An experimental study on the effect of spacer on concentration polarization in a long channel reverse osmosis membrane cell

This study was to experimentally investigate the performance and organic fouling behaviour in a 1-m long RO membrane channel with or without spacer for desalting. It was found that local permeate flux distributed heterogeneously along the long membrane channel without a spacer inserted due to exponential growth of concentration polarization, which also resulted in decreasing salt rejection and increasing organic fouling along the membrane channel in the downstream direction. This heterogeneity could be lessened by inserting a spacer into the channel, which mitigated concentration polarization due to the enhanced turbulence caused by a spacer, especially at the downstream portion of the channel. However, in the upstream of the channel, inserting a spacer exerted an additional vertical resistance which might counteract the effect of concentration polarization mitigation by a spacer and caused a lower permeate flux. This suggests that it is necessary to consider the integral effect of spacer for designing an RO membrane module and an overall RO system in order to prevent extra resistance, reduce concentration polarization and membrane fouling.

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Organic fouling development in a long channel RO membrane cell

Water Science & Technology Water Supply ◽

10.2166/ws.2010.180 ◽

2010 ◽

Vol 10 (4) ◽

pp. 672-678 ◽

Cited By ~ 1

Author(s):

H. Mo ◽

H. Y. Ng

Keyword(s):

Organic Compound ◽

Salt Concentration ◽

Concentration Polarization ◽

Research Work ◽

Membrane Channel ◽

Charge Screening ◽

Organic Fouling ◽

Ro Membrane ◽

Long Channel ◽

Membrane Cell

This study was to experimentally investigate organic fouling development in a 1-m long RO membrane channel using alginate as a model organic compound. Five parallel local permeate fluxes with a distance interval of 20 cm along the channel were monitored continuously during the organic filtration tests. It was found that organic fouling became more severe towards the outlet of the channel. This might be mainly attributed to the salt concentration polarization formation along the channel. The higher salt concentration downstream increased the interactions involved in organic fouling such as charge-screening and alginate-calcium bridging, which intensively promoted organic fouling formation in the downstream. A higher feed flow was a common option to mitigate fouling at most lab-scale RO research work, but not the case in this long membrane channel. A higher feed flow changed the organic fouling development profile along the channel, but would not eliminate organic fouling.

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Organic Fouling Impact in a Direct Contact Membrane Distillation System Treating Wastewater: Experimental Observations and Modeling Approach

Membranes ◽

10.3390/membranes11070493 ◽

2021 ◽

Vol 11 (7) ◽

pp. 493

Author(s):

Amine Charfi ◽

Fida Tibi ◽

Jeonghwan Kim ◽

Jin Hur ◽

Jinwoo Cho

Keyword(s):

Particle Size ◽

Membrane Fouling ◽

Direct Contact ◽

Feed Solution ◽

Membrane Distillation ◽

Mixed Solution ◽

Permeate Flux ◽

Direct Contact Membrane Distillation ◽

Organic Fouling ◽

Specific Cake Resistance

This study aims to investigate the effect of operational conditions on organic fouling occurring in a direct contact membrane distillation (DCMD) system used to treat wastewater. A mixed solution of sodium alginate (SA) and bovine serum albumin (BSA) was used as a feed solution to simulate polysaccharides and proteins, respectively, assumed as the main organic foulants. The permeate flux was observed at two feed temperatures 35 and 50 °C, as well as three feed solution pH 4, 6, and 8. Higher permeate flux was observed for higher feed temperature, which allows higher vapor pressure. At higher pH, a smaller particle size was detected with lower permeate flux. A mathematical model based on mass balance was developed to simulate permeate flux with time by assuming (i) the cake formation controlled by attachment and detachment of foulant materials and (ii) the increase in specific cake resistance, the function of the cake porosity, as the main mechanisms controlling membrane fouling to investigate the fouling mechanism responsible of permeate flux decline. The model fitted well with the experimental data with R2 superior to 0.9. High specific cake resistance fostered by small particle size would be responsible for the low permeate flux observed at pH 8.

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Topology Optimization of Spacers for Maximizing Permeate Flux on Membrane Surface in Reverse Osmosis Channel

Volume 5: 37th Design Automation Conference, Parts A and B ◽

10.1115/detc2011-48933 ◽

2011 ◽

Author(s):

Seungjae Oh ◽

Semyung Wang ◽

Minkyu Park ◽

Joonha Kim

Keyword(s):

Topology Optimization ◽

Pressure Drop ◽

Reverse Osmosis ◽

Membrane Surface ◽

Design Development ◽

Permeate Flux ◽

Membrane Channel ◽

Initial Attempt ◽

Membrane Surfaces ◽

Ro Membrane

The objective of this study is to design spacers using fluid topology optimization in 2D crossflow Reverse Osmosis (RO) membrane channel to improve the performance of RO processes. This study is an initial attempt to apply topology optimization to designing spacers in RO membrane channel. The performance was evaluated by the quantity of permeate flux penetrating both upper and lower membrane surfaces. A coupled Navier-Stokes and Convection-Diffusion model was employed to calculate the permeate flux. To get reliable solutions, stabilization methods were employed with standard finite element method. The nine reference models which consist of the combination of circle, rectangular, triangle shape and zigzag, cavity, submerge configuration of spacers were simulated. Such models were compared with new model designed by topology optimization. The permeate flux at both membrane surfaces was determined as an objective function. In addition, permissible pressure drop along the channel and spacer volume were used as constraints. As a result of topology optimization as the permissible pressure drop changes in channel, characteristics of spacer design development was founded. Spacer design based on topology optimization was reconstructed to a simple one considering manufactuability and characteristics of development spacer design. When a simplified design was compared with previous 9 models, new design has a better performance in terms of permeate flux and wall concentration at membrane surface.

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Critical design considerations for harnessing reverse osmosis processes in water/wastewater treatment

Water Science & Technology Water Supply ◽

10.2166/ws.2006.950 ◽

2006 ◽

Vol 6 (6) ◽

pp. 61-70 ◽

Cited By ~ 1

Author(s):

L.F. Song ◽

K.G. Tay ◽

G. Singh

Keyword(s):

Mass Transfer ◽

Membrane Fouling ◽

Transfer Rate ◽

Mass Transfer Rate ◽

Full Scale ◽

Driving Pressure ◽

Feed Water ◽

Permeate Flux ◽

Membrane Channel ◽

Permeable Membrane

In this paper, the performance of the full-scale RO process with highly permeable membranes and the governing mechanisms were carefully studied. It was found that the performance of a full-scale RO process could be controlled by two possible mechanisms, namely mass transfer rate and thermodynamic limitations. Under relatively low driving pressure, it was controlled by mass transfer rate (water flux) of the membrane. However, with the highly permeable membrane, it is possible that the performance is limited by the thermodynamic limitation, in which the osmotic pressure becomes equal to the driving pressure inside of the membrane channel. A process controlled by thermodynamic limitation is an extremely case of the hydraulic imbalance problem. When it occurs, it means part of the membranes in the processes do not contribute to permeate production. More complicated are situations in the intermediate pressure range, in which both mechanisms contribute to, but none of them can dominate, the performance of the process. Some innovative concepts and theories on the performance of the full-scale RO processes were developed. These concepts and theories may provide better qualitative explanations for the behaviors often observed in the full-scale RO processes. A better quantitative simulations or predictions of the performance of the process were developed upon these concepts and theories. Experiments were carried out on a pilot membrane process of 6 m membrane channel to imitate the performance of the full-scale RO under various conditions. The experimental performance data were compared with theoretical simulations and excellent agreement was obtained. Another focus of this current study was on characterization and modeling of membrane fouling in the full-scale RO process. Colloidal fouling experiments were conducted to study the fouling potential of feed water and a new fouling indicator was proposed. The indicator can be directly used in the mathematical model to simulate fouling development in the full-scale RO processes. Model simulations showed that under certain condition (thermodynamic restriction), the recovery or average permeate flux of a full-scale RO process would maintain a constant value even membrane fouling was taking place. Experimental verification of the simulation results is currently under way. With the new developments and findings in this area, methods or protocols for optimization of full-scale processes of the highly permeable RO membranes were suggested.

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Comparison of reverse osmosis membrane fouling characteristics in full-scale leachate treatment systems with chemical coagulation and microfiltration pre-treatments

Water Science & Technology ◽

10.2166/wst.2014.468 ◽

2014 ◽

Vol 71 (4) ◽

pp. 580-587 ◽

Cited By ~ 6

Author(s):

Weerapong Rukapan ◽

Benyapa Khananthai ◽

Thirdpong Srisukphun ◽

Wilai Chiemchaisri ◽

Chart Chiemchaisri

Keyword(s):

Reverse Osmosis ◽

Membrane Fouling ◽

Full Scale ◽

Permeate Flux ◽

Leachate Treatment ◽

Chemical Coagulation ◽

Cake Layer ◽

Ro Membrane ◽

Pre Treatment ◽

Fouling Characteristics

Fouling characteristics of reverse osmosis (RO) membrane with chemical coagulation and microfiltration (MF) pre-treatment were investigated at full-scale leachate treatment systems. In chemical coagulation pre-treatment, solid separation from stabilized leachate was performed by ferric chloride coagulation followed by sand filtration. Meanwhile, MF pre-treatment and the RO system utilized direct filtration using a 0.03 µm membrane without chemical addition. MF pre-treatment yielded better pollutant removals in terms of organics and nitrogen. The study on effect of pre-treatment on RO membrane fouling revealed that accumulated foulant on the RO membrane in MF pre-treatment was significantly lower than that of chemical coagulation. Nevertheless, NaOH cleaning of the fouled RO membrane after chemical coagulation pre-treatment could better recover its permeate flux, thus suggesting that the formation of a loose-structure cake layer by chemical coagulation pre-treatment could allow effective penetration of chemical cleaning and detachment of foulant layer from the membrane surface.

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Novel Spacer Design Using Topology Optimization in a Reverse Osmosis Channel

Journal of Fluids Engineering ◽

10.1115/1.4025680 ◽

2013 ◽

Vol 136 (2) ◽

Cited By ~ 4

Author(s):

Seungjae Oh ◽

Semyung Wang ◽

Minkyu Park ◽

Joon Ha Kim

Keyword(s):

Topology Optimization ◽

Reverse Osmosis ◽

Membrane Surface ◽

Navier Stokes ◽

Permeate Flux ◽

Membrane Channel ◽

Reference Models ◽

Membrane Surfaces ◽

Ro Membrane ◽

And Performance

The objective of this study is to design spacers using topology optimization in a two-dimensional (2D) crossflow reverse osmosis (RO) membrane channel in order to improve the performance of RO processes. This study is the first attempt to apply topology optimization to designing spacers in a RO membrane channel. The performance was evaluated based on the quantity of permeate flux penetrating both the upper and lower membrane surfaces. Here, Navier–Stokes and convection-diffusion equations were employed to calculate the permeate flux. The nine reference models, consisting of combinations of circle, rectangle, and triangle shapes and zig-zag, cavity, and submerged spacer configurations were then simulated using finite element method so that the performance of the model designed by topology optimization could be compared to the reference models. As a result of topology optimization with the allowable pressure drop changes in the channel, characteristics required of the spacer design were determined. The spacer design based on topology optimization was then simplified to consider manufacturability and performance. When the simplified design was compared to the reference models, the new design displayed a better performance in terms of permeate flux and wall concentration at the membrane surface.

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Numerical study of concentration polarization in a rectangular reverse osmosis membrane channel: Permeate flux variation and hydrodynamic end effects

Journal of Membrane Science ◽

10.1016/j.memsci.2007.07.003 ◽

2007 ◽

Vol 303 (1-2) ◽

pp. 140-153 ◽

Cited By ~ 75

Author(s):

Eric Lyster ◽

Yoram Cohen

Keyword(s):

Reverse Osmosis ◽

Concentration Polarization ◽

Numerical Study ◽

Reverse Osmosis Membrane ◽

Permeate Flux ◽

Flux Variation ◽

Membrane Channel ◽

End Effects

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FFD Analysis for the Effect of Fouling on the Permeate Flux in High-Pressure Membranes

European Journal of Engineering Research and Science ◽

10.24018/ejers.2019.4.1.1061 ◽

2019 ◽

Vol 4 (1) ◽

pp. 12-16

Author(s):

Hisham A. Maddah

Keyword(s):

High Pressure ◽

Salt Concentration ◽

Membrane Fouling ◽

Concentration Polarization ◽

Water Flux ◽

Side Surface ◽

Permeate Flux ◽

Salt Accumulation ◽

Initial Salt ◽

Negative Flux

Porous high-pressure membranes have been widely used for both brackish water and seawater desalination. However, fouling (concentration polarization) extensively reduces permeate flux in high-pressure membranes such that reverse osmosis (RO) and/or nanofiltration (NF). In this study, we have attempted to understand the effect of membrane fouling on the permeate water flux by modeling the salt concentration profile within a membrane of interest. A parabolic (or diffusion) partial differential equation was used to describe the change in salt concentration inside the membrane. Subsequently, the PDE equation was solved numerically, under certain assumptions, by using forward finite difference (FFD) explicit method. It was found that salt accumulation occurs at the membrane feed-side surface and there was a noticeable decrease in water flux as fouling increased. For waters with an initial salt concentration of 10000 ppm (NaCl) and with an average diffusivity of , results showed that both RO/NF would have flux rates of 74.9, 67.4, 22.5, 0, –37.4, –74.9 LMH for the feed-side surface concentrations 0, 1000, 7000, 10000, 15000 and 20000 ppm, respectively, where negative flux indicates a back-flow scenario.

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