Toray Singapore Water Research Center


Toray Singapore Water Research Center

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Suwarno S.R.,Nanyang Environment and Water Research Institute | Hanada S.,Toray Singapore Water Research Center | Chong T.H.,Nanyang Environment and Water Research Institute | Chong T.H.,Nanyang Technological University | And 4 more authors.
Desalination | Year: 2016

Reverse osmosis (RO) biofouling is a problem of biofilm development which is initiated by bacterial attachment to the membrane surface following the surface conditioning. In this study, the impact of the initial fouling layers on bacterial attachment was investigated. Both model foulants and MBR permeate water were used to simulate conditioning layers on RO membranes by performing fouling experiments at constant flux and crossflow velocity. Analysis of the properties of different conditioning layers included zeta potential, contact angle, roughness, and adhesive force. Results in this study show that the bacterial attachment was greater on pre-conditioned surfaces and the load of attached bacteria was closely correlated to the change of adhesive force rather than to the change of zeta potential and hydrophilicity. Additionally, the amount of the pre-conditioning layer also influenced the bacterial attachment. Differences in surface roughness were found to be unimportant. To examine the effect of pretreatment bacterial attachment tests were performed on a secondary effluent filtered by microfiltration or ultrafiltration. The UF pretreatment showed significantly less attachment. Results in this study confirm the role of the initial conditioning layer and highlight which surface characteristics of the conditioning layer are the most important for the initial bacterial attachment. © 2016 Elsevier B.V.

Wu B.,Nanyang Technological University | Kitade T.,Toray Singapore Water Research Center | Chong T.H.,Nanyang Technological University | Uemura T.,Toray Singapore Water Research Center | Fane A.G.,Nanyang Technological University
Desalination | Year: 2013

This study compares fouling propensities of reverse osmosis (RO) membranes in two parallel MBR-RO systems. Two MBRs were operated at different food to microorganism (F/M) ratios and the permeate was fed to the respective RO membrane. The results show that greater amounts of organic substances in the high F/M (0.50g/gday-1)-MBR permeate led to higher RO fouling rates (>4.5-fold) compared to the low F/M ratio (0.17g/gday-1)-MBR permeate. The presence of filters (~5μm) in the RO feed line and recycled RO concentrate line significantly alleviated RO fouling. Chemical analysis of RO foulants indicated that the soluble polysaccharides and transparent exopolymer particles (TEP) accumulated on the RO membranes were strongly associated with RO fouling. However, propagation of bacterial cells on the membranes did not determine RO fouling development. This finding was further confirmed by confocal laser scanning microscopy images. Furthermore, excitation-emission matrix (EEM) fluorescence spectroscopy was used to trace the fate and transport of the potential soluble foulants in the MBR-RO system. © 2012 Elsevier B.V.

Wu B.,Nanyang Technological University | Kitade T.,Toray Singapore Water Research Center | Chong T.H.,Nanyang Technological University | Lee J.Y.,Nanyang Technological University | And 2 more authors.
Separation Science and Technology (Philadelphia) | Year: 2013

This paper investigated the effect of food to microorganisms (F/M) ratios in the MBRs on membrane fouling propensities at fluxes of 10, 20, and 30 L/m2 hr (LMH). The high F/M-MBR had different biomass properties, more soluble extracellular polymeric substances (EPS), and faster fouling rate compared to the low F/M-MBR. However, the fouling mechanisms at the three fluxes were dissimilar. At a low flux, the microbial flocs dominant cake layers facilitated catching the soluble EPS to increase resistance. At a high flux, the great accumulation of soluble EPS (especially soluble polysaccharides) to form gel-like cake layers predominantly induced membrane fouling. Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science and Technology to view the free supplemental file. © 2013 Copyright Taylor and Francis Group, LLC.

Kitade T.,Toray Singapore Water Research Center | Wu B.,Nanyang Technological University | Chong T.H.,Nanyang Technological University | Fane A.G.,Nanyang Technological University | Uemura T.,Toray Singapore Water Research Center
Desalination and Water Treatment | Year: 2013

This work investigated fouling propensities of microfiltration membranes and reverse osmosis (RO) membranes and analyzed the characteristics of deposited foulants on the membranes in two parallel Membrane bioreactor (MBR)-RO systems, with MBRs operated at different food to micro-organism (F/M) ratios. The results show that a high F/M ratio (0.50 g/g MLSS day) in the MBR caused greater membrane fouling rates of the MBR and RO membranes than a low F/M ratio (0.17 g/g MLSS day). In the MBRs, deposited microbial flocs were major foulants at low flux (10 L/m2 h), whereas soluble substances in the cake foulants predominantly induced membrane fouling at high fluxes (20 and 30 L/m2 h). In order to investigate the contributions of the protein, polysaccharides, and transparent exopolymer in the soluble substances to membrane fouling, bovine serum albumin, sodium alginate, and gum xanthan were used as model compounds, respectively, in experiments with the activated sludge samples from the MBR. The results imply that soluble polysaccharides (SP) and soluble transparent exopolymer particles (sTEP) were associated with fouling propagation. On the RO membranes, SP and sTEP were identified as major contributors to RO fouling rather than microbial cells and soluble protein. Our findings emphasize that the important role of the nature of soluble substances in membrane fouling and highlight that optimization of MBR operation is crucial to alleviate RO membrane fouling. © 2013 Copyright Balaban Desalination Publications.

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