Go Beyond Conventional Hydraulic Tools for Optimized Flow Distribution in Your Wastewater Plant

Authors:

  • S. Galst, X. Tian, P. Saurer, P. Pitt - Hazen and Sawyer
  • J. Xia, K. Mahoney - BWT, New York City Department of Environmental Protection

The Bowery Bay Wastewater Treatment Plant (WWTP) is a 150 mgd plant located in Queens, New York. As a result of the increasingly stricter limits on effluent Total Nitrogen (TN) discharges into the East River, the Bowery Bay WWTP recently completed upgrades to Biological Nutrient Removal (BNR) to treat wastewater from combined sewers in June 2012. Operation of the BNR process requires optimal primary effluent (PE) flow distribution to each of the four passes of the step feed secondary treatment system.

Traditional treatment hydraulics usually calculates hydraulic profiles along a selected flow path of the most loss and focuses on the total head required to the treatment train for average and peak flows. Even the popular treatment hydraulics modeling programs provide little or no information on flow splits to passes and tanks, which is often left to the plant operation on trial-and-error basis. The primary goal of this work was to develop a tool to provide gate settings for desired flow splits. The objectives were to develop a hydraulic model, perform model calibrations, and implement the model to a variety of operational conditions including gate settings for desired flow splits, flow splits for given gate settings, sensitivity analysis on early tipping, etc.

InfoWorks CS, better known for its superior capability of modeling sewer collection systems, was adapted to solve this complex treatment hydraulics problem. InfoWorks rebalances the hydraulic profile and flow splits of the interconnected hydraulic system automatically. It also determines the exact tipping point for any given set of gate openings. A hydraulic model was developed based on the best information available. Drawings from historical contract documents were reviewed to verify physical dimensions and interconnections. The conditions of critical hydraulic structures such as overflow weirs and secondary bypass Parshall flume were inspected.

The model was calibrated based on multiple aeration tank TSS profiles used to calculate flow distribution, where gate settings were recorded. Comparisons of flow distribution between model predictions and observations of eleven TSS profiles obtained in June and July of 2013 show excellent agreement, mostly within 10%. The model was used to provide optimal and preventative gate settings, as well as wet weather gate settings.

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

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