What Are Sequencing Batch Reactors (SBRs)?

The Sequencing Batch Reactor (SBR) is a wastewater treatment process where wastewater is treated in a single batch reactor to remove undesirable components, then discharged.

This system allows for equalization, aeration, and clarification using only one reactor. To improve performance, multiple batch reactors are used in a set sequence.

SBRs have proven successful in treating both municipal and industrial wastewater, and are ideal for low or unpredictable flow wastewater treatment applications.

What Are The Five Sequential Steps Of Sequencing Batch Reactor SBR Operation?

The functioning of SBRs follows the fill-and-draw principle, which involves 5 steps: Idle, Fill, React, Settle, and Draw.

There are several strategies to operate SBRs during most of these steps, but treatability studies are usually only required for industrial wastewater to determine the best operating sequence.

Municipal wastewater treatment plants do not require such studies as the flowrates and characteristics are predictable, and conservative design methods are applied.

The Idle step is a period between Draw and Fill when treated effluent is removed and influent wastewater is added.

Its length varies and equalization and mixing can be done, depending on the operating strategy.

During Fill, influent wastewater is added and can be done through static fill, mixed fill, or aerated fill.

React is where the biological reactions occur and can be aerated or mixed. Settle is a quiescent stage to allow for settling and the Draw step involves removing the treated effluent using a decanter, which can be floating or fixed.

What Are The Advantages Of SBR?

The advantages of SBR systems include:

Efficient use of space: SBR uses a single reactor basin for all unit operations, compared to a conventional activated sludge plant which requires two basins.

This results in a smaller footprint, with a space of around 100m2/1000m3 only required for SBR tanks.

Flexible operation: SBR offers operational flexibility and control, allowing for efficient removal of organic matter, solids, nitrogen, and phosphorus under varying loading conditions.

This process can also enhance biological phosphorus removal and control the growth of filamentous bacteria.

Cost savings: SBR eliminates the need for final sedimentation tanks, leading to cost savings in the long run.
Modular expansion: SBR allows for simple population increase through modular expansion and cycle operation, providing continuous input and outflow hydraulic profiles.
Versatile: SBR may be used in combination with main clarifiers and power generation arrangements, especially when the VSS:TSS ratio is large.
Eliminates requirement for outflow hydraulic balancing: SBR’s simple modular setup and cycle operation eliminate the need for outflow hydraulic balancing.

What Are The Disadvantages Of SBR Technology?

The drawbacks of SBR systems include:

Higher maintenance due to automated switches/valves compared to traditional activated sludge system.
Need for sufficient basin depth to avoid entrainment of settled solids.
Effluent flow balancing may be required for systems less than 10 MLD for downstream processing.
Risk of process failure in some SBRs due to short circuiting of influent parameters.
Larger aeration system needed compared to traditional activated sludge system.
Need for sophisticated timing units and controls in bigger systems.
Possibility of discharge of floating/settled sludge during decant phase.
Risk of aeration devices becoming plugged during certain cycles depending on aeration system.
Equalization needed post-SBR process for downstream processes such as filtration/disinfection.
Need for clear water depth allowance and limited decant volume to prevent sludge carryover.
All SBR plants must be designed for peak flows, requiring a minimum of two tank system.
High power consumption due to extended aeration.

What Are Sequencing Batch Reactors (SBRs)?