The pollution caused by heavy metals is one of the major environmental problems that is imperative to be solved. New technologies, easy to implement and to adapt to any system, deserve special attention and are a focus of this work. The ability of a biofilm of Escherichia coli supported on kaolin to remove Cr(VI), Cd(II), Fe(III) and Ni(II) from aqueous solutions was investigated in batch assays for the treatment of diluted aqueous solutions. The biosorption performance, in terms of uptake, followed the sequence: Fe(III) > Cd(II) > Ni(II) > Cr(VI). The equilibrium data in batch systems were described by Langmuir, Sips and Redlich-Peterson model isotherms. The best fit for chromium and nickel was obtained with the Redlich-Peterson model and for cadmium the best fit was obtained with the Sips model. The presence of functional groups on the cell wall surface of the biomass that may interact with the metal ion was confirmed by FTIR. Kaolin samples have been fully characterized by chemical analyses. The results obtained are very promising for the removal of metal ions from effluents.

The aim of this study is the preparation and characterization of new catalytic materials to be used in oxidation reactions through the recovery of heavy metals in wastewater. The recovery of Cr(III) and Cr(VI) from aqueous solutions by an Arthrobacter viscosus biofilm supported on NaY zeolite was investigated. Experiments were repeated without the bacteria for comparison purposes. The batch method has been employed, using solutions with chromium concentrations of 10 mg L À1 , 25 mg L À1 , 50 mg L À1 and 100 mg L À1. Cr(III) was easily removed from solution due to its positive charge which allows the entrapment in the framework zeolite by ion exchange. However, due to its anionic form Cr(VI) was only removed in the presence of the biofilm that performs its reduction to Cr(III), followed by ion exchange in the zeolite. The best uptake was achieved for initial concentration of 100 mg L À1 : 14 mg g À1 zeolite for Cr(III) by both systems and 3 mg g À1 zeolite for Cr(VI) by the zeolite with the bacterium biofilm. The modified zeolite samples have been fully characterized by surface analysis (XRD, XPS), chemical analyses (ICP-AES), spectroscopic method (FTIR) and microscopic analysis (SEM). The results show that the biofilm of A. viscosus supported on NaY zeolite is able to recover chromium from dilute solutions and the framework zeolite remains unchanged after chromium biosorption.

The ability of three different bacterial species supported on granular activated carbon (GAC) to remove hexavalent chromium from low concentration liquid solutions was investigated, in batch and column studies. The microorganisms tested were Cr(VI) reducing types: Streptococcus equisimilis (CECT 926), Bacillus coagulans (CECT 12) and Escherichia coli (CECT 515). The results showed metal uptake values of 5.82, 5.35 and 4.12 mg/g(bios.), respectively, for S. equisimilis, B. coagulans and E. coli, for an initial metal concentration of 100 mg/l. In the same order and for the initial concentration of 50 mg/l, metal uptake values were 2.33, 1.98 and 3.60 mg/g(bios.). Finally, for the initial metal concentration of 10 mg/l, those values were, respectively, 0.66, 1.51 and 1.12 mg/g(bios.). Studies made with an industrial effluent, with the aim of testing these biofilms in a real situation, showed values of Cr uptake of 0.083, 0.090 and 0.110 mg/g(bios.), respectively, for S. equisimilis, B. coagulans and E. coli, for an initial concentration of 4.2 mg/l of total Cr. The quantification of polysaccharides, playing a key role in the whole process, was made and it was concluded that the production of polysaccharides is higher for B. coagulans followed by S. equisimilis and E. coli (9.19, 7.24 and 4.77 mg/g(bios.)). The batch studies data were described using the Freundlich, Langmuir, Redlich-Peterson, Dubinin-Radushkevich, Sips and Toth model isotherms. The best fit was obtained with Sips and Toth model isotherms, respectively, for the S. equisimilis and for the B. coagulans biofilms. For the E. coli biofilm the Freundlich, Redlich-Peterson, Sips and Toth models fitted very well to the experimental data. The Adams-Bohart, Wolborska and Yoon and Nelson models were applied to column studies data. Those models were found suitable for describing the dynamic behaviour of the columns with respect to the inlet chromium concentration. Obtained results showed that the biofilms tested are very promising for the removal of Cr(VI) in diluted industrial wastewater. Despite differences in the cell wall structure and composition, the three bacteria exhibit comparable sorption affinities towards chromium, in the open systems studies. The Gram-positive bacteria tested (B. coagulans and S. equisimilis) presented best metal removal percentages in batch studies.

The aim of the present work was to optimize the reduction and removal of chromium from aqueous solutions by a biosorption system consisting of a bacteria supported on a zeolite. The system proposed combines the biosorption properties of Arthrobacter viscosus, with the ion exchange capacity of NaY zeolite. Experiments were also performed without the zeolite for comparison purposes. Experimental parameters such as solution pH, biomass concentration and initial Cr(VI) concentration were investigated in order to assess their influence on the biosorption system. The results revealed that chromium biosorption was highly pH dependent. The lower pH values favored Cr(VI) reduction, while higher solution pH enhanced total chromium removal. After the optimization of the parameters in study, the highest content of chromium in the zeolite (0.9%) and best uptake (13.0 mg Cr /g zeolite ) were obtained for the experiment at pH 4, biomass concentration of 5 g L À1 and initial Cr(VI) concentration of 100 mg L À1 . After the biosorption process, the samples were characterized by chemical analyses (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The XPS spectra of bacteria revealed that the chromium loaded on the biomass surface was in the trivalent form.

The aim of this work is to evaluate the applicability of a biofilm to the removal of chromium in solution, at a pilot scale. The effect of the initial concentration of metal on the biosorption behavior of an Arthrobacter viscosus biofilm supported on granular activated carbon, in batch and column essays was also analyzed. Six isotherm equations have been tested in the present study. The best fit was obtained with the Freundlich model. It was observed that as the initial chromium concentration increases, the uptake increases too, but the removal percentage decreases, with values between 95.20% (C(0)=5mg/l) and 38.28% (C(0)=1000 mg/l). The batch adsorption studies were used to develop a pilot bioreactor able to remove chromium from aqueous solutions. Data obtained in a pilot-scale reactor showed an average removal percentage of 99.9%, during the first 30 days, for the initial concentration of 10mg/l and an average removal percentage of 72%, for the same period and for the initial concentration of 100mg/l. Uptake values of 11.35 mg/g and 14.55 mg/g were obtained, respectively, for the initial concentration of 10 and 100mg/l. The results obtained are very promising and encourage the utilization of this biofilm in environmental applications.

The ability of a biofilm of Bacillus coagulans supported on granular activated carbon (GAC) to biosorb Cr(VI) was investigated in batch and column studies so it may be applied to low metal concentration wastewater treatment. The quantification of polysaccharides and polymeric net revealed a value of 9.19 mg/g biosorbent for the polysaccharides and 75 mg/g biosorbent , for the polymeric net. The results obtained with open systems showed uptake values of 1.50, 1.98 and 5.34 mg/g biosorbent , respectively, for initial concentrations of 10, 50 and 100 mg/L of Cr(VI). Column studies performed with an industrial effluent showed values of Cr uptake of 0.090 mg/g biosorbent , for an initial concentration of 4.2 mg/L. The presence of functional groups on the cell wall surface of the biomass that may interact with the metal ion, was confirmed by FTIR. The equilibrium studies in batch systems were described by Freundlich, Langmuir, Reddlich-Peterson, Dubinin-Radushkevich, Sips and Toth model isotherms. Best fit was obtained with Toth model isotherm. Data from column studies were described by Adams-Bohart and Wolborska models. These models were found suitable for describing the dynamic behaviour of the columns with respect to the inlet chromium concentration. The whole study showed that the biofilm tested is very promising for the removal of Cr(VI) in industrial wastewater.

The catalytic oxidation of 1,2-dichlorobenzene was investigated over NaYand NaX zeolites, loaded with chromium through the action of a robust biosorption system consisting of a bacterial biofilm supported on the zeolites. The results of biosorption showed that the maximum metal removal efficiency was 20%, in both systems based on NaYor NaX, starting from solutions with chromium(VI) concentrations ranging from 50 to 250 mg Cr /L. The bacterial biofilm, Arthrobacter viscosus, supported on the zeolite reduces Cr(VI) to Cr(III). The Cr(III) is retained in the zeolite by ion exchange. The new catalysts were characterized by spectroscopic methods (FTIR ), chemical analyses (ICP-AES), surface analysis (XRD) and thermal analysis (TGA). The various techniques of characterization show that this biosorption process does not modify the morphology and structure of the FAUzeolites. These catalysts, Cr/FAU, prepared through this new procedure present good activity and selectivity for dichlorobenzene oxidation in wet air at 350 8C. The Cr 50 -Y was selected as the most active, selective and stable catalyst for oxidation of 1,2-dichlorobenzene in wet air. #

a b s t r a c tOne of the major environmental concerns of nowadays is the presence of heavy metals in industrial effluents. Aiming a solution for this problem, various efforts have been made towards research and implementation of economic and easily adaptable processes to remove heavy metals. The ability of a biofilm of Escherichia coli supported on NaY zeolite to biosorb Cr(VI), Cd(II), Fe(III) and Ni(II) was investigated in batch experiments aiming the treatment of wastewater with low metal concentrations. The biosorption performance, in terms of uptake, followed the sequence: Fe(III) > Ni(II) > Cd(II) > Cr(VI). The equilibrium data in batch systems were described by Langmuir, Sips and Toth isotherms. The best fit for chromium was obtained with the Toth model isotherm and for cadmium and nickel the best fit was the obtained with the Sips model. The presence of functional groups on the cell wall surface of the biomass that may interact with the metal ion, was confirmed by FTIR. The whole study showed that the biofilm tested is very promising for the removal of metal ions from effluents.