NC0026441_Nutrient Optimization Report (Q4 2023)_20240130

Town of Slier Citv
NPDES#NC0026441
WWTP Nutrient Removal Optimization
Quarterly Report: 4th 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 4th 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 0.02 mg/I during the 4th 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 4th Quarter
2023
Flow (mgd)
3.26
2.29
BOD (mg/1)
228
253
NH3 (mg/1)
19.5
26
TN (mg/1)
35.0
51
TKN (mg/L)
34.1
TSS (mg/1)
167
TP (mg/1)
3.34
2.3
The report recommends utilizing Simultaneous Nitrification/De nitrification (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 an 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 4th quarter of 2023 the overall performance of the Siler City WWTP has been very good with
average effluent BOD of 0.22 mg/l, and Ammonia of 0.23 mg/I. The influent BOD has remained relatively

low, similar to the 3rd quarter, but it is noted that the influent TN concentrations were higher this
quarter.
The effluent TN concentration has been somewhat higher than desirable at an average of 25.54 mg/I for
the quarter. The MLVSS concentration averaged 2,898 mg/I which is just below the range recommended
by the optimization report. The dissolved oxygen concentration trended downward during the quarter
as the operators continued to work to optimize the manual control strategy. 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 for two of the three months
but as the DO levels trended downward the TN levels have also. Flow during this quarter has remained
relatively low although December increased some with winter rainfall impacts. 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. In the 4th quarter the average mass TN discharged was 9,389
Ibs/month. The annual total Ibs TN discharged was 127,749 which is below the permit limit for 2023.
Further optimization will be needed in 2024 to comply with the reduced annual limit.
Table 2: Nutrient Removal Performance for 4th Quarter 2023.
influent
Effluent
October
November
December
Average
October
November
'December
Average
Flow
2.11
2.05
2.72
2.29
BOD
245
248
267
253
0.00
0.66
0.00
0.22
NH3
29
26
24
26
0.00
0.00
0.68
0.23
TN
56.9
49.2
46.8
51.0
18.15
18.08
13.30
16.51
TP
3.68
1.99
1.27
2.3
0.00
0.01
0.05
0.02
1. All concentrations reported in mg/l. Flow reported in MGD
Table 3: Operating Parameter Summary
October
November
December
Average
MLSS (mg/I)
4521
4294
4099
4305
MLVSS (mg/1)
2986
2884
2824
2898
Ditch 1 DO (mg/1)
3.21
2.86
1.92
2.67
Ditch 2 DO (mg/I)
2.50
1.70
0.84
1.68
Conclusion
Overall plant performance during the 4th 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 was good and continues to show improvement as operations are adjusted
for optimization.