Sulfur Oxidation Rate Research Articles

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrateat 45-47 degrees C and pH 1.8-2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the micioorganisms from thie experimental and aboriginal communities during oxidation of sulfide ore flotation concentrate at 47 degrees C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus strains (the most active sulfur oxidizers) and Sulfobacillus thermotolerans strains (active oxidizers of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrates at high pulp density (S:L = 1:4).

Aerobic desulfurization of biogas by acidic biotrickling filtration in a randomly packed reactor

Biotrickling filters for biogas desulfurization still must prove their stability and robustness in the long run under extreme conditions. Long-term desulfurization of high loads of H2S under acidic pH was studied in a lab-scale aerobic biotrickling filter packed with metallic Pall rings. Reference operating conditions at steady-state corresponded to an empty bed residence time (EBRT) of 130s, H2S loading rate of 52gS–H2Sm−3h−1 and pH 2.50–2.75. The EBRT reduction showed that the critical EBRT was 75s and the maximum EC 100gS–H2Sm−3h−1. Stepwise increases of the inlet H2S concentration up to 10,000ppmv lead to a maximum EC of 220gS–H2Sm−3h−1. The H2S removal profile along the filter bed indicated that the first third of the filter bed was responsible for 70–80% of the total H2S removal. The oxidation rate of solid sulfur accumulated inside the bioreactor during periodical H2S starvation episodes was verified under acidic operating conditions. The performance under acidic pH was comparable to that under neutral pH in terms of H2S removal capacity. However, bioleaching of the metallic packing used as support and chemical precipitation of sulfide/sulfur salts occurred.

Comparative Study of Fluoride-Tolerance of Five Typical Bioleaching Microorganisms

In the bioleaching of uranium ore, fluoride that ever accreted with the ore floats into solution, inhibiting the growth and metabolic processes of microorganism or even killing them, further reducing the efficiency of uranium leaching. In order to study the fluoride tolerance of the bioleaching microorganisms, five typical bioleaching strains includingAcidithiobacillus ferrooxidansATCC 23270,Leptospirillum ferriphilumYSK,Sulfobacillus thermosulfidooxidansST,Acidithiobacills thiooxidansA01,Acidithiobacills caldusS1 were selected to compare their growth fluctuation and their oxidation rate of iron or sulfur in the presence of different concentration of fluoride. The results showed thatAt. ferrooxidansATCC 23270 held the best fluoride tolerance, whileS. thermosulfidooxidansST took the worst. In order to explore the mechanism of microbial resistance to fluoride, whole-genome array (WGA) was used to analyze the genome-wide expression profiling ofAt. ferrooxidansATCC 23270 upon 4.8 mM fluoride stress. The results showed that gene categories closely related to fluoride tolerance include cell membrane, energy metabolism, transport and binding functions of proteins, DNA metabolism, cell processing, synthesis and transportation of protein and other functional and metabolic pathways. Most of the genes associated with iron-sulfur metabolic system ofAt. ferrooxidanswere highly expressed during 10 to 120 minutes, while in the long-term stress for 4 hours, the gene expression returned to normal level or even were down regulated. All these results provide useful information for further research on domesticating bacteria and increasing the efficiency of uranium leaching.

Cell-Specific Thioautotrophic Productivity of Epsilon-Proteobacterial Epibionts Associated with Shinkaia crosnieri

In this study, we report experimental evidence of the thioautotrophic activity of the epibiotic microbial community associated with the setae of Shinkaia crosnieri, a galatheid crab that is endemic to deep-sea hydrothermal systems in the Okinawa Trough in Japan. Microbial consumption of reduced sulfur compounds under in situ hydrostatic and atmospheric pressure provided evidence of sulfur-oxidizing activity by the epibiotic microbial community; the rate of sulfur oxidation was similar under in situ and decompressed conditions. Results of the microbial consumption of reduced sulfur compounds and tracer experiments using 13C-labeled bicarbonate in the presence and absence of thiosulfate (used as a thioautotrophic substrate) convincingly demonstrated that the epibiotic microbial community on S. crosnieri drove primary production via an energy metabolism that was coupled with the oxidation of reductive sulfur compounds. A combination of tracer experiments, fluorescence in situ hybridization (FISH) and nano-scale secondary ion mass spectrometry (Nano-SIMS) indicated that the filamentous cells of the genus Sulfurovum belonging to the class Epsilonproteobacteria were thioautotrophs in the epibiotic community of S. crosnieri. In conclusion, our results strongly suggest that thioautotrophic production by Sulfurovum members present as the epibiotic microbial community play a predominant role in a probable nutritional ectosymbiosis with S. crosnieri.

Aqueous oxidation of galena and pyrite with nitric acid at moderate temperatures

The aim of the present work was to study the nitric acid leaching of galena and pyrite, above the melting point of sulfur (119°C), to determine under which conditions anglesite (PbSO4) and plumbojarosite (PbFe6(SO4)4(OH)12) are formed. Pure galena and pyrite particles, both separate and together, were leached in autoclave experiments with 0.13–0.91M HNO3 solutions at temperatures ranging from 130 to 170°C. Additionally, particles of anglesite were leached with ferric nitrate-nitric acid solutions at temperatures in this same range to determine the conditions for jarosite formation.At 130°C, with galena alone, increased acid concentration had a favorable effect on the initial lead dissolution, however promoted the sulfur oxidation rate, which accelerated subsequent lead precipitation and surface passivation. Elevated temperatures did not result in higher lead extractions, probably due to a larger and more rapid sulfate production. On the other hand, with pure pyrite, higher acid concentrations promoted increased pyrite oxidation (100% transformation with 0.91M after only 15min) and initial iron dissolution.Comparison between galena leaching products in the presence and absence of pyrite show marked differences in the mechanism; while in the former case, highly oxidized products are formed, in the latter, only unoxidized galena is detected for the same conditions. The solid residues of the combined galena-pyrite leach were examined with X-ray diffraction and scanning electron microscope, finding evidence of both anglesite and plumbojarosite. This is probably due to the role of the oxidation by ferric ion under these conditions. It was proven that anglesite, in nitrated solutions, reacts with ferric ions to form Pb-jarosite, especially at the higher temperatures.

Elemental Sulfur Oxidation by Thiobacillus spp. and Aerobic Heterotrophic Sulfur-Oxidizing Bacteria

The prediction of the oxidation rate of elemental sulfur (S 0) is a critical step in sulfur (S) fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S 0 oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S 0 applied to the soil were oxidized at 20 and 30 °C, respectively. The oxidation of S 0 proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm −2 d −1 was measured during the first two weeks at 30 °C. At 20 °C the highest oxidation rate of 10.2 μg S cm −2 d −1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S 0 the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 10 5 and 1.4 × 10 5 g −1 soil at the start of the experiment to 4 × 10 8 and 5.6 × 10 8 g −1 soil 14 days after S 0 application, respectively. No Thiobacillus spp. was present eight weeks after S 0 application. The results suggested that oxidation of residual S 0 completely relied on aerobic heterotrophic S-oxidizing bacteria.

DsrR, a Novel IscA-Like Protein Lacking Iron- and Fe-S-Binding Functions, Involved in the Regulation of Sulfur Oxidation inAllochromatium vinosum

In the purple sulfur bacterium Allochromatium vinosum, the reverse-acting dissimilatory sulfite reductase (DsrAB) is the key enzyme responsible for the oxidation of intracellular sulfur globules. The genes dsrAB are the first and the gene dsrR is the penultimate of the 15 genes of the dsr operon in A. vinosum. Genes homologous to dsrR occur in a number of other environmentally important sulfur-oxidizing bacteria utilizing Dsr proteins. DsrR exhibits sequence similarities to A-type scaffolds, like IscA, that partake in the maturation of protein-bound iron-sulfur clusters. We used nuclear magnetic resonance (NMR) spectroscopy to solve the solution structure of DsrR and to show that the protein is indeed structurally highly similar to A-type scaffolds. However, DsrR does not retain the Fe-S- or the iron-binding ability of these proteins, which is due to the lack of all three highly conserved cysteine residues of IscA-like scaffolds. Taken together, these findings suggest a common function for DsrR and IscA-like proteins different from direct participation in iron-sulfur cluster maturation. An A. vinosum DeltadsrR deletion strain showed a significantly reduced sulfur oxidation rate that was fully restored upon complementation with dsrR in trans. Immunoblot analyses revealed a reduced level of DsrE and DsrL in the DeltadsrR strain. These proteins are absolutely essential for sulfur oxidation. Transcriptional and translational gene fusion experiments suggested the participation of DsrR in the posttranscriptional control of the dsr operon, similar to the alternative function of cyanobacterial IscA as part of the sense and/or response cascade set into action upon iron limitation.

Comparative study of inorganic arsenic resistance of several strains of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans

The growth characteristics of several strains of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans were studied in the presence of soluble inorganic arsenic(III) and (V) with regard to media pH changes, total bacterial populations and sulfur oxidation rates. Most of these bacteria could reach large populations and have strong sulfur oxidation activity in the absence of arsenic. However, in the presence of up to 120 mM arsenite or arsenate, different strains showed different inorganic arsenic resistance. A. thiooxidans LYS and A. ferrooxidans BY-3 were two of the best performers which showed high arsenite resistance: up to 80 mM and 60 mM, respectively. On the other hand, A. thiooxidans JY and A. ferrooxidans TKY-2 could adapt up to 120 mM and 100 mM arsenate, respectively. These bacteria strains may play key roles in the bioleaching of arsenopyrite or in the bio-oxidation pretreatment of arsenic-bearing refractory gold sulfide ores and concentrates.

Characterization of Oxidizing Activity of a Microbial Community in an Industrial Bioleaching Heap

In order to explore new options to optimize the low-grade copper ore bioleaching process, it is important to understand the kinetics of microbial oxidation at industrial level. This work studies the changes of iron and sulfur oxidation rates of microbial communities in solution from an industrial low grade copper bioleaching heap process at Escondida Mine in Chile. Pregnant leach solution (PLS) samples were analyzed periodically to determine physico-chemical parameters. The total numbers of the different microorganism species in industrial samples were determined by Real Time PCR. In addition, Most Probable Number assays (MPN) were performed for iron and sulfur oxidizing microorganisms. Kinetics incubation tests of PLS in the presence of iron or sulfur were performed to study the iron and sulfur oxidation, in total, 102 oxidation profile tests were obtained. Based on the oxidation profiles obtained, the tests were divided into four groups, labeled as fast, normal, stepped shape, and incomplete. The grouping system was established by considering oxidation time and rates, during the initial oxidation stages and accounted for any lag phase. A data mining technique, called decision trees was used to analyze the data and to generate rules that represented patterns in the data. Strong correlations were found between the predominant microorganisms and the behavior of the oxidation tests. Preliminary results indicate that the magnitude order of MPN of the iron oxidizing microorganisms is an important factor in the microbial oxidizing activity, followed by the predominant specie within the microbial population, PLS temperature and Eh.

Impacts of growth kinetics of sulfur-oxidizing Acidithiobacillus ferrooxidans on kinetic models

The purpose of this study was to evaluate changes in kinetics of growth and elemental sulfur oxidation in Acidithiobacillus ferrooxidans cultures from the point of view of kinetic models of sulfuric acid formation. The values of maximum sulfur oxidation rate (v) and growth yield on sulfur (Y) were determined from data obtained in 86 batch cultures using bioreactors and shakers under the conditions described earlier. Both the constants demonstrated very different values in different cultures of the same strain. No significant correlation between the v and Y values was observed. Two metabolic phases of ATP formation occurred. During the second one, the rate of cell growth did not correlate with the rate of ATP formation. The reasons for the above changes remain unclear. Whether or not the background of the kinetic changes is related to the natural property of sulfur metabolism in the studied strain or other sulfur-oxidizing bacteria remains to be determined. As a result of this, the comparison and prediction of the kinetic constants is uncertain. Traditional kinetic approaches (exponential growth, the Monod equation) could be used for data of growth and sulfur oxidation. However, high variations of kinetic parameters represented substantial limits for the kinetic model application to predict the bioprocess course.

Mechanism of formation of the heaviest pollution episode ever recorded in the Yangtze River Delta, China

The heaviest aerosol pollution day in the historical record of the Yangtze River Delta occurred on 19 January 2007, in which the daily concentration of PM 10 reached 512 μg m −3 in Shanghai, 463 μg m −3 in Suzhou, 354 μg m −3 in Hangzhou, and 282 μg m −3 in Nanjing. The hourly concentrations of PM 2.5 and PM 10 reached peak values of 466 and 744 μg m −3, respectively, in Shanghai. With visibility <0.6 km, the regional haze covered nearly the entire Yangtze River Delta. High ratios of PM 2.5/PM 10 (61%), SO 2/PM 10 (0.38) and NO 2/PM 10 (0.24) were observed. The unusual stagnant dispersion conditions before a cold front played the predominant role in this high pollution episode, with relative humidity (RH) of 88%, both surface and upper-level inversions, as well as low wind speed (<1 m s −1). The sulfur oxidation rate (SOR) reached 0.67 and the nitrogen oxidation rate (NOR) reached 0.61, signifying that formation of sulfate and nitrate contributed significantly to the high secondary aerosol concentration of PM 2.5. The enrichment factors of As, Cd, and Pb reached 4058, 6971, and 3972, which were 4.45–6.68 times higher than those on good/moderate days. It was demonstrated that emissions from anthropogenic sources, especially stationary sources such as power plants, industrial boilers, and furnaces, were the major contributors to the heaviest aerosol pollution in the delta. More attention should be paid to the increases in emissions and the higher occurrence of haze days that have accompanied the rapid development of the economy in the Yangtze River Delta.

Sulfur surface chemistry on the platinum gate of a silicon carbide based hydrogen sensor

We have investigated the effects of sulfur contamination on a Pt-gate silicon carbide based field-effect gas sensor, under ultrahigh vacuum conditions, at a temperature of 527°C. Exposure to hydrogen sulfide, even in the presence of hydrogen or oxygen at partial pressures of 20–600 times greater than the H2S level, rapidly coated the gate with a monolayer of sulfur. Sulfur contamination reduced the magnitude of the sensor’s response to alternating hydrogen and oxygen pulses by about 70%, as compared to the uncontaminated gate. There was no evidence of irreversible changes in device behavior due to sulfur deposition and removal. The adsorbed sulfur could not be removed by exposure to hydrogen at the pressures accessible. Oxygen was effective at removing the sulfur. The rate of sulfur oxidation was suppressed at high sulfur coverages, but not as strongly as on low-index single-crystal surfaces. These results are discussed in the context of prior experiments on Pt crystals and films.

Sulfur mustard destruction using ozone, UV, hydrogen peroxide and their combination

Numerous methods are used for destruction of sulfur mustard. Oxidation is one of those methods. There have been only limited data concerning application of the advanced oxidation technologies (AOTs) for mustard destruction available before. In this study sulfur mustard oxidation rate depending on kind of the oxidative system and process parameters used was assessed using selected AOT. The following were selected for mustard oxidation: ozone (O 3), UV light (UV), hydrogen peroxide (H 2O 2); double systems: UV/O 3, UV/H 2O 2, and O 3/H 2O 2; a triple system: O 3/H 2O 2/UV and Fenton reaction. Effectiveness of the selected AOT methods has been evaluated and the most suitable one for mustard destruction was chosen. Using ozone in various combinations with hydrogen peroxide and UV radiation mustard can be destroyed much quicker comparing to the classical oxidizers. Fast mustard oxidation (a few minutes) occurred in those systems where ozone alone was used, or in the following combinations: O 3/H 2O 2, O 3/UV and O 3/H 2O 2/UV. When those advanced oxidation technologies are used, mustard becomes destroyed mainly in course of the direct oxidation with ozone, and reactions of mustard with radicals formed due to ozone action play a secondary role. Rate of sulfur mustard oxidation in the above mentioned ozone-containing oxidative systems decreases with pH value increasing from 2 to 12. Only when pH value of reaction solutions is close to pH 5, mustard oxidation rate is minimal, probably due to “disappearance” of radicals participating in oxidation in this pH. Sulfur mustard can be most effectively destroyed using just ozone in pH 7. In that case mustard destruction rate is only slightly lower than the rate achieved in optimal conditions, and the system is the simplest.

Kinetic Constant Variability in Bacterial Oxidation of Elemental Sulfur

Wide ranges of growth yields on sulfur (from 2.4 x 10(10) to 8.1 x 10(11) cells g(-1)) and maximum sulfur oxidation rates (from 0.068 to 1.30 mmol liter(-1) h(-1)) of an Acidithiobacillus ferrooxidans strain (CCM 4253) were observed in 73 batch cultures. No significant correlation between the constants was observed. Changes of the Michaelis constant for sulfur (from 0.46 to 15.5 mM) in resting cells were also noted.

Drop size effect on the rate and mechanism of SO2 oxidation in tropospheric clouds

The drop size effect on the rate and mechanism of sulfur dioxide oxidation in tropospheric clouds is analyzed. In the daytime, the oxidation rate decreases as the drops grow. This effect is due to the fact that the liquid-phase reactions slow down because of a decreasing influx of oxidizing species, namely, H2O2, OH., HO.2, and O3. The effect of the nonuniformity of OH. and O3 distribution in the drop bulk on the reaction rate is discovered.

Characterization of a thermophilic sulfur oxidizing enrichment culture dominated by a Sulfolobus sp. obtained from an underground hot spring for use in extreme bioleaching conditions

A thermoacidophilic elemental sulfur and chalcopyrite oxidizing enrichment culture VS2 was obtained from hot spring run-off sediments of an underground mine. It contained only archaeal species, namely a Sulfolobus metallicus-related organism (96% similarity in partial 16S rRNA gene) and Thermoplasma acidophilum (98% similarity in partial 16S rRNA gene). The VS2 culture grew in a temperature range of 35-76 degrees C. Sulfur oxidation by VS2 was optimal at 70 degrees C, with the highest oxidation rate being 99 mg S(0 )l(-1 )day(-1). At 50 degrees C, the highest sulfur oxidation rate was 89 mg l(-1 )day(-1 )(in the presence of 5 g Cl(-) l(-1)). Sulfur oxidation was not significantly affected by 0.02-0.1 g l(-1) yeast extract or saline water (total salinity of 0.6 M) that simulated mine water at field application sites with availability of only saline water. Chloride ions at a concentration above 10 g l(-1) inhibited sulfur oxidation. Both granular and powdered forms of sulfur were bioavailable, but the oxidation rate of granular sulfur was less than 50% of the powdered form. Chalcopyrite concentrate oxidation (1% w/v) by the VS2 resulted in a 90% Cu yield in 30 days.

Adhesion to metal sulfide surfaces by cells of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans

Attachment of four strains of Acidithiobacillus ferrooxidans to pyrite, chalcopyrite, galena, sphalerite or quartz was found to be mineral-selective. The bacterial extracellular polymeric substances (EPS) are responsible for mediating this process. Attachment of cells of A. ferrooxidans as well as of Acidithiobacillus thiooxidans was diminished, when depleted of their EPS. After 5 days of cultivation cells of A. ferrooxidans cover mineral surfaces with a dense biofilm, as visualised by fluorescence microscopy and AFM. Primary attachment was restricted to surface sites with visible defects. Chemical analyses of EPS of A. ferrooxidans, A. thiooxidans and Leptospirillum ferrooxidans indicated neutral sugars, fatty acids and uronic acids. The composition differed with the strain and the growth substrate. IronIII ions were only detectable in EPS of ironII ion- and pyrite-grown cells, but not in EPS of sulfur grown cells. Pyrite oxidation rates correlated with the amount of EPS-complexed ironIII ions in the case of A. ferrooxidans and L. ferrooxidans. Furthermore, pyrite oxidation rates of L. ferrooxidans were correlated with the genetic affiliation of the strains. The data for A. ferrooxidans seem to indicate a similar correlation, however, the results were not as clear-cut as those obtained for L. ferrooxidans. Sulfur oxidation rates of A. thiooxidans did not require EPS complexed ironIII ions.

Chemical Characteristics of PM2.5 and PM10 in Haze−Fog Episodes in Beijing

Aerosol samples of PM2.5 and PM10 in a period of intensive haze-fog (HF) events were collected to investigate the chemical characteristics of air pollution in Beijing. The air quality in HF episodes was much worse than that in nonhaze-fog (NHF) days. The concentrations of elements and water-soluble (WS) ions (K+, So4(2-), and NO3-) in HF episodes were more than 10 times higher than those in NHF days. Most of the chemical species in PM2.5 and the secondary species (NH4+, So4(2-), and NO3-) in PM10 showed significant difference between HF from westerly direction (HFW) and southerly direction (HFS). The concentrations of secondary species in HFS were much higher than those in HFW, and other chemical species in HFS were lower than those in HFW. The sources of PM2.5 were more from areas on the regional scale due to its tendency for long-range transport, while PM10 was more limited to the local sources. Aerosol particles were more acidic in HFS and more alkaline in HFW. The secondary species were the major chemical components of the aerosol in HF episodes, and their concentrations increased in the order of NHF < HFW < HFS. High concentrations of the secondary aerosol in HF episodes were likely due to the higher sulfur and nitrogen oxidation rate in aqueous-phase reactions. The serious air pollution in HF episodes was strongly correlated with the meteorological conditions and the emissions of pollutants from anthropogenic sources.

Removal of hydrogen sulfide by sulfate-resistant Acidithiobacillus thiooxidans AZ11

Toxic H2S gas is an important industrial pollutant that is applied to biofiltration. Here, we examined the effects of factors such as inlet concentration and space velocity on the removal efficiency of a bacterial strain capable of tolerating high sulfate concentrations and low pH conditions. We examined three strains of Acidithiobacillus thiooxidans known to have sulfur-oxidizing activity, and identified strain AZ11 as having the highest tolerance for sulfate. A. thiooxidans AZ11 could grow at pH 0.2 in the presence of 74 g l(-1) sulfate, the final oxidation product of elemental sulfur, in the culture broth. Under these conditions, the specific sulfur oxidation rate was 2.9 g-S g-DCW (dry cell weight)(-1) d(-1). The maximum specific sulfur oxidation rate of A. thiooxidans AZ11 was 21.2 g-S g-DCW(-1) d(-1), which was observed in the presence of 4.2 g-SO4(2-) l(-1) and pH 1.5, in the culture medium. To test the effects of various factors on biofiltration by this strain, A. thiooxidans AZ11 was inoculated into a porous ceramic biofilter. First, a maximum inlet loading of 670 g-S m(-3) h(-1) was applied with a constant space velocity (SV) of 200 h(-1) (residence time, 18 s) and the inlet concentration of H2S was experimentally increased from 200 ppmv to 2200 ppmv. Under these conditions, less than 0.1 ppmv H2S was detected at the biofilter outlet. When the inlet H2S was maintained at a constant concentration of 200 ppmv and the SV was increased from 200 h(-1) to 400 h(-1) (residence time, 9 s), an H2S removal of 99.9% was obtained. However, H2S removal efficiencies decreased to 98% and 94% when the SV was set to 500 h(-1) (residence time, 7.2 s) and 600 h(-1) (residence time, 6 s), respectively. The critical elimination capacity guaranteeing 96% removal of the inlet H2S was determined to be 160 g-S m(-3) h(-1) at a space velocity of 600 h(-1). Collectively, these findings show for the first time that a sulfur oxidizing bacterium has a high sulfate tolerance and a high sulfur oxidizing activity below pH 1.

Effect of different types of elemental sulfur on bioleaching of heavy metals from contaminated sediments

The application of two different types of elemental sulfur (S 0) was studied to evaluate the efficiency on bioleaching of heavy metals from contaminated sediments. Bioleaching tests were performed in suspension and in the solid-bed with a heavy metal contaminated sediment using commercial sulfur powder (technical sulfur) or a microbially produced sulfur waste (biological sulfur) as substrate for the indigenous sulfur-oxidizing bacteria and thus as acid source. Generally, using biological sulfur during suspension leaching yielded in considerably better results than technical sulfur. The equilibrium in acidification, sulfur oxidation and metal solubilization was reached already after 10–14 d of leaching depending upon the amount of sulfur added. The metal removal after 28 d of leaching was higher when biological sulfur was used. The biological sulfur added was oxidized with high rate, and no residual S 0 was detectable in the sediment samples after leaching. The observed effects are attributable to the hydrophilic properties of the biologically produced sulfur particles resulting in an increased bioavailability for the Acidithiobacilli. In column experiments only poor effects on the kinetics of the leaching parameters were observed replacing technical sulfur by biological sulfur, and the overall metal removal was almost the same for both types of S 0. Therefore, under the conditions of solid-bed leaching the rate of sulfur oxidation and metal solubilization is more strongly affected by transport phenomena than by microbial conversion processes attributed to different physicochemical properties of the sulfur sources. The results indicate that the application of biological sulfur provides a suitable means for improving the efficiency of suspension leaching treatments by shortening the leaching time. Solid-bed leaching treatments may benefit from the reuse of biological sulfur by reducing the costs for material and operating.