Full-Scale Demonstration Testing of Ntensify Low Energy Biological Nutrient Removal

Background
The Rochester Water Reclamation Facility (WRF) treats an average daily flow of roughly 12 million gallons per day (mgd). The WRF consists of a two-stage high purity oxygen activated sludge train and parallel air activated sludge biological nutrient removal train. The City faces three impeding challenges of (1) its existing cryogenic oxygen plant is reaching the end of its useful life, (2) more restrictive nutrient discharges requirements, and (3) need for additional treatment capacity. To address these challenges, the WRF is converting its existing processes to a single sludge nitrifying enhanced biological phosphorus removal (EBPR) system with consideration to implement Ntensify low energy biological nutrient removal (BNR) which includes advanced aeration control coupled with a metabolic selector and hydrocyclone gravimetric selector to promote excellent sludge quality. Objective Conduct full-scale demonstration testing of the low energy BNR configuration which promotes simultaneous nitrification-denitrification (SND) with EBPR to define treatment performance, energy and chemical reduction, and sludge quality impacts. Evaluate full-scale testing results along with subsequent process modeling to determine facility needs for implementation and methods to optimize BNR performance. Lessons learned during the demonstration test will also be presented.
Methodology
Full-scale demonstration testing was conducted on the air activated sludge train (ABC) from March 2021 through present. The ABC test train was modified to include a hydrocyclone wasting station and effluent nitrogen sensor. (Figure 1). Throughout the test, sampling and field testing was completed to document system performance including the following: - Routine demonstration test train operating data including influent and effluent concentrations. - Bioreactor nitrogen and phosphorus profiles. - Specific ammonia removal rate testing under low and high dissolved oxygen (DO) concentrations. - Column settling and flocculation testing to define settling and flocculation impacts. A BioWinTM process model was then calibrated to the test results and will be used to evaluate full-scale facility requirements and methods to optimize system performance.
Results
Nitrogen. Figure 2 shows the effluent total inorganic nitrogen (TIN) discharges during testing. Low energy operations reduced effluent TIN discharges that ranged from 20 to 28 mg N/L to an average of 12 mg N/L after optimizing DO and airflow settings. Bioreactor nitrogen profiling showed TIN reduction is complete by Zone 2/3 (Figure 3). Specific ammonia removal rate (SARR) testing showed reducing the operating DO to 1.0 mg/L or less decreased the SARR by roughly 50 percent. However, the SARR can be recovered by simply increasing the DO operating level (Figure 4), which is critical for this facility which has a history of suppressed nitrification rates due to industrial contributions.
Phosphorus. Figure 5 presents the effluent ortho-phosphate during the demonstration test. Demonstration test effluent phosphate discharges were excellent with reduced discharges and variability compared to the same period of previous years. Alum usage for phosphate control also decreased by 25 percent or more. (Figure 6) Bioreactor phosphate profiles will be presented showing phosphorus release and uptake were not impact by low DO operations.
Aeration. Aeration airflows required under low DO operations were 50 to 60 percent of past operations with DO levels of 1.5 mg/L. (Figure 7).
This paper will present how the target operating DO concentration and airflow distribution between zones were key factors in reducing aeration requirements.
Sludge Quality. Full-scale testing showed sludge quality was not impacted by low DO operations as sludge volume index values (SVIs) and effluent suspended solids were typical of past operations. Flocculation testing showed the low DO solids flocculated equal to or better than previous testing at higher DO concentrations. Settling column tests showed the low DO solids settled and compacted as expected based upon measured SVI. (Figure 8)
Full-scale Implementation. Facility requirements for full-scale implementation will be compared to a more traditional approach. In addition, methods to improve system performance such as a fully automated ABAC system and increasing mixed liquor recycle flows will be presented.
Conclusions
Full-scale testing of the Ntensify low energy BNR configuration has shown to improve and stabilize effluent quality, reduced chemical usage, and significantly reduce aeration energy without impacting sludge quality.