Domenico Pirozzi

Microbial Conversion of Olive Oil Mill Wastewaters into Lipids Suitable for Biodiesel Production

Lipomyces starkey were able to survive and proliferate in the presence of olive oil mill wastewaters (OMW), a medium difficult to process by biological treatments, due to the antimicrobial activities of their phenolic components. The microorganisms were grown in the presence of undiluted OMW, without external organic supplements, producing a significant reduction of both the total organic carbon (TOC) and the total phenols content. The OMW treated by L. starkey showed a significant increase of the germination index. The preliminary dilution of OMW enhanced the reduction of polluting components of OMW, leading to a complete TOC removal, as well as to lower levels of residual phenols. The activities of extracellular lipases and esterases significantly increased in the course of the OMW fermentation. A significant increase in lipid yield was observed in L. starkey in the course of the OMW treatment, particularly enhanced when the feedstock was preliminarily diluted. The fatty acid distribution showed a prevalence of oleic acid, demonstrating the potential of L. starkeyi as a source of lipids to be used as a feedstock for the synthesis of II generation biodiesel.

Remediation of Waters Contaminated with MCPA by the Yeasts Lipomyces starkeyi Entrapped in a Sol-Gel Zirconia Matrix

A single-stage sol-gel route was set to entrap yeast cells of Lipomyces starkeyi in a zirconia (ZrO(2)) matrix, and the remediation ability of the resulting catalyst toward a phenoxy acid herbicide, 4-chloro-2-methylphenoxyacetic acid (MCPA), was studied. It was found that the experimental procedure allowed a high dispersion of the microorganisms into the zirconia gel matrix; the ZrO(2) matrix exhibited a significant sorption capacity of the herbicide, and the entrapped cells showed a degradative activity toward MCPA. The combination of these effects leads to a nearly total removal efficiency (>97%) of the herbicide at 30 °C within 1 h incubation time from a solution containing a very high concentration of MCPA (200 mg L(-1)). On the basis of the experimental evidence, a removal mechanism was proposed involving in the first step the sorption of the herbicide molecules on the ZrO(2) matrix, followed by the microbial degradation operated by the entrapped yeasts, the metabolic activity of which appear enhanced under the microenvironmental conditions established within the zirconia matrix. Repeated batch tests of sorption/degradation of entrapped Lipomyces showed that the removal efficiency retained almost the same value of 97.3% after 3 batch tests, with only a subsequent slight decrease, probably due to the progressive saturation of the zirconia matrix.

Use of a New Hybrid Sol−Gel Zirconia Matrix in the Removal of the Herbicide MCPA: A Sorption/Degradation Process

A class II hybrid sol-gel material was prepared starting from zirconium(IV) propoxide and 2,4-pentanedione and its catalytic activity in the removal of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) was revealed. The thermal and structural characterization, performed by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier transform infrared spectroscopy, demonstrated the hybrid nature of the material. The structure of the material can be described as a polymeric network of zirconium oxo clusters, on the surface of which large part of Zr(4+) ions are involved in strong complexation equilibria with acetylacetonate (acac) ligands. The incubation of MCPA in the presence of this material yielded an herbicide removal fraction up to 98%. A two-step mechanism was proposed for the MCPA removal, in which a reversible first-order adsorption of the herbicide is followed by its catalytic degradation. The nature of the products of the MCPA catalytic degradation as well as the reaction conditions adopted do not support typical oxidation pathways involving radicals, suggesting the existence of a different mechanism in which the Zr(4+):acac enol-type complex can act as Lewis acid catalyst.

Lipase-catalyzed transformations for the synthesis of butyl lactate: a comparison between esterification and transesterification.

The α‐hydroxy esters are increasingly employed in cosmetic, food, and pharmaceutical formulations as they determine reduced skin‐irritant effects in comparison with the respective acids, offering similar hygroscopic, emulsifying, and exfoliating properties. The enzymatic synthesis of lactate esters in nonaqueous systems was studied as regards the influence of the critical process parameters, to enable a comparison between the most commonly used synthetic routes, namely, esterification and transesterification. The experimental results showed that the direct esterification of lactic acid with butanol may be limited by the reduced lipase stability in the presence of the acid (substrate) and of the water (product), in particular when solvent‐free media are used. The stability of the enzyme is further reduced as polar solvents are required as a result of the polarity of the lactic acid. Therefore, the use of the lactic acid as substrate is of practical interest only when the acid is significantly cheaper in comparison with its short‐chain esters. If this is not the case, the transesterification of the ethyl lactate with butanol is to be preferred for the higher flexibility in the choice of the experimental conditions, the operability of solvent‐free systems, and the simplicity of the product removal assembly.

Decontamination of waters polluted with simazine by sorption on mesoporous metal oxides

Two mesoporous metal oxides, Al(2)O(3) and Fe(2)O(3), were evaluated as regards their ability to remove simazine, a highly persistent herbicide of s-triazines, using a batch equilibrium method. The effect of several experimental parameters such as pH, contact time, initial concentration and sorbent dosage on the sorption of the herbicide was investigated. The maximum sorption of simazine on Al(2)O(3) and Fe(2)O(3) was observed at pH 6.5 and 3.5, respectively. The different sorption capacities of the two oxides were explained considering a set of factors affecting the sorption process such as the surface area and the porosity. The kinetics of sorption on both oxides was described using a pseudo second-order model. The sorption of simazine on Fe(2)O(3) was faster in comparison to that observed on Al(2)O(3). It was shown that aluminum oxide can be regenerated by incineration, and consequently can be considered for industrial treatment systems designed to mitigate the pesticide pollution in the aquatic environments.

Enzyme stability in the presence of organic solvents

SummaryThe thermal stability of vacuum-dried acid-phosphatase has been investigated, both in the absence and in the presence of pure hexadecane. Preliminary experimental results indicate that: i) in both solid-phase runs, acid-phosphatase is much more stable than the free enzyme in aqueous solution, ii) the presence of the organic solvent slightly reduces thermal stability of the solid-phase enzyme. As regards the deactivation mechanism, when acid-phosphatase operates in free aqueous solution it follows a two-step in series deactivation. Initially the native configuration decays towards an intermediate, still active form. This, in turn, irreversibily yields a totally inactive structure. In the thermal deactivation of solid-phase enzyme it has been observed that: i) the first step is substantially retarded, ii) the final transition is completely hindered, iii) the intermediate configuration is more active than that produced in aqueous solution, by more than one order of magnitude.

Origin and Electronic Features of Reactive Oxygen Species at Hybrid Zirconia-Acetylacetonate Interfaces

The hybrid sol-gel zirconia-acetylacetonate amorphous material (HSGZ) shows high catalytic activity in oxidative degradation reactions without light or thermal pretreatment. This peculiar HSGZ ability derives from the generation of highly reactive oxygen radical species (ROS) upon exposure to air at room conditions. We disclose the origin of such unique feature by combining EPR and DRUV measurements with first-principles calculations. The organic ligand acetylacetonate (acac) plays a pivotal role in generating and stabilizing the superoxide radical species at the HSGZ-air interfaces. Our results lead the path toward further development of HSGZ and related hybrid materials for ROS-based energy and environmental applications.

Electronic properties of TiO2-based materials characterized by high Ti3+ self-doping and low recombination rate of electron–hole pairs

Factors tuning the functional performances of the various TiO2-based materials in the wide range of their possible applications are poorly understood. Here the electronic structure of TiO2-based materials characterized by Ti3+ self-doping, obtained by a sol–gel route wholly performed in air at room temperature, is reported. In the amorphous hybrid TiO2–acetylacetonate (HSGT) material the formation of the Ti(IV)–acac complex makes it photoresponsive to visible light and allows us to obtain by means of a simple annealing in air at 400 °C a very stable black Ti3+ self-doped anatase TiO2 nanomaterial (HSGT-400), characterized by an extraordinary high concentration of Ti atoms with oxidation states lower than IV (about 26%), which absorbs light in the entire visible range. The very high stability of HSGT-400 is mainly related to the process, which does not require the use of harsh conditions nor external reducing agents. The electronic structure of HSGT, owing to the presence of the Ti(IV)–acac complex, allows the stabilization of superoxide anion radicals on its surface for a very long time (months) at room temperature. The extraordinary low recombination rate of electron–hole pairs gives to HSGT unusual catalytic performances at room temperature allowing the complete removal of 2,4-dichlorophenol from water in about one hour without any light irradiation. Our results clearly highlight the connection among the production process of TiO2-based materials, their electronic structure and, finally, their functional behaviour.

Technical difficulties and solutions of direct transesterification process of microbial oil for biodiesel synthesis

Microbial oils are considered as alternative to vegetable oils or animal fats as biodiesel feedstock. Microalgae and oleaginous yeast are the main candidates of microbial oil producers’ community. However, biodiesel synthesis from these sources is associated with high cost and process complexity. The traditional transesterification method includes several steps such as biomass drying, cell disruption, oil extraction and solvent recovery. Therefore, direct transesterification or in situ transesterification, which combines all the steps in a single reactor, has been suggested to make the process cost effective. Nevertheless, the process is not applicable for large-scale biodiesel production having some difficulties such as high water content of biomass that makes the reaction rate slower and hurdles of cell disruption makes the efficiency of oil extraction lower. Additionally, it requires high heating energy in the solvent extraction and recovery stage. To resolve these difficulties, this review suggests the application of antimicrobial peptides and high electric fields to foster the microbial cell wall disruption.

Kinetics of enzyme deactivation: a case study

Abstract Acid phosphatase (EC 3.1.3.2, from potato) thermal deactivation was studied by kinetic methods with specific reference to the effect of medium properties. The time-course of activity decay was employed as an indirect probe for analysing the structural changes undergone by the protein. The experimental data show convex log (activity) vs. time curves. Usually, departure from simple first-order kinetics is explained by postulating enzyme aggregation, or enzyme heterogeneity, or formation of partially deactivated forms of the enzyme. None of the above models was entirely satisfactory in interpreting the experimental data. The current models for enzyme thermal deactivation therefore appear to be purely correlative. The effects of medium changes were accounted for on the basis of a phenomenological approach, the ‘equivalent temperature’ yielding a monoparametric model.