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Aachen, Germany

Buetehorn S.,RWTH Aachen | Carstensen F.,RWTH Aachen | Wintgens T.,RWTH Aachen | Melin T.,RWTH Aachen | And 2 more authors.
Desalination | Year: 2010

Microfiltration processes are frequently used to separate solids from aqueous suspensions. The rejection of suspended matter is facilitated by means of a size exclusion mechanism and is affected by membrane properties, characteristics of the suspension and operating conditions. Therefore, the filtration performance of a single polymeric hollow-fibre membrane was investigated by monitoring the permeate flux decline for a filtration at constant transmembrane pressure (TMP). For these bench-scale experiments, a model suspension consisting of silica particles in xanthan gum solutions was used in order to represent the characteristics of biological suspensions such as activated sludge properly. In the framework of this study, it was confirmed that the permeate flux declines rapidly during the first stage of filtration until an equilibrium of particle deposition and entrainment is reached. The steady-state permeate flux was found to increase with an increase in cross-flow velocity, a decrease in solid concentration, a decrease in particle size (for this ratio of particle to pore diameter) and a decrease in apparent viscosity of the suspension. However, the equilibrium permeate flux was not affected by variations in TMP, which is in agreement with the limiting flux theory. © 2009 Elsevier B.V. All rights reserved.


Buetehorn S.,RWTH Aachen | Volmering D.,Koch Membrane Systems GmbH | Vossenkaul K.,Koch Membrane Systems GmbH | Wintgens T.,RWTH Aachen | And 3 more authors.
Journal of Membrane Science | Year: 2011

The performance of submerged membrane bioreactors (sMBRs) treating municipal or industrial wastewater is significantly affected by hydrodynamic conditions in the membrane unit. These hydraulics are induced by air bubbles injected into the stagnant suspension to remove the cake layer. The aeration sequence consumes the biggest proportion of the overall energy input of sMBRs. Therefore, the objective of this study was to investigate the impact of irregular fiber arrangement on the aeration efficiency. For this purpose, a geometry model based on X-ray computer tomography (CT) scans was developed to map the instantaneous displacement of fibers. The scanned images were processed and implemented into the CFD code as porosity and friction factor matrices. Single-phase simulations show the impact of local fiber arrangement, superficial inlet velocity and solids concentration on the distribution of liquid velocity and turbulent viscosity. Bypass streams were found to reduce the expected cake removal averaged over the corresponding cross-section of the hollow-fiber bundle. Initial multi-phase simulations suggest higher mixture velocities in cross-sectional regions without fibers compared to fiber segments. These results serve as a proof of principle and indicate the potential of this novel CFD approach in module design optimization to reduce aeration requirements. © 2011 Elsevier B.V.


Patent
Koch Membrane Systems Gmbh | Date: 2010-04-16

The invention relates to a membrane filter for water treatment, comprising a head piece including a permeate collecting chamber with a permeate outlet, and at least one fiber bundle made from capillary membranes, which are secured into the head piece with an end that is open towards the permeate collecting chamber and sealed on the opposite end thereof. The head piece contains an air duct to which the mouth piece that protrudes into the fiber bundle is connected with at least one air outlet. At its other end, the fiber bundle terminates in freely movable manner in the untreated water.


Buetehorn S.,RWTH Aachen | Brannock M.,University of New South Wales | Le-Clech P.,University of New South Wales | Leslie G.,University of New South Wales | And 6 more authors.
Separation and Purification Technology | Year: 2012

Membrane bioreactor (MBR) processes for the treatment of municipal and industrial wastewater have been extensively investigated in the past years. For this purpose, synthetic model feeds containing dissolved macromolecules and/or suspended solids were used to allow for a stable and reproducible feed composition. Lab-scale setups equipped with single membrane filaments and pilot plants containing single-bundle configurations were applied. Despite the fact that numerous of the corresponding findings were successfully transferred to large-scale MBR processes, it is expected that the filterability of activated sludge differs significantly from that of common model substances. Moreover, phenomena linked to the highly complex multi-phase flow of liquid, suspended solids and dispersed air bubbles which physically interacts with the membrane filaments make downsizing difficult. Therefore, the overall objective of this study was to evaluate the transferability of lab-scale microfiltration results to large-scale MBR processes. Our investigations have shown that the rheology of a model feed containing silica particles is similar to that of activated sludge with MLSS ≤ 3.5 g/L. A noticeable sub-critical fouling was observed, but was removable by an intensive chemical cleaning using sodium hypochlorite. Lower fouling rates when increasing the aeration frequency with the same net aeration rate were found for both single-fibre and single-bundle tests, but are more pronounced on the larger scale. A macroscopic circulation flow affects the filtration performance of full-scale MBRs, but is difficult to mimic on a smaller scale. Fibre motion enhances the filtration performance, but is insensitive to packing density variations for bundles of up to four filaments. © 2012 Elsevier B.V. All rights reserved.


Patent
Koch Membrane Systems Gmbh | Date: 2010-12-29

The invention relates to a membrane filter for water treatment, comprising a head piece including a permeate collecting chamber with a permeate outlet, and at least one fiber bundle made from capillary membranes, which are secured into the head piece with an end that is open towards the permeate collecting chamber and sealed on the opposite end thereof. The head piece contains an air duct to which the mouth piece that protrudes into the fiber bundle is connected with at least one air outlet. At its other end, the fiber bundle terminates in freely movable manner in the untreated water.

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