CSBR (Colubris Sequence Batch Reactor)

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A sequencing batch reactor is an activated sludge type wastewater treatment system that can carry out various treatment operations in one tank. A specific volume of wastewater, called a batch, is first screened and pre-treated to remove larger particles and FOG within the water. The reactor is a tank into which air is pumped to ensure that a sufficient supply of oxygen is present for aerobic biochemical processes to occur. The addition of oxygen allows microorganisms to consume dissolved organic matter in the wastewater that are not removed by a screening or settling process. After a specified period of aeration, the wastewater in the reactor is allowed to settle.

The sludge that settles on the bottom now primarily consists of the microorganisms that have fed on the organics in the wastewater. Sequencing batch reactors utilize an activated sludge treatment process. After the treated effluent is discharged, all but a small portion of the sludge, which is rich in microorganisms, is removed from the reactor. This helps quickly re-establish a population of microorganisms within the next batch of wastewater delivered to the reactor, reducing the amount of time necessary for treating each batch. Usually more than one reactor is needed so that while one batch of wastewater is being treated, additional flow can be directed elsewhere. The number of reactors ultimately depends on the expected volume of wastewater flow and the amount of time allowed for treatment of each batch in the reactor.

Sequencing batch reactor process cycles

The operating principles of a batch activated sludge process, or SBR, are characterized into five discrete periods:

  1. Fill: The influent wastewater is distributed throughout the settled sludge through the influent distribution manifold to provide good contact between the microorganisms and the substrate. The influent can be either pumped in or allowed to flow in by gravity. Aeration is started during filling period.
  2. React: During this period aeration continues until complete biodegradation of BOD and nitrogen is achieved.
  3. Settle: Aeration is discontinued at this stage and solids separation takes place leaving clear, treated effluent above the sludge blanket. During this clarifying period no liquids should enter or leave the tank to avoid turbulence in the supernatant.
  4. Decant: This period is characterized by the withdrawal of treated effluent from approximately two feet below the surface of the mixed liquor by the floating solids excluding decanter. This removal must be done without disturbing the settled sludge.
  5. Idle: The time in this stage can be used to waste sludge. The wasted sludge is pumped into an anaerobic digester to reduce the volume of the sludge to be discarded. The frequency of sludge wasting ranges between once every cycle to once every two to three months depending upon system design.

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