NC0026441_Nutrient Remove Optimization Plan_20091005

pp, .. : 1644 1
Hobbs, Upchurch
& Associates, P.A.
Consulting Engineers
TRANSMITTAL P.O. Box 1737
300 S.W. Broad Street
Southern Pines, North Carolina 28387
[phone] FAX[phone]
TO: Central Files
NCDENR/Division of Water Quality/Water Quality Section
1617 Mail Service Center
Raleigh,NC 2 7699-1 61 7
FROM: Eric Wagner
Hobbs, Upchurch &Associates,P.A.
DATE: October 5,2009
RE: Nutrient Removal Optimization Plan
for the Siler City Wastewater Treatment Plant
MESSAGE: Enclosed please find three (3) revised copies of the project referenced above.
Please let me know if you have any questions.
cc: Gil Vinzani—NCDENR
Danny Smith -NCDENR
Joel Brower—Town of Siler City
Terry Green—Town of Siler City
Chris McCorquodale—Town of Siler City
RECEIVED
OCT - E 2^^9
DENR - WATER QUALITY
POINT SOURCE BRANCH

NUTRIENT REMOVAL
OPTIMIZATION PLAN
FOR
THE SILER CITY
WASTEWATER TREATMENT PLANT
September 3o, 2009
SUBMITTED BY:
Siler City, NC
Town Manager: Joel Brower
311 North Second Avenue
Siler City, NC 27344
P: [phone] F: [phone]
Prepared By:
Eric Wagner, P.E.
Barry King, P.E.
Hobbs, Upchurch &Associates, P.A.
Consulting Engineers
30o SW Broad Street
Southern Pines, NC 28388
T: 910-692-5616; F: 910-692-4795

Nutrient Removal Optimization Plan September 2009
I. Introduction
The Town of Siler City owns and operates a 4.0 million gallon per day (MGD) wastewater
treatment plant (WWTP) located east of State Highway 421 and south of State Highway 64. The
plant operates under NPDES permit #NC0026441 effective from October 1, 2008 until October
31, 2011. The purpose of this Nutrient Removal Optimization Plan is to satisfy requirements
specified by the current NPDES permit. Item A(3) within the permit requires that the Siler City
WWTP develop this plan in an effort to maximize the current treatment capabilities of the plant
as it relates to nutrient removal. Concern regarding nutrient loading to Love's Creek and the
Rocky River are the basis for the optimization plan.
In accordance with the permit requirements, the optimization plan for the WWTP will provide
the following information:
1. An evaluation of the sources of nitrogen and phosphorus received by the WWTP.
2. An analysis of the current WWTP removal rates for nitrogen and phosphorous.
3. A discussion of ways the WWTP operation may be optimized using the existing
equipment in order to further increase nutrient removal.
Influent sources for the WWTP were analyzed using water and sewer billing data, GIS customer
data and Industrial pretreatment data. Known sample results and typical wastewater
characterization values were used to provide a mass balance of the WWTP and to verify source
constituents. Current WWTP removal rates were calculated by sample data used for the mass
balance, Daily Monitoring Report (DMR) records from April 2008 through June 2009 and
independent water sampling and analysis. The measured water quality concentrations also
provided clues to where and how the treatment process could be altered to improve its
nutrient removal capabilities within the existing plant. Recommendations for process
optimization are provided based on capabilities of existing plant processes and equipment and
include further monitoring of process indicators so that operational modifications can be
measured.
Although the optimization plan does not consider capital improvements at the plant, data from
the implementation of the plan may be utilized to assist the Town in meeting future nutrient
reduction goals and providing energy efficient operations as well.
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Nutrient Removal Optimization Plan September 2009
II. Nutrient Sources to the Siler City WWTP
The Siler City WWTP receives wastewater from residential, commercial, industrial and
institutional customers within the Town's jurisdiction via approximately 50 miles of sanitary
sewer lines, 7 pump stations and associated force mains. Figure 1 displays a map of the existing
Siler City wastewater collection system. In order to identify the influent sources of nutrients,
the Town needed to first identify flow rates from its customer base from its billing records,
water treatment plant flow data and an analysis of unbilled accounts. Types of wastewater
contributors described by the Town billing are residential, commercial, and industrial.
Additional customers identified via GIS records and Town data include institutional (schools,
hospitals) customers. Residential and Commercial sewer connections to the collection system
are combined into one accounting group with 3301 customers in June 2009, with 11 industrial
customers, plus 199 non-billable connections. Additional flow to the plant that is not indicated
within the billing records includes sludge haulers and additional non-billed Town uses such as
process water at the Town pool and process water from the Town's Water Treatment Plant.
The second task is to identify estimated flow rates from unaccounted sources such as
infiltration and inflow (I/I) within the system. This was done by comparing plant flow to billing
records, non-billable flow and analyzing GIS data to confirm customer numbers and type.
Once the sources of flow and identification of flow rates have been established for each
customer type, the nutrient concentrations and associated influent loading to the plant can be
established. This was accomplished by assigning typical concentrations to unsampled flow
streams such as residential, commercial and institutional sources and assigning known sample
data from the industrial users who are required to sample prior to discharge to the plant.
Once the data for the influent flow rates and characteristics was assembled and summarized, a
mass balance was performed with respect to the plant's influent flow and characteristics as a
method of calibrating and verifying unknowns utilizing typical design values.
The following discussion summarizes the results of the billing records analysis, the influent
wastewater characterization and nutrient loading pertaining to residential, commercial,
institutional and industrial waste streams as well as the waste stream as a whole. The
information will be utilized within this nutrient optimization plan to identify influent waste
streams impacting the plant's performance and influent operational controls that can be
implemented to improve the WWTP's nutrient removal rates.
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Nutrient Removal Optimization Plan September 2009
Water and Sewer Billings
Sewer billing is partitioned into 3 categories, Residential/Commercial, Industrial/Large (some
multiple meters), and non-billable. Residential and Commercial customers are grouped
together and all larger users are billed as industrial. City offices and facilities are listed as non-
billable, however additional facilities contribute to the wastewater flow, including the Town
pool, the Water Treatment Plant and other maintenance activities such as line flushing. Water
billing and treated water pumped are also included within the discussion to further calibrate
wastewater flow to the plant with respect to non-billable flow not associated with an account.
Influent Wastewater Characteristics
Typical values of pollutants from residential sewage are illustrated in Table 1 below (Syed
Qasim, Wastewater Treatment Plants: Planning, Design and Operation, 2006). These typical
water quality values were used as guides for supplying numbers to wastewater influent streams
when component concentrations were unknown. The values would be applicable to
residential, commercial, and institutional flows but industrial compositions may vary more
widely. Industrial concentrations were applied through actual sample data as required by the
Town's Pretreatment program.
Table 1 Typical Chemical Quality of Raw Domestic Wastewater
TYPICAL CHEMICAL QUALITY OF RAW DOMESTIC WASTEWATER
DESCRIPTION Concentration mg/L
TOTAL SOLIDS 730
Settleable 10
Suspended (TSS) 230
Fixed (mineral) 55
Volatile 175
Dissolved 500
Fixed (mineral) 300
Volatile 200
BIOLOGICAL OXYGEN DEMAND 5 210
CHEMICAL OXYGEN DEMAND 400
TOTAL ORGANIC CARBON 150
TOTAL NITROGEN 40
Organic 20
Ammonia 20
NO2, NO3 0
TOTAL PHOSPHORUS 6
Organic 2
Inorganic 4
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Nutrient Removal Optimization Plan September 2009
TYPICAL CHEMICAL QUALITY OF RAW DOMESTIC WASTEWATER
DESCRIPTION Concentration mg/L
pH 7.0 1
ALKALINITY 100
HARDNESS 240
CHLORIDE 50
OILS &GREASE 100
Influent Volumes and Nutrient Flows
The Town of Siler City measures the flow rate and water quality parameters at the WWTP as
required by the NPDES permit and reports those values in their DMR records. Merging the
average values of constituent concentrations reported with the billable and non-billable record
flow rates resulted in approximated mass contributions for each category. Not unexpectedly
the volume of water entering the metering weir was more than the sum of the billable
connections.
Known influent nutrient sources within the collection system included two industrial locations
with recorded flow rates and concentrations, and flow rates and concentration analyses from
pumping haulers who discharge to the plant. The remaining average mass of nutrients
measured entering the plant was calibrated using well documented typical concentrations and
calibrated based on a mass balance of known and typical concentrations compared to influent
sampling data.
In the following tables presenting mass nutrient loading for various influent sources, measured
values are shown in BOLD typeface while the remaining values were calculated from material
balance, typical values, and billing information.
Table 2 lists the daily average flow from residential and commercial sources with the calculated
wastewater constituent values.
Table 2 Flow and Nutrients Residential and Commercial Connections
FLOW, GPD 569,337 MASS LOADING, LBS/DAY
CBOD, MG/L 229.0 1,087.8
TN, MG/L 18.4 87.3
TKN, MG/L 18.1 86.0
NO2/NO3, MG/L 0.3 1.4
TP, MG/L 4.5 21.57
TSS, MG/L 100.9 479.6
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Nutrient Removal Optimization Plan September 2009
Table 3 lists the daily average flow for institutions such as schools and hospitals as estimated by
the utilities director and GIS information.
Table 3 Flow and Nutrients Institutional Connections
FLOW, GPD 19,068 MASS LOADING, LBS/DAY
CBOD, MG/L 229.0 36.4
TN, MG/L 18.4 2.9
TKN, MG/L 18.1 2.9
NO2/NO3, MG/L 0.3 0.1
TP, MG/L 4.5 0.7
•
TSS, MG/L 100.9 16.1
Table 4 Flow and Nutrients Industrial Connections to Siler City WWTP lists the industrial
connections to the Siler City WWTP. Of the 11 industrial connections listed in the Utility Bill
Analysis Report, two are required to pre-treat, measure, and record their discharge volume and
concentration. It should be noted that significant reductions in plant flow and associated waste
loading have been realized in the past few years. Three industrial users who were previously
required to sample have closed down, Pilgrim Pride in May of 2008, Mastercraft textiles in
March of 2008 and Glendale textiles (Acme McCrary). The combined permitted flow from
these facilities was just over 1,000,000 GPD. The resulting flow reduction to the plant is
indicated in Figure 2 in Section III of this report.
Table 4 Flow and Nutrients Industrial Connections to Siler City WWTP
TOWNSEND
FLOW, GPD 525,000 MASS LOADING, LBS/DAY
CBOD, MG/L 114.9 503.1
TN, MG/L 105.0 459.7
TKN, MG/L 105.0 459.7
NO2/NO3, MG/L 0.2 0.9
TP, MG/L 15.8 69.2
TSS, MG/L 79.0 345.9
BR00KW00D
FLOW, GPD 12,000 MASS LOADING, LBS/DAY
CBOD, MG/L 80.1 8.0
TN, MG/L 34.2 3.4
TKN, MG/L 30.0 3.0
NO2/NO3, MG/L 4.2 0.4
TP, MG/L 5.1 0.5
TSS, MG/L 242.3 1061.4
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Nutrient Removal Optimization Plan September 2009
TOTAL OTHER INDUSTRIAL
FLOW, GPD 106,789 MASS LOADING, LBS/DAY
CBOD, MG/L 229.0 204.0
TN, MG/L 18.4 16.4
TKN, MG/L 18.1 16.1
NO2/NO3, MG/L 0.3 0.3
TP, MG/L 4.5 2.5
TSS, MG/L 100.9 90.0
The Townsend and Brookwood Plants are currently permitted for a flow of 1.0 MGD and 0.035
MGD respectively. They are currently operating at approximately 52% capacity, which is
indicative of the current economic downturn. It is anticipated that this flow will increase as the
economy improves.
In addition to connected industrial users, the Siler City WWTP receives flow from Pumper truck
waste haulers. Table 5 below summarizes data from truck source sampling required in 2009.
Flow rates and loading for the pumping haulers will be included in the industrial category for
the overall summary of nutrient sources.
Table 5 Flow and Nutrients contributed by Pumping Haulers
FLOW, GPD 5,449.6 MASS LOADING, LBS/DAY
CBOD, MG/L 220.7 10.0
TN, MG/L 64.2 2.9
TKN, MG/L 63.8 2.9
NO2/NO3, MG/L 0.4 0.0
TP, MG/L 71.6 3.3
TSS, MG/L 9350.0 425.0
NH3, MG/L 441.8 20.1
Pumping haulers contribute 0.24% of the total volume of the plant, 0.39%of the Total Nitrogen,
and 2.37% of the Total Phosphorus. While the concentrations are high, the overall loading from
the haulers remains relatively low as compared to the entire influent wastewater.
The total industrial users average 649,239 gallons per day, adding an estimated 488 pounds per
day of Nitrogen and 76 pounds per day of Phosphate.
The difference between the measured volumes of the WWTP influent and the billed volumes
consist of non-billable flow and unaccountable flow. The non-billable flow can be made up of
unmetered sewer connections consisting of Town facilities such as the Town pool, process
water and the Water Treatment Plant itself. In order to identify this flow, water records and
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Nutrient Removal Optimization Plan September 2009
additional metered wastewater flow records were analyzed. Treated water from the Town's
WTP was compared to account information. In order to negate the effects of irrigation
differences, winter months were used so that a direct correlation from water usage to
wastewater discharges could be made to further compare treated water flow rates to
wastewater flow rates. Table 6 below presents the non-billable portion of flow to the WWTP,
which is considered consistent in water quality to residential, commercial and institutional uses.
Specific flow rates for the non-billable category include an average flow of 74,800 gpd from the
WTP and 11,000 gpd from the Town Pool (seasonally adjusted). Non-irrigation, non-billable flow
from the WTP consistently averaged 30% of the treated water volume. Therefore, 30% of the
WWTP influent is attributed to non-billable flow rates from Town facilities.
Table 6 Non-Billable Flows to the Siler City WWTP
FLOW, MGD 0.686 MASS LOADING, LBS/DAY
CBOD, MG/L 229.0 1310.8
TN, MG/L 18.4 105.2
TKN, MG/L 18.1 103.6
NO2/NO3, MG/L 0.3 1.7
TP, MG/L 4.5 26.0
TSS, MG/L 100.9 577.8
Unaccounted for flow rates to a WWTP consist of additional unmetered accounts and
infiltration and inflow (I/I) within the collection system. Typical rates for a new system may be
in the 10% range with older systems being as high as 30% or more. The average DMR recorded
flow into the WWTP is 2.287 MGD. The average flow recorded in the city billable records is
1.238 MGD plus the non-billable flow of 0.686 MGD totals 1.924 MGD. The difference between
the two is 0.363 MGD, or approximately 15% of the WWTP influent. This indicates that the
Town has done an exceptional job at minimizing I/I within the collection system, particularly
considering its age. The Town actively continues their I/I program to further maintain the
system. The calculated volume and mass loading from the unaccounted for flows are indicated
in Table 7.
Table 7 Unaccountable Flows to Siler City WWTP
FLOW, MGD 0.363 MASS LOADING, LBS/DAY
CBOD, MG/L 229.0 730.1
TN, MG/L 18.4 58.6
TKN, MG/L 18.1 57.7
NO2/NO3, MG/L 0.3 0.9
TP, MG/L 4.5 14.5
TSS, MG/L 100.9 321.8
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Nutrient Removal Optimization Plan September 2009
Measured Influent Water Quality Values
Historically water samples were obtained and reported from the incoming influent stream. The
samples are analyzed for pH, Temperature, BODS, and Total Suspended Solids. No information
describing the Nitrogen or Phosphorus concentrations are reported in the DMR for the
incoming waste stream. However, as a requirement by the renewed NPDES permit, the plant
began measuring monthly samples of Total Nitrogen, TKN, and Nitrates in the incoming flow
which are displayed in Table 8 Influent Nutrient Measurements.
Table 8 Influent Nutrient Measurements
DATE TOTAL N, MG/L TKN, MG/L NO2/NO3, MG/L
DEC 2008 72.5 72.4 0.1
JAN 2009 28.1 27.7 0.4
FEB 2009 43.0 42.6 0.4
MAR 2009 10.4 10.2 0.3
APR 2009 22.6 22.6 0
MAY 2009 60.6 60.6 0
The new nitrogen measurements along with the original influent water quality measurements
establish the mass flow of water and nutrients, displayed below. In Table 9 the average
measured values for Influent flow at the metering weir and the wastewater constituent
concentrations are compiled to calculate the flow in MGD and waste stream constituents in
pounds per day (lbs/d).
Table 9 Influent from Collection System,Volume and Quality
FLOW, MGD 2.287 MASS LOADING, LBS/DAY
NH3, MG/L 31.57 602.4
TSS, MG/L 173.03 3,301.9
CBOD, MG/L 202.00 3,854.7
TN, MG/L 38.50 734.7
TKN, MG/L 38.23 729.4
NO2/NO3, MG/L 0.29 5.5
TP, MG/L 7.20 137.4
Table 10 shows the mass loading from a typical WWTP as described in treatment plant design
texts and applied to the influent volume measured entering the plant from all sources. The
differences between the measured and typical influent concentrations are shown in Table 11.
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Nutrient Removal Optimization Plan September 2009
Table 10 Mass Flow under Typical Concentrations (Text Book Average Values)
FLOW, MGD 2.287 MASS LOADING, LBS/DAY
NH3, MG/L 20.00 381.5
TSS, MG/L 230.00 4,386.9
BOD5, MG/L 210.00 4,005.5
TN, MG/L 40.00 762.9
TKN, MG/L 40.00 762.9
NO2/NO3, MG/L 0.00 0.0
TP, MG/L 6.00 114.4
Table 11 Comparison of Measured and Typical Influent Strengths
Component Typical Measured Difference %difference of Typical
NH3 20.00 32.57 12.57 62.9%
TSS 230.00 173.03 -56.97 -24.7%
BOD5 210.00 202.00 -8.00 -3.8%
TN 40.00 38.50 -1.50 -3.7%
TKN 40.00 38.23 -1.73 -4.3%
NO2/NO3 0.00 0.29 0.29 N/A
TP 6.00 7.20 1.20 20.0%
In Table 11 the measured values containing Nitrogen (TN, TKN) and suspended solids (TSS)
follow close to the typical values while TP is slightly higher as a result of industrial users.
However, the industrial users maintain their pretreatment requirements and the influent levels
of phosphorus have not affected plant results. Ammonia appears high but represents a form of
nitrogen that is transformable within the treatment process and does not appear to cause
excessive total nitrogen. Total Phosphorus appears to be the only component of the
wastewater influent stream which would possibly require extra effort to extract from the
effluent stream. The plant has been successful in doing so.
As a summary of the nutrient input sources for the Siler City WWTP, Table 12 presents the
wastewater constituent loading to the plant based on categorical sources. The information in
this table can then be used as a management tool for not only identifying nutrient sources but
also for implementing influent control strategies as needed, particularly under the Town's
Pretreatment Program. Maintaining this summary table on a regular basis will be part of the
recommendations for optimizing removal rates (presented further in Section IV) as a
management tool.
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Nutrient Removal Optimization Plan September 2009
Table 12 Siler City WWTP Nutrient Source Summary
Unbillable/
Parameter Res./Com. Institutional Industrial Total
Unaccounted
FLOW, MGD 0.569 0.019 _ 0.649 1.049 2.287
NO2/NO3, LBS/DAY 1.4 0.0 1.5 2.6 5.6
TKN, LBS/DAY 86.0 2.87 _ 482.1 158.5 729.4
TN, LBS/DAY 87.3 2.91 483.6 160.8 734.7
TP, LBS/DAY 21.6 0.72 75.4 39.8 137.4
CBOD5, LBS/DAY 1,087.9 36.3 _ 725.9 2004.6 3854.7
TSS, LBS/DAY 479.6 16.0 1922.7 883.6 3301.9
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Nutrient Removal Optimization Plan September 2009
III. Effluent Nutrient Characteristics /Removal Efficiencies
DMR reports for the Siler City WWTP were analyzed over a 16 month period to identify current
effluent parameters. The effluent parameters could then be used to determine the current
nutrient removal efficiency of the existing plant and identify ultimate effluent loading.
DMR reports for the Siler City WWTP discharge were complete for their NPDES permit which
did not require reporting oxidation products of ammonia but rather the ammonia itself. The
plant operators had been monitoring effluent concentrations of Nitrogen and were recently
required to track nitrogen in both the effluent and influent as part of their NPDES permit
renewal requirements.
Table 13 uses 16 months of average water quality concentrations to calculate the average daily
load in pounds per day of the listed compounds. The flow shown is 1) the incoming volume
from the collection system plus 2) the volume dumped by the pumping haulers averaged per
day, and 3) minus the land application volumes reportedly withdrawn by the disposal haulers.
The remaining volume must exit the process through the discharge.
Table 13 Average Effluent Volume and Water Quality Concentrations
FLOW, MGD 2.273 MASS LOADING, LBS/DAY
NH4, MG/L 0.52 9.9
TSS, MG/L 0.00 24.1
BOD5, MG/L 2.63 49.9
TN, MG/L 29.6 561.5
TKN, MG/L 0.22 4.2
NO2/NO3, MG/L 27.63 524.2
TP, MG/L 1.09 20.8
DO, MG/L 7.7300 146.6
The total phosphorus discharge concentration changes per season since Alum is added April 1
through Sept. 31 which results in a TP concentration of 0.292 mg/L, while during Oct. 1 through
March 31 no Alum is added and the average TP concentration is 3.18 mg/L. A winter permit
limit for phosphorus of 2.0 mg/I will take effect on January 1, 2010, at which time the Town will
add alum year round.
Figure 3 plots the concentrations of TN, TKN, and Nitrates in the Siler City effluent stream. The
plant has been trending towards lower values of Total Nitrogen from June 2008 to June of
2009, indicating that either the plant is removing more of the process nitrogen or there is less
nitrogen flowing into the plant. This does correlate to closing of industrial plants.
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Nutrient Removal Optimization Plan September 2009
SILER CITY WWTP FLOW MGD
7.000
• —4—FLOW MGD
6.000 -`
♦
♦ 1
5.000 -
•
•
4.000 •
I 1
o •
w
2 I I
I . it I 1
3.000 ,
il :i‘ '' • I
11 ill I1.
2.000 - A I II 1 . . __-- - --
;I I
1.000
0.000 r
February-08 June-08 September-08 December-08 March-09 July-09
DATE - -
The average influent flow over the 16 months ending in July 2009 _
Figure 2 Influent Flow to Siler City WWTP averaged 2.28 MGD. From the data there appeared to be a step
change in measured flow downward by about 1.0 MGD during
May of 2008

Nutrient Removal Optimization Plan September 2009
60 •
TKN SILER CITY EFFLUENT TOTAL NITROGEN,TKN, NITRATES
—♦—NITRATES
TOTAL NITROGEN
50
♦
40
A
♦ �-
A-
30 -
Ar—
kr—
at— Arlr—
Arr
10 Ir ♦
0
Feb-08 Jun-08 Sep-08 Dec-08 Mar-09 Jul-09
DATE
Figure 3 Plot of Siler City Effluent TKN, Nitrates,and TN over time.
The plot of Nitrogen concentrations in the effluent stream shows no remaining
TKN of ammonia, ammonium, or organic N being discharged. All of the nitrogen
exiting in the effluent is in a Nitrate form indicated by the nitrate and TN being
equal. Nitrification is occurring within the plant.
P : _ e I17

SILER CITY WWTP INFLUENT/EFFLUENT BOD5 mg/L
600
—•--INFLUENT BOD
—}—EFFLUENT BOD
500 •
♦
•
•
400
•
♦ ♦
•
300 4 ♦ t
♦ I 1; r• • • 1
• .
•
10
. Z
200 ♦ :ii1li 1 r 4;
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1.1
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1 • • I
1oai
j •
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•
--' - — F— — 1 - - —'4! - --‘ - ♦ - 1 — — r - _
Feb-08 Mar-08 Apr-08 May-08 Jun-08 Jul-08 Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09
Figure 4 Slier City Effluent vs. Influent BOD5 concentration The activated sludge process is being supplied adequate oxygen since virtually all of the
influent BOD5 is consumed.
P a ;-- ‘' 118

Nutrient Removal Optimization Plan September 2009
SILER CITY WWTP EFFLUENT TP mg/L
6
f EFFLUENTTP
5
■
4 ■ ■
■
■ •
■■
3
■
■
■
2 ■ ■ •
■
■
1
■
■ ■ ■
•
0
Feb-08 Mar-08 Apr-08 May-08 Jun-08 Jul-08 Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09
Figure 5 Siler City Effluent Total Phosphorus In Figure 5 Total Phosphorus concentration in the effluent flow is shown over a 1.5 year period cycling from
on P limits to off P limits and back again. The records show that the addition of Alum is effective in
sequestering dissolved P and removing it via the waste sludge stream.
1E I 19

Nutrient Removal Optimization Plan September 2009
Sludge Nutrient Characteristics
Table 14 Mass of Material Removed in Waste Sludge
MASS PER DAY IN SLUDGE From land application appliers the volume of sludge
removed from the Siler City WWTP is measured. To
VOL M3 51.53 M3 accurately assess the application rate of nutrients applied
TSS 1334.74 KG to agricultural land, samples are taken and analyzed of
TKN 353.01 KG the hauled material. Those concentrations were
P 195.24 KG multiplied by the volume removed and distributed by day
K 15.79 KG to approximate the waste sludge mass flow per day by
S 40.05 KG each waste component. The resulting masses analyzed
CA 143.38 KG are within reason with high counts for TVS and organic
MG 13.20 KG Nitrogen being expected from the slurry of cells.
NA 8.76 KG
FE 78.94 KG The measured mass of TKN in the waste sludge almost
AL 310.46 KG equals the TN in the total influent which would represent
MN 4.66 KG a 100% diversion of N to the sludge which from effluent
CU 1.84 KG measurements show 70% of the incoming N exiting in the
ZN 4.76 KG effluent, plus the P reported is twice as much as that in
NH4 20.24 KG the influent. Aluminum is measured as approximately
ORG N 332.83 KG twice that of the Al contributed by the Alum. The larger
NO3/NO2 4.87 KG Ca mass is only a fraction of the total 854 kg of Ca
introduced each day within the 1195 kg of lime.
CD 0.05 KG
CR 0.35 KG The hauler's sludge mass analysis confirms that almost all
NI 0.16 KG of the pollutants introduced to the process do actually
PB 0.17 KG exit within that stream as they should.
AS 0.10 KG
Discrepancies of sludge mass removal are likely the result
HG 0.05 KG
SE 0.09 KG of sampling time displacement from the other plant
operations and volume estimations by semi-monthly
PH 6.84 KG pump-outs but gives a good picture of the general plant
TVS 3259.87 KG
MO 0.10 KG operation.
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Nutrient Removal Optimization Plan September 2009
Siler City WWTP Nutrient Removal Efficiencies
With the volumetric and mass flows within the plant established, the mass of material that moves in any
direction can be calculated. The objective of the Siler City WWTP is to remove pollutants from the
influent stream and return the treated water to surface waters.
The overall efficiency of the plant at removing the wastewater components from the effluent stream is
expressed as the percent of the pollutant in the incoming stream removed from the wastewater and is
calculated as 1 — (effluent mass / influent mass). The effluent is the discharge stream falling into the
receiving waters of Loves Creek and is assumed to be the influent flow from the collection system, plus
the volume contributed by the haulers, minus the volume diverted to sludge storage for land application.
From the material balance of the plant the following removal rates were calculated.
Table 15 SILER CITY WWTP PLANT POLLUTANT REMOVAL RATES
Wastewater Influent Effluent Overall Percent Monthly
Component Mass Mass Removal 4/1-10/3 1 1 11/1-3/3 1
Kg/day Kg/day NPDES Measured
mg/L mg/L
FLOW 8676.664 8604.501 0.832% 4.00 MGD 2.28 MGD
NH3 282.396 4.532 98.395% 1.0 2.0 0.5 0.5
TSS 1690.615 10.928 99.354% 30 1.2
BOD5 1753.037 22.669 98.707% 5.0 10.0 2.52 2.79
TN 334.581 234.071 30.041% n/a 29.6
TKN 332.192 1.916 99.423% n/a 0.228
NO2/NO3 2.519 237.781 N/A n/a 27.634
TP 63.800 9.421 85.234% 0.5 2.0 0.292 1.79
The results of the percent removal calculations in Table 15 show that most all of the water is retained,
returning 99.991% of the treated water to the stream. Significant are the removal rates for TKN of 99.4
% of the influent ammonia and organic nitrogen compounds were removed or converted to NO3 which
increased in concentration by 94 times. After nitrification, the TN would be reduced by denitrification.
The current process operation removes 30% of the TN between the influent and the discharge.
There are three pathways for the Nitrogen to exit the WWTP. One is through the effluent as a dissolved
solid, a second is through the waste sludge as part of the digested cell mass, and third is through
denitrification and the liberation of nitrogen gas to the atmoshere.
Denitrification requires zones of low oxygen and the presence of a carbon source such as a volatile fatty
acid (VFA) like acetic acid in the adequate ratio of C:N for the carbon source. If the influent stream does
not carry enough BOD then an auxilary carbon source is required which is often methanol. Frequently
the benefit of denitrification is the recapture of a theoretical 5/8ths of the hardness consumed by nitrification.
The hardness release is often enough to stabilize pH and cease lime addition at a cost savings.
Page 21

•
' Nutrient Removal Optimization Plan September 2009
On average the WWTP works well in removing 85% of the influent Phosphorus stream. However if the
rates are compared seasonally, the summer rate averages discharge concentrations of 0.292 mg/L for a
removal efficiency of 96.1%. The winter discharge concentration averages 1.79 mg/L for a removal
efficiency of 75.6%. The difference in the two discharge concentrations is the result of the addition of
Alum to the sludge stream for the direct purpose of precipitating phosphorus, see Figure 5 for plotted
concentrations of effluent phosphorus.
Table 16 and Table 17 show the concentration and mass of pollutants in the discharge stream during
both summer and winter.
Table 16 Summer Percent Removal and Limits
WASTEWATER SUMMER SUMMER SUMMER MASS SUMMER % OF CON. % OF MASS
COMPONENT LIMIT MEASURED LIMIT/KG/D MASS KG/D LIMIT LIMIT
FLOW (MGD) 4.00 2.279 15141.65 8625.13 NA 56.96%
NH3 (MG/L) 1.00 0.527 15.14 4.54 52.67% 30.00%
TSS (MG/L) 30.00 1.270 454.25 10.95 4.23% 2.41%
BOD5 (MG/L) 5.00 2.790 75.71 24.06 55.80% 31.79%
TN (MG/L) 0.00 29.600 0.00 255.30 NA NA
TKN (MG/L) 0.00 0.223 0.00 1.92 NA NA
NO2/NO3 (MG/L) 0.00 27.634 0.00 238.35 NA NA
TP (MG/L) 0.50 0.292 7.57 2.52 58.40% 33.27%
DO (MG/L) 6.00 7.730 0.00 66.67 128.83% 128.83%
Summer limits are imposed on NH3, BOD5, and on Total Phosphorus. From records during the summer
months the plant attained 58.4 % of the permitted discharge concentration limit. However from a total
mass limit of 4.00 MGD at 0.5 mg/L the Siler City plant discharged only 33.2% of its allocation. Figure 5
illustrates the effectiveness of adding Alum at the head of the secondary clarifiers in precipitating TP to
be carried out of the process stream in the waste sludge.
Page I22

Nutrient Removal Optimization Plan September 2009
ITable 17 Winter Percent Removal and Limits.
WASTEWATER WINTER WINTER WINTER MASS WINTER MAS % OF CONC. % OF MASS
COMPONENT LIMIT MEASURED LIMIT/KG/D S KG/D LIMIT LIMIT
IFLOW (MGD) 4.00 2.279 15141.65 8625.13 56.96% 56.96%
NH3 (MG/L) 2.00 0.527 30.28 4.54 26.34% 15.00%
TSS (MG/L) 30.00 1.270 454.25 10.95 4.23% 2.41%
BOD5 (MG/L) 10.00 2.520 151.42 21.74 25.20% 14.35%
TN (MG/L) 0.00 29.600 0.00 255.30 NA NA
TKN (MG/L) 0.00 0.223 0.00 1.92 NA NA
NO2/NO3 (MG/L) 0.00 27.634 0.00 238.35 NA NA
TP (MG/L) 2.00 1.790 30.28 15.44 89.50% 50.98%
DO (MG/L) 6.00 7.730 0.00 66.67 128.83% 128.83%
Table 17 shows the percent removal rates and limits for the Siler City WWTP operated during winter
months. From the winter DMRs it can easily be seen that the concentration and mass limits are
controlled within the specified limits.
Process Samples
To evaluate the operation of the treatment process, grab samples were taken at inter process locations.
The evaluation of the samples was intended to quantify the nutrients held within the process and
investigate ways to control their fate.
Aeration Ditch water quality parameters, Table 18, from a grab sample in late August 2009 showed
elevated values of TP which indicates that the activated sludge retains large amounts of Phosphorus
within its cell structure. This observation is corroborated by the large proportion of TP in the waste
sludge. The sample further showed that the bulk of the NH3 was being converted to Nitrates but little
denitrification was occurring within the reactor as indicated by the 39.3 mg/L reading of Nitrate.
Table 18 Aeration Ditch August Grab Sample
FLOW, MGD 4.400 MASS LOADING, LBS/DAY
NH3, MG/L 0.1850 6.79
TSS, MG/L -5000 183,480.00
BOD5, MG/L 0.00
TN, MG/L 0.00
TKN, MG/L 0.00
NO2/NO3, MG/L 39.30 1,442.15
TP, MG/L 351.00 12,880.30
Page I23

Nutrient Removal Optimization Plan September 2009
Sludge grab samples in August also showed higher TP concentrations but should have measured higher if
the sludge were transporting the TP out of the process since the sludge was concentrated by a ratio of
11000/5000 as measured by the TSS while the TP concentration fell from 351mg/L to 259mg/L. Total
Nitrogen in the sludge stream results from proteins in the cell mass of the activated sludge.
Table 19 Sludge August Grab Sample
FLOW, MGD 1.488 MASS LOADING, LBS/DAY
NH3, MG/L 0.252 3.1
TSS, MG/L -/1,000 136,509.12
BOD5, MG/L 0.00
TN, MG/L 248 3,077.66
TKN, MG/L 210 2,606.08
NO2/NO3, MG/L 38.2 474.06
TP, MG/L 259 3,214.17
A grab sample from the secondary supernatant stream showed, Table 20, that the majority of the TP
entering the clarifier was removed in the settled solids resulting in a low TP concentration. The stream
would flow from this point in the process to a sand filter that would further remove suspended solids
and reduce the TP in the stream.
Table 20 Secondary Clarifier Supernatant
FLOW, MGD 2.300 MASS LOADING, LBS/DAY
NH3, MG/L 0.10 1.92
TSS, MG/L 0.00
BOD5, MG/L 0.00
TN, MG/L 39.3 753.85
TKN, MG/L 0.20 3.84
NO2/NO3, MG/L 39.3 753.85
TP, MG/L 0.533 10.22
Page I24

Nutrient Removal Optimization Plan September 2009
Chemical Additions
Alum [ Al2 (SO4)3 ]was introduced into the treatment stream after the Aeration ditch and before the
secondary clarifier. The purpose of the Alum is to precipitate Phosphorus out of solution such that it will
settle out of the water stream and not be discharged into the receiving waters. Alum was added during
the summer months to control the effluent concentration of TP < 0.5 mg/L but was not required during
the winter months when the treatment process could maintain 1.79 mg/L TP. Alum added during the
summer months was reported to be 400 Gallons/day of a 50% solution of a bulk supply. If the bulk
supply were 50 %wt, then the resulting mass of Alum per day would be 1101.7 Kg/day.
Table 21 Mass of Alum AI2(SO4)3 added during Summer Months
KG ALUM PER DAY 1101.69
KG AL PER DAY 173.75
KG S PER DAY 309.75
KG 0 PER DAY 618.20
Lime was added to the Aeration Ditch reactor at an estimated rate of 40 tons per month which translates
into 1195 Kg/ Day, Table 22. The elemental flow is:
Table 22 Lime Added per Day
CAO (LIME) 1195 KG/D
CA 854 KG/D
0 341 KG/D
Figures 6 through 9 present a WWTP site plan, WWTP process flow diagram, Mass Balance worksheet
and aerial photograph, respectively. Section IV presents a discussion of recommended optimization
strategies for the Siler City WWTP based on the prior analysis of influent sources and current nutrient
removal rates.
Page I25

Nutrient Removal Optimization Plan September 2009
IV. Nutrient Removal Optimization
The Town of Siler City WWTP utilizes the following unit processes to achieve tertiary levels of treatment
in accordance with the NPDES permit requirements:
1. Influent screening 7. Secondary Clarification
2. Influent Flow Monitoring 8. Sand Filtration
3. Grit Removal 9. Chlorine Disinfection
4. Influent Pumping 10. Dechlorination
5. Oxidation Ditches 11. Step Aeration
6. Alum addition 12. Aerobic Digestion
The objective of this nutrient survey is to identify possible operational modifications that may result in
higher removal rates for nitrogen and phosphorus. Since the plant currently removes up to 96% of
phosphorus during summer months and converts 99.4% of the ammonia to nitrates/nitrites, the
recommendations will focus not only on additional removal but on more efficient removal.
Considerations for maximizing removal rates and minimizing power consumption and chemical addition
are considered. Monitoring of results is recommended to indicate the success of process modifications
and to analyze the potential to denitrify within the existing plant infrastructure. As a result, current
recommended modifications and associated monitoring to the existing process include the following:
1. Increased Monitoring of Hauler discharges to the WWTP. The Town's WWTP operators have
sampling protocols for truck discharges to the WWTP. As a result, the Town was able to
identify the constituents in the influent from truck discharges as indicated in Table 6 of this
report. Operators are currently investigating measures to increase the monitoring of sludge
haulers so that they may achieve consistent plant loading and blending of the relatively
higher concentration waste stream.
Currently the dischargers send the plant sample results of each truck on an annual basis.
Implementation of improved monitoring will require each truck to deliver a batch ticket to
the WWTP upon delivery, indicating time, volume and constituents for each truck.
Further implementation, may include the addition of security cameras which will be able to
verify truck deliveries while improving overall plant security. The Town is currently planning
on adding a security camera system to the WWTP.
Page l30

Nutrient Removal Optimization Plan September 2009
2. Increase Process Monitoring. Since efficiency of the nutrient removal process from both a
treatment and energy perspective is fairly sensitive to the biological and chemical activity
providing the removal, measurement of certain process indicators is critical to identifying
process optimization. As a result, the WWTP staff proposes to perform additional sampling
for the following process indicators, targeting the optimum values to identify process
efficiency:
Table 23 Process Monitoring with Optimum Values
SAMPLE OPTIMUM RANGE FREQUENCY
SLUDGE VOLUME INDEX, SVI 80-100 ML/G DAILY/WEEKLY
OXIDATION DITCH D.O. 2.0 MG/L DAILY
SRT 20-30 DAYS MONTHLY
•
SIDESTREAM NUTRIENTS MONITOR MONTHLY/QUARTERLY
RAS FLOW RATIO 50-100% OF INFLUENT WEEKLY
WAS FLOW RATE RELATIVE TO SLUDGE AGE WEEKLY
The above parameters can be used to monitor process indicators and also to directly
calculate process efficiency by yielding the variables for Oxygen Uptake Rates. Additionally,
the above parameters will be coordinated with the existing testing protocols for the WWTP
along with visual observation of the system. Results of the monitoring can be used to make
process modifications to improve efficiency and removal rates. Plant staff will perform
modifications to one of the existing process trains at a time, where feasible, so that a direct
comparison can be made for that process modification.
Additionally, sampling of the process at interprocess locations to better gauge the sludge
and nutrient concentrations in the ditch and recycle streams is part of the side stream
sampling recommendation in Table 23 above. The sludge age and food to mass ratio are
important parameters to manage in an activated sludge treatment process. The rate of
sludge wasting can control the age and F/M ratio and result in an improved operation.
3. Consideration for Improved aeration/control/denitrification capabilities The air distribution
equipment in the oxidation ditches is currently limited to the full capacity of the blowers
and to providing single zone aeration capabilities. The purpose of the Nutrient Optimization
Plan is to optimize the existing plant performance, however it should be noted that the
Town is looking to utilize this plan as a means for improving plant performance as may be
required in the future and as a means of potentially reducing power consumption.
Page 131

•
Nutrient Removal Optimization Plan September 2009
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Page 16

Nutrient Removal Optimization Plan September 2009
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Page 126

Nutrient Removal Optimization Plan September 2009
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Page I27

Nutrient Removal Optimization Plan September 2009
Figure 8 Siler City WWTP Material Balance Calculation Sheet
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T.`�' ill*]; SCREEN TOTAL OF 16655.82 CUOC METERS IN 4.4.%ID. G CLARIFIER wEOFI trio �+ x
/1
CHAMBER MLS54000-6000 Nos t''ft 'S
10 Flow
POLYMER SID'DIAMETER a •
sWF ADDITION D a CIILOMNE S ��p(
®LJ4Zffi101UEZ1a Q MIXER AODMION 3 r 104 n rt :re S[411
zo▪osMI I�ron�raI®ErI bores r.r'oo wA .w - PG al
MI .1P• �WaTilinrn IWiETIMMIErItIlmo"""'
3 Exi o_man�r� m
Gra : airnr®m11Gi
%4f
kor DM un n Z:: d 107.1:+�N�m ..
NOS rlor:A •�..: n.. __ NV r1 SLUDGE
F'I'0^tide SOLOS
PUMP
3 —:•s'-1 t`t1:.:n braAlb . a.m.
Q ,,Y, INFLUENT 4 Ea PUSS
sr 146.00 Nan .._ STATIONS
AENO0IC AERATED
DIGESTED
...." SLUDGE SLUDGE HOLOMG I WASTEDSLUDGE i
Ft./ 11112CULMEANELICI&IDGICEITGE 0 GAS ION
IDNEW.RS SFRil<m1F. ETQtlf]rt
T.. i n+11A m[1N®FERN
N0rYo3 SX1 EIMEI®<E,AI
SI i1R1 �IJJ E L._f ./0% I... .nm R..i •. —'ra.� ROKs . rl ,
n% rs?.LSI IIMla 0111.0,r ' .'i .0r 3a w 4rwF...
µ��u; ... r. N Io
t125:: Fn � ,•l.I :1 r3
IiiMI!'�n+ x
S. ® ®RmFiSf -1.11 rrnl.uv.�1l n.Ar E L MICA{eA>f
or Star ; tun .as PE.: ,.« , jI �Mr-11;-f �S t aL V
>.
n OOJ. 4 EOM
sr LF.O EINI MT RT1 �R.'R71 ENATEO MLTEN o-1 IN 34
o S!•<IIID©srrrn GCNWKN 0S
01R� �11'TI SOLIDS as
........ I +"�l^.S�i"TI2 �R'FT1 ZONE I A
�1rT1if 1s7'TI e 740.4
H,J AL*LIZATION TOTAL VOLUME Z AI MGAL 01 3'
S.
F.w SOS GPO MeZ1R
RR' .Y 0' .r
Tg
No6N4 4.M
ea
Page 128

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Nutrient Removal Optimization Plan September 2009
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CHATHAM COUNTY, NC
"``�0Property Map
.r1 .
r / Disclaimer
date provided on this si us prepared for Ise inuehk at real property found wain
Chatham Coin..MC end are oeepa.d from recorded Use,deeds.modeller public records
-,V�' -;T,.' and dere.Tile dale le for nlaraenienal purposes only and.add not be euhsaluted One Inch= 132 Feet
fore rue bee sserch,properly perusal,survey,or for coring wrMcaion.
Page I29