Kumudini V. Marathe

Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal.

Chronic contamination of groundwaters by both arsenic (As) and fluoride (F) is frequently observed around the world, which has severely affected millions of people. Fluoride and As are introduced into groundwaters by several sources such as water-rock interactions, anthropogenic activities, and groundwater recharge. Coexistence of these pollutants can have adverse effects due to synergistic and/or antagonistic mechanisms leading to uncertain and complicated health effects, including cancer. Many developing countries are beset with the problem of F and As laden waters, with no affordable technologies to provide clean water supply. The technologies available for the simultaneous removal are akin to chemical treatment, adsorption and membrane processes. However, the presence of competing ions such as phosphate, silicate, nitrate, chloride, carbonate, and sulfate affect the removal efficiency. Highly efficient, low-cost and sustainable technology which could be used by rural populations is of utmost importance for simultaneous removal of both pollutants. This can be realized by using readily available low cost materials coupled with proper disposal units. Synthesis of inexpensive and highly selective nanoadsorbents or nanofunctionalized membranes is required along with encapsulation units to isolate the toxicant loaded materials to avoid their re-entry in aquifers. A vast number of reviews have been published periodically on removal of As or F alone. However, there is a dearth of literature on the simultaneous removal of both. This review critically analyzes this important issue and considers strategies for their removal and safe disposal.

Simultaneous removal of nickel and cobalt from aqueous stream by cross flow micellar enhanced ultrafiltration

Nickel and cobalt were simultaneously removed from aqueous feed using cross flow micellar enhanced ultrafiltration. Twenty kiloDalton polysulfone membrane was used and the rejection more than 99% was obtained. The effect of operating variables like inlet flow rate, inlet pressure, feed metal ions concentration, surfactant to metal ion (S/M) ratio and pH on the rejection of metal ions was investigated. Gel layer formation and concentration polarization was insignificant under the present experimental condition. Presence of salt in the aqueous feed results in drop in rejection from 99% to 88%. The distribution coefficient of solutes in the micellar phase and aqueous phase was estimated from ultrafiltration data. The loading of micelles was also estimated for both the nickel and cobalt ions which confirmed the reproducibility of the micellar enhanced ultrafiltration (MEUF) experiments.

Dynamic Analysis and Optimization of Surfactant Dosage in Micellar Enhanced Ultrafiltration of Nickel from Aqueous Streams

Abstract The micellar enhanced ultrafiltration of Ni(II) ions from the aqueous solution was studied for the dead end system using 20KD Polysulfone membrane. Dynamic behavior of the system was studied with respect to the rejection, yield, and normalized flux. The effect of feed metal ion concentration, surfactant concentration, pH, transmembrane pressure, and S/M ratio was investigated and the optimization of S/M ratio was done. The optimum S/M ratio was 10 while the critical S/M ratio was 5. The effect of monovalent salts was studied on the rejection of metal ions for the salt concentration between 10 mM to 500 mM.

Membrane Characteristics and Fouling Study in MEUF for the Removal of Chromate Anions from Aqueous Streams

Abstract Micellar‐Enhanced Ultrafiltration (MEUF) of the chromate anions from aqueous solutions has been studied at room temperature (28±2°C) using cationic surfactants, cetyltrimethylammonium bromide (CTAB), and cetylpyridinium chloride (CPC), micelles of which adsorb the chromate ions by electrostatic interactions. The solution is processed by ultrafiltration, using a membrane with a pore size small enough to block the passage of the micelles and the adsorbed ions. The process is highly efficient in removing the chromate ions. In the absence of other electrolytes, chromate ion rejections up to 99% were observed at optimal conditions of pH, pressure, temperature, feed chromate, and surfactant concentrations. The presence of added NaCl reduces the chromate rejection, but it was still considerable (up to 82%), even in the presence of 100 mM NaCl. The rejection rate of chromate was found to be highly dependent on the pH of the feed solution. The influence of membrane characteristics on the chromate ion removal was also studied. Various resistances like fouling resistance, concentration polarization resistance, and membrane resistance were also estimated to quantify their effects on the removal efficiency and on the flux behavior.

Adsorption of Lactic Acid on Weak Base Polymeric Resins

Abstract Sorption of lactic acid from a simulated broth has been investigated using weak base ion exchange polymeric resins which behave as functionalized polymers because of tertiary amino groups on the polymer matrix. The equilibrium data for the uptake of lactic acid are represented by Langmuir‐Freundlich combination isotherm. The sorption has been modeled by a phase equilibrium approach using the extended Flory‐Huggins theory of polymer solutions. The interaction of media components, such as glucose and inorganic salts, with the resins and their effect on lactic acid sorption, also has been investigated.

Removal of Ni(II) ions from wastewater by micellar enhanced ultrafiltration using mixed surfactants

Ni(II) ions were removed from aqueous waste using micellar enhanced ultrafiltration (MEUF) with a mixture of surfactants. The surfactant mixture was the nonionic surfactant Tween 80 (TW80) mixed with the anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios ranging from 0.1–1.5. The operational variables of the MEUF process such as pH, applied pressure, surfactant to metal ion ratio and nonionic to ionic surfactant molar ratio (α) were evaluated. Rejection of Ni and TW80 was 99% and 98% respectively whereas that for SDS was 65%. The flux and all resistances (fouling resistance, resistance due to concentration polarization) were measured and calculated for entire range of α respectively. A calculated flux was found to be declined with time, which was mainly attributed to concentration polarization rather than resistance from membrane fouling.

Separation of Dissolved Phenolics from Aqueous Waste Stream using Micellar Enhanced Ultrafiltration

The micellar enhanced ultrafiltration (MEUF) process has been used for the separation of phenol and o-cresol from aqueous solutions at room temperature (30 + 2°C) using a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and polyethersulfone membrane of molecular weight cut-off 10 kDa. The effect of the cross-flow rate, the surfactant to pollutants (S/P) concentration ratio in feed, the variation of pollutants concentration in the feed keeping S/P constant, the presence of Na2SO4 and NaCl salts and mixed surfactants on the rejection of each solute and permeate flux have been studied in detail. The % rejection of phenol and o-cresol without using the surfactant observed was 24% and 41% respectively, which was increased to 60% for phenol and 80% for o-cresol at S/P ratio of 8. The effect of salts was also investigated. There was no significant effect of the cross-flow rate on the % rejection of the solutes. The effect of the membrane pore size was also investigated using 1 KDa and 30 KDa PES membranes. Characteristic parameters of MEUF such as the distribution coefficient, micelle loading, and the micelle binding were also estimated.

Simulation of micellar enhanced ultrafiltration by multiple solute model.

Multiple solute ultrafiltration models in micellar enhanced ultra filtration (MEUF) have been studied, for experimental results of selective separation of Cu (II) and Co (II) with anionic surfactant, sodium dodecyl sulfate (SDS) and imino diacetic acid (IDA) as chelating agent using synthetic waste water. This model is based on mass balance analysis coupled with the filtration theory, resistance-in-series model and gel polarization model. This model is characterized by the parameters, membrane resistance R(m), membrane permeability P(m), back transport coefficient K(b), K(bi) and mass transfer coefficient k(i). These parameters are estimated by using the Levenberg-Marquardt method coupled with the Gauss-Newton algorithm. Due to cross currents caused by the superficial velocity, some solutes are removed from the membrane surface and go into the bulk known as back transport effect. Hence back transport coefficient plays significant role in explaining the extent of micellization. The simulation results show a good agreement with the experimental data of permeate quality and flux. The consideration of negligible gel thickness is suitable for dilute solutions.

Modeling and Performance Study of MEUF of Divalent Metal Ions in Aqueous Streams

Abstract Modeling of micellar enhanced ultrafiltration (MEUF) was studied for the removal of Ni from aqueous phase by using sodium dodecyl sulphate for micellisation. Localized adsorption equilibrium model was used to predict the bound and unbound counter ions. The retentate concentration was predicted using localized adsorption equilibrium and a material balance model, and the experimental values are in close agreement with less than 1% deviations. Experimental values of the permeate flux were in close agreement with the predicted values obtained by resistances in the series model. An algorithm was developed for the prediction of the retentate concentration.

Mathematical Modelling for Removal of Mixture of Heavy Metal Ions from Waste-Water Using Micellar Enhanced Ultrafiltration (MEUF) Process

The micellar enhanced ultrafiltration (MEUF) was studied for the removal of heavy metals using a mixture of non-ionic surfactant TWEEN-80 and anionic surfactant sodium dodecyl sulphate (SDS). The gel polarization model and resistance-in-series model were used to estimate the mass transfer coefficient (3 x 10-6 m/s) and the permeate flux. The total metal ion concentration was varied from 1 mM-4 mM and the corresponding effect of the trans-membrane pressure and limiting fluxes were studied. The modified resistance-in-series model was applied to these experimental data to correlate the flux with the feed concentration and applied pressure.