Flow-Paced Batch Operation


Flow-paced batch operation is generally preferable to time-paced batch or continuous inflow systems. Under a flow-paced batch system, a plant receives the same volumetric loading and approximately the same organic loading during every cycle. The SBR basin already has stabilized supernatant in it, which dilutes the batch of incoming influent.

Under a time-paced mode, each basin receives different volumetric and organic loading during every cycle, and the plant is not utilizing the full potential of this treatment method—the ability to handle variable waste streams. After each loading, the plant faces a whole new set of treatment conditions, making the operator’s job more difficult.

Time-paced operation (if you are not adjusting the cycle time) can lead to under-treated effluent. A plant that receives heavy morning loadings, with a flow pattern that drops off after the first cycle, must deal with two different biologies in the basin unless adjustments are made to the cycle time. For example, one basin could be receiving an early morning load, which has a high organic and volumetric loading. The second basin could be receiving the afternoon loading, which has a lower organic and volumetric loading. Unless the time cycle is adjusted, it becomes difficult to operate under these conditions because the operator is essentially running two separate plants.

Another problem with time-paced operation is that if the plant is required to denitrify, it may not bring in an adequate carbon source needed for the bacteria to strip oxygen from the nitrate. This scenario would be especially problematic during periods of low flow.
For an SBR to be effective, the plant must have proper monitoring, allow operators to
adjust the cycle time, and have knowledgeable operators who are properly trained to make
the necessary adjustments to the cycle.

lesson from the field


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