Oluranti Agboola

Characterization and performance of nanofiltration membranes

The availability of clean water has become a critical problems facing the society due to pollution by human activities. Most regions in the world have high demands for clean water. Supplies for freshwater are under pressure. Water reuse is a potential solution for clean water scarcity. A pressure-driven membrane process such as nanofiltration has become the main component of advanced water reuse and desalination systems. High rejection and water permeability of solutes are the major characteristics that make nanofiltration membranes economically feasible for water purification. Recent advances include the prediction of membrane performances under different operating conditions. Here, we review the characterization of nanofiltration membranes by methods such as scanning electron microscopy, thermal gravimetric analysis, attenuated total reflection Fourier transform infrared spectroscopy, and atomic force microscopy. Advances show that the solute rejection and permeation performance of nanofiltration membranes are controlled by the composition of the casting solution of the active layer, cross-linking agent concentration, preparation method, and operating conditions. The solute rejection depends strongly on the solute type, which includes charge valency, diffusion coefficient, and hydration energy. We also review the analysis of the surface roughness, the nodule size, and the pore size of nanofiltration membranes. We also present a new concept for membrane characterization by quantitative analysis of phase images to elucidate the macro-molecular packing at the membrane surface.

Microscopical characterizations of nanofiltration membranes for the removal of nickel ions from aqueous solution

The nanofiltration (NF) process is electrostatically governed and the surface free energy plays a key role in the separation of particulates, macromolecules, and dissolved ionic species. Streaming potential measurement and the surface charge mapping by Kelvin probe atomic force mircoscopy (AFM) have been carried out. Forces of interaction near the surface of nanofiltration membranes were further studied by a force spectroscopy using atomic force microscopy. The two membranes used are more negatively charged at high pH values; hence the higher the solution chemistry, the higher and faster will be adhesion of ions on the surface of the nanofiltration membranes. It was observed that the three acquired signals from non-contact AFM (contact potential difference, amplitude and phase) were rigorously connected to the surface structure of the nanofiltration membranes. In addition to the surface structure (roughness), electrostatic interactions can also enhance initial particle adhesion to surfaces of nanofiltration membranes. The performance of the NF membranes was further investigated for the removal of nickel ions from aqueous solution, and the results were correlated to the mechanical responses of the nanofiltration membranes obtained from AFM and the streaming potential measurement.

Theoretical performance of nanofiltration membranes for wastewater treatment

Abstract Mechanisms of ionic transport in nanofiltration are poorly known. Modelling can be used to predict membrane performance, to reveal separation mechanisms, to select appropriate membranes, and to design processes. Several models have been proposed to describe nanofiltration membranes. Some models rely on simple concepts, while other models are more complex and require sophisticated solution techniques. Here, we review predictive models used for characterizing nanofiltration membranes for the separation of wastewater. The most popular model uses the extended Nernst–Planck equation, which describes the ionic transport mechanisms in details. Results obtained by using the extended Nernst–Planck equation show that the performance of nanofiltration membranes is strongly dependent on charge, steric, and dielectric effects.

Deposition of toxic metal particles on rough nanofiltration membranes

Two nanofiltration (NF90 and Nano-Pro-3012) membranes were investigated for their capacity to remove metal ions. This study presents the effect of membrane roughness on the removal of toxic metal ions during dead end membrane filtration. Atomic force microscopy, scanning electron microscopy, WSXM software and ImageJ were used to characterize the roughness of the membranes. Gradual decrease in filtration permeate flux was observed as foulants accumulated at the interface of the membranes; filtration permeate flux varied from 20 L/m2/h to 14 L/m2/h and 11 L/m2/h to 6 L/m2/h for NF90 and Nano-Pro-3012, respectively. NF90 membrane was more prone to fouling than the Nano-Pro-3012 membrane: the percentage flux reduction was higher for NF90 (3.6%) than Nano-Pro-3012 (0.98%). The bearing ratio of the fouled NF90 exhibited a high peak of 7.09 nm than the fouled Nano-Pro-3012 with the peak of 6.8 nm.

Current Methods for the Remediation of Acid Mine Drainage Including Continuous Removal of Metals From Wastewater and Mine Dump

Abstract The remediation of acid mine drainage (AMD) in terms of effluents/dumps treatment can be highly complicated due to several factors to be considered such as, but not limited to, its composition. The majority of economically mine deposits are associated with potentially hazardous trace and harmful elements. AMD is water body rich in acidic metal formed by the reaction between the water and rock containing sulfur-bearing minerals. In the last twodecades, researchers have used various techniques such as chemical precipitation, solvent extraction, ultrafiltration, microfiltration, nanofiltration, reverse osmosis, organic and inorganic ion exchange, and adsorption in mine water/dump treatment. The importance, achievements, and limitations of various techniques with references to their major functions were identified in this section. In this regard, comprehensive investigation was done on the previous and recent/novel methods in reversing the environmental damages caused by AMD. Moreover, technology screening in selecting suitable treatment technique based on the factors such as cost, appropriateness, health and environmental impact, public perception, and acceptance of the techniques was analyzed based on the literature review.

Performance Of An Acid Stable NanofiltrationMembrane For Nickel Removal FromAqueous Solutions: Effects Of Concentration,Solution PHAnd Ionic Strength

The performance of a nanofiltration membrane for the removal of the nickel ion was studied as a function of the nickel concentration, solution pH, and the background ionic strength of the solution. Nanofiltration is investigated as a means to determine to what extent the nickel ions could be removed from acid mine drainage; thus the effect of solution chemistry on nanofiltration performance is investigated. Higher fluxes (47.6l/m²/h) were experienced at the lower nickel concentration (10mg/l) than at the higher (28.9l/m²/h) nickel concentration (100mg/l). Higher nickel ion rejections (97.3%) were obtained at the higher nickel concentration (100mg/l) than at the lower nickel concentration (93.6%). Higher flux was obtained at the higher pH (pH 4) with a 0.01M NaCl background solution than at lower pH (pH 3) when a 0.05M NaCl was used as background solution. Higher nickel ion rejections were obtained at higher pH (pH 4) for the two ionic strength background solutions. Higher fluxes were also obtained with the lower NaCl background solution. Slightly higher ion rejections were obtained with the lower NaCl background concentration. It therefore appears that this nanofiltration membrane should be successfully applied for the removal of nickel ions from acid mine drainage.

Thermoplastic-Thermoset Nanostructured Polymer Blends

Polymer blends are presently attracting both scientific and industrial interest because of their potentials as economical alternatives to more expensive engineering polymers and non-polymeric materials. More importantly, nanostructure polymer blends could lead to the design and production of low-cost materials with valuable properties in comparison to conventional polymer blends. However, thermoplastics/thermosets blends are problematic because such blends naturally tend to phase separation on the macroscopic scale. Therefore, controlling the phase behavior and morphology by reducing phase size and improving interfacial adhesion become key factors in converting these immiscible blends into useful polymeric products. This can be achieved by adding some copolymers as compatibilizers. Also, addition of nanoparticles can reduce interfacial tension and improve miscibility between polymers and thus have significant effect on phase behavior of polymer blends. Some of the methods of blending are melt extrusion, higher shear processing, physical blending, and reactive blending.

Flux Decline and Rejection Characteristics During Nanofiltration of Iron and Deionized Water

This work was studied to determine the flux decline during nanofiltration of iron and deionised water. The rejection characteristic of iron was also studied. A stirred-cell was used for the experiment and Inductively Coupled plasma optical emission was used for iron analysis at various pH and pressure. The significant increased in flux declined at pH 3.01 and 3.44 is possibly caused by crystallized solids formed at the surface of the membrane and thus lead to the reduction of iron rejection at pH 3.01 and 3.44. At higher pressure more water passes through the membrane, thereby increasing the iron rejection. Experiment of clean water flux was done using the deionised water after the different pH experiment to see if the membrane is not fouling. The rejection characteristic of iron was also studied.