A Tale of Two Plants: Same City, Same Process, Different Effluent TN and TP
Abstract:The City of Durham, North Carolina, owns and operates two 20 million gallon per day (mgd) wastewater treatment facilities, the North and South Durham Water Reclamation Facilities (NDWRF and SDWRF). Both plants receive similar influents and utilize a 5-stage Bardenpho biological nutrient removal (BNR) process with a 23-hour detention time at design flow. Both facilities produce treated effluent with total nitrogen (TN) concentrations of less than 7 mg/L (without supplemental carbon) and total phosphorus (TP) concentrations of less than 0.5 mg/L. However, the NDWRF has produced a higher quality effluent (TN < 3 mg/L), compared to the South Durham Water Reclamation Facility (SDWRF). In addition, the NDWRF is able to achieve its low TP limits without alum addition, whereas the SDWRF adds alum to comply with its seasonal TP limit. The objective of this paper is to discuss the results of a study aimed at identifying what influent characteristics, process units, and/or operating parameter(s) are responsible for improved nitrogen and phosphorus removal at the NDWRF. Operational differences and influent characteristics were attributed to differences in performance. These reasons include but are not limited to: (1) more favorable carbon to nitrogen and carbon to phosphorus ratios for BNR at the NDWRF; (2) a higher anoxic solids retention at the NDWRF; and (3) increased competition for volatile fatty acids in the SDWRF anaerobic zone.
Document Type: Research Article
Publication date: January 1, 2008
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