CFD simulation of a novel anaerobic-anoxic reactor for biological nutrient removal: Model construction, validation and hydrodynamic analysis based on OpenFOAM®

Abstract

AnoxAn is a novel multi-environment reactor for biological nutrient removal (BNR) from wastewater. Although its biological efficacy has been demonstrated on a pilot scale, hydrodynamics is observed to significantly affect the performance of AnoxAn. To study its complex hydraulic behaviour, a model based on Computational Fluid Dynamics 3D (CFD) is constructed using the OpenFOAM® open source toolbox and validated by experimental tests of Residence Time Distribution (RTD). Reactor elements represent a key factor in the modelling process. In this sense, the impeller of the anoxic zone is modelled as a flat disk, and the baffle after the anoxic zone as a porous media. According to CFD model simulations, stagnant, short-circuit zones and mixing quality are established and quantified. Finally, the influence on the hydrodynamics of reactor elements is also evaluated. The results of this detailed hydrodynamic analysis will form the basis for the design and optimization of scalable AnoxAn configurations.

Simulation based investigation of 2D soft-elastic reactors for better mixing performance

“…It is known that baffles (flow-directing or obstructing panels used in some industrial containers for mixing efficiency improvement) can promote mixing in an agitated vessel (Hashimoto et al, 2011), but whether baffles can influence mixing behaviors in such a soft-elastic system as well as how to configure baffle size and locations for better mixing performance are still open questions. This work implements baffles by a porous media modeling approach, the method was also adopted by Blanco-Aguilera et al (2020) to account for the effects of baffles in an anaerobic-anoxic reactor.…”

Hydrodynamic optimization of multi-environment reactors for biological nutrient removal: A methodology combining computational fluid dynamics and dimensionless indexes

“…One possible hydrodynamic modelling approach is the development of the widely used compartment-based models such as the tank-inseries and the dispersion model (Levenspiel, 1999). However, the black-box nature of this kind of models does not provide any information regarding spatial flow or concentration distribution (Plascencia-Jatomea et al 2015;Qi et al 2013;Blanco-Aguilera et al 2020). Moreover, in general they are only useful for specific operational conditions, not allowing to test the effect of changing any geometrical parameter of the studied reactor.…”

“…Their complex hydraulic behaviour generates non-ideal flows that reduces the hydrodynamic performance, and in consequence, the biological efficiency. To our knowledge, there are only few studies based on CFD for evaluation and optimization of the hydrodynamics of multi-environment reactors (Calder et al 2013;Blanco-Aguilera et al 2020). Calder et al (2013) changed a baffle geometry to assess the hydraulic behaviour of the aerobic-anoxic BioCAST reactor based on velocity fields, but did not use a systematized methodology of hydraulic indexes.…”

“…Calder et al (2013) changed a baffle geometry to assess the hydraulic behaviour of the aerobic-anoxic BioCAST reactor based on velocity fields, but did not use a systematized methodology of hydraulic indexes. Blanco-Aguilera et al (2020) performed a comprehensive analysis assessing the presence of dead zones, channelling and studying the mixing efficiency and hydrodynamic influence of some feature elements (deflector and baffles) in the anaerobic-anoxic AnoxAn reactor, but did not deepen into a holistic and systematic hydrodynamic optimization. At this respect, the need for comprehensive hydrodynamic analysis to carry out the geometric optimization and propose other reactor configurations applicable on a large scale has been pointed out (Díez-Montero et al 2019;Blanco-Aguilera et al 2020).…”

Scaling up microreactors for kilogram‐scale synthesis of piperacillin: Experiments and computational fluid dynamics simulations

“…A global analysis of the flow field is crucial to the design and amplification of most reactor types. Using computational fluid dynamics (CFD) simulations to visualize the stream field and concentration distribution inside a unit offers advantages of short processing time, low cost, and global visualization, which are important for the structure optimization 26,27 of the mixing-reaction devices and result in excellent consistence with experiments. 28,29 The porous media model (PMM) 30 was applied to simplify the membrane dispersion simulation in this study, and the parameters of porosity, viscosity resistance, and inertia resistance were set in this model.…”