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Laboratory and Semi-Pilot Bioreactor Feasibility Tests for Desulphurization of Turkish Lignite using Leptospirillum ferriphilum
Abstract
The low rank coal lignite stands out to be a profuse source of energy in Turkey and accounts for nearly 43% of its total fossil fuel production. However, the high sulfur content associated with lignite averts its application in several sectors due to various health and environmental issues. In the present work, biodesulphurization of Turkish lignite was studied in 1 and 20 L aerated bioreactors using an iron oxidizing acidophile, Leptospirillum ferriphilum (L. ferriphilum). Additionally, the effect of Span 80 (S80) on biodesulphurization of the sample was studied, under the optimum concentration derived from our previous shake flask study, in order to notice its effect under scale-up aerated bioreactor conditions. Under lab scale (using 1 L bioreactors), in the absence of S80, L. ferriphilum could desulphurize a maximum of 65.6% sulfur from the lignite sample, while 56% desulphurization was achieved in the presence of 0.05% (v/v) S80. Further scale-up studies under semipilot conditions (in 20 L reactors) indicated a maximum desulphurization of 63% from the sample in absence of S80. The pH, oxidation–reduction potential (ORP), and Fe2+ iron and total iron concentrations were periodically monitored in all the reactors during the course of the experiments. XRD and FTIR characterization of the lignite samples pre and post biodesulphurization provided valuable information on the structural and phase changes due to the microbial action.
... Table 3 provides a detailed account of the major differences between the pyrometallurgy, conventional hydrometallurgy, and biometallurgical processes. Although biotechnology has made remarkable advances in various fields, including medicine, pharmaceuticals, agriculture, and biofuels, its application to coal [71][72][73] and coal-derived products has been relatively less explored. CFA waste, in particular, presents significant challenges owing to its heterogeneous chemical and physical nature, which makes it difficult to propose a robust workflow. ...
Coal fly ash (CFA) is a highly versatile raw material that has the potential to yield multiple value-added products, including cenospheres, zeolites, carbon nanotubes, and fertiliser substrates. Despite its versatility, a majority of these components are often overlooked, and CFA is primarily used for construction. Conventional processing methods of CFA are known to pose significant environmental challenges, including the leaching of hazardous materials, emission of toxic gases, and the high energy consumption needed to extract the value-added components. Herein, we explore the potential of biometallurgical approaches as an eco-friendly alternative to conventional processing methods for the comprehensive utilisation of CFA. Our focus is on the application of different microorganisms to CFA, the domestication of microorganisms, preprocessing of CFA to facilitate effective biometallurgical processes, the use of bioreactors, and synthesis of nano silica particles. We also propose a novel method for extracting the value-added components from CFA using a preprocessing technique (i.e., washing cycle), combined with multiple interactions with biometallurgical processes. Adopting this approach, we not only enhance environmental stewardship but also improve the circular economic aspects of multi-component utilisation, while providing valuable insights for the development of sustainable techniques for utilising CFA.
... Mesophilic acidophiles can grow at optimum conditions of temperature ranging 20-40ºC and at a pH range of 1.5-2.5. This group of microorganisms include (to name a few) Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Leptospirillum ferriphilum, that have been widely used in bioleaching studies (Mishra et al. 2018c;Panda et al. 2013;Sukla et al. 2014). The genus Acidithiobacillus is comprised of gram-negative, rod-shaped, autotrophic bacteria with a size of about 0.4 × 2 µm. ...
Mineral biotechnological applications e.g. bioleaching and bio-beneficiation, for waste treatment and resource recovery have invited due attention owing to their economic and eco-friendly benefits in comparison to the conventional methods. Although research has progressed well, there are several aspects that are still not well understood and require more attention in view of full scale industrial application of these processes. For example, microbe-mineral/galvanic interactions, passivation phenomenon, synergistic effects among the microbes, identification of novel and robust microbial strains etc., require more studies to explore the fundamental aspects. In addition, mode of treatment for a wide variety of ores and/or concentrates, advances in engineering applications and scaling-up of bio-processes to industrial level along with the assessment of techno-economic feasibility, life-cycle and environmental impact can provide numerous opportunities for the researchers to further explore the applied aspects. This paper presents comprehensive details, including the latest research, on the fundamentals and applications of bioleaching, bioflotation and bioflocculation for the readers. The key microorganisms and their mode of action, factors affecting each bio-processes and aspects related to their scale-up and industrial applications are reviewed, analyzed and compared. It is believed that the recent advances, emerging dimensions and future directions of research presented in this paper will serve as a guide for the researchers to further explore this exciting field of research.
... It was concluded that at 0.05% v/v Span-80, 61% of total sulphur could be removed in shake flasks. The study was further scaled-up and tested in both laboratory (IL) and semi-pilot scale (20L) bioreactors using the same microbe [26]. In yet another study using the same lignite sample, Mishra et al. [27] also studied the biodesulphurization ability of Rhodococcus erythropolis DSM 44308 strain. ...
Of late, sustainable energy development has received considerable importance throughout the world due to the growing concerns regarding climate change and environment protection. This in turn, has led to the search for alternatives, which are ecofriendly and cost-effective. Turkey possesses vast resources of lignite and renewable energies, which if utilized properly can reduce the current energy deficit and imports from other countries. Though renewables have received more attention in the past few years; yet, the vast lignite reserves of Turkey cannot be averted while considering the major indigenous energy resources of the country. The present review briefly discusses the existing energy situation in Turkey with particular focus on the indispensable role of coal as a valuable energy resource in meeting the country’s growing energy demand. Biodesulphurization as a green treatment technique for sulphur removal from coal is discussed along with some of the recent advances made with respect to the Turkish lignite. A brief description relating to the impact of COVID-19 on the energy sector is also discussed. Furthermore, future outlooks towards sustainable development are presented.
... Leptospirillum spp. have been seen to be a better performer compared to other acidophilic microbial species, e.g., L. ferrooxidans with respect to sphalerite bioleaching (Xia et al. 2009) and also in a number of other microbial applications, e.g., L. ferriphillum for lignite processing (Mishra et al. 2018a(Mishra et al. , 2018b. In order to activate the strain, repeated sub-culturing was ensured using a 9 K medium: 3 g/L (NH 4 ) 2 SO 4 , 0.5 g/l MgSO 4 Á7H 2 O, 0.5 g/l K 2 HPO 4 , 44 g/ l FeSO 4 Á7H 2 O, and 0.1 g/l KCl at pH ¼ 1.85. ...
In this study, the effect of graphite on sphalerite dissolution was investigated using a Leptospirillum ferrooxidans (L. ferrooxidans) dominated meso-acidophilic bacterial consortium. Results of the studies indicated that Zn dissolution enhanced from 18.75% (in control tests) to 78.46% (using L. ferrooxidans) without graphite in the system (the conventional approach). Addition of graphite further improved sphalerite bio-oxidation up to 10% i.e. from 78.46 to 87.83% indicating bio-catalytic effect and a possible galvanic interaction between sphalerite and graphite. Through the conventional route, the system’s pH eventually lowered from 1.8 to 1.4 and ORP increased from 300 to 700 mV. In presence of graphite, the pH lowered to nearly 1.0 and ORP reached 600 mV. This indicated efficient bacterial activity and stabilized leaching conditions in both the cases. Analytical characterization studies through XRD and SEM-EDAX indicated the presence of sulfur and K-type jarosite (KFe3+3(OH)6(SO4)2), ascribed to the passivation layers formed during sphalerite bioleaching.
... To improve the biodesulfurization, effective coal slurry reactors were designed (Malika et al., 2001;Mishra et al., 2018). Moreover, the direct electrical current was applied to improve the growth of Thiobacillus ferrooxidans (T. ...
Indigenous microorganisms were used to remove inorganic sulfur from high sulfur fat coal, and effect of L-cysteine on coal surface and biodesulfurization was investigated. It was found that L-cysteine addition enhanced coal biodesulfurization, and the optimal L-cysteine dosage was 1.6 g/L. With the optimal L-cysteine dosage, the Sulfobacillus were the dominant pyrite-oxidizing bacteria. After biodesulfurization for 30 days, the inorganic sulfur in coal decreased from 3.038% to 0.437%. L-cysteine was adsorbed on the coal surface through amino, carboxyl and sulfhydryl groups, and cysteine-Fe complex was formed by the interaction between interfacial –SH group of L-cysteine and pyrite, which was beneficial to sulfur transfer. Meanwhile, L-cysteine addition improved the adsorption of microorganisms on coal surface though reducing the Zeta potential of coal particle. The structural change of coal during the biodesulfurization showed that the pyrite was solubilized by Sulfobacillus to realize the removal of inorganic sulfur from coal, and L-cysteine addition inhibited the jarosite formation through improvement of pyrite bio-oxidation and corresponding pH decrease, which avoided the dissolved sulfur returning back to coal again. Moreover, the coal biodesulfurization with L-cysteine addition also presented obvious environmental benefit.
... wileyonlinelibrary.com/jctb that provides better insights into scale-up factors and their applicability. [59][60][61][62][63] Metal dissolution efficiencies, changes in ORP, pH, Fe (II) and dissolution of total iron [Fe (T)] under bench-scale conditions are shown in Fig. 9. The dissolution of the targeted metals in the bioreactor was greater when compared to its chemical control [ Fig. 9 (a) and (b)]. ...
BACKGROUND
Waste printed circuit boards (WPCBs) are a resource containing a wide array of metals and are of great importance because their metal concentration is much greater than that in the ores. Previous studies have been devoted mostly to copper (Cu) bioleaching from WPCBs because it has the highest proportion ( ∼ 10–30%) of all their component metallic elements. The present study focused on an intensified mixed meso‐acidophilic bacterial leaching of multi‐metals from WPCBs of spent mobile phones, with the system operating under high oxido‐reductive potentials (HORPs). Inductively coupled plasma‐optical emission spectrometry (ICP‐OES), X‐ray diffraction (XRD) and scanning electron microscopy‐energy dispersive X‐ray (SEM‐EDX) characterization indicated the WCPB sample had recoverable contents of Cu, aluminium (Al), nickel (Ni) and zinc (Zn) which were targeted for bioleaching.
RESULTS
Shake flask optimization studies, under HORP >750 mV indicated dissolutions of 98.1% Cu, 55.9% Al, 79.5% Ni and 66.9% Zn under optimized conditions of 9 g L–1 iron [Fe (II)], 10% pulp density, initial pH 1.8 and 10% (v/v) as initial inoculum. Under these conditions, at ORP >650 mV, 97.3% Cu, 55.8% Al, 79.3% Ni and 66.8% Zn were achieved in bench‐scale (1 L) bioreactor systems without any significant reduction in efficiency (compared to shake flasks) after 8 days of operation.
CONCLUSION
Variations in co‐relatable parameters, such as pH, ORP and Fe (II) concentrations, indicated that these parameters significantly contributed to metal leaching. Operating the system under high and controlled ORPs is a faster and more efficient way to leach multi‐metals from WPCBs. © 2020 Society of Chemical Industry
... The cultures were originally grown in shake flasks (at 150 rpm, 32°C) using chalcopyrite concentrate as an energy source. Due to potential toxicity of molybdenum, the cultures were subsequently adapted to grow with molybdenite as the sole energy source since adaptation is an unique biotechnological feature of these microorganims (Panda et al., 2013;Mishra et al., 2018). This involved successive enrichment steps for a period of 3 months with gradual increment in the molybdenite concentration (maximum up to 10% w/v), while decreasing the concentration of chalcopyrite. ...
This paper presents the application of an artificial neural network (ANN) in order to predict the effects of operational parameters on the dissolution of Cu, Mo and Re from molybdenite concentrate through meso-acidophilic bioleaching. The initial pH, solid concentration, inoculum percent and time (days) were used as inputs to the network. The outputs of the models included the percent of Cu, Mo and Re recovered. The development and training of a feed-forward back-propagation artificial neural network (BPNN) was used to model and predict their recoveries. 105 sets of data were used to develop the neural network architecture and train it. To reach the network with highest generalizability, the space of neural networks with different hidden layers (one up to three hidden layers) and with the varying number of neurons each layer were searched. As a result, it was found that (4-5-5-2-1); (4-7-5-2-1) and (4-7-1-1-1) arrangements could give the most accurate prediction for Cu, Mo and Re extraction respectively. The regression analysis of the models tested gave a good correlation coefficient of 0.99968, 0.99617 and 0.99768 respectively for Cu, Mo and Re recoveries. The results demonstrated that ANN has a good potential to predict Cu, Mo and Re recoveries. Also, genetic algorithm (GA) was used to find out the optimum levels of parameters in the best models defined by ANN. The maximum recovery of Cu, Mo and Re on the 30th day were nearly 73%, 2.8% and 27.17% respectively.
The quest for scientifically advanced and sustainable solutions is driven by growing environmental and economic issues associated with coal mining, processing, and utilization. Consequently, within the coal industry, there is a growing recognition of the potential of microbial applications in fostering innovative technologies. Microbial-based coal solubilization, coal beneficiation, and coal dust suppression are green alternatives to traditional thermochemical and leaching technologies and better meet the need for ecologically sound and economically viable choices. Surfactant-mediated approaches have emerged as powerful tools for modeling, simulation, and optimization of coal-microbial systems and continue to gain prominence in clean coal fuel production, particularly in microbiological co-processing, conversion, and beneficiation. Surfactants (surface-active agents) are amphiphilic compounds that can reduce surface tension and enhance the solubility of hydrophobic molecules. A wide range of surfactant properties can be achieved by either directly influencing microbial growth factors, stimulants, and substrates or indirectly serving as frothers, collectors, and modifiers in the processing and utilization of coal. This review highlights the significant biotechnological potential of surfactants by providing a thorough overview of their involvement in coal biodegradation, bioprocessing, and biobeneficiation, acknowledging their importance as crucial steps in coal consumption.
Developing efficient methods for deep desulphurization of commercial fuel is of utmost importance due to the
environmental impact of sulphur and stringent government regulations for sulphur-free fuel. This review high�lighted the significance of photo-assisted biocatalytic desulphurization of coal and introduced novel strategies
that combine coal desulphurization with CO2 mitigation. The interactions between microbes and the mechanisms
underlying the biodesulphurization of coal were thoroughly discussed. Furthermore, the effect of coal structure
and porosity on the desulphurization of inorganic sulphur was analyzed. It is acknowledged that achieving high
catalytic efficiency and stability of the catalyst during photocatalytic desulphurization remains a challenge. The
review also identified microbial species that are most suitable for simultaneous biodesulphurization and CO2
mitigation, taking into account their mutualistic growth patterns. Besides, the mechanisms and cost-benefit
analysis of coal biodesulphurization with high CO2 consumption by bacterial communities in a hybrid system
were further examined. The insights provided in this review can offer a comprehensive understanding of the
design of a hybrid system capable of self-capturing CO2 from polluted atmospheres and utilizing it in a reactor for
cost-effective coal biodesulphurization, which holds great potential for combating smog and global warming.
Developed economies such as the USA and European Union (EU) have classified antimony as a critical raw material. China leads the global antimony production (67% on an average from 2015 to 2019) followed by Russia and Tajikistan. Antimony has been applied in the industry (plastics, etc.) and new/emerging technologies (cell panels, infrared, etc.) where antimony trioxide (Sb2O3) is its most produced and used compound. With technological advances, recent trends indicate a growing demand for this metal; however, with the on-going production rate, antimony is anticipated to become one of the scarcest metals by 2050. Several minerals of antimony exist; nevertheless, stibnite (Sb2S3) is the primary mineral. Extractive metallurgical routes such as pyro and hydro-metallurgy have found industrial applications for stibnite processing; however, bio-hydrometallurgy is slowly gaining momentum. In this piece of review, the world-wide scenario of antimony production, recent market trends along with the common and current research advances related to applications of antimony in emerging technologies is presented. Comprehensive details along with the recent advances related to stibnite processing through the aforementioned extractive metallurgy routes, their technological improvements and antimony purification/recovery methods from leach solutions are also discussed. Furthermore, the future perspectives in terms of research and industrial needs are discussed and summarized.
Mineralogically distinct coal samples respond differentially to microbial attack. In the present study, a mixed meso-acidophilic bacterial consortium predominantly comprising of Acidithiobacillus ferrooxidans strain was investigated for its biodesulphurization abilities for three distinct sulphur bearing samples (Goa CPC, Rajasthan Lignite, Assam Coal) of Indian origin in iron (9K+) and iron-free (9K-) media. A media devoid of Fe (II) iron was seen to be more effective for sulphur removal with maximum desulphurization of 45.19% for Assam coal followed by 36.8% for Rajasthan Lignite and 23.38% for CPC respectively. The proximate analysis, FTIR patterns and XRD analysis of the samples provided better insights into understanding the mineralogical and compositional changes in the coal matrix. Owing to the higher efficiency, Assam coal was additionally subjected to further optimization studies and characterization of the treated coal through TGA. The study indicated that the gross calorific values for all the samples increased following microbial treatment in 9K- media thereby providing a scope for further scale-up studies.
This study demonstrates the Fourier transform infrared (FTIR) spectroscopic characterization of natural kao-linite from northeastern India. The compositional and structural studies were carried out at room temperature by using X-ray fluorescence (XRF), electron microprobe (EPMA) analyses and Fourier transform infra-red (FTIR) spectroscopic techniques. The main peaks in the infrared spectra reflected Al-OH, Al-O and Si-O functional groups in the high frequency stretching and low frequency bending modes. Few peaks of infrared spectra inferred to the interference peaks for quartz as associated minerals. The present study demonstrates usefulness of the spectroscopic techniques in determining quality and crystalline nature of kaolinite from the Assam and Meghalaya, northeastern India.
One of the perspective methods for clean solid fuels production is biodesulphurization. In order to increase the effect of this approach it is necessary to apply the advantages of more informative analytical techniques. Atmospheric pressure temperature programming reduction (AP-TPR) coupled with different detection systems gave us ground to attain more satisfactory explanation of the effects of biodesulphurization on the treated solid products.Subbituminous high sulphur coal from “Pirin” basin (Bulgaria) was selected as a high sulphur containing sample. Different types of microorganisms were chosen and maximal desulphurization of 26% was registered. Biodesulphurization treatments were performed with three types of fungi: “Trametes Versicolor” – ATCC No. 200801, “Phanerochaeta Chrysosporium” – ME446, Pleurotus Sajor-Caju and one Mixed Culture of bacteria – ATCC No. 39327. A high degree of inorganic sulphur removal (79%) with Mixed Culture of bacteria and consecutive reduction by ∼13% for organic sulphur (Sorg) decrease with “Phanerochaeta Chrysosporium” and “Trametes Versicolor” were achieved.To follow the Sorg changes a set of different detection systems i.e. AP-TPR coupled “on-line” with mass spectrometry (AP-TPR/MS), on-line with potentiometry (AP-TPR/pot) and by the “off-line” AP-TPR/GC/MS analysis was used. The need of applying different atmospheres in pyrolysis experiments was proved and their effects were discussed. In order to reach more precise total sulphur balance, oxygen bomb combustion followed by ion chromatography was used.
This study demonstrates the Fourier transform infrared (FTIR) spectroscopic characterization of natural kaolinite from north-eastern India. The compositional and structural studies were carried out at room temperature by using X-ray fluorescence (XRF), electron microprobe (EPMA) analyses and Fourier transform infrared (FTIR) spectroscopic techniques. The main peaks in the infrared spectra reflected Al-OH, Al-O and Si-O functional groups in the high frequency stretching and low frequency bending modes. Few peaks of infrared spectra inferred to the interference peaks for quartz as associated minerals. The present study demonstrates usefulness of the spectroscopic techniques in determining quality and crystalline nature of kaolinite from the Assam and Meghalaya, northeastern India.
Sulfur emission from coal combustion presents many environmental problems. The techniques used to reduce the amount of sulfur in coal before combustion, include physical, chemical and biological processes. Biological processes based on degradation of sulfur compounds by microorganisms offer many advantages over the conventional physical and chemical processes. The processes are performed under mild conditions with no harmful reaction products and the value of coal is not affected. In this article the progress achieved to date in biodesulfurization of Tabas coal in pilot plant is reviewed. Effect of particle size and pulp density at constant temperature on coal biodesulfurization investigated in this research. The best results obtained was 45% of pyritic sulfur and 20% of total sulfur in reduction at pulp density of 10% and 0-0.5 mm particle size within 14 days.
The effect of hydrogen peroxide solution alone and in the presence of dilute sulfuric acid on desulfurization and demineralization of coal collected from the Makum coalfield situated at North-Eastern region, India, was investigated and the process conditions (temperature, time, and hydrogen peroxide and sulfuric acid concentrations) were optimized. Hydrogen peroxide (15%) alone leads to removal of over 76% pyritic sulfur and 70% sulfate sulfur and around 5% organic sulfur and 14% ash at 25 °C, which increases to almost complete removal of pyritic and sulfate sulfur and over 26% organic sulfur and 43% ash in the presence of 0.1 N H2SO4. The oxidation rate was found to increase significantly with increasing temperature (15 to 40 °C) and hydrogen peroxide concentration (2.5 to 15%). The rate of reaction was found to be well represented by a continuous reaction model that was second order with respect to pyritic sulfur. The activation energy for pyritic conversion in Boragolai and Ledo coal are, respectively, 19.33 × 106 J kmol-1 and 39.72 × 106 J kmol-1.
More than 10 tons of coal samples from Luxing Coal Mining Company, Guizhou Province have been collected from various points and sieved into different sizes from the as mined products according to its market demand and utilization. The series samples with different sizes have been characterized using X-Ray diffraction (XRD), Laser Raman (LR), Infrared spectroscope(IR), 13 C solid state magic angle spinning nuclear magnetic resonance (13 C MAS NMR), and scanning electron microscope. It is seen that the bigger lump coal has higher pyrite content and quartz, the big lump coal normally has higher inorganic sulphur content, while the coal powder has higher organic sulphur content. In addition, the coal powders with smaller size have higher dolomite content. The kaolinite and quartz are present in the coal with various particles size. The carbon in the Luxing Coal is present in good crystalline structure, in which 95% of the coal is graphitic structural in the coal with smaller size.
High sulphur coal sample from Ledo colliery of Makum coalfield, Assam, India was studied using FT-IR and XRD methods. FT-IR
study shows the presence of aliphatic -CH, -CH2 and -CH3 groups, aliphatic C-O-C stretching associated with -OH and -NH stretching vibrations and HCC rocking (single and condensed
rings). XRD pattern of the coal shows that it is amorphous in nature. Function of Radial Distribution Analysis (FRDA) indicates
that coal is lignite in type and there is no evidence of graphite-like structure. The first maximum in the G(r) plot of FRDA at r = 0.14 nm relates to the aliphatic C-C bond (Type C-CH=CH-C), the second maximum at r = 0.25 nm relates to the distance between carbon atoms of aliphatic chains that are located across one carbon atom. The curve
intensity profiles obtained from FRDA show quite regular molecular packets for this coal. The coal was found to be lignite
in nature.
The issue of the effects of corrosion on structural integrity of metal surfaces has been a question of concern for some time. The uses of chemical corrosion inhibitors are common in production and processing operations. Nevertheless, the challenge is to develop a new class of corrosion inhibitors to protect the materials, which are environment friendly under various conditions. Surfactants as corrosion inhibitors are environmentally acceptable and are very economical and easily available. The aim of this review article is to delineate the ability of surfactants to inhibit the corrosion on different metal surfaces. Various potential application and properties of different types surfactants have also been discussed. Various parameters like, effect of surfactant concentration, temperature and the mechanism of corrosion inhibition and mode of adsorption are also discussed in this review article.
Bioleaching of metal sulfides is caused by astonishingly diverse groups of bacteria. Today, at least 11 putative prokaryotic divisions can be related to this phenomenon. In contrast, the dissolution (bio)chemistry of metal sulfides follows only two pathways, which are determined by the acid-solubility of the sulfides: the thiosulfate and the polysulfide pathway. The bacterial cell can effect this sulfide dissolution by "contact" and "non-contact" mechanisms. The non-contact mechanism assumes that the bacteria oxidize only dissolved iron(II) ions to iron(III) ions. The latter can then attack metal sulfides and be reduced to iron(II) ions. The contact mechanism requires attachment of bacteria to the sulfide surface. The primary mechanism for attachment to pyrite is electrostatic in nature. In the case of Acidithiobacillus ferrooxidans, bacterial exopolymers contain iron(III) ions, each complexed by two uronic acid residues. The resulting positive charge allows attachment to the negatively charged pyrite. Thus, the first function of complexed iron(III) ions in the contact mechanism is mediation of cell attachment, while their second function is oxidative dissolution of the metal sulfide, similar to the role of free iron(III) ions in the non-contact mechanism. In both cases, the electrons extracted from the metal sulfide reduce molecular oxygen via a complex redox chain located below the outer membrane, the periplasmic space, and the cytoplasmic membrane of leaching bacteria. The dominance of either At. ferrooxidans or Leptospirillum ferrooxidans in mesophilic leaching habitats is highly likely to result from differences in their biochemical iron(II) oxidation pathways, especially the involvement of rusticyanin.
Microorganisms are used in large-scale heap or tank aeration processes for the commercial extraction of a variety of metals from their ores or concentrates. These include copper, cobalt, gold and, in the past, uranium. The metal solubilization processes are considered to be largely chemical with the microorganisms providing the chemicals and the space (exopolysaccharide layer) where the mineral dissolution reactions occur. Temperatures at which these processes are carried out can vary from ambient to 80 degrees C and the types of organisms present depends to a large extent on the process temperature used. Irrespective of the operation temperature, biomining microbes have several characteristics in common. One shared characteristic is their ability to produce the ferric iron and sulfuric acid required to degrade the mineral and facilitate metal recovery. Other characteristics are their ability to grow autotrophically, their acid-tolerance and their inherent metal resistance or ability to acquire metal resistance. Although the microorganisms that drive the process have the above properties in common, biomining microbes usually occur in consortia in which cross-feeding may occur such that a combination of microbes including some with heterotrophic tendencies may contribute to the efficiency of the process. The remarkable adaptability of these organisms is assisted by several of the processes being continuous-flow systems that enable the continual selection of microorganisms that are more efficient at mineral degradation. Adaptability is also assisted by the processes being open and non-sterile thereby permitting new organisms to enter. This openness allows for the possibility of new genes that improve cell fitness to be selected from the horizontal gene pool. Characteristics that biomining microorganisms have in common and examples of their remarkable adaptability are described.
This study examined the hypothesis that solid surfaces may stimulate attached bacteria to produce exopolymers. Addition of sand to shake-flask cultures seemed to induce exopolymer synthesis by a number of subsurface isolates, as revealed by optical microscopy. Several additional lines of evidence indicated that exopolymer production by attached cells (in continuous-flow sand-packed columns) was greater than by their free-living counterparts. Total carbohydrates and extracellular polysaccharides, both normalized to cell protein, were greater (2.5- and 5-fold, respectively) for attached cells than for free-living cells. Also, adsorption of a polyanion-binding dye to the exopolymer fraction was sixfold greater for attached cells than for unattached cells. When surface-grown cells were resuspended in fresh medium, exopolymer production decreased to the level characteristic of unattached cells, which ruled out the possibility that attached cells comprised a subpopulation of sticky mucoid variants. The mechanism by which attachment stimulated exopolymer synthesis did not involve changes of the specific growth rate, growth stage, or limiting nutrient.
Coal has been serving as a profuse source of energy since centuries and several attempts are being made to reduce sulphur emission levels from coal. Recently, pretreatment techniques such as ultrasonication and utilization of surfactants as additives have surfaced aiming at improving the biodesulphurization of coal. In the present study, biodesulphurization of Turkish lignite was studied for the first time using Leptospirillum ferriphilum. Attempts have been made to study the biodesulphurization aspects of the lignite sample where the effect of Fe²⁺ iron, surfactant Span 80 and ultrasonication were studied under shake flask conditions. The study indicated Fe²⁺ to be an essential component in the growth media for improving biodesulphurization performance (with 56.2% total sulphur removal). Span 80 (0.05% v/v) marginally enhanced the biodesulphurization of the lignite sample (nearly 61% of total sulphur removal). The carbon content in the lignite sample increased following biodesulphurization. Ultrasonication of the lignite sample, on the other hand, did not yield significant sulphur removal when compared to the effect of Span 80. About 57.6% of total sulphur could be removed from the sample when ultrasonicated for 60 min. Mineralogical characterization along with thermal analysis of the samples pre and post biodesulphurization provided more information on different phases present in coal and the effect of microbial treatment on them.
In the current era, the alarming rate at which coal is being burned as a fuel is causing concern with regard to the release of sulphur oxides. According to reports, global coal consumption has increased by 0.4% in 2014. While countries like UK, Ukraine etc. have witnessed a decline in coal consumption, some others like India, China, Africa and North America have increased their use of coal to meet the energy requirements of the growing human population. The increasing use of coal has led to extensive investigations for finding an ecofriendly clean coal technology. Dibenzothiophene (DBT) and some of its alkylated derivatives present in the form of organic sulphur in coal have received a great deal of attention in the past few years because of their recalcitrant nature. Considering the economic and environmental prospects, biodesulphurization is being regarded as an effective tool for the degradation of DBT, with concomitant application towards sulphur removal from coal. Owing to the importance of microbial applications towards production of clean coal, the present review discusses some of the recent findings in the area of DBT biodegradation. In addition, current advances in coal biodesulphurization are reviewed, concluding with a consideration of future prospects for the rapidly growing energy sector.
Chalcopyrite is the primary copper mineral used for production of copper metal. Today, as a result of rapid industrialization, there has been enormous demand to profitably process the low grade chalcopyrite and "dirty" concentrates through bioleaching. In the current scenario, heap bioleaching is the most advanced and preferred eco-friendly technology for processing of low grade, uneconomic/difficult-to-enrich ores for copper extraction. This paper reviews the current status of chalcopyrite bioleaching. Advanced information with the attempts made for understanding the diversity of bioleaching microorganisms; role of OMICs based research for future applications to industrial sectors and chemical/microbial aspects of chalcopyrite bioleaching is discussed. Additionally, the current progress made to overcome the problems of passivation as seen in chalcopyrite bioleaching systems have been conversed. Furthermore, advances in the designing of heap bioleaching plant along with microbial and environmental factors of importance have been reviewed with conclusions into the future prospects of chalcopyrite bioleaching.
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Coal collected from Meghalaya state situated in northeastern (NE) region of India contains about 6.17% total sulphur (4.7% organic) with a gross calorific value of 26,208 J/g. In the present study, the coal sample was subjected to biodesulphurization along with optimization of various process parameters using a bacteria isolated from the native coal mine site. The native bacterium was identified to be Sinomonas flava 1C and reported first time for the capability to remove about 40% of sulphur from the coal. An innovative two-step sequential leaching using S. flava 1C followed by Acidithiobacillus ferrooxidans was used in the present study to enhance desulphurization. Sequential leaching resulted in 50-53% of sulphur removal from the coal sample. Sequential leaching reduced the sulphur content to 3.08% (organic 2.15% + pyritic 0.1% and 0.85% of sulphate sulphur) in -500+300 mu m size fraction of coal. Analytical characterization indicated that the energy value of coal was not affected adversely due to the biodesulphurization process rather its calorific value increased from 26,208 J/g to 29,481 J/g.
Coal beneficiation is one of the most effective methods for removing minerals (such as gangues and pyrite) and pollutants (such as sulfur) before the burning of coal. In general, the beneficiation process of low rank coals is more difficult to achieve than that of bituminous and/or anthracite coals. However, about 50% of the world's total coal deposits are low rank coals. It is urgently required to develop effective beneficiation technologies for low rank coals. This review highlights recent advances in beneficiation technologies for low rank coals. Physical (gravity and magnetic separation), chemical (leaching), physico-chemical (flotation and oil agglomeration) and bio-beneficiation technologies are summarized in detail. Effective beneficiation technologies for low rank coals in the future are also suggested throughout this paper.
In the present investigation, 37 numbers of high sulphur tertiary coal samples from Meghalaya, India have been studied on the basis of proximate and ash analysis. Various statistical tools like Bivariant Analysis, Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA), and also the geochemical indicators were applied to determine the dominant detrital or authigenic affinity of the ash forming elements in these coals. The genetic interpretation of coal as well as the coal ash has been carried out based on chemical compositions of high temperature ash (HTA) by using Detrital/Authigenic Index. X-Ray Diffraction (XRD) analysis was also carried out to study the mineralogy of the studied coal ashes. Both statistical tools and geochemical indicators have confirmed the detrital nature of these coals as well as the ash forming elements.
The effects of inoculum percentage, initial pH, growth temperature, shaking rate, substrate type and initial substrate concentration on the growth kinetics of Rhodococcus rhodochrous, a sulfur-removing bacterium, were investigated. The optimum value for each parameter that favoured the maximum specific growth rate was calculated from models established through linear of non-linear regression of the relevant data. Around these optima, biodesulfurization experiments were performed with sterile lignite. An increase in sulfate, pyritic and organic sulfur reduction with increasing reaction time were observed. The highest decreases in the total (30.2%) and organic sulfur (27.1%) contents were obtained with Mengen lignite at 75 h of biodesulfurization.
Extracellular polymeric substances (EPS) produced by acidophilic bioleaching microorganisms play an important role in the production of acid mine drainage and metal sulfide bioleaching. EPS mediate the contact between microbial cells and growth substrates, having a pivotal role in organic film formation and bacterium-substratum interactions. The production and chemical composition of EPS produced by seven bioleaching strains grown with different substrates were studied. Analysis of the EPS extracted from these strains indicated that the EPS consisted of carbohydrates, proteins and galacturonic acid. The contents of EPS, carbohydrates, proteins and galacturonic acid of EPS were largely related to the kind of strain used and culture condition. The results show that EPS productions of microbes grown with pyrite were significantly higher than those of microbes grown with sulfur or FeSO4·7H2O. The highest EPS production of the seven acidiphilic strains was (159.43±3.93) mg/g, which was produced by Leptospirillum ferriphilum CBCBSUCSU208015 when cultivated with pyrite.
The effects of surfactant Tween-80 on the growth, sulfur oxidation, and expression of selected typical sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans ATCC 23270 were investigated. The results showed that in the presence of 10−2 g/L Tween-80, the growth of A. ferrooxidans and its metabolism on the insoluble substrate S0 and CuFeS2 were promoted. After 24 d of bioleaching, the copper extraction yield of chalcopyrite at 10−2 g/L Tween-80 increased by 16% compared with the bioleaching experiment without Tween-80. FT-IR spectra analysis revealed that the result was probably caused by the extracellular polymeric substances whose composition could be changed by the surfactant addition. RT-qPCR was used to analyze the differential expressions of 17 selected sulfur metabolism relevant genes in response to the addition of Tween-80. Down-regulation of the extracellular protein genes indicated the influence of Tween-80 on bacteria-sulfur adsorption. Variation of the expression level of the enzymes provided a supplement to sulfur metabolism investigation.
The biodesulfurization capability of a strain having sulfur and iron metabolism isolated from acidic mine drainage of Balya (Balikesir, Turkey) was studied. Molecular identification of the 16S rRNA gene showed that this bacterium was a strain of Acidithiobacillus ferrivorans. Desulfurization optimization experiments were performed by Taguchi’s method. Statistical experimental arrangement L16 (45) was prepared to determine optimum sulfur removal. The optimum conditions for these parameters were found to be pH of 2.5, inoculum amount of 2%, pulp density of 1%, particle size of −500 + 250 μm, and incubation time of 14 days. A value of “Prob > F” less than 0.0500 indicates that model terms are significant. The obtained yields of total sulfur removal were approximately 33%. According to variance analysis, it was seen that all parameters were effective in removal of total sulfur. Scanning electron microscopy and Fourier transform infrared spectroscopy analyses also indicated a modification of the coal surface after biodesulfurization. The redox potential was measured as 818 mV (7 days) and 788 mV (14 days) during the biodesulfurization experiment by the Pt–Ag/AgCl system of cyclic voltammetry, which suggested that the Fe3+/Fe2+ redox pair could be thermodynamically competitive with the O2/H2O couple as the electron acceptor during bacterial sulfur oxidation, demonstrating that S0 oxidation was coupled with Fe3+ reduction. Thermogravimetry, differential thermal analysis, and differential thermogravimetry curves for untreated and biotreated coal showed the differences in combustion profiles, possibly relating to structural alterations derived from biotreatments.
A total of 48 samples, feed (run-of-mine) coals and their combustion residues (fly ash and bottom ash) were systematically collected twice a week over a 4 week period (June 1998) from two boiler units (I and II) of the Cayirhan power plant (630 MW) that burns zeolite-bearing coals of late Miocene age. The feed coals are high in moisture (22.8% as-received) content and ash (44.9%) yield and total S content (5.1%), and low in calorific value (2995 kcal/kg). The mineralogy of the feed coals contains unusually high contents of the zeolites (clinoptilolite/heulandite and analcime), which are distributed within the organic matter of coal. Other minerals determined are gypsum, quartz, feldspar, pyrite, dolomite, calcite, cristobalite and clays. Common minerals in the crystalline phase of the combustion residues are anhydrite, feldspar, quartz, hematite, lime and Ca–Mg silicate. Minor and trace amounts of magnetite, cristobalite, maghemite, gehlenite, calcite and clinoptilolite/heulandite are also present in the combustion residues. Trace element contents of the feed coals, except for W, fall within the estimated range of values for most world coals; however, the mean values of Mn, Ta, Th, U and Zr are near maximum values of most world coals. Elements such as As, Bi, Ge, Mo, Pb, Tl, W and Zn are enriched more in the fly ash compared to the bottom ash.
This study has two aims: to improve the biodesulphurization of a semi-anthracite by packed-column leaching by reducing the insoluble sulphate on the coal surface, and to determine whether after the combustion of treated and untreated coal, sulphate sulphur is transformed completely into sulphur dioxide or part remains in the ashes without reacting. Combustion tests were analysed by TG-MS. To reduce the precipitation of salts, two parameters are worked on: solution pH, which is reduced to 1.3, and the idle time between washes (ITBW), which is altered. After 125 days of treatment, comparison with the results of previous studies showed that the precipitated salt content was reduced pyritic desulphurization was increased up to 43%, and total desulphurization to 24%.
The biodesulphurisation of coal carried out in pile could be an interesting option to clean coal. In view of the good results obtained in biodesulphurisation test column at lab scale on a sample of semianthracite coal that proceed of an industrial plant with a high sulphur content, mainly pyritic sulphur, the feasibility of the process at pilot plant scale was studied. The pile was formed with 6ton of gravity middlings coal sample with a grain size −12+0.5mm from S.A. Hullera Vasco-Leonesa industrial plant. The coal has a total sulphur content of 3.78% and a pyritic sulphur content of 2.88%, the rest of sulphur is organic sulphur. The biodesulphurisation process in pilot plant follows three stages: stabilization of the pile, biodesulphurisation and washing. Heap was sampled twice during stabilisation stage, at the end of desulphurisation process and finally once washed. A pyritic sulphur removal of 39% and total sulphur removal of 23% was obtained. To complete the bioleaching process, the treatment of purge of leachate was carried out with the objective to recycling to head of process. The best treatment was a pre-treatment of the leachate until pH 4, and further treatment by reverse osmosis of the clarified water. Comparing this process with conventional precipitation to reach disposal limits, the reagents consumption and sludges were reduced considerably and due to the high quality of permeate it permits to recycle it to head of process.
The effects of inoculum percentage, initial pH, growth temperature, shaking rate, substrate type and initial substrate concentration on the growth kinetics of Rhodococcus rhodochrous, a sulfur-removing bacterium, were investigated. The optimum value for each parameter that favoured the maximum specific growth rate was calculated from models established through linear of non-linear regression of the relevant data. Around these optima, biodesulfurization experiments were performed with sterile lignite. An increase in sulfate, pyritic and organic sulfur reduction with increasing reaction time were observed. The highest decreases in the total (30.2%) and organic sulfur (27.1%) contents were obtained with Mengen lignite at 75 h of biodesulfurization.
With an increase in environmental degradation, the environmental norms are becoming more and more stringent day by day. Research work is currently being undertaken around the world to bring about deeper desulfurization of crude oils. Presently, two crude oil samples, i.e., heavy crude oil (HCO, 1.88% S) and light crude oil (LCO, 0.378% S) were procured from a local petroleum refinery. Bio-desulfurization (BDS) of LCO using Pantoea agglomerans D23W3 resulted in 61.40% removal of sulfur, whereas HCO showed 63.29% S removal under similar conditions. The use of P. agglomerans D23W3 under anaerobic conditions showed marginally better results than those under aerobic conditions. However, the use of thermophile Klebsiella sp. 13T resulted in 62.43% S removal from LCO and 68.08% S removal from HCO. Studies have also been extended on the use of reactive adsorption techniques for the removal of sulfur from crude oils. Among all of the different adsorbents studied, residual coal obtained after the solvent extraction of Samla coal showed the maximum removal of sulfur, i.e., 78.90% from LCO and 74.46% from HCO. Hydro-desulfurization is an established technology for the deep desulfurization of petroleum and its products. Widening the choice and exploring further developments in deeper desulfurization of petroleum alternative technologies may also be developed. Comparative studies were extended on the use of BDS, reactive adsorption, oxy-desulfurization, photo-desulfurization, and solvent extraction for the removal of sulfur from HCO and LCO. Among all of these techniques, oxy-desulfurization was found to be the best. To study the deep desulfurization of LCO and HCO, two- and three-step integrated processes were developed for the removal of sulfur from HCO and LCO. BDS under anaerobic conditions followed by oxy-desulfurization followed by reactive adsorption integration resulted in maximum removal, i.e., 95.21% removal of sulfur from HCO and 94.30% removal of sulfur from LCO.
In this paper, a two-step desulfurization process for high-sulfur coal was investigated. Two Chinese coals with the addition of 10 wt % potassium hydroxide or sodium hydroxide were pyrolyzed under an atmosphere of nitrogen or hydrogen in a fixed-bed reactor at 600 °C, and then the obtained chars were washed with hot water. The results indicated that, without the addition of an alkali component, the sulfur removal of these two coals by pyrolysis and hydropyrolysis is 40%−50% and the sulfur content of chars is reduced only slightly, in comparison with the original coals; with the addition of 10 wt % potassium hydroxide or sodium hydroxide into the original coals and the chars being washed with hot water, the sulfur removal is 70%−80% and the sulfur content in chars is reduced dramatically. The combustion behavior of chars was also investigated, using thermogravimetric analysis. The results showed that those chars that had an added alkali component and were subjected to water-washing were more reactive and can be burned more easily than those without added alkali, which was also confirmed by a kinetics analysis of char combustion.
Chars and activated carbons were produced from raw, HCl-washed, and HCl/HF-washed Elbistan lignites at 700 °C, 800 °C, 900 °C, and 1000 °C. The pyrolysis and activation reactions increased the BET areas (m2/g carbon) of the acid-washed samples almost 10-fold. The increase of the BET areas (m2/g carbon) by increasing the temperature of pyrolysis or activation from 700 °C to 1000 °C was explained with the burn-out of carbon which led to the development of porosity. The values of the stacking heights, Lc of HCl/HF-washed samples seemed to increase from 1.0 nm to 1.5 nm, the average number of graphene sheets increased from 2.8 to 4.4, and the lateral size of the crystallites, La, increased very faintly from 5.0 nm to 5.5 nm when the pyrolysis temperature was increased from 700 °C to 1000 °C. Activation reactions performed at the same temperature range did not change the stacking heights. The values of Lc for activated HCl/HF-washed samples stayed almost constant in the same range as for the carbonized samples within 1.0−1.5 nm. This indicated that oxidative reactions during activation did not alter the stacking heights of the crystallites significantly in the temperature range of 700−1000 °C. The results presented in the present work can be considered as indications for the development of turbostratic (fully disordered) structures in the temperature range of 700−1000 °C.
Experiments have been carried out to determine the effects of biodesulfurization time on the removal of sulfur constituents of six Turkish lignites by Sulfolobus solfataricus. The changes in sulfur content of Tuncbilek, Karliova, Beypazari, Can, Elbistan, and Mengen lignites are shown as functions of time. A decrease in all sulfur forms with increasing time was observed for each coal. The highest total and organic sulfur reductions were observed with Beypazari lignite as 57.1 and 47.8%, respectively. The influence of analyses of the original samples on total and organic sulfur reductions has been investigated through multiple linear regression analysis. The resulting determination coefficients are compared to obtain the beat fitting parameter set. For the six lignites the experimental values of total and organic sulfur reductions appeared to agree with the values calculated for the models.
The purpose of the present work was to investigate the effect of the concentration of HI and reaction time in the chemical desulfurization of Cayirhan lignite in a microwave energy set up and to compare the results with those obtained in a thermal heating system. As the concentration of the HI was increased, the extent of desulfurization was also increased in all the experiments done for all of the samples of lignite. The main difference between the thermal and microwave heating was the extremely short times for desulfurization in the case of microwave experiments. After desulfurization experiments Stotal/C ratio of all of the samples decreased to a lower value than that of the raw lignite which was 0.034. The loss of the sulfur containing bands in the FTIR spectra of the desulfurized lignite showed that the HI treatment was effective in the cleavage of dithioethers and thioetheric groups. Sulfur containing functionalities like thioethers and thiols although usually requiring strong reducing agents could be removed in significant amounts with concentrated hydroiodic acid from the coal matrix. The rapidity of the desulfurization reactions with microwave heating in concentrated HI was probably due to localized superheating which made HI more effective in the reactions such as with thioethers and thiols that normally resisted to cleavage by HI under thermal heating conditions.
Organic matter present in lignite samples collected from different depths (i.e. top, mid and bottom) of lignite source, Ilgın, Konya province, was examined by using subtractive-FTIR-ATR spectroscopy. FTIR spectra were recorded on (i) original samples, (ii) the samples dried at 105°C and (iii) the samples acid-treated and dried. After a combustion process performed for each sample at 650°C for 15min, the spectra of samples were recorded and subtracted from the spectra of untreated samples. Hence, a software-based subtraction made it possible to acquire a representative spectra related with organic matter. As the contribution of the bands related with inorganic constituents in lignite samples were eliminated after spectrum-subtraction procedure, difference-spectra led analyzing the spectra related with organic matter in lignite samples, reasonably. Furthermore, the bands related with acidic functional groups, aromatic and aliphatic structures were analyzed on the basis of difference-spectra, easily. From the difference-spectra it was shown that an acid-treatment process under mild conditions caused shift in some specific bands related with carbonyl groups of carboxyls so that the band at around 1710cm(-1) arisen, while the intensity of the band at around 1420cm(-1) was diminished. Through the acid-treatment process, acidic groups in lignite samples from different depths were thought to be turned into similar forms by protonation and/or stripping of metal ions originally bonded. Difference-spectra acquired for acid-treated samples made it possible to evaluate the form of carboxylic acid groups present in the studied samples under specific environmental conditions. Hence, a facile and environmentally-friendly methodology was used to analyze organic matter in lignite by using FTIR spectra, and valuable information was acquired about the aliphatic, aromatic and acidic character of the studied lignite samples collected from different depths. The proposed methodology seems to be promising in acquiring approximate representative spectra for lignite organic matter by using little or no chemicals.
This study focuses on the determination and concentration of twelve elements (Na, K, Ca, Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn and Cd) occurring in sub-bituminous Assam coals and their geochemical association. Distribution of these elements between organic and mineral matters was studied. Comparison of the results of three coals has shown that three elements (Mg, Ca and Mn) are significantly organic bound, while five elements (Fe, Co, Ni, Cu and Zn) are significantly mineral bound; Cd is 50% bound to either organic or mineral matter. FTIR and XRD studies reveal qualitative information about the bonding pattern and nature of components of the mineral matters. The results obtained in this study have considerable geochemical and technological interests.
Effects of two typical surfactants, Tween-80 and sodium isobutyl-xanthate (NaIBX), with different concentrations on the growth and sulfur-oxidizing activities of a new strain Acidithiobacillus albertensis BY-05, an acidophilic sulfur-oxidizing bacterium, were investigated. The results indicate that both surfactants can enhance the growth and sulfur-oxidizing activities of A. albertensis BY-05 only at some special concentrations, e.g., 10−4–10−8 g/L for NaIBX and lower than 10−8 g/L for Tween-80, but were inhibited and even harmful at higher concentrations. Both surfactants can not be metabolized by A. albertensis BY-05. The contact between the bacteria and the sulfur particles may be dependent upon both the extracellular substance and the surfactants, both of which provide the amphiphilic environment improving the attachment for bacteria to the sulfur particles surface. These data could be significant for enlarging the applications of both A. albertensis BY-05 and some typical surfactants for industrial bioleaching of sulfides minerals.
In this paper, data obtained during the oxidative desulphurization of some low-rank Turkish lignites with crude laccase enzyme produced from Trametes versicolor ATCC 200801 are presented. In order to optimize desulphurization conditions, effects of incubation time, pulp density, incubation temperature, medium pH, and also lignite source on the desulphurization have been examined. The values for incubation period, pulp density, temperature and pH in optimum incubation condition were found as 30 min, 5%, 35 degrees C, and pH 5.0, respectively. Under optimum conditions, treatment of coal samples with crude laccase has caused nearly 29% reduction in their total sulphur content. During the study, the rate of desulphurization of coal sample provided from Tuncbilek with crude laccase was found to be relatively higher than the other examined coal samples. Results of analytical assays have indicated that the treatment of coals with crude laccase has caused no change in their calorific values but reduced their sulphur emissions. 35%, 13%, and 25% reductions of pyritic sulphur, sulphate and organic sulphur in a period of 30 min were achieved, for a particle size of 200 mu m under optimal conditions with enzymatic desulphurization. Also, statistical analyses such as Tukey Multiple Comparison tests and ANOVA were performed.
The oxidation of ferrous iron by Acidithiobacillus ferrooxidans in the pH range 2.5-7.0 was characterized. In order to measure the rate of bacterial oxidation of ferrous iron with A. ferrooxidans in this high pH range, a novel experimental methodology was developed. The results showed that the inhibition of ferrous iron oxidation activity by A. ferrooxidans observed at pH values above 3.0 is partially linked to the formation of ferric iron precipitates, which apparently hinder transport processes on the cell surface. By carefully controlling the amount of iron precipitates formed during the oxidation of ferrous iron in this pH range, enhanced bacterial activity was obtained.
Iron and sulfur oxidation by Thiobacillus ferrooxidans as well as growth on ferrous iron were inhibited by a variety of low molecular weight organic compounds. The influences of chemical structure of the organic inhibitors, pH, temperature, physical treatment of cells, and added inhibitory or stimulatory inorganic ions and iron oxidation suggest that a major factor contributing to the inhibitory effects on iron oxidation is the relative electronegativity of the organic molecule. The data also suggest that inhibitory organic compounds may (i) directly affect the iron-oxidizing enzyme system, (ii) react abiologically with ferrous iron outside the cell, (iii) interfere with the roles of phosphate and sulfate in iron oxidation, and (iv) nonselectively disrupt the cell envelope or membrane.
The stringent new regulations to lower sulfur content in fossil fuels require new economic and efficient methods for desulfurization of recalcitrant organic sulfur. Hydrodesulfurization of such compounds is very costly and requires high operating temperature and pressure. Biodesulfurization is a non-invasive approach that can specifically remove sulfur from refractory hydrocarbons under mild conditions and it can be potentially used in industrial desulfurization. Intensive research has been conducted in microbiology and molecular biology of the competent strains to increase their desulfurization activity; however, even the highest activity obtained is still insufficient to fulfill the industrial requirements. To improve the biodesulfurization efficiency, more work is needed in areas such as increasing specific desulfurization activity, hydrocarbon phase tolerance, sulfur removal at higher temperature, and isolating new strains for desulfurizing a broader range of sulfur compounds. This article comprehensively reviews and discusses key issues, advances and challenges for a competitive biodesulfurization process.
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