Browsing by Author "Fonseca, Bruna"
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- Bioleaching of hexavalent chromium from soils using acidithiobacillus thiooxidansPublication . Fonseca, Bruna; Rodrigues, Joana L.; Queiroz, Ana; Tavares, TeresaThe continuous and growing degradation of the environment, due to several anthropogenic activities, is a main concern of the scientific community. Consequently, the development of low cost techniques to clean air, water and soils are under intense investigation. In this study, the focused problem is the soil contamination by hexavalent chromium, which is known for its several industrial applications - production of stainless steel, textile dyes, wood preservation and leather tanning - its high toxicity and mobility. Bioleaching has been presented as a low cost effective technique to decontaminate soils polluted with heavy metals. Sulphur oxidizing bacteria, like Acidithiobacillus thiooxidans, were already applied with this technique as they produce sulphuric acid, lowering the pH and promoting the dissolution of heavy metals [1, 2]. On the other hand, it also known that polythionates, generated during the oxidation process, have high reducing power. Considering this information and since few studies have been made concerning the bioleaching of hexavalent chromium from soils, this work pretended to investigate this matter. Specifically, eighteen Erlenmeyers flasks (250 mL) with a working volume of 150 mL, containing 10% ( V / V ) of inoculum (Acidithiobacillus thiooxidans DSM 504), 90% ( V / V ) of growing medium (DSM 35) and 3% ( W / V ) of contaminated soil were agitated in a rotary shaker, at 150 rpm, for 70 days. Also three controls were undertaken by sterilizing the soil and/or suppressing the inoculum. Two levels of soil contamination were evaluated within this work. This study presented bioleaching as a competitive technique in soil cleaning, as it is efficient and inexpensive.
- Bioleaching of hexavalent chromium from soils using Acidithiobacillus thiooxidansPublication . Fonseca, Bruna; Rodrigues, Joana L.; Queiroz, Ana; Tavares, Teresa
- Combined remediation technology for the reduction and bioleaching of hexavalent chromium from soils using acidithiobacillus thiooxidansPublication . Fonseca, Bruna; Rodrigues, Joana L.; Mendes, Tânia S.; Queiroz, Ana; Tavares, TeresaContamination of soils due to the release of effluents or deposition of wastes containing hexavalent chromium has been arising serious environmental problems. Therefore, the development of cost effectiveness but also ecological cleaning techniques is a matter of great concern among the scientific community. Bioremediation is attracting more and more attention due to its efficiency, low impact in the ecosystems and low cost. In particular, this study approaches a bioleaching technique using an Acidithiobacillus thiooxidans DSM504 pure culture to clean a soil contaminated with hexavalent chromium. Eight batch tests were performed in order to evaluate the effect of combined parameters: operational temperature (26ºC and Troom), hexavalent chromium concentration (50 mg kg-1 and 100 mg kg-1) and pH of the contaminant solution (2 and pHfree). The bioleaching technique herein exposed presented removal values between 33.3% and 83.3%, undergoing higher deviations due to changes on the contamination pH. Generally, it was more efficient when applied to soils contaminated with acid solutions. The lowest and highest values were both observed for operational temperatures of 26ºC and hexavalent chromium concentrations of 50 mg kg-1. Moreover, the highest value was observed for the soil contaminated with a hexavalent chromium solution of pH 2.
- Mobility of Cr, Pb, Cd, Cu and Zn in a loamy sand soil: a comparative studyPublication . Fonseca, Bruna; Figueiredo, Hugo; Rodrigues, Joana L.; Queiroz, Ana; Tavares, TeresaInterest in soil contamination has been growing in recent years due to the ongoing degradation of soil environments. Therefore, the development of remediation techniques and the study of contaminant sorption and migration are areas of intense research. In this study, the authors sought to evaluate the scenario of co-contamination of a loamy sand soil by multiple heavy metals. To that end, the sorption and transport of five metals—Cr, Pb, Cd, Cu and Zn—was evaluated using representative samples of a soil from the north of Portugal. The tests were conducted in batch and continuous systems using single- and multiple-metal acid solutions to evaluate the effect of metal competition. In accordance with the type of assay—batch or continuous—Langmuir or Convection Dispersion Two-Site Nonequilibrium models were adjusted to explain the sorption/transport data. FTIR analyses were performed on the final samples of the continuous systems. Generally, the results revealed good fitting of the tested models for the metals in competitive and noncompetitive scenarios, with the exception of Zn that was originally present in soil samples at higher concentrations. As expected, the influence of competition was observed in both batch and continuous systems, but with different tendencies. The FTIR spectra also revealed a strong influence of clay minerals and organic matter on the sorption of the metals.