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Papers by Maria Elena Russo

The local atomic structure and chemical nature of newly synthesized silver nanoparticles (AgNPs) ... more The local atomic structure and chemical nature of newly synthesized silver nanoparticles (AgNPs) function-alized with the organic thiol allylmercaptane (AM) have been probed combining synchrotron radiation-based techniques: X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). Complementary information about the chemical and electronic structure is obtained combining XAFS and XPS data. These results coherently suggest a core shell morphology of the NPs resulting in metallic Ag cores surrounded by Ag 2 S-like phase. The external layer of AM molecules is grafted to the NPs surface through Ag−S chemical bonds. NP size and composition were found as a function of the chemical synthetic route (i.e., Ag/AM molar ratio). It was observed that by increasing the Ag/AM ratio, larger AgNPs were obtained. It was found that a higher Ag/AM molar ratio leads to an increasing of the Ag 2 S layer thickness, while the external AM layer remains unvaried. TEM analysis showed well-separated and dispersed nanoparticles, and ED pattern allowed one to identify two different phases of single crystal corresponding to the presence of Ag face-center-cubic single-crystal symmetry, together with weak diffraction spots in agreement with Ag 2 S cubic symmetry in Im3m space groups.

Journal of Industrial Microbiology & Biotechnology, 2010

In this study, we report on a butanol production process by immobilized Clostridium acetobutylicu... more In this study, we report on a butanol production process by immobilized Clostridium acetobutylicum in a continuous packed bed reactor (PBR) using Tygon® rings as a carrier. The medium was a solution of lactose (15–30 g/L) and yeast extract (3 g/L) to emulate the cheese whey, an abundant lactose-rich wastewater. The reactor was operated under controlled conditions with respect to the pH and to the dilution rate. The pH and the dilution rate ranged between 4 and 5, the dilution rate between 0.54 and 2.4 h−1 (2.5 times the maximum specific growth rate assessed for suspended cells). The optimal performance of the reactor was recorded at a dilution rate of 0.97 h−1: the butanol productivity was 4.4 g/Lh and the selectivity of solvent in butanol was 88%w.

Bioresource Technology, 2011

An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is... more An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a continuous stirred tank reactor under controlled conditions adopting a complex medium supplemented with lactose as carbon source to mimic cheese whey. The effects of acids (acetic and butyric), solvents (acetone, ethanol and butanol) and pH on the growth rate of acidogenic cells were assessed. The conversion process was characterized under steady-state conditions in terms of concentration of lactose, cells, acids, total organic carbon and pH. The growth kinetics was expressed by means of a multiple product inhibition and interacting model including a novel formulation to account for the role of pH. The model has the potential to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production.

Journal of Biotechnology, 2010

Chemical Engineering Journal, 2010

Dyes adsorption on granular particles of lyophilised Cunninghamella elegans was characterized in ... more Dyes adsorption on granular particles of lyophilised Cunninghamella elegans was characterized in terms of adsorption isotherm and kinetics. The study refers to dyes of an acid bath for wool: Acid Blue 62, Acid Red 266 and Acid Yellow 49. The dye concentration in model solutions -containing a single dye or the three dyes all together in order to mimic the wastewater -was increased up to about 500 mg/L. Tests showed that the maximum adsorption capacity of the biomass ranges between 300 and 600 mg dye /g DM . Mutual interferences among dyes caused the reduction of the adsorption capacity of the biomass towards the model wastewater. An experimental procedure for the assessment of biosorption kinetics was developed in order to control the effects of the interphase mass transfer on the biosorption rate. The biosorption kinetics were described by both pseudo-first order and pseudo-second order models, depending on the saturation level of the sorbent, and was characterized by a time scale of 1-10 min. The role of the molecular structures of the dyes was discussed. In particular, both kinetics and equilibrium tests confirm that the biomass is more selective towards AR266, probably for the high negative charge density of the -CF 3 functional group that can interact with -NH x active sites of the biomass.

Journal of Biotechnology, 2010

Journal of Biotechnology, 2008

A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-p... more A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-phase internal loop airlift operated continuously with respect to the liquid and gaseous phases, and batchwise with respect to the immobilized cells. The model has been applied to the conversion of phenol by means of immobilized cells of Pseudomonas sp. OX1 whose metabolic activity was previously characterized (Viggiani, A., Olivieri, G., Siani, L., Di Donato, A., Marzocchella, A., Salatino, P., Barbieri, P., Galli, E., 2006. An airlift biofilm reactor for the biodegradation of phenol by Pseudomonas stutzeri OX1. Journal of Biotechnology 123, 464-477). The model embodies the key processes relevant to the reactor performance, with a particular emphasis on the role of biofilm detachment promoted by the fluidized state. Results indicate that a finite loading of free cells establishes even under operating conditions that would promote wash out of the suspended biophase. The co-operative/competitive effects of free cells and immobilized biofilm result in rich bifurcational patterns of the steady state solutions of the governing equations, which have been investigated in the phase plane of the process parameters. Direct simulation under selected operating conditions confirms the importance of the dynamical equilibrium establishing between the immobilized and the suspended biophase and highlights the effect of the initial value of the biofilm loading on the dynamical pattern.

Enzyme and Microbial Technology, 2008

This paper reports on the assessment of two enzyme-based processes for the conversion of syntheti... more This paper reports on the assessment of two enzyme-based processes for the conversion of synthetic dyes. A crude laccase mixture from Pleurotus ostreatus was immobilised on EUPERGIT C 250L © , an acrylic resin with epoxy functionalities. This biocatalyst was used in the conversion of the anthraquinonic dye Remazol brilliant blue R. Two different fixed bed reactors were used to assay the solid biocatalyst activity and to characterize the dye conversion kinetics. The immobilisation procedure was optimized providing a maximum immobilisation yield of 7% of the initial laccase activity in solution. The kinetics of dye conversion was in line with a product-inhibited kinetic model. The biocatalyst underwent moderate deactivation along with conversion. The kinetic models were implemented to describe dye conversion in a continuous fixed bed reactor (CFBR), operated with immobilised laccases, and in a stirred tank reactor (STR), operated with free laccases. The CFBR option enables the remediation of a wastewater volume larger than the one processed in the STR under comparable operating conditions. The better performance of CFBR results from the balanced effect of an improved stability of immobilised laccases and of a loss of activity following immobilisation.

Chemical Engineering Science, 2011

Effects of liquid properties on the hydrodynamics of gas-liquid systems were investigated in lab-... more Effects of liquid properties on the hydrodynamics of gas-liquid systems were investigated in lab-scale bubble column (BC) and internal loop airlift (ILA). Alginate solutions, a glycerol solution and a Boger fluid were adopted to separately address the effects of viscosity and of surface tension for Newtonian fluids, and the effects of relaxation time for non-Newtonian fluid characterized by approximately constant viscosity (low shear thinning). Hydrodynamic regimes were characterized in terms of overall gas holdup, gas-liquid mass transfer coefficient, drift-flux and liquid circulation velocity. The superficial gas velocities at the transition between hydrodynamic regimes (homogenous regime-vortical-spiral regime-heterogeneous regime) as a function the liquid viscosity was characterized by a maximum. The same behavior was observed for the maximum stable gas holdup and gas-liquid mass transfer coefficient in BC. Viscosity enhances homogeneous regime stability for mo4.25 mPa s, in BC, and mo7.68 mPa s, in ILA. For non-Newtonian fluids the transition velocity increases with liquid elasticity.

Journal of Biotechnology

Microorganism kinetic growth characterized by substrate inhibition was investigated by means of a... more Microorganism kinetic growth characterized by substrate inhibition was investigated by means of a continuous stirred tank reactor equipped with a feedback controller of the medium feeding flow rate. The aerobic growth of Pseudomonas sp. OX1 with phenol as carbon/energy source was adopted as a case study to test a new control strategy using dissolved oxygen concentration as a state variable. The controller was successful in steadily operating bioconversion under intrinsically unstable conditions. A simple model of the controlled system was proposed to set the feedback controller. The specific growth rate of Pseudomonas sp. OX1 was successfully described by means of the Haldane model. The regression of the experimental data yielded μ(M)=0.26 h(-1), K(Ph)=5×10(-3)g/L and K(I)=0.2g/L. The biomass-to-substrate fractional yield as a function of the specific growth rate did not change moving from substrate-inhibited to substrate-deficient state. The data was modelled according to the Pirt model: m=1.7×10(-2)g/(gh), Y(X/Ph)(Th)=1.3g/g. The specific growth rates calculated for batch and continuous growth were compared.

The local atomic structure and chemical nature of newly synthesized silver nanoparticles (AgNPs) ... more The local atomic structure and chemical nature of newly synthesized silver nanoparticles (AgNPs) function-alized with the organic thiol allylmercaptane (AM) have been probed combining synchrotron radiation-based techniques: X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). Complementary information about the chemical and electronic structure is obtained combining XAFS and XPS data. These results coherently suggest a core shell morphology of the NPs resulting in metallic Ag cores surrounded by Ag 2 S-like phase. The external layer of AM molecules is grafted to the NPs surface through Ag−S chemical bonds. NP size and composition were found as a function of the chemical synthetic route (i.e., Ag/AM molar ratio). It was observed that by increasing the Ag/AM ratio, larger AgNPs were obtained. It was found that a higher Ag/AM molar ratio leads to an increasing of the Ag 2 S layer thickness, while the external AM layer remains unvaried. TEM analysis showed well-separated and dispersed nanoparticles, and ED pattern allowed one to identify two different phases of single crystal corresponding to the presence of Ag face-center-cubic single-crystal symmetry, together with weak diffraction spots in agreement with Ag 2 S cubic symmetry in Im3m space groups.

Journal of Industrial Microbiology & Biotechnology, 2010

In this study, we report on a butanol production process by immobilized Clostridium acetobutylicu... more In this study, we report on a butanol production process by immobilized Clostridium acetobutylicum in a continuous packed bed reactor (PBR) using Tygon® rings as a carrier. The medium was a solution of lactose (15–30 g/L) and yeast extract (3 g/L) to emulate the cheese whey, an abundant lactose-rich wastewater. The reactor was operated under controlled conditions with respect to the pH and to the dilution rate. The pH and the dilution rate ranged between 4 and 5, the dilution rate between 0.54 and 2.4 h−1 (2.5 times the maximum specific growth rate assessed for suspended cells). The optimal performance of the reactor was recorded at a dilution rate of 0.97 h−1: the butanol productivity was 4.4 g/Lh and the selectivity of solvent in butanol was 88%w.

Bioresource Technology, 2011

An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is... more An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a continuous stirred tank reactor under controlled conditions adopting a complex medium supplemented with lactose as carbon source to mimic cheese whey. The effects of acids (acetic and butyric), solvents (acetone, ethanol and butanol) and pH on the growth rate of acidogenic cells were assessed. The conversion process was characterized under steady-state conditions in terms of concentration of lactose, cells, acids, total organic carbon and pH. The growth kinetics was expressed by means of a multiple product inhibition and interacting model including a novel formulation to account for the role of pH. The model has the potential to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production.

Journal of Biotechnology, 2010

Chemical Engineering Journal, 2010

Dyes adsorption on granular particles of lyophilised Cunninghamella elegans was characterized in ... more Dyes adsorption on granular particles of lyophilised Cunninghamella elegans was characterized in terms of adsorption isotherm and kinetics. The study refers to dyes of an acid bath for wool: Acid Blue 62, Acid Red 266 and Acid Yellow 49. The dye concentration in model solutions -containing a single dye or the three dyes all together in order to mimic the wastewater -was increased up to about 500 mg/L. Tests showed that the maximum adsorption capacity of the biomass ranges between 300 and 600 mg dye /g DM . Mutual interferences among dyes caused the reduction of the adsorption capacity of the biomass towards the model wastewater. An experimental procedure for the assessment of biosorption kinetics was developed in order to control the effects of the interphase mass transfer on the biosorption rate. The biosorption kinetics were described by both pseudo-first order and pseudo-second order models, depending on the saturation level of the sorbent, and was characterized by a time scale of 1-10 min. The role of the molecular structures of the dyes was discussed. In particular, both kinetics and equilibrium tests confirm that the biomass is more selective towards AR266, probably for the high negative charge density of the -CF 3 functional group that can interact with -NH x active sites of the biomass.

Journal of Biotechnology, 2010

Journal of Biotechnology, 2008

A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-p... more A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-phase internal loop airlift operated continuously with respect to the liquid and gaseous phases, and batchwise with respect to the immobilized cells. The model has been applied to the conversion of phenol by means of immobilized cells of Pseudomonas sp. OX1 whose metabolic activity was previously characterized (Viggiani, A., Olivieri, G., Siani, L., Di Donato, A., Marzocchella, A., Salatino, P., Barbieri, P., Galli, E., 2006. An airlift biofilm reactor for the biodegradation of phenol by Pseudomonas stutzeri OX1. Journal of Biotechnology 123, 464-477). The model embodies the key processes relevant to the reactor performance, with a particular emphasis on the role of biofilm detachment promoted by the fluidized state. Results indicate that a finite loading of free cells establishes even under operating conditions that would promote wash out of the suspended biophase. The co-operative/competitive effects of free cells and immobilized biofilm result in rich bifurcational patterns of the steady state solutions of the governing equations, which have been investigated in the phase plane of the process parameters. Direct simulation under selected operating conditions confirms the importance of the dynamical equilibrium establishing between the immobilized and the suspended biophase and highlights the effect of the initial value of the biofilm loading on the dynamical pattern.

Enzyme and Microbial Technology, 2008

This paper reports on the assessment of two enzyme-based processes for the conversion of syntheti... more This paper reports on the assessment of two enzyme-based processes for the conversion of synthetic dyes. A crude laccase mixture from Pleurotus ostreatus was immobilised on EUPERGIT C 250L © , an acrylic resin with epoxy functionalities. This biocatalyst was used in the conversion of the anthraquinonic dye Remazol brilliant blue R. Two different fixed bed reactors were used to assay the solid biocatalyst activity and to characterize the dye conversion kinetics. The immobilisation procedure was optimized providing a maximum immobilisation yield of 7% of the initial laccase activity in solution. The kinetics of dye conversion was in line with a product-inhibited kinetic model. The biocatalyst underwent moderate deactivation along with conversion. The kinetic models were implemented to describe dye conversion in a continuous fixed bed reactor (CFBR), operated with immobilised laccases, and in a stirred tank reactor (STR), operated with free laccases. The CFBR option enables the remediation of a wastewater volume larger than the one processed in the STR under comparable operating conditions. The better performance of CFBR results from the balanced effect of an improved stability of immobilised laccases and of a loss of activity following immobilisation.

Chemical Engineering Science, 2011

Effects of liquid properties on the hydrodynamics of gas-liquid systems were investigated in lab-... more Effects of liquid properties on the hydrodynamics of gas-liquid systems were investigated in lab-scale bubble column (BC) and internal loop airlift (ILA). Alginate solutions, a glycerol solution and a Boger fluid were adopted to separately address the effects of viscosity and of surface tension for Newtonian fluids, and the effects of relaxation time for non-Newtonian fluid characterized by approximately constant viscosity (low shear thinning). Hydrodynamic regimes were characterized in terms of overall gas holdup, gas-liquid mass transfer coefficient, drift-flux and liquid circulation velocity. The superficial gas velocities at the transition between hydrodynamic regimes (homogenous regime-vortical-spiral regime-heterogeneous regime) as a function the liquid viscosity was characterized by a maximum. The same behavior was observed for the maximum stable gas holdup and gas-liquid mass transfer coefficient in BC. Viscosity enhances homogeneous regime stability for mo4.25 mPa s, in BC, and mo7.68 mPa s, in ILA. For non-Newtonian fluids the transition velocity increases with liquid elasticity.

Journal of Biotechnology

Microorganism kinetic growth characterized by substrate inhibition was investigated by means of a... more Microorganism kinetic growth characterized by substrate inhibition was investigated by means of a continuous stirred tank reactor equipped with a feedback controller of the medium feeding flow rate. The aerobic growth of Pseudomonas sp. OX1 with phenol as carbon/energy source was adopted as a case study to test a new control strategy using dissolved oxygen concentration as a state variable. The controller was successful in steadily operating bioconversion under intrinsically unstable conditions. A simple model of the controlled system was proposed to set the feedback controller. The specific growth rate of Pseudomonas sp. OX1 was successfully described by means of the Haldane model. The regression of the experimental data yielded μ(M)=0.26 h(-1), K(Ph)=5×10(-3)g/L and K(I)=0.2g/L. The biomass-to-substrate fractional yield as a function of the specific growth rate did not change moving from substrate-inhibited to substrate-deficient state. The data was modelled according to the Pirt model: m=1.7×10(-2)g/(gh), Y(X/Ph)(Th)=1.3g/g. The specific growth rates calculated for batch and continuous growth were compared.