Sampling method for the determination of methane emissions from landfill surfaces.

The first aim of this work is the definition and the study of a suitable sampling method for the measurement of landfill gas (LFG) emissions from landfill surfaces, since, up to now, there are no codified nor universally accepted sampling methods for this specific task. The studied sampling method is based on the use of a static hood. The research work involves a preliminary theoretical study for the hood design, experimental tests for the definition of the optimal sampling procedures, and simulations of the hood fluid-dynamics for the system validation. The second aim of this study is the investigation of the correlations between LFG emissions and meteorological conditions, whose identification would be very useful in terms of effective landfill management and pollution control. This involved a wide literature study for the selection of those parameters that seem to have an influence on LFG emission, and the collection of a great number of experimental data on a target site, which led to the conclusion that atmospheric pressure and soil humidity are the parameters that mostly affect LFG emissions.

A model for the evaluation of organic compounds emission from aerated liquid surfaces.

The purpose of this study is to deepen the knowledge of the various emission phenomena present in aerated tanks, widely used systems for municipal and industrial wastewater treatment. In order to investigate the emission mechanism, a specific model was developed. The theoretical model proposes to consider three different contributions to the emission of organic compounds from aerated wastewater tanks: the convection due to the sweep air flow rate, the rising bubbles stripping and the aerosol formation and successive evaporation. To compare the modeled results, an experimental campaign was conducted with two different solutes, acetone and butanol. The sampling was carried out with a Wind Tunnel system and the outflow gas samples were analysed with gas chromatographic technique. Moreover, this study investigates the dependence of the concentration in the gaseous phase from the speed of the air on the surface (1-5 cm/s) and from the flow of air diffused inside the liquid body (50-200 L/h). The empirical data were compared with theoretical curves. The results confirm two facts: the gas solute concentration decreases as the air velocity increases and, instead, increases with the air flow diffused through the tank.

Assessment of the chemical-physical variables affecting the evaporation of organic compounds from aqueous solutions in a sampling wind tunnel.

The aim of this work is the evaluation and the analysis of the different chemical-physical variables that affect the emission of volatile organic compounds (VOC) and odours from passive liquid area sources inside a wind tunnel, which is typically used for emission sampling. Three different compounds (acetone, butanol and ethanol), having different volatilization properties (e.g., boiling point, solubility), were studied in solution with water at different concentrations. The following physical parameters affecting the VOC volatilization in the Wind Tunnel system were evaluated: the velocity of the air flowing through the device, in a range from 0.01 to about 0.05 m/s, and the temperature of both the liquid source and the sweep air flow, in a range from 12 °C to 42 °C. The experimental results were compared with the existing volatilization models available in literature. In most cases the proposed theoretical model predicts well the experimentally measured concentration. Some discrepancies were observed for lower velocities and also by moving from the room temperature (20 °C); and those were discussed by making some considerations about the volatilization phenomenon. Moreover, the study clearly shows that it is not the gas phase temperature that controls the emission, but the temperature of the liquid phase, due to the effect of the latter on the vapour pressure of the compound, which is the main driving force of the phenomenon.

Dust emission and dispersion from mineral storage piles.

Dust pollution is a complex problem of growing interest because of its environmental, health, economic and political impact. Environmental impact assessment methods for dust pollution management are often based on the simulation of dust dispersion, which requires a precise characterization of the source term and of the source parameters. The source term model should be as simple and as accurate as possible and requires low time consumption in order to be easily connected to a more complex algorithm for the dispersion calculations. This work focuses on dust emissions from mineral storage piles, which are usually modelled as source terms by means of the algorithm proposed in the AP-42 US EPA standard. Unfortunately, this algorithm tends to overestimate emissions, and when coupled with a Gaussian dispersion model, it leads to inaccurate results in terms of estimation of both concentration and spatial distribution. This paper proposes a new methodology drawn from the original standard US EPA AP-42 https://www3.epa.gov/ttnchie1/ap42/ch13/ scheme with the purpose to account for the actual dynamics of erosion and to enhance the accuracy of the concentration and the pollutant spatial distribution assessment, thereby considering the effects of the wind interactions. The standard EPA methodology and the new one were compared by means of the AERMOD and CALPUFF dispersion models. Results are superimposable in terms of concentration values, leading to a quantification of the same order of magnitude, although with a different and more variable spatial distribution.

Investigation of the influence of spacer arm on the structural evolution of affinity ligands supported on agarose.

The influence of the spacer arm on the interaction between agarose and a supported ligand was investigated through molecular dynamics for a combination of several spacers. The spacers differ for degree of hydrophobicity, length, and chemical composition, which was varied through insertion of thio, ether, and CH(2) groups. Agarose was modeled through a modified Glycam force field, whose parameters were determined through ab initio calculations. The structural model of agarose used for the calculations was obtained through MD studies of the conformational evolution of several agarose single and double helixes. The simulations showed that a modification of the spacer properties could determine a change of the stable structure of the ligand with respect to the support. In particular, if the spacer is hydrophilic and rigid, the favored structure is with extended spacer and solvated ligand. Either increasing the spacer length, and thus its flexibility, or decreasing its solvation free energy, which corresponds to diminishing its affinity for water, rapidly leads to a conformational change in which the ligand adsorbs on agarose. Interestingly, we found that if the spacer is long and hydrophilic, a third metastable structure, in which the spacer is sandwiched between the ligand and agarose, is possible. Simulations of several ligands adsorbed on neighboring sites on agarose showed that if the support is not held fixed through restraints, the interaction force between vicinal ligands is sufficient to determine a major conformational change of the system.

Use of CFD for static sampling hood design: An example for methane flux assessment on landfill surfaces.

The work focuses on the principles for the design of a specific static hood and on the definition of an optimal sampling procedure for the assessment of landfill gas (LFG) surface emissions. This is carried out by means of computational fluid dynamics (CFD) simulations to investigate the fluid dynamics conditions of the hood. The study proves that understanding the fluid dynamic conditions is fundamental in order to understand the sampling results and correctly interpret the measured concentration values by relating them to a suitable LFG emission model, and therefore to estimate emission rates. For this reason, CFD is a useful tool for the design and evaluation of sampling systems, among others, to verify the fundamental hypotheses on which the mass balance for the sampling hood is defined. The procedure here discussed, which is specific for the case of the investigated landfill, can be generalized to be applied also to different scenarios, where hood sampling is involved.

Definition of a short-cut methodology for assessing earthquake-related Na-Tech risk.

Na-Tech (Natural and Technological) refers to industrial accidents triggered by natural events such as storms, earthquakes, flooding, and lightning. Herein, a qualitative methodology for the initial assessment of earthquake Na-Tech risk has been developed as a screening tool to identify which situations require a much more expensive Quantitative Risk Analysis (QRA). The proposed methodology, through suitable Key Hazard Indicators (KHIs), identifies the Na-Tech risk level associated with a given situation (i.e., a process plant located in a given territory), using the Analytical Hierarchy Process as a multi-criteria decision tool for the evaluation of such KHIs. The developed methodology was validated by comparing its computational results with QRA results that involved Na-Tech events previously presented in literature.

Molecular modeling of protein A affinity chromatography.

The properties of the complex between fragment B of Protein A and the Fc domain of IgG were investigated adopting molecular dynamics with the intent of providing useful insight that might be exploited to design mimetic ligands with properties similar to those of Protein A. Simulations were performed both for the complex in solution and supported on an agarose surface, which was modeled as an entangled structure constituted by two agarose double chains. The energetic analysis was performed by means of the molecular mechanics Poisson Boltzmann surface area (MM/PBSA), molecular mechanics generalized Born surface area (MM/GBSA), and the linear interaction energy (LIE) approaches. An alanine scan was performed to determine the relative contribution of Protein A key amino acids to the complex interaction energy. It was found that three amino acids play a dominant role: Gln 129, Phe 132 and Lys 154, though also four other residues, Tyr 133, Leu 136, Glu 143 and Gln 151 contribute significantly to the overall binding energy. A successive molecular dynamics analysis of Protein A re-organization performed when it is not in complex with IgG has however shown that Phe 132 and Tyr 133 interact among themselves establishing a significant pi-pi interaction, which is disrupted upon formation of the complex with IgG and thus reduces consistently their contribution to the protein-antibody bond. The effect that adsorbing fragment B of Protein A on an agarose support has on the stability of the protein-antibody bond was investigated using a minimal molecular model and compared to a similar study performed for a synthetic ligand. It was found that the interaction with the surface does not hinder significantly the capability of Protein A to interact with IgG, while it is crucial for the synthetic ligand. These results indicate that ligand-surface interactions should be considered in the design of new synthetic affinity ligands in order to achieve results comparable to those of Protein A right from the ligand design stage.

Understanding ligand-protein interactions in affinity membrane chromatography for antibody purification.

Affinity chromatography with Protein A beads has become the conventional unit operation for the primary capture of monoclonal antibodies. However, Protein A activated supports are expensive and ligand leakage is an issue to be considered. In addition, the limited production capabilities of the chromatographic process drive the research towards feasible alternatives. The use of synthetic ligands as Protein A substitutes has been considered in this work. Synthetic ligands, that mimic the interaction between Protein A and the constant fragment (Fc) of immunoglobulins, have been immobilized on cellulosic membrane supports. The resulting affinity membranes have been experimentally characterized with pure immunoglobulin G (IgG). The effects of the membrane support and of the spacer arm on the ligand-ligate interaction have been studied in detail. Experimental data have been compared with molecular dynamic simulations with the aim of better understanding the interaction mechanisms. Molecular dynamic simulations were performed in explicit water, modelling the membrane as a matrix of overlapped glucopyranose units. Electrostatic charges of the ligand and spacer were calculated through ab initio methods to complete the force field used to model the membrane. The simulations enabled to elucidate how the interactions of surface, spacer and ligand with IgG, contribute to the formation of the bond between protein and affinity membrane.

Molecular dynamic investigation of the interaction of supported affinity ligands with monoclonal antibodies.

Diagnostics and therapeutic treatments based on monoclonal antibodies have been attaining an increasing importance in the past decades, but their large scale employment requires the optimization of purification processes. To obtain this goal, research is focusing on affinity chromatography techniques and the development of new synthetic ligands. In this work we present a computational investigation aimed at obtaining some guidelines for the rational design of affinity ligands, through the study of their interactions with both monoclonal antibodies (modeled as the FC domain of human IgG) and a model support material (agarose). The study was carried out performing molecular dynamics simulations of the support-spacer-ligand-IgG complex in explicit water. Binding energies between IgG and two supported ligands, a disubstituted derivative of trichlorotriazine and a tetrameric peptide, were determined with the linear interaction energy and MM-GBSA approaches. A detailed study of the possible binding sites of the considered ligands was performed exploiting docking protocols and MD simulations. It was found that both ligands bind IgG in the same site as protein A, which is the hinge region between the CH2 and CH3 domains of IgG. However this site is not easily accessible and requires a high mobility of the ligands. The energetic analysis revealed that van der Waals and electrostatic energies of interaction of the triazine ligand with the support are significant and comparable to those with the protein, so that they limit its capability to reach the protein binding site. A similar result was found also for the tetrameric peptide, which is however able to circumvent the problem; for steric reasons only two of its arms can interact at the same time with the agarose support, thus leaving the remaining two available to bind the protein. These results indicate that the interaction between ligand and support material is an important parameter, which should be considered in the computational and experimental design of ligands for affinity chromatography.

A combinatorial library of lipid-like materials for delivery of RNAi therapeutics.

The safe and effective delivery of RNA interference (RNAi) therapeutics remains an important challenge for clinical development. The diversity of current delivery materials remains limited, in part because of their slow, multi-step syntheses. Here we describe a new class of lipid-like delivery molecules, termed lipidoids, as delivery agents for RNAi therapeutics. Chemical methods were developed to allow the rapid synthesis of a large library of over 1,200 structurally diverse lipidoids. From this library, we identified lipidoids that facilitate high levels of specific silencing of endogenous gene transcripts when formulated with either double-stranded small interfering RNA (siRNA) or single-stranded antisense 2'-O-methyl (2'-OMe) oligoribonucleotides targeting microRNA (miRNA). The safety and efficacy of lipidoids were evaluated in three animal models: mice, rats and nonhuman primates. The studies reported here suggest that these materials may have broad utility for both local and systemic delivery of RNA therapeutics.

Apatite formation and cellular response of a novel bioactive titanium.

The modification of titanium and titanium alloy surface properties by chemical and electrochemical techniques has opened new possibilities to improve the bioactivity and, in general, the biological performance of the implants once in vivo. One of the main aims is the achievement of a surface oxide layer that stimulates hydroxylapatite mineralization and, also, shows osteoconductive properties once in the host. In the present study, two different bioactive surfaces have been prepared following the method purposed by the group of Kokubo and a new method, BioSpark, involving high voltage anodic polarisation and alkali etching both on surface mineralization potential. The aim of the present work was to evaluate and compare the mineralization capability and the early cell response of titanium modified with a new bioactive method and with a well-known and widely tested biomimetic treatment, both compared to non treated titanium. Physical and chemical (energy dispersion spectroscopy, thin film X-ray diffractometry) and morphological (scanning electron microscopy) characterisation of the novel surface features has been performed. Also the effect of the novel surface properties on both hydroxyapatite precipitation and early cellular response has been investigated using in vitro models. The results have shown that both treatments produce an active outer layer on titanium but do not impair cells activity and support osteoblasts processes. BioSpark showed high bioactivity and good mineral phase deposition even after early incubation time, these properties were found in Kokubo's surface as previously published. Mineralisation mechanisms of the two materials were different, and while this mechanisms was well characterised and reported for Kokubo's surface, it was still unclear for BioSpark. In this paper an explanation was given and catalytic properties of the latter surface was bound to both well known crystal titanium oxide exhibiting anatase lattice and a certain level of calcium and phosphorus doping, which promoted chemical and physical variation in anatase properties. At the same time early osteoblasts response to Kokubo's and BioSpark's surface was characterised and, no significant differences was found.