Subhas K. Sikdar

Membrane technologies for remediating contaminated soils: a critical review

Regulatory compliance requires that soils contaminated with toxic organic and metallic compounds be cleaned up. Several chemical and thermal detoxification technologies are commercially available for directly treating the contaminated soils excavated from contaminated sites. In contrast, soil washing with aqueous solutions transfers the contaminants from the solid matrix to the aqueous fraction which, then, needs to be further treated. Membranes have not been used much for treating these effluents. However, several membrane techniques appear promising. In these techniques, the main objective is to find ways of concentrating the contaminants with much higher volume reduction than is customarily available. Applications of membranes to soil washings should primarily be looked upon as an inexpensive aid to destruction, disposal, or recovery technologies that determine the ultimate fate of the contaminants.

Enzyme and protein mass transfer coefficient in aqueous two-phase systems. I: Spray extraction columns

Fractional dispersed phase hold-up and dispersed side mass transfer coefficients for bovine serum albumin (BSA) and amyloglucosidase were measured in 22, 34, 50, 56, 70 and 95 mm i.d. spray columns using salt-polyethylene glycol (potassium phosphate-PEG and sodium sulphate-PEG) systems. The effect of distributor design and column height were investigated. The effect of phase compositions of the aqueous phase system was also studied. Empirical and semi-empirical correlations have been developed for fractional dispersed phase hold-up and dispersed side mass transfer coefficients.

Application of osmotic dewatering to the controlled crystallization of biological macromolecules and organic compounds

Abstract Several methods of crystallization of biological macromolecules depend upon the transport of water through the vapor phase - a process that is sensitive to ambient conditions (temperature, relative humidity). Other methods depend on the transport of solute by diffusion or through a membrane. By regulating the solute concentration on the outside of a reverse-osmosis membrane it is possible to control the rate at which macromolecules and other solutes are concentrated inside a membrane-bound fluid. The effect of dewatering rate on lysozyme crystal quality and growth rate was assessed. A 3-fold increase in concentration over a 9 day period yielded tetragonal crystals 0.5 mm on a side with sharp edges and with ordering at least to 1.73 A. Transparent crystals of triglycine sulfate were grown by osmotic dewatering; in this case crystal growth could be enhanced or reversed by manipulating the external solution.

Thin and composite high-flux membranes of perfluorosulfonated ion-exchange polymer

Abstract We report the techniques of casting thin and composite membranes of perfluorosulfonic acid polymer (PFSA). The thin PFSA membrane was prepared by a hot-casting method using an aqueous methanol solution with nonsolvents cyclohexanol and dimethylformamide. The composite PFSA membrane was cold-cast and subsequently cured at a higher temperature. Scanning electron micrographs showed the thin membrane to be asymmetric, whereas the composite membrane had a thin homogeneous polymer layer on the porous support. Permeation through the membranes was tested using several amino acids and their mixtures as model permeants. We found that membranes of both types provided higher fluxes than the commercial membrane of the same polymeric material. Permeation studies on amino acid mixtures using the composite membrane revealed that glycine permeated faster than either L-alanine or L-phenylalanine, and that glycine separation factors were higher for the composite PFSA membrane than for other polymeric membranes.

Protein extraction in a spray column using a polyethylene glycol-maltodextrin two-phase polymer system

Protein recovery, with bovine serum albumin (BSA) as a model, was performed in a laboratory spray column using inexpensive aqueous two-phase systems. A light phase rich in polyethylene glycol (PEG) was steadily dispersed into a heavy continuous phase containing maltodextrin (MDX). The PEG phase holdup and BSA mass transfer coefficients were measured in spray columns with internal diameters of 22 and 33 mm, using several sparger designs. The overall BSA mass transfer coefficients were greater in the PEG-maltodextrin systems than those encountered in PEG-dextran systems with similar BSA partition coefficients. Empirical correlations are proposed for mass transfer coefficients and PEG phase holdup.

Glycine Permeation through Na+, Ag+, and Cs+ Forms of Perfluorosulfonated Ion-Exchange Membranes

Abstract We have studied the effect of counterions in perfluorosulfonated ion-exchange membranes on glycine permeation and found that counterions controlled permeation behavior. The Na+ form of the membrane exhibited saturation kinetics of the Michaelis-Menten type; that is, the flux rapidly increased with concentration and reached a limiting flux at a concentration of about 2 mol/L. The Cs+ form exhibited markedly lower fluxes which were nearly Fickian. For the Ag+ form, however, the fluxes increased rapidly and nonlinearly at low concentrations, but attained Fickian linearity at high concentrations. Ionizability of the sulfonate groups and hydration numbers of the counterions appeared to cause departure from Fickian behavior.

Mass transfer coefficients in two-phase aqueous extraction

Abstract Mass transfer coefficients were measured in a 51 mm i.d. stirred cell with a plane interface. An aqueous solution of Dextran formed the heavy phase and an aqueous solution of polyethyleneglycol formed the light phase. The transfer of bovine serum albumin (BSA) was investigated. The effects of stirring speed, pH and phase concentrations on the mass transfer coefficient were studied. Values of the partition coefficient for BSA are reported at different values of pH and phase concentrations. A new method is suggested for finding individual phase mass transfer coefficients, using the effect of pH on partition coefficient.

Two phase aqueous extraction: rheological properties of dextran, polyethylene glycol, bovine serum albumin and their mixtures

Rheological properties have been measured for aqueous solutions of dextran, polyethylene glycol and bovine serum albumin. Mixtures of these materials have also been studied. A rotating concentric cylinder viscometer was used to study the rheological properties of these materials over the temperature range 10 to 40°C. Over the range of concentrations, molecular weights, temperature and shear rates covered in this work, all aqueous solutions exhibited Newtonian behaviour. Correlations have been reported for viscosities of dextran, polyethylene glycol, and bovine serum albumin. The viscosity of mixtures of these materials is not linear with respect to concentration.

Partition coefficient of bovine serum albumin in two-phase aqueous systems

We measured partition coefficients of bovine serum albumin in the following two-phase aqueous systems: polyethylene glycol-dextran and polyethylene glycol-potassium phosphate. We report the effects on partition coefficients of variables such as relative molecular masses of polyethylene glycol and dextran, phase composition and temperature.