Simultaneous loading and draining as a means to enhance efficacy of sequencing biofilm batch reactors

In a sequencing biofilm batch reactor (SBBR) wastewater is treated by bacteria growing on support media packed in the reactor body. In addition, the packing serves as filter media to minimize the concentration of suspended solids in the effluent. Mathematical simulation studies and tracer experiments at lab-scale and semi-full-scale reactors were conducted to investigate the hydraulic retention time distribution function and flow patterns under various hydraulic loading rates. Results obtained reveal that introduction of a new batch of wastewater and withdrawal of the purified water can be executed at the same time without running the risk of polluting the effluent of the reactor with not yet treated wastewater. At a volumetric exchange rate of 68% in the lab-scale SBBR and 90% in the semi-full-scale system, respectively, the front of the tracer remained well underneath the effluent weir. Application of the fill/displacement strategy allows reduction of the cycle time and enhanced exploitation of the reactor volume.