Moderate Thermophilic Bacterium Research Articles

An experimental study of the effects of bacteria on asphaltene adsorption and wettability alteration of dolomite and quartz

The adsorption of asphaltene on the rock surface and the changes in its wettability are very relevant issues in flow assurance and oil recovery studies, and for carbonate reservoirs, they are even more important. During microbial enhanced oil recovery (MEOR) processes, wettability alteration is considered a crucial mechanism leading to improved oil recovery. Therefore, it is essential to understand the mechanisms of surface wettability changes by bacteria and biosurfactants and find new and reliable methods to prevent asphaltene adsorption. Hence, the main aim of this research was to investigate the effect of a mixture of thiobacillus thiooxidans and thiobacillus ferooxidans microorganisms with an optimum effective temperature of around 30 °C (referred to as mesophilic bacteria), as well as a mixture of two moderate thermophiles Sulfobacillus thermosulfidooxidans for operating temperatures around 50 °C (referred to as moderately thermophilic bacteria) on the adsorption of asphaltene samples isolated from two different crude oils onto main reservoir minerals (i.e., quartz and dolomite). The results indicated that after two weeks of mineral aging in moderate thermophilic bacteria, the adsorption of asphaltene on both minerals increased between 180 and 290%. Fourier-transform infrared spectroscopy (FTIR) analysis for quartz and dolomite samples demonstrated that after aging in bacterial solution, bonds related to the adsorption of bacterial cells and biosurfactant production appear, which are the main factors of change in wettability. Alteration in wettability towards hydrophilicity expands hydrogen bonds on the surface, thus improving asphaltene adsorption due to polar interaction. Asphaltene 1 changed the contact angle of dolomite from 53.85° to 90.51° and asphaltene 2 from 53.85° to 100.41°. However, both strains of bacteria caused a strong water-wetting effect on the dolomite rock samples. The influence of moderate thermophilic bacteria on surface wettability is more significant than that of mesophilic bacteria, which may be caused by the high protein content of these bacteria, which expands hydrogen bonding with the surface. Adsorption of asphaltenes on dolomite rocks previously aged with bacteria showed that the wetted rock samples retained their water-wet state. This study highlights the dual impact of the used microorganisms. On one hand, they significantly reduce contact angles and shift wettability towards a strongly water-wet condition, a crucial positive factor for MEOR. On the other hand, these microorganisms can elevate the adsorption of asphaltenes on reservoir rock minerals, posing a potential challenge in the form of formation damage, particularly in low-permeability reservoirs.

Biooxidation of hydrogen sulfide to sulfur by moderate thermophilic acidophilic bacteria.

The copper industry utilizes significant amounts of sulfuric acid in its processes, generating sulfate as waste. While sulfate-reducing bacteria can remove sulfate, it produces hydrogen sulfide (H2S) as a byproduct. This study examined the capability of a consortium consisting of Sulfobacillus thermosulfidooxidans and Sulfobacillus acidophilus to partially oxidize H2S to S° at a temperature of 45°C. A fixed-bed bioreactor, with glass rings as support material and sodium thiosulfate as a model electron donor, was inoculated with the consortium. Formation of biofilms was crucial to maintain the bioreactor's steady state, despite high flow rates. Afterward, the electron donor was changed to H2S. When the bioreactor was operated continuously and with high aeration, H2S was fully oxidized to SO42-. However, under conditions of low aeration and at a concentration of 0.26g/L of H2S, the consortium was able to oxidize H2S to S° with a 13% yield. S° was discovered attached to the glass rings and jarosite. The results indicate that the consortium could oxidize H2S to S° with a 13% yield under low aeration and at a concentration of 0.26g/L of H2S. The findings highlight the capability of a Sulfobacillus consortium to convert H2S into S°, providing a potential solution for addressing environmental and safety issues associated with sulfate waste generated by the mining industry.

Biotechnological Conversion of Grape Pomace to Poly(3-hydroxybutyrate) by Moderately Thermophilic Bacterium Tepidimonas taiwanensis.

Polyhydroxyalkanoates (PHA) are microbial polyesters that have recently come to the forefront of interest due to their biodegradability and production from renewable sources. A potential increase in competitiveness of PHA production process comes with a combination of the use of thermophilic bacteria with the mutual use of waste substrates. In this work, the thermophilic bacterium Tepidimonas taiwanensis LMG 22826 was identified as a promising PHA producer. The ability to produce PHA in T. taiwanensis was studied both on genotype and phenotype levels. The gene encoding the Class I PHA synthase, a crucial enzyme in PHA synthesis, was detected both by genome database search and by PCR. The microbial culture of T. taiwanensis was capable of efficient utilization of glucose and fructose. When cultivated on glucose as the only carbon source at 50 °C, the PHA titers reached up to 3.55 g/L, and PHA content in cell dry mass was 65%. The preference of fructose and glucose opens the possibility to employ T. taiwanensis for PHA production on various food wastes rich in these abundant sugars. In this work, PHA production on grape pomace extracts was successfully tested.

Cell-Free Protein Synthesis by Diversifying Bacterial Transcription Machinery

We have evaluated several approaches to increase protein synthesis in a cell-free coupled bacterial transcription and translation system. A strong pargC promoter, originally isolated from a moderate thermophilic bacterium Geobacillus stearothermophilus, was used to improve the performance of a cell-free system in extracts of Escherichia coli BL21 (DE3). A stimulating effect on protein synthesis was detected with extracts prepared from recombinant cells, in which the E. coli RNA polymerase subunits α, β, β’ and ω are simultaneously coexpressed. Appending a 3′ UTR genomic sequence and a T7 transcription terminator to the protein-coding region also improves the synthetic activity of some genes from linear DNA. The E. coli BL21 (DE3) rna::Tn10 mutant deficient in a periplasmic RNase I was constructed. The mutant cell-free extract increases by up to four-fold the expression of bacterial and human genes mediated from both bacterial pargC and phage pT7 promoters. By contrast, the RNase E deficiency does not affect the cell-free expression of the same genes. The regulatory proteins of the extremophilic bacterium Thermotoga, synthesized in a cell-free system, can provide the binding capacity to target DNA regions. The advantageous characteristics of cell-free systems described open attractive opportunities for high-throughput screening assays.

Moderate thermophilic chemoorganoheterotrophic bacterium in surface layer of anthropogenic grounds of industrial estate area of Al-Mafraq, Jordan

Surface of oil-contaminated soil from Industrial Estate of Al-Mafraq city, Jordan, was investigated for the presence of aerobic oil-degrading moderately thermophilic bacteria. A pure culture of spore forming aerobic chemoorganogeterotrophic rod shaped bacterial isolate, designated as strain j3n, was obtained. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain j3n is closely related to gram-positive bacteria of kaustophilus thermoleovorans cluster of Geobacillus genus. Strain j3n grew aerobically with oil, hexadecane, benzoate and acetate. Growth data indicated that utilization of hexadecane but not of oil and benzoate might be under catabolite repression control. Possibility of a regulation of alkane degradation by acetate in aerobic thermophilic gram-positive bacteria of Geobacillus spp. was shown for the first time.

Development of a Cas12a-Based Genome Editing Tool for Moderate Thermophiles.

The ability of CRISPR-Cas12a nucleases to function reliably in a wide range of species has been key to their rapid adoption as genome engineering tools. However, so far, Cas12a nucleases have been limited for use in organisms with growth temperatures up to 37 °C. Here, we biochemically characterize three Cas12a orthologs for their temperature stability and activity. We demonstrate that Francisella novicida Cas12a (FnCas12a) has great biochemical potential for applications that require enhanced stability, including use at temperatures >37°C. Furthermore, by employing the moderate thermophilic bacterium Bacillus smithii as our experimental platform, we demonstrate that FnCas12a is active in vivo at temperatures up to 43°C. Subsequently, we develop a single-plasmid FnCas12a-based genome editing tool for B. smithii, combining the FnCas12a targeting system with plasmid-borne homologous recombination (HR) templates that carry the desired modifications. Culturing of B. smithii cells at 45°C allows for the uninhibited realization of the HR-based editing step, while a subsequent culturing step at reduced temperatures induces the efficient counterselection of the non-edited cells by FnCas12a. The developed gene-editing tool yields gene-knockout mutants within 3 days, and does not require tightly controllable expression of FnCas12a to achieve high editing efficiencies, indicating its potential for other (thermophilic) bacteria and archaea, including those with minimal genetic toolboxes. Altogether, our findings provide new biochemical insights into three widely used Cas12a nucleases, and establish the first Cas12a-based bacterial genome editing tools for moderate thermophilic microorganisms.

Modeling study of the bio-dissolution of copper concentrate in a continuous bioreactors system

The objective of the present research was to use two different bacterial cultures in continuous tank bioleaching circuits and to use this knowledge for mathematical modeling of the chalcopyrite bioleaching kinetic. Using three different particle size distributions (PSD) with the indices (d80) of 45, 32 and 16 µm of a chalcopyrite concentrate from the main Iranian copper processing plant and two types of bacteria, one and two-step continuous tests were performed in stirred tanks. In the first phase, tests were performed at 50 ± 2 °C using moderate thermophilic bacteria. The second part consisted of two-step continuous tests at 50 ± 2 °C using moderate thermophilic bacteria in the first reactor and extremely thermophilic bacteria at 65 ± 2 °C in the second reactor. The results of one-step continuous tests indicated that the highest rate of copper dissolution (5.21 g/l·day) resulted from test using feed with d80 = 16 µm. The Field Emission Scanning Electron Microscopy (FE-SEM) analysis of bioleaching residue indicated that the surface of particles was mostly covered with secondary layers. The Energy-dispersive X-ray spectroscopy (EDS) analysis of the formed layer revealed high concentrations of iron, sulfur and a certain amount of potassium. The results of two-step tests showed that under the specified conditions of this study, about 95% of copper was leached and transferred to solution. The analysis of FE-SEM and EDS residue indicated that the particle surface activity at this stage was higher than that of a single-step system probably due to the high temperature of the reaction medium (50 °C for the first reactor and 65 °C for the second reactor) and the presence of Oxidation-Reduction Potential (ORP) of solution in the range between 360 and 480 mV, Ag/AgCl. The results of the mathematical modeling for predicting the PSD of existing particles in the one -step reactor indicated that the maximum rate of size reduction kinetics was related to the first five days. The maximum difference between the experimental and predicted results was 19%. In case of two-step system, the reduction in particle size between the first and fifth days was significantly more than the next days. From the results of this study, it can be pointed out that firstly the two-steps bioleaching of chalcopyrite concentrate is more effective than the one-step and the reduction of particle size distribution can be predicted using the presented mathematical modeling.

First Insights into the Genome Sequence of Clostridium thermopalmarium DSM 5974, a Butyrate-Producing Bacterium Isolated from Palm Wine.

ABSTRACTClostridium thermopalmarium is a moderate thermophilic, rod-shaped, and endospore-forming bacterium, which was isolated from palm wine in Senegal. Butyrate is produced from a broad variety of sugar substrates. Here, we present the draft genome sequence of C. thermopalmarium DSM 5974 (2.822 Mb) containing 2,665 predicted protein-encoding genes.

Production and Characterization of an Extracellular Acid Protease from Thermophilic Brevibacillus sp. OA30 Isolated from an Algerian Hot Spring.

Proteases have numerous biotechnological applications and the bioprospection for newly-thermostable proteases from the great biodiversity of thermophilic microorganisms inhabiting hot environments, such as geothermal sources, aims to discover more effective enzymes for processes at higher temperatures. We report in this paper the production and the characterization of a purified acid protease from strain OA30, a moderate thermophilic bacterium isolated from an Algerian hot spring. Phenotypic and genotypic study of strain OA30 was followed by the production of the extracellular protease in a physiologically-optimized medium. Strain OA30 showed multiple extracellular proteolytic enzymes and protease 32-F38 was purified by chromatographic methods and its biochemical characteristics were studied. Strain OA30 was affiliated with Brevibacillus thermoruber species. Protease 32-F38 had an estimated molecular weight of 64.6 kDa and was optimally active at 50 °C. It showed a great thermostability after 240 min and its optimum pH was 6.0. Protease 32-F38 was highly stable in the presence of different detergents and solvents and was inhibited by metalloprotease inhibitors. The results of this work suggest that protease 32-F38 might have interesting biotechnological applications.

Bioleaching of Valuable Components from a Pyrometallurgical Final Slag

Pyrometallurgical copper final slag was subjected to leaching by means microbial cultures of three different groups based on their optimum temperature for growth and activity: mesophilic and moderate thermophilic bacteria, and extreme thermophilic archaea. The leaching experiments were performed by the shake-flask technique and in agitated bioreactors under batch and continuous-flow conditions. The effect of the most essential factors (particle size, pulp density, pH, aeration) on this process was studied. The highest rates of extraction of the non-ferrous metals (Cu, Zn, Co) and iron were achieved by means of some archaea but at relatively low pulp densities (5 – 10%). Some moderate thermophilic bacteria were the most efficient at the higher pulp densities (15 – 20 %). The, leaching by some mesophiles at pH 3.0 – 3.5 was also very attractive since it was connected with high extractions of these metals (about 85 – 92% at 20% pulp density), much lower acid consumption and low solubiliation of fayalite which resulted in the production of pregnant solutions suitable for the recovery of the dissolved non-ferrous metals.

Comparative Variants of Microbial Pretreatment and Subsequent Chemical Leaching of a Gold-Bearing Sulphide Concentrate

A sulphide concentrate containing 31.4% total sulphur (in which 30.7% was sulphidic), 31.8% iron, 8.0% arsenic, 18.5 g/t gold and 32.9 g/t silver finely disseminated in pyrite and arsenopyrite as the most essential components was subjected to microbial pretreatment to expose the precious metals from the sulphide matrix. Three different types of microbial cultures were tested for their ability to oxidize the sulphides and to expose the precious metals for the subsequent chemical leaching: mesophilic chemolithotrophic bacteria with a temperature optimum for their growth and activity at about 32 – 37°C, moderate thermophilic bacteria with the relevant optimum at 53 – 59°C, and hyperthermophilic archaea at 75 – 84°C. The microbial pretreatment of the concentrate was carried out in reactors with mechanical stirring and enhanced aeration by air enriched in CO2. It was found that sulphide oxidation of about 40 – 45 % was sufficient for achieving gold extraction higher than 90% during the subsequent leaching of the pretreated concentrate by different gold-solubilizing reagent (cyanide, thiourea, thiosulphate). The highest rate of sulphide oxidation was achieved by a mixed culture of hyperthermophilic archaea at 82°C but at relatively low pulp densities (within 7 – 9%). At higher pulp densities (within 10 – 25%) the highest rates were achieved by means of moderate thermophilic bacteria at 57 – 59°C.

TfoI produced by Tepidimonas fonticaldi PL17, a moderate thermophilic bacterium, is an isoschizomer of MseI.

A moderately thermophilic Gram-negative bacterium isolated from the Polok hot spring, Sikkim, India, was identified as a strain (PL17) of Tepidimonas fonticaldi by 16S rDNA sequencing. T. fonticaldi PL17 produces a Type IIP restriction endonuclease; named TfoI. Restriction mapping, run-off sequencing of TfoI-digests of dsDNA fragments, and end compatibility of TfoI with NdeI confirmed that the enzyme recognizes and cleaves the sequence 5'-T^TAA-3', and is thus an isoschizomer of MseI. The TfoI restriction-modification genes in the T. fonticaldi PL17 genome were identified, and the annotated TfoI protein encodes a protein of 181 amino acid residues that shares 47.2% sequence identity with MseI. The native enzyme was purified using a four-column chromatography protocol, and its functional homogeneity was confirmed by standard quality control tests. The ESI-MS measured molecular weight of purified TfoI (20.696kDa) is in agreement with that of the calculated monomeric molecular weight of the predicted TfoI protein sequence (20.694kDa). TfoI exhibits optimal activity in the temperature range of 55-70 °C with Mg+2 or Co+2 as cofactor. Similar to its isoschizomers, TfoI can be used as the frequent cutter for genome analysis.

Production of thermostable extracellular α-amylase by a moderate thermophilic Bacillus licheniformis isolated from Qinarje Hot Spring (Ardebil prov. of Iran)

Background and Purpose: Amylases are most important industrial enzymes that account for about 30% of the world’s food, feed, fermentation, textile, detergent and cellulosic industries. This study aimed at optimum production of thermostable α-amylase via moderate thermophilic bacterium (Bacillus licheniformis) which was recently isolated from Qinarje Hot spring.Material and Methods: Initially, ability of bacterium for amylase activity was determined by starch hydrolysis test using Gram’s iodine staining. Then bacterial growth pattern and amylase production curves in basal production medium were graphically determined at different time intervals. Finally, effect of different temperature, pH, carbon source, nitrogen source, minerals and inoculum size were studied on bacterial growth and amylase production using turbidimetric and DNS method, respectively.Results: Optimum enzyme production achieved after 84 hours of inoculation from cultures growing at 40 ˚C and pH 9.0 in a medium containing 0.03% (w/v) of CaCl2, compared to the basal medium, results showed that the best enzyme production happened with inoculum size of 4% (v/v). The addition of 1% (w/v) rice husk (as a Carbon source) enhanced enzyme productivity up to 160% and substitution of the peptone and yeast extract with 1% (w/v) of tryptone (as a Nitrogen source) increased the α-amylase production up to 160%.Conclusion: Our findings show that B. licheniformis-AZ2 strain has an ability to produce the thermostable α-amylase which is suitable in starch processing and food industries. To be commercialized, further investigation is required for enhancement of the enzyme production.Keywords: Bacillus licheniformis; Optimization; Basal medium; Agricultural by-products.

Production of l(+)-lactic acid from acid pretreated sugarcane bagasse using Bacillus coagulans DSM2314 in a simultaneous saccharification and fermentation strategy.

BackgroundSugars derived from lignocellulose-rich sugarcane bagasse can be used as feedstock for production of l(+)-lactic acid, a precursor for renewable bioplastics. In our research, acid-pretreated bagasse was hydrolysed with the enzyme cocktail GC220 and fermented by the moderate thermophilic bacterium Bacillus coagulans DSM2314. Saccharification and fermentation were performed simultaneously (SSF), adding acid-pretreated bagasse either in one batch or in two stages. SSF was performed at low enzyme dosages of 10.5–15.8 FPU/g DW bagasse.ResultsThe first batch SSF resulted in an average productivity of 0.78 g/l/h, which is not sufficient to compete with lactic acid production processes using high-grade sugars. Addition of 1 g/l furfural to precultures can increase B. coagulans resistance towards by-products present in pretreated lignocellulose. Using furfural-containing precultures, productivity increased to 0.92 g/l/h, with a total lactic acid production of 91.7 g in a 1-l reactor containing 20% W/W DW bagasse. To increase sugar concentrations, bagasse was solubilized with a liquid fraction, obtained directly after acid pretreatment. Solubilizing the bagasse fibres with water increased the average productivity to 1.14 g/l/h, with a total lactic acid production of 84.2 g in a 1-l reactor. Addition of bagasse in two stages reduced viscosity during SSF, resulting in an average productivity in the first 23 h of 2.54 g/l/h, similar to productivities obtained in fermentations using high-grade sugars. Due to fast accumulation of lactic acid, enzyme activity was repressed during two-stage SSF, resulting in a decrease in productivity and a slightly lower total lactic acid production of 75.6 g.ConclusionsIn this study, it is shown that an adequate production of lactic acid from lignocellulose was successfully accomplished by a two-stage SSF process, which combines acid-pretreated bagasse, B. coagulans precultivated in the presence of furfural as microorganism, and GC220 as enzyme cocktail. The process may be further improved by enhancing enzyme hydrolysis activities at high lactic acid concentrations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0646-3) contains supplementary material, which is available to authorized users.

Copper extraction from coarsely ground printed circuit boards using moderate thermophilic bacteria in a rotating-drum reactor

The current work reports on a new approach for copper bioleaching from Printed Circuit Board (PCB) by moderate thermophiles in a rotating-drum reactor. Initially leaching of PCB was carried out in shake flasks to assess the effects of particle size (−208μm+147μm), ferrous iron concentration (1.25–10.0g/L) and pH (1.5–2.5) on copper leaching using mesophile and moderate thermophile microorganisms. Only at a relatively low solid content (10.0g/L) complete copper extraction was achieved from the particle size investigated. Conversely, high copper extractions were possible from coarse-ground PCB (20mm-long) working with increased solids concentration (up to 25.0g/L). Because there was as the faster leaching kinetics at 50°C Sulfobacillus thermosulfidooxidans was selected for experiments in a rotating-drum reactor with the coarser-sized PCB sheets. Under optimal conditions, copper extraction reached 85%, in 8days and microscopic observations by SEM–EDS of the on non-leached and leached material suggested that metal dissolution from the internal layers was restricted by the fact that metal surface was not entirely available and accessible for the solution in the case of the 20mm-size sheets.

Studies on the effect of coal particle size on biodepyritization of high sulfur coal in batch bioreactor

Abstract The moderate thermophilic mix culture bacteria were used to depyritize the Illinois coal of varying particle sizes (-100 μm, 100-200 μm, +200 μm). Mineral libration analysis showed the presence of pyrite along with other minerals in coal. Microbial depyritization of coal was carried out in stirred tank batch reactors in presence of an iron-free 9K medium. The results indicate that microbial depyritization of coal using moderate thermophiles is an efficient process. Moreover, particle size of coal is an important parameter which affects the efficiency of microbial depyritization process. At the end of the experiment, a maximum of 75% pyrite and 66% of pyritic sulphur were removed from the median particle size. The XRD analysis showed the absence of pyrite mineral in the treated coal sample. A good mass balance was also obtained with net loss of mass ranging from 5-9% showing the feasibility of the process for large scale applications.

Adenosine-5′-phosphosulfate kinase from Thermobifida fusca

Sulfur, as a macronutrient, is essential for all kinds of organisms. Sulfate, the primary available source of sulfur, is firstly activated by adenylation catalyzed by ATP sulfurylase (ATPS) to form adenosine 5′-phosphosulfate (APS), which will be further phosphorylated into 3′-phosphoadenosine 5′-phosphosulfate (PAPS) by APS kinase (APSK). In some organisms, sulfate activating related enzymes are assembled to form sulfate-activating complex (SAC) to facilitate APS synthesis, the thermodynamically unfavorable reaction. In genome of a moderate thermophilic bacterium, Thermobifida fusca, there are presumably GTPasecoupled ATPS and one putative bifunctional ATPS/APSK type SAC. In this study, this putative SAC of T. fusca was prokaryotically expressed, purified and characterized. Activity assays showed that it contained APSK activity, while lacked ATPS activity. SAC of T. fusca was further used as a coupling enzyme to assay APS formation catalyzed by yeast ATPS. Based on the sequence alignment and modeled structure, we infer that the divergences of two conserved motifs and the missing of a loop and a helix-turn-helix motifs may contribute to the deficiency of ATPS activity.

Catalytic effect of Ag+ on arsenic bioleaching from orpiment (As2S3) in batch tests with Acidithiobacillus ferrooxidans and Sulfobacillus sibiricus

Orpiment is one of the major arsenic sulfide minerals which commonly occurs in the gold mine environment and the weathering of this mineral can lead to the contamination of arsenic. In this study, chemical leaching experiments using 10g/L Fe3+ at 35°C and 50°C were carried out and the results show that orpiment can be leached by Fe3+ and the leaching rate of orpiment was significantly enhanced in the presence of Ag+. The bioleaching experiments with mesophilic bacteria Acidithiobacillus ferrooxidans and moderate thermophilic bacteria Sulfobacillus sibiricus were carried out, showing that these two strains can survive in the mineral pulp and oxidize Fe2+ to regenerate Fe3+. Based on above results, it is believed that the leaching action of the acidic mining drainage by some bacteria can lead to the release of arsenic from orpiment. Different performances of At. ferrooxidans and S. sibiricus in the tests suggest they follow two different mechanisms and this point of view is further confirmed based on analyses of the composition and morphology of the mineral residue by SEM and EDS.

Bioleaching of high grade Zn–Pb bearing ore by mixed moderate thermophilic microorganisms

In this research, the bioleaching mechanism of zinc and lead from high-grade Zn–Pb ore has been investigated. It is done by using mixed culture of iron and sulfur oxidizing moderate thermophilic bacteria at 45°C. Pulp density, initial pH and ferrous concentration were studied as influential parameters in bioleaching experiments. The optimum conditions were achieved at pulp density=50 (g/L), initial pH=1 and FeSO4.7H2O concentration=75 (g/L) with 98.5% zinc recovery after 25days treatment. Generally, an increase in ferrous concentration caused an improve zinc recovery, and an increase in initial pH and pulp density caused reduction in zinc recovery. However, in the test with optimum condition the lead dissolution was just 0.027% due to the lower Pb solubility. Furthermore, cadmium dissolution was 98% under optimum condition and results showed the cadmium dissolution was in direct proportion with zinc dissolution. Finally, 7.82% of arsenic and 8.52% of antimony dissolved during zinc bioleaching after 25days treatment, both under above mentioned optimum condition.

Bioleaching of metals from spent refinery petroleum catalyst using moderately thermophilic bacteria: Effect of particle size

The present work investigated the leaching potential of moderately thermophilic bacteria in the recovery of metals from spent petroleum catalyst of varying particle sizes. The batch bioleaching experiments were conducted by employing a mixed consortium of moderate thermophilic bacteria at 45°C and by using five different particle sizes (from 45 to >2000 μm) of acetone-washed spent catalyst. The elemental mapping by FESEM confirmed the presence of Al, Ni, V and Mo along with sulfur in the spent catalyst. During bioleaching, Ni (92–97%) and V (81–91%) were leached in higher concentrations, whereas leaching yields of Al (23–38%) were found to be lowest in all particle sizes investigated. Decreasing the particle size from >2000 μm to 45–106 μm caused an increase in leaching yields of metals during initial hours. However, the final metals leaching yields were almost independent of particle sizes of catalyst. Leaching kinetics was observed to follow the diffusion-controlled model showing the linearity more close than the chemical control. The results of the present study suggested that bioleaching using moderate thermophilic bacteria was highly effective in removing the metals from spent catalyst. Moreover, bioleaching can be conducted using spent catalyst of higher particle size (>2000 μm), thus saving the grinding cost and making process attractive for larger scale application.