M. Luisa Blázquez

Characterization of exopolymeric substances (EPS) produced by Aeromonas hydrophila under reducing conditions

The aim of this work was to investigate the production of extracellular polymeric substances (EPS) by Aeromonas hydrophila grown under anaerobic conditions. EPS composition was studied for planktonic cells, cells attached to carbon fibre supports using a soluble ferric iron source and cells grown with a solid ferric iron mineral (gossan). Conventional spectrophotometric methods, Fourier transform infrared (FTIR) and confocal laser scanning microscopy (CLSM) were used to determine the main components in the biofilm extracted from the cultures. The key EPS components were proteins, indicating their importance for electron transfer reactions. Carbohydrates were observed mostly on the mineral and contained terminal mannosyl and/or terminal glucose, fucose and N-acetylgalactosamine residues.

Biosorption of Zn(II) from industrial effluents using sugar beet pulp and F. vesiculosus: From laboratory tests to a pilot approach

The aim of this work was to demonstrate the feasibility of the application of biosorption in the treatment of metal polluted wastewaters through the development of several pilot plants to be implemented by the industry. The use as biosorbents of both the brown seaweed Fucus vesiculosus and a sugar beet pulp was investigated to remove heavy metal ions from a wastewater generated in an electroplating industry: Industrial Goñabe (Valladolid, Spain). Batch experiments were performed to study the effects of pH, contact time and initial metal concentration on metal biosorption. It was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises from 2 to 5. The adsorption kinetic was studied using three models: pseudo first order, pseudo second order and Elovich models. The experimental data were fitted to Langmuir and Freundlich isotherm models and the brown alga F. vesiculosus showed higher metal uptake than the sugar beet pulp. The biomasses were also used for zinc removal in fixed-bed columns. The performance of the system was evaluated in different experimental conditions. The mixture of the two biomasses, the use of serial columns and the inverse flow can be interesting attempts to improve the biosorption process for large-scale applications.

Interrelation between Cells and Extracellular Polymeric Substances (EPS) from Acidiphilium 3.2Sup(5) on Carbon Surfaces

The interrelation between cells and extracellular polymeric substances (EPS) from the acidophilic bacterium Acidiphilium 3.2Sup(5) was investigated on two different carbon surfaces (carbon fibre cloth and graphite rods). This bacterium was chosen due to its ability to directly transfer electrons to carbon surfaces in aerobic conditions, which makes its use especially attractive in microbial fuel cells (MFC). The characterization of the bacterial adhesion and interrelation with the EPS was carried out using a combination of scanning (SEM) and transmission (TEM) electron microscopy. The extraction of the EPS was performed using EDTA and their characterization accomplished by chemical analyses and FTIR spectroscopy. The cellular lysis provoked by the extraction of EPS was determined by the protein/carbohydrate ratio. Chemical analyses showed that the main components of the EPS were proteins and carbohydrates, whereas FTIR spectroscopy showed the presence of a great majority of carboxyl, hydroxyl and amino groups. The tendency of cells was to adhere to superficial carbon imperfections, which after certain time were covered by a matrix of EPS.

The Influence of Disimilatory Fe(III) Reducers on Iron Ore Dissolution

The biological reduction rate of Fe(III) was studied using dissimilatory ferric reducing bacterial cultures (FeRB) in an attempt to establish a biotechnological via for the metallurgical treatment of iron ores. Enrichment cultures of dissimilatory ferric reducers were obtained from samples collected from a flooded acidic open pit in an abandoned Pb and Zn sulphide mining site nearby La Unión (Murcia, Spain). Adapted cultures were able to reduce 3 g/L of soluble Fe(III) with 100 efficiency in 36 hours. The growth of mixed cultures was also tested in solids. Ferrihydrite and ammonium jarosite served as electron acceptors in cultures where lactate acted as electron donor. Bacterial growth was also positive in both cases. This result represents an effective alternative to the chemical reduction of ferric minerals that avoids extreme temperatures when pyrometallurgical reactors are used. In addition, three species of FeRB were isolated and identified as Serratia fonticola, Aeromonas hydrophila and Clostridium celerecrescens. One of them, Aeromonas hydrophila, results of particular interest and, at the present moment, is being studied in depth. The particular significance of Aeromonas hydrophila is related to the characteristics of its exhausted cultures, where ferrous iron remains solved at pH values next to 7. At the present moment, the identification and characterization of the Fe(II) soluble complex is being account.

Biogenic Iron Compounds for Hazardous Metal Remediation

Biogenic minerals possess particular characteristics, such as high specific surface area and high reactivity, which lead to interesting properties useful in different fields (adsorbents, catalysts, oxidants or reductants). The treatment of effluents charged with heavy metals is attracting growing interest because of environmental and sanitary problems. The anaerobic bioreduction of soluble Fe(III) compounds by a natural consortium from an abandoned mine originates an iron containing precipitate. The aim of this study is the evaluation of the adsorption capacity of the biogenic compounds to treat diluted solutions containing arsenate, chromate and zinc after characterization by Scanning Electron Microscopy and X-ray diffraction analysis.

Removal of Arsenic from Aqueous Solution by Aeromonas hydrophila

Arsenic contamination is considered as a global environmental problem. This metalloid is known to be carcinogenic in some forms, and is mostly found in the environment as arsenate As (V) and arsenite As (III). Several chemical methods have been established for decontamination of arsenic from ground water including biological treatments. In the present work, the effect of the anaerobic bioreduction of soluble Fe (III) by the strain Aeromonashydrophila on arsenic immobilization has been investigated. The tolerance of this strain to arsenic concentration and the effect of the iron concentration in arsenic immobilization have been studied. The release of ferrous ion indicated the bioreduction of iron and promoted the subsequent arsenic co-precipitation, leading to the formation of various iron-bearing minerals. This precipitate has been observed and identified by Scanning Electron Microscopy and X-ray diffraction analysis as Fe3(AsO4)2(H2O)8.