Written By: Bryan Martin, PE, ENV SP


A sequencing batch reactor (SBR) is a type of wastewater treatment system that uses a fill-and-draw process to treat wastewater in a series of steps. SBRs are a variation of the activated sludge process, and they offer a number of advantages over traditional activated sludge systems, including:

  1. Smaller footprint
  2. Reduced energy consumption
  3. Greater flexibility in operation
  4. Improved treatment performance


An SBR system consists of a single tank that is operated in four sequential phases:

  1. Fill: The tank is filled with wastewater and the sludge is mixed.
  2. Aerate: Oxygen is added to the tank while mixing, providing treatment.
  3. Settle: The mixing stops and sludge is allowed to settle.
  4. Decant: The supernatant is drawn from the tank, and the excess sludge is wasted.
Phases of the SBR Process


The advantages of SBRs over traditional activated sludge systems include:

Smaller Footprint | SBRs can be much smaller than traditional activated sludge systems, which can save space and reduce capital costs.

Reduced Energy Consumption | SBRs can operate more efficiently than traditional activated sludge systems, which can save energy costs.

Greater Flexibility in Operation | SBRs can be operated more flexibly than traditional activated sludge systems, which can be beneficial for facilities with variable wastewater flows.

Improved Treatment Performance | SBRs can often achieve better treatment performance than traditional activated sludge systems.


As a task order issued by the City of Bartow under the Master Professional Services Agreement, Chastain-Skillman, LLC (CS) was contracted to provide improvements at the City of Bartow Doug Allen Water Reclamation Facility (WRF). The WRF serves all of Bartow and receives flows from Polk County and Eagle Lake. The facility currently processes 2.6 mgd annual average daily flow (AADF).

The plant is expanding its permitted capacity from 4 mgd to 5.33 mgd AADF. Improvements include the construction of two new one-million-gallon sequencing batch reactors, new vertical turbine transfer and effluent pumps, the replacement of multistage centrifugal blowers with four new screw compressors, the conversion of a chlorine gas system to sodium hypochlorite, a new center flow mechanical bar screen, a standby diesel generator, and various solids handling improvements.

During our review, it was determined that the original design did not provide the additional capacity required. An additional basin was added via change order to achieve the required capacity.

CS is currently providing design, construction administration, full-time construction observation, and American Iron & Steel (AIS) and Davis-Bacon certification for this project. Funding for the project is through the State Revolving Fund (SRF).

Aerial Photograph of the Water Reclamation Facility in Bartow, FL


SBRs are a versatile and efficient wastewater treatment technology that offer a number of advantages over traditional activated sludge systems.

If you are considering wastewater treatment processes for your facility, SBRs should be a top consideration. If you are interested in learning more about SBRs, please contact the Chastain-Skillman team.

Interested in services? Give us a shout! ↓

Let’s start the conversation.

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About the Author

Bryan Martin, PE, ENV SP has over 17 years of experience specializing in water and wastewater treatment plant and pipeline design, including site assessment, site planning, permitting, and construction phase services. Mr. Martin has served as a design engineer, engineer of record, and project manager for projects including water and wastewater treatment, pump stations, and pipelines.

About Chastain-Skillman

CS is a leading engineering firm headquartered in Lakeland, FL, with satellite offices in Orlando, FL, and Nashville, TN. Established in Lakeland in 1950, our company provides Civil Engineering, Water/Wastewater Engineering, Land Surveying, Geology/Hydrogeology, and Construction Management/Inspection services.

At CS, we treasure our role in creating thriving communities, always respecting the impact our work has on their foundations and their futures. For more information, visit


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