Influence of process variables on biooxidation of ferrous sulfate by an indigenous Acidithiobacillus ferrooxidans. Part II: Bioreactor experiments

The oxidation of ferrous iron in solution using Acidithiobacillus ferrooxidans has industrial applications in the regeneration of ferric iron as an oxidant agent for the removal of hydrogen sulfide from waste gases, desulphurization of coal, leaching of non-ferrous metallic sulfides and treatment of acid mine drainage. The aim of this attempt was to increase the biooxidation rate of ferrous sulfate by using immobilized cells. Rate of ferrous iron oxidation was determined in a packed-bed reactor configuration with low density polyethylene (LDPE) particles as support material in order to find the most practical system for scale-up. The present work studies the influence of basic parameters on the ferrous iron biooxidation process using an indigenous iron-oxidizing microorganism, namely A. ferrooxidans, in a 2 L packed-bed bioreactor. Effects of several process variables such as initial pH, temperature, dilution rate, initial concentrations of ferrous and ferric ions on oxidation of ferrous sulfate were investigated. Experimental results indicate that in the temperature range of 31–34 °C the biooxidation of ferrous ions to ferric ions could be resulted efficiently. A pH range of 2–2.2 was optimum for the growth of the culture and effective bacterial activity for oxidation of ferrous ions to ferric ions. The highest oxidation rate of 2.9 g Fe²⁺ L⁻¹ h⁻¹ was obtained using a culture initially containing 25 g L⁻¹ Fe⁺² at the dilution rate of 0.4 h⁻¹. This rate is very high compared to that achieved in other bioreactors found in the literature. In addition the biooxidation of Fe²⁺ to Fe³⁺ conversion could be achieved effectively in the presence of the Fe³⁺ in the concentration range of 0.1–0.7 g/L.     

Experiments and CFD simulation of ferrous biooxidation in a bubble column bioreactor

In the present attempt a set of experiments and a 3D simulation using a commercially available computational fluid dynamics package (FLUENT) were adopted to investigate complex behavior involving hydrodynamics and ferrous biological oxidation in a gas–liquid bubble column reactor. By combining the hydrodynamics and chemical species transport equations, the velocity field, air volume fraction and ferrous biooxidation rate in the column were simulated. The kinetic model proposed by Nemati and Webb [Nemati, M., & Webb, C. (1997). A kinetic model for biological oxidation of ferrous iron by Thiobacillus ferrooxidans. Biotechnology and Bioengineering, 53, 478–486] was used to simulate the biooxidation rate in the column. Gas–liquid interactions were modeled using an Eulerian model in three dimensions. The effects of inlet air velocity and initial substrate (Fe²⁺) concentration on the velocity field, air volume fraction and biooxidation rate of ferrous iron in the column were investigated. To validate the model, simulation was compared with the experimental data in the presence of Acidithiobacillus ferrooxidans in an aerated column where the superficial gas velocity was adjusted between 0 and 0.5 m/s. It was found that the initial ferrous concentration and the inlet air velocity had a pronounced effect on the ferrous biooxidation rate. The results indicated that the maximum biooxidation rate can be obtained at superficial air velocity of 0.1 m/s and initial ferrous concentration of 6.7 g/L.     

The phenomenology and the mathematical modeling of the silicone‐supported chemical oxidation of aqueous sulfide to elemental sulfur by ferric sulphate

When pumping a sulfide solution through a silicone cylinder immersed in a solution of ferric sulfate, a cloud of elemental sulfur is formed in the ferric sulfate if the pH of the sulfide solution is below about 8.5. The elemental sulfur subsequently sediments as orthorhombic α‐sulfur particles. H₂S(aq) diffuses through the pores of the hydrophobic silicone membrane and simultaneously reacts to become sulfur. This was confirmed by a mass balance between the amount of sulfide removed from the sulfide solution and the amount of solid product formed in the ferric solution. During the experiment, the pH of the non‐buffered sulfide solution rises up to a maximum of 8.5; this is explained by the continuous protonation of HS caused by the removal of H₂S(aq). The pH of the strongly acidic (pH 1.5) ferric sulfate solution hardly decreased. A mathematical model has been developed to quantify the phenomena related to the removal of H₂S(aq). The model has been succesfully validated with the data of batch experiments. An Arrhenius‐like relationship was found between the process temperature and the overall mass transfer coefficient K. A sulfide oxidation rate of 2.5 g S dm⁻³ day⁻¹ was predicted for a plug flow reactor. The integration of the novel process with biological sulfate reduction was studied. © 1999 Society of Chemical Industry     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Removal of sulfur inorganic compounds by a biofilm of sulfate reducing and sulfide oxidizing bacteria in a down‐flow fluidized bed reactor

BACKGROUND: Biological sulfate removal is a process based on the biological sulfur cycle that consists of two steps: (1) production of sulfide by sulfate reduction; and (2) biological or physico‐chemical sulfide oxidation to elemental sulfur (S⁰). The objective of this work was to transform soluble sulfur (sulfate) into insoluble sulfur (elemental sulfur) coupling sulfate reduction and sulfide oxidation in one reactor. To accomplish this, a 2.3 L down‐flow fluidized bed reactor was used. Lactate was supplied as electron donor, sulfate and oxygen (air) were the electron acceptors. RESULTS: After 55 days of batch operation a biofilm with sulfate reducing and sulfide oxidizing activities was developed over a plastic support. Continuous operation for 90 days at a down‐flow superficial velocity of 7.7 m h^?1 and 30 °C, showed that sulfate reduction amounted to 72–77% and carbon removal to 20–31%. Under low aeration rates (2.3 L d^?1) 50% of the sulfate was transformed to elemental sulfur, when aeration increased to 5.4 L d^?1 elemental sulfur recovery was only 30% and sulfide in the effluent amounted to 27% of the sulfur fed. CONCLUSION: It was possible to obtain elemental sulfur through a coupled anaerobic/aerobic process in one reactor using lactate, sulfate and oxygen (air) as substrates. The development of a biofilm with sulfate reducing and sulfide oxidizing activities was the key of the process. Copyright © 2007 Society of Chemical Industry     

Biological oxidation of ferrous iron: study of bioreactor efficiency

The bio‐oxidation of ferrous iron is a potential industrial process for the regeneration of ferric iron in the removal of H₂S. In the first stage, H₂S is selectively oxidized to elemental sulfur using ferric sulfate. The ferrous sulfate produced is oxidized to ferric sulfate using Thiobacillus ferrooxidans for recycle and reuse in the process. The aim of the work described here was to investigate continuous oxidation of ferrous iron by immobilized T ferrooxidans and the factors which can directly affect the oxidation rate in order to assess the feasibility of this technique on an industrial scale. An analysis of the evolution of bioreactor performance with time (125 days) was performed in order to assess the feasibility of this technique on an industrial scale. A good oxidation rate was obtained despite the transport problems encountered due to occlusion of the porous support. On the other hand, the toxic effects due to absorption in the ferric solution of one or more compounds from the gas digester were studied using a ferric iron solution from the absorption process. The results indicate the feasibility of the biological system for the regeneration of the ferric‐absorbing solution. Finally, a previous study for the design of an industrial bioreactor to regenerate ferric sulfate solutions, used to remove H₂S from biogas in a wastewater‐treatment plant (Jerez de la Frontera, Spain), is introduced. Good biological oxidation performances have been obtained using a pilot plant bioreactor of 500 dm³. Copyright © 2003 Society of Chemical Industry     

Selective recovery of valuable metals from partial silicated sphalerite at elevated temperature with sulfuric acid solution

The purpose of this work was to study the feasibility at laboratory-scale of a hydrometallurgical process for the selective recovery of valuable metals from partial silicated sphalerite in an oxygen pressure acid leaching system. The factors influencing dissolution efficiency of the ore were investigated and optimized. Under optimum conditions (i.e., temperature of 433 K, sulfuric acid concentration of 41.2 g/L, leaching time of 2.5 h, liquid/solid ratio of 6 mL/g, and pressure of 1.6 MPa) over 97% Zn was extracted into the leach liquor together with 0.3% SiO₂ and 2.9% Pb. The leaching slurry had good solid–liquid separation characteristics, and the filtration rate could be as high as 716 L/m² h. About 96% oxidation of sulfide sulfur to sulfate was achieved under these conditions. Analysis of the content of elemental sulfur in the leaching residues indicated that the fraction of sulfide sulfur determined as elemental sulfur was about 10% at 393 K, and that it decreased with temperature down to 0.5% at 453 K. Ultimate solid residues, which have been concentrated in silica and lead, can be oriented toward the lead smelter after alkali roasting-water washing pretreatment for metal recovery.     

Bio-dissolution of copper from Khetri lagoon material by adapted strain of Acidithiobacillus ferrooxidans

Bioleaching involves the use of iron and sulfur oxidizing microorganisms to catalyze the dissolution of valuable metals. In this investigation, lagoon material contains 0.39% Cu, in which the major copper bearing mineral is chalcopyrite associated with other minerals present as minor phase. Leaching experiments were carried out using an adapted strain of Acidithiobacillus ferrooxidans with various parameters such as presence/absence of iron, pH, pulp density and temperature. Base of the medium was 9 K (without ferrous) Bio-dissolution of copper was found to be maximum, i.e., 80.9% with 9 K⁺ (with ferrous) at pH-2.0, 10% pulp-density and 35 °C within an incubation period of 30 days.     

Effect of Ni<Superscript>2+</Superscript>, V<Superscript>4+</Superscript> and Mo<Superscript>6+</Superscript> concentration on iron oxidation by <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis>

The ferrous oxidation ability of Acidithiobacillus ferrooxidans was studied in the presence of Ni²⁺, V⁴⁺ and Mo⁶⁺ in 9 K media in order to implement the culture in the bioleaching of spent catalyst. The rate of iron oxidation decreased with increasing concentration of metal ions, but the rate of inhibition was metal-ion dependent. The tolerance limit was critical at a concentration of 25 g/L Ni²⁺, 5 g/L V⁴⁺ and 0.03 g/L Mo⁶⁺. The growth rate of microorganisms was negligible at concentrations of 6 g/L V⁴⁺ and 0.04 g/L Mo⁶⁺. Levels and degree of toxicity of these ions have been quantified in terms of a toxicity index (TI). The toxicity order of metal ions was found to be Mo⁶⁺>V⁴⁺>Ni²⁺. The significance and relevance of multi-metal ion tolerance in Acidithiobacillus ferrooxidans has been highlighted with respect to bioleaching of spent refinery catalyst.     

Bioleaching of acid‐consuming low‐grade nickel ore with elemental sulfur addition and subsequent acid generation

The bioleaching of a nickel concentrate and an acid‐consuming nickel ore was studied using a co‐culture of Acidithiobacillus ferrooxidans and A. thiooxidans, as well as a thermophilic enrichment culture, VS2. The VS2 was dominated by a Sulfolobus species related to Sulfolobus metallicus. Nickel concentrate was readily solubilized with A. ferrooxidans and the VS2, resulting in nickel yields of 56% and 100%, respectively. Low‐grade nickel ore required 350 g H₂SO₄ kg^?1 ore for maintaining the pH of the leaching solution below 3. To overcome the high acid demand, biological elemental sulfur oxidation was combined with the ore leaching. Leaching of a 2% (wt/vol) nickel ore with a co‐culture of A. thiooxidans and A. ferrooxidans resulted in nickel yield of up to 86% with acid supplementation of 290 g H₂SO₄ kg^?1 ore. When coupled with biological sulfur oxidation, an 86% nickel recovery was achieved with 0.5% (wt/vol) ore concentration without further sulfuric acid addition. The VS2 oxidized sulfur at a rate of 0.063 g L^?1 d^?1 and the simultaneous nickel ore leaching resulted in 100% nickel yield. In summary, the potential of using elemental sulfur addition and subsequent biological acid generation to maintain the low pH during bioleaching of an acid‐consuming nickel ore was demonstrated. Copyright © 2005 Society of Chemical Industry     

Removal of high concentrations of H2S from simulated natural gas by Acidithiobacillus ferrooxidans immobilized on polyurethane foam

A chemo‐biochemical process for desulfurization of simulated natural gas containing hydrogen sulfide (H₂S) was investigated. The results showed that using polyurethane foam as a support for immobilization of Acidithiobacillus ferrooxidans obtained good biological oxidation performance and the maximum oxidation rate of ferrous iron was 4.12 kg m^?3 h^?1. Moreover, a semi‐empirical formula was set up for calculating theoretical ferrous oxidation rate as a function of influent Fe²⁺ and Fe²⁺ concentration in the bioreactor. The integrated chemical and biological process achieved removal efficiencies of about 80% when treating high concentrations of H₂S (15 000 ± 100 ppmv). © 2012 Society of Chemical Industry     

Synthesis,characterization and catalytic study of [N,N′-bis(3-ethoxysalicylidene)-m-xylylenediamine]oxovanadium(IV) complex

The study of the synthesis and catalytic properties of the oxovanadium(IV) complex [N,N′-bis(3-ethoxysalicylidene)-m-xylylenediamine]oxovanadium(IV) ([VO(L)]) is the principal objective in this work. The Schiff base (L) and the its oxovanadium complex ([VO(L)]) have been characterized by elemental analysis, melting point, Fourier Transform Infra-red (FTIR), UV–Vis., ¹H and ¹³C NMR spectroscopy. The catalytic study of the [VO(L)] in the oxidation of methyl phenyl sulfide was carried out in the homogeneous and heterogeneous systems. The catalysts were characterized by elemental analysis by flame atomic absorption spectroscopy (FAAS), IR, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The progress of the catalytic reaction was followed by gas chromatographic analysis (GC). The oxidation of methyl phenyl sulfide after 24 h of reaction, presented for [VO(L)], [VO(L)]-alumina and [VO(L)]-Y was 50 mol%, 98 mol% and 34 mol%, respectively. In the [VO(L)]-Y system it was noted an increase in the oxidation of the methyl phenyl sulfide from 34 mol% to 92 mol% after four days. In the systems [VO(L)] and [VO(L)]-alumina the sulfide oxidation reached a maximum after 24 h of reaction. [VO(L)]-supported Y and [VO(L)]-Wessalith^®P were inactive under the same reaction conditions.     

Electrochemical oxidation of sulfide ion at a Ti/IrO<Subscript>2</Subscript>–Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> anode in the presence and absence of naphthenic acids

Electrochemical oxidation of sulfide ion at a Ti/IrO₂–Ta₂O₅ anode followed partial order kinetics (between current and mass transport control) in the absence and presence of chloride ion and of naphthenic acids, at sulfide concentrations typical of sour brines. The desired outcome was to promote the 2-electron oxidation of sulfide to elemental sulfide rather than the 8-electron oxidation to sulfate. Although elemental sulfur accumulated to some extent at low conversion of sulfide, sulfate ion became the principal product as the reaction progressed. At high conversion, the overall current efficiencies were typically higher than 50%, with material balance about 90%. However, this anode material was gradually poisoned by sulfide in long term use.     

Assessment of desulfurization of natural gas by chemoautotrophic bacteria in an anaerobic baffled reactor (ABR)

The purpose of this study is to evaluate an anaerobic system (ABR) cultured by chemoautotrophic bacteria for biodesulfurization of natural gas. In this study anaerobic baffled reactor with five compartments and active volume of 10 l was used. For increasing solid retention time, reactor was packed by pumice with 0.5–2 cm diameter which active volume decreased to 9 l. Inoculation was performed by activated sludge from municipal sewage treatment, which was kept in anaerobic condition for 1 year. The synthetic wastewater which contains S₂O₃²⁻ ion was used in start-up and S⁻² for running of ABR. Performance of the reactor was evaluated at three equivalent hydraulic retention times (HRT) of 50, 28, and 9 h, with the equivalent loading rate of 0.11, 0.2, and 0.62 mmol S⁻² l⁻¹ h⁻¹. Sulfide was converted to elemental sulfur and sulfate, so that more than 61% of the sulfur in the end products was elemental sulfur. Throughout the experiment, biodesulfurization of sulfur waste using ABR system, showed that the process is extremely efficient, and the maximum sulfide removal rate was about 3.03 mmol S⁻² l⁻¹ h⁻¹.     

Combined biological and chemical oxidation of ferrous sulfate using immobilised Thiobacillus ferrooxidans

Thiobacillus ferrooxidans immobilised in biomass support particles with activated carbon coating were used in a packed‐bed bioreactor to study the combined effects of chemical and biological catalysis on the oxidation of ferrous iron. The effect of ferrous iron concentration (in the range 5–30 kg m⁻³) and of its volumetric loading on the kinetics of reaction were investigated. With low concentrations of ferrous iron, 5–10 kg m⁻³, the combined catalysis did not offer a significant advantage to oxidation of ferrous iron and the kinetics of reaction were slightly faster than those achieved with just the biological catalyst. With ferrous iron at a concentration of 20 kg m⁻³, the combination of chemical and biological catalysis resulted in a remarkable enhancement of the reaction rate. The maximum oxidation rate of ferrous iron in the presence of combined catalysts, 21.9 kg m⁻³ h⁻¹, was twice as high as that achieved with just the biological catalyst. © 1999 Society of Chemical Industry     

Mechanism study of iron-based catalysts in co-liquefaction of coal with waste plastics

The state and active site of iron-based catalysts in co-liquefaction of coal with low-density polyethylene (LDPE) have been discussed. The catalysts used were sulfur-promoted iron oxides (Fe₂O₃+S), ferrous sulfide (FeS), ferrous sulfate (FeSO₄·7H₂O) and the mineral pyrite (FeS₂). It was found by X-ray photoelectron spectrometry that the active site in the working state of Fe₂O₃+S catalyst was not Fe_1−XS and the main form of sulfur existing in the spent Fe₂O₃+S catalyst was sulfate, followed by sulfite (SO₃²⁻). A finding from autoclave tests was that the ferrous sulfate before and after oxidation treatments showed sufficiently high activity for the co-liquefaction of coal with LDPE. It was concluded that an active site of the iron-based catalysts was sulfate species formed on the catalyst surface during the hydroliquefaction process of coal.     

微生物燃料电池处理模拟含硫废水的初步研究

采用微生物燃料电池(Microbial fuel cell,MFC)处理模拟含硫废水,硫化物能全部被氧化戍单质硫或硫酸盐.MFC的最大功率密度达到(20±1)W·m~(-3),库仑效率为(20±2)%.阳极中有机质的氧化与硫化物的氧化存在一定竞争关系,进水碳硫比是影响单质硫生成率的关键因素.试验中,进水碳硫质量比大于1250:1,S~(2-)质量浓度为50mg·L~(-1)时,硫化物氧化成单质硫的转化率可达61%～77%.此外,阳极表面单质硫的积累很可能是造成MFC电极失效或运行不稳定的原因之一.     

A Crosslinked Copolymer with N‐Bromosulfonamide Pendant Groups as Oxidant for Residual Sulfides in Alkaline Media

A redox copolymer, a macromolecular analogue of Bromamine T was prepared and developed as a solid phase oxidizing reagent for sulfides being in trace concentration in aqueous solutions. The resin was prepared starting from Amberlyst 15 by a four‐step transformation of the sulfonic groups to N‐bromosulfonamide. The product containing 3.30 meq active bromine/g showed strong oxidizing properties and was employed in batch as well as in flow processes for removal of sulfides from solutions by their transformation to sulfates. The starting solution contained 64.0 or 320.0 mg S^2–/dm³. The effects of various parameters on the reaction course have been studied (mole ratio of reagents, alkalinity of the reaction media, flow rate in the column processes). The solid phase oxidation carried out in a dynamic regime provided to drive the reaction to completion. Thus, sulfide free effluents (< 10 μg S^2–/dm³) were obtained in the column processes. The permissible flow rate, close to 10–12 bed volumes/h, was satisfactory. The sulfide oxidation proceeded quickly in aqueous media of various alkalinity, especially in those of strong alkalinity. As the transformation of sulfides to sulfates was accompanied by a drop of the pH value of the reaction medium, it was necessary to maintain it not lower than 6.0. Otherwise, the active bromine content in the resin decreased and the yield of the column process was unsatisfactory. Moreover, in acidic media a considerable part of sulfides transformed to elemental sulfur which contaminated the resin phase and caused turbidity of the effluent. By reacting a stoichiometric amount of reagents in batch regime not only sulfate, but also various intermediate products were found in the solution. The exhausted copolymer contained unsubstituted sulfonamide groups; it could be regenerated and reused repeatedly for the next processes.     

Effect of the sulfide concentration on zinc bio-precipitation in a single stage sulfidogenic bioreactor at pH 5.5

Dissolved zinc is present in natural waters and process streams generated by the mining and metallurgical industry. These streams usually have a low pH. By using sulfate reducing bacteria, sulfide can be produced that precipitates with zinc as zinc sulfide (sphalerite), which can be easily separated from the wastewater and even reused as zinc concentrate. In this study, a sulfate reducing gas-lift bioreactor was operated at pH 5.5 using hydrogen as electron donor for sulfate reduction. We demonstrate effective zinc removal (7.2 mmol L⁻¹ d⁻¹) with low zinc effluent concentrations (0.65–8.8 μM) in a system combining sulfide generation by sulfate reducing bacteria (7.2–10.6 mmol SO₄²⁻ L⁻¹ d⁻¹) at low pH (5.5) with the bio-precipitation of crystalline sphalerite. To investigate the effect of the sulfide excess on the settling properties of the sphalerite precipitates, the sulfide excess concentration was varied about two orders of magnitude (0.008–2.2 mM). The results show that crystalline sphalerite was formed in all cases, but larger particles with better settling properties were formed at lower sulfide concentrations.     

H2S adsorption/oxidation on unmodified activated carbons: importance of prehumidification

Three microporous activated carbons supplied by Norit^® (of peat and bituminous coal origin) were used in this study as hydrogen sulfide adsorbents. Their surface properties were evaluated by means of nitrogen adsorption, Boehm titration, potentiometric titration, and thermal analysis. The results show that the carbons significantly differ in their pore structure and surface chemistry. This is reflected in their hydrogen sulfide breakthrough capacity. The breakthrough capacity is underestimated when not enough water is adsorbed on the carbon surface. The performance follows the expectations after extensive humidification of the sorbents’ surfaces. Moderately low pH in the acidic range of coal-based carbon, Vapure 612, promotes the oxidation of H₂S to sulfur oxides which is important from the point of view of water regeneration. The high pH of peat-based carbon, RB 4, results in H₂S oxidation to elemental sulfur.