scholarly journals Simulation and optimization of airlift external circulation membrane bioreactor using computational fluid dynamics

2014 ◽  
Vol 69 (9) ◽  
pp. 1846-1852 ◽  
Author(s):  
Zhang Qing ◽  
Xu Rongle ◽  
Zheng Xiang ◽  
Fan Yaobo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Membrane Fouling ◽  
Membrane Bioreactor ◽  
Membrane Surface ◽  
Aeration Tank ◽  
Low Velocity ◽  
Simulation And Optimization ◽  
External Circulation ◽  
Membrane Modules

The airlift external circulation membrane bioreactor (AEC-MBR) is a new MBR consisting of a separated aeration tank and membrane tank with circulating pipes fixed between the two tanks. The circulating pipe is called a H circulating pipe (HCP) because of its shape. With the complex configuration, it was difficult but necessary to master the AEC-MBR's hydraulic characteristics. In this paper, simulation and optimization of the AEC-MBR was performed using computational fluid dynamics. The distance from diffusers to membrane modules, i.e. the height of gas–liquid mixing zone (hm), and its effect on velocity distribution at membrane surfaces were studied. Additionally, the role of HCP and the effect of HCP's diameter on circulation were simulated and analyzed. The results showed that non-uniformity of cross-flow velocity existed in the flat-plate membrane modules, and the problem could be alleviated by increasing hm to an optimum range (hm/B ≥ 0.55; B is total static depth). Also, the low velocity in the boundary layer on the membrane surface was another reason for membrane fouling. The results also suggested that HCP was necessary and it had an optimum diameter to make circulation effective in the AEC-MBR.

Comparison of four types of membrane bioreactor systems in terms of shear stress over the membrane surface using computational fluid dynamics

2013 ◽  
Vol 68 (12) ◽  
pp. 2534-2544 ◽  
Author(s):  
N. Ratkovich ◽  
T. R. Bentzen
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Membrane Fouling ◽  
Two Phase Flow ◽  
Membrane Surface ◽  
Cross Flow ◽  
Membrane Bioreactors ◽  
Phase Flow ◽  
Two Phase ◽  
Computational Fluid Dynamics Cfd

Membrane bioreactors (MBRs) have been used successfully in biological wastewater treatment to solve the perennial problem of effective solids–liquid separation. A common problem with MBR systems is clogging of the modules and fouling of the membrane, resulting in frequent cleaning and replacement, which makes the system less appealing for full-scale applications. It has been widely demonstrated that the filtration performances in MBRs can be greatly improved with a two-phase flow (sludge–air) or higher liquid cross-flow velocities. However, the optimization process of these systems is complex and requires knowledge of the membrane fouling, hydrodynamics and biokinetics. Modern tools such as computational fluid dynamics (CFD) can be used to diagnose and understand the two-phase flow in an MBR. Four cases of different MBR configurations are presented in this work, using CFD as a tool to develop and optimize these systems.

scholarly journals Computational fluid dynamics simulation as a tool for optimizing the hydrodynamic performance of membrane bioreactors

RSC Advances ◽  
2019 ◽  
Vol 9 (55) ◽  
pp. 32034-32046 ◽  
Author(s):  
Yan Jin ◽  
Cheng-Lin Liu ◽  
Xing-Fu Song ◽  
Jian-Guo Yu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Membrane Fouling ◽  
Membrane Bioreactor ◽  
Membrane Bioreactors ◽  
Dynamics Simulation ◽  
Hydrodynamic Performance ◽  
Shear Stresses ◽  
Computational Fluid Dynamics Simulation ◽  
Hydrodynamic Properties

The hydrodynamic properties and shear stresses experienced by a membrane bioreactor (MBR) are directly related to its rate of membrane fouling.

Study on the Effects of Shear Strength and Aeration Method on Membrane Fouling in Vertical A/O-MBR Process

2011 ◽  
Vol 374-377 ◽  
pp. 951-955
Author(s):  
Xiu Bo Chen ◽  
Zhi Qiang Liu ◽  
Xu Hua Liu ◽  
Gai Jing Yu ◽  
Zhi Hua Zhang
Keyword(s):  
Membrane Fouling ◽  
Large Scale ◽  
Membrane Bioreactor ◽  
Positive Impact ◽  
Hollow Fiber Membrane ◽  
Membrane Surface ◽  
Slowing Down ◽  
Circulation Velocity ◽  
Membrane Modules ◽  
Function Relationship

Vertical Anoxic/Oxic Membrane Bioreactor (A/O-MBR) was used to treat domestic sewage. PVDF hollow fiber membrane has been used in MBR. According to the comparison of intercommunity between three non-Newtonian fluid models (Bingham model, Ostwald model and Herschel-Bulkley model) and the test data, the Ostwald model was chose to describe the function relationship between shear intensity and aeration amount. In order to initiating a circulation velocity and to enhancing the scour to the MBR, the traditional aeration method was changed in this experiment. Two baffles were placed on both sides of the membrane modules, and aeration heads were scattered between two baffles. The influence of shear intensity and new aeration method to membrane fouling was investigated in this paper at shear intensity of 20s-1, 40s-1, 60s-1 and 80s-1. The result shows that the stronger shear intensity is, the heavier is the MBR been scoured and the smaller is the change of TMP. The best shear intensity was G=60s-1 after considering all factors comprehensively. Finally, the membrane modules were analyzed by scanning electron microscope (SEM). By the SEM pictures we can see that there are some spots on the membrane surface which deposited by fine grains, EPS and SMP. The spots have different size and location, large scale or compact contamination layer can not been found in the pictures. So it indicates that the changing of aeration method and the controlling of shear intensity has a positive impact on slowing down the membrane fouling.

scholarly journals Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics

Membranes ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 111
Author(s):  
Alexander J. Charlton ◽  
Boyue Lian ◽  
Gaetan Blandin ◽  
Greg Leslie ◽  
Pierre Le-Clech
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Shear Rate ◽  
Membrane Surface ◽  
Forward Osmosis ◽  
Transmembrane Pressure ◽  
Channel Height ◽  
Operating Pressure ◽  
Channel Geometry

In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young’s modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.

Computational fluid dynamics modelling of hydraulics and sedimentation in process reactors during aeration tank settling

2006 ◽  
Vol 53 (12) ◽  
pp. 257-264 ◽  
Author(s):  
M.D. Jensen ◽  
P. Ingildsen ◽  
M.R. Rasmussen ◽  
J. Laursen
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Control Method ◽  
Waste Water Treatment ◽  
Aeration Tank ◽  
Cfd Modelling ◽  
Design Changes ◽  
Dynamics Modelling ◽  
Tank Design ◽  
Tank Settling

Aeration tank settling is a control method allowing settling in the process tank during high hydraulic load. The control method is patented. Aeration tank settling has been applied in several waste water treatment plants using the present design of the process tanks. Some process tank designs have shown to be more effective than others. To improve the design of less effective plants, computational fluid dynamics (CFD) modelling of hydraulics and sedimentation has been applied. This paper discusses the results at one particular plant experiencing problems with partly short-circuiting of the inlet and outlet causing a disruption of the sludge blanket at the outlet and thereby reducing the retention of sludge in the process tank. The model has allowed us to establish a clear picture of the problems arising at the plant during aeration tank settling. Secondly, several process tank design changes have been suggested and tested by means of computational fluid dynamics modelling. The most promising design changes have been found and reported.

Exerting ultrasound to control the membrane fouling in filtration of anaerobic activated sludge—mechanism and membrane damage

2008 ◽  
Vol 57 (5) ◽  
pp. 773-779 ◽  
Author(s):  
Xianghua Wen ◽  
Pengzhe Sui ◽  
Xia Huang
Keyword(s):  
Activated Sludge ◽  
Hydroxyl Radicals ◽  
Membrane Fouling ◽  
Membrane Bioreactor ◽  
Chemical Interaction ◽  
Membrane Surface ◽  
Membrane Damage ◽  
Operational Conditions ◽  
Fouling Control ◽  
Cake Layer

In this study, ultrasound was applied to control membrane fouling development online in an anaerobic membrane bioreactor (AMBR). Experimental results showed that membrane fouling could be controlled effectively by ultrasound although membrane damage may occur under some operational conditions. Based upon the observation on the damaged membrane surface via SEM, two mechanisms causing membrane damage by exerting ultrasound are inferred as micro particle collide on the membrane surface and chemical interaction between membrane materials and hydroxyl radicals produced by acoustic cavitations. Not only membrane damage but also membrane fouling control and membrane fouling cleaning were resulted from these mechanisms. Properly selecting ultrasonic intensity and working time, and keeping a certain thickness of cake layer on membrane surface could be effective ways to protect membrane against damage.

scholarly journals Biomass Characteristics and Their Effect on Membrane Bioreactor Fouling

Molecules ◽  
2019 ◽  
Vol 24 (16) ◽  
pp. 2867 ◽  
Author(s):  
Petros K. Gkotsis ◽  
Anastasios I. Zouboulis
Keyword(s):  
Membrane Fouling ◽  
Membrane Bioreactor ◽  
Suspended Solids ◽  
Extracellular Polymeric Substances ◽  
Membrane Surface ◽  
Membrane Resistance ◽  
Soluble Microbial Products ◽  
Gelling Properties ◽  
Microbial Products ◽  
Soluble Part

Biomass characteristics are regarded as particularly influential for fouling in Membrane Bio-Reactors (MBRs). They primarily include the Mixed Liquor Suspended Solids (MLSS), the colloids and the Extracellular Polymeric Substances (EPS). Among them, the soluble part of EPS, which is also known as Soluble Microbial Products (SMP), is the most significant foulant, i.e., it is principally responsible for membrane fouling and affects all fundamental fouling indices, such as the Trans-Membrane Pressure (TMP) and the membrane resistance and permeability. Recent research in the field of MBRs, tends to consider the carbohydrate fraction of SMP (SMPc) the most important characteristic for fouling, mainly due to the hydrophilic and gelling properties, which are exhibited by polysaccharides and allow them to be easily attached on the membrane surface. Other wastewater and biomass characteristics, which affect indirectly membrane fouling, include temperature, viscosity, dissolved oxygen (DO), foaming, hydrophobicity and surface charge. The main methods employed for the characterization and assessment of biomass quality, in terms of filterability and fouling potential, can be divided into direct (such as FDT, SFI, TTF100, MFI, DFCM) or indirect (such as CST, TOC, PSA, RH) methods, and they are shortly presented in this review.

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