Mahmoud Dhahbi

Removal of hexavalent chromium by nanofiltration

Abstract Removal of chromate CrO42− from water was investigated using nanofiltration as a possible alternative to the conventional methods of CrVI removal from aqueous solution. Retention measurements with single reference salt revealed that Donnan exclusion plays an important role. The phenomenological parameters σ and P were calculated using the Spiegler-Kedem equation. The rejection rate depends on the ionic strength and pH. The increasing of ionic strength decreases the retention. The effect of pH was clarified by using a stable diagram of the CrVIH2O system. Better retention was obtained at basic pH.

Treatment of textile wastewater by a hybrid electrocoagulation/nanofiltration process

Untreated effluents from textile industries are usually highly coloured and contain a considerable amount of contaminants and pollutants. Stringent environmental regulation for the control of textile effluents is enforced in several countries. Previous studies showed that many techniques have been used for the treatment of textile wastewater, such as adsorption, biological treatment, oxidation, coagulation and/or flocculation, among them coagulation is one of the most commonly used techniques. Electrocoagulation is a process consisting in creating metallic hydroxide flocks within the wastewater by the electrodissolution of soluble anodes, usually made of iron or aluminium. This method has been practiced for most of the 20th century with limited success. In recent years, however, it started to regain importance with the progress of the electrochemical processes and the increase in environmental restrictions in effluent wastewater. This paper examines the use of electrocoagulation treatment process followed by nanofiltration process of a textile effluent sample. The electrocoagulation process was studied under several conditions such as various current densities and effect of experimental tense. Efficiencies of COD and turbidity reductions and colour removal were studied for each experiment. The electrochemical treatment was indented primarily to remove colour and COD of wastewater while nanofiltration was used to further improve the removal efficiency of the colour, COD, conductivity, alkalinity and total dissolved solids (TDS). The experimental results, throughout the present study, have indicated that electrocoagulation treatment followed by nanofiltration processes were very effective and were capable of elevating quality of the treated textile wastewater effluent.

Extraction of phenol from aqueous solutions by means of supported liquid membrane (MLS) containing tri-n-octyl phosphine oxide (TOPO)

This paper deals with the liquid-liquid extraction and the facilitated transport through a supported liquid membrane (SLM) system of aqueous phenol using tri-n-octyl phosphine oxide (TOPO) dissolved in an appropriate organic solvent. Phenol has been quantitatively extracted from aqueous acidic solutions using TOPO dissolved in kerosene as organic phase. The effect of TOPO concentration dissolved in kerosene on the extraction efficiency reveals that TOPO combined with phenol in the ratio of 1:1. Using a flat-sheet SLM (FSSLM) system, more than 65% of the initial phenol content in the feed phase was extracted and stripped in a NaOH aqueous receiving phase. The important operational variables affecting the facilitated transport of phenol through the FSSLM system studied are concentration of TOPO, membrane viscosity, feed phase pH, initial phenol concentration, polymeric support type and membrane stability. Regardless of its comparatively low extraction efficiency of phenol, the SLM based on TOPO exhibits higher long-term stability as compared to tributyl phosphate (TBP). Elaborated SLM system retained its stability and initial performance during the 5 days long experiment contrary to the TBP-SLM system where a time dependent negative tendency (transport efficiency decline) was observed.

Removal of Eriochrome Blue Black R from wastewater using micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) represents a potentially attractive tool for the removal of different contaminants from wastewater. In this study, MEUF was carried out to investigate the retention of Eriochrome Blue Black R (EBBR), an anionic dye, from aqueous stream. N-Alkyltrimethylammonium bromide i.e. dodecyltrimethylammonium bromide (C(12)TAB), tetradecyltrimethylammonium bromide (C(14)TAB), cetyl-trimethylammonium bromide (C(16)TAB) and octadecyltrimethylammonium bromide (C(18)TAB) were taken as cationic surfactants, and NaCl, Na(2)SO(4), Na(2)HPO(4) as electrolytes. A hydrophilic membrane made of cellulose (molecular weight cut-off 10000 Da) was used in a cross-flow ultrafiltration unit. The removal of EBBR was studied as a function of dye and surfactant concentrations, ionic strength, transmembrane pressure and pH. The MEUF experiments showed that the highest dye rejection was about 99% for the used range of dye and surfactant concentrations. This retention depended slightly on dye and surfactant concentrations, ionic strength, pH and transmembrane pressure. However, permeate flux changed significantly with those parameters due mainly to concentration polarisation and osmotic pressure.

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.

Transport and Thermodynamic Properties of Ethylammonium Nitrate–Water Binary Mixtures: Effect of Temperature and Composition

Physical properties such as densities, ρ, viscosities, η, and conductivities, κ, have been measured for the binary mixtures of the ionic liquid ethylammonium nitrate, EtNH3NO3, with water over the entire molar fraction range at various temperatures ranging from 293.15 to 318.15 K and under ambient pressure. Strong effects of the composition and temperature on these properties have been observed. Experimental densities and viscosities were used to calculate the corresponding excess properties. The variations of excess molar volume and excess Gibbs energy against the ionic liquid fraction show complementary extrema (minima and maxima with opposite signs). The excess molar volumes and excess viscosity deviations are well fitted using the Redlich–Kister polynomial. Moreover, the viscosity was found to be temperature dependent and followed the Arrhenius law. Variations of the activation energies for viscous flow versus the ionic liquid content revealed a modification in the medium’s structure. The conductivity–temperature relationship was found to be better represented by the Vogel–Tammann–Fulcher model than with the Arrhenius equation. In addition, variations of the conductivity with composition are well described by the Casteel–Amis equation. The impact of addition of the ionic liquid to water on the viscosity and the conductivity have been also examined using Walden’s rule, which shows that viscosity is highly correlated to conductivity for ionic liquid molar fractions higher than ca. 0.2. Activation thermodynamic parameters for viscous flow, calculated from the viscosity data, reveal that changes in the medium structure occur at ca. 0.2 and 0.8 molar fractions of ionic liquid.

Spectral study of Eriochrome Blue Black R in different cationic surfactant solutions

Interactions of anionic dye Eriochrome Blue Black R (EBBR) with various cationic micelles of surfactants n-alkyltrimethylammonium CnTAB (n=12; 14; 16 and 18) have been investigated spectrophotometrically at 25°C in premicellar and postmicellar region. The results have shown that with increasing the alkyl chain length of surfactants, the maximum absorbance of EBBR shifted to a higher wavelength and the binding constants of EBBR to cationic micelles (Kb) increases. This confirms that the surfactant micelle, which has a longer alkyl hydrocarbon chain, enables greater solubilization of dye. Thus, the hydrophobic interaction of the dye with micelles increases in the order: C12TAB

Removal of heavy metals from aqueous solution by polyacrylic acid enhanced ultrafiltration

AbstractOne of the recently developed water treatment processes is the polyelectrolyte-enhanced ultrafiltration (PEUF). This technique combines a membrane filtration process (ultratfiltration) and a cation–polyectrolyte complexation technique. PEUF is shown to be an efficient technology for the removal of heavy metals from liquid effluents even at low concentrations. In this proposal, the removal of three heavy metals (cadmium, copper and zinc) from aqueous solutions by PEUF process was investigated. The poly(acrylic acid) (PAA) with an average molecular weight 100 kDa was used as complexing agent. The ultrafiltration experiments were performed using a tangential cell system equipped with a polyethersulphone membrane having a 10.000 molecular weight cut-off (MWCO). To improve the retention of the heavy metal ions, the effect of some operating parameters and solution characteristics were studied. For different PAA concentrations, this study showed that all permeate fluxes increased linearly by increasing t...

Denitrification of brackish water by electrodialysis: Effect of process parameters and water characteristics

The aim of this work is to study the removal of nitrate from brackish polluted water using electrodialysis. The influence of several parameters, such as flow rates, initial feed concentration, co-existing anions and initial pH on process efficiency were studied. This efficiency is evaluated by the removal rate, demineralization rate and power consumption. The denitrification process showed to be independent of pH of feed solution. Although The flow rate as well as the initial salt concentration and also the coexisting anions on the feed solution play a significant role on the denitrification efficiency and mainly on the specific power consumption. The decrease of this parameter induces a decrease on the total energy needed to perform required operation. The denitrification of a contaminated real water sample was investigated so as to improve the efficiency of denitrification process. The nitrate concentration could be reduced from 225 to 25.5 mg L−1 (88% removal) which was lower than World Health Organization (WHO) standard (50 mg L−1). Moreover the concentrations of different species in the obtained treated water are below the amounts recommended by WHO for drinking water.

Electrodialytic Removal of Cadmium from Brackish Water: Effects of Operating Parameters

The continuous increase of environmental regulations make interesting to find effective and efficient methods for processing effluents containing metal ions. This research focuses on cadmium removal from brackish water by an electro-membrane process: The electrodialysis. Experiments were carried out on synthetic brackish water solutions and using a laboratory scale electrodialysis system. The influence of several parameters on process efficiency was investigated. The efficiency of this process was assessed by the determination of five parameters: The demineralization rate, the removal rate and the transport flux of cadmium, the current efficiency and the specific power consumption. The applied voltage, the feed flow rate, the pH and cadmium initial concentration of the feed solution have a significant effect on the process efficiency and mainly on the cadmium transfer from dilute to concentrate compartment. In contrast, feed ionic strength seems to affect only the SPC and not the R(Cd).