NC0026441_Nutrient Optimization Report (Q2 2023)_20230728

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Public Works and Utilities
07/24/2023
Scott Vinson, Raleigh Regional Office Supervisor
Division of Water Resources/Water Quality Operations Section
3800 Barrett Drive
Raleigh NC 27609
Water Quality Permitting Section/NPDES
1617 Mail Service Center
Raleigh NC 27699-1617
Introduction
NC Dept of Environmental Quality
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Raleigh Regional Office
Subject: WWTP Nutrient Removal Optimization
Quarterly Progress Report
2nd Quarter 2023
NPDES Permit N00026441
Chatham County
In accordance with NPDES Permit requirements this report is provided to document implementation of the optimization
report and performance of the W WTP during the 2n1 quarter of 2023. The primary focus of this information is nutrient
removal, however data on plant operations for other parameters are included as they influence the nutrient removal
performance.
Phosphorus (TP) removal is achieved with chemical precipitation and performance has been consistently good with
effluent TP averaging less than 0.1 mg/I during the 11t quarter 2023. Therefore, no further review of TP operation is
included.
Optimization Report Recommendations
The optimization report was prepared in 2020 based on data from January to September of 2020.Operating parameters
at the time are shown in Table 1 below.
Table 1: Influent Wastewater during Optimization Study
Daily
Daily Average
Parameter
Average during
for 2nd Quarter
Optimization
2023
2020
Flow (mgd)
3.26
2.98
Chris McCorquodale
Director of Public Utilities
PO Box 769.311 N. Second Avenue
Slier City, NC 27344-0769
[e-mail]
Phone: [phone]•Fax: [phone]
www.silercity.org
To advance a framework for our success through balanced governance, dynamic partnerships, and an engaged community.

BOD (mg/1)
228
255.6
NH3(mg/1)
19.5
26.7
TN (mg/1)
35.0
33.23
TKN (mg/L)
34.1
32.6
TSS (mg/1)
167
148
TP (mg/1)
3.34
2.22
The report recommends utilizing Simultaneous Nitrification/Denitrification (SNDN) to achieve nitrogen reduction. The
recommended parameters include maintaining dissolved oxygen (DO) in the oxidation ditches between 0.8 to 1.2 mg/I
and maintaining a FM ratio of 0.04 to 0.05 Ibs BOD/Lbs MLVSS with MLVSS between a concentration of 3,400 to 4,200
mg/I.
Optimization Implementation
During the 2"d quarter of 2023 the overall performance of the Siler City W WTP has been very good with average effluent
BOD of 3.6 mg/I, Ammonia of 1.18 mg/I and TN of 14.41 mg/1. The MLVSS concentration averaged 2,991 mg/I which is
just below the range recommended by the optimization report. The dissolved oxygen concentration had some variability
with loading on the plant and averaged below the previous quarter. The performance in June appears to show the
impact of the new aerators which reduced BOD and Ammonia but increase in TN. Operations staff are monitoring DO
and if DO levels rise above 2 mg/I a blower is turned off keep the DO in an appropriate range for simultaneous
nitrification and denitrification. Given the rise in TN for June, further adjustment to the procedures is being considered
to ensure TN is maintained at low levels. TN effluent was the lowest during April at 9.3 mg/I and average for the 3-
month period is below 14.41 mg/I which remains below the 15 mg/I targeted in the Optimization Report.
It is noted that a failure in the sludge collector has caused a clarifier to be taken offline in June. The Town is currently
working to get repairs made as quickly as possible to get this equipment back in service.
The 2023 TN limit is the equivalent of 12 mg/I at 4 MGD plant flow. The plant performance during the 2nd quarter 2023
averaged 14.41 mg/1 at flow 2.98 MGD and is therefore on track to maintain compliance.
Table 2: Nutrient Removal Performance for 2"d Quarter 2023.
Influent
Effluent
April
May
June
Average
April
May
June
Average
Flow
3.50
2.69
2.74
2.98
BOD
225.7
277.2
260.1
255.6
5.1
5.0
0.6
3.6
NH3
28.24
28.66
23.12
26.67
1.59
1.94
0.00
1.18
TN
25.30
37.10
37.28
33.23
9.30
12.34
21.60
14.41
TP
1.09
3.40
2.18
2.22
0.22
0.02
0.01
0.08
1. All concentrations reported in mg/I. Flow reported in MGD
Table 3: Operating Parameter Summary
April
May
June
Average
MLSS(mg/I)
4931
4934
4107
4657
MLVSS (mg/1)
3162
3112
2839
3038
Ditch 1 DO (mg/1)
0.61
0.64
2.97
1.40
Ditch 2 DO (mg/1)
0.01
0.16
0.19
0.12
Chris McCorquodale
Director of Public Utilities
PO Box 769.311 N. Second Avenue
Siler City, NC 27344-0769
[e-mail]
Phone: [phone] Fax: [phone]
www.silercity.org
To advance a frarnework for our success through balanced governance, dynamic partnerships, and an engaged community.

Conclusion
Overall plant performance during the 2nd quarter of 2023 has remained similar to the last quarter and is substantially
improved from before August of 2022. Implementation of the action items to improve influent by reducing chlorine
from Mountaire Farms and Iron from the Water Treatment Plant have allowed the plant biology to improve. The plant is
continuing to prioritize sludge handling and solids levels in the basins are within optimization report recommendations.
The performance during this period for nutrient removal is good and on track for compliance with tightening nutrient
limits.
Sincerely,
G�
Chris McCorgw
Town of Siler CI
Chris McCorquodale
Director of Public Utilities
PO Box 769.311 N. Second Avenue
Stier City, NC 27344.0769
[e-mail]
Phone: [phone] a Fax: [phone]
www.silercity.org
To advance atramework/br our success through balanced governance, dynamic partnerships, and an engager) community.