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HomeMy WebLinkAboutNC0026441_Nutrient Optimization Report (Q4 2022)_20230130Town of Slier Citv NPDES#NC0026441 WWTP Nutrient Removal Optimization Quarterly Report: 4ch 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 4m 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 41h 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 4ch 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 Parameter ' Daily Average Flow (mgd) 3.26 BOD (mg/1) 228 NH3 (mg/1) 19.5 TN (mg/1) 35.0 TKN (mg/L) 34.1 TSS (mg/1) 667 TP (mg/1) 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 Ibs BOD/Lbs MLVSS with MLVSS between a concentration of 3,400 to 4,200 mg/I. Optimization Implementation 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/l. 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 W WTP. The 2023 TN limit is the equivalent of 12 mg/I at 4 MGD plant flow. The plant performance during the 41h 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 41h 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/1) 6658.4 5849.5 5402.3 5981.9 MLVSS (mg/1) 4360.0 4117.2 3746.8 4077.9 Ditch 1 DO (mg/1) 2.04 1.64 3.92 2.51 Ditch 2 DO (mg/1) 0.73 0.26 2.52 1.12 Conclusion Overall plant performance during the 41h 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 k 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.