Acidothiobacillus Ferrooxidans Research Articles

Leaching of metals from spent fluid catalytic cracking catalyst using Acidothiobacillus ferrooxidans and comparing its leaching efficiency with organic and inorganic acids

Bioleaching is an eco-friendly alternative for the extraction of metals from the spent fluid catalytic cracking catalyst (SFCCC). Acidothiobacillus ferrooxidans (A. ferrooxidans) are the most widely reported bacteria in leaching but remained unexplored for SFCCC till date. The present study proposes a cleaner, environmentally friendly process to leach metals from SFCCC by A. ferrooxidans. Batch bioleaching of metals was carried out with unadapted and adapted A. ferrooxidans. Experiments were performed by varying the pulp density (PD) (1–20%) at two different initial Fe(II) concentrations i.e. 2 g/L [M2Fe(II)] and 8.84 g/L [M8.84Fe(II)]. The results showed that adapted A. ferrooxidans leached out metals better than unadapted ones. Even though the loss of Iron to Jarosite formation was higher in M8.84Fe(II) than in M2Fe(II), leaching remained higher in M8.84Fe(II). Jarosite formation was minimized by maintaining the pH of the medium to 2 ± 0.1. Maximum leaching efficiency was observed at 1% PD. At this concentration. A. ferrooxidans growth was triggered which increased the production of Fe(III), thereby increasing leaching efficiency. Increase in PD led to a decrease in metal leaching efficiency. The maximum leaching observed by A. ferrooxidans is Al (35%), Ti (14%), Ni (27%) and V (56.5%). The amount of Al leached (70 mg/gm of SFCCC) suggests SFCCC be the potential secondary source of Al compared to popular secondary sources such as red mud and other spent catalysts. Al and V were better leached by A. ferrooxidans while organic acids were more suitable to extract Ti and Ni from SFCCC.

Bioleaching of rare earth elements from spent fluid catalytic cracking catalyst using Acidothiobacillus ferrooxidans

Acidothiobacillus ferrooxidans (A. ferrooxidans), an iron-oxidizing bacteria oxidizes Fe(II) to Fe(III), which is an excellent leaching agent to leach out rare earth elements (REEs) from spent fluid catalytic cracking catalyst (SFCCC). Batch leaching studies were carried out with two different types of A. ferrooxidans (unadapted (uAF) and adapted at 20% pulp density (PD) of SFCCC (aAF20)) and with two different initial concentrations of Fe(II) (2 and 8.84 g/L) in the leaching media. The rapid growth of A. ferrooxidans was observed within 24 h of incubation in the media. An increase in PDs resulted in an increase in pH and decrease in ORP, Fe(III) concentration suggesting inhibition of A. ferrooxidans growth at higher PDs. The amount of Fe(III) formed at any point of time in the leaching media followed the order aAF20 > uAF and 1% > 3%> 5,7%> 10%> 20% PDs. Higher leaching of La was observed at 1% PD while for Ce it was at 5% and 7% PDs. The maximum percentage of La and Ce leaching achieved was 83% and 23% respectively. This corresponds to 11.5 mg of La/gm of SFCCC, 0.211 mg of Ce/gm of SFCCC and these are of high economic importance. The amount of La and Ce bioleached is the highest reported from SFCCC to date. The competitive La leaching efficiency resulted by A. ferrooxidans compared to that of chemical leaching recommend bioleaching for La recovery from SFCCC. While citric acid is preferred for Ce extraction.

Optimization Routes for the Bioleaching of MSWI Fly and Bottom Ashes Using Microorganisms Collected from a Natural System

This paper presents a route for the treatment of MSWI fly (FA) and bottom ashes (BA) using microorganisms to critically assess whether bioleaching is within reach of effective industrial application. The leaching of metals from BA and FA was investigated in a controlled laboratory environment using a culture isolated from a natural system where the dominant strains are acidophilic bacteria, mainly Acidothiobacillus thiooxidans and Acidothiobacillus ferrooxidans. The community of microorganisms (mostly acidophilic, S- and Fe-oxidizing bacteria) was collected directly from overflows and ponds at the sediment–water interface of a natural system near a post-mining site. Pre-cultivation was done in 250 mL flasks followed by the adaptation to the different substrates (both FA and BA). The effect of different material pre-treatment and elemental sulphur concentrations were evaluated for both BA and FA, at a starting pH of 4. The bioleaching of BA and FA substrates experienced good yields of metal extraction with an optimum duration of two weeks. The results showed that more than 90% Zn, Cu, and 10% Pb are removed from FA; while 100% Cu, 80% Zn and 20% Pb are removed from BA samples. Batch experiments with regenerating ion-exchange resins did not perform well for metal recovery, but could serve as a valuable decontamination step. The techniques used here with FA and BA can be used for urban mining purposes (e.g. ashes and other meal-rich anthropogenic wastes), but also low-grade ores in the mining industry, contributing to resource recovery or decontamination agendas.

Biological oxidation of iron sulfides.

The biological oxidation of minerals and ores, called bioleaching, has been studied for the last decades to solubilize metals and recover them. In particular, iron sulfides are the most studied ores for an optimum extraction of different metals, such as copper or zinc. The use of chemolithotrophic bacteria, as Acidothiobacillus ferrooxidans, to oxidize both iron and sulfur species in aerobic conditions and at acidic pH shows promising results. In the field of heritage preservation, the development of "green" treatments is more and more studied. Waterlogged archeological wood presents an accumulation of iron sulfides within its structure, which, after exposition to oxygen, lead to salt precipitation and acidification and so to the degradation of the wooden artifact. A new extraction method, based on the dissolution of iron sulfides by the use of bacteria could be an alternative to the current chemical extraction methods, as being more respectful and ecological. While A. ferrooxidans is very effective in mines and groundwater, in the field of conservation-restoration of wood, Thiobacillus denitrificans is a better candidate as it grows at neutral pH, which is less aggressive for organic substrates (wood here). Preliminary studies show the efficiency of T. denitrificans for the dissolution of iron sulfides, as the concentration of nitrates used as electron donors decreases while the concentration of sulfates produced increases without degrading the wooden matrix. Long-term behavior should be studied to assess the stability of the artifacts after treatment.

Environmentally Benign Bio-Leaching Extraction of Rare Earth Elements from Non-Conventional Resources

The bio-leaching approaches are environmentally benign and economically viable. We investigated the bacterial Acidothiobacillus ferrooxidans (Af) and the fungal Aspergillus niger (An) for bio-leaching of REEs from a phosphate ore, and examined the factors governing the leaching processes. Based on the shake flask leaching studies, an increase in surface area with the increase in pulp density level (1-15 wt.%) was found to lead to an increase in the amounts of REEs leached.

Removal of arsenic by Acidothiobacillus ferrooxidans bacteria in bench scale fixed-bed bioreactor system

ABSTRACTIn the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1–1.5 gL−1), flowrate (0.06–0.18 Lh−1), and initial As (III) concentration (100–1000 µgL−1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10 µgL−1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions.

Microbially assisted arsenic removal using Acidothiobacillus ferrooxidans mediated by iron oxidation

Abstract The aim of this investigation was to determine the efficiency of arsenic removal present in acidic water using the biochemical method in presence of Acidothiobacillus ferrooxidans bacteria and ferrous ions. The process includes the bio-oxidation of ferrous to ferric by bacteria with simultaneous conversion of arsenite to arsenate and its removal by chemical method. The experiments were carried out in shake flasks with or without A.ferrooxidans culture. The variables of the pH, temperature, cell density and initial concentration of ferrous ions in the growth medium of A.ferrooxidans bacteria were examined in the laboratory to determine how they affect the removal of arsenic. It was found that the maximum arsenic removal (80%–85%) occurred at ferrous ions concentration of 2 gL−1 at the temperature of 35 °C with the initial cell density of 3.66 × 107 cells/mL and initial pH value of 2.5 with 70%–75% bio-oxidation of ferrous ions. The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses have confirmed the growth of bacteria and identify the nature of precipitate generated by the bacteria. The finding showed that arsenic can be removed considerably in this process in an efficient and greener way, but also removing efficiency was much more ( 80 % ) in acidic wastewater. The ANOVA and LSD statistical analysis were performed to assess any significant differences occurred among the four different levels of each variable. This study verified that combination of bio-oxidation with filtration improves the removal efficiency of arsenic.

Integrated bio-oxidation and adsorptive filtration reactor for removal of arsenic from wastewater

ABSTRACTRecently, removal of arsenic from different industrial effluent discharged using simple, efficient and low-cost technique has been widely considered. In this study, removal of arsenic (As) from real wastewater has been studied employing modified bio-oxidation followed by adsorptive filtration method in a novel continuous flow through the reactor. This method includes biological oxidation of ferrous to ferric ions by immobilized Acidothiobacillus ferrooxidans bacteria on granulated activated carbon (GAC) in fixed bed bio-column reactor with the adsorptive filtration unit. Removal efficiency was optimized regarding the initial flow rate of media and ferrous ions concentration. Synthetic wastewater sample having different heavy metal ions such as Arsenic (As), Cobalt (Co), Chromium (Cr), Copper (Cu), Iron (Fe), Lead (Pb) and Manganese (Mn) were also used in the study. The structural and surface changes occurring after the treatment process were scrutinized using FT-IR and Scanning Electron Microscopy (SEM) analysis. The finding showed that not only arsenic can be removed considerably in the bioreactor system, but also removing efficiency was much more (<90%) for other heavy metals in real wastewater sample. The results from TCPL test confirms that solid spent media was non-hazardous and can be safely disposed of. This study verified that combination of bio-oxidation with adsorptive filtration method improves the removal efficiency of arsenic and other heavy metal ions in wastewater sample.

Co-Generation of Fuels and Chemical in Mining Processes

We have developed an electrofuels method coupling an electrochemical reactor and a biological reactor containing chemolithoautrophic bacteria that have been engineered to produce chemicals or fuels [1,2]. Together, the two coupled reactors can use electricity generated from renewable sources to produce a chemical such as isobutyric acid or a fuel such as heptadecane from water and dilute CO2 from air. The process contains no other stoichiometric inputs, is scalable, and currently is undergoing improvements to the engineering of the bugs. While such a process is feasible, the cost of the electrical energy and the equipment motivates the exploration of alternative approaches An alternative is discussed here, where we explore the feasibility of using chemical energy released during bioleaching processes to co-produce chemicals. Here the ore or mineral waste is the sole source of the energy required to convert CO2 and water into the chemical. The same chemolithoautrophic bacteria is exploited, since it is already used in the processing of between 10 and 25 % of the world’s copper from ore. This organism grows under acidic conditions (pH of 2) using iron and/or sulfur as it energy source. Its sole source of carbon is CO2. In theory, the organism can thus be used for co-generation of chemicals in a large variety of mining processes. We explain the concept, present results for product formation obtained with simulated and real copper ores. Furthermore, the economic feasibility is discussed in terms of techno-economic analysis. Long term and short term possibilities for the technology are presented. [1]. Xiaozheng Li, Roel Mercado, Sarah Berlinger, Scott Banta, and Alan C. West, ” Engineering Acidothiobacillus ferrooxidans Growth Media for Enhanced Electrochemical Processing,” AICHE Journal, accepted (September, 2014). [2] Xiaozheng Li, Roel Mercado, Timothy Kernan, Alan C. West and Scott Banta, ”Addition of Citrate to Acidothiobacillus ferrooxidans Cultures Enables Precipitate-Free Growth at Elevated pH and Reduces Ferric Inhibition,” Biotechnology and Bioengineering, 111, 1940 (2014).

Electrofuel Production Using Genetically Engineered Acidithiobacillus Ferrooxidans

We have been developing an electrofuels platform for the production of fuels and chemicals from dilute CO2 using electricity. The electricity can come from diverse sources which enables this technology to serve as an alternative means for storing and utilizing renewable energy. The process uses Acidothiobacillus ferrooxidans which are chemolithoautotrophic bacteria that can oxidize iron at low pH. The oxidized iron can be reduced electrochemically and recycled to the bioreactor. We have extensively characterized the growth of the wild type Acidothiobacillus ferrooxidans cells in continuous cultures and we have found that the use of chelators such as citric acid can enable growth at higher pH ranges which can improve growth efficiency, maximum cell yields, and steady state cell densities. We have also developed a platform for genetically modifying the Acidothiobacillus ferrooxidans cells and we have now expressed 4 different exogenous genes in this host organism. This is enabling us to explore new promoters and regulatory sequences to direct carbon flux through new synthetic metabolic pathways. For example, we have introduced a pathway for isobutyric acid production and the results of the characterization of these new cell lines will be presented. We have developed an optimized media formulation for combining the biochemical and electrochemical reactors together, and we have performed extended experiments of the integrated system using wild type cells, allowing us to calculate biomass produced per kWhr of electricity under different operating conditions. We have also build a prototype system with some process control to enable longer term evaluation of the electrofuels platform, and the latest results of this technology will be presented.

Improvement of sludge dewaterability and removal of sludge-borne metals by bioleaching at optimum pH

Bio-acidification caused by bio-oxidation of energy substances during bioleaching is widely known to play an important role in improving sludge-borne metals removal. Here we report that bioleaching also drastically enhances sludge dewaterability in a suitable pH level. To obtain the optimum initial concentrations of energy substances and pH values for sludge dewaterability during bioleaching, bio-oxidation of Fe2+ and S0 under co-inoculation with Acidithiobacillus thiooxidans TS6 and Acidothiobacillus ferrooxidans LX5 and their effects on sludge dewaterability and metals removal during sludge bioleaching were investigated. Results indicated that the dosage of energy substances with 2g/L S0 and 2g/L Fe2+ could obtain bio-oxidation efficiencies of up to 100% for Fe2+ and 50% for S0 and were the optimal dosages for sludge bioleaching. The removal efficiencies of sludge-borne Cu and Cr could reach above 85% and 40%, respectively, and capillary suction time (CST) of bioleached sludge decreased to as low as ∼10s from initial 48.9s for fresh sludge when sludge pH declined to ∼2.4 through bioleaching. These results confirm the potential of bioleaching as a novel method for improving sludge dewaterability as well as removal of metals.

Biodesulphurized low rank coals appraisal: Initial, treated, their bitumens and solid residues

Low rank high sulphur containing Bulgarian coals are biodesulphurized on laboratory scale. Treatment of Maritza East lignites by bacteria Pseudomonas putida B2 ( PP) attained 44% total desulphurization, while biodesulphurization of Bobov dol subbituminous coal by Acidothiobacillus ferrooxidans F3 ( AFe) demonstrated 14%. The caloric values were slightly altered, 0.8% for lignites and 4.7% for subbituminous coal. Bitumens from the initial and biotreated coals and fractions of their neutral oils are studied. For subbituminous coal treated by AFe F3 bacteria increase in polar diterpenoids is registered by GC/MS. Concerning the set of polar diterpenoids produced during lignites treatment by PP B2 their relative contents are comparable with the ones for initial lignites. GC/MS analyses of soluble products from both coals did not give any information for sulphur containing compounds. Temperature programmed reduction coupled “on-line” with mass spectrometry (AP-TPR/MS) and its “off-line” TD-GC/MS version are used for sulphur tracking in solid residues after bitumen extraction. Quantitative interpretation of TD-GC/MS profiles revealed changes in organic sulphur compounds, elemental sulphur and SO 2. Results gave us ground to conclude that AFe F3 bacteria decrease pyritic sulphur content and slightly oxidize coal organic matter while PP B2 bacteria influence lignite organic matter and also affect pyritic sulphur.

The geomicrobiology of gold

Microorganisms capable of actively solubilizing and precipitating gold appear to play a larger role in the biogeochemical cycling of gold than previously believed. Recent research suggests that bacteria and archaea are involved in every step of the biogeochemical cycle of gold, from the formation of primary mineralization in hydrothermal and deep subsurface systems to its solubilization, dispersion and re-concentration as secondary gold under surface conditions. Enzymatically catalysed precipitation of gold has been observed in thermophilic and hyperthermophilic bacteria and archaea (for example, Thermotoga maritime, Pyrobaculum islandicum), and their activity led to the formation of gold- and silver-bearing sinters in New Zealand's hot spring systems. Sulphate-reducing bacteria (SRB), for example, Desulfovibrio sp., may be involved in the formation of gold-bearing sulphide minerals in deep subsurface environments; over geological timescales this may contribute to the formation of economic deposits. Iron- and sulphur-oxidizing bacteria (for example, Acidothiobacillus ferrooxidans, A. thiooxidans) are known to breakdown gold-hosting sulphide minerals in zones of primary mineralization, and release associated gold in the process. These and other bacteria (for example, actinobacteria) produce thiosulphate, which is known to oxidize gold and form stable, transportable complexes. Other microbial processes, for example, excretion of amino acids and cyanide, may control gold solubilization in auriferous top- and rhizosphere soils. A number of bacteria and archaea are capable of actively catalysing the precipitation of toxic gold(I/III) complexes. Reductive precipitation of these complexes may improve survival rates of bacterial populations that are capable of (1) detoxifying the immediate cell environment by detecting, excreting and reducing gold complexes, possibly using P-type ATPase efflux pumps as well as membrane vesicles (for example, Salmonella enterica, Cupriavidus (Ralstonia) metallidurans, Plectonema boryanum); (2) gaining metabolic energy by utilizing gold-complexing ligands (for example, thiosulphate by A. ferrooxidans) or (3) using gold as metal centre in enzymes (Micrococcus luteus). C. metallidurans containing biofilms were detected on gold grains from two Australian sites, indicating that gold bioaccumulation may lead to gold biomineralization by forming secondary 'bacterioform' gold. Formation of secondary octahedral gold crystals from gold(III) chloride solution, was promoted by a cyanobacterium (P. boryanum) via an amorphous gold(I) sulphide intermediate. 'Bacterioform' gold and secondary gold crystals are common in quartz pebble conglomerates (QPC), where they are often associated with bituminous organic matter possibly derived from cyanobacteria. This may suggest that cyanobacteria have played a role in the formation of the Witwatersrand QPC, the world's largest gold deposit.

Iron isotope fractionation during microbially stimulated Fe(II) oxidation and Fe(III) precipitation

Interpretation of the origins of iron-bearing minerals preserved in modern and ancient rocks based on measured iron isotope ratios depends on our ability to distinguish between biological and non-biological iron isotope fractionation processes. In this study, we compared 56Fe/ 54Fe ratios of coexisting aqueous iron (Fe(II) aq, Fe(III) aq) and iron oxyhydroxide precipitates (Fe(III) ppt) resulting from the oxidation of ferrous iron under experimental conditions at low pH (<3). Experiments were carried out using both pure cultures of Acidothiobacillus ferrooxidans and sterile controls to assess possible biological overprinting of non-biological fractionation, and both SO 4 2− and Cl − salts as Fe(II) sources to determine possible ionic/speciation effects that may be associated with oxidation/precipitation reactions. In addition, a series of ferric iron precipitation experiments were performed at pH ranging from 1.9 to 3.5 to determine if different precipitation rates cause differences in the isotopic composition of the iron oxyhydroxides. During microbially stimulated Fe(II) oxidation in both the sulfate and chloride systems, 56Fe/ 54Fe ratios of residual Fe(II) aq sampled in a time series evolved along an apparent Rayleigh trend characterized by a fractionation factor α Fe(III)aq–Fe(II)aq ∼ 1.0022. This fractionation factor was significantly less than that measured in our sterile control experiments (∼1.0034) and that predicted for isotopic equilibrium between Fe(II) aq and Fe(III) aq (∼1.0029), and thus might be interpreted to reflect a biological isotope effect. However, in our biological experiments the measured difference in 56Fe/ 54Fe ratios between Fe(III) aq, isolated as a solid by the addition of NaOH to the final solution at each time point under N 2-atmosphere, and Fe(II) aq was in most cases and on average close to 2.9‰ ( α Fe(III)aq–Fe(II)aq ∼ 1.0029), consistent with isotopic equilibrium between Fe(II) aq and Fe(III) aq. The ferric iron precipitation experiments revealed that 56Fe/ 54Fe ratios of Fe(III) aq were generally equal to or greater than those of Fe(III) ppt, and isotopic fractionation between these phases decreased with increasing precipitation rate and decreasing grain size. Considered together, the data confirm that the iron isotope variations observed in our microbial experiments are primarily controlled by non-biological equilibrium and kinetic factors, a result that aids our ability to interpret present-day iron cycling processes but further complicates our ability to use iron isotopes alone to identify biological processing in the rock record.

Potential for Using Isotopically Altered Metalloproteins in Species-Specific Isotope Dilution Analysis of Proteins by HPLC Coupled to Inductively Coupled Plasma Mass Spectrometry

The production and evaluation of an isotopically enriched metalloprotein standard for use as a calibrant in species-specific isotope dilution analysis by HPLC coupled to inductively coupled plasma mass spectrometry is described. Using a model system involving the copper-containing protein rusticyanin (Rc) from the bacterium Acido-thiobacillus ferrooxidans, it was possible to demonstrate the analytical conditions that could be used for the measurement of metalloproteins by on-line IDMS analysis. Rc was chosen because it is a well-characterized protein with an established amino acid sequence and can be produced in suitable quantities using a bacterial recombinant system. Three different forms of the protein were studied by organic and inorganic mass spectrometry: the native form of the protein containing a natural isotopic profile for copper, an isotopically enriched species containing virtually all of its copper as the 65Cu isotope, and the nonmetalated apo form. Incorporation of the copper isotopes into the apo form of the protein was determined using a UV-vis spectrophotometric assay and shown to be complete for each of the copper-containing species. The experimental conditions required to maintain the conformational form of the protein with a nonexchangeable copper center were established using +ve electrospray mass spectrometry. A pH 7.0 buffer was found to afford the most appropriate conditions, and this was then used with HPLC-ICP-MS to verify the stability of the copper center by analysis of mixtures of different isotopic solutions. No exchange of the enriched copper isotope from Rc with an added naturally abundant inorganic copper cation was observed under a neutral pH environment, indicating that species-specific ID-MS analysis of metalloproteins is possible.

Enhanced Introduction of Gold Nanoparticles into Vital Acidothiobacillus ferrooxidans by Carbon Nanotube-based Microwave Electroporation

A novel method was developed to electroporate gram-negative bacteria (Acidothiobacillus ferrooxidans) via multiwall carbon nanotubes (CNTs). CNTs are metallic, ultra strong nanofibers of ∼10 nm in ...

A broad host range plasmid vector that does not encode replication proteins

The 640-bp minimal replication region derived from a plasmid DNA preparation from an Acidothiobacillus ferrooxidans strain capable of autonomous replication in a range of Gram-negative bacteria ( Escherichia coli, Pseudomonas aeruginosa, Acinetobacter calcoaceticus and Alcaligenes faecalis) was identified. This DNA fragment (named TFK replicon) does not encode Rep proteins and appears to be unrelated to other known replicons.

A broad host range plasmid vector that does not encode replication proteins.

The 640-bp minimal replication region derived from a plasmid DNA preparation from an Acidothiobacillus ferrooxidans strain capable of autonomous replication in a range of Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Acinetobacter calcoaceticus and Alcaligenes faecalis) was identified. This DNA fragment (named TFK replicon) does not encode Rep proteins and appears to be unrelated to other known replicons.

Development of an optimal medium for continuous ferrous iron oxidation by immobilized Acidothiobacillus ferrooxidans cells.

This study was aimed at developing an immobilized bioreactor system in which long-term continuous ferrous iron oxidation can be realized with no formation of jarosite, which causes clogging of support pores and reactor lines. For this purpose, a medium with no jarosite formation was developed first by selecting optimal nitrogen and phosphate sources and their concentrations. Then with the developed medium containing ammonium phosphate instead of ammonium sulfate and potassium phosphate, repeated batch and continuous operations of ferrous iron oxidation by Acidothiobacillus ferrooxidans cells immobilized in a depth filter were successfully performed for an extended period of time. For about 510 h of operation including 450 h of continuous operation at dilution rates of 0.1, 0.2, and 0.3 h(-)(1), no formation of jarosite and thus no clogging of the reactor system were observed. The maximum ferrous iron oxidation rate was as high as 2.6 g/(L.h) at a dilution rate of 0.3 h(-)(1).

97/01597 Trace elements in coals and lignites

Low rank high sulphur containing Bulgarian coals are biodesulphurized on laboratory scale. Treatment of Maritza East lignites by bacteria Pseudomonas putida B2 (PP) attained 44% total desulphurization, while biodesulphurization of Bobov dol subbituminous coal by Acidothiobacillus ferrooxidans F3 (AFe) demonstrated 14%. The caloric values were slightly altered, 0.8% for lignites and 4.7% for subbituminous coal.Bitumens from the initial and biotreated coals and fractions of their neutral oils are studied. For subbituminous coal treated by AFe F3 bacteria increase in polar diterpenoids is registered by GC/MS. Concerning the set of polar diterpenoids produced during lignites treatment by PP B2 their relative contents are comparable with the ones for initial lignites. GC/MS analyses of soluble products from both coals did not give any information for sulphur containing compounds.Temperature programmed reduction coupled “on-line” with mass spectrometry (AP-TPR/MS) and its “off-line” TD-GC/MS version are used for sulphur tracking in solid residues after bitumen extraction. Quantitative interpretation of TD-GC/MS profiles revealed changes in organic sulphur compounds, elemental sulphur and SO2.Results gave us ground to conclude that AFe F3 bacteria decrease pyritic sulphur content and slightly oxidize coal organic matter while PP B2 bacteria influence lignite organic matter and also affect pyritic sulphur.