CFD-aided modelling for hydrodynamic analysis of biological reactor

The performance testing of treatment plants is of great concern in the field of environmental engineering, especially regarding the management of wastewater plants devoted to treatment and reuse. The efficiency of the treatment process is strictly related to both biological kinetics and hydrodynamics, influencing each other. In fact, the actual hydrodynamic behaviour of a biological reactor can deviate significantly from the design hypotheses, leading to hydraulic defects such as formation of dead volume and bypass. These problems exert a strong influence on the biological process and therefore affect the treatment efficiency of the plant. The Residence Time Distribution (RTD) analysis is commonly adopted for quantifying the type and amount of the functioning deficiencies affecting the process. However, to address the corrective intervention, these deficiencies should be localized by integrating RTD method with Computational Fluid Dynamics (CFD). This paper shows the early studies of a wider research project aiming at developing a standardized method combining RTD and CFD techniques for mitigating or eliminating functioning defects in biological reactors. An application of CFD-aided modelling for assessing hydrodynamic behaviour of an activated sludge (AS) pilot plant is illustrated. The obtained results are compared with experimental results from RTD analysis, showing how the CFD model can help supporting design of new facilities and the optimization or retrofitting of existing facilities for wastewater treatment.