NC0026441_Report_20230203

RECEIVED
Town of Slier City FEB 0 3 2023
NPDES#NC0026441
WWTP Nutrient Removal Optimization NCDE�/DWR/NPDES
Quarterly Report: 4th Quarter 2022
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 2022.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 4th quarter 2022.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. It is noted that the average influent
during the 4th quarter of 2022 was substantially different with flows approximately 80%and BOD 143%
of the 2020 values. Influent for all parameters was higher than during the period of the optimization
report.
Table 1: Influent Wastewater during Optimization Study
Daily
Parameter Average
Flow(mgd) 3.26
BOD (mg/I) 228
NH3(mg/I) 19.5
TN (mg/I) 35.0
TKN (mg/L) 34.1
TSS (mg/I) 167
TP(mg/I) 3.34
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 lbs BOD/Lbs MLVSS with
MLVSS between a concentration of 3,400 to 4,200 mg/I.

Optimization Implementation
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During the 4th quarter of 2022 the overall performance of the Siler City WWTP has been good with
average effluent BOD of 1.3 mg/I, Ammonia of 0.7 mg/I and TN of 11.7 mg/I.The MLVSS concentration
averaged 4,077 mg/I which is within the range recommended by the optimization report.The dissolved
oxygen concentration had some variability with loading on the plant.The average DO was 2.51 mg/I in
oxidation ditch 2 and 1.12 in oxidation ditch 1. It is noted that the DO levels rose during winter months
due to better oxygen transfer efficiency with colder temperatures and reduction in the MLVSS. TN
effluent was the lowest during October at 5.7 mg/I and did increase some in November and December
although it remained below 15 mg/I targeted in the Optimization Report.The plant is continuing to work
on DO Control optimization as all adjustments are manual.
Mountaire Farms effluent BOD averaged 562 mg/I in October and November, and 543 mg/I in
December.These values are excess of the daily maximum limit of 540 mg/I and well above the monthly
limit of 450 mg/I.TN levels have also been elevated with the period average of 82 mg/I. Mountaire has
started operational modifications to their facility and is hopeful that these changes will improve the
effluent sent to the Town's WWTP.
The 2023 TN limit is the equivalent of 12 mg/I at 4 MGD plant flow.The plant performance during the 4th
quarter 2022 averaged 11.7 mg/I and it is anticipated that performance can be further improved during
2023.
Table 2: Nutrient Removal Performance for 4th Quarter 2022.
Influent Effluent
October November December Average October November December Average
Flow 2.43 2.50 2.93 2.62
BOD 371.6 353.6 255.6 327.1 0.5 1.0 2.4 1.3
NH3 33.8 30.3 27.1 30.5 0.3 0.7 1.1 0.7
TN 41.2 45.0 31.1 39.5 5.7 14.1 14.8 11.7
TP 5.4 5.0 3.1 4.5 0.06 0.13 0.05 0.08
1. All concentrations reported in mg/I. Flow reported in MGD
Table 3: Operating Parameter Summary
October November December Average
MLSS (mg/I) 6658.4 5849.5 5402.3 5981.9
MLVSS (mg/I) 4360.0 4117.2 3746.8 4077.9
Ditch 1 DO (mg/I) 2.04 1.64 3.92 2.51
Ditch 2 DO (mg/I) 0.73 0.26 2.52 1.12
Conclusion
Overall plant performance during the 4th quarter of 2022 has been very good in comparison to previous
quarters. 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 work on 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.