OPERATING STRATEGIES FOR VARIABLE FLOW SEQUENCING BATCH REACTORS

Sequencing Batch Reactors (SBR) are variable volume, non-steady state, suspended growth biological wastewater treatment reactors. Their treatment process is characterized by a repeated treatment cycle consisting of a series of sequential process phases; fill, react, settle, decant, and idle. The design and operation of an SBR must take into consideration; 1) the biological process requirement for treating the influent wastewater, 2) the hydraulic requirement to enable the throughput of the water through the reactor without compromising the quality of biological treatment. During routine operation, the priority between the process and hydraulic consideration can change depending on the influent flow rate and its rate of change. The importance of the interaction between these considerations will vary depending on the fill strategy, and the cycle time control strategy. Where flow proportional cycle times are utilised to optimise the treatment process, the operating strategy must be capable of accurately adjusting the inter-cycle phase times to prevent loss of biological treatment, or volumetric capacity. This paper considers various operating strategies that are required to prevent loss of treatment capacity under high flow rates or where there is a significant rate of change in the influent flow rate. Key words: Cycle time; flow proportional; hydraulic consideration; process consideration; variable flow