Ana Elías

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.

Long-term changes of ozone and traffic in Bilbao

It is well known that ozone levels are the result of the interaction among emissions of VOCs and NOx, on the one hand, and meteorological effects on the other hand. In this work, using the low-pass KZ filter developed by Kolmogorov and Zurbenko, the original time series consisting of the logarithm of daily maximum ozone concentrations measured at three locations in the Bilbao area, are splitted into long-term, seasonal and short-term effects. Next, meteorological effects are moderated or removed from filtered ozone series using multiple linear regression. The long-term evolution of ozone forming capability due to changes in precursor emissions can be obtained applying the KZ filter to the residuals of this regression. The present work is an application of the widely used and well known KZ filter technique and focuses on analyzing the joint evolution of the long-term components of ozone time series on the one hand, and mean traffic in the Bilbao area (Spain) on the other hand during years 1993, 1994, 1995 and 1996. To that end, regression analysis between the long-term fractions of ozone and traffic has been performed. The results show that long-term changes of the mean traffic flow are responsible for the long-term changes in ozone forming capability due to changes in precursor emissions of the area. Long-term trend of daily mean traffic can explain between 81% and 99.6% of the total variance of long-term ozone changes at the three locations of Bilbao studied.

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...

Short-term, real-time forecasting of hourly ozone, NO2 and NO levels by means of multiple linear regression modelling

ConclusionsThe results are at least as good as those obtained with much more sophisticated models. Furthermore, the models can be easily run on a simple PC. This approach may provide a good diagnostic network (as seen in Bilbao) with real-time, short-term prognostic capabilities for a given location. The models have been built for Bilbao and are applicable only in this location. However, using the same methodology, similar results could be obtained in other environments if a good diagnostic network is available.

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.

Biomachining: metal etching via microorganisms

The use of microorganisms to remove metal from a workpiece is known as biological machining or biomachining, and it has gained in both importance and scientific relevance over the past decade. Conversely to mechanical methods, the use of readily available microorganisms is low-energy consuming, and no thermal damage is caused during biomachining. The performance of this sustainable process is assessed by the material removal rate, and certain parameters have to be controlled for manufacturing the machined part with the desired surface finish. Although the variety of microorganisms is scarce, cell concentration or density plays an important role in the process. There is a need to control the temperature to maintain microorganism activity at its optimum, and a suitable shaking rate provides an efficient contact between the workpiece and the biological medium. The systems tolerance to the sharp changes in pH is quite limited, and in many cases, an acid medium has to be maintained for effective performance. This process is highly dependent on the type of metal being removed. Consequently, the operating parameters need to be determined on a case-by-case basis. The biomachining time is another variable with a direct impact on the removal rate. This biological technique can be used for machining simple and complex shapes, such as series of linear, circular, and square micropatterns on different metal surfaces. The optimal biomachining process should be fast enough to ensure high production, a smooth and homogenous surface finish and, in sum, a high-quality piece. As a result of the high global demand for micro-components, biomachining provides an effective and sustainable alternative. However, its industrial-scale implementation is still pending.