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Improving Nutrient Removal Capabilities While Reducing Operating Costs

Walkway used to access activated sludge reactors and association instrumentation

Tetra Tech implemented wastewater treatment process modifications to the process for the City of Tampa, Florida, to achieve enhanced nitrogen removal, reduce methanol use, and decrease operating costs.

Tetra Tech’s wastewater team used our Leading with Science® approach to assist the City with evaluating options and implementing solutions to improve their biological nutrient removal (BNR) at the 96 million gallons per day Howard F. Curren Advanced Wastewater Treatment Plant. Our team developed four distinct alternative operating schemes that could lead to lower power and chemical costs. Factors considered in the initial screening of alternatives included approximate capital cost, potential energy and cost savings, ease of operation, flexibility, reliability, and future effluent limits that may be imposed resulting from new total maximum daily load requirements.


  • More than 300 tons of CO2e per year of initial reduction in carbon footprint
  • $240,000 annual estimated savings from reduced methanol at full implementation
  • $60,000 annual estimated savings from reduced power use at full implementation
  • No additional tankage or structural improvements needed to realize savings

In the second work phase, Tetra Tech designed BNR improvements that reduced methanol costs by decreasing aeration energy, allowing nitrate reduction to occur. These improvements also involved implementing the Modified Ludzack-Ettinger process as a full-scale demonstration project using aerobic/anoxic swing zones in one activated sludge reactor based on GPS-X process modeling. Tetra Tech also designed the upgrade and replacement of the diffused aeration system, submersible mixers, and improvements to the process monitoring and control systems.

Activated sludge basin at 96 million gallons per day advanced wastewater treatment facility
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