Sequential Batch Reactor

Overview :

The biological stage of the wastewater treatment plant is designed as a “sequenced batch reactor “(SBR) and represents one of the most modern treatment concepts being used for sewage treatment plants. The central characteristics of the biological stage can be described as followed:

• The process takes place in one or more SBR-reactors, depending on the chosen plant design.
• Each SBR-reactor operates according to the activated sludge process, but with a modified operation-concept, which uses the reactor as an aeration tank as well as a clarification system.
• Due to the SBR process, an extensive removal of dissolved organic substances from the wastewater can be achieved by nitrification and denitrification as well as by the removal of phosphorus.
• The special characteristic of the SBR process is due to the fact that the individual process phases of an activated sludge plant (aerobic, anoxic and anaerobic, mixture as well as sedimentation) run along the time axis in one single tank. Thus, the times of the individual process stages are adapted to the load and thus the required effluent parameters can be maintained with security.

The purification of wastewater by SBR process has compared to traditional continuous flow process, a number of economic and technical advantages:

• Rugged cleaning performance even with fluctuating hydraulic and organic load
• Significant minimized footprint compared with conventional wastewater treatment plants with lower costs for civil works
• Technically mature and widely used method
• Economical operation of the plant
• Possible modular configuration of the plant adjusted to the current impact load
• Simple tank construction and geometry
• Excellent treatment performances due to Nitrification, Denitrification, Phosphate elimination and Disinfection depending on the requirements
• High operation safety / process stability
• Easy maintenance

The standard SBR-process can be explained by the following illustrations:

Treatment Process – working Principal

Fill-up phaseMixing phaseBiological treatment phaseSettling phaseDischarging phase

A cycle starts with the filling (Phase 1) via the feeding pump the wastewater free of rejects is fed from the buffer tank into the SBR- tank. The filling occurs in batches, till the maximum filling level of Hw (max) is reached.

Along with the feeding the denitrification is initiated (Phase 2), while the „new “wastewater” is mixed with the available activated sludge volume. This is the Anoxic phase with the optimal ratio between carbon and nitrogen. Denitrification.

Following the time limited denitrification phase the plant is changing to operation mode Aeration and Mixing (Phase 3). The required oxygen for reduction of carbon and the nitrification is thus entered through aeration. The aeration care for an optimal air entry and the mixing of wastewaters.

After the completion of aeration and mixing phase, there starts the sedimentation phase (Phase 4), while the activated sludge is sedimented. This phase lasts about 1,0 to 1,5h. The activated sludge is settling down in the treatment basin. A perfect separation of the activated sludge and the cleared water is obtained.

Within the sedimentation phase there is built a clear water zone, which is evacuated in the following clear water discharge phase (Phase 5). The discharge phase is concluded with the reach of filling level Hw(min) in the SBR tank. To the end of the cycle a defined part of the excess sludge will be pumped out from the SBR into the preliminary sedimentation respective into a provided sludge storage tank. The Cycle is ready to start again.