António Fiúza

Heterogeneous kinetics of the reduction of chromium (VI) by elemental iron.

Zero valent iron (ZVI) has been extensively used as a reactive medium for the reduction of Cr(VI) to Cr(III) in reactive permeable barriers. The kinetic rate depends strongly on the superficial oxidation of the iron particles used and the preliminary washing of ZVI increases the rate. The reaction has been primarily modelled using a pseudo-first-order kinetics which is inappropriate for a heterogeneous reaction. We assumed a shrinking particle type model where the kinetic rate is proportional to the available iron surface area, to the initial volume of solution and to the chromium concentration raised to a power alpha which is the order of the chemical reaction occurring at surface. We assumed alpha=2/3 based on the likeness to the shrinking particle models with spherical symmetry. Kinetics studies were performed in order to evaluate the suitability of this approach. The influence of the following parameters was experimentally studied: initial available surface area, chromium concentration, temperature and pH. The assumed order for the reaction was confirmed. In addition, the rate constant was calculated from data obtained in different operating conditions. Digital pictures of iron balls were periodically taken and the image treatment allowed for establishing the time evolution of their size distribution.

Phytoremediation of salt-affected soils: a review of processes, applicability, and the impact of climate change

Soil salinization affects 1–10 billion ha worldwide, threatening the agricultural production needed to feed the ever increasing world population. Phytoremediation may be a cost-effective option for the remediation of these soils. This review analyzes the viability of using phytoremediation for salt-affected soils and explores the remedial mechanisms involved. In addition, it specifically addresses the debate over plant indirect (via soil cation exchange enhancement) or direct (via uptake) role in salt remediation. Analysis of experimental data for electrical conductivity (ECe) + sodium adsorption ratio (SAR) reduction and plant salt uptake showed a similar removal efficiency between salt phytoremediation and other treatment options, with the added potential for phytoextraction under non-leaching conditions. A focus is also given on recent studies that indicate potential pathways for increased salt phytoextraction, co-treatment with other contaminants, and phytoremediation applicability for salt flow control. Finally, this work also details the predicted effects of climate change on soil salinization and on treatment options. The synergetic effects of extreme climate events and salinization are a challenging obstacle for future phytoremediation applications, which will require additional and multi-disciplinary research efforts.

Exposure Assessment to Heavy Metals in the Environment: Measures to Eliminate or Reduce the Exposure to Critical Receptors

The anthropogenic sources for heavy metals include mining, industrial productions, untreated sewage sludge and combustion by-products produced by coal burning power plants. Atmospheric emissions are probably the most preoccupant to human health and to the environment due to either the great quantity involved, or their widespread dispersion. Mercury, lead and cadmium represent a great issue, mostly due to their ability to travel long distances in the atmosphere before deposition. Exposure assessment to emissions of heavy metals implies to identify and quantify the sources, how heavy metals may be dispersed in the environment and which adverse effects they might cause on human health and on the ecosystem. Heavy metals emissions and releases into the environment are available at the European Pollutant Release and Transfer Register (E-PRTR, 2010). In this data base main sources from 27 European countries are identified. Data concerning Cd, Hg and Pb were extracted for the year of 2007. This work focuses on the review and analysis of the principal sources of heavy metals emissions into the environment and their role in critical receptors’ environmental exposure. The review of the principal sources may give a clearer picture of the situation: the potential regions at risk and the extension of the contamination, essential to the exposure assessment by critical receptors. On the other hand, exposure assessments studies and consequent research allow a better knowledge of heavy metals sources, emissions, pathways and fate in the environment. Therefore both a complete exposure assessment and a consequent risk assessment are needed to establish the identification and implementation of measures to eliminate or to reduce the exposure.

Role of three different plants on simultaneous salt and nutrient reduction from saline synthetic wastewater in lab-scale constructed wetlands.

Constructed Wetlands (CWs) can be a valuable technology to treat high salinity wastewaters but it is not known their potential for removal of both nutrients and salt, and the type of plants to use. This study evaluated the effect of three plants on salt reduction and simultaneous nutrient removal in CWs microcosms with expanded clay and in hydroponic conditions. Initial values of the synthetic wastewater tested were EC=15dSm-1, SAR=151; NH4+-N=24mgL-1; PO43--P=30mgL-1 and NO3--N=34mgL-1. With expanded clay CW removal efficiency for NH4+-N was 21, 88 and 85%, while for NO3--N, it was 4, 56 and 68% for Spartina maritima, Juncus maritimus and Arundo donax, respectively. PO43--P was adsorbed completely in the expanded clay. However, in hydroponic system, removal efficiencies for NH4+-N were 53 and 50%, while PO43--P removal was 89 and -14% for Spartina maritima and Juncus maritimus, respectively. Nutrient removal in planted microcosms was statistically higher than unplanted controls for NH4+-N and PO43--P. However, salt removal was apparent in the hydroponic system only after 23days of HRT, despite clear salt excretion visible in both Spartina maritima and Juncus maritimus. This study demonstrates the potential of two halophytic plants for saline wastewater treatment. However, salt removal in such a scenario could not be well documented and might prove to be impractical in future work.

Extensive review of shale gas environmental impacts from scientific literature (2010–2015)

Extensive reviews and meta-analyses are essential to summarize emerging developments in a specific field and offering information on the current trends in the scientific literature. Shale gas exploration and exploitation has been extensively debated in literature, but a comprehensive review of recent studies on the environmental impacts has yet to be carried out. Therefore, the goal of this article is to systematically examine scientific articles published between 2010 and 2015 and identify recent advances and existing data gaps. The examined articles were classified into six main categories (water resources, atmospheric emissions, land use, induced seismicity, occupational and public health and safety, and other impacts). These categories are analyzed separately to identify specific challenges, possibly existing consensus and data gaps yet remained in the literature.

Recycling of pultrusion production waste into innovative concrete-polymer composite solutions

In this study, the added value resultant from the incorporation of pultrusion production waste into polymer based concretes was assessed. For this purpose, different types of thermoset composite scrap material, proceeding from GFRP pultrusion manufacturing process, were mechanical shredded and milled into a fibrous-powdered material. Resultant GFRP recyclates, with two different size gradings, were added to polyester based mortars as fine aggregate and filler replacements, at various load contents between 4% up to 12% in weight of total mass. Flexural and compressive loading capacities were evaluated and found better than those of unmodified polymer mortars. Obtained results highlight the high potential of recycled GFRP pultrusion waste materials as efficient and sustainable admixtures for concrete and mortar-polymer composites, constituting an emergent waste management solution.

Insight into the phenomenology of the Cr(VI) reduction by metallic iron using an electron probe microanalyzer.

Research was performed to gain insight into the heterogeneous reaction of Cr(VI) reduction by zero-valent iron, which is frequently used in the treatment of contaminated groundwater using permeable reactive barriers. An electron probe microanalyzer was used to clarify in detail relevant aspects of the reaction with consequences for the conception of interpretative kinetic models. Spherical particles of iron with controlled grain sizes were used after being subjected to a previous washing with diluted acid in order to remove oxidation products. These spheres were immersed in solutions of Cr(VI) in nonagitated flasks using different operating procedures. The iron particles were photographed so that the time evolution of the grain size distribution could be established. A sample of the iron balls after the reaction and samples of the raw material and the precipitates of the reaction products were analyzed by backscattering electron images and elemental mapping produced by wavelength-dispersive spectroscopy. The analysis of the spatial distribution of the concentrations in iron, oxygen, and chromium indicates that there are three distinct mechanisms for the reaction with different limiting steps.

Integrated Methodology for the Environmental Risk Assessment of an Abandoned Uranium Mining Site

We developed an integrated approach to evaluate quantitatively the fundamental data required to perform a risk assessment induced by the existence of uranium mine tailings disposals or any other form of low activity waste storage. From the characteristics of the radioactive sources the different types of possible releases are evaluated using phenomenological models. The concentrations in the main environmental compartments are deduced. To this data we apply models of environmental transport, dispersion and fate within each environmental compartment, as well as models of inter-compartment transfer. The activity is then predicted at predefined exposition locations, in each environment compartment. Models of transfer to the food chain were also developed allowing to estimate concentration of different radioisotopes in all the media. This data, complemented with an exposure scenario, allows a quantitative environmental risk assessment.

Exposure Assessment to Radionuclides Transfer in Food Chain

Generally sites with radioactive contamination are also simultaneously polluted with many other different t oxics, especially heavy metals. Besides the radioactivity, these wastes may also hold different amounts of chemicals, toxic pollutants and precipitates. Th e radionuclides released into the environment can give rise to human exposure by the transport through the atmosphere, aquatic systems or through soil sub-compartments. The exposure may result from direct inhalation of contaminated a ir or ingestion of contaminated water, or from a less direct pathway, the ingestion of contaminated food products. Contamination of the tr ophic chain by radionuclides released into the environment will be a component of human exposure to ionizing radiations by transferring the radionuclides into animal products that are components of the human diet. Thi s can occur by first ingestion of contaminated pasture by animals and th en by ingestion of animal products contaminated. The relevant incorporation o f the radionuclides into cows milk is usually due to the ingestion of conta minated pasture. This transfer process is often called the pasture-cow-milk exposure route. A compartment dynamic model is presented to describe mathematically the radium behaviour in the pasture-cow-milk exposure route and predict the activity concentrat ion in each compartment. The dynamic model is defined by a system of linear differential equations with constant coefficients b ased 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 concentration within each compartment is then trans cribed to doses values based on a simplified exposure pathway and a pre-de fined critical group.

Simulation of Liberation and Transport of Radium from Uranium Tailings

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 represented by the basic diffusion/dispersion — advection equation. Our algorithm uses the analytical solution for the one dimensional steady-state 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.