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- Cristina Vila, António Fiúza, “Signal Treatment Applied To Environmental Biological Systems”
- M.L.Dinis, A. Fiúza, “Simulation of Liberation and Transport of Radium from Uranium Tailings” , in “Uranium in the Environment – Mining Impact and Consequences”
- Cristina Vila, António Fiúza, “Soils contaminated by petroleum hydrocarbons - Modelling contaminant degradation with parameters optimization through Monte Carlo method”
- Carvalho, J.M., Fiúza, A., “Application of Geostatistics to Soil and Groundwater Samples Contaminated by Petroleum Products – A Case Study”
- L. Dinis and A. Fiúza, Simulation of Liberation and Dispersion of Radon From a Waste Disposal
- Gilberto A. Pinto, Fernando O. Durão, António M. A. Fiúza, Margarida M. B. L. Guimarães and C. M. Novais Madureira, “
- M. L. Dinis* and A. Fiúza, “Simulation of Liberation and Dispersion of Radon from a Waste Disposal”
Aurora Silva, Cristina Delerue-Matos, A. Fiúza, “Use of solvent extraction to remediate soils contaminated with hydrocarbons”, Journal of Hazardous Materials, Volume 124, Issues 1-3, Pages 224-229 (30 September 2005), Elsevier; ISI Web of Knowledge: Times Cited: 4, References: 16The main objective of this research is to exploit the possibility of using an ex situ solvent extraction technique for the remediation of soils contaminated with semi-volatile petroleum hydrocarbons. The composition of the organic phase was chosen in order to form a single phase mixture with an aqueous phase and simultaneously not being disturbed (forming stable emulsions) by the soil particles hauling the contaminants. It should also permit a regeneration of the organic solvent phase. As first, we studied the miscibility domain of the chosen ternary systems constituted by ethyl acetate–acetone–water. This system proved to satisfy the previous requirements allowing for the formation of a single liquid phase mixture within a large spectrum of compositions, and also allowing for an intimate contact with the soil. Contaminants in the diesel range within different functional groups were selected: xylene, naphthalene and hexadecane. The analytical control was done by gas chromatography with FID detector. The kinetics of the extractions proved to be fast, leading to equilibrium after 10 min. The effect of the solid–liquid ratio on the extraction efficiency was studied. Lower S/L ratios (1:8, w/v) proved to be more efficient, reaching recoveries in the order of 95%. The option of extraction in multiple contacts did not improve the recovery in relation to a single contact. The solvent can be regenerated by distillation with a loss around 10%. The contaminants are not evaporated and they remain in the non-volatile phase. The global results show that the ex situ solvent extraction is technically a feasible option for the remediation of semi-volatile aromatic, polyaromatic and linear hydrocarbons.
The mass transfer processes between two liquid phases have great technical and commercial importance in certain industries, namely petrochemical, hydrometallurgical, organic, pharmaceutical and environmental protection. In mineralurgical and environmental industries, the most commonly used type of equipment is the association of mixer-settlers. The settler is responsible for most of the space requirements of these installations, although it has a secondary phenomenological role. The analysis of the dynamic behaviour of rectangular gravity settlers, where the dispersion mainly flows horizontally, is complicated. This is because the drop velocity and density, the dispersion band thickness, and the drop size distributions all vary along the length of the settler. Mathematically, this corresponds to a formulation in terms of partial differential equations (distributed parameters model), contrasting with the simpler, concentrated parameters models used for the simulation of the compartmented extraction columns. Usually, gravity settlers are designed for steady state operation starting from the experimental data obtained from small-scale batch (non-stationary) tests, thus eliminating the need for pilot-scale equipment. However, transient conditions frequently occur in industrial continuous-flow systems, due to uncontrolled variations in feed-rate and/or in agitation speed; such transient regimes may imply variations in the thickness and length of the dispersion band, which, in turn, may have damaging consequences. Thus, it is important for the designer to understand the effects of such variations in order to achieve safe design and trouble-free operation.
The respirometry of soils contaminated by petroleum products offers a potential of research that has not been thoroughly exploited. During the last years we performed a long sequence of experiments in laboratorial reactors of different capacities, shifting from 1 L to 5L, where we measured continuously, on-line, the oxygen and carbon dioxide concentrations at the reactors inlet and in the immediate atmospheric vicinity of the contaminated soil submitted to biodegradation. The air flow was kept constant using a control system and the environmental properties, such as the temperature, were also simultaneously measured and recorded. The experimental conditions that favour the biodegradation, such as the moisture and the addition of nutrients, were periodically adjusted. Each experiment lasted, at least, around 30 days. A single experiment creates an enormous quantity of data, with several millions of registers. We have been treating this enormous amount of information using several mathematical techniques. The first step is always the filtration of the data in order to eliminate anomalies strange to the process, such as voltage breakages and current losses. The length of the data is also reduced using conventional methodologies. One of the methodologies we use is the signal treatment by Fourier Analysis. The periodograms allowed the detection of a daily cyclical behaviour in the activity of the microorganisms. Directional circular statistics allowed the establishment of circular correlations between the daily patterns of the temperature oscillation and the biological activity. Time series analysis is used to produce auto-correlograms as well as cross-correlation diagrams between the main variables involved. The wavelet analysis is used to detect variation patterns at smaller scales and we investigated its usage as a method of filtration the data that keeps the inner core structure of the information without aliasing. We have been using the system identification theory to create digital data-driven models, either single input-single output or multiple input-multiple outputs. These models were applied to data filtered by conventional methods as well as using wavelets. It is also possible to create phenomenological relationships between the different measures allowing the determination not only of the kinetics but also of the stoichiometry of the biodegradation reactions.
The uranium tailings contain a large amount of radium, besides other radionuclides like uranium, thorium, polonium and lead. The transport and fate of radionuclides in groundwater are assumed to follow the theoretical approach re-sented by the basic diffusion/dispersion – advection equation. Our algorithm uses the analytical solution for the one dimensional steady-sate transport problem of a reactive substance with simultaneous retardation and radioactive decay. The final output is the radionuclides concentration in a hypothetical well location as function of the elapsed time. 
Abstract: Biodegradation and abiotic decay are the most important mechanisms of natural attenuation of soils and groundwater contaminated by petroleum hydrocarbons. The efficient implementation of natural attenuation requires a previous stage of simulation and prediction of results due to the diversity and heterogeneity of petroleum hydrocarbons coexisting in contaminated sites. Focusing on the remediation of a real contaminated site - a refinery located in the north of Portugal with an associated petrochemical complex - laboratory studies were performed with soil and groundwater samples collected in the contaminated area. Soil samples were submitted to different types of preliminary characterization: microbiologic enrichment tests in order to select natural degraders, kinetic tests, physical and chemical description (texture, moisture, TPH and BTEX contents, carbon-nitrogen-phosphor relationship, pH) and also, subsequently, to respirometry. The experimental data provided the basis for the development of a comprehensive model (Fiúza-Vila Model) describing simultaneously the time evolution of biomass and contaminant degradation. Several phenomena were globally taken into account in this model: the volatilization, a fast kinetics component, a slow kinetics component and the refractory hydrocarbons for the time scale used in the experiments. This model is in turn linked to the kinetics of the biomass evolution. In such a model involving parameters which are intrinsically difficult to measure it is necessary to optimize the parameters using a heuristic approach due to the intrinsic non-linearity of the model.
Respirometric tests on a soil contaminated by crude oil were performed. Continuous measurements of oxygen and carbon dioxide concentrations and temperature in the soil atmosphere resulted in a large volume of data. Time series and system identification theories were used to analyze data as a biological signal, allowing us to detect some particularities related to daily cycles of the studied variables as well as its time relationships through autocorrelation and cross-correlation functions. Using system identification techniques, it was possible to build black box models, namely autoregressive moving average models which enable to predict oxygen concentration at the outlet in a good agreement with measured data. 
A geoenvironmental site investigation/characterization survey took place in a contaminated costal area in the surroundings of an active oil refinery having an associated petrochemical complex, located north of Porto, in the north-western part of Portugal. In this context, several soil and groundwater samples were collected, respectively in trenches and boreholes, and chemically analyzed allowing the characterization of their chemical pollution, in terms of the different contamination products and respective concentrations, namely BTEX, TPH, PHA’s and lead, as well as of some physical/chemical soil properties and characteristics, namely density, pH and organic matter content. At this stage of the investigation, a multivariate statistical analysis has been previously carried out. The present study is focused on comparing alternative geostatistical procedures, namely different kriging methods as well as strategies, used to characterize the qualitative and quantitative spatial contamination dispersion in the investigated area leading to different mapped models prior to the definition of remediation strategies. In addition, it is also summarized a risk analysis study, also based on geostatistical procedures, leading to a partition of the studied zone in terms of their assessed relative remediation needs.
Radon emissions from a radioactive waste disposal may constitute a major source of environment contamination and subconsequently a potential health hazard to the nearby population. Gaseous Radon-222 is generated from the radioactive decay of Radium-226 present in the tails. When it is formed, radon is free to diffuse along the pores of the residues to the surface and escape to the atmosphere. Waste management and long term stabilisation has a major concern in reducing radon emissions to near-background levels. The common theoretical approach is done by calculating the cover thickness that allows a radon flux inferior to a stipulated and accepted value. The fundamentals of the conceptual model are based in the principles of diffusion across a porous medium, which allows the mathematical description of the radon transport through the waste and the cover. The basic diffusion equations are used for estimating the theoretical values of the radon flux formed from the decay of the Radium-226 contained in the waste material. The algorithm incorporates the radon attenuation originated by an arbitrary cover system placed over the radioactive waste disposal. As an alternative, the thickness of the cover that allows a radon flux inferior to the acceptable one can be estimated. Once the Radon is released into the atmosphere, it is available for atmospheric transport by the wind. Radon atmospheric dispersion is modelled by a modified Gaussian plume equation, which estimates the average dispersion of radon released from a point source representative of one or several uniform area sources. The model considers the medium point release between all the areas contaminated. The concentration available for the dispersion is calculated from the total flux released. The dispersion can be simulated in different wind directions, with different wind velocities, as well as in the dominant wind direction.
It is a well-known fact that a typical engineering design problem usually deals with more than one design criterion. If each design criterion is stated as an objective function to be optimised, then the engineering design problem becomes a multicriteria optimisation problem, requiring the simultaneous optimisation of more than one objective function. In this paper, it is shown how the design of solvent extraction flow-sheets can be stated as a multicriterion optimisation problem, using the positive weighted sum approach. This is used not only to obtain parametric optimisation (i.e., the best operating conditions: agitation speed, residence time and phase flow ratio) but also to help in structural optimisation (i.e., to synthesise the best process flow-sheet: number of stages, flow structure and phase recycle ratio). We demonstrate this over a case study, namely, the selective separation of two chemically akin and hard to separate metals, zinc and cadmium, commonly found together in the leaching liquor of complex ores. With this case study, it is shown that the design solutions are richer and more wide-ranging when put together from the vantage point of multicriterion optimization, whereas they become narrow-minded and/or biased if the starting point is a single criterion point of view. Three other conclusions of less general validity were also obtained: (i) the opposite effects of feed phase flow-rates on recovery and purity; (ii) the high sensitivity of short optimum residence times to variations in agitation speed; (iii) the ability of counter-flow associations of a variable number of mixer–settler units to accommodate changes in metal purity and overall recovery in response to drivers in market prices and environmental policies.
Radon emissions from a radioactive waste disposal may constitute a major source of environment contamination and subconsequently a potential health hazard to the nearby population. Radon-222 gas is generated from the radioactive decay of Radium-226 present in the particles. When it is formed, radon is free to diffuse along the pores of the residues to the surface and escape to the atmosphere. Waste management and long term stabilisation has a major concern in reducing radon emissions to near-background levels. The common theoretical approach is done by calculating the cover thickness that allows a radon flux inferior to a stipulated and accepted value. The fundamentals of the conceptual model are based in the principles of diffusion across a porous medium, which allows the mathematical description of the radon transport through the waste and the cover. The basic diffusion equations are used for estimating the theoretical values of the radon flux formed from the decay of the Radium-226 content in the waste material. The algorithm incorporates the radon attenuation originated by an arbitrary cover system placed over the radioactive waste disposal. As an alternative, it can be estimated the thickness of the cover that allows a radon flux inferior to the acceptable one. Once the Radon is released into the atmosphere, it is available for atmospheric transport by the wind. Radon atmospheric dispersion is modelled by a modified Gaussian plume equation which estimates the average dispersion of radon released from a point source representative of one or several uniform area sources. The model considers the medium point release between all the areas contaminated. The concentration available for the dispersion is calculated from the total flux released. The dispersion can be simulated in different wind directions, with different wind velocities, as well as in the dominant wind direction.
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