M. L. Dinis and A. Fiúza, “Modeling the Transfer and Fate of Contaminants in the Environment: Soil, Water and Air”, in Chemicals as Intentional and Accidental Global Environmental Threats, L. Simeonov and E. Chirila Editors, Springer, ISBN-10: 1-4020-5097-6; ISBN-13: 978-1-4020-5097-8; 2006, ISI Web of Knowledge: Times Cited: 1, References: 5
The environmental effects originated by uranium mining activities result mainly from the wastes generated by the ore processing.
Large quantities of radioactive wastes are generated in this extractive process requiring a safe management. Besides the radioactivity these wastes mar algo hold different amounts of chemicals used in the extraction process, toxic pollutants associated with the mineralization and precipitates provoked by pH or Eh alterations.
The main concem of waste management and long term stabilization is to confine the residues in order to reduce the dispersion of contaminants to concentrations that not exC'eed the trigger values considered to be safe: there is thus a need to ensure that the environmental and health risk from these materiaIs are reduced to an acceptable leveI. However, the confinement will always represent a potential source of environmental contamination to the air, soil, superficial water and groundwater, due to the contaminants release and transport in the environment, which mar occur by natural erosion agents like rainfall or wind.
M. L. Dinis and A. Fiúza, “Exposure Assessment to Radionuclides Transfer in Food Chain”, Nato AISI, Minsk.
Generally sites with radioactive contamination are also simultaneously polluted with many other different toxics, especially heavy metals.
The environmental effects originated by uranium mining activities result mainly from the wastes generated by the ore processing. Besides the radioactivity these wastes may also hold different amounts of chemicals, toxic pollutants and precipitates originated by pH or Eh alterations. The radionuclides released from these wastes can give rise to human exposure by transport through the atmosphere, aquatic systems or through soil sub-compartments. The exposure may result from direct inhalation of contaminated air or ingestion of contaminated water, or from a less direct pathway - the ingestion of contaminated food products. Nevertheless this pathway can be quite significant as a result of biological concentration in the foodstuff.
The exposure resulting from airborne particulates containing 230Th, 226Ra, and 210Pb as well as uranium, is primary by the inhalation of particles and or through the food chain. The predominant target effective dose from these radionuclides is to the bones. Non-radioactive metals and other chemical reagents may also induce chronic or acute health effects. The harmful effects of radionuclides do not come from their chemistry within tissue, but from the radiation associated with radioactive decay which increases the risk of cancer.
Contamination of the trophic chain by radionuclides released into the environment can be a component of human exposure to ionizing radiations by transferring the radionuclides into animal products that are components of the human diet. Plants in general tend to accumulate radionuclides in a scale dependent on many factors and within animals and humans, certain tissues tend to accumulate selected radionuclides.
Radionuclides deposition can be a significant pathway to human exposure by first ingestion of contaminated pasture by animals and then by the ingestion of animal products contaminated (dairy or meat). The relevant incorporation of the radionuclides in the milk is usually due to the ingestion of contaminated pasture. This transfer process is often called the pasture-cow-milk exposure route.
We developed a compartment dynamic model to describe mathematically the radionuclide behavior in the pasture-cow-milk exposure route and predict the activity concentration in each compartment following an initial radionuclide deposition. The dynamic model is defined by a system of linear differential equations with constant coefficients based in a mass balance concept. For each compartment a transient mass balance equation defines the relations between the inner transformations and the input and output fluxes. The fluxes between the compartments are estimated with a transfer rate proportional to the amount of the radionuclide in the compartment. The model also considers possible transformations within the compartment.
The first model considered for the propagation through the food chain is relatively simple and classic and considers as initial state a contaminated pasture that is consumed by a cow that produces a certain quantity of milk. A more sophisticated model is also described taking into account the spread of 226Ra within the cow by the inclusion of several sub-compartments: the gastrointestinal system (GIT), the plasma and the bones.
For the exploration of the model we defined several radionuclides as relevant but, for the present, only radium was considered in the calculations, due to the availability of data. The endpoints are radium concentrations in the soil, pasture, GIT, plasma, bone and milk. The concentration within each compartment can then be transcribed to doses values on the bases of a simplified exposure pathway and a pre-defined critical group.
M. L. Dinis, A. Fiúza, “Simulation of Radon Flux Attenuation in Uranium Tailings”. Apresentação de poster em: “Nato Advanced Workshop: Methods and Techniques for Cleaning-up Contaminated Sites”, Sinaia, Romania, 09 - 11 October 2006.
Radon exhalation from uranium mining and milling sites can constitute a complex environmental situation and subsequently become a health risk to the population in the vicinity.
Post closure and rehabilitation site involves, among other situations, controlling and estimating radon release from the surface pile. Generally the primary cleanup method consists of enclosing the tailings in which the contaminated area is covered with compacted clay or native soil, to prevent the release of radon, and then covered with rocks and vegetation. This implies a cover design and placement which will give long term stability and control to acceptable levels of radon emission, gamma radiation, erosion of the cover and the tailings and infiltration of the precipitation into the tailings. Not only are these situations being prevented with the cover but also the transport of other pollutants from the tailings to the environment and restraining the access of people and animals.
Cover design involve estimating the cover thickness assuring a radon flux inferior of the acceptable values. Cover thickness depends on the properties of the materials to apply in the cover and the tailings characteristics. Usually radon flux is estimated with diffusion equations across a porous medium which describes mathematically the radon movement in the tailings and in the cover characterized by the radon diffusion coefficient, porosities, moistures of the tailings and cover, the radium content and the tailings emanation coefficient. Radon exhalation rates are controlled mostly by the amount of radium and the moisture present in the tailings.
An algorithm based on the theoretical approach of diffusion was developed to estimate radon attenuation originated by a cover system placed over the tailings pile and subsequently the resulting concentration in the breathing atmosphere. The one dimensional steady-state radon diffusion equation was applied to a porous and multiphase system. Also the thickness of a cover that limits the radon flux to a stipulated value can be performed.
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: 16
The 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.
Marília C.F. Baptista, Rui P.M. Silva, M. Margarida M. Ribeiro, Margarida M.B.L. Guimarães, António M. A. Fiúza, “Measuring Dispersion Band Quantities In Shallow-Layer Settlers”, Communication to the “Chemical Engineering 7th World Congress”.
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.
Cristina Vila, António Fiúza, “Signal Treatment Applied To Environmental Biological Systems”, 9th International FZK / TNO Conference on Contaminated Soil CONSOIL, Bordeau, France.Pgd. 2231-2400;
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.
M.L.Dinis, A. Fiúza, “Simulation of Liberation and Transport of Radium from Uranium Tailings”, in “Uranium in the Environment – Mining Impact and Consequences”, pgs 609 a 618, Editors: Broder J. Merkel and Andrea Hasche-Berger, Springer-Verlag, Berlin, 2006. Hardcover, ISBN 10 3-540-28363-3; ISBN 13 978-3-540-28368-8, ISI Web of Knowledge: Times Cited: 1, References: 6
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.
Cristina Vila, António Fiúza, “Soils contaminated by petroleum hydrocarbons - Modelling contaminant degradation with parameters optimization through Monte Carlo method”, 2nd European Conference on Natural Attenuation, Soil and Groundwater Risk Management, May 18-20, Frankfurt am Main, Germany
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.
Fiúza A, Vila Cristina, “An insight into soil bioremediation through respirometry” Environment International, Volume 31, Issue 2, February 2005, Pages 179-183, Recent Advances in Bioremediation, ISI Web of Knowledge:Times Cited: 2, References: 11
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.
Carvalho, J.M., Fiúza, A., “Application of Geostatistics to Soil and Groundwater Samples Contaminated by Petroleum Products – A Case Study”, 9 pags, Fifth European Conference on Geostatistics for Environmental Applications, Centre for Hydrogeology, University of Neuchâtel, Switzerland, on October 13-15, 2004.
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.
L. Dinis and A. Fiúza, Simulation of Liberation and Dispersion of Radon From a Waste Disposal, Proceedings of the NATO Advanced Research Workshop “Advances in Air Pollution Modelling for Environmental Security" - Borovetz, Bulgária, 8 to 12 May 2004. Series: Nato Science Series: IV: Earth and Environmental Sciences, Vol. 5. 4 Farago, I.; páginas 133-142; Georgiev, Krassimir; Havasi, Ágnes (Eds.) 2005, XI, 406 p., Hardcover ISBN: 1-4020-3349-4; Springer Verlag, ISI Web of Knowledge: Times Cited: 0, References: 7
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.