Microfluidic Membrane Filtration Systems to Study Biofouling

In wastewater treatment, the membrane functions as a semipermeable barrier that restricts transport of undesired particulates. A major problem related to membrane filtration processes is fouling of membranes by colloidal particles, organic matter, and biomaterials. Among the various types of fouling, biofouling is one of the most severe, as it is a dynamic process. Even a few surviving cells that adhere to the membrane surface multiply exponentially at the expense of biodegradable substances in the feed solution. To analyze the mechanism of biofouling, membrane cell is typically considered as a black-box, where only the input and the output can be measured and put into use for analysis. Microfluidic devices are being used to study and understand the nature, properties, and evolution of biofouling. A primary advantage of a microfluidic membrane is the ability to conduct real-time observations of biofilm. This chapter presents an overview of the biofouling in membrane processes and different fabrication technique of microfluidic membrane systems

Effect of Internal and External Concentration Polarizations on the Performance of Forward Osmosis Process

Forward osmosis (FO) as an osmotically driven membrane process is severely affected by the concentration polarization phenomenon on both sides of the membrane as well as inside the support layer. Though the effect of internal concentration polarization (ICP) in the porous support on the draw solution side is far more pronounced than that of the external concentration polarization (ECP), still the importance of ECP cannot be neglected. The ECP becomes particularly important when the feed flow rate is enhanced to increase the permeation flux by increasing the agitation and turbulence on the membrane surface. To capture the effect of ECP a suitable value of mass transfer coefficient must be determined. In this chapter, an FO mass transport model that accounts for the presence of both ICP and ECP phenomena is first presented on the basis of solution-diffusion model coupled with diffusion-convection. Then, three methods for the estimation of mass transfer coefficient based on empirical Sherwood (Sh) number correlations, pressure-driven reverse osmosis (RO), and osmosis-driven pressure retarded osmosis (PRO) are proposed. Finally, a methodology for the prediction of water flux through FO membranes using the theoretical model and calculated/measured parameters (hydraulic permeability, salt resistivity of the support layer, and mass transfer coefficient) is presented

Nanofiltration for the Treatment of Oil Sands-Produced Water

This chapter summarizes nanofiltration (NF) studies focused on the treatment of thermal in-situ steam-assisted gravity drainage (SAGD)-produced water streams in the Alberta, Canada, oil sands industry. SAGD processes use recycled produced water to generate steam, which is injected into oil-bearing formations to enhance oil recovery. NF has potential applications in the produced water recycling treatment process for water softening, dissolved organic matter removal, and partial desalination, to improve recycle rates, reduce make-up water consumption, and provide an alternative to desalination technologies (thermal evaporation and reverse osmosis). The aim of this study was to provide proof-of-concept for NF treatment of the following produced water streams in the SAGD operation: warm lime softener (WLS) inlet water, boiler feed water (BFW), and boiler blowdown (BBD) water. Commercial NF membranes enabled removal of up to 98% of the total dissolved solids (TDS), total organic carbon (TOC), and dissolved silica, which is significant compared to the removal achieved using conventional SAGD-produced water treatment processes. More than 99% removal of divalent ions was achieved using tight NF membranes, highlighting the potential of NF softening for oil sands-produced water streams. The NF process configurations studied provide feasible process arrangements suitable for integration into existing and future oil sands and other produced water treatment schemes

Electrified Pressure-Driven Instability in Thin Liquid Films

The electrified pressure-driven instability of thin liquid films, also called electrohydrodynamic (EHD) lithography, is a pattern transfer method, which has gained much attention due to its ability in the fast and inexpensive creation of novel micro- and nano-sized features. In this chapter, the mathematical model describing the dynamics and spatiotemporal evolution of thin liquid film is presented. The governing hydrodynamic equations, intermolecular interactions, and electrostatic force applied to the film interface and assumptions used to derive the thin film equation are discussed. The electrostatic conjoining/disjoining pressure is derived based on the long-wave limit approximation since the film thickness is much smaller than the characteristic wavelength for the growth of instabilities. An electrostatic model, called an ionic liquid (IL) model, is developed which considers a finite diffuse electric layer with a comparable thickness to the film. This model overcomes the lack of assuming very large and small electrical diffuse layer, as essential elements in the perfect dielectric (PD) and the leaky dielectric (LD) models, respectively. The ion distribution within the IL film is considered using the Poisson-Nernst-Planck (PNP) model. The resulting patterns formed on the film for three cases of PD-PD, PD-IL, and IL-PD double layer system are presented and compared

Abiotic streamers in a microfluidic system

In this work, we report the phenomenon of formation of particle aggregates in the form of thin slender strings when a polyacrylamide (PAM) solution, laden with polystyrene (PS) particles is introduced into a microfluidic device containing an array of micropillars. PAM and dilute solution of PS beads is introduced into the microfluidic channel through two separate inlets and localized particle aggregation is found to occur under certain conditions. The particle aggregates initially have a string-like morphology that remain tethered at their ends to the micropillar walls, while the rest of the structure remains suspended in the fluid medium. It is this morphology that inspired us to name these structures streamers. The flow regime under which streamer formation is observed is quantified using through a phase diagram. We discuss the streamer formation time-scales and also show that streamer formation is likely the result of flocculation of the PS beads. These streamers can serve as excellent model systems to study a biological phenomenon by the same name.Comment: 14 PAGES, 6 FIGURE

Development of advanced nanocomposite membranes using graphene nanoribbons and nanosheets for water treatment

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.memsci.2018.04.034 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Water-intensive industries have to comply with stringent environmental regulations and evolving regulatory frameworks requiring the development of new technologies for water recycling. Development of polymeric membranes may provide an effective solution to improve water recycling, but require finely-tuned pore size and surface chemistry for ionic and molecular sieving to be efficient. Additionally, fouling is a major challenge that limits the practical application of the membranes in water recycling in these industries. In this work, four different graphene oxide (GO) derivatives were incorporated into a polyethersulfone (PES) matrix via a non-solvent induced phase separation (NIPS) method. The GO derivatives used have different shapes (nanosheets vs nanoribbons) and different oxidation states (C/O = 1.05–8.01) with the potential to enhance water flux and suppress fouling of the membranes through controlled pore size, hydrophilicity, and surface charge. The permeation properties of the PES/GO membranes were evaluated using a water sample from the Athabasca oil sands of Alberta. The results for contact angle and streaming potential measurements indicate the formation of more hydrophilic and negatively charged PES/GO nanocomposite membranes. All graphene-based nanocomposite membranes demonstrated better water flux and rejection of organic matter compared to the unmodified PES membrane. The fouling measurement results revealed that fouling was impeded due to enhanced membrane surface properties. Longitudinally unzipped graphene oxide nanoribbons (GONR-L) at an optimum loading of 0.1 wt% (wt%) provided the maximum water flux (70 LMH at 60 psi), organic matter rejection (59%) and antifouling properties (30% improvement compared to pristine PES membrane). Flux recovery ratio experiments indicated a remarkable enhancement in the fouling resistance property of PES/GO nanocomposite membranes.Natural Sciences and Engineering Research Council of Canada [33413]Natural Resources Canada [32462]Suncor Energy IncorporatedConocoPhillipsUniversity of WaterlooDevon Canad

Impact of bacterial streamers on biofouling of microfluidic filtration systems

We investigate the effect of biofouling in a microfluidic filtration system. The microfluidic platform consists of cylindrical microposts with a pore-spacing of 2 mu m, which act as the filtration section of the device. One of our key findings is that there exists a critical pressure difference above which pronounced streamer formation is observed, which eventually leads to rapid clogging of the device with an accompanying exponential decrease in permeate flow. Moreover, when streamers do form, de-clogging of pores also occurs intermittently, which leads to small time scale fluctuations O(10(1) s)] superimposed upon the large time scale O(10(2) min)] clogging of the system. These de-clogging phenomena lead to a sharp increase in water permeation through the microfluidic filtration device but rates the water quality as biomass debris is transported in the permeate. Streamer-based clogging shares similarities with various fouling mechanisms typically associated with membranes. Finally, we also show that the pH of the feed strongly affects biofouling of the microfluidic filtration system. Published by AIP Publishing