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Nitrogen Removal Upgrades Improve Great Bay Water Quality

Nitrogen Removal Upgrades Improve Great Bay Water Quality

Dover, NH Wastewater Treatment Facility Upgrade

Due to water quality concerns in Great Bay, and an interim total nitrogen (TN) limit of 8 mg/L, Wright-Pierce worked with the City of Dover to design an upgrade to the City’s conventional activated sludge facility to achieve nitrogen removal. The selected Biological Nutrient Removal (BNR) process was the Modified Ludzack Ettinger (MLE) process. The MLE process modifications were completed in 2015, and the plant is currently performing well with effluent TN levels below 8 mg/L. Based on an EPA mandate to other New Hampshire seacoast communities, the City anticipates potentially having to further upgrade their treatment facility to achieve a 3 mg/L TN limit within 15 years, and will use the operational experience gained from the MLE process to base the design of the next upgrade. An aerial of the Dover facility is shown in the photo above.

Durham, NH Wastewater Treatment Facility

In 2003, Wright-Pierce assisted the Town of Durham, home to the University of New Hampshire, convert its extended aeration wastewater treatment plant to a Modified Ludzack-Ettinger (MLE) process in order to recover alkalinity lost during nitrification, improve effluent pH, and to voluntarily reduce nitrogen load to Great Bay. The Town successfully ran this process for many years, but, like other New Hampshire seacoast communities, is anticipating more stringent effluent total nitrogen (TN) limits in the future. In order to help address water quality issues in Great Bay and to prepare for these anticipated lower limits, the Town opted to convert the MLE process to a Four-Stage Bardenpho process as a full-scale pilot test to ascertain if the existing tankage could biologically achieve low level effluent TN without supplemental carbon or additional tertiary treatment. There are significant challenges with operating a Biological Nutrient Removal (BNR) Facility in a community with large variations in flow due to the university. The new Four-Stage Bardenpho process has recently been brought on-line and is currently being optimized.