Astrid Barona

Metal associations in soils before and after EDTA extractive decontamination: implications for the effectiveness of further clean-up procedures

The distribution of Pb, Ni and Zn in two contaminated soils was determined before and after treating the soils with an EDTA solution. After the EDTA extraction, the proportion of Pb accumulated in the acid-extractable fraction considerably increased, which was related to the greater degree of metal extraction from the other fractions. EDTA was also able to extract certain amounts of Pb, Zn and Ni from the silicate matrix, which implied that these extractable amounts were not so strongly fixed to the residual fraction as previously supposed. As a consequence, after EDTA application, metal content (especially Pb) remained more weakly adsorbed to soil components (more easily leachable), potentially favouring the application of phytoremediation technologies. The extraction recoveries (for only one application) were generally low for the three metals (33-37% for Pb, 5-11% for Ni and 14-19% for Zn), although this fact is an advantage as plants would not be able to assimilate very high mobilised contents of metals.

Evaluation of a packing material for the biodegradation of H2S and product analysis

A packing material based on pig manure and sawdust was used for biofiltration purposes. The biofilter was made up of three exchangeable modules and the operation was carried out for 2500 h, during which the H2S mass loading rate was increased from 10 to 45 g m−3 h−1 with two superficial gas velocities (100 and 200 m h−1). The removal efficiencies of the whole biofilter were due mainly to the degradation activity of the first and second modules and the packing material proved to be chemically and mechanically suitable during the operation. The main by-product obtained in the biodegradation process was elemental sulphur, as it accounted for more than 82% of the total sulphur amount accumulated in the packing material. Sulphur deposition does not plug the bed for operation periods of 2500 h and the biofilter is easily cleaned by flushing water through the inlet.

Assessment of metal extraction, distribution and contamination in surface soils by a 3-step sequential extraction procedure

A 3-step sequential extraction procedure was used in order to assess the environmental risk of Cu, Ni and Zn in contaminated soils. The non-residual fraction was the most abundant pool for Cu in all soils, which means that this metal is highly available in these soils. Ni was mostly concentrated in the residual fraction. Zn was found in all the fractions but its distribution pattern was different in each soil. Individual and global contamination factors were calculated from the non-residual and residual contents and their values allowed us to classify the soils according to their environmental risk.

A review of indoor air treatment technologies

Indoor air pollution is a complex issue involving a wide diversity and variability of pollutants that threats human health. In this context, major efforts should be made to enhance indoor air quality. Thus, it is important to start by the control of indoor pollution sources. Nevertheless, when the suppression or minimization of emission sources is insufficient, technically unfeasible, or economically unviable, abatement technologies have to be used. This review presents a general overview of single treatment techniques such as mechanical and electrical filtration, adsorption, ozonation, photolysis, photocatalytic oxidation, biological processes, and membrane separation. Since there is currently no technology that can be considered fully satisfactory for achieving “cleaner” indoor air, special attention is paid to combined purification technologies or innovative alternatives that are currently under research and have not yet been commercialized (plasma-catalytic hybrid systems, hybrid ozonation systems, biofilter-adsorption systems, etc.). These systems seem to be a good opportunity as they integrate synergetic advantages to achieve good indoor air quality.

Relationships among metals in the solid phase of soils and in wild plants

The relationships between plant and soil systems were investigated using multivariate statistical methods and relative ionic impulsions. Soil samples were taken from three locations and wild plant species consisted of:Poa, Pteridium aquilinum, Diplotaxis, Plantago lanceolata andTrifolium repens. The content of Mg, Ca, Na, K, Mn, Fe, Pb, Co, Ni, Cu, Zn and Cr in soils and plants was determined. A five-step chemical fractionation procedure (speciation) was applied to soil samples. Total metal contents were determined and amounts extracted with HCl, EDTA and DTPA were measured. Pb, Co, Ni, Cu, Fe, Zn, Cd and Cr in soils (considered as microconstituents for plants) show a greater number of statistically significant relationships with plant contents than those shown by macroconstituents (Mg, Ca, Na, K and Mn). On the other hand, only Zn and Pb extracted with EDTA and DTPA seem to be related to metal contents in wild plants. When using relative ionic impulsions, any soil fraction (obtained from the fractionation procedure, including the soluble fraction, which is the sum of all the fractions except the residual) is suitable for the study of soil-plant system, suggesting a global balance among all the fractions. Our results suggested an active assimilation for K and a passive uptake for Na, Ca and Mn. Furthermore, Fe seemed to favour the active assimilation of the other microelements.

Fractionation of Lead in Soils and Its Influence on the Extractive Cleaning with EDTA

A sequential extraction (fractionation) procedure was adapted for this study and was carried out to compare the distribution of Pb in the soils of three locations, with varying levels of pollution. In all cases, Pb was predominantly accumulated in the residual fraction and in the fraction associated with Fe/Mn oxides. Soil samples were also treated with 0.1 M EDTA (ethylenediaminetetraacetic acid), which was used as an extractive cleaning solution for removing Pb from the soils. Possible relationships between the amounts of Pb extracted with EDTA and the Pb amounts associated with the different sequential fractions were investigated by using multiple regression analysis. The amount of Pb extracted with the cleaning solution was found to be related to the fractions associated with oxides and organic matter (and/or sulphides) which in turn appeared to be interdependent, as a probable consequence of the simultaneous complexation process when the EDTA solution is used. The sand fraction (particle size ranging...

Char-formation kinetics in the pyrolysis of sawdust in a conical spouted bed reactor.

Both the generation of a microporous structure and char formation kinetics have been studied in the pyrolysis of sawdust of Pinus insignis in a conical spouted bed reactor, in the range 350-700°C. The BET surface area (representative of the physical evolution of the solid) and the C/H ratio of the solid (representative of the chemical structural change) have been taken as conversion indices. From the measurement of the C/H ratio of the solid (the more significant variable), it has been determined that the reaction order is 0.5 and that the kinetic constant is between 0.18 min -1 at 350°C and 1.26 min -1 at 700°C. However the value of the constant is almost independent of temperature, at 1 min -1 in the range 500-700°C.

Application of biofiltration to the degradation of hydrogen sulfide in gas effluents

A laboratory scale bioreactor has been designed and set up in order to degrade hydrogen sulfide from an air stream. The reactor is a vertical column of 7 litre capacity and 1 meter in height. It is divided into three modules and each module is filled with pellets of agricultural residues as packing bed material. The gas stream fed into the reactor through the upper inlet consists of a mixture of hydrogen sulfide and humidified air. The hydrogen sulfide content in the inlet gas stream was increased in stages until the degradation efficiency was below 90%. The parameters to be controlled in order to reach continuous and stable operation were temperature, moisture content and the percentage of the compound to be degraded at the inlet and outlet gas streams (removal or elimination efficiency). When the H2S mass loading rate was between 10 and 40 g m-3h-1, the removal efficiency was greater than 90%. The support material had a good physical performance throughout operation time, which is evidence that this material is suitable for biofiltration purposes.

Biotechnology as an alternative for carbon disulfide treatment in air pollution control

Biotechnology has emerged as an affordable, effective, and eco-friendly alternative to treat carbon disulfide (CS2) containing waste gases. Carbon disulfide is a chemical of widespread use both in the past and in the present. Its industry demand has dramatically changed over the last two decades and is expected to grow in future in step with those industries involving fibre, mining, rubber products, and the agro-chemical sector. This compound, classified as a hazardous air pollutant about 20 years ago, has been re-appraised, as increasingly restrictive pollution standards are expected to be introduced. An array of physical–chemical technologies for treating CS2 containing air are already in use, but they have a series of drawbacks, such as high energy consumption (incineration, thermal oxidation), the immobilization of the contaminant solely from one phase to another (adsorption), and the generation of secondary by-products that require additional treatment (hydrolysis). Thus, technological research on af...

Evaluating the impact of water supply strategies on p-xylene biodegradation performance in an organic media-based biofilter.

The influence of water irrigation on both the long-term and short-term performance of p-xylene biodegradation under several organic loading scenarios was investigated using an organic packing material composed of pelletised sawdust and pig manure. Process operation in a modular biofilter, using no external water supply other than the moisture from the saturated inlet air stream, showed poor p-xylene abatement efficiencies (≈33 ± 7%), while sustained irrigation every 25 days rendered a high removal efficiency (RE) for a critical loading rate of 120 g m(-3)h(-1). Periodic profiles of removal efficiency, temperature and moisture content were recorded throughout the biofilter column subsequent to each biofilter irrigation. Hence, higher p-xylene biodegradation rates were always initially recorded in the upper module, which resulted in a subsequent increase in temperature and a decrease in moisture content. This decrease in the moisture content in the upper module resulted in a higher removal rate in the middle module, while the moisture level in the lower module steadily increased as a result of water condensation. Based on these results, mass balance calculations performed using measured bed temperatures and relatively humidity values were successfully used to account for water balances in the biofilter over time. Finally, the absence of bed compaction after 550 days of continuous operation confirmed the suitability of this organic material for biofiltration processes.