The Importance of Site Specific Conditions on the Economics of Replacing Aeration Equipment


  • Joe Rohrbacher, Wendell Khunjar, Janice Carroll, Phill Yi - Hazen and Sawyer
  • Maureen O’Shaughnessy - PWCSA

A 24 mgd WWTP recently performed a plant-wide energy audit and reduction evaluation. The evaluation recommended installing high speed direct drive (turbo) blowers to reduce the costs of secondary process aeration compared to operating the plant’s existing multistage centrifugal blowers. Although the facility typically operates a single blower to meet aeration demand requirements, a second blower needs to be operated at certain times. The facility has to discharge excess air when two blowers are in service because there is a gap in process air supply capacity (i.e. maximum airflow from one blower is less than the turndown capacity for two blowers in operation).

The facility initiated a design project to install a turbo blower as recommended in the preliminary study. As part of the preliminary design a more detailed analysis was performed to confirm the potential economic benefit of utilizing turbo blowers in parallel with the existing multistage centrifugal blowers. This evaluation indicated installation of a turbo blower was not economical at current flows since operation of the second blower was relatively infrequent but would result in greater potential savings as plant flows and the frequency of operation of the second blower increased. Furthermore, this study identified that increasing horsepower of the motors on the existing multistage blowers would decrease the frequency of two blower operation, providing similar operational benefits to installation of new turbo blowers.

The blower evaluation illustrates how the potential process and economic benefits of replacing existing aeration equipment with more efficient equipment is highly site specific and is controlled by a multitude of factors including how the influent loads and operational strategy are expected to change over the design life of the equipment. A detailed analysis considering a variety of current and potential future conditions is necessary to establish the true potential savings of aeration improvements.

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