallon of BNR treatment
capacity was US$3.25.
Operation and Maintenance Costs
The plant uses both biological phosphorus and nitrogen removal, with minimal use of alum
and no use of supplemental carbon sources. This means that costs for nutrient removal are
essentially all electrical. A summary of the electrical calculations is provided in Attachment
2. The total electrical usage for phosphorus removal was 884,000 kilowatt-hours per year
20 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
(kWh/yr). When the average electrical rate of US$0.047/kWh was applied, the cost for
phosphorus removal was US$41,500 for the year. The total electrical usage for nitrogen
removal was 4,100,000 kWh/yr, or US$193,000.
Unit Costs for Nitrogen and Phosphorus Removal
During the 1-year case study period, the plant removed 150,000 lb of phosphorus. With the
results above, the unit O&M cost for phosphorus removal is US$0.27 and the unit capital
cost is US$3.97/lb of phosphorus removed.
During the same period, the plant removed 781,000 lb of TN. With the results above, the unit
O&M cost for TN removal is US$0.14 and the unit capital cost is US$3.05/lb of ammonia
removed.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the unit capital and unit O&M costs. Thus, the life-cycle
cost for phosphorus removal is US$4.24/lb phosphorus removed and the life-cycle cost for
nitrogen removal is US$3.19/lb TN removed.
Assessment of magnitude of costs: The costs are shown to be on the high side in capital cost
and very low in O&M costs. This reflects the innovative technologies used at the plant,
which resulted in increasing the treatment capacity while still using the existing facilities.
Summary
The Kelowna, British Columbia, plant's retrofit of the original five-stage Bardenpho process
into the three-stage Westbank process has provided excellent reliability in both nitrogen and
phosphorus removal, especially for this cold-weather region. The phosphorus removal is
achieved biologically to the mean concentration of 0.14 mg/L with a low COV of 21 percent.
The nitrogen removal is achieved biologically to the mean concentration of 4.38 mg/L with
an extremely low COV of 12 percent without using an external carbon source. The Kelowna
plant is one of the best-performing BNR plants in North America. Many factors have
contributed to this remarkable achievement. They include flexibility in design for
bioreactors, adequate VFA production in separate fermenters, online monitoring and
automatic controls, and the plant personnel developing optimal operating strategies.
Key factors include downsizing the anoxic zones; maintaining 2- to 3-foot-deep blankets in
the secondary clarifier for added denitrification, thereby downsizing the pre-anoxic zone;
simultaneous nitrification and denitrification; DO controls in the range of 1 to 2 mg/L in the
aerobic zone; maintaining a short sludge age of about 10 days, a short HRT of about
11 hours, and sufficient internal recirculation for denitrification at 6Q; and a computer
control system. Recycle loads from sludge handling were minimized by maintaining separate
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 21

-------
Nutrient Removal Technology Assessment Case Study
September 2008
processes for secondary sludge and primary sludge. No sludge digestion was practiced, and
thus the total recycle loads were 13 percent in TP.
The capital cost was moderately high at US$3.25 per gallon per day, and the O&M costs
were extremely low at US$0.28/lb of phosphorus removed and $ US$0.29/lb of nitrogen
removed. The capital cost reflects added costs for flexible flow patterns with multiple swing
zones for both anoxic and aerobic zones, fermenters, and tertiary filters. The O&M costs are
low because of efficient use of power and no chemical addition for either nitrogen or
phosphorus removal. The life-cycle costs are low at US$3.19/lb of nitrogen and US$4.25/lb
of phosphorus removed.
As a result of the continuous improvements, the Kelowna plant treats 70 percent more flow
than the original plant did using the same bioreactor tanks.
Acknowledgments
The authors are grateful to Earth Tech Canada, Ltd., and Gerry Stevens, Earth Tech Canada,
Ltd., for the bulk of the information contained in this case study. Mr. Stevens worked for
Kelowna through implementing and optimizing the BNR process until 1990. He helped to
obtain records and analyze and present technical data about the innovations achieved at the
plant. Mr. Stevens' expertise in BNR technologies in general and his accomplishments in
Kelowna, British Columbia, are recognized and appreciated.
The authors are also grateful to the city of Kelowna and members of the WWTP staff for
participating in this study. They include Jim White, plant manager; Sheila Carey, lab
supervisor; and Marj Van de Mortel, lab technician.
References/Bibliography
Barnard, J.L., G.M. Stevens, and P.J. Leslie. 1984. Design Strategies for Nutrient Removal
Plant. IAWPRC 1984 Post-Conference Sessions, Paris, France.
Oanda Corporation. 2007. FXHistory: historical currency exchange rates and FX Converter
Results, http://www.oanda.com/convert/fxhistory.
http://www.oanda.com/convert/classic.
Stevens, G.M., J.L. Barnard, L. Forty, and C. Cameron. 1996. Verification of anoxic
phosphorus uptake in a full-scale plant. In Proceedings of Water Environment
Federation 69th Annual Technical Exhibition & Conference.
Stevens, G.M., J.L. Barnard, and B. Rabinowitz. 1997. Optimizing Biological Nutrient
Removal in Anoxic Zones. Australia BNR 3 Conference, 1997.
22 - Kelowna. British Columbia. Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Stevens, G.M., C. Cameron, S. Hunt, and S. Carey. 2002. Operational Experiences with
Sludge Fermenters. In Proceedings of Water Environment Federation 75th Annual
Technical Exhibition & Conference, Chicago, IL, September 28-October 2, 2002.
Stevens, G.M., M.K. Fries, and J.L. Barnard. 1995. Biological Nutrient Removal Experience
at Kelowna, British Columbia. In Proceedings of Water Environment Federation 68th
Annual Technical Exhibition & Conference.
Stevens, G.M., and W.K. Oldham. 1992. Biological Nutrient Removal Experience at
Kelowna British Columbia. European Conference on Nutrient Removal from
Wastewater. University of Leeds, Wakefield, U.K.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
Wilson, A.W., G.M. Stevens, and P. Do. 1992. Retrofitting Biological Nutrient Removal
Processes at Existing Wastewater Treatment Facilities. European Conference on
Nutrient Removal from Wastewater. University of Leeds, Wakefield, U.K., 1992.
Appendix A
Kelowna. British Columbia. Canada • Wastewater Treatment Plant - 23

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Attachment 1: Design Basis
Design Flows and Loads

1980
Design value

Bardenpho



Units
upgrade
Stage 1
Flow Data

Phase 1
Phase 2
Phase 3
Sewered Population
per
56,000
64,000
95,000
Flow per Capita
L/c.d
400
400
400
Base Infiltration
ML/d
1.0
1.0
1.0
BCTWP Industrial Effluent
ML/d


1.0
Average Daily Flow
ML/d
22.5
27.5
40.0
Maximum Month Flow
ML/d
25.1
31.0
44.0
Maximum Daily Flow
ML/d
28.7
35.5
50.0
Peak Hourly Flow
ML/d
34.8
43.0
69.0
BOD, TSS, TKN, TP Loads




BOD




Average Daily Unit Load
kg/c.d
0.080
0.080
0.080
Allowance for BCTWP
kg/d


200
Average Daily Total
kg/d
4,480
5,120
7,800
Maximum Month Unit Load
kg/c.d
0.095
0.095
0.095
Maximum Month Total
kg/d
5,320
6,080
9,225
Maximum Week Unit Load
kg/c.d
0.105
0.105
0.105
Maximum Week Total
kg/d
5,880
6,720
10,175
TSS



Average Daily Unit Load
kg/c.d
0.080
0.080
0.080
Allowance for BCTWP
kg/d


20
Average Daily Total
kg/d
4,480
5,120
7,620
Maximum Month Unit Load
kg/c.d
0.100
0.100
0.100
Maximum Month Total
kg/d
5,600
6,400
9,520
Maximum Week Unit Load
kg/c.d
0.120
0.120
0.120
Maximum Week Total
kg/d
6,720
7,680
11,420
TKN



Average Daily Unit Load
kg/c.d
0.015
0.015
0.015
Allowance for BCTWP
kg/d


10
Average Daily Total
kg/d
840
960
1,435
Maximum Month Unit Load
kg/c.d
0.017
0.017
0.017
Maximum Month Total
kg/d
952
1,090
1,625
Maximum Week Unit Load
kg/c.d
0.019
0.019
0.019
Maximum Week Total
TD
kg/d
1,064
1,215
1,815
1 r
Average Daily Unit Load
kg/c.d
0.003
0.003
0.003
Allowance for BCTWP
kg/d


5
Average Daily Total
kg/d
168
192
290
Maximum Month Unit Load
kg/c.d
0.003
0.003
0.003
Maximum Month Total
kg/d
168
192
290
Maximum Week Unit Load
kg/c.d
0.004
0.004
0.004
Maximum Week Total
kg/d
224
256
385
WASTEWATER TEMPS



Summer
°C
20
20
20
Winter
°C
10
10
10
24 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Process Design Data
Units
1980
Bardenpho
upgrade
Design value
Stage 1
-upgrade
Phase 1
Phase 2
Phase 3
Raw Sewage Pumping




Station 1




Number of Units

6
6

Capacity
L/s
380
380

Station 2




Number of Units



3
Capacity
L/s


440
Comminutor




Number of Units




Mechanical

2


Manual

--


Capacity per unit
ML/d
16.0


Bar Screen




Number of Units




Mechanical


1
1
Manual


1
1
Capacity per unit
ML/d

75.0
75.0
Grit Removal




Number of Units

2
1
1
Capacity per Unit
ML/d
16.0
75.0
75.0
Primary Clarifiers




Number of Units

3
4
6
Length
m
27.4
27.4
27.4
Width
m
6.1
6.1
6.1
SWD, 1-3
m
2.2
2.2
2.2
SWD, 4-6
m
2.5
2.5
2.5
SWD, 7-10
m



Peak OFR, 1 out of service
m^/m^-d
62.7
94.1
91.1
Primary Flow Equalization




Fraction of Average Flow
percent
8.4
6.9
7.50
Volumes




NE Trunk

1,200
1,200
-
Existing Tanks

700
700
700
Future Primary Clarifiers


-
1,150
New Equalization Tanks


-
1,200
Primary Sludge Fermenters




SRT, avg
d
7
5
5
Number of Units

1
1
2
Dimensions




Diameter
m
17
15
15
SWD, 1-2
m
4.5
3.5
3.5
SWD, 3-4
m
-
-
-
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 25

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Process Design Data
Units
1980
Bardenpho
upgrade
Design value
Stage 1
-upgrade
Phase 1
Phase 2
Phase 3
Bioreactors




Basic Design Parameters




SRT, Summer
d
15
12
10
SRT, Winter
d
20
15
12
Bioreactor




Existing Modules 1 and 2




No. of Anaerobic Cells

3


Anaerobic Volume

1,365


No. of Anoxic Cells

6-10


Anoxic Volume

3,640


No. of Aerobic Cells

9-13


Aerobic Volume

5,005


No. of Anaerobic Stirrers

3


Anaerobic Stirrer hp

5


No. of Swing Zone Mixers

19


Swing Zone Mixers hp

7.5/15


Bioreactor




Modified Modules 1 and 4




No. of Anaerobic Cells


1
1
No. of Anaerobic Stirrers


1
1
Anaerobic Stirrer hp


5
5
Anaerobic Volume


225
225
No. of Anoxic Cells


2
2
No. of Anoxic Stirrers


2
2
Anaerobic Stirrer hp


5
5
Anoxic Volume


680
680
No. of Aerobic Cells


4
4
Aerobic Volume


1,820
1,820
No. of Anaerobic Stirrers


1
1
Anaerobic Stirrer hp


2.5
2.5
No. of Aerobic Mixers


1
1
Aerobic Mixer hp


40
40
No. of Aerobic Mixers


1
1
Aerobic Mixer hp


30
30
No. of Swing Zone Mixers


3
3
Swing Zone Mixers hp


7.5/15
7.5/15
26 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Process Design Data
Units
1980
Bardenpho
Upgrade
Design Value
Stage 1-
-Upgrade
Phase 1
Phase 2
Phase 3
Modified Modules 2 and 3




No. of Anaerobic Cells


1
1
Anaerobic Volume


455
455
No. of Anoxic Cells


3
3
Anoxic Volume


1,365
1,365
No. of Aerobic Cells


10
10
Aerobic Volume


4,550
4,550
No. of Anaerobic Stirrers


1
1
Anaerobic Stirrer hp


5
5
No. of Aerobic Mixers


2
2
Aerobic Mixer hp


40
40
No. of Aerobic Mixers



2
Aerobic Mixer hp



30
No. of Swing Zone Mixers


7
5
Swing Zone Mixers hp


7.5/15
7.5/15
Blowers




No. of Blowers

4
4
4
Size
hp
100
100
250
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 27

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Process Design Data
Units
1980
Bardenpho
Upgrade
Design Value
Stage 1
-Upgrade
Phase 1
Phase
2
Phase 3
Secondary Clarifiers




Clarifiers




Number

3
4
5
Dimensions




Diameter
m
26
26
26
SWD
m
4.5
4.5
4.5
RAS Pumps




Number

6
8
9
Capacity
Us
80
80
80
Maximum RAS Flow
Us
240
320
400
WAS Pumps




Number

2
3
4
Capacity
Us
8
12
12
Filtration




Peak OFR, 1 unit out of service

290
290
290
Existing Units




Number

4
4
4
Area per Unit
m2
64
64
64
New Units




Number



1
Area per Unit
m2


96
Ultraviolet Disinfection




Dosage
mWs/cm^
chlorine
chlorine
48
Transmissivity
percent


65
Number of Lamps



1,152
Arrangement




Number of Channels



2
Banks per Channel



3
Racks per Bank



24
Lamps per Rack



8
WAS Thickening




Design Load, Peak
kgTSS/d


4,615
DAF Units




Number

2
2
3
Area per Unit
m2
18.9
18.9
18.9
Dewatering




PS Flow, peak
m^/d
none
none
90
WAS Flow, Peak
m^/d
none
none
195
Centrifuges




Number



2
Capacity
Us
none
none
4.7
28 - Kelowna, British Columbia, Canada • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Attachment 2: Electrical Cost
Electrical cost










Anoxic/Anaerobic mixers










kW

kWh
kWh
%BOD
%P
%N
for P
for N


power
hours/
draw /
draw /





HP Number
draw
day
day
year



draw
draw
Anaerobic mixer










5
2
7.46
24
179.04
65,349.6
0
100
0
65,349.6
0
2.5
1
1.865
24
44.76
16,337.4
0
100
0
16,337.4
0
Fermenter rake mechanism drive








5
1
3.73
24
89.52
32,674.8
0
100
0
32,674.8
0
Anoxic mixers










5
8
29.84
24
716.16
261,398.4
0
0
100
0
261,398.4
2.5
2
3.73
24
89.52
32,674.8
0
0
100
0
32,674.8
Blowers










250 1
25
233.125
24
5,595
2,042,175
45
10
45
204,217.5
918,978.75
Swing zone stirrers—
-19 available, can go either anoxic (7.5 hp) or aerobic (15 hp)




7.5
9
50.355
24
1,208.52
441,109.8
0
0
100
0
441,109.8
15
10
111.9
24
2,685.6
980,244
45
10
45
98,024.4
441,109.8
Aerobic zone mixers









40
5
149.2
24
3,580.8
1,306,992
45
10
45
130,699.2
588,146.4
30
5
111.9
24
2,685.6
980,244
45
10
45
98,024.4
441,109.8
15
11
123.09
24
2,954.16
1,078,268.4
45
10
45
107,826.84
485,220.78
Recirculation pump









20
2
29.84
24
716.16
261,398.4
0
0
100
0
261,398.4
15
1
11.19
24
268.56
98,024.4
0
0
100
0
98,024.4
Filter pumps










7.5
4
22.38
24
537.12
196,048.8
0
50
50
98,024.4
98,024.4
10
1
7.46
24
179.04
65,349.6
0
50
50
32,674.8
32,674.8
Appendix A
Kelowna, British Columbia, Canada • Wastewater Treatment Plant - 29

-------

-------
Marshall Street Water Reclamation Facility
Clearwater, Florida
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Marshall Street Water Reclamation Facility (WRF) in Clearwater, Florida, is designed
for a capacity of 10 million gallons per day (MGD). This facility was selected as a case study
because it has achieved low levels of nitrogen and phosphorus in the effluent using the five-
stage Bardenpho process. The plant processed an average of 5.48 MGD during the evaluation
period, October 2005 through September 2006. Some of the reclaimed water is sent for reuse
(irrigation); the remainder is discharged under a permit via Stevenson's Creek to Clearwater
Harbor. The WRF uses a five-stage Bardenpho process to remove both total nitrogen (TN)
and total phosphorus (TP) to below 3 milligrams per liter (mg/L) and 1 mg/L on an annual
average, respectively.
The relevant National Pollutant Discharge Elimination System (NPDES) permit limits for the
facility are shown in Table 1.
Table 1. NPDES permitted discharge limits
Parameter
Annual
average
Monthly
average
Weekly
average
BODs
5 mg/L
6.25 mg/L
7.5 mg/L
TSS
5 mg/L
6.25 mg/L
7.5 mg/L
TN
3 mg/L
3.75 mg/L
4.5 mg/L
TP
1 mg/L
1.25 mg/L
1.5 mg/L
Dichlorobromo methane
24 |jg/L
Report
-
Dibromochloro methane
46 |jg/L
Report
-
Notes:
[jg/L = micrograms per liter
BOD5 = biochemical oxygen demand
TSS = total suspended solids
TN = total nitrogen
TP = total phosphorus
Plant Process
Figures 1 and 2 present a plant layout and a process flow diagram for the Marshall Street
WRF.
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
2 - Marshall Street, Clearwater, FL 9 Water Reclamation Facility
Appendix A

-------
f
§
8
&
&
TREATMENT PROCESS FLOW DIAGBAM
MARSHALL STREET WATER REC.L A MATIQN.FACJLIIY
RFTURM ACTIVATED SLUDGE (RAS)
40 INTERNAL RECYCLE tlR>
24" FORCE MAIL FROM BAY
FRONT PUMP STATION
INFLUENT
PUMP STATION
WITH SCREENING
METER
',L''
at nMNl
PRIMARY TANKS
FEHMEMlAFQN AMQX|C
TANKS
OO'GOO
noiooo
oo 3 OOCr
ErFLUENT FILTERS
2ND ANOXIC REAERATION
~
OOO

—•>

ooo

i

coo

—J
L-
9 o o

-J
,H[
SCREEN
PUMP LIFE
.STATION
r
DECHLORINATION
I DISSOLVED
OXYGEN	EFFLUENT
BOOST	OUTFALL
i —STEVENSON
¦creek *
So
s
Hi
CD
£
cs:
a
{
'REACTOR
" THICKENERS
PPESSATE i-WEP
RECYCLE
Q^SL
Pl/WP
SLUDGE

BEIT FILTER 1
BLENDING
4



DEWAT ER.ING
TPUCK EKSP05AL
OF PESTERED
SLUDGE
1=0
5
6
C?"
§
&
D
Figure 2, Marshall Street WRF process flow diagram.
,
e*s

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The plant uses a five-stage Bardenpho biological nutrient removal (BNR) process. The liquid
train consists of the following components: an on-site influent pumping station with three
variable-rate, dry-pit pumps; preliminary treatment consisting of two mechanically cleaned
fine-bar screens, a four-unit vortex-cyclonic grit removal system with associated grit
classifier, and an influent flow measurement via a 36-inch Parshall flume with an ultrasonic
flow meter; primary treatment consisting of sedimentation in four 49,370-gallon rectangular
basins and four 52,960-gallon rectangular basins; a biological treatment process consisting of
a five-stage Bardenpho BNR process that includes three 250,000-gallon fermentation basins,
three 333,000-gallon first anoxic reactors, 13 aeration basins or nitrification reactors (three
363,170-gallon basins, and ten 127,160-gallon basins), four 280,000-gallon second anoxic
basins, and four 63,000-gallon re-aeration basins; four 100-foot-diameter secondary
clarifiers; four return-activated sludge pumps; an intermediate effluent pumping station using
three 60-inch-diameter Archimedes screw lifts and three centrifugal pumps; polishing
filtration consisting of 12 rapid-sand, pulsed-filtration, gravity-type automatic backwash
filters with a total surface area of 4,320 square feet; an effluent disinfection system using
gaseous chlorination and a 315,000-gallon, dual-channel chlorine contact basin. Alum is
added before the effluent reaches the polishing filters to aid in total suspended solids (TSS)
removal and thereby reduce trihalomethane (THM) formation potential. Also on-site is a
5-million-gallon (MG) reclaimed water storage tank and accompanying high-service pumps.
Chlorinated effluent from the chlorine contact basin is directed to the Master Reuse System
or to a 315,000-gallon dechlorination basin that uses flow-paced sulfur dioxide to eliminate
the remaining chlorine residual. It then flows through a 100,000-gallon re-aeration basin and
finally through a 48-inch-diameter outfall pipe that discharges to Stevenson's Creek, 20 feet
from shore.
Waste sludge from the primary clarifiers is pumped to one 930,000-gallon anaerobic digester.
Waste sludge from the secondary clarifiers is pumped to two 108,000-gallon-per-day (gpd)
rotary drum thickeners equipped with polymer injection, then to the anaerobic digester. The
digested sludge is then directed to a 127,000-gallon sludge blend tank. The blended sludge is
dewatered using two 2-meter belt filter presses.
Basis of Design and Actual Flow
Flow
The design flow for the facility is 10 MGD; the average flow for the study period was
5.48 MGD, and the maximum month flow during the study period was 6.85 MGD during
September 2006.
4 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Loadings
Plant design loadings and equipment parameters are as follows:
Average day	10 MGD
Peak day	15 MGD
Primary settling tanks: 4 each at 49,370 gallons, 4 each at 52,960 gallons
The plant operates four units regularly.
Activated-sludge
Fermentation basins:	3 each at 250,000 gal
First anoxic basin:	3 each at 333,000 gal
Aerobic basin:	3 each at 367,000 gal
Aerobic basin:	10 each at 127,000 gal
Anoxic basin:	4 each at 280,000 gal
Re-aerobic basin:	4 each at 63,000 gal
Total hydraulic retention time (HRT):	20 hours
Design mixed liquor suspended solids (MLSS): 4,000 mg/L
Return activated sludge (RAS) rate:	80-120 percent
Internal recycle rate:	400-600 percent
Food-to-microorganism (F-to-M) ratio:	0.05
Mean cells residence time (MCRT):	25-40 days
Secondary clarifier: 4 each, diameter = 100 ft at 12.5-ft depth
Surface loading rate: 318 gpd/ft2 at average daily flow (ADF)
Detention time:	7 hours at ADF
The plant operates three units regularly.
Rapid sand, pulsed filter: 12 each, 12 ft by 30 ft, or a total of 4,320 sf
ADF capacity:	2 MGD each
Peak capacity:	28 MGD
Hydraulic loading rate: 3.8 gpm/sf at ADF
4.5 gpm/sf at peak
Sludge thickener—Carter rotary drum
Capacity:	2 each, 75 gpm
Thicken sludge:	Waste-activated sludge (WAS) at 4-6 percent
Volume:	15,552 gpd
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Anaerobic digester
Primary digester: Diameter = 85 ft, volume = 0.93 million gallons
Digesters—The sludge-heating system and gas-mixing system were not operational in
the primary digester from October 2005 through September 2006 because the primary
digester system was being rebuilt. During that period, all sludge was pumped directly
to the blending tank for dewatering. The primary digester was back online in January
2007.
Dewatering—The primary sludge and WAS are blended with polymer for dewatering with an
Andritz belt filter press. The cake is hauled away by truck.
Plant Parameters
Overall plant influent and effluent average results for the period October 2005 to September
2006 are shown in Table 2.
Table 2. Influent and effluent averages
Parameter
(mg/L unless stated)
Average
value
Maximum
month
Max
month vs.
avg.
Maximum
week
Sample
method/frequency
Flow (MGD)
5.48
6.85
25%
7.62
--
Influent TP
5.0
5.53
10%
6.35
Weekly/composite
Effluent TP
0.13
0.21
62%
0.26
Weekly/composite
Influent BOD
188
234
24%
263
Daily/composite
Effluent BOD
2.3
4.1
78%
5.3
Daily/composite
Influent TSS
231
277
20%
317
Daily/composite
Effluent TSS
0.89
1.11
24%
1.6
Daily/composite
Influent NH4-N
28.0
32
16%
34.0
Daily/composite
Effluent NH4-N
0.036
0.045
25%
0.062
Daily/composite
Influent Total N
28.0
32
16%
34.0
Daily/composite
Effluent Total N
2.32
3.1
35%
3.75
Daily/composite
Notes:
BOD = biochemical oxygen demand
Max month vs. average = (max month - average) / average x 100
NH4-N = ammonia measured as nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
6 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 3 presents the plant's monthly averages for the Bardenpho process parameters.
Table 3. Monthly averages for plant process parameters

MLSS
Sludge age
HRT
Temperature
Month
(mg/L)
(d)
(hr)
(°C)
Oct 2005
3,979
51
27
29.3
Nov 2005
4,106
44
28
27.2
Dec 2005
4,181
44
30
24.6
Jan 2006
4,425
36
30
23.8
Feb 2006
4,094
27
28
23
Mar 2006
3,951
25
28
25
Apr 2006
3,857
34
27
27
May 2006
3,340
31
28
28
June 2006
3,704
41
29
30
July 2006
4,205
34
26
30
Aug 2006
3,701
37
25
31
Sep 2006
3,921
36
22
30
Notes:
HRT = hydraulic retention time
MLSS = mixed liquor suspended solids
Performance Data
Figures 3 and 4 present reliability data for TP removal. The removal is good, with the
effluent TP averaging 0.13 mg/L and having a medium coefficient of variation (COV) of 40
percent. The COV is defined as the standard deviation divided by the mean, and it is a
measure of the reliability of a system. The lower the COV, the less the data are spread and so
the higher the reliability.
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Marshall Street Advanced WWTP Clearwater, FL
100
Monthly Average Frequency Curves
or Total Phosphorus
10
oi
E
o
Q. 1
(/!
o
CL
Mean = 0.132 mg/L
e Std. Dev. = 0.052 mg/L
iC.O.V. = 40%
0.01
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent	x Final Effluent
Figure 3. Monthly average frequency curves for TP.
100
Marshall Street Advanced WWTP Clearwater, FL
Weekly Average Frequency Curves for Total Phosphorus
10
oi
E
o
.c
~ ~ ~ *
*****
. Mean = 0.132 mg/L
: Std. Dev. = 0.058 mg/L
; C.O.V. = 44%
0.01
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
* Raw Influent
x Final Effluent
Figure 4. Weekly average frequency curves for TP.
Figures 5 and 6 present reliability data for ammonia nitrogen removal. Removal of ammonia
nitrogen is very good, with a mean effluent of 0.038 mg/L and a very low COV of 18
percent.
8 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Marshall Street Advanced WWTP Clearwater, FL
Monthly Average Frequency Curves for Ammonia Nitrogen
; Mean = 0.038mg/L
: Std. Dev. = 0.007 mg/L
C.O.V. = 18%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N	x Final Effluent - Ammonia N
Figure 5. Monthly average frequency curves for ammonia nitrogen.
9899 99.5 99.999.95
oi
E
c
o
at
o
10
o
E
E
<
0.1
0.01
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 9899 99.5 99.999.95
Percent Less Than or Equal To
« Raw Influent - Ammonia-N	x Final Effluent - Ammonia N
Figure 6. Weekly average frequency curves for ammonia nitrogen.
Figures 7 and 8 present reliability data for removal of TN. With the two anoxic stages, the
plant gives outstanding TN removal, with effluent TN of 2.32 mg/L and a COV of 16
percent.
Marshall Street Advanced WWTP Clearwater, FL
Weekly Average Freguency Curves for Ammonia Nitrogen
Mean = 0.036
Std. Dev. = 0.(
C.O.V. = 21%
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
100
Marshall Street Advanced WWTP Clearwater, FL
Monthly Average Frequency Curves for Nitrogen
10
~ ~ ~
~ ~
*	~	~
at
£
: Mean = 2.32 mg/L
Std. Dev. = 0.38 mg/L
C.O.V. = 16%
0.1
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 9999.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N	x Final Effluent - Total N
Figure 7. Monthly average frequency curves for nitrogen.
100
Marshall Street Advanced WWTP Clearwater, FL
Weekly Average Frequency Curves for Nitrogen
10
~ ~
~ ~~~**
~ ~ ~ ~
at
£
0.1
: Mean = 2.32 mg/L
Std. Dev. = 0.43 mg/L
C.O.V. = 19%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 9999.5 99.9 99.95
Percent Less Than or Equal To
« Raw Influent - Ammonia-N	x Final Effluent - Total N
Figure 8. Weekly average frequency curves for nitrogen.
Reliability Factors
This facility's design is unique in several ways. The plant has multiple treatment processes in
series to provide efficiency and reliability in meeting nitrogen and phosphorus limits. They
include primary settling, a five-stage Bardenpho process for biological nitrogen and
10 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
phosphorus removal, and tertiary filtration. In addition, some chemical removal of
phosphorus can be obtained when alum is added before the tertiary filters for THM control.
The results are excellent: the plant achieves a phosphorus mean concentration of 0.13 mg/L
with a COV of 40 percent and a TN mean concentration of 2.32 mg/L with a COV of only
16 percent as a monthly average. The plant's maximum average week results were good,
with the maximum average week phosphorus at 0.26 mg/L versus the weekly standard of
1.5 mg/L, the maximum average week ammonia nitrogen at 0.062 mg/L, and the maximum
average week TN at 3.75 mg/L versus the weekly standard of 4.5 mg/L. These results are
well within the normal range of variation from average for a wastewater treatment process, as
reflected in the low to very low COVs shown in Figures 3, 5, and 7. As shown in Table 2, the
fractions by which the monthly effluent maxima exceeded the corresponding annual averages
(62 percent, 25 percent, and 35 percent for TP, ammonia nitrogen, and TN, respectively)
were consistent with or better than the literature suggestion of 63 percent (Brandao et al.
2005). The key factors for this exceptional performance are discussed below.
Wastewater characteristics: The BOD-to-TP ratio was favorable, with an average value of
37.5, and ranged monthly between 31 and 44. A ratio of 20 is recommended in the literature
(WEF and ASCE 1998). The average BOD-to-total Kjehldahl nitrogen (TKN) ratio was
6.7 and ranged monthly between 6.1 and 7.6. Both ratios are favorable for BNR. The soluble
BOD-to-ammonia nitrogen ratio has been in the range of 4 to 5, less than what was originally
recommended (6). It should be noted that on weekdays 160,000 gal/day of filtrate from the
belt filter presses is returned to the head of the plant; this filtrate contains 51 mg/L of TP and
131 mg/L of ammonia nitrogen. These loads amount to 30 percent of the influent TP and
14 percent of influent ammonia, with the effective minimum BOD-to-TP and BOD-to-TN
ratios dropping to 24 and 5.3, respectively. The soluble BOD-to-ammonia nitrogen ratio
similarly drops to 3.7. Despite these recycle stream loads and the low BOD-to-ammonia
nitrogen ratio, no adverse effect was reported under the operating parameters developed at
this facility.
Primary settling tanks: The plant regularly operates four tanks out of the eight available, and
the efficiencies in removal are typical—30 percent in BOD and 50 percent in TSS.
Activated sludge: The five-stage Bardenpho process at the facility is a typical design. It
includes a fermentation zone, followed by the first anoxic and aerobic zones in series, a
second anoxic zone, and the re-aeration zone. The typical internal recirculation of MLSS to
the first anoxic zone from the second aerobic zone is five times the influent flow rate. Some
unique features of this process are two separate anoxic zones, each with long detention times
of approximately 1.5 hours, long sludge age ranging between 30 and 50 days, and high water
temperature.
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Phosphorus removal far exceeds the permit requirement with good reliability and is achieved
by two processes: first by the Bardenpho process as the primary process, then later as a side
benefit to alum addition, which is done primarily to reduce TSS and so reduce potential THM
formation. The Marshall Street WRF has to meet a limit on dichlorobromomethane of
22 micrograms per liter (jig/L) and a dibromochloromethane limit of 34 pg/L to meet
Florida's state requirements for water reuse. The typical dosage of alum is 27 mg/L, or 2.4
mg/L as aluminum (Al). This dosage is equivalent to an Al-to-TP ratio of 1.6 on a molar
basis in the plant influent. For the effluent concentration the plant produces, this ratio is
considered low for a strictly chemical removal process.
Nitrogen removal has been excellent with good reliability. No external carbon source is used.
The use of two anoxic zones with an internal recirculation flow rate of five times the influent
flow rate has been found to be sufficient to produce low nitrogen concentrations (WEF and
ASCE 1998). It is also noteworthy that the plant maintains a sludge blanket in the secondary
clarifiers. The depth ranges between 2 and 3 feet and is a part of the TN removal strategy and
the biological phosphorus removal strategy.
Another key operational factor is the automated process control system, which uses
Chemscan and supervisory control and data acquisition (SCADA). These programs monitor
online at the second anoxic zone nitrate-nitrogen, dissolved oxygen (DO), oxidation-
reduction potential (ORP), and ortho-phosphorus to optimize nitrogen removal. Table 4 lists
the sensors used at the Marshall Street facility. The minimum ORP is set at -60 millivolts
(mV), and the nitrate-nitrogen is set at a minimum of 0.5 mg/L. The DO is adjusted on the
basis of these two parameters. In addition, the system monitors MLSS and the sludge blanket
in the secondary clarifiers. The plant also has monitors for turbidity, in accordance with the
permit, and conductivity, to monitor for salts that could intrude by means of seawater and
adversely affect irrigation reuse. All the automation and controls have contributed to an
efficient phosphorus removal and full denitrification with good reliability.
Table 4. Probe and sensor suppliers
Parameter
Supplier(s)
Dissolved oxygen
Hach, Royce
MLSS
Hach
Nitrate-nitrogen
Chemscan
Ammonia nitrogen
Chemscan
Clarifier sludge blanket depth
Hach, Royce
pH
Hach
Oxidation-reduction potential (ORP)
Hach
Ortho-phosphorus
Chemscan
Turbidity
Hach
12 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
In addition, this plant has the flexibility of operating as a four-stage Bardenpho process,
thereby providing additional tank volume dedicated to nitrogen removal. Under this mode of
operation, the phosphorus removal is achieved primarily by alum addition.
Secondary clarifiers: The plant regularly operates three out of four units at the current flow.
One practice to note is the maintenance of the sludge blanket at between 2 and 3 feet, which
is monitored with the new blanket monitors installed in 2002.
Tertiary filter. The tertiary filter is an original Zimpro filter with air and water backwash
provisions. The system is effective in suspended solids removal: the effluent TSS averages
1 mg/L or less. This, in turn, is a key to achieving the low phosphorus concentration in the
final effluent.
Recycle flows from dewatering and thickening go back to the primary clarifier influent. The
returns are controlled to flow uniformly around the clock and avoid a shock loading to the
treatment processes. No adverse impact has been observed under this practice at this facility.
Another key parameter to note is the long sludge age maintained at this plant. Because of this
long sludge age at warm temperature ranges, a sludge yield of around 0.25-0.4 lb volatile
suspended solids (VSS) per lb of BOD removed has been reported. This is consistent with
Manual of Practice No. 8 (WEF and ASCE 1998). This low yield naturally contributes to a
low cost in sludge handling.
Costs
Capital Costs
The main upgrade of the plant for BNR occurred in 1988 when the basins were reconfigured
for the five-stage Bardenpho process. The upgrade then cost $16.8 million, which was
updated to $29.5 million in 2007 dollars using the Engineering News-Record (USDA 2007).
The upgrade included additional tanks or dividing walls, mixers, pumps, blowers/aerators
and tertiary filtration.
It was assumed that 17 percent of the upgrade was attributed to phosphorus removal, while
63 percent of the upgrade was for nitrogen removal. This allocation was done in consultation
with plant personnel and was based on the fraction of the secondary system volume that
could be attributed to phosphorus or nitrogen removal. Specifically, all anaerobic tank
volume plus 10 percent of the volume of the aerobic tanks (based on oxygen usage) was
attributed to phosphorus removal, while all anoxic tank volume plus 50 percent of the aerobic
tanks (based on oxygen usage) was attributed to nitrogen removal. The balance of the
upgrade was attributed to BOD removal or other activities required by permit. The tertiary
filters were installed to meet the requirements for surface water discharge under reuse rule
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
62-610 in Florida. This meant that the capital expenditure in 2007 dollars that was attributed
to phosphorus removal was $5.02 million. The annualized capital charge (20 years at
6 percent) was $438,000 for phosphorus removal.
The capital expenditure attributed to nitrogen removal was $10.6 million in 2007 dollars. The
annualized capital charge (20 years at 6 percent) was $1.6 million for nitrogen removal.
The total capital expenditure attributed to BNR was $29.5 million in 2007 dollars. For the
10-MGD facility, the capital expenditure per gallon of BNR treatment capacity was $2.95.
Operation and Maintenance Costs
In all case studies prepared for this document, the O&M costs considered were for electricity,
chemicals, and sludge disposal. Labor costs for O&M were specifically excluded for three
reasons:
1.	Labor costs are highly sensitive to local conditions, such as the prevailing wage rate,
the relative strength of the local economy, the presence of unions, and other factors;
thus, they would only confound comparison of the inherent cost of various
technologies.
2.	For most processes, the incremental extra labor involved in carrying out nutrient
removal is recognized but not significant in view of the automatic controls and
SCADA system that accompany most upgrades.
3.	Most facilities were unable to break down which extra personnel were employed
because of nutrient removal and related overtime costs, making labor cost
development difficult.
CAPDETWorks was used to provide a relative comparison of labor costs compared to power
costs. CAPDETWorks is a software package developed by Hydromantis Corporation
(Hamilton, Ontario, Canada). It is used to estimate conceptual capital and operating cost
estimates for wastewater treatment facilities. It is based on work originally done by EPA and
the U.S. Army Corps of Engineers. Two flow scenarios were run for a model consisting of a
five-stage Bardenpho reactor, a secondary clarifier, a tertiary filter, and an anaerobic
digester: (1) 5.5 MGD to mimic the current flow at the plant and (2) 10 MGD to match the
design flow. For 5.5 MGD, the CAPDET electrical cost estimate using the plant's overall
average rate of $0.11 per kilowatt-hour (kWh) was $960,000, while the O&M labor cost at an
average regional rate of $35/hour was $540,000. For a 10-MGD facility, the CAPDET
electrical cost estimate was $1.7 million, while the labor cost was $680,000. By comparison,
as shown below, the Marshall Street facility's electrical cost for similar equipment at an
average flow of 5.5 MGD was $840,000, including electrical costs for BOD removal.
14 - Marshall Street, Clearwater, FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
The plant uses both biological phosphorus and nitrogen removal, with minimal use of alum
and no use of supplemental carbon sources. The plant could use minimal chemicals because
the ratios of influent BOD to TP and influent BOD to TN were both very high (37.6 and 6.7,
respectively). This means that costs for nutrient removal are essentially all electrical. A
summary of the electrical use calculations is provided in the Attachment. The specific
electrical usage for phosphorus removal was 931,000 kWh per year (kWh/yr). The average
electrical rate for the plant was $0.11/kWh, and it was based on the cost per kWh plus a
demand charge plus a Florida-required fuel surcharge. When that rate was applied, the cost
for phosphorus removal was $102,400 for the year. The total electrical usage for nitrogen
removal was 4,620,000 kWh/yr, or $509,000. The electrical usage for BOD removal in the
system was 2,091,000 kWh/yr, or $230,000.
Alum is applied as an effluent-polishing step primarily for reducing THM formation
potential; however, some phosphorus removal does occur with alum addition. The total cost
of alum used over the evaluation period was $74,000. On the basis of the dosage of alum and
the possible removal that could occur, it was assumed that 10 percent of the alum could be
attributed to phosphorus removal; the chemical cost for phosphorus removal was therefore
$7,400. All the alum added (2.4 mg/L as Al) was assumed to convert to aluminum hydroxide
sludge; at the average flow of 5.48 MGD, this was 317 lb of aluminum sludge per day, or
58 dry tons/yr. Assuming that phosphorus removal accounted for 10 percent of the sludge
and using the plant's cost of sludge disposal of $253/dry ton, the chemical sludge cost for
phosphorus removal was $1,463.
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 81,200 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal was $1.37 per pound, while the
annualized unit capital cost was $5.39/lb of phosphorus removed. At design flow, the
annualized capital would drop to $2.95/lb of phosphorus removed.
During the evaluation period, the plant removed 428,000 lb of TN. With the results above,
the unit O&M cost for TN removal was $1.18/lb, while the annualized unit capital cost is
$3.79/lb of nitrogen removed. At design flow, the annualized capital cost would drop to
$2.07/lb of TN removed.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the annualized unit capital and unit O&M costs. Thus, the
life-cycle cost for phosphorus removal was $6.76/lb phosphorus removed, while the life-
cycle cost for TN removal was $4.97/lb nitrogen removed, all at current flows. At design
flows, assuming the O&M costs increase proportionally to flow and loadings, the life-cycle
costs would be $4.32/lb of phosphorus removed and $3.25/lb of TN removed.
Appendix A
Marshall Street, Clearwater, FL • Water Reclamation Facility -15

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Assessment of magnitude of costs: The capital cost of $2.95/gpd capacity is relatively high,
but the O&M costs remain low. One of the key factors is that no methanol is purchased
because of the use of the incoming carbon source for both nitrogen and phosphorus removal
with the five-stage Bardenpho process.
Discussion
Reliability factors. The treatment processes at the Marshall Street plant represent a traditional
layout for the original five-stage Bardenpho process for both biological nitrogen and
phosphorus removal—one anaerobic zone, two anoxic zones with a high rate of internal
recirculation, an aeration zone in between, and the final re-aeration zone. This is
accomplished with a conservative design basis—a long HRT, a long sludge age, and a low
clarifier loading rate in a warm-temperature region. Another key is the automated controls
the plant personnel use, which are based on online monitoring with multiple sensors and
process control parameters for the Bardenpho process. In addition, good primary settling
tanks and efficient tertiary filters added reliability along with alum addition for effluent THM
reduction. This process as operated by the plant personnel has proven to be efficient and
reliable in meeting the permit limits of 3 mg/L for nitrogen and performing significantly
better than the limit of 0.2 mg/L in phosphorus.
Cost factors'. The costs are relatively high for capital but low for O&M. This plant was
designed with conservative design parameters, at $2.95/gpd capacity. The O&M costs are
low at $ 1.37/lb of phosphorus removed and $1.18/lb of TN removed. The main reasons for
these low costs are efficient operation of the biological processes and no need for an external
carbon source (e.g., methanol). Even though the power cost in Florida, compared to that of
other states, is high at $0.11/ kWh, the overall O&M cost is relatively low. In addition, the
alum addition is at a reduced dosage and thus the cost impact is low because the Bardenpho
process removes a significant amount of phosphorus biologically. All these costs are based
on the plant's current flow. As the plant flow increases to the full design loadings, these unit
costs would be expected to decrease.
Summary
The Marshall Street WRF is an advanced wastewater treatment plant with a five-stage
Bardenpho process that meets the effluent discharge limit for nitrogen and exceeds that for
phosphorus. The reliability has been excellent in achieving low concentrations—0.13 mg/L
in phosphorus with a COV of 40 percent and 2.32 mg/L in nitrogen with a COV of 16
percent monthly average. The cost for this facility is considered high with a capital cost at
$2.95/gpd capacity, but the O&M costs are low. The unit costs are low at $6.76/lb of
phosphorus removed and $4.97/lb of TN removed.
16 - Marshall Street. Clearwater. FL • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Key contributing factors for reliability include favorable wastewater characteristics,
conservative design with multiple processes in series, good operating procedures for the
Bardenpho process developed by the plant personnel, and automation with online sensors and
control devices.
Key contributing factors to facility costs include a conservative design originally, an efficient
operation without an external carbon source, and optimization of energy and chemical usage,
while minimizing sludge production from the biological process.
Acknowledgments
The authors are grateful for the significant assistance and guidance provided by John
Milligan, superintendent of the Wastewater Environmental Technologies Division,
Clearwater; Tom Nietzel, coordinator of the Wastewater Environmental Technologies
Division, Clearwater; and Jeff Borden, chief operator of the Marshall Street WRF. This case
study would not have been possible without their prompt response with well-deserved pride
in the facility and its operation. EPA thanks Clearwater, Florida, for participating in this case
study.
References and Bibliography
Brandao, D., G.T. Daigger, M. O'Shaughnessy, andT.E. Sadick. 2005. Comprehensive
Assessment of Performance Capabilities of Biological Nutrient Removal Plants
Operating in the Chesapeake Bay Region. In Proceedings of the Water Environment
Federation, 78th Annual Conference, Washington, DC, October 29-November 2,
2005.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html. Accessed May 15,
2007.
WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers).
1998. Design of Municipal Wastewater Treatment Plants. Manual of Practice No.8,
Figure 11.7, Net sludge production versus solids retention time. Water Environment
Federation, Alexandria, VA.
Appendix A
Marshall Street. Clearwater. FL • Water Reclamation Facility -17

-------
I
&
iO
S
-
CD
9
05
$
§3
&
5
6
Q"
§
$
n
Attachment: Electrical Use and Chemical Costs

Horse-
power
#
kW
power
draw
hours/
day
kWh
draw/day
kWh
draw/year
% BOD
%P
%N
Usaqe for
BOD
Usaqe
forP
Usage
for N
Ferment basin
mixers
10
6
44.76
24
1,074.24
392,097.6
0%
100%
0%
0
392,097.6
0
1st anoxic mixers
7.5
9
50.355
24
1,208.52
441,109.8
0%
0%
100%
0
0
441,109.8
Aerator
400
2
596.8
24
14,323.2
5,227,968
40%
10%
50%
2,091,000
522,796.8
2,613,984
Pumps—internal
recycle
50
3
111.9
24
2,685.6
980,244
0%
0%
100%
0
0
980,244
2nd anoxic mixers
7.5
12
67.14
24
1,611.36
588,146.4
0%
0%
100%
0
0
588,146.4
Filter lift pumps
50
1
37.3
24
895.2
326,748
0%
5%
0%
0
16,337.4
0
Total draw kWh/yr

7,629,566



2,091,187
931,231.8
4,623,484
Alum
$74,000
use
% for P
10
Alum

cost for
$7,400
P

t
3
I

-------
Noman M. Cole, Jr., Pollution Control Plant
Fairfax County, Virginia
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
This facility was selected for as case study because it employs a step-feed activated-sludge
strategy with tertiary filters and a ferric chloride feed.
The Noman M. Cole, Jr., Pollution Control Plant serves the area of Fairfax County, Virginia,
in the Washington, D.C., metropolitan area. The plant was originally placed in operation in
1970. The average wastewater treatment capacity of the plant was 18 million gallons per day
(MGD) when commissioned; this has risen to 67 MGD after a series of successful
expansions. Biological nutrient removal (BNR) was added in 2002 as part of a 13-MGD
expansion.
The Virginia Pollutant Discharge Elimination System (VPDES) permit limits for the Noman
M. Cole, Jr., Pollution Control Plant are shown in Table 1.
Table 1. VPDES permit limits
Parameter
Monthly
average
(mg/L)
Monthly
average
(lb/day)
Weekly average
(mg/L)
Weekly
average
(lb/day)
CBOD
5
2,790
8
4,464
TSS
6
3,348
9
5,020
Ammonia-N (April-Oct)
1.0
559
1.5
836
Ammonia-N (Nov-Mar)
2.2
-
2.7
-
Total N
Report
-
Report
-
Total P
0.18
101
0.27
150
Notes:
CBOD = carbonaceous biochemical oxygen demand
N = nitrogen
P = phosphorus
TSS = total suspended solids
Appendix A
Fairfax County, VA. • Noman M. Cole, Jr., Pollution Control Plant -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Treatment Processes
The facility uses a step-feed strategy to distribute organic matter throughout the biological
treatment basins. Following primary settling, the flow goes to a set of nine aeration basins
that are operated in anaerobic, aerobic, or anoxic modes. The activated-sludge process was
designed for a normal detention time of 8.9 hours with up to five feed points into the basin.
Feed is typically distributed to three anaerobic or anoxic points in the system. Polymer can be
added to aid secondary clarification. The facility uses ferric chloride and polymer to polish
the secondary effluent, primary-to-tertiary clarification, and filtration. The final effluent is
chlorinated/dechlorinated before discharge to Pohick Creek, a tributary to the Potomac River.
The primary sludge is fermented in the gravity thickeners at a sludge residence time (SRT) of
3 days and a hydraulic retention time (HRT) of less than 24 hours. The secondary sludge is
thickened at the dissolved air flotation (DAF) units. The fermented primary sludge and
thickened secondary sludge are mixed together for dewatering by centrifuge, followed by
incineration. Lime can be added to the dewatering process to minimize recycle loads of
nutrients.
Figure 1 shows the plant's flow schematic. The secondary system consists of nine parallel
aeration basins—six small (1.67 million gallon [MG] total volume each) and three large
(4.89 MG total volume each). Figure 2 shows how the step-feed works in the larger basins.
The feed can be provided at five anoxic zones through each basin, although in practice only
four (A, C, D, and E) receive feed. The smaller basins have three points for step-feeding
primary effluent. Under normal circumstances, the flow split between zones A, B, and C in
the smaller basins is 40 percent, 40 percent, and 20 percent, respectively, while the larger
basins, zones A, C, D, and E, each get 25 percent of the flow. Other design information on
the facility is provided in Table 2 and the attachment.
2 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
f
§
B.
PROCESS FLOW DIAGRAM
Sq
&J
l
1?
s
£
rs
p
5?
§
i
S
13
NOMAN M. COLE.JR., POLLUTION CONTROL PLANT. COUNTY OF FAIRFAX . VIRGINIA
Hi. itr>T-U'«
PONOHI
EC
FlSHEwAsii
YANK
BACKWASH TANK EFFLUENT

2
POLYMER
KK1
3
FERRIC CHLORIDE
QQ
OBAV'TV
ffcttWKtm
h A .7
SEWAGE
SCREENS
MlV
TANKS m
*kst* I IL'W
TANKS '»
IRNKS IV
r,
FILTERS ¦ !)}
CHEMICAL SLUDGE RECYCLED
TO MEAD OP PLANT

2
POLYMER
RECEIVING
FACILITY
Q1/Q2
SCREENINGS
TO I - 95
COOISPCSAL
MO" STm .•*
POLYMER
TWCAfliEftS
t1lCKEt,ERE
I11/R2
Tanks CE THICKENERS
SLIIO(it PBOCESStNG BUU3ING < IWC NO 1.7 t
SLUDGE PROCESSING BU'LDINQ IIMC NO Hi)
I 3LITDGC PflOCtSSNG QUiLOtMC ( CCNTfttFUGC |
R OTATION TflCKFKFRS
I SLlfDG[ SIOKAGt TANKS
S SCCOHOARY CHEMICAL fCCD BUILDING
T AW WASHTENANCE SJILD NG
U (Mill Owes ANtl CiRC l , Wr>3 BUI HI WO
69 AM PU«P»NG STATION
CC AW WJMW?CRSiTERTtAR-YCLAIUFWRSj
DO GRAVITY FUTSR 6U>-0SNG
ffc WALMfcDIA FILTERdUiUKNG
r? monomceha F'lter building
H»l AW" CMLORINAT1QM AND OECttLOfUKADOtt 81
MMT APWfWPStATKJN
'M W-UNE M
JJ AW" 5LU0QC THICKENERS
KK1 FOOEWN SLUDGE HAHCtRM BWUMNOS
KK2 FOfiEtG* 5LUOGE HANDLING BJ LWKG5
Pl> SODIUM BI&ULTTE BLIIDIMC
OQ CQUAl CATION BASIN?
RR BULK VTGRADE
snr scftace rccdwng r agility
TT PLAWT OUTFAU STRUCTURE
Figure 1. Noman M. Cole, Jr., Pollution Control Plant process flow.
e*s

-------
"ft
Sj
I
o
§
#
s
I
1
&
I
§
D
§
I
Si
PE
~RAS
PE
PE
ML
WassA 'nox'cZone

JAJ	
ML
A Swing Zone
rte
^	7Af?
7B5
7B3
7C1-D/op1
Pa'ss C Jog
Anoxic Zone
7D5


7D3
Aeration Zone

Aeration Zone
7B1
7C1-Drop2„
A
Swing Zone
ML
7E1-Drop1
Pass E
Anoxic Zone
7E1-Drop2,
/?
Swing Zone
7F5
7F3
Aeration Zone
4
ML

ML
~
7C3
AerationjZone	A
i A
! 7C5
7D1-Drop2
Swing Zone
7D1-Drop1

Pass D
Anoxic Zone
7E3
ML^>
DO)	Aeration fcone (pp)
7E5

7F1-Drop2
Swing Zone
7F1-Drop1
Pass F
Anoxic Zone
PE

PE
73
0
CD
O
o_
o
CjQ
>
CO
(/)
0
CO
U)
3
0
13
o
Q)
U)
0
(J)
c
CL
f
§
I
Figure 2. Woman M. Cole, Jr., Pollution Control Plant step-feed detail.
I in
I 0
I "D
I	0
I	3
I	^
I	0
I ro
I o
I o
I CO

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 2. Facility design data
Secondary tanks
Tanks 1-6
Tanks 7-9
Volume
1.67 MG
4.89 MG
Anoxic volume
3.5-5 MG
5.1-7.3 MG
HRT (average)
8.9 hr
8.9 hrs
SRT at maximum month loading
(last MLSS 4,400 mg/L)
18 days
18 days
Gravity thickeners (2)

Volume
0.146 MG each
SRT
3 days
HRT
>12 hours
Tertiary clarifier

Diameter
152 ft
Hydraulic loading rate
735 gpd/sf (average flow)
Tertiary filters
Monomedia
Gravity filters
Number
8
10
Media type
Anthracite
Garnet/sand/anthracite
Depth
5 ft
2.25 ft
Design loading rate, gpm/sf
2.9
2.6
Dimensions
30 ft x 17 ft x 2 cells
30 ft x 30 ft x 2 cells
Notes:
gpd/fs = gallons per day per square foot
HRT = hydraulic retention time
MG = million gallons
MLSS = mixed liquor suspended solids
SRT = solids retention time
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Plant Parameters
Overall plant influent and effluent average results for the 2006 calendar year are shown in
Table 3.
Table 3. Influent and effluent averages
Parameter
(mg/L unless stated)
Average
value
Maximum
month
Max
month
vs. Avg.
Maximum
week
Sample
method/frequency
Flow (MGD)
47.4
51.4
8%
54.4
Daily
Influent TP (mg/L)
6.39
7.06
10%
8.16
Composite/daily
Effluent TP (mg/L)
0.09
0.12
33%
0.16
Composite/daily
Influent BOD (mg/L)
189
205
8%
305
Composite/daily
Effluent BOD (mg/L)
2.0
2.0
0%
2.0
Composite/daily
Influent TSS (mg/L)
225
253
12%
353
Composite/daily
Effluent TSS (mg/L)
1.0
2.2
120%
3.06
Composite/daily
Influent NH4-N (mg/L)
18.9
22.5
19%
24.8
Composite/weekly
Effluent NH4-N (mg/L)
0.12
0.15
25%
0.29
Composite/weekly
Influent TKN (mg/L)
34.6
40.4
17%
48.1
Composite/weekly
Effluent TKN (mg/L)
0.9
1.12
26%
1.6
Composite/weekly
Effluent N03/N02 (mg/L)
4.35
5.03
16%
6.41
Composite/weekly
Notes:
TP = total phosphorus
BOD = biochemical oxygen demand
TSS = total suspended solids
TKN = total Kjeldahl nitrogen
NH4-N = ammonia measured as nitrogen
N03 = nitrate
N02 = nitrite
NH4-N = ammonia measured as nitrogen
N03 = nitrate
N02 = nitrite
6 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 4 presents plant monthly average plant process parameters.
Table 4. Monthly averages for plant process parameters


Sludge age/mean cell



MLSSa
residence time
HRT
Temperature
Month
(mg/L)
(d)
(hr)
(°C)
Jan 2006
3,626
18
9.2
17.9
Feb 2006
3,267
19
9
15.3
Mar 2006
3,390
19
9.2
17.4
Apr 2006
2,851
19
10
19.5
May 2006
3,142
18
9.8
20.6
June 2006
2,784
18
8.8
22.5
July 2006
2,383
17
8.3
23.8
Aug 2006
3,139
17
8
25.7
Sept 2006
3,192
17
7.8
25.4
Oct 2006
2,922
16
8.2
23.5
Nov 2006
2,403
16
9.4
21.2
Dec 2006
2,852
18
10
19.4
a MLSS is the combined average of last pass (C-PASS for AST 1-6, F-PASS for AST 7-9).
Table 5. Monthly average BOD/TP and BOD/TKN ratios
Month
Influent BOD/TP
Primary
effluent
BOD/TP
Influent BOD/TKN
Jan 2006
33.1
29.8
6.1
Feb 2006
33.7
29.5
5.4
Mar 2006
28.3
27.4
5.3
Apr 2006
28.2
27.1
5.5
May 2006
27.2
26.8
4.7
June 2006
28.9
24.4
5.5
July 2006
28.8
26.1
5.9
Aug 2006
29.4
28.1
4.6
Sept 2006
31.5
32.4
5.0
Oct 2006
33.5
33.8
4.9
Nov 2006
32.2
32.0
5.4
Dec 2006
28.2
26.3
5.4
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Performance Data
This section provides information about the operational performance of nutrient removal at
the plant. Figures 3 and 4 present the facility's 2006 monthly and weekly reliability data for
phosphorus removal. The average phosphorus effluent concentration was 0.09 mg/L with a
coefficient of variation (COV) of 21 percent on a monthly average basis. The COV is defined
as the standard deviation divided by the mean and is a measure of the reliability of a system.
The lower the COV, the less the data are spread and the higher the reliability. The
phosphorus concentration exhibited a low COV of 28 percent for the weekly averages. The
plant's performance in 2006 was excellent: the weekly average never exceeded even the
monthly limit. The secondary effluent exhibited an average of 0.7 mg/L for the year. These
figures demonstrate that both the tertiary clarifier with chemical addition and tertiary filters
are key factors in meeting the permit limit at all times. Note also that the primary influent
contains higher total phosphorus (TP) than the raw influent because of internal recirculation
flows at the facility.
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Monthly Average Frequency Curves for Total Phosphorus
-	Mean = 0.086 mg/L
-	Std. Dev. = 0.018 mg/L
-COV = 21%
30 40 50 60 70 80
Percent Less Than or Equal To
99 99.5 99.9 99.95
~ Raw Influent
X Tertiary Clarifier Influent
~ Primary Influent
X Tertiary Clarifier Effluent
¦ Primary Effluent
A Final Effluent
A Secondary Effluent
Figure 3. Monthly average frequency curves for TP.
8 - Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Weekly Average Frequency Curves for Total Phosphorus
U)
E
_ Tertiary Influent
Mean = 0.85 mg/L
1 . _ Std. Dev. = 0.35 mg/L
B COV = 42%
~
o
¦E
Q.
¦Tertiary Effluent
Mean = 0.36 mg/L
Std. Dev. = 0.118 mg/L
o
Secondary Effluent
Mean = 0.74 mg/L
0.1 - Std. Dev. = 0.37 mg/L
Mean = 0.09 mg/L
Std. Dev. = 0.025 mg/L
0.05
0.1
0.5
1
2
5
10
20
30 40 50 60 70
80
90
95
98
99
99.5
99.9 99.95
Percent Less Than or Equal To
~ Raw Influent	~ Primary Influent	¦ Primary Effluent	A Secondary Effluent
X Tertiary Clarifier Influent X Teitiary Clarifier Effluent A Final Effluent
Figure 4. Weekly average frequency curves for TP.
Figures 5 and 6 present the 2006 monthly and weekly reliability data for ammonia nitrogen
removal. The weekly effluent ammonia concentration averaged 0.12 mg/L, with a standard
deviation of 0.035, giving a COV of 29 percent. The plant's performance in 2006 was
excellent: the weekly average never exceeded 0.3 mg/L, compared to the monthly standard of
1 mg/L during the summer months.
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Monthly Average Frequency Curves for Ammonia Nitrogen















~ ~



































	. 	. 	 v ¦ w 1 III lit"

1 1 Mfian = 0 1? mg/l


	Sid. Dev. = 0.016 mg/L 	












0.05 0.1 0.5 1 2 5	10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia N X Final Effluent - Ammonia N
Figure 5. Monthly average frequency curves for ammonia nitrogen.
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Weekly Average Frequency Curves for Ammonia Nitrogen














~~~ ~ ~ ~ ~ ~




































	x	x	x	x	_x	» MHW

Mean =0.12 mg/L =














0.05 0.1 0.5 1 2 5	10 20 30 40 50 60 70 80 90 95	98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N X Final Effluent - Ammonia N
Figure 6. Weekly average frequency curves for ammonia nitrogen.
10 - Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Figures 7 and 8 present the 2006 monthly and weekly reliability data for total nitrogen (TN)
removal. The weekly effluent TN averaged 5.12 mg/L, with a standard deviation of
1.02 mg/L, giving a COV of 20 percent.
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Monthly Average Frequency Curves for Nitrogen











•	4	
































Std. Dev. = 0.63 mq/L


COV = 12%






0.05 0.1 0.5 1 2 5	10 20 30 40 50 60 70 80 90 95	98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - TKN	X Final Effluent - Total N
Figure 7. Monthly average frequency curves for nitrogen.
Noman M. Cole Pollution Control Plant - Fairfax County, VA
Weekly Average Frequency Curves for Nitrogen











A** ~ ~ ~ ~ *
	 			


~










Std. Dev. = 1.02 mg/L


COV = 20%





















0.05 0.1	0.5 1 2 5	10 20 30 40 50 60 70 80 90 95	98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent - TKN	X Final Effluent - Total N
Figure 8. Weekly average frequency curves for nitrogen.
Appendix A	Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Reliability Factors
The plant has a permit limit for phosphorus of 0.18 mg/L as a year-round monthly average
and monthly average ammonia nitrogen limits of 1.0 mg/L for the summer months and
2.2 mg/L for the winter months. The plant personnel have a policy of operating the plant such
that these limits are seldom even approached much less exceeded. The overall reliability was
good, with COVs of 21 percent for TP at the mean concentration of 0.09 mg/L, 14 percent
for ammonia nitrogen at the mean concentration of 0.12 mg/L, and 12 percent for TN at the
mean concentration of 5.25 mg/L for the monthly average.
A key factor in the high reliability of this step-feed plant is the care that operating staff take
to ensure that any process problems do not become uncontrollable. Attention to operating
details and taking appropriate and timely actions in response to plant performance data go a
long way toward attaining good plant performance. It has been found that encouraging
operating staff to use field test kits (e.g., Hach kits) to determine nitrogen and phosphorus
concentrations provides a number of benefits, including allowing staff to take immediate
action to fine-tune chemical addition and any adjustments to the biological system rather than
waiting for laboratory results. It also results in a sense of ownership of the test data because
they did the tests themselves. The plant has an operator for the secondary system on duty
24 hours a day, 7 days a week, and there is daily interaction between operators and engineers
to review the process. A BioWin model is also used to run scenarios.
Phosphorus removal is achieved in three steps—biological removal in activated sludge,
chemical removal in a tertiary clarifier, and then tertiary filters. McGrath et al. (2005)
reported that biological phosphorus removal occurs when low nitrates cause the first
unaerated zone to become anaerobic. Thus, the amount of nitrate returns through return
activated sludge could directly affect biological removal. When nitrate levels go above
6 mg/L in the secondary effluent, biological phosphorus removal is greatly reduced. This is
why the main removal mechanism for phosphorus is chemical addition followed by tertiary
clarification and filtration. This sequence of operations ensures sufficient phosphorus
removal, especially with chemical addition under close control by plant operators. Under
current operating conditions, the operators treat any removal of phosphorus in the biological
system as a bonus.
Primary sludge was fermented in gravity thickeners with an SRT of 3 days and an HRT of
less than 24 hours. The volatile fatty acids (VFA) production was equivalent to 10 mg/L in
chemical oxygen demand (COD) in the primary effluent, and the VFAs consisted of 33
percent acetic acid, 49 percent propionic acid, and 18 percent others (McGrath et al. 2004).
The secondary sludge was thickened at the DAF unit, thereby preventing release of
phosphorus and ammonia.
12 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Using step-feed is the primary means by which nitrogen removal through multiple anoxic
zones is achieved. In the smaller biological reactors, the flow is split among three passes on a
40 percent, 40 percent, and 20 percent basis, with each pass having an anoxic zone and an
oxic zone. Thus, the flow entering the first pass goes through three sets of anoxic/oxic zones,
while the flow from the second pass goes through two sets of zones. In the larger basins, feed
is sent to four points on the basis of 25 percent each. The system offers reliable operation
because it allows using the carbon in the wastewater for denitrification rather than having to
add a supplemental carbon source like methanol. Avoiding the need for supplemental carbon
ensures a more economical operation because there is no need for additional feed pumps,
storage tanks, and distribution and control equipment or additional sludge handling.
Recycle loads went to the primary influent, and they averaged 10 percent in biochemical
oxygen demand (BOD), 19 percent in total suspended total suspended solids (TSS) and
23 percent in TP. All processes were sized to treat these recycle flows, including lime
addition to the dewatering to minimize recycle loads.
The wet-weather operation included four distinct steps—retention basin (5.7 MG) first, then
equalization at the headworks (4 MG), step-feed activated sludge, and finally equalization of
secondary effluent (13.2 MG). The step-feed makes the process more stable than that at other
plants. The holding capacity at the headworks area was equivalent to 15 percent of the design
flow rate, a significant factor for good reliability.
Finally, the reliability of the plant is enhanced by a well-designed and maintained control and
monitoring system, supplemented by field testing. The dissolved oxygen probes are
frequently calibrated and maintained, and the plant's supervisory control and data acquisition
(SCADA) system is well designed. An instrument technician is available on-site and ensures
proper maintenance at this facility.
Costs
Capital Costs
The main upgrades of the plant for BNR occurred in 1979, when the Advanced Wastewater
Treatment (AWT) plant was installed for phosphorus removal, and in 1997, when the
aeration basins were retrofitted for step-feed operation to accomplish nitrogen removal. The
AWT is a chemical phosphorus-removal facility that includes mixing and reaction tanks with
filtration. The step-feed retrofit consisted of piping modifications and tank additions and
filtration.
The costs for installation of the AWT facility were not available; however, they would have
been typical of retrofits where chemical is added before tertiary clarifiers and filters because
such facilities would be used for normal BOD/TSS removal. This means that the capital
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
expenditure for a retrofit for chemical phosphorus removal is fairly low because all that
would be needed would be storage tanks, pumps, and controls, with many of those possibly
available by reusing existing equipment.
Plant personnel provided the estimate that the capital expenditure in 1997 that could be
attributed to nitrogen removal is $52.5 million. This estimate was updated to 2007 dollars
using the Engineering News-Record Construction Cost Index (ENR CCI). The ENR CCI is
compiled by McGraw-Hill and provides a means of updating historical costs to account for
inflation, thereby allowing comparison of costs on an equal basis. From a Web site provided
by the U.S. Department of Agriculture, the ENR index for 1997 was 5,826, while the ENR
index for May 2007 was 7,942 (USDA 2007). Multiplying the above results by the ratio
7,942/5,826 obtained the result of $71.6 million in 2007 dollars.
This result was annualized using the interest rate formula for determining a set of annual
payments for a present value, given an interest rate and payback period. For this and all other
case studies for this report, a 6 percent interest rate and 20-year payback were assumed,
resulting in a multiplication factor of 0.0872. The annualized capital cost for nitrogen
removal was $6.2 million. This annualized capital for nitrogen removal was used for later
unit cost estimates for TN and ammonia nitrogen.
The total capital attributed to BNR in 1997 dollars was $52.5 million, which was adjusted to
$71.6 million in 2007 dollars using the ENR index. For this 67-MGD facility, this means the
capital expenditure per gallon of BNR treatment capacity is $1.07.
Operation and Maintenance Costs
In all case studies prepared for this document, the O&M costs considered were for electricity,
chemicals, and sludge disposal. Labor costs for operation and maintenance were specifically
excluded for three reasons:
1.	Labor costs are highly sensitive to local conditions, such as the prevailing wage rate,
the relative strength of the local economy, the presence of unions, and other factors;
thus, they would only confound comparison of the inherent cost of various
technologies.
2.	For most processes, the incremental extra labor involved in carrying out nutrient
removal is recognized but not significant in view of the automatic controls and
SCADA system that accompany most upgrades.
3.	Most facilities were unable to break down which extra personnel were employed
because of nutrient removal and related overtime costs, making labor cost
development difficult.
The Noman M. Cole, Jr., plant uses primarily chemical phosphorus removal and biological
nitrogen removal. This means that the primary O&M costs for phosphorus removal are for
14 - Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
electricity, chemicals, and sludge disposal, while the primary O&M costs for nitrogen
removal are for electricity. Chemical sludge is recycled to the plant headworks, but it
contributes to the eventual primary sludge.
The Attachment lays out the electrical usage for the plant. The entire electrical usage for
phosphorus removal lies in the AWT portion of the plant, at 280,000 kilowatt-hours (kWh)
per month, or 3,360,000 kWh/yr. Using the average electrical rate of $0.055/kWh, which
includes all demand charges, the cost of electricity for phosphorus removal is $185,000. The
power usage for nitrogen removal was 18,059,000 kWh/hr. At the average electrical rate, the
cost of electricity for nitrogen removal is $993,300.
Plant personnel estimated that chemical (ferric chloride) usage for phosphorus removal cost
$l,076/day. In addition, plant personnel estimated that the ferric chloride generated an
additional 2 dry tons of primary sludge per day, which cost an additional $l,076/day for
disposal. This meant that the additional cost for phosphorus removal for chemical and sludge
disposal totaled $785,500/yr. Over the evaluation period, plant personnel used an estimated
$250,000 worth of caustic for pH adjustment, which is needed for nitrogen removal.
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 909,600 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal was $1.07/lb, while the annualized unit
capital cost for phosphorus removal was $0.
During the evaluation period, the plant removed 4,240,000 lb of TN. With the results above,
the unit O&M cost for TN removal was $0.29/lb of TN, while the annualized unit capital cost
for TN removal was $1.47.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle cost is the sum of the annualized unit capital and unit O&M costs. Thus, the
life-cycle cost for phosphorus removal was $1.07/lb and the life-cycle cost for TN removal
was $1.76/lb.
Assessment of magnitude of costs: The capital cost of $1.07/gpd capacity is low because of
the existing facility before the upgrade. The O&M cost for phosphorus removal is high due to
chemical use to reach a low concentration limit, while the O&M cost for nitrogen removal
are in the middle range, compared with those for other facilities.
Summary
The Noman M. Cole, Jr., plant retrofit to a step-feed strategy has provided excellent
reliability in meeting both nitrogen and phosphorus limits. The COVs were 21 percent for
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant -15

-------
Nutrient Removal Technology Assessment Case Study
September 2008
TP at the annual average of 0.09 mg/L, 14 percent for ammonia nitrogen at the average
concentration of 0.12 mg/L, and 12 percent for TN at the average concentration of
5.25 mg/L. The phosphorus removal is achieved primarily by chemical addition followed by
tertiary filters. The nitrogen removal is achieved with multiple anoxic zones in the process. In
addition, the step-feed provides operational benefits during wet-weather conditions because
the strategy allows the operators to distribute the increased flows throughout the aeration
basins in steps, thereby protecting the clarifiers from added solids loadings during high-flow
periods. Removal costs for both phosphorus and nitrogen were reasonable, with low capital
at $1.07/gpd capacity, and O&M costs at $1.07/lb TP removed and $1.77/lb TN removed.
Acknowledgments
The authors are grateful for the significant help and guidance provided by Michael McGrath,
operations director, and Roger Silverio, process engineer, at the Noman M. Cole, Jr.,
Pollution Control Plant. This case study would not have been possible without their prompt
response with well-deserved pride in the facility and its operation. The authors also
acknowledge Fairfax County for its participation in this case study.
References and Bibliography
McGrath, M, K. Gupta, and G.T. Daigger. 2005. Operation of a Step-Feed BNR Process for
Both Biological Phosphorus and Nitrogen Removal. In Proceedings of Water
Environment Federation 78th Annual Technical Exhibition & Conference,
Washington, DC, October 29-November 2, 2005.
McGrath, M., S. Shero, and J. Wleton, 2004. Fermentation for Improving Nutrient Removal
at a Virginia Wastewater Facility. In Proceedings of Water Environment Federation,
October 2004.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html. Accessed
May 2007.
16 - Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Attachment: Facility Design Information
Design Flow
Minimum flow
Average daily flow
Peak instantaneous flow
Peak process flow
Design Average Loadings
BOD
TSS
TKN
TP
Retention Basin 1 (QQ1)
Retention QQ1
Quantity
Type
Volume
Retention basin pumps
Quantity
Type
Capacity
Large
Small
Screen Building (B1)
Bar screens
Quantity
Total channel width
Opening size
RAW Wastewater Pump Station (B)
RAW wastewater pumps
Quantity
5
Type
Vertical, centrifugal
Speed

A-1
Adjustable
A-2
Two-speed
A-3
Constant
A-4
Adjustable
A-5
Constant
Appendix A	Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant -17
26.8 MGD
67.0 MGD
134.0 MGD
107.2 MGD
118,000 Ib/d
126,000 Ib/d
21,000 Ib/d
4,100 Ib/d
1
Open
5.7 MG
4
Submersible
3,300 gpm at 27 ft
350 gpm at 27 ft
3
8 ft
3/4 in

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Capacity
A-1	20,500 gpm at 30 ft TDH
A-2	19,165 gpm at 30 ft TDH
A-3	20,700 gpm at 30 ft TDH
A-4	20,700 gpm at 30 ft TDH
A-5	18,500 gpm at 30 ft TDH
RAW Wastewater/EQ Tank Pump Station (B2)
Equalization tank pumps
Quantity
Type
Capacity, each
Raw wastewater pumps
Quantity
Type
Capacity, each
3
Submersible
6,544 gpm at 84 ft TDH
2
Submersible
9,682 gpm at 47 ft TDH
Equalization Tanks (B3)
Equalization tanks
Quantity	4
Type	Concrete
Dimensions, each	200 ft long X 100 ft wide X 27 ft Deep (SWD)
Volume, each	4 MG
Flash Mix Tanks (CI)
Quantity	2
Dimensions	30 ft L X 18 ft W X 10 ft SWD
Volume, each	40,400 gallons
Detention time	1.74 minutes at average daily flow
Primary Settling Tanks (C)
Primary settling tanks
Quantity
Type
Size
Weir length, each
Weir loading
Hydraulic overflow rate
Primary influent odor control scrubber
Quantity
Type
Depth of packing
Cross section area
Capacity
8
Rectangular
139 ft L X 45 ft WX 10 SWD
120 ft
69,800 gpd/linear foot at average daily flow
1,340 gpd/ft2 at average daily flow
1
Packed bed
12 ft min
19.6 ft2
5,000 CFM
18 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Scrubber recirculation pump

Quantity
1
Type
Vertical wet pit centrifugal
Capacity, each
100 gpm at 30 ft TDH
Horsepower
2
Small Activated Sludge Tanks 1 TO 6 (D)
Small activated sludge tanks

Quantity
6
Number of passes, each
3
Size, each pass
182 ft L X 30 ft W X 13.6 ft SWD
Volume, each tank
1.67 MG
Total volume
10.0 MG
Total anoxic volume
3.5 to 5.0 MG
HRT @ average flow
8.9 hours
SRT @ max mo load,
18 days
& last pass MLSS OF 4,400

Mixers

Quantity
78
Type
Submersible, mast-mounted
Horsepower, each
4 HP
Process oxygen requirements

BNR operation

Average
48,000 Ib/d
Maximum month
51,000 Ib/d
Maximum day
71,400 Ib/d
Nitrification only operation

Average
70,800 Ib/d
Maximum month
76,200 Ib/d
Maximum day
115,000 Ib/d
Diffused aeration equipment

Type
9-in porous flexible membrane

Full floor coverage
Large Activated Sludge Tanks 7 TO 9 (D1)
Large activated sludge tanks

Quantity
3
Number of passes, each
6
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant -19

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Size, each pass
Volume, each tank
Total volume
Total anoxic volume
HRT @ average flow
SRT @ max mo load,
& last pass MLSS of 4,400
2at165ftl_X18ftWX22ft SWD
4 at 165 ft L X 36 ft W X 22 ft SWD
4.89 MG
14.7 MG
5.1 to 7.3 MG
8.9 hours
18 days
Mixers
Quantity
Type
Horsepower, each
57
Vertical turbine
Platform-mounted
24 at 3 HP
12 at 5 HP
9 at 7.5 HP
12 at 15 HP
PE channel mixers
Quantity
Type
Horsepower, each
18
Submersible, mast-mounted
2.5 HP
Process oxygen requirements
BNR operation
Average
Maximum month
Maximum day
Nitrification only operation
Average
Maximum month
Maximum day
88,200 Ib/d
95,700 Ib/d
149,000 Ib/d
101,000 Ib/d
108,000 Ib/d
164,000 Ib/d
Diffused aeration equipment
Type
9-in porous flexible membrane
Full floor coverage
AST dewatering pumps
Quantity
Large
Small
20 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008	Nutrient Removal Technology Assessment Case Study
Type	Submersible
Capacity, each
Large	2,025 gpm at 25 ft TDH
Small	75 gpm at 60 ft TDH
Horsepower, each
Large	25 HP
Small	5 HP
Blower Building (E1)
Small AST aeration blowers
Quantity
Type
Capacity, each
Horsepower, each
4
Multistage centrifugal
16,000 SCFM at 8.0 psi
800 HP
Clarifiers 12-15 RAS pumps
Quantity	5
Type	Single-passage screw impeller, centrifuge
Speed	Adjustable
Capacity, each	4,400 gpm at 28 ft TDH
Horsepower, each	50 HP
WAS pumps
Quantity	4
Type	Horizontal centrifugal
Capacity, each	510 gpm at 30 ft TDH
Blower Building (E2)
Aeration blowers
Quantity
Small AST blowers
Large AST blowers
Type
Capacity
Small AST blowers
Large AST blowers
Horsepower, each
Small AST blowers
Large AST blowers
2
4
Multistage centrifugal
17,500 at 8.0 psi
14,000 at 12.7 psi
800 HP
1,250 HP
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 21

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Clarifiers 5-8 RAS pumps
Quantity
Type
Capacity
5
Horizontal centrifugal
6,500 gpm at 37 ft TDH
Clarifiers 16-17 RAS pumps
Quantity	2
Type	Single-passage screw impeller, centrifuge
Speed	Adjustable
Capacity, each	4,400 gpm at 28 ft TDH
Horsepower, each	50 HP
Secondary Clarifiers 5 to 8 (F)
Quantity	4
Type	Circular
Diameter	145 ft
Sidewater depth	14.75 ft
Hydraulic overflow rate	540 gpd/ft2 at peak process flow
Solids loading rate	31 lp/d/ft2 at peak process flow
Secondary Clarifiers 12 to 17 (F1)
Secondary clarifiers
Quantity
Type
Dimensions, each
Hydraulic overflow rate
Solids loading rate
Secondary clarifier dewatering pumps
Quantity
Type
Capacity, each
Horsepower, each
6
Rectangular chain & flight
260 ft L X 55 ft W X 16 ft SWD
540 gps/ft2 at peak process flow
31 lf/d/ft2 at peak process flow
2
Submersible
500 gpm at 50 ft TDH
15 HP
Chlorination Facility (G)
SPH pumps
Quantity
Type
Capacity, each
SPH strainers
Quantity
Type
Capacity, each
Vertical turbine
3,100 gpm at 216 ft TDH
Automatic, self-cleaning
1,050 gpm
22 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Sodium hypochlorite feed pumps
Quantity
Large NaOCI pumps
Small NaOCI pumps
Type
Capacity
Large NaOCI pumps
Small NaOCI pumps
Sodium hypochlorite storage tanks
Quantity
Dimensions, each
Volume, each
Chemical Feed Building (S)
Caustic feed pumps
Quantity	4
Type	Tubular diaphragm chemical metering
Control	Adjustable stroke & speed
Capacity, each	420 gph max
Typical dose	11 mg/L as CAC03 for PH control
Caustic storage tanks
Quantity	3
Dimensions, each	12 ft diameter X 19 ft high
Volume, each	16,000 gallons
Polymer feed pumps
Quantity	12
Type	Progressing cavity
Speed	Adjustable
Capacity, each	250 gph max
Typical dose	0.5-1.0 mg/L
Polymer transfer pump
Quantity	1
Type	Progressing cavity
Capacity	80 gpm
4
2
Tubular diaphragm chemical metering
200 gph max
50 gph max
4
11.5 ft diaX 15.5 ft high
12,000 gallons
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 23

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Polymer mixing, aging, and storage tanks
Quantity	2
Dimensions, each	7 ft dia X 7 ft high
Volume	2,000 gallons
Chemical feed pumps for primary settling tank odor control
Quantity
Caustic	1
Sodium hypochlorite	1
Type	Eccentric lobe peristaltic
Capacity
Caustic	8.6 gpm
Sodium hypochlorite	7.0 gmp
Sodium hypochlorite storage tank (exist)
Quantity	1
Dimensions, each	12 ft dia X 19 ft high
Volume	16,000 gallons
Equalization Basins 2 & 3 (QQ2 & QQ3)
Equalization basins
Type
Volume
Basin QQ2
Basin QQ3
Concrete-lined, open
7.4 MG
5.8 MG
Wash water return pumps
Quantity
Type
Speed
Capacity, each
Horsepower, each
2
Submersible
Constant
600 gpm at 50 ft TDH
20 HP
ASE Pump Station (BB)
ASE pumps
Quantity
Type
Capacity
Adj speed
Constant speed
Constant speed
5
Vertical turbine
2 at 29,400 gpm
1	@ 22,600 gpm
2	@ 16,000 gpm
24 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Tertiary Clarifiers (CC)
Tertiary clarifiers
Quantity
Type
Nominal inside diameter
Hydraulic overflow rate
4
Octagonal
148 ft
735 gpd/ft2 at average flow
Tertiary clarifier dewatering pumps
Quantity
Type
Speed
Capacity, each
Horsepower
2
Horizontal centrifugal
Constant
2,400 gpm at 50 ft TDH
50 HP
Tertiary Clarifiers (CC1)
Flow distribution structure mixer
Quantity
Type
Horsepower
1
Vertical turbine, platform-mounted
15 HP
Tertiary clarifier
Quantity
Type
Diameter
Hydraulic loading rate
1
Circular
152 ft
735 gpd/ft2 at average flow
Tertiary clarifier dewatering pumps
Quantity
Type
Speed
Capacity, each
Horsepower, each
1
Horizontal centrifugal
Constant
1,000 gpm at 21 ft TDH
15 HP
TCE Pump Station (CC)
Tertiary clarifier effluent pumps
Quantity
Type
Speed
Capacity, each
Horsepower, each
3
Vertical turbine
Adjustable
22,700 gpm at 35 ft TDH
300 HP
Foreign Sludge Incinerator Building (KK)
Ferric chloride pumps
Quantity
Type
4
Tubular diaphragm chemical metering
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 25

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Control	Adjustable stroke & speed
Capacity	200 gpm max
Typical dose	25-30 mg/L
Polymer feed pumps
Quantity
Type
Speed
Capacity
Typical dose
6
Progressing cavity
Adjustable
2.0 gpm max
0.1-0.2 mg/L
Monomedia Filter Building (FF)
Monomedia filters
Quantity
Type
Media type
Number cells, each
Dimensions, each cell
Media depth
Design loading rate
Backwash pump
Quantity
Type
Capacity
Center gullet
Anthracite
2
30 ft L X 17 ft W
5 ft
2.9 gpm/ft2 at average daily flow with
all units in service
1
Vertical turbine
20,400 gpm
Gravity Filter Building (DD)
Gravity filters
Quantity
Media type
Dimensions, each cell
Media depth
Design loading rate
Backwash pump
Quantity
Type
Capacity
10
Anthracite/sand
30 ft L X 30 ft W
2.25 ft
2.6 gpm/ft2 at average daily flow with
all units in service
1
Vertical turbine
18,000 gpm
Gravity filter effluent pumps
Quantity
Constant speed	2
Adj speed	2
Type	Vertical turbine
26 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Capacity, each
Constant speed
Adj speed
22,500 gpm
27,000 gpm
Backwash Effluent Tanks (EE)
Quantity
Dimensions, each
Volume, each
3
85 ft L X 20 ft W X 11.3 ft SWD
144,000 gallons
Reaeration Tank (HH)
Quantity
Dimensions
Volume
1
72 ft L X 70 ft W X 22 ft SWD
830,000 gallons
APW Pump Station (HH1)
Advanced plant water pumps
Quantity
Type
Speed
Capacity, each
Horsepower, each
4
Vertical turbine
Adjustable
4,400 gpm at 212 ft TDH
300 HP
Blended Sludge Storage Tanks (R1/R2)
Odor control scrubber system
Quantity
Type
Chemicals treated
Capacity, each
Depth of bedding
Cross-sectional area
1
Two-stage, packed-bed wet type
nh3, h2s
5,000 cfm
7 ft
19.6 ft2
Chemical feed pumps for odor control
Quantity
Caustic
Sodium hypochlorite
Sulfuric acid
Type
Capacity, each
2
2
2
Tubular diaphragm, chemical metering
23 gph
Chemical storage tanks
Chemical
Quantity
Dimensions, each
Volume, each
NAOH
1
6 ft dia X 10 ft high
2,100 gallons
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 27

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Chemical
Quantity
Dimensions, each
Volume, each
Chemical
Quantity
Dimensions, each
Volume, each
NAOCL
1
4 ft dia X 11 ft 7 in high
1,000 gallons
H2S04
1
38 in dia X 82 in long
400 gallons
Degritting Building (H1)
Cyclone separators
Quantity
Capacity, each
Grit classifiers
Quantity
Capacity, each
6
465 gpm at 12 psi
3
108 ft3/hr
Primary Sludge Thickeners (J1/J2)
Gravity thickeners
Quantity	4
Type	Circular
Diameter	50 ft
Sidewater depth	10 ft
Flotation Thickeners (Q1/Q2)
DAF thickeners
Quantity	3
Type	Rectangular
Size	40.2 ft L x 12 ft W x 12 ft SWD
Capacity, each	960 gpm
Sludge Storage (R1/R2)
Sludge storage tanks
Quantity
Diameter
Sidewater depth
Volume, each
2
367,000 gallons
Sludge Dewatering (K3)
Centrifuge
Quantity	4
Type	Bowl and scroll conveyor
Sludge loading, each
With lime	5,351 Ib/hr
Excluding lime	4,730 Ib/hr
Sludge feed concentration (percent)
28 - Fairfax County, VA • NomanM. Cole, Jr., Pollution Control Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Minimum	3.00%
Maximum	6.00%
Minimum cake solids concentration	29.00%
Minimum solids capture	95.00%
Capacity, each, based on 3.5% solid feed
95% solids capture, 29% cake solid	60 dry tons per day
Sludge Incineration (K1/K2)
Incinerators Nos. 1 & 2
Quantity
Type
Capacity, each
Incinerators Nos. 3 & 4
Quantity
Type
Capacity, each
2
Multiple hearth
45 dry tons per day
2
Multiple hearth
92 dry tons per day
Appendix A
Fairfax County, VA • Noman M. Cole, Jr., Pollution Control Plant - 29

-------

-------
North Cary Water Reclamation Facility
North Cary, North Carolina
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The North Cary, North Carolina, Water Reclamation Facility (WRF) is a 12-million-gallon-
per-day (MGD) facility that included biological nutrient removal (BNR) as part of a 1997
expansion. This facility, which was a replacement/expansion of the 4-MGD Schreiber
process on the same site, was selected as a case study because of its phased isolation ditch
(PID) technology with tertiary filters.
The WRF does not have primary settling and uses the PID technology or the BioDenipho
process by Kruger. The facility uses two pairs of oxidation ditches with anaerobic selectors
ahead of the ditches and a second anoxic zone following the ditches. Each pair of ditches is
operated in an aerobic/anoxic sequencing mode or phases. The effluent from the ditches goes
to two 130-foot-diameter clarifiers. Before discharge to Crabtree Creek, effluent is passed
through an upflow Dynasand filter by Parkson and ultraviolet disinfection and is aerated. The
original Schreiber tank was converted into a 7-million-gallon (MG) equalization basin in
addition to a 2-MG equalization basin at the headworks area, and the stored water is drained by
gravity to the influent pump station for subsequent treatment. Sludge is thickened and
aerobically digested before it is transported to the South Caiy WRF for dewatering and drying
for final disposal.
The relevant permit limits that the North Carolina Department of Environment and Natural
Resources (NCDENR) established for the plant are shown in Table 1. Compliance limits are
primarily for the monthly averages shown for carbonaceous biochemical oxygen demand
(CBOD), total suspended solids (TSS), and ammonia nitrogen. Additional limits are specified
for the quarterly limit for total phosphorus (TP) and for the annual maximum limit of
144,000 lb for total nitrogen (TN), which is equivalent to 3.94 milligrams per liter (mg/L) as
nitrogen.
A distinguishing feature of the BioDenipho process is the alternating flow pattern and
process conditions (aerobic and anoxic) occurring within the oxidation ditches. This
operating strategy allows nitrogen and CBOD removal to occur within the active process
volume, eliminating the need for internal recycle pumping. The operation is executed by a
programmable logic controller (PLC)-based system that coordinates the operation of the
mechanical process equipment and controls the phase lengths within each ditch. The PLC
system allows both manual and automatic control of the treatment process. The PLC panel
Appendix A
North Cary, NC • Water Reclamation Facility -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 1. NCDENR permit limits
Parameter
Summer limits
(mg/L)
Winter limits
(mg/L)
Quarterly limits
(mg/L)
Annual limits
CBOD
4.1
8.2
--
--
TSS
30
30
--
--
NH3-N
0.5
1.0
--
--
TN
--
--
--
144,000 lb (max)3
TP
--
--
2.0
--
Coliforms
--
--
200/100 mL
--
Notes:
NH3-N = ammonia nitrogen
a Equivalent to 3.94 mg/L as TN for 12 MGD
also includes preprogrammed operational modes, such as the stormwater mode to address
infiltration/inflow (I/I) concerns. For example, automatic or manual activation of the
stormwater mode incorporates a sedimentation phase into the BioDenipho process to prevent
solids washout during severe rain events. This innovation allows reduction of the required
size of the secondary clarifiers or eliminates the requirement for redundant clarifiers.
Plant Design and Process Parameters
A schematic for the North Caiy WRF is shown in Figure 1. To ensure economical and
efficient treatment, the system also controls the aeration equipment by automatic dissolved
oxygen (DO) control. DO probes continuously monitor and report residual DO levels within
the oxidation ditches to the PLC panel that controls the aeration equipment to meet, but not
exceed, the current oxygen demand. This eliminates costly and wasteful over-aeration that
can compromise process stability and operational budgets. Table 2 and Attachment 1 present
relevant design data for the facility and Attachment 2 presents a plant operating process
diagram. The sludge residence time (SRT) for an oxidation ditch was 12 days at 12 degrees
Celsius (°C).
Table 2. Facility design data
Units
Number
Volume
Anaerobic selectors
4 each train
0.093 MG x 4 = 0.372 MG
Oxidation ditch
2 each train
1.5 MG x 2 = 3 MG
Secondary anoxic zone
3 each train
0.111 MG x 3 = 0.333 MG
Reaeration zone
1 each train
0.111 MG
Clarifiers
2 each
130 ft diameter
Note: MG = million gallons
2 - North Cary, NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
1N3P1JKI .9C
Appendix A
North Cary, NC • Water Reclamation Facility -3

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Table 3 presents operational results for the October 2005 to September 2006 period. Table 4
presents plant monthly average plant process parameters.
Table 3. Influent and effluent averages
Parameter
(mg/L unless stated)
Average
value
Maximum
month
Max
month
vs. avg.
Maximum
week
Sample
method/frequency
Flow (MGD)
7.0
8.71
24%
10.8
--
Influent TP (mg/L)
7.7
9.2
20%
11.1
Composite, 3x/week
Effluent TP (mg/L)
0.38
1.06
180%
1.45
Composite, 3x/week
Influent BOD (mg/L)
244
271
11%
296
Composite, 5x/week
Effluent BOD (mg/L)
0.8
1.26
50%
1.84
Composite, 5x/week
Influent TSS (mg/L)
366
418
14%
594
Composite, 5x/week
Effluent TSS (mg/L)
1.0
1.47
45%
2.28
Composite, 5x/week
Influent NH4-N (mg/L)
45.5
49.4
8%
53.5
Composite, 5x/week
Effluent NH4-N (mg/L)
0.08
0.34
316%
1.03
Composite, 5x/week
Influent TKN (mg/L)
56.4
62.2
10%
65.6
Composite, 3x/week
Effluent TN (mg/L)
3.67
4.46
21%
5.87
Composite, 3x/week
Note:
TKN = total Kjeldahl nitrogen
BOD = biochemical oxygen demand
Table 4. Monthly averages for plant process parameters

MLSS
Sludge age
HRT
Temperature
Month
(mg/L)
(days)
(hours)
(°C)
Oct 2005
2,665
13.1
28
23
Nov 2005
2,628
13.8
29
20
Dec 2005
2,736
13.0
26
19
Jan 2006
2,672
13.3
27
18
Feb 2006
2,720
12.8
27
16
Mar 2006
2,692
13.3
29
18
Apr 2006
2,661
12.6
27
19
May 2006
2,625
13.5
28
21
June 2006
2,700
11.3
21
24
July 2006
2,713
12.3
25
26
Aug 2006
2,709
12.6
25
27
Sep 2006
2,685
12.1
24
26
Notes:
HRT = hydraulic retention time
MLSS = mixed liquor suspended solids
4 - North Cary, NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Plant Performance
This section of the case study provides information about the operational performance of
nutrient removal at the facility. Figures 2 and 3 present monthly and weekly reliability data
for ammonia nitrogen removal. These data cover the period of October 2005 through
September 2006. Note that the apparent outlier values are from the period in June 2006 when
the plant's service area was subjected to nearly 8 inches of rain in a 24-hour period from
Tropical Storm Alberto. Note also that despite that upset, the plant still met the monthly limit
of 0.5 mg/L for ammonia nitrogen. Overall, ammonia nitrogen oxidation was complete, with
a mean of 0.06 mg/L and a 31 percent coefficient of variation (COV) for non-tropical storm
months.
North Cary, NC
Monthly Average Frequer
cv Curves for Ammonia Nitroaen



¦	~—~—~ 9 *





















¦ ' '
^***	


	Mean = 0.081 mg/L —
	Std. Dev. = 0.082 mg/L —


C.O.V. = 102%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 9999.5 99.999.95
Percent Less Than or Equal To
« Raw Influent - Ammonia-N	x Final Effluent - Ammonia-N
Figure 2. Monthly average frequency curves for ammonia nitrogen.
Appendix A
North Cary, NC • Water Reclamation Facility - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
100
10
O)
E
North Cary, NC
Weekly Average Frequency Curves for Ammonia Nitrogen
~ ~~
: Mean = 0.81 mg/L
-Std. Dev. = 0.142 mg/L
- C.O.V. = 174%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 989999.5 99.999.95
Percent Less Than or Equal To
+ Raw Influent - Ammonia-N x Final Effluent - Ammonia-nitrogen
Figure 3. Weekly average frequency curves for ammonia nitrogen.
Figures 4 and 5 present monthly and weekly reliability data for TP removal. Phosphorus
removal was completely by biological means and worked well, with a monthly mean of
0.38 mg/L and a COV of 64 percent. This removal was sufficient to meet the facility's
quarterly limit of 2 parts per million (ppm).
100
CT)
E

-------
September 2008
Nutrient Removal Technology Assessment Case Study
North Cary, NC
Weekly Average Frequency Curves for Total Phosphorus
100
_l
O
E
o
-C
Q.

o
sz
CL
2
o
Mean = 0378 mg/L
Std. Dev. = 0.273 mg/L
C.O.V. = 72%
0.01
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent	x Final Effluent
Figure 5. Weekly average frequency curves for TP.
Figures 6 and 7 present reliability data for removal of TN at the facility. TN removal was
excellent, with the effluent mean 3.7 mg/L with a COV of 14 percent on a monthly average
basis, including the period with heavy precipitation caused by the tropical storm.
North Cary, NC
Monthly Averaqe Frequ
encv Curves for Total Nitroaen





























Mean = 3.67 mg/L


	Std. Dev. = 0.512 mg/L —


C.O.V. = 14%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 9899 99.5 99.999.95
Percent Less Than or Equal To
~ Raw Influent - Total Nitrogen x Final Effluent - Total Nitrogen
Figure 6. Monthly average frequency curves for TN.
Appendix A
North Cary, NC • Water Reclamation Facility - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
North Cary, NC
Weekly Average Frequency Curves for Total Nitrogen
4 ~ ~ ~ MMi





































Moan = 3.67 mg/L








C.O.V. = 21%
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 9899 99.5 99.999.95
Percent Less Than or Equal To
~ Raw Influent - Ammonia-N x Final Effluent - Ammonia-nitrogen
Figure 7. Weekly average frequency curves for TN.
Reliability Factors
The performance was efficient and reliable for entirely biological phosphorus and nitrogen
removal at North Caiy. The COVs were 102 percent for ammonia nitrogen at the mean
concentration of 0.08 mg/L, 64 percent for total phosphorus at the mean concentration of
0.38 mg/L, and 14 percent for total nitrogen at the mean concentration of 3.67 mg/L.
The following points summarize the factors affecting the reliability of the North Cary WRF:
• The BioDenipho process at North Cary is a flexible process with regard to varying
wastewater strength and flow rate. The reliability is achieved through well-controlled
oxidation of ammonia and subsequent denitrification in two distinct anoxic steps. The
anoxic cycle phase in the ditch can be adjusted from 60 minutes to 90 minutes, for
example, during a low-flow period, while it can be reversed during a high-flow
period. The rotors are controlled to provide sufficient oxygen to maintain the DO
concentration at 1 to 1.5 mg/L in the ditch, while mixers keep the organisms in
suspension during the anoxic phase. This flexibility to control mixing separately from
aeration is one of the keys to this plant's reliability. The low DO in the ditch effluent
ensures good denitrification in the second anoxic step to reach the desired nitrogen
level in the effluent. No external carbon source is needed to meet the permit limit.
8- North Cary, NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
•	Another key reliability factor is the automated control system, which consists of
sensors and DO controllers operating with the PLC and associated supervisory
control and data acquisition (SCADA) system. The exact phasing decision is made on
the basis of the preset control logic, which is site-specific and fully automated.
•	A key reliability factor for biological phosphorus removal is the feed point of the
influent. The influent is fed to the second anaerobic selector, while return activated
sludge is fed to the first selector to ensure that the returning nitrate from the clarifier
will be denitrified in the first selector zone. The second, third, and fourth selector
zones thus become anaerobic and allow full energy exchange for polyphosphate-
accumulating organisms (PAOs). The wastewater exhibited a favorable ratio of
biochemical oxygen demand (BOD) to TP, greater than 30 as an average. The plant
performance has been proven reliable through this process (WEF and ASCE 1998).
•	A key reliability factor for nitrogen removal is the three phases of anoxic cycles. The
first is in the anaerobic selector before the ditch, the second is in the ditch, and the
third is in the anoxic zone after the ditch. These multiple opportunities to denitrify in
the presence of BOD in the wastewater are unique and ensure good removal of
nitrogen. The wastewater exhibited a favorable BOD/TKN ratio of 5 as an average,
which is adequate for good denitrification (USEPA 1993).
•	Training is another key factor for achieving high reliability. Online monitoring and
automatic controls make training easy but require continuous maintenance by the
plant personnel.
•	Less power is used because of the maximum use of nitrate during the anoxic phase
and the prevention of over-aeration during the oxic phase. Pumping of oxidized
effluent to 3 to 4 times the discharge (Q) is not required to reach the same level of
denitrification.
•	Tertiary filters are effective in suspended solids removal.
•	Recycle loads are minimized; aerobic digestion occurs on-site, and the digested
sludge is shipped away for processing at another facility.
•	Wet-weather flows are handled in two ways: The equalization basins have a total of
9 MG storage, or 75 percent of the influent design flow; the PID has a storm mode in
the process control, under which the program switches into a sedimentation phase,
thereby preventing solids washout. These helped manage high flows during the June
2006 event, when Tropical Storm Alberto brought high flows to the plant. All the
storage volume was used, and the PID went into the storm mode for a short duration.
The plant treated all flows and complied with the permit.
Appendix A
North Cary, NC • Water Reclamation Facility - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Costs
Capital Costs
The main upgrade of the plant for BNR was in 1997 when the ditches were installed. The
upgrade then cost $25 million. The upgrade included additional ditches, the selector, pumps,
aerators, and tertiary filtration.
Because all phosphorus and nitrogen removal is biological, the capital costs were attributed
to different removal processes on the basis of the amount of oxygen used during biological
treatment, which is 12 percent for TP removal, 48 percent for nitrogen removal, and
40 percent for other (i.e., BOD removal). This means that the capital expenditure attributed to
TP removal was $3 million, and the expenditure attributed to nitrogen removal was
$12 million.
These capital cost results were updated to 2007 dollars using the Engineering News-Record
Construction Cost Index (ENR CCI). The ENR CCI is compiled by McGraw-Hill and
provides a means of updating historical costs to account for inflation, thereby allowing
comparison of costs on an equal basis. From a Web site provided by the U.S. Department of
Agriculture, the ENR index for 1997 was 5,826, while the ENR index for May 2007 was
7,942 (USDA 2007). Multiplying the above results by the ratio 7,942/5,826 obtained the
result of $4.09 million for phosphorus removal and $16.9 million for nitrogen removal in
2007 dollars.
The total capital expenditure attributed to BNR in 2007 dollars was $34.1 million. For the
12-MGD facility, the capital expenditure per gallon of BNR treatment capacity was $2.84.
Operation and Maintenance Costs
In all case studies prepared for this document, the O&M costs considered were for electricity,
chemicals, and sludge disposal. Labor costs for O&M were specifically excluded for three
reasons:
1.	Labor costs are highly sensitive to local conditions, such as the prevailing wage rate,
the relatively strength of the local economy, the presence of unions, and other factors;
thus, they would only confound comparison of the inherent cost of various
technologies.
2.	For most processes, the incremental extra labor involved in carrying out nutrient
removal is recognized but not significant in view of automatic controls and SCADA
system that accompany most upgrades.
3.	Most facilities were unable to break down which extra personnel were employed
because of nutrient removal and related overtime costs, making labor cost development
difficult.
10 - North Cary, NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
The plant uses an entirely biological phosphorus removal process to achieve the limit;
therefore, the primary operating cost is electrical use for operating the mixers, pumps, and
selector. Attachment 3 presents the electrical cost calculations for one train; the second train
is a duplicate. Power usage was attributed on the basis of discussions with plant personnel,
who suggested 5 percent for phosphorus removal and 95 percent for nitrogen removal, except
for units that could be entirely attributed to phosphorus or nitrogen (i.e., anaerobic mixers for
phosphorus, anoxic mixers for nitrogen). From this, the total power usage attributed to
phosphorus removal was 377,000 kilowatt-hours per year (kWh/yr). When calculated using
the average electrical cost of $0.056/kWh (which includes all demand charges), the cost for
power for phosphorus removal was $17,400. The total power usage attributed to nitrogen
removal was 2,558,000 kWh/yr; applying the electrical unit price, the cost for power for
nitrogen removal was $118,000.
The sludge generated during the process is transported to another town of Caiy facility for
disposal. From consultation with plant personnel, the sludge generated (4.91 tons/day) was
attributed at 5 percent to phosphorus removal and 95 percent to nitrogen removal. The cost
for the plant to send the sludge out for treatment was $200/ton. The cost for sludge disposal
for phosphorus removal was $17,900, while the sludge disposal for nitrogen removal was
$341,000.
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 156,000 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal was $0.23/lb, while the annualized unit
capital cost for phosphorus removal was $2.28.
During the evaluation period, the plant removed 1,121,000 lb of total nitrogen. With the
results above, the unit O&M cost for total nitrogen removal was $0.41/lb of TN, while the
annualized unit capital cost for TN removal was $1.27.
Life-Cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the annualized unit capital and unit O&M costs. Thus, the
life-cycle cost for phosphorus removal was $2.51/lb and the life-cycle cost for TN removal
was $1.68/lb.
Assessment of magnitude of costs: The capital cost of $2.84 per gallon per day (gpd) capacity
is relatively high, but the O&M costs are very low. One of the key factors is that chemicals
are not used for nutrient removal, saving both those costs as well as costs that would be
attributed to additional sludge generation.
Appendix A
North Cary, NC • Water Reclamation Facility -11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Summary
The North Cary facility is unique in that it provides reliable nutrient removal by means of a
PID process followed by tertiary filters. The phosphorus removal is achieved entirely by a
biological process with a mean concentration of 0.38 mg/L with a COV of 64 percent. The
nitrogen removal is also achieved entirely by a biological process with a mean of 3.67 mg/L
with an extremely low COV of 14 percent. The process is flexible enough to accommodate
varying flow conditions and the wastewater characteristics through the year, including the
severe rain caused by Tropical Storm Alberto in June 2006. Automatic controls incorporated
into the plant ensure reliable operation and control through these operating periods. The
wastewater characteristics are favorable to both nitrogen and phosphorus removal, and no
external carbon sources are needed with this PID process.
The capital cost is relatively high at $2.84/gpd capacity as a new facility but compares well
with others, which normally exceed $3/gpd. The O&M costs are estimated at $1.26/lb of TP
removed and $0.41/lb of TN removed. These costs are remarkably low, reflecting the
inherent advantages of this unique treatment process. The total costs were $2.21/lb of TP
removed and $2.92/lb of TN removed.
Acknowledgments
The authors are grateful for the significant assistance and guidance that Chris Parisher, North
Caiy WRF superintendent, provided. This case study would not have been possible without
his prompt response with well-deserved pride in the facility and its operation. The authors
also wish to thank the town of Caiy for its participation.
References and Bibliography
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates.
U.S. Department of Agriculture, Natural Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html. April 3, 2007.
USEPA (U.S. Environmental Protection Agency). 1993. Nitrogen Control Manual.
EPA/625/R-93/010. U.S. Environmental Protection Agency, Washington, DC.
WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers).
1998. Design of Municipal Wastewater Treatment Plants. Manual of Operation No. 8,
4th ed. Water Environment Federation, Alexandria, VA.
12 North Cary. NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Attachment 1: Key Design Parameters
SECTION 5: KEY DESIGN PARAMETERS
Design Basis:

Influent
Expected Secondary
Effluent
Unit
Annual Average Daily Flow
10
—
MGD
Peak Daily Flow
20
—
MGD
BOD
250
<10
mg/l
TSS
300
<10
mg/l
TKN
35
—
mg/l
NH;N'
—
<0.5/1.0
mg/l
TP
7
2
mg/l
TN
—
6
mg/l
Temp
12/27
-
2C
'Summer/Winter
system parameters:
Unit
Number of Trains
2

Anaerobic Selector


Physical Parameters


Number of Stages/Train
4

Volume per Stage
0.093
MG
Length per Stage
35.3
ft
Width per Stage
17.6
ft
SWD
20.0
ft
Equipment/Stage


Mixers


Number
1

Model
POP-I

HP
4.9
HP
RPM
180
RPM
Appendix A
North Cary, NC • Water Reclamation Facility -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Attachment 2: Operating Stages of the BioDenipho
Process
Dhaa& A (000-0150 h)
imiiwnt
Denerr'calior.
EH uant
AfrmroCK
Ncr^c^iion
Anaefotnc
Tank
Phase B(DS(J-1jl}h)
[nfiuerU
Nitrification
F-Ijeni
~enrti .Ticatksn
Pfasa Cf-i^O-^.Doh)
.'^enl
*naeicfc--r
Nitrification
Enfant
MilrilKTdtiQn
P|"fB3fr D (5jOO-2.50 h)
Indent
rttwcalion
GNUent
AnMro&e/
Tank —
Oenrtrittcahcn
Phase E [2.50-j.OOh)
Itiflusml
Anaerofcic^
Tar*
N [I CiJlinr
Eilue-it
Qenitrrficarrai
PMase F (aSO-4.0!)h>
IrfUent
Anaerobe
Tank
Nitnhcaricfi

Nibm canon
Figure 8. Operating stages for the BioDenipho process (WEF and ASCE 1998).
14 - North Cary, NC • Water Reclamation Facility
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
CL
i-
o
o
<4—
0-
1-
£
*
<0
X "O
11
"D
§
o
§
o
Q-
Q.
I





LO
CO
CM

CO
CO
r->
o

CO


CO
CD
CO

CO
CO


co"
cm"


CO
CO
CM

CD




CO



CO

CM
CO
CM

LO

c\i
o
CO
o
LO

CD

CO

co"
ctT


CM







o
LO
LO
o

cd
CD
o




o
LO
LO
o
o







CM

r-»
CO
r-«
LO
CO
¦
^—
CO
CO

CO

-------

-------
Western Branch Wastewater Treatment Plant
Upper Marlboro, Maryland
Nutrient Removal Technology Assessment Case Study
Introduction and Permit Limits
The Western Branch Wastewater Treatment Plant (WWTP) was selected as a case study
because of a unique feature—three separate activated-sludge systems operating in series to
remove nutrients.
The Western Branch WWTP is part of the Washington Suburban Sanitary Commission
(WSSC), and it is in Upper Marlboro, Maryland. It is permitted for a flow of 30 million
gallons per day (MGD); in 2006 it processed an average of 19.3 MGD. The plant is permitted
to discharge to the Western Branch of the Patuxent River.
The relevant National Pollutant Discharge Elimination System (NPDES) permit limits for the
facility are shown in Table 1.
Table 1. NPDES permit limits
Parameter
Annual
loading
(mg/L)
Monthly average
(mg/L)
Weekly average
(mg/L)
BODs
4/1-10/31

9
14
BODs
11/1-3/31

30
45
TSS

30
45
Total phosphorus
0.3
1.0
N/A
Total nitrogen
4.0
3.0
4.5
Ammonia-N 4/1-10/31

1.5
N/A
Ammonia-N 11/1-3/31

5.5
N/A
Notes:
BOD = biochemical oxygen demand
mg/L = milligrams per liter
N/A = not applicable
TSS = total suspended solids
Note that 0.3 mg/L TP and 4 mg/L TN on an annual load basis will be required after completion of enhanced
nutrient removal upgrades funded by Maryland.
aTotal nitrogen and total phosphorus are based on a design flow of 30 MGD.
Appendix A
Western Branch, MD • Wastewater Treatment Plant -1

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Plant Process
Figures 1 is an overall process flow diagram, and Figure 2 is a detailed liquid side process
flow diagram for the Western Branch Facility. The plant has three separate activated-sludge
systems in series: a high-rate activated-sludge (HRAS) system, intended primarily for BOD
removal; a nitrification activated-sludge (NAS) system, for conversion of ammonia nitrogen
to nitrate; and a denitrification activated-sludge (DNAS) system, for conversion of nitrate to
nitrogen gas. The return activated sludge for each system is kept separated to allow for
independent setting of sludge residence times. The system does not include primary settling,
and grit removal and screenings are provided ahead of the HRAS. The effluent is filtered
prior to ultraviolet (UV) disinfection. Waste activated sludge from the three systems is
mixed, thickened by dissolved air flotation (DAF), dewatered by centrifuge, and incinerated
in two multiple-hearth incinerators. Process water from the DAF, centrifuge, and incinerator
air scrubbers is returned to the headworks.

-

H

~
J
t
RAW
SEWAGE
	sT-
PRELIMINARY
TREATMENT HIGH RATE
ACTIVATED
SLUDGE
WASTE
ACTIVATED
SLUDGE
FILTRATION
NITRIFICATION
DENITRIFI
CATION
TO
WESTERN
BRANCH
CHLORINE
CONTACT & POST-
AERATION
(FUTURE UV
DISINFECTION)
	fi-
ASH TO
DISPOSAL
(LANDFILL)
FLOATATION
THICKENING
CENTRIFUGE
DEWATERING
INCINERATION
Figure 1. Western Branch WWTP process flow.
2 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
FLOW SPLIT STRUCTURE
(FOUR WEIRS WITH GATES)
PARSHALL FLUMES
GRIT/SCREEN UNITS
HIGH RATE AERATION
HIGH RATE CLARIFIERS
NITRIFICATION AERATION
FROM RAW WWPS
NITRIFICATION
CLARIFIERS
DENITRIFICATION
REACTORS
NITROGEN
STRIPPING
CHANNELS
DENITRIFICATION
CLARIFIERS
CO
o C
n
c
"co

C
"co
CO
0)
c
1	[
c
"co
O

i	r+i——y
0)
C
TO GRAVITY FILTERS AND UV
Figure 2. Western Branch WWTP liquid process flow.
Appendix A
Western Branch, MD • Wastewater Treatment Plant - 3

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Basis of Design and Actual Flow
Flow
The design flow for the facility is 30 MGD. The average flow for the study period was
19.3 MGD (23.0 MGD including recycles), while the maximum month flow during the study
period was 26.5 MGD (including recycles) during November 2006.
Loadings
Plant design based on the following:
Plant influent: BOD	200 mg/L
TSS	200 mg/L
HRAS effluent: BOD	60 mg/L
NAS effluent: BOD	20 mg/L
TKN 2 mg/1 L
Nitrate-nitrogen	15-30 mg/L
VLR
BOD lb/kcf/d
112
16
Process	Size	Detention time
(hours)
HRAS	3.35 (0.84 MG, 4 each)	2.68
NAS	6.89 (1.72 MG, 4 each)	5.51
DNAS -Anoxic	3.35 0.84 MG, 4 each	2.68
-	Stripping/reaeration = 0.68 MG (0.28 MG, 2 each) 0.45
-	TKN loading rate = 5.5 lb TKN/kcf/d
-	Sludge age = 5-10 days
-	RAS = 100% of plant flow
-	Methanol reed rate =100 mg/L
-	Alum feed point is the stripping/reaeration channel
Clarifiers
Size
Overflow rate
SLR
HRAS
120 x 80 x 13 ft, 4 each
781 gpd/ft2
34 lb/ft2/d
NAS
150 x 80 x 11.5 ft, 4 each
625 gpd/ft2
27.4
DNAS
Diameter - 160 ft, 4 each
373
16.3
Note:
SLR = sludge loading rate and is based on a mixed liquor suspended solids concentration of 3,000 mg/L.
Tertiary filters-gravity filters, with air-water backwash capability
-	30 ft x 30 ft, 11 each, total area 9,900 ft2
-	Filter bottom = Leopold clay tiles
-	Media-20 inches of anthracite, 8 inches of sand, 12 inches of gravel
-	Hydraulic loading rate = 2.1 gpm/ft2
4 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Plant Parameters
Overall plant influent and effluent average results for the period January 2006 to December
2006 are shown in Table 2.
Table 2. Influent and effluent averages
Parameter
(mg/L unless
stated)
Average
value
Maximum
month
Max
month vs.
ave.
Maximum
week
Sample
method/frequency
Flow incl recycle
(MGD)
23.0
26.5
15%
30.9

Influent TP
3.70
4.22
14%
5.57
Twice weekly/
composite
Effluent TP
0.43
0.89
89%
0.99
Five times weekly/
composite
Influent COD
332
417
26%
641
Twice weekly/
composite
Effluent COD
16.1
25.8
60%
38.6
Five times weekly/
composite
Effluent BOD
2.69
3.94
46%
6.08
Five times weekly/
composite
Influent TSS
222
282
27%
400
Twice weekly/
composite
Effluent TSS
1.23
2.28
85%
4.60
Five times weekly/
composite
Influent NH4-N
19.6
22.3
14%
25.1
Twice weekly/
composite
Effluent NH4-N
0.22
0.93
323%
3.41
Five times weekly/
composite
Influent Total N
23.9
28.7
20%
44.8
Twice weekly/
composite
Effluent Total N
1.63
2.46
45%
4.22
Five times weekly/
composite
Notes:
BOD = biochemical oxygen demand
Max month vs. average = (max month - average)/average x 100
NH4-N = ammonia measured as nitrogen
TN = total nitrogen
TP = total phosphorus
TSS = total suspended solids
Appendix A
Western Branch, MD • Wastewater Treatment Plant - 5

-------
Nutrient Removal Technology Assessment Case Study
September 2008
Tables 3, 4, 5, and 6 present plant monthly averages for the process parameters, as available.
Table 3. Monthly averages for HRAS process parameters
Month
HRAS MLSS
(mg/L)
HRAS sludge age
(d)
HRAS HRT
(hr)
Jan 2006
4,710
1.9
3.4
Feb 2006
4,232
1.8
3.3
Mar 2006
3,808
1.9
3.6
Apr 2006
3,798
1.7
3.7
May 2006
4,208
2.7
3.8
June 2006
5,454
7.3
3.5
July 2006
4,028
1.8
3.5
Aug 2006
4,306
1.9
3.8
Sept 2006
5,545
2.7
3.5
Oct 2006
4,066
1.7
3.4
Nov 2006
3,431
0.9
3.0
Dec 2006
4,017
2.0
3.6
Table 4. Monthly averages for NAS process parameters
Month
NAS MLSS
(mg/L)
NAS sludge age
(d)
NAS HRT (hr)
Jan 2006
4,264
34.8
7.1
Feb 2006
3,800
29.9
6.7
Mar 2006
3,617
46.6
7.4
Apr 2006
2,794
34.7
7.7
May 2006
3,644
24.3
7.7
June 2006
3,706
21.4
7.2
July 2006
3,523
72.5
7.3
Aug 2006
4,286
65.6
7.9
Sept 2006
4,987
84.6
7.1
Oct 2006
4,806
79.7
6.9
Nov 2006
4,212
34.4
6.2
Dec 2006
5,117
43.2
7.3
6 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Table 5. Monthly averages for DNAS process parameters
Month
DNAS MLSS
(mg/L)
DNAS sludge age
(d)
DNAS HRT
(hr)
Jan 2006
5,006
32.6
3.4
Feb 2006
4,329
24.4
3.3
Mar 2006
3,541
17.8
3.6
Apr 2006
3,818
8.8
3.7
May 2006
2,795
5.8
3.8
June 2006
3,427
11.9
3.5
July 2006
4,201
23.3
3.5
Aug 2006
3,192
10.9
3.8
Sept 2006
3,939
58.4
3.5
Oct 2006
3,968
18.9
3.4
Nov 2006
4,081
40.2
3.0
Dec 2006
4,990
17.0
3.6
Table 6. Monthly averages for influent temperature
Month
Temperature
(°F)
Temperature
(°C)
Jan 2006
58.5
14.7
Feb 2006
56.3
13.5
Mar 2006
57.5
14.2
Apr 2006
61.9
16.6
May 2006
64.4
18.0
June 2006
68.2
20.1
July 2006
72.4
22.4
Aug 2006
73.6
23.1
Sept 2006
71.4
21.9
Oct 2006
67.7
19.8
Nov 2006
63.9
17.7
Dec 2006
61.1
16.2
Performance Data
Figure 3 presents reliability data for the removal of total phosphorus (TP). The removal is
good, with the effluent TP averaging 0.43 mg/L, and a coefficient of variation (COV) of
62 percent.
Appendix A
Western Branch, MD • Wastewater Treatment Plant - 7

-------
Nutrient Removal Technology Assessment Case Study
September 2008
100
!9
b
£
0.01
0.001
Western Branch WWTP, WSSC
Monthly Average Frequency Curves for Total Phosphorus
Mean = 0.43 mg/L
Std. Dev. = 0.27 mg/L
C.O.V. = 62%
0.05 0.1 0.5 1
10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
o Plant Influent
o NAS Effluent
~ HRAS Influent
A DNAS Effluent
x HRAS Effluent
x Final Effluent
Figure 3. Monthly average frequency curves for TP.
Figure 4 presents reliability data for ammonia nitrogen removal. Removal of ammonia
nitrogen is very good, with a mean effluent of 0.13 mg/L and a high C0V of 163 percent.
Western Branch WWTP, WSSC
Monthly Average Frequency Curves for Ammonia-Nitrogen
100

O)
E
c
CD
O)
O
L_
4->
2
'c
o
E
E
<
Mean = 0.13 mg/L
Std. Dev. = 0.22 mg/L
C.O.V. = 163%
0.01
0.001
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.999.95
Percent Less Than or Equal To
o Combined Raw Influent n HRAS Influent	x HRAS Effluent
o NAS Effluent	A DNAS Effluent	x Final Effluent
Figure 4. Monthly average frequency curves for ammonia nitrogen.
8 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Figure 5 presents reliability data for the removal of total nitrogen (TN). The plant gives
outstanding total nitrogen removal, with effluent TN of 1.63 mg/L and a COV of 36 percent.
100
Western Branch WWTP, WSSC
Monthly Average Frequency Curves for Total Nitrogen
§ '»
-o	8 9 • 8
10
u>
E
u>
o
AAA
A A A
- Mean = 1.63 mg/L
: Std. Dev. = 0.59 mg/L
: C.O.V. = 36%
0.1
0.05 0.1 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
o Combined Raw Influent ~ HRAS Influent	o NAS Effluent
A DNAS Effluent	x Final Effluent
Figure 5. Monthly average frequency curves for TN.
Reliability Factors
This facility is unique in three ways: (1) three separate activated-sludge systems operated in
series with dedicated clarifiers and RAS lines for biochemical oxygen demand (BOD)
removal, nitrification, and denitrification with methanol feed; (2) chemical phosphorus
removal; and (3) tertiary filtration. The facility also is unusual in that it has no primary
settling. All sludge generated is biological and chemical sludge combined, which is
incinerated after thickening by DAF and dewatering by centrifugation.
The results were excellent. The plant achieved a TN concentration of 1.63 mg/L with a COV
of 36 percent and a TP concentration of 0.43 mg/L with a COV of 62 percent. Many factors
accounted for this performance, and the key factors are presented below.
Wastewater characteristics: Because this facility uses a separate stage for denitrification, the
use of an external carbon source (methanol) is a requirement. In addition, phosphorus
removal is designed to be achieved with alum feed. The typical ratio for characterizing the
adequacy of BOD is not applicable because the plant does not rely on internal carbon sources
for biological removal of nitrogen or phosphorus.
Appendix A
Western Branch, MD • Wastewater Treatment Plant - 9

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The plant added a new process for nitrogen removal as the third step of the treatment train
and called it DeNitrifying Activated Sludge, or DNAS, with separate clarifiers. The existing
plant had a two-stage activated-sludge process before the current expansion: high-rate
activated-sludge, or HRAS, for BOD removal and nitrifying activated sludge, or NAS. Both
had separate aeration basins and dedicated clarifiers. The first two stages provided effluent
with good BOD removal and full nitrification. The average concentrations in NAS effluent
were 16.5 mg/L in nitrate-nitrogen with a COV of 12 percent and 1 mg/L in ammonia
nitrogen. Note that nitrate-nitrogen is high because denitrification was not designed for. The
third step, DNAS, proved effective in nitrogen removal. The control strategy included daily
testing of key parameters, as well as adjustment of the dosage on an as needed basis. No
online sensors are used in the DNAS basin.
A comparison of design vs. actual parameters follows:
Parameters
Design
Actual
HRAS HRT (hours)
2.68
3.0-3.8
HRAS Sludge age (days)

0.9-7.3
NAS HRT (hours)
5.51
6.7-7.9
NAS sludge age (days)

21-84
DNAS HRT (hours)
2.68
3.0-3.8
DNAS sludge age (days)
5-10
5-58
Another key feature of the plant is chemical phosphorus removal. Alum is added to the
stripper/reaeration channel of the DNAS process at an average concentration of 10 mg/L and
has proven effective. The tertiary filter is another key in providing reliability in nitrogen and
phosphorus removal.
Methanol is added to the DNAS tanks at an average rate of 1,165 gpd to provide sufficient
carbon for denitrification to occur. The methanol dosage is approximately 2.5 lb per pound of
nitrate entering the DNAS tanks. Nitrate is checked by chemical testing three times a day to
allow methanol dosage adjustment. The sludge generated is settled out with the rest of the
DNAS sludge, mixed with the HRAS and NAS sludge, and thickened in the DAF units.
The facility employs online monitoring of dissolved oxygen (DO) in the HRAS and NAS
basins, with one DO probe per reactor cell. The probe signals are used to control air valves
and thus control the air feed to the basins. The plant also has online suspended solids probes
in the aeration basins, which are used for monitoring, as well as sludge blanket monitors in
the DNAS clarifiers.
Another key feature of the plant is that there is no primary settling. All sludge comes from
the three biological systems, and the sludge is thickened aerobically at DAFs before
dewatering and incineration. The recycle loads of nitrogen and phosphorus, therefore, remain
low because there is no anaerobic digestion.
10 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Wet-weather operation. Normal operating procedures are followed. No off-line storage is
available.
Costs
Capital Costs
The plant was constructed in three phases. Phase 1, carried out in the early 1970s, included a
dual sludge system for achieving BOD removal and nitrification, as well as filters that
accomplish both nitrogen and phosphorus removal. The Phase 1 construction was sized for
15 MGD. Phase 2, completed in the late 1970s, consisted of additional tanks and filters to
bring the dual sludge system to 30 MGD. Chemical addition for phosphorus removal was
installed temporarily in the late 1980s, but not as a capital expense. Phase 3, carried out in the
early 1990s, added a third sludge system for denitrification, along with making the alum
addition system for phosphorus removal permanent. Table 5 shows the costs of those
improvements, along with capital cost updates based on the Engineering News-Record
Capital Cost Index (ENR CCI). The ENR CCI, which is compiled by McGraw-Hill, provides
a means of updating historical costs to account for inflation, thereby allowing comparison of
costs on an equal basis. From a Web site provided by the U.S. Department of Agriculture
(USDA 2007), the ENR index for 1973 was 1,895; for 1976, 2,401; for 1991, 4,835; and for
May 2007, 7,942.
Table 5. Plant improvement costs

Year
Original
cost
2007 cost
%P
%N
%
other
Phosphorus
cost
Nitrogen
cost
Phase 1
1973
$15,000,000
$62,865,435
0%
20%
80%
$0
$12,573,087
Phase 2
1976
$7,500,000
$24,808,413
0%
30%
70%
$0
$7,442,524
Phase 3
1991
$30,000,000
$49,278,180
5%
60%
35%
$2,463,909
$29,566,908
Total


$136,952,028



$2,463,909
$49,582,519
The table also shows the percentage of capital cost for each phase that was attributed to
phosphorus or nitrogen removal; the rest of the capital cost was attributed to other treatment,
particularly BOD and TSS removal. Because the plant does not do biological phosphorus
removal, it was assumed that only 5 percent of the Phrase 1,2, and 3 costs could be attributed
to phosphorus removal, which is a portion of the costs for filtration, plus the alum addition
system. Nitrification was installed during both Phase 1 and Phase 2, but Phase 1 included
additional activities not included in Phase 2, such as incineration and disinfection systems.
Thus, 15 percent of the Phase 1 cost was attributed to nitrogen removal, whereas 30 percent
of the Phase 2 costs were attributed to nitrogen removal. Since a large part of Phase 3 was the
denitrification unit, it was assumed that 60 percent of the Phase 3 costs were for nitrogen
removal.
Appendix A
Western Branch, MD • Wastewater Treatment Plant 11

-------
Nutrient Removal Technology Assessment Case Study
September 2008
The above analysis resulted in a total of $6,850,000 in capital attributed to phosphorus
removal and $41,500,000 attributed to nitrogen removal, in 2007 dollars. The annualized
capital charge for phosphorus removal (20 years at 6 percent) was $598,000. The annualized
capital charge for nitrogen removal was $3,620,000.
The total capital attributed to nutrient removal, in 2007 dollars, was $48.4 million. For the
30-MGD facility, this means the capital expenditure per gallon of treatment capacity was
$1.73.
Operation and Maintenance Costs
The plant uses chemical phosphorus removal and biological nitrogen removal, with extensive
use of alum for the former and methanol as a supplemental carbon source for the latter. This
means that the cost for phosphorus removal is essentially all chemical and for the disposal of
the resulting sludge, with a small amount of electricity; the cost for nitrogen removal is
electrical (for the aeration basins), chemical for the methanol, and for the disposal of the
extra sludge resulting from methanol addition. A summary of the electrical calculations is
provided in the Attachment. When the average electrical rate of $0.10/kWh (including
demand charges) was applied, the cost of electricity for nitrogen removal was $229,000.
The average amount of alum applied for phosphorus removal over the period was
14.4 gallons per MG of flow, or 502 tons; at a cost of $212.25/ton, the cost of alum was
$106,000. This cost was entirely attributed to phosphorus removal.
Methanol is applied at the DNAS to promote nitrate removal. The total amount of methanol
added over the study period was 425,000 gallons. At an average cost of $1.00/gallon, the
chemical cost for nitrogen removal was $425,000.
The alum added (9.5 mg/L as alum, or 0.86 mg/L as aluminum) was assumed to all convert
to aluminum hydroxide sludge; at the average flow of 19.2 MGD, this was 400 lb of
aluminum sludge per day, or 73 dry tons/year. The plant's average cost of disposal,
considering trucking and incineration, was $440/diy ton. This made the cost of sludge for
phosphorus removal $32,400.
The 425,000 gal/yr (2.8 million lb/yr) of methanol has a chemical oxygen demand (COD) of
1.5 lb COD/lb of methanol, or 4.2 million lb COD/yr. The typical yield of volatile suspended
solids (VSS) on methanol is 0.4 lb VSS/lb of COD, giving 1.7 million lb sludge/yr, or 839
tons sludge/yr from methanol addition. At a cost of $440/dry ton, this made the cost of sludge
for nitrogen removal $372,000.
12 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
Unit Costs for Nitrogen and Phosphorus Removal
During the evaluation period, the plant removed 213,000 lb of phosphorus. With the results
above, the unit O&M cost for phosphorus removal is $0.78, while the unit capital cost is
$1.01/lb of phosphorus removed.
During the evaluation period, the plant removed 1.32 million lb of total nitrogen. With the
results above, the unit O&M cost for nitrogen removal is $0.99, while the capital cost is
$3.27/lb of TN removed.
Life-cycle Costs for Nitrogen and Phosphorus Removal
The life-cycle costs are the sum of the unit capital and unit O&M costs. Thus, the life-cycle
cost for phosphorus removal is $1.78/lb of phosphorus removed, and the life-cycle cost for
TN removal is $4.27/lb of TN removed.
Assessment of magnitude of costs: The capital cost of $1.73 per gpd capacity is about average
for the case studies. The capital for phosphorus removal is low, whereas the capital for
nitrogen removal is high because of the use of the separate third stage for nitrogen removal.
The O&M costs for phosphorus removal are low, whereas those for nitrogen removal are
high because of the large amounts of chemical use with associated sludge generation.
Discussion
Reliability factors. This facility has a unique feature—three activated-sludge systems for
biological treatment for nitrogen removal and chemical addition for phosphorus removal,
followed by tertiary filtration. The reliability was excellent: the average concentrations were
1.63 mg/L in TN with a COV of 36 percent and 0.43 mg/L in TP with a COV of 62 percent.
For nitrogen removal, the third process, DNAS, relies on the external carbon source (in this
case methanol), and the dosage was reasonable at 2.5 lb per pound of nitrate-nitrogen
applied. The high level of nitrate in the NAS was noted. Chemical phosphorus removal was
consistent in meeting the current limits.
Many factors have contributed to this reliable performance. The first key factor is the three
separate processes in series—BOD and ammonia removal in the first two activated-sludge
systems, followed by a separate activated-sludge system to denitrify with an independent
supply of carbon. The fluctuations in wastewater or operating parameters and thus
performance in one stage possibly can be balanced by the succeeding processes to achieve
overall reliability in the plant's performance. An increased reliability for nitrogen removal
was achieved through the use of an external carbon source; thus, the performance was not
dependent on favorable wastewater characteristics. In addition, operating all four trains
Appendix A
Western Branch, MD • Wastewater Treatment Plant -13

-------
Nutrient Removal Technology Assessment Case Study
September 2008
(30-MGD capacity) while having a 19.3-MGD average influent flow contributed to excellent
performance.
Note, however, that this unique system required a significant amount of land for aeration and
clarification tanks; separate sludge return systems; and associated control equipment to
operate, maintain, and monitor.
The cost for capital was low at $1.73 per gpd capacity as an upgrade. The O&M costs for
phosphorus and nitrogen removal were $0.78/lb and $0.99/lb, respectively. The life-cycle
cost for nutrient removal was $1.78/lb for phosphorus and $.4.27/lb for nitrogen.
Summary
The Western Branch WWTP is an advanced facility with a unique, multiple-system
activated-sludge system followed by tertiary filtration. The facility was expanded and
upgraded to meet new requirements with the maximum use of existing technologies. The
latest upgrade included a third activated-sludge system for nitrogen removal, or DNAS.
The nitrogen removal was efficient and reliable at the mean concentration of 1.63 mg/L in
TN with a COV of 36 percent. The phosphorus removal was also efficient and reliable at the
mean concentration of 0.43 mg/L with a COV of 62 percent.
Many factors have contributed to this reliable performance. The first key factor is the three
separate processes operating in series—BOD and ammonia removal in the first two
activated-sludge systems, followed by a separate activated-sludge system to denitrify with an
independent supply of carbon. The fluctuations in wastewater and/or operating parameters
and thus performance in one stage were balanced by the succeeding processes to ensure the
overall reliability of the plant's performance. Performance was also enhanced by operating
all four treatment trains (30-MGD capacity) while the influent flow was only 19.3 MGD.
Phosphorus removal was achieved by adding chemicals to the DNAS.
Capital costs for the upgrade were low at $1.73 per gpd capacity. The O&M costs for
phosphorus and nitrogen removal were $0.78/lb and $0.99/lb, respectively, and the life-cycle
cost for nutrient removal was $1.78/lb for phosphorus and $.4.27/lb for nitrogen.
Key contributing factors for reliability include the inclusion of a separate third stage for
denitrification. The separate stage with substantial methanol feed is able to provide a high
degree of denitrification. That extra volume also provides further dampening of wastewater
fluctuations, resulting in a very consistent effluent quality.
14 - Western Branch, MD • Wastewater Treatment Plant
Appendix A

-------
September 2008
Nutrient Removal Technology Assessment Case Study
A separate stage for denitrification not only increases capital costs for the equipment but also
necessitates the use of significant amounts of methanol to effect the needed denitrification.
Phosphorus removal costs are reasonable with the use of alum for precipitation.
Acknowledgments
The authors acknowledge with gratitude the significant assistance and guidance provided by
Robert Buglass, principal scientist for WSSC, and Nick Shirodkar, Plant Engineering
supervisor at the Western Branch facility. This report would not have been possible without
their prompt response with well-deserved pride in their facility and operation. EPA
acknowledges the WSSC for its participation in this case study.
References and Bibliography
TKW Online. 2007. http://www.tkwonline.com/enviromental.html. Accessed July 15, 2007.
USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates. Natural
Resources Conservation Service.
http://www.economics.nrcs.usda.gov/cost/priceindexes/index.html.
Voorhees, J.R., W.G. Mendez, and E.S. Savage. 1987. Produce an AWT Effluent for Florida
Waters, Environmental Engineering Proceedings. (EE Div) ASCE, Orlando, Florida,
July 1987.
WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers)
1998. Design of Municipal Wastewater Treatment Plants, Manual of Practice No.8,
Figure 11.7, Net sludge production versus solids retention time.
Appendix A
Western Branch. MD • Wastewater Treatment Plant -15

-------
®5
I
13
§•
i
I
s3
&
§
s2
13
Attachment: Electrical Costs


kW

kWh
kWh
%P
%N
P kWh
N kWh

HP
Number
Power draw
hours/
day
draw/day
draw/year




HRAS/NAS blowers
1,500
1
1,119
24
26,856
9,802,440
0%
50%
0
4901220
Raw pumps
250
2
373
24
8,952
3,267,480
5%
20%
163,374
653496
Denite mixers
20
16
238.72
24
5,729.28
2,091,187.2
0%
70%
0
1463831.04
ID fans
75
1
55.95
24
1,342.8
490,122
0%
10%
0
49012.2
Final RAS pumps
100
4
298.4
24
7,161.6
2,613,984
0%
0%
0
0
Stripping channel
blowers
200
2
298.4
24
7,161.6
2,613,984
0%
20%
0
522796.8
Centrifuge
300
1
223.8
24
5,371.2
1,960,488
5%
5%
98,024.4
98024.4
Air lift pump blowers
60
6
268.56
24
6,445.44
2,352,585.6
0%
50%
0
1176292.8
Total draw





25,192,270.8


261,398.4
8864673.24
t
3
I

-------
September 2008
Municipal Nutrient Removal Technologies Reference Document
Appendix B: Reliability, Variability, and Coefficient of
Variation
When operating a treatment facility, the objective is to regularly produce an effluent that
meets the discharge standards specified in the permit. Such regularity can be difficult to
obtain because the measured effluent concentration of all constituents will vary. Some
variations will be due to process upsets caused by weather conditions, accidents, and
equipment failure. Others will be due to natural variations in influent conditions, as well as
natural variability in laboratory measurements, sampling, and flow. In selecting a process,
one possible criterion is finding one that has a higher probability of regularly producing a
high-quality effluent and thereby keeps the facility well within permit compliance. The
reliability reflects the overall performance of the facility in regularly meeting the treatment
objectives, exclusive of extraordinary events like process upsets. Evaluating reliability or
variability allows for screening of technologies by an assessment of how well a system might
perform daily.
The variability of a data set can be represented by the coefficient of variation (COV). The
COV is one standard deviation divided by the mean, expressed as a percentage.
Figure B-l illustrates the meaning and determination of COV. By definition, a normally
distributed population of data, such as measurements of total phosphorus in an effluent,
results in a straight line when plotted on probability paper, as shown in Figure B-l. The mean
of the data set falls at the 50 percent position, while one standard deviation from the mean
can be found at plus or minus 34 percent, or at the 84 percent and 16 percent positions
(McBean and Rovers 1998). This means that if the data are normally distributed, 68 percent
of the results will have values within one standard deviation above or below the mean value.
For the given period of evaluation, the slope of the line represents the reliability, or COV
(i.e., the steeper the slope, the less reliable the performance; conversely, the flatter the slope,
the higher the reliability). For example, Figure B-l, which shows effluent phosphorus for the
Noman M. Cole Pollution Control Plant in Fairfax County, Virginia, indicates that the COV
is 21 percent for the monthly averages for total phosphorus.
Note that the calculated reliability is a function of the data-averaging period. For the same
year, COVs can be determined for the monthly average concentrations as well as the weekly
average concentrations. In the example above, the COV of the Fairfax County facility is
higher for the weekly averages, while the mean value is practically the same—29 percent on
the weekly average, as compared to 21 percent on the monthly average. The same can be true
with the COVs on the basis of a daily maximum at 45 percent.
For the purposes of this document, COVs are primarily based on monthly averages for
consistent interpretation and easy comparison. When necessary because of the permit
Appendix B: Reliability and Coefficient of Variation
B-l

-------
Municipal Nutrient Removal Technologies Reference Document
September 2008
requirements, however, COVs with reference to the weekly averages are added. The decision
to select a given averaging period is important and should be based on the permit conditions.
1
Daily-
Mean = 0.086 mg/L
Std. Dev. = 0.039 mg/L
COV = 45%
Weekly-
Mean = 0.086 mg/L
Std. Dev. = 0.0248 mg/L
COV = 29%
Monthly-
Mean = 0.086 mg/L
Std. Dev. = 0.0179 mg/L
COV = 21%
0.1
0.01
0.05 0.1
0.5 1
2
5
10
20 30 40 50 60 70 80 86 92.3 95 98.1 99
99.7 99.9 99.95
Percent Less Than or Equal To
Figure B-1. Noman M. Cole Pollution Control Plant, Fairfax County, Virginia—daily frequency
curves for total phosphorus.
The overall reliability of a facility increases with the increase in the number of processes
installed in series, as shown in Figure B-2. For example, the reliability of a tertiary treatment
facility would be higher than that of a secondary treatment facility. The designer of a facility
can select multiple processes in series to increase the reliability of the entire treatment
system. For example, the following data from the Noman Cole facility show total phosphorus
concentration and COVs at each step of the treatment system:
•	Secondary effluent: 0.74 mg/L at COV of 50 percent
•	Tertiary clarifier effluent: 0.36 mg/L at COV of 33 percent
•	Tertiary filter effluent: 0.09 mg/L at COV of 29 percent
The decision to add a particular level of reliability depends on the proposed permit limit and
the degree of safety to be incorporated.
B-2
Appendix B: Reliability and Coefficient of Variation

-------
September 2008
Municipal Nutrient Removal Technologies Reference Document
10
_ Primary Effluent
Mean = 4.88 mg/L
Std. Dev. = 0.55 mg/L
COV=11%
1
Tertiary Effluent
Mean = 0.36 mg/L
Std. Dev. = 0.118 mg/L
COV = 33%
—	Secondary Effluent
-	Mean = 0.74 mg/L
Std. Dev. = 0.37 mg/L
~ COV = 50%
0.1
Final Effluent
Mean = 0.09 mg/L
Std. Dev. = 0.025 mg/L
COV = 29%
0.01
0.05 0.1
0.5 1
2
5
10
20 30 40 50 60 70 80
90
95 98 99 99.5 99.9 99.95
Percent Less Than or Equal To
~ Raw Influent ¦ Primary Effluent A Secondary Effluent X Tertiary Effluent ~ Final Effluent
Figure B-2. Noman M. Cole Pollution Control Plant, Fairfax County, Virginia—weekly average
frequency curves for total phosphorus.
Reference
McBean, E.A. and F.A. Rovers 1998. Statistical Procedures for Analysis of Environmental
Monitoring Data and Risk Assessment. Prentice Hall PTR.
Appendix B: Reliability and Coefficient of Variation	B-3

-------