Novel hole-pillar spacer design for improved hydrodynamics and biofouling mitigation in membrane filtration

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Three spacer designs, namely a non-woven commercial spacer (varying filament cross-section), a symmetric pillar spacer, and a novel hole-pillar spacer (constant filament diameter) were studied using Direct Numerical Simulations (DNS), 3-D printed and subsequently experimentally tested in a lab-scale ultrafiltration set-up with high biofouling potential feed water at various feed pressures. Independent of the applied pressure, the novel hole-pillar spacer showed initially the lowest feed channel pressure drop, the lowest shear stress, and the highest permeate flux compared to the commercial and pillar spacers. Furthermore, less biofilm thickness development on membrane surface was visualized by Optical Coherent Tomography (OCT) imaging for the proposed hole-pillar spacer. At higher feed pressure, a thicker biofilm developed on membrane surface for all spacer designs explaining the stronger decrease in permeate flux at high pressure. The findings systematically demonstrated the role of various spacer designs and applied pressure on the performance of pre-treatment process, while identifying specific shear stress distribution guidelines for engineering a new spacer design in different filtration techniques

Practical considerations for operability of an 8″ spiral wound forward osmosis module: Hydrodynamics, fouling behaviour and cleaning strategy

© 2016 Elsevier B.V. A better understanding of large spiral wound forward osmosis (SW FO) module operation is needed to provide practical insight for a full-scale FO practical implementation desalination plant. Therefore, this study investigated two different 8″ SW FO modules (i.e. cellulose tri acetate, CTA and thin film composite, TFC) in terms of hydrodynamics, operating pressure, water and solute fluxes, fouling behaviour and cleaning strategy. For both modules, a significantly lower flow rate was required in the draw channel than in the feed channel due to important pressure-drop in the draw channel and was a particularly critical operating challenge in the CTA module when permeate spacers are used. Under FO and pressure assisted osmosis (PAO, up to 2.5 bar) operations, the TFC module featured higher water flux and lower reverse salt flux than the CTA module. For both modules, fouling tests demonstrated that feed inlet pressure was more sensitive to foulant deposition than the flux, thus confirming that FO fouling deposition occurs in the feed channel rather than on the membrane surface. Osmotic backwash combined with physical cleaning used in this study confirmed to be effective and adapted to large-scale FO module operation

Thin-film composite membrane on a compacted woven backing fabric for pressure assisted osmosis

© 2016 Elsevier B.V. The water flux in forward osmosis (FO) process declines substantially when the draw solution (DS) concentration reaches closer to the point of osmotic equilibrium with the feed solution (FS). Using external hydraulic pressure alongside the osmotic driving force in the pressure assisted osmosis (PAO) has been found effective in terms of enhancing water flux and even potentially diluting the DS beyond osmotic equilibrium. The net gain in water flux due to the applied pressure in the PAO process closely depends on the permeability of the FO membrane. The commercial flat sheet cellulose triacetate (CTA) FO membrane has low water permeability and hence the effective gain in water flux in the PAO process is low. In this study, a high performance thin film composite membrane was developed especially for the PAO process through casting polyethersulfone (PES) polymer solution on a compacted woven fabric mesh support followed by interfacial polymerisation for polyamide active layer. This PAO membrane possesses a water flux of 37 L m2h− 1using 0.5 M NaCl as DS and deionised water as the feed at an applied hydraulic pressure of 10 bar. Besides, the membrane was able to endure the external hydraulic pressure required for the PAO process owing to the embedded backing fabric support. While the membranes with low structural parameters are essential for higher water flux, this study shows that for PAO process, polymeric membranes with larger structural parameters may not be suitable for PAO. They generally resulted in compaction and poor mechanical strength to withstand hydraulic pressure

Techno-economic assessment of fertiliser drawn forward osmosis process for greenwall plants from urban wastewater

© 2019 Institution of Chemical Engineers Pressure-assisted osmosis (PAO) has been suggested to integrate with fertiliser driven forward osmosis (FDFO) to improve the overall efficiency of simultaneous wastewater reuse and fertiliser osmotic dilution. This study aims to demonstrate the techno-economic feasibility of pressure-assisted fertiliser driven forward osmosis (PAFDO) hybrid system compared to the existing ultraviolet and reverse osmosis (UV–RO) process. The results showed that coupling FDFO with PAO (i.e. PAFDO) could help fulfill the water quality required for greenwall fertigation. An economic analysis on capital and operational costs for the PAFDO showed that the PAO mode application at a lower FDFO dilution stage could significantly reduce the costs. However, when considering the different applied pressures in PAO (i.e. 2, 4, and 6 bar), the increase in the total water cost was not significant. This indicates that the dilution stage for applying PAO is more sensitive to the total water cost of the PAFDO than the applied pressure. A coupling of higher average water flux (>10 L/m2h) and lower draw solution (DS) dilution factor (DF < 60) is recommended. Therefore, this could make the PAFDO system economically viable compared to the benchmark for the UV-RO disinfection system

Thin film composite hollow fibre forward osmosis membrane module for the desalination of brackish groundwater for fertigation

© 2015 Elsevier B.V. The performance of recently developed polyamide thin film composite hollow fibre forward osmosis (HFFO) membrane module was assessed for the desalination of brackish groundwater for fertigation. Four different fertilisers were used as draw solution (DS) with real BGW from the Murray-Darling Basin in Australia. Membrane charge and its electrostatic interactions with ions played a significant role in the performance of the HFFO module using fertiliser as DS. Negatively charged polyamide layer promotes sorption of multivalent cations such as Ca2+ enhancing ion flux and membrane scaling. Inorganic scaling occurred both on active layer and inside the support layer depending on the types of fertiliser DS used resulting in severe flux decline and this study therefore underscores the importance of selecting suitable fertilisers for the fertiliser drawn forward osmosis (FDFO) process. Water flux under active layer DS membrane orientation was about twice as high as the other orientation indicating the need to further optimise the membrane support structure formation. Water flux slightly improved at higher crossflow rates due to enhanced mass transfer on the fibre lumen side. At 45% packing density, HFFO could have three times more membrane area and four times more volumetric flux output for an equivalent 8040 cellulose triacetate flat-sheet FO membrane module

Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance

It is proposed that the presence of a tilted and anisotropic Dirac cone can be verified using the interlayer magnetoresistance in the layered Dirac fermion system, which is realized in quasi-two-dimensional organic compound \alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic Landau level wave functions and assuming local tunneling of electrons. It is shown that the resistivity takes the maximum in the direction of the tilt if anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.

Membrane autopsy of a 10year old hollow fibre membrane from Sydney Olympic Park water reclamation plant

Membrane autopsy was performed for a 10. year old polypropylene (PP) hollow fibre microfiltration membrane from Sydney Olympic Park water reclamation plant. The properties of the membrane were studied using scanning electron microscope (SEM) imaging, contact angle, bubble test, thermogravimetric analysis, tensile strength test and functional group. The old and fouled membrane exhibited a significant difference in surface properties and material strength in comparison to the virgin membrane. The old and fouled membrane surface is less hydrophilic and less negatively charged indicating that aged membrane is more vulnerable to fouling than virgin membrane. The fibre material of the old fouled membrane appears less flexible and brittle. Foulant analysis indicated that major components of the metallic elements were silicon and calcium. The dissolved organic matter was mainly composed of biopolymers (hydrophilic) and humic substances (hydrophobic). © 2011 Elsevier B.V

Comparison of granular activated carbon bio-sorption and advanced oxidation processes in the treatment of leachate effluent

Landfill leachate is a toxic effluent of a decomposing landfill that is produced when rainwater percolates through the landfill leaching out contaminants and pollutants. Untreated leachate is a potential source for the contamination of soil, surface and ground water. In this study, the treatment processes such as granular activated carbon (GAC) adsorption/bio-sorption (batch), and advanced oxidation processes (AOP) viz. photocatalysis and Fenton's process were evaluated and compared by using synthetic landfill leachate (SLL) as a contaminant. TiO2 was used as a catalyst in photocatalysis, and Fenton's reagent (H2O2/Fe+2) was used in Fenton's process. The degradation of SLL effluent by the three above-mentioned processes was characterized by the % TOC removal. The % TOC removed by photocatalysis, Fenton oxidation and bio-sorption (which includes adsorption and biodegradation) was 30, 60 and 85%, respectively. The bio-sorption increased with the increasing GAC dose. The optimum dose of Fenton's reagent in advanced oxidation was 15 and 400 milli moles of Fe+2 and H2O 2, respectively. The Fenton's process showed faster degradation kinetics compared to biodegradation and photocatalysis. © 2009 Springer

A transverse current rectification in graphene superlattice

A model for energy spectrum of superlattice on the base of graphene placed on the striped dielectric substrate is proposed. A direct current component which appears in that structure perpendicularly to pulling electric field under the influence of elliptically polarized electromagnetic wave was derived. A transverse current density dependence on pulling field magnitude and on magnitude of component of elliptically polarized wave directed along the axis of a superlattice is analyzed.Comment: 12 pages, 6 figure