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The fouling potential of transparent exopolymer particles (TEP) was evaluated to reveal its role in the biofouling mechanism of reverse osmosis (RO) membrane process. A methodology to determine the fouling potential of TEP was systematically developed based on cake filtration theory. The resulting cake fouling index of TEP (CFI TEP ) was then correlated to initial bacterial deposition observed in RO biofouling tests. Alginic acid was employed to simulate TEP and Pseudomonas aeruginosa PA14 was inoculated for biofouling test. The results showed that the fouling propensity of TEP could be assessed by cake fouling potential of particulate TEP (>0.45 μm). Furthermore, the analysis of biofouled RO membranes indicated that bacterial deposition on RO membranes was enhanced significantly with increasing the cake fouling potential of TEP (i.e., CFI TEP ). This work demonstrated the importance of TEP at the initial stage of biofilm formation, suggesting TEP control by pretreatment for mitigating biofouling in RO applications. [ABSTRACT FROM AUTHOR]

Abstract: Anti-adhesion and antimicrobial coatings were prepared and applied on commercial thin-film-composite (TFC) polyamide (PA) membrane to enhance anti-biofouling performance. Polyvinyl alcohol (PVA) coating was modified with cationic polyhexamethylene guanidine hydrochloride (PHMG) polymer to obtain antimicrobial performance. ATR-FTIR, SEM and AFM investigated the surface chemistry and morphology of the coated membranes. The contact angle measurement was used to determine hydrophilicity and surface energy. All coated membranes revealed more hydrophilic and lower surface roughness compared to uncoated membrane. Lower number of adhered Pseudomonas aeruginosa (P. aeruginosa) bacteria was detected on coated membranes, indicating anti-adhesion performance. The colony forming unit (CFU) and diffusion inhibition zone (DIZ) tests determined antimicrobial activity of the coated membranes against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), showing the antimicrobial performance of PHMG. The results suggested that an optimal anti-fouling surface could be obtained applying a coating, which combines anti-adhesion and antimicrobial performance. [Copyright &y& Elsevier]

Biofouling control by quorum sensing (QS) inhibition and the influence of membrane surface characteristics on biofilm formation and QS inhibition were investigated. Pseudomonas putida isolated from the bio-fouled reverse osmosis (RO) membranes in a real plant was used. Acylase was chosen as a model QS inhibitor. Bacteria on the membrane coupons were quantified with the heterotrophic plate count method. Cell distribution was imaged by a confocal laser scanning microscope. Results showed that biofilm formation on the membrane was reduced by acylase as it inhibits the activity of N-acylhomoserine lactone (Al-IL) which is a signal molecule of QS. It was also shown that membrane surface characteristics were influential factors affecting bacterial adhesion, biofilm formation, and QS inhibition. [ABSTRACT FROM AUTHOR]

Abstract: Contact angle measurement is conducted to determine surface hydrophilicity of RO membrane with the intention of predicting membrane performance or fouling potential. Most researchers of membrane technology have used contact angles without considering effective factors for contact angle measurement such as measurement time, drop volume and membrane sample preparation. In fact, significantly different contact angles are reported even on the same RO membrane. In this study, contact angles were measured by the sessile drop method and captive bubble method and were compared with various conditions such as measurement time, drop volume, membrane sample preparation and liquid type in the commercialized RO membranes. As a result, sessile drop method showed unreliable contact angles, which varied dramatically with the preparation conditions. On the other hand, the captive bubble method, which represents conditions closer to the real RO membrane process, showed reproducible contact angles. For the different commercially available RO membranes, similar hydrophilicity was observed. Overall, the captive bubble method appears to be a more adequate method for measuring contact angle of RO membranes. [Copyright &y& Elsevier]

Abstract: Biofouling of reverse osmosis (RO) membranes, which occurs as a result of biofilm growth following initial bacterial adhesion, is well known as one of the most serious problems. Although membranes with surfaces resistant to bacterial adhesion are expected to have higher resistance to biofouling as well, our recent study reported that membrane surface properties have no significant relationship with biofouling under no filtration condition (Lee et al., 2010 ). The purpose of this study is to investigate the effects of surface properties of RO membranes (hydrophobicity, surface charge, and roughness) on biofouling under a lab-scale cross-flow RO membrane system using three commercial RO membranes with different surface properties. This study reports that the extent of biofouling, which was demonstrated through flux decline with time, appeared to remain constant despite the apparent difference in surface properties among the three commercial RO membranes selected. As a result, it seems that surface properties of RO membrane have no relationship with biofouling occurrence. [Copyright &y& Elsevier]

Abstract: In order to evaluate the effect of membrane surface properties on the initial stage of biofouling, in the reverse osmosis (RO) membrane process, initial bacterial adhesion and biofilm formation experiments were performed under no filtration condition. In this study, five commercialized polyamide thin-film composite RO membranes (SW30HRLE, SW30HR (Dow FilmTec Co., USA), TM820 (Toray Co., Japan), RE-BE, RE-FE (Woongjin Chemical Co., Korea)) were chosen and their surface properties such as surface charge, roughness, hydrophobicity and surface morphology were measured. For examining initial bacterial adhesion, a flow channel reactor was employed for 3h, while for examining a biofilm formation, the CDC reactor was employed for 48h. Pseudomonas aeruginosa PAO1 tagged with GFP was selected as a model bacterial strain. Major findings in this study indicate that although the initial bacterial cell adhesion in a flow channel reactor indicated more bacterial cells attachment on the membrane surface with higher hydrophobicity, the extent of biofilm grown in CDC reactor for 48h became similar regardless of the difference of the membrane surface properties, indicating that the membrane surface properties become a less important factor affecting the biofilm growth on the membrane surface. This finding will be helpful in improving the understanding of biofouling issue occurring in the real RO membrane system, although practical implication is somewhat limited since this study was performed under no filtration condition. [Copyright &y& Elsevier]

Abstract: An optimal system design as well as advanced fault tolerant control is required to propose a cost-effective design and control of a seawater reverse osmosis (SWRO) desalination plant. Contrary to the steady-state model which is useful for only design, a dynamic model is essential to complete a plant design that includes embedded model-based control as well as analysis of transient behavior of a SWRO plant. In this paper, a model for fouling factors (i.e., water and salt transport permeability factors) is proposed to consider the membrane degradation influenced by not only temperature but also time variant fouling. The cycle NCR (Normal operation – Cleaning – Replacement) is also modeled by means of a hybrid automaton for a fault tolerant control. The simulation results of the model, which are generally satisfied to explain the membrane degradation effect, show that it can be feasible to obtain the optimized control using the dynamic hybrid model and applicable to operational cost-saving for SWRO desalination plants. [Copyright &y& Elsevier]

A large-scale pilot distribution study was conducted to investigate the impacts of blending different source waters on distribution water qualities, with an emphasis on metal release (i.e. corrosion). The principal source waters investigated were conventionally treated ground water (G1), surface water processed by enhanced treatment (S1), and desalted seawater by reverse osmosis membranes (RO). Due to the nature of raw water quality and associated treatment processes, G1 water had high alkalinity, while S1 and RO sources were characterized as high sulfate and high chloride waters, respectively. The blending ratio of different treated waters determined the quality of finished waters. Iron release from aged cast iron pipes increased significantly when exposed to RO and SI waters: that is, the greater iron release was experienced with alkalinity reduced below the background of G1 water. Copper release to drinking water, however, increased with increasing alkalinity and decreasing pH. Lead release, on the other hand, increased with increasing chloride and decreasing sulfate. The effect of pH and alkalinity on lead release was not clearly observed from pilot blending study. The flat and compact corrosion scales observed for lead surface exposed to S1 water may be attributable to lead concentration less than that of RO water blends. [ABSTRACT FROM AUTHOR]