A trickle bed reactor for ferrous sulphate oxidation using Thiobacillus ferrooxidans

Summary A trickle bed reactor was used to improve ferrous sulphate oxidation rate with Thiobacillus ferrooxidans immobilised in BSPs (Biomass Support Particles). A maximum iron(II) oxidation rate of 4.4 gL^–1h^–1 was observed at a dilution rate D = 0.9 h^–1. The ability of the reactor to operate under non-aseptic conditions due to the chemoautotrophy and acidophilia of the bacterium makes industrial application promising.     

A kinetic model for biological oxidation of ferrous iron by Thiobacillus ferrooxidans

The kinetics of bacterial oxidation of ferrous iron in the presence of Thiobacillus ferrooxidans cells were studied using an initial-rate method. Measurements of the redox potential of the solution during the oxidation of ferrous iron were used to assess the initial rate of the reaction. Effects on the rate of reaction were determined for ferrous iron concentration in the range 0.25 to 30 kg m(-3), bacterial concentration in the range 3.25 x 10(7) to 4.47 x 10(8) cells mL(-1), and temperature in the range 20 to 35 degrees C. Using these experimental results and an approach based on Michaelis-Menten kinetics, a model for biological oxidation of ferrous iron was developed. The model, which incorporates terms for the effect of temperature and substrate and cell inhibition, was successfully used to simulate the full range of experimental data obtained. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 478-486, 1997.     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures was examined, using on-line off-gas analyses to measure the oxygen and carbon dioxide consumption rates continuously. A cell suspension from continuous cultures at steady state was used as the inoculum. It was observed that a dynamic phase occurred in the initial phase of the experiment. In this phase the bacterial ferrous iron oxidation and growth were uncoupled. After about 16 h the bacteria were adapted and achieved a pseudo-steady state, in which the specific growth rate and oxygen consumption rate were coupled and their relationship was described by the Pirt equation. In pseudo-steady state, the growth and oxidation kinetics were accurately described by the rate equation for competitive product inhibition. Bacterial substrate consumption is regarded as the primary process, which is described by the equation for competitive product inhibition. Subsequently the kinetic equation for the specific growth rate, μ, is derived by applying the Pirt equation for bacterial substrate consumption and growth. The maximum specific growth rate, μ _max, measured in the batch culture agrees with the dilution rate at which washout occurs in continuous cultures. The maximum oxygen consumption rate, q _O2,max, of the cell suspension in the batch culture was determined by respiration measurements in a biological oxygen monitor at excess ferrous iron, and showed changes of up to 20% during the course of the experiment. The kinetic constants determined in the batch culture slightly differ from those in continuous cultures, such that, at equal ferric to ferrous iron concentration ratios, biomass-specific rates are up to 1.3 times higher in continuous cultures. Received: 8 February 1999 / Accepted: 17 February 1999     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in continuous cultures

The oxidation and growth kinetics of ferrous iron with Thiobacillus ferrooxidans in continuous cultures was examined at several total iron concentrations. On-line off-gas analyses of O₂ and CO₂ were used to measure the oxygen and carbon dioxide consumption rates in the culture. Off-line respiration measurements in a biological oxygen monitor (BOM) were used to measure directly the maximum specific oxygen consumption rate, qO₂,max, of cells grown in continuous culture. It was shown that these reproducibly measured values of qO₂,max vary with the dilution rate. The biomass-specific oxygen consumption rate, qO₂, is dependent on the ratio of the ferric and ferrous iron concentrations in the culture. The oxidation kinetics was accurately described with a rate equation for competitive ferric iron inhibition, using the value of qO₂,max measured in the BOM. Accordingly, only the kinetic constant Ks/K _i needed to be fitted from the measurements. A new method was introduced to determine the steady-state kinetics of a cell suspension in a batch culture that only takes a few hours. The batch culture was set up by terminating the feeding of a continuous culture at its steady state. The kinetic constant K _s/K _i determined in this batch culture agreed with the value determined in continuous cultures at various steady states. Received: 8 February 1999 / Accepted: 17 February 1999     

Adaptation of Thiobacillus ferrooxidans to nickel ion and bacterial oxidation of nickel sulfide

Summary The Ni²⁺ resistance of Thiobacillus ferrooxidans was enhanced by repeated culturing in medium containing Ni²⁺ and gradually increasing the Ni²⁺ concentration. The extraction of nickel sulfide was enhanced by the adapted strain following the direct leaching mechanism of the microorganism.     

The effect of ferric ion on the rate of ferrous oxidation by Thiobacillus ferrooxidans

 In this study, the effect of ferric ion and cell concentrations on the oxidation of ferrous ion by T. ferrooxidans was investigated. Ferric ions competitively inhibited ferrous ion oxidation by the bacteria. The inhibitory effect of ferric ion was, however, reduced by increasing cell concentration. The apparent ferric ion inhibition constant did not change with increasing cell concentration. The ferrous ion oxidation kinetics in the absence and presence of ferric ion changes from the standard Michaelis-Menten type at low cell concentrations to pseudo-first-order kinetics at high cell concentration. Received: 8 August 1995/Received revision: 31 October 1995/Accepted: 10 November 1995     

Continuous bacterial ferrous iron oxidation by Thiobacillus ferrooxidans in rotating biological contactors

Summary Fe oxidation in rotating biological contactors has been studied over a range of influent Fe concentrations. Rotation speeds greater than 20 rpm did not affect the oxidation rate. Hydraulic loading rates above a critical value reduce the oxidation rat at influent Fe>4g/L.     

A structured model for Thiobacillus ferrooxidans growth on ferrous iron

A structured model for Thiobacillus ferrooxidans growth dependence on ferrous and ferric iron, arsenic, oxygen, carbon dioxide, pH, and temperature is presented. A new kinetic mechanism for ferrous oxidation by T. ferrooxidans is introduced. Data from several earlier experimental studies of T. ferroaxidans growth are used for model development. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 310-319, 1997.     

Selective inhibition of the oxidation of ferrous iron or sulfur in Thiobacillus ferrooxidans

The oxidation of either ferrous iron or sulfur by Thiobacillus ferrooxidans was selectively inhibited or controlled by various anions, inhibitors, and osmotic pressure. Iron oxidation was more sensitive than sulfur oxidation to inhibition by chloride, phosphate, and nitrate at low concentrations (below 0.1 M) and also to inhibition by azide and cyanide. Sulfur oxidation was more sensitive than iron oxidation to the inhibitory effect of high osmotic pressure. These differences were evident not only between iron oxidation by iron-grown cells and sulfur oxidation by sulfur-grown cells but also between the iron and sulfur oxidation activities of the same iron-grown cells. Growth experiments with ferrous iron or sulfur as an oxidizable substrate confirmed the higher sensitivity of iron oxidation to inhibition by phosphate, chloride, azide, and cyanide. Sulfur oxidation was actually stimulated by 50 mM phosphate or chloride. Leaching of Fe and Zn from pyrite (FeS(2)) and sphalerite (ZnS) by T. ferrooxidans was differentially affected by phosphate and chloride, which inhibited the solubilization of Fe without significantly affecting the solubilization of Zn.     

Biological ferrous sulfate oxidation by A. ferrooxidans immobilized on chitosan beads

The immobilization of Acidithiobacillus ferrooxidans cells on chitosan and cross-linked chitosan beads and the biooxidation of ferrous iron to ferric iron in a packed-bed bioreactor were studied. The biofilm formation was carried out by using a glass column reactor loaded with chitosan or cross-linked chitosan beads and 9 K medium previously inoculated with A. ferrooxidans cells. The immobilization cycles on the carrier matrix with the bioreactor operating in batch mode were compared. Then, the reactor was operated using a continuous flow of 9 K medium at different dilution rates. The results indicate that the packed-bed reactor allowed increasing the flow rate of medium approximately two fold (chitosan) and eight fold (chitosan cross-linked) without cells washout, compared to a free cell suspension reactor used as control, and to reach ferric iron productivities as high as 1100 and 1500 mg l(-1) h(-1) respectively. Scanning electron microscopy micrographs of the beads, infrared spectroscopy and the X-ray diffraction patterns of precipitates on the chitosan beads were also investigated.     

Mathematical model of the oxidation of ferrous iron by a biofilm of Thiobacillus ferrooxidans

Microbial oxidation of ferrous iron may be a viable alternative method of producing ferric sulfate, which is a reagent used for removal of H(2)S from biogas. The paper introduces a kinetic study of the biological oxidation of ferrous iron by Thiobacillus ferrooxidans immobilized on biomass support particles (BSP) composed of polyurethane foam. On the basis of the data obtained, a mathematical model for the bioreactor was subsequently developed. In the model described here, the microorganisms adhere by reversible physical adsorption to the ferric precipitates that are formed on the BSP. The model can also be considered as an expression for the erosion of microorganisms immobilized due to the agitation of the medium by aeration.     

An ultraviolet spectrophotometric method for the determination of pyrite and ferrous ion oxidation by Thiobacillus ferrooxidans

Summary An ultraviolet spectrophotometric method was used to monitor the formation of soluble ferric iron in acid culture solutions of Thiobacillus ferrooxidans. This methodology was demonstrated to be applicable for determining both pyrite and ferrous ion oxidation. Kinetic parameters of Fe²⁺ oxidation determined with the use of this method were in close agreement with those previously obtained by measurement of oxygen uptake rates.     

Potential of Thiobacillus ferrooxidans for waste gas purification. Part 1. Kinetics of continuous ferrous iron oxidation

Kinetic data of ferrous iron oxidation by Thionacillus ferrooxidans were determined. The aim was to remove H₂S (<0.5 ppm) from waste gas by a process proposed earlier. Kinetic data necessary for industrial scale-up were investigated in a chemostat airlift reactor (dilution rate 0.02–0.12 h^–1; pH 1.3). Due to the low pH, ferric iron precipitation and wall growth could be avoided. The maximum ferrous iron oxidation rate of submersed bacteria was 0.77 g 1^–1 h^–1, the maximum specific growth rate about 0.12 h^–1 and the yield coefficient was found to be 0.007 g g^–1 Fe²⁺. The specific O₂ demand of an exponentially growing, ironoxidizing batch culture was 1.33 mg O₂ mg^–1 biomass h^–1. The results indicate that a pH of 1.3 has no negative influence on the kinetics of iron oxidation and growth. Correspondence to: W. Schäfer-Treffenfeldt     

Use of Thiobacillus ferrooxidans for iron oxidation and precipitation

Fe(II) oxidation reaction was carried out using an acidophilic microorganism, Thiobacillus ferrooxidans. Four different parameters such as pH, Fe(II), Fe(III) and biomass concentration were studied. The oxida-tion reaction follows a pseudo first order rate equation. Apparent reaction rate constants were calculated. Unified rate equation was developed using the four parameters. Along with oxidation, a part of the iron also was precipitated. The extent of Fe(III) precipitation in each case was calculated. © Rapid Science 1998     

Kinetics of the liquid-phase oxidation of acid ferrous sulfate by the bacterium Thiobacillus ferrooxidens

The kinetics of the batch-wise liquid-phase oxidation of ferrous sulfate by the organism Thiobacillus ferrooxidans has been studied over a range of temperatures from 20°C to 31°C and in the presence of an abundant supply of oxygen, carbon dioxide, and other nutrients. The rate of oxidation was found to be accurately described by the equation where t = time hr, S = concentration of ferrous ions g Fe⁺⁺/1., μ_m = maximum specific growth rate of bacteria, hr^?1. Y = mass of bacteria produced per gram of iron oxidized g/g, K = saturation constant, g Fe⁺⁺/l., and X = concentration of bacteria g/1. The value for the maximum specific growth rate, μ_m, was found to vary from 0.12 hr^?1 at 20°C to 0.20 hr^?1 at 31°C, while the value for the saturation constant K varied randomly between 1 and 2 g/1. A method has also been described which permitted evaluation of the relevant rate constants μ_m and K without direct knowledge of the bacterial population. This method was found to yield values of μ_m and K which agreed with values determined accurately by a statistical regression analysis of the experimental data.     

氧化亚铁硫杆菌氧化亚硫酸盐的动力学研究

实验用Ms培养基,利用去除铁离子的氧化亚铁硫杆菌(Thiobacillus ferrooxidans)进行了细菌亚硫酸盐的生长代谢研究。实验结果表明氧化亚铁硫杆菌对亚硫酸根具有一定的氧化能力。用Origin 7.0对实验数据进行拟合处理,表明了氧化亚铁硫杆菌催化氧化亚硫酸盐的动力学方程符合Hill方程。氧化亚铁硫杆菌催化氧化亚硫酸盐是一个底物抑制的细胞反应,其KS值随pH值和底物浓度的改变而变化。pH值对反应有很大的影响,pH值越接近中性KS就越小,反应速率就越大。     

Potential of Thiobacillus ferrooxidans for waste gas purification. Part 2. Increase in continuous ferrous iron oxidation kinetics using immobilized cells

Thiobacillus ferrooxidans could be used to regenerate ferrous sulphate solution produced in a process to remove H₂S from waste gas if the reaction rate could be increased. The aim of the present study was to increase the volumetric productivity by using immobilized cells. Kinetic data of ferrous iron oxidation were determined in fixed-bed and fluidized-bed reactor configurations with different support materials in order to find the most practical system for scale-up. By using a fixed-bed reactor the iron oxidation rate can be increased to 3.6 g l^–1 h^–1, fivefold higher than suspended cells, and results in a bioreactor of reasonable size. With the kinetic data obtained, the biological reaction is no longer a limiting factor for industrial-scale application.Correspondence to: W. Schäfer-Treffenfeldt     

Sulfide oxidation by spheroplasts of Thiobacillus ferrooxidans.

Thiobacillus ferrooxidans is an acidophilic organism important to metal leaching of low-grade ores. The aforementioned importance is related to the ability of the bacterium to oxidize reduced iron and sulfur, principally found in nature as pyrite (FeS2). The present study dealt with sulfide oxidation at low pH values and the involvement of the cell envelope in the process of the inorganic oxidations. Sulfide oxidation was noted in spheroplasts of T. ferrooxidans prepared by enzymatic and chemical treatments and partially purified by differential centrifugation. No enzyme activities were noted in membrane fractions containing enrichments of lipopolysaccharide symbolic of outer membrane material or in membrane vesicles containing (or associated with) higher levels of proteins. Results to date indicate that in an acid milieu the envelope structure containing both the outer membrane and the intact inner cytoplasmic membrane is required for sulfide oxidation.