Sourav Mondal

Kinetic modeling for dye removal using polyelectrolyte enhanced ultrafiltration

A generalized kinetic model is proposed for the first time for dye removal using polyelectrolytes in application of polyelectrolyte enhanced ultrafiltration. Three polyelectrolyte-dye systems, reported in the literature have been taken up for case studies. Different cases, namely, nature of dye and polyelectrolyte system and their concentration, effect of solution pH and electrolyte concentration have been included in the general framework of the modeling. The equilibrium constants are evaluated by minimizing the errors involved in the measured and experimental values of dye retention data. The matching between the calculated and the experimental data is found to be adequate. A general phase space analysis involving the equilibrium constants has also been carried out to determine the region of feasible solution, in order to facilitate dye removal using engineered polyelectrolyte.

Effects of non-Newtonian power law rheology on mass transport of a neutral solute for electro-osmotic flow in a porous microtube

Mass transport of a neutral solute for a power law fluid in a porous microtube under electro-osmotic flow regime is characterized in this study. Combined electro-osmotic and pressure driven flow is conducted herein. An analytical solution of concentration profile within mass transfer boundary layer is derived from the first principle. The solute transport through the porous wall is also coupled with the electro-osmotic flow to predict the solute concentration in the permeate stream. The effects of non-Newtonian rheology and the operating conditions on the permeation rate and permeate solute concentration are analyzed in detail. Both cases of assisting (electro-osmotic and poiseulle flow are in same direction) and opposing flow (the individual flows are in opposite direction) cases are taken care of. Enhancement of Sherwood due to electro-osmotic flow for a non-porous conduit is also quantified. Effects if non-Newtonian rheology on Sherwood number enhancement are observed.

Mass transport in a porous microchannel for non‐Newtonian fluid with electrokinetic effects

Quantification of mass transfer in porous microchannel is of paramount importance in several applications. Transport of neutral solute in presence of convective‐diffusive EOF having non‐Newtonian rheology, in a porous microchannel was presented in this article. The governing mass transfer equation coupled with velocity field was solved along with associated boundary conditions using a similarity solution method. An analytical solution of mass transfer coefficient and hence, Sherwood number were derived from first principles. The corresponding effects of assisting and opposing pressure‐driven flow and EOF were also analyzed. The influence of wall permeation, double‐layer thickness, rheology, etc. on the mass transfer was also investigated. Permeation at the wall enhanced the mass transfer coefficient more than five times compared to impervious conduit in case of pressure‐driven flow assisting the EOF at higher values of κh. Shear thinning fluid exhibited more enhancement of Sherwood number in presence of permeation compared to shear thickening one. The phenomenon of stagnation was observed at a particular κh (∼2.5) in case of EOF opposing the pressure‐driven flow. This study provided a direct quantification of transport of a neutral solute in case of transdermal drug delivery, transport of drugs from blood to target region, etc.

Modeling of Gel Layer-Controlled Fruit Juice Microfiltration in a Radial Cross Flow Cell

An analysis of gel layer-controlled microfiltration in a radial cross flow cell is presented in this study. Clarification of a real fruit juice, i.e., cactus pear juice is considered. An expression of Sherwood number is derived using an integral method under the framework of boundary layer theory. The effects of viscosity and temperature are incorporated in the Sherwood number relationship through the Sieder–Tate type correction factor and Stokes–Einstein equation, respectively. The transient flux behavior is modeled successfully both for the total recycle mode and batch concentration mode of operation. The model parameters are evaluated from the total recycle mode and are used in the predictive calculation of the batch concentration mode. In batch concentration mode of filtration, the model predicted results match excellently with the experimental data.

Mass transfer of a neutral solute in porous microchannel under streaming potential.

The mass transport of a neutral solute in a porous wall, under the influence of streaming field, has been analyzed in this study. The effect of the induced streaming field on the electroviscous effect of the fluid for different flow geometries has been suitably quantified. The overall electroosmotic velocity profile and expression for streaming field have been obtained analytically using the Debye–Huckel approximation, and subsequently used in the analysis for the mass transport. The analysis shows that as the solution Debye length increases, the strength of the streaming field and, consequently, the electroviscous effect diminishes. The species transport equation has been coupled with Darcys law for quantification of the permeation rate across the porous wall. The concentration profile inside the mass transfer boundary layer has been solved using the similarity transformation, and the Sherwood number has been calculated from the definition. In this study, the variation of the permeation rate and solute permeate concentration has been with the surface potential, wall retention factor and osmotic pressure coefficient has been demonstrated for both the circular as well as rectangular channel cross‐section.

A socio-economic study along with impact assessment for laterite based technology demonstration for arsenic mitigation

Arsenic contamination mitigation technologies have been adsorption-based, but the most widely-used and traditionally available adsorbents suffered inherent limitations, including cost infeasibility and problems associated with regeneration and disposal of the spent adsorbent. The present technology is based on indigenously developed activated laterite prepared from the naturally and abundantly available material, and can hence easily be scaled up for community usage and large scale implementation. The total arsenic removal capacity is 32.5mg/g, which is the highest among all naturally occurring arsenic adsorbents. A major issue in earlier adsorbents was that during regeneration, the adsorbed arsenic would be released back into the environment (leaching), and would eventually contaminate the groundwater again. But the adsorbent in this filter does not require regeneration during its five-year lifespan and does not leach upon disposal. An attempt is made to test and demonstrate the practical implementation of the technology - its effectiveness and viability in three community (primary schools - one in Malda and two in north 24 Parganas, West Bengal, India) and 20 household filters, catering to over 5000 people in different areas of West Bengal exposed to high arsenic contamination of groundwater (ranging from 0.05 to 0.5mg/l). The work also focuses on the social impact of the real life technological solution on the lives on the affected people in the worst hit arsenic affected communities, perhaps the greatest public health risk emergency of the decade.

A molecular simulation based assessment of binding of metal ions on micelles.

An assessment of the ability of a micellar surface to bind different metal ions using molecular simulation is presented in this study. Sodium dodecyl sulfate (SDS) is considered as the anionic surfactant. Various relevant characteristics of SDS-metal ion systems are estimated to quantify preferential binding of metal ions. These are electrostatic energy, total potential energy of the system, radial distribution function, and entropy and free energy change of the system. By examining these parameters, the relative extents of binding of different metal ions to the micellar surface are assessed.

Advances in Dye Removal Technologies

The presence of colored wastewater in the aquatic streams is hazardous to the environmental ecology affecting the aquatic life severely. With the growth of textile industry, dye-containing effluent is a potential water treatment issue. Moreover, dye-containing wastewater (even in trace amounts) is toxic to human consumption. There have been several conventional water treatment technologies based on adsorption which purifies dye-containing wastewater. The present chapter explains an overview to the different processes, types of dye compounds, and the safe discharge limits of different types of contamination-containing dyes.

Adsorption of Dyes

Adsorption is one of the most commonly used, traditional separation technologies utilized for separation. Since it is an equilibrium-governed process, the process efficiency is excellent, but the throughput is relatively low. Nevertheless, because of its simplicity, this is one of the normally used technologies for dye removal from aqueous stream. Therefore, it is imperative to understand the modeling aspects of such adsorbent-based systems which is necessary for design and implementation of the technology. Additionally, the chapter describes the characteristics of the different commonly used adsorbents and its applicability.

Atomistic level molecular dynamics simulation on the solubilization mechanism of aromatic molecules in anionic micelles

Molecular dynamics simulation of micelle–organic complex reveals interesting insights into the solubilization and stability of such systems. Various interpretations based on measurement of size, solubilization isotherm, time resolved fluorescence decay, etc., provide qualitative information about solubilization of organic molecules, mostly benzene and alkanols. The present simulation, based on all-atom CHARMM force-field parameters analyzes the solubilization mechanism. It is observed that solubilization of benzene and toluene occurs in the palisade and inner core of the micelle. Polar aromatics such as pyridine and phenol are solubilized in the micelle–water interface and Stern layer. The hydrophobicity, polarity and size of the aromatic molecule influence solubilization. Thermodynamic free energy and entropy change of the system are responsible for deformation in the shape of the micelle and its binding efficiency. The present work helps in selection of surfactant–solute pairs and fundamental understanding of the micellar enhanced ultrafiltration process for removal of toxic organic components from water.