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Lutchmiah K.,KWR Watercycle Research Institute | Lutchmiah K.,Technical University of Delft | Harmsen D.J.H.,KWR Watercycle Research Institute | Wols B.A.,KWR Watercycle Research Institute | And 3 more authors.
Journal of Membrane Science | Year: 2015

Forward osmosis (FO) processes, due to internal concentration polarisation, are limited with regards to flux. Improved flux performance will allow FO to compete with fluxes achieved by hydraulically driven membrane processes. Pressure assisted osmosis (PAO) is proposed to enhance FO performance, by adding hydraulic pressure (0.1-0.8. bar) on the feed side. An FO mass transport model (active layer to feed side orientation) incorporating pressure was developed to describe the fluxes in PAO. Continuous and discontinuous PAO operations on laboratory scale were proposed and evaluated using draw solutions equivalent to 24. bar osmotic pressure. The fluxes increased with increasing hydraulic feed pressures for all PAO experiments, including activated sludge feeds, owing to the increased driving force and membrane deformation. Discontinuous PAO was found to have an adverse effect on the salt fluxes, due to the subsequent pressure release. This study emphasizes the benefits of PAO for use in innovative membrane systems, while illustrating the importance of developing more rigid membranes and better support designs. © 2014 Elsevier B.V.

Oo M.H.,National University of Singapore | Oo M.H.,PUB Consultants Pte Ltd. | Ong S.L.,National University of Singapore
Journal of Membrane Science | Year: 2010

Boron removal by reverse osmosis (RO) membranes has been improved through raised pH and its removal mechanism was suggested as either charge repulsion or size exclusion. In the present study, boron removal by different RO membranes at different salinities was investigated along with their respective zeta potentials. While the impact of salinity on zeta potential of RO membranes was similar, its impact on boron removal by brackish water reverse osmosis (BWRO) membranes was different from that by SWC4+ and ESPAB membranes. RO membranes used in this study showed negative zeta potential value at high pH. However, at pH 9 and with higher salinity, their zeta potentials shifted to positive values. Boron removal by BWRO membranes decreased with increasing salinity at pH 9. The shift of zeta potential towards positive values at higher salinity suggested that charge repulsion mechanism became less dominant. Boron removal by ESPAB and SWC4+ decreased initially when NaCl concentration was increased towards 2000 mg/L at pH 9. However, removal increased slowly when NaCl was beyond 2000 mg/L. This observation suggested that boron removal by these membranes at low salinity was partially contributed by charge repulsion mechanism. At higher salinity, size exclusion could be the dominant factor for boron removal by SWC4 and ESPAB. © 2010 Elsevier B.V. All rights reserved.

Qin J.-J.,PUB Consultants Pte Ltd. | Oo M.H.,PUB Consultants Pte Ltd. | Kekre K.A.,PUB Consultants Pte Ltd. | Liberman B.,IDE Technologies
Journal of Membrane Science | Year: 2010

The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation. © 2009 Elsevier B.V. All rights reserved.

Cornelissen E.R.,KWR Watercycle Research Institute | Harmsen D.,KWR Watercycle Research Institute | Beerendonk E.F.,KWR Watercycle Research Institute | Qin J.J.,PUB Consultants Pte Ltd. | And 3 more authors.
Water Science and Technology | Year: 2011

An innovative osmotic membrane bioreactor (OMBR) is currently under development for the reclamation of wastewater, which combines activated sludge treatment and forward osmosis (FO) membrane separation with a RO post-treatment. The research focus is FO membrane fouling and performance using different activated sludge investigated both at laboratory scale (membrane area of 112 cm2) and at on-site bench scale (flat sheet membrane area of 0.1m2). FO performance on laboratory-scale (i) increased with temperature due to a decrease in viscosity and (ii) was independent of the type of activated sludge. Draw solution leakage increased with temperature and varied for different activated sludge. FO performance on bench-scale (i) increased with osmotic driving force, (ii) depended on the membrane orientation due to internal concentration polarization and (iii) was invariant to feed flow decrease and air injection at the feed and draw side. Draw solution leakage could not be evaluated on bench-scale due to experimental limitation. Membrane fouling was not found on laboratory scale and bench-scale, however, partially reversible fouling was found on laboratory scale for FO membranes facing the draw solution. Economic assessment indicated a minimum flux of 15 L.m -2h-1 at 0.5M NaCl for OMBR-RO to be cost effective, depending on the FO membrane price. © IWA Publishing 2011.

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