Eric Hoek

Organic fouling plagues many environmental membrane processes. In this study, well-controlled laboratory experiments were performed to elucidate seawater RO membrane fouling by alginic acid. Interfacial free energies derived from multiple probe liquid contact angle analyses (including different seawater matrices) correlated strongly with the rates of membrane fouling. More importantly, the Lewis acid-base interfacial free energy quantitatively described the impacts of calcium-carboxylate complex formation and predicted membrane fouling and cleaning behavior. Calcium ions made polyamide composite RO membranes (and alginic acid) more hydrophobic, enhanced the rate and extent of flux decline, and reduced the effectiveness of chemical cleaning. The implications for seawater RO membrane fouling are clear. Selective removal of calcium ions via pretreatment can reduce the gel forming ability of carboxylate rich biomacromolecules and, hence, the extent to which they foul RO membranes. In addition, RO membranes should be produced with smooth, hydrophilic interfaces comprising monopolar electron-donor functionality and no carboxylic acid residue. More broadly, this paper presents a facile approach for quantifying the impacts of specific ion interactions on aquatic colloid stability, aggregation, and deposition.

... Titre du document / Document title. Effect of mobile cation on zeolite-polyamide thin film nanocomposite membranes. Auteur(s) / Author(s). LIND Mary Laura ; JEONG Byeong-Heon ; SUBRAMANI Arun ; XIAOFEI HUANG ; HOEK Eric MV ; Revue / Journal Title. ...

Direct microscopic observation and an interfacial force model were used to better understand and control microbial adhesion to polymeric ultrafiltration membranes. The model was used to predict a "critical flux", below which cells deposited reversibly, and direct observation was used to visually quantify cell deposition and removal. In preliminary direct observation experiments, permeate reversal (backpulsing) was more effective than cross-flow hydrodynamics at removing deposited cells. In experiments conducted below the critical flux, no cell accumulation was observed over repeated forward-reverse filtration cycles; however, a small fraction of cells deposited irreversibly regardless of the flux, membrane, or solution chemistry. The fraction of irreversibly deposited cells was consistent with the equilibrium surface coverage attained without permeation (i.e., due to heterogeneous adsorption). Although steric forces were not invoked to establish a critical flux, when operating above the critical flux, a balance between permeation drag and steric repulsion appeared to determine the strength of adhesion of cells to membranes. Direct observation also confirmed that above the critical flux fouling occurred and pressure losses accumulated over several backpulse cycles, whereas below the critical flux there were no observable pressure losses or fouling.

Here, we model the effects of fouling on the performance of a reverse osmosis (RO) system treating micro-filtered secondary effluent. The model considers system properties, water quality, and transport phenomena. The model is fitted to operating data from the Orange County Water District's Groundwater Replenishment System RO pilot plant, which experienced severe fouling over a period of 3–4 months. Modeling

Results from well-controlled colloidal fouling experiments with reverse osmosis (RO) and nanofiltration (NF) membranes suggest the existence of a new source of flux decline for salt-rejecting membranes-cake-enhanced osmotic pressure. The physical mechanisms leading to this enhanced osmotic pressure are a combination of hindered back-diffusion of salt ions and altered cross-flow hydrodynamics within colloidal deposit layers, which lead to an enhanced salt concentration polarization layer. A model that accounts for both hindered diffusion of salt ions and altered hydrodynamics within colloidal deposit ("cake") layers is presented. The model successfully links permeate flux and salt rejection to cake-enhanced concentration polarization and provides new insight into the mechanisms through which salt-rejecting membranes foul. Experimental data support the model calculations and highlight the role of enhanced concentration polarization phenomena in the performance (i.e., water flux and salt rejection) of polymeric thin-film composite RO/NF membranes in environmental applications.