Beyond energy savings: A deep dive into carbon efficiency of low DO BNR

The Seneca Water Resource Recovery Facility (WRRF) uses a 5-stage Bardenpho process for nutrient removal, meeting strict regulations (<4 mgN/L Total Nitrogen, <0.27 mgP/L Total Phosphorus). In Spring 2021, one process train was modified to increase efficiency, including a reduction of the Internal Mixed Liquor Recycle (IMLR) from 400% to 200% of influent flow, the implementation of Ammonia-based Aeration Control (ABAC), the discontinuation of methanol addition in the post-anoxic zone, and a decrease in the volume of the post-anoxic zone from 17% to 9%. These modifications resulted in excellent effluent quality without additional chemical use, achieving effluent NH4-N < 0.2 mgN/L, Total Inorganic Nitrogen (TIN) < 2.0 mgN/L, and orthophosphate < 0.2 mgP/L. This success was attributed to simultaneous nitrification-denitrification (SND) and post-anoxic denitrification, facilitated by ABAC's regulation of dissolved oxygen (DO) levels. The test train achieved significant aeration savings and utilized internally stored carbon for post-denitrification under low DO conditions, eliminating the need for supplemental carbon. Analysis revealed that glycogen, more than polyhydroxyalkanoates (PHA), likely played a major role in this, aligning with the high abundance of glycogen-accumulating organisms (GAO), particularly Competibacter, and Tetrasphaera, the dominant phosphate-accumulating organism (PAO) observed. This system's efficiency suggests an innovative approach to carbon management for enhanced nutrient removal in wastewater treatment.