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Mark Pamperin
Product Manager - Biological Processes

The Orbal® System for Biological Nutrient Removal

Most energy efficient, lowest maintenance and safest oxidation ditch available

Easily identified by its concentric loop design, the Orbal® system, part of the Envirex® product family, uses an activated sludge process designed to address today’s nutrient and stormflow issues. 

The simultaneous nitrification/denitrification (SND) process is the backbone. The Orbal system features​​ dedicated zones for specific treatment purposes. These treatment zones operate in series during the SND treatment process. The Orbal system has been on the leading edge of SND plant designs for more than 50 years.

The Orbal system now has ALL NEW COMPONENTS to provide even better performance with reduced maintenance. Scroll down to learn more.



  • TrueSND™ biological treatment — TrueSND treatment in the same zone results in 80% denitrification without the need for an internal recycle pump.
  • Process adaptability/flexibility — Adaptable to achieve lower TN or TP as
    regulations change. Complete mix characteristics and ability to operate at high MLSS concentrations form a high buffer capacity for shock loads.
  • Energy efficient — Operating a majority of system volume at a strong oxygen deficit allows for much higher oxygen transfer efficiency.
  • Stormflow capabilities — Operating tanks in series allows for diverting the Stormflow downstream of the first reactor, preventing clarifier washout of biomass. Proven effective in treating greater than 7x peak flow.
  • Eliminates structures — Allows for elimination of a dedicated anoxic zone typically used in biological nutrient removal processes. Reduces footprint, concrete cost, mechanical mixers and operational energy costs.
  • Easy maintenance — Only routine greasing of bearings is required; aerator discs are non-fouling.


  • OX™ Disc Aerator – Doubles oxygen transfer to reduce maintenance, construction and capital costs
  • Weather Hood – Enables easy removal with onsite, portable gantry crane
  • Direct Drive – Ensures 5-10 percent more energy efficiency than first-generation drive
  • Bearings – Minimize downtime with fast replacements, remote grease lines with direct greasing and optional automatic greasing, plus eliminate overtightening with optical sensor
  • Couplings – Allow replacement in less than 30 minutes

 Video - TrueSND Biological Treatment

​Technical Sales Manager, Freddy Kade, discusses Evoqua's Orbal System, which provides simultaneous nitrification-denitrification, reducing energy costs and maintaining flexibility and redundancy for changing conditions.


  • Conventional activated sludge
  • Advanced secondary sludge treatment
  • Simultaneous nitrification-denitrification
  • Biological phosphorus removal
  • Storm water treatment The Orbal® System for Biological Nutrient Removal