Gas–liquid flow in a 2D column: Comparison between experimental data and CFD modelling

Effect of aeration on oxygen transfer characteristics in integrated wastewater treatment systems utilizing mass transfer model and computation fluid dynamics methods

This paper investigates the aeration and oxygen transfer characteristics within the aeration tank of an integrated wastewater treatment system (IWTS) using Computational Fluid Dynamics coupled with Population Balance Model and oxygen transfer model. The findings suggest that increasing the air flow rate significantly enhances the oxygen transfer rate, albeit at a decreasing rate of growth. The oxygen overall mass transfer coefficient is primarily influenced by the interfacial area per unit volume and to a lesser by the oxygen mass transfer coefficient (kL). A strong positive correlation is found between turbulence intensity and kL, which, along with dissolved oxygen distribution, confirms the critical role of turbulence in the oxygen transfer process. For small-scale IWTS, an air flow rate of 30 L/min may be the optimal choice.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5 mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

Optimization of membrane unit location in a full-scale membrane bioreactor using computational fluid dynamics

The location of membrane units in the membrane tank is a key factor in the construction of a full-scale membrane bioreactor (MBR), as it would greatly affect the hydrodynamics in the tank, which could in turn affect the membrane fouling rate while running. Yet, in most cases, these units were empirically installed in tanks, no theory guides were currently available for the design of a proper location. In this study, the hydrodynamics in the membrane tank of a full-scale MBR was simulated using computational fluid dynamics (CFD). Five indexes (i_Lu, i_La, i_Lb, i_Lint, i_Lw) were used to indicate the unit location, and each of them was discussed for their individual impact on the risk water velocity (v_0.05) in the membrane unit region. An optimal design with all the indexes equaling 0.6 was proposed, and was found to have a promotion of 146.9% for v_0.05.

Hydraulic optimization of membrane bioreactor via baffle modification using computational fluid dynamics

Baffles are a key component of an airlift membrane bioreactor (MBR), which could enhance membrane surface shear for fouling control. In order to obtain an optimal hydraulic condition of the reactor, the effects of baffle location and size were systematically explored in this study. Computational fluid dynamics (CFD) was used to investigate the hydrodynamics in a bench-scale airlift flat sheet MBR with various baffle locations and sizes. Validated simulation results showed that side baffles were more effective in elevating membrane surface shear than front baffles. The maximum average shear stress was achieved by adjusting baffle size when both front and side baffles were installed. With the optimized baffle configuration, the shear stress was 10-30% higher than that without baffles at a same aeration intensity (specific air demand per membrane area in the range of 0-0.45m(3)m(-2)h(-1)). The effectiveness of baffles was particularly prominent at lower aeration intensities.