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Schreiber Continuously Sequencing Reactor (CSR)

The Schreiber Continuously Sequencing Reactor, or CSR, is a Biological Nutrient Removal (BNR) system contained in a single basin. It produces the three process phases required for BNR - oxic, anoxic and anaerobic - in one basin, performed sequentially and repetitively over time.

During the oxic phase, the entire basin is oxic (aerobic). When the air is turned off, the entire basin becomes anoxic and then ultimately anaerobic. The air is then turned back on and the cycle repeats.

The secret to this “phase sequence-ability” lies in its unique design for complete separation of aeration and mixing. It has a 100 percent aeration turndown capability, turning off the aeration while the CSR applies low-energy, biologically-friendly, flocculant mixing - without adding air. Through the use of Schreiber FlexControls, the CSR process can be advanced to meet the most stringent requirements for today and the future.

  • Less than 1mg/L on phosphorus biologically
  • Less than 1 mg/L phosphorous with chemicals and additional use of the Schreiber Fuzzy Filter
  • Can meet a 3 mg/L nitrogen

The GRO configuration is the basic single-basin CSR configuration. It consists of one circular basin with a rotating bridge that supplies both the low energy mixing and the mixing-independent aeration to achieve BNR in a single basin. The GR configuration is designed for smaller treatment plants. It consists of a central circular clarifier surrounded by an outer concentric aeration basin. The nested arrangement combines biological treatment and final clarification in one simple, compact package, optimizing the space required for a treatment plant. With outside diameters up to 168’, a single GR aeration/clarification system can handle average daily flows of up to 1.5 MGD.


  • Biological wastewater treatment 
  • Industrial wastewater 
  • Municipal water
  • Reclamation facilities
  • ENR applications 
  • Wastewater aeration
  • BNR applications


  • Sequential BNR in a single basin
  • Separation of aeration and mixing
  • Adjusts automatically to variable influent loading
  • Equipment serviceable without basin dewatering
  • Energy efficient (30% more efficient)

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Features & Benefits

Improved function

Cyclical aeration
allows BNR to occur in a single basin without separate anaerobic and anoxic zones

Low Power

Counter current aeration
offers up to 30% energy savings versus conventional aeration systems

Improved function

Rotating bridge concept
utilizes suspended aeration diffusers with mixing baffles to achieve complete mix with or without blowers operating

Reduced Maintenance

Retrievable diffuser design
allows access to aeration diffusers from the bridge allowing maintenance to occur without tank dewatering


GR configuration
reduces footprint required since aeration and clarification are located within the same structure

Improved function

FlexControls strategy
achieves ENR level effluent quality through continuous process monitoring and control


Schreiber CSR GR installation
Preview image for the video "Schreiber CSR".
Schreiber CSR bridge and installation
Schreiber Continuously Sequencing Reactor (CSR)
Schreiber Continuously Sequencing Reactor installation