SUBAIR Process

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Biological Nutrient Removal / Continuous Batch Reactor


The PEI SUBAIR CBR/NBR is the most recent improvement to the proven Sequencing Batch Reactor (SBR) process for wastewater treatment. The PEI SUBAIR CBR/NBR continues the pronouned advantages of the conventional SBR process such as stable performance, efficient BOD/TSS removal, nutrient removal via nitrification/ denitrification/ phosphorus luxury uptake, lower sludge yield and automated process operation. It also answers common design issues such as larger tank cost, separate aeration/ mixing requirements, proprietary positive solids separation, instant high flow discharge and tank level fluctuations.

The SUBAIR BNR/CBR improves the SBR process by using SUBAIR Aerators/ Mixers and TRIAD high capacity rotary thickeners which answer all of the above deficiencies while reducing both capital investment and O&M costs. The SUBAIR BNR/CBR process is easily applicable to most municipal and industrial wastewater biological treatment needs. The TWO-TANK design has literally turned batch treatment back to continuous-feed continuous-discharge (CONTINUOUS-BATCH) operation while maintaining SBR performance.


With PLC-based controls, two bioreactor tanks are operated in parallel under staggered batch operating conditions. Wastewater feed is continuous to one tank or the other during the entire batch cycle. Mixed liquor is continuously drained, by gravity, from one of the tanks to a rotary filter thickener. MLSS is maintained at 1%-2% concentration. Mixed liquor is thickened to 4-6% solids and most of it returned to the SBR tanks. Filtrate (effluent) drains to a microscreen for tertiary solids removal to meet more stringent criteria. Waste sludge, at 4-6% solids, is sent to disposal or further processing. Aeration and mixing is provided in both tanks by PEI’s SUBAIR submerged aerators/mixers.


  1. SUBAIR Submerged Aerator/ Mixer

    • The SUBAIR is a submerged, motor driven pump, which recirculates mixed liquor, combined with air, drawn from the surface or a booster blower. The aerator discharges, at the tank bottom, through a static vane arrangement throughout the 360º arc around the mixer. Air is discharged as fine bubbles and dispersed in the high velocity discharged liquor, where it rises to the surface, transfers oxygen and induces greater mixing due to its density difference with the surround water. During the mixing-only phase (anoxic, anaerobic periods), the pump continues to provide mixing without aerating. This is achieved by simply closing a valve or turning off the booster blower.

  2. TRIAD Rotating Drum Thickener

    • From the SUBAIR BNR/CBR tank(s), mixed-liquor, of 1%-2% concentration, is received by gravity, thickened to 4-6% solids and then discharged from the rotating filter thickener to the RAS/WAS return pump. The RAS and WAS is pumped back to the reactor tank(s) or to waste using a PEI progressive cavity pump.

  3. ROTOFILTER Microscreen

    • The PEI ROTOFILTER Microscreen provides a positive means to remove residual TSS from the final effluent to tertiary discharge levels (<10 mg/l). This durable screening unit, using 20- 40 micron screen openings, eliminates any concern for hard to settle solids. Automated, simple operation and minimum maintenance are inherent features in this equipment.

  4. Optional TRIAD Belt Filter Press

    • Thickened WAS is received and dewatered from 4-6% to 15-18% solids for final disposal. Standard features of the TRIAD Belt Filter Press include 304 SS construction, equalization tank with mixer, automated belt tracking, manual or automated belt tensioning, belt wash assembly, doctor blade and drive motors/reducers. Local control panel is typically included.


System Design

  • Continuous-Batch Operation:

    • No Decanter

    • No Decant Pumps

    • No High Rate Discharge

    • No Settling/Decanting/Idling Periods

  • Smaller Tanks

  • Single Unit Aeration and Mixing

  • Simplified Installation and Operation

System Performance

  • Retained High Performance Levels of SBR Process For Removal of BOD/TSS, Ammonia, and Phosphorus.

  • Produces Thickened (4-6%) Wasted Activated Sludge For Optional Dewatering.

  • Produces Less and More Stabilized Sludge

  • Reduces operating energy

  • Increases capacity for shock loads


  • Municipal Wastewater

  • Pulp & Paper

  • Meat Processing

  • Dairy

  • Winery

  • Distiller

  • Fruit Processors

  • Other Industrial Wastewater