Aeration Considerations in the Design and Operation of Biological Nutrient Removal Processes


  • Joe Rohrbacher PE, Paul Pitt PhD, PE, Jim Cramer PE, Diego Rosso PhD

Aeration system design and control is a critical consideration in the performance of biological nutrient removal (BNR) systems. Excessive aeration not only increases energy costs, but it can limit the reliability of nitrogen and phosphorus removal processes and decrease process stability and sludge settleability, compromising compliance and leading to increased chemical usage to meet effluent permit limits. Important considerations in aeration system design of nutrient removal systems include:

  • Providing an effective taper to control dissolved oxygen concentrations in various zones
  • Limiting the return of dissolved oxygen in RAS and internal recycle streams
  • Decreasing dissolved oxygen prior to supplemental carbon addition
  • Eliminating the potential of back mixing into anoxic or anaerobic zones
  • Providing access for maintenance of diffused aeration systems
  • Maintaining aerobic conditions to avoid secondary phosphorus release
  • Providing zone dissolved oxygen control
  • The use of instrumentation (i.e. ammonia analyzers) to control aeration

This paper will present several case studies illustrating these points.

For more information, please contact the author at

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