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Aeration for Waste Water Treatment Plant

Low Speed Aerator (LSA)


East Rockingham, Western Australia


In 2014-15 Water Corporation constructed Stage 1A of the East Rockingham WWTP, which included two (2) Oxidation Ditches (ODs). Each OD with approx. dimensions 115m L x 25m W x 6.1m D at (Top Water Level) TWL, was fitted with two (2) pier mounted surface aerators. Initially each OD would treat 3 ML/day increasing to 10 ML/day of screened & degritted sewage.
The system was designed so that in subsequent upgrade stages Primary Settling Tanks will be installed upstream of the ODs, that will allow future treatment of up to 20 ML/d per OD.

The NSA-series Low Speed Aerator model NSA5-300B (220 kW) supplied by DBS Manufacturing was selected for this project due to its low power usage and demonstrated performance in many similar applications.


Design specifications include

  • Average / Peak Standard Oxygen Transfer Rate (SOTR) per aerator of 410 / 472 kgO2/h respectively
  • Turn-down ability to 140 kgO2/h per aerator
  • Aerator motor power limited to 220 kW
  • Aerator rotor tip speed not to exceed 5.5 m/s

design features

  • NSA aerators use a planetary gearbox to drive the aerator rotor. This type of gearbox is commonly used in applications where power/cost ratio is important.
  • NSA5-300B aerator can provide mixing down to a depth of 6.5m without the need for a draft tube, baffles, or any other device.
  • For this project, each aerator is fixed onto a Mounting Platform that fits into a recessed hole in the concrete structure of the OD. When maintenance to the rotor is required, the entire aerator and mounting platform is lifted out, and placed onto a working platform located adjacent to the OD.


  • Efficiency. With Standard Aeration Efficiency (SAE) of 2.0 kgO2/kWh the NSA5-300B aerator offers exceptionally high efficiency, and turn-down capability, resulting is low power costs.
  • Low Maintenance. Aerator design allows for simple and low-cost maintenance.