| Decanters used for sequencing batch reactor (SBR) were systematically studied through analyzing their structure, operation principle, hydraulic characteristics and models for automatic control. The criterions for decanter selection were brought out and the developing tendency of decanters was predicted.With the evolution of SBR process, various types of decanters were developed. Rotary decanters were driven by linear electromechanical actuators. Floating decanters were operated to control effluent drainage with valves while keeping balance between gravity and floatation. Siphon decanters were operated by inducing the siphon pipe to discharge with airlift effect.Hydraulic characteristics and performance of rotary decanter and siphon decanter were studied respectively. As for rotary decanters, their effluents were typical weir flows and the overflow capacities were related to height (the distance between weir and water surface). As for siphon decanters, their drainage capacities were related to the level differences between inlet and outlet.The rugged construction of rotary decanter was fabricated of stainless steel. The seals and bearing assembly were tolerant to the harsh conditions. The structure of vertical traveling decanters and siphon decanters were also analyzed. The key points of design and fabrication of multi-weir decanter were made out.Automatic control model and hydraulic performance were studied. Three control models were compared and the model of PLC + Frequency Converter was recommended. Synchronization of the operation for two or more decanters in one reactor was investigated.The criterions for decanter selection were put forward after the case study ofdecanters. As for a small-scale reactor, no-power-driven decanters were recommended. As for a large-scale reactor, rotary decanters driven by motors were recommended.The future development of decanter was discussed and the decanters should be modified in the automatic control, scum float removing and powerless requirement.
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