CFD as a Tool to Optimize Aeration Tank Design and Operation

Anna M. Karpinska, John Bridgeman
2018 Journal of environmental engineering  
Citation: Karpinska AM and Bridgeman J (2018) CFD as a tool to optimize aeration tank design and operation. Journal of Environmental Engineering 144(2). ABSTRACT 8 In a novel development on previous computational fluid dynamics (CFD) studies, the work 9 reported here employed an Eulerian two-fluid model with the shear stress transport (SST) 10 − turbulence closure model and bubble interaction models to simulate aeration tank 11 performance at full scale and to identify process performance
more » ... s performance issues resulting from design 12 parameters and operating conditions. The current operating scenario was found to produce a 13 fully developed spiral flow. Reduction of the air flow rates to the average and minimum 14 design values led to a deterioration of the mixing conditions and formation of extended 15 unaerated fluid regions. The influence of bubble-induced mixing on the reactor performance 16 was further assessed via simulations of the residence time distribution (RTD) of the fluid. 17 Internal flow recirculation ensured long contact times between the phases; however, hindered 18 axial mixing and the presence of dead zones were also identified. Finally, two optimization 19 schemes based on modified design and operating scenarios were evaluated. The adjustment 20 of the air flow distribution between the control zones led to improved mixing and a 20 % 21 improvement to the mass transfer coefficient. Upgrading the diffuser grid was found to be an 22 expensive and ineffective solution, leading to worsening of the mixing conditions and 23 yielding the lowest mass transfer coefficient compared to the other optimization schemes 24 studied. 42 modelling of WWTPs has been recognized as a powerful tool, providing detailed knowledge 43 of the unit processes, as well as reactor behaviour in response to varying input conditions. 44 Over the last two decades the fast growth in computational power and commercialization of 45 advanced software suites for the solution and visualization of complex flows has contributed 46 to the successful spread of computational fluid dynamics (CFD) in wastewater engineering 47 (Karpinska and Bridgeman 2016). 48 A key advantage of CFD-aided modelling of aeration tanks over the traditional and relatively 49 well-established Activated Sludge Models (ASM) is its capacity to predict the actual flow tank are suspected to have a significant impact on the oxygen transfer and the reaction 495 yield, and thus the treatment process performance. 496  Considering the optimization scenarios investigated, adjustment of the air flow 497 distribution between the control zones led to improved mixing and reduction of the 498 dead volumes, and furthermore yielded the highest 20 of 67 d -1 in Z1 499 outperforming the original design scenario by 20 %. The more capital intensive 500 optimization scenario related to upgrade of the diffuser grid provided a more uniform reactors: simulation and experiment." Chem. Pap. -Chem. Zvesti, 54(6A), 361-369. 595 Glover, G. C., Printemps, C., Essemiani, K., and Meinhold, J. (2006). "Modelling of 596 wastewater treatment plants -how far shall we go with sophisticated modelling
doi:10.1061/(asce)ee.1943-7870.0001307 fatcat:jutlfoksive2zhgvyyeoyyf67a