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 mgl phosphorous with chemicals and additional use of the 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.


  • Sequential BNR in a single basin
  • Energy efficient (30% more efficient)
  • Separation of aeration and mixing
  • Operator-friendly process
  • Adjusts automatically to variable influent loading
  • Engineered and built for long life
  • Equipment serviceable without basin dewatering
  • Proven system backed by a proven company


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