WWTP Optimization Study Provides Actionable Insights for Reducing Operating Expenses

Authors:

  • Katya Bilyk - Hazen and Sawyer

This presentation will summarize an extensive optimization study for a BNR plant in Virginia. The evaluation included extensive historical data review and BioWin™ calibration and optimization.

The 75 mgd facility has total nitrogen and phosphorus discharge standards of 5.0 and 0.5 mg/L, respectively. The main stream wastewater treatment process incorporates preliminary treatment, primary/secondary clarification, BNR activated sludge with glycerin addition, filtration, and disinfection. The BNR tanks operate 5-stages including: RAS fermentation, aeration, and anoxic zones before and after aeration. The facility utilizes eight basins with two different sizes and configurations.

The main findings of the historical data evaluation and modeling include:

(1) The optimal RAS rate is approximately 50 percent of the influent flow. Modeling illustrated that a rate too high or too low increased the effluent TN by up to 1.3 mg/L due to reduced nitrate removal and ammonia release in the RAS fermentation cell.

(2) Guidance for the anticipated carbon dose and optimal NRCY rate to meet the TN goal for each tank based on influent carbon to nitrogen ratios was developed as follows:
a. Glycerin (gpd) = (influent cBOD:TKN – 5.4)/0.001
b. NRCY (mgd) = (influent cBOD:TKN – 2.3)/0.0324

(3) The facility has the ability to feed carbon to the first and second anoxic zone. It was determined that feeding 100% of the supplemental carbon to the second anoxic zone was appropriate and will simplify operations.

(4) Denitrification in the larger BNR tanks was more effective than in the small tanks as evidenced by the COD_added/NOx-N_removed ratio for each tank. One potential explanation is that glycerin is unintentionally but preferentially diverted to the larger tanks.

The facility will adjust operations based upon the study’s insights and guidance. Operating data from the plant as a result of these recommendations will be presented at the conference.

For more information, please contact the author at kbilyk@hazenandsawyer.com.

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