NC0026441_Nutrient Optimization Report (Q3 2023)_20231030

Town of Siler City
NPDES #NC0026441
WWTP Nutrient Removal Optimization
Quarterly Report: 3rd Quarter 2023
Introduction
In accordance with NPDES Permit requirements this report is provided to document implementation of
the optimization report and performance of the WWTP during the 3rd 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 0.2 mg/I during the 3rd 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
Parameter
Daily
Average during
Optimization
2020
Daily Average
for 3rd Quarter
2023
Flow (mgd)
3.26
BOD (mg/1)
228
234
NH3 (mg/1)
19.5
28
TN (mg/1)
35.0
38.8
TKN (mg/L)
34.1
TSS (mg/1)
167
TP (mg/1)
3.34
2.8
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 3rd quarter of 2023 the overall performance of the Siler City WWTP has been very good with
average effluent BOD of 0.74 mg/I, and Ammonia of 0.07 mg/I. The influent BOD has been somewhat

lower than in previous quarters, which appears to be influenced from Mountaire's improved
performance in July and August. The September BOD is somewhat higher as Mountaire's BODs were
also higher at that time.
The TN concentration has been somewhat higher than desirable at an average of 25.54 mg/I for the
quarter. The MLVSS concentration averaged 2,825 mg/I which is just below the range recommended by
the optimization report. The dissolved oxygen concentration was somewhat variable and ditch 2 has
trended lower DO than ditch one as in previous quarters. 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.
The performance for TN is above the optimization report target of 15 mg/I and operators are continuing
to work on the manual DO control in the ditches. The relatively low flows over the summer at the WWTP
impact the mass of TN present in the discharge. The average mass TN discharged in Quarter 2 was
approximately 10,142 Ibs/month. In the 3rd quarter the average mass TN discharged was 15,322
Ibs/month. The total mass discharged in 2023 is approximately 99,593 Ibs through the first 3 quarters
leaving 46,534 Ibs remaining to meet the permit limit. This is an average of 15,511 Ibs/month and the
plant is therefore on track to maintain compliance but will need to closely monitor TN in the final
quarter.
Table 2: Nutrient Removal Performance for 3rd Quarter 2023.
Influent
Effluent
July
August
September
Average
July
August
September
Average
Flow
2.56
2.35
2.11
2.34
BOD
194
223
285
234
0.13
0.64
1.45
0.74
NH3
24
28
31
28
0.00
0.04
0.16
0.07
TN
33.7
34.5
48.1
38.8
22.58
31.42
22.63
25.54
TP
2.00
2.34
4.18
2.8
0.16
0.00
0.38
0.18
1. All concentrations reported in mg/I. Flow reported in MGD
Table 3: Operating Parameter Summary
April
May
June
Average
MLSS (mg/1)
3992
4607
4714
4437
MLVSS (mg/1)
2634
2853
2989
2825
Ditch 1 DO (mg/1)
2.26
2.66
2.37
2.43
Ditch 2 DO (mg/1)
0.80
1.43
1.60
1.28
Cnnclusinn
Overall plant performance during the 3rd quarter of 2023 was very good and remains substantially
improved from before August of 2022. The plant is continuing to prioritize sludge handling and solids
levels in the basins are close to optimization report recommendations. The performance during this
period for nutrient removal is ok and on track for compliance, however the final quarter will be
important for meeting the 2023 limits.