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Biodesulphurization of Turkish Lignite by Leptospirillum ferriphilum: Effect of Ferrous iron, Span-80 and Ultrasonication
Abstract
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.
... Because of the importance of such studies, the present work focuses on the scale-up biodesulphurization aspects of a Turkish Lignite sample using an iron oxiding acidophile, Leptospirlillum ferriphilum based on the outcomes/ optimum conditions obtained from our lab scale shake flask experiments. 20 It is very important to note that scale-up aspects on biodesulpurization of Turkish Lignites has not been reported in literature and the use of Leptospirillum ferriphilum for Turkish coal desulphurization also stands out to be a novel aspect of research. ...
... The optimized parameters obtained through our previous shake-flask studies were taken into consideration for the present studies. 20 The studies (experimental conditions discussed in subsections below) were initially performed in a laboratory scale reactor (1 L working volume) followed by a semipilot scale reactor (20 L working volume). A water heating system was connected to each of the reactors, which circulated heated water into the double layers of the reactors for temperature maintenance. ...
... The sulfur distribution studies had indicated that the lignite sample contained 2.71% of pyritic sulfur, 1.57% sulfate sulfur, and 2.59% organic sulfur. 20 In the present study, the proximate analysis of the biotreated TL sample (20L reactor) revealed that the ash content in the sample was 18.2% following microbial treatment, whereas, the volatile matter content was 40.05%. There was a notable increase in the fixed carbon content, which was observed to be 22.2% and the moisture content in the treated sample was found to be 19.54%. ...
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.
... Hence, lower size fraction of −75 + 45 µm was used for carrying out preliminary biodesulphurization experiments in order to obtain optimum results, which were further followed up by scale-up studies. Sulphur distribution studies of Turkish lignite had revealed the presence of 2.71% of pyritic sulphur, 1.57% sulphate sulphur and 2.59% organic sulphur (Mishra et al., 2018). It is thus important to note that the organic sulphur in the sample accounted to nearly 37.7% of the total sulphur, which can be considered as a vital aspect to treat the sample with R. erythropolis. ...
... A maximum enhancement of 27.4% in sulphur removal was achieved in the 10L reactor in the presence of surfactant when compared with shake-flask studies where only 23.8% of desulphurization was achieved in the absence of chemical surfactant. Our previous studies carried on biodesulphurization of Turkish lignite using a pure acidophilic strain, Leptospirillum ferriphilum DSM 14,647, had indicated a maximum enhancement of 6% in sulphur removal when Span 80 (0.08%) was used in the medium (Mishra et al., 2018). Further increase in the surfactant concentration had an adverse effect on the microbial growth and activity. ...
... Proximate analysis of the original Turkish Lignite had revealed that the sample contained 24.7% ash, 39.13% volatile matter and 16.72% fixed carbon (Mishra et al., 2018). Following treatment, the ash percentage reduced to 21.02% in 1L bioreactor having no surfactant. ...
Turkey is a country with vast lignite reserves, which can serve as a potential source of energy to meet the rising energy demands. However, the sulphur present in coal delimits its application in several sectors. Recently, various techniques have emerged for sulphur removal from coal. In the present study, the efficacy of Rhodococcus erythropolis DSM 44308 towards biodesulphurization of a Turkish lignite (TL) sample has been studied. Additionally, the effects of ultrasonication and surfactant, Span 80 (S80), on biodesulphurization of the lignite sample have been studied and compared. Optimum parameters obtained through shake-flask experiments have been considered for further scale up in laboratory (1L) and semi-pilot (10L) bioreactors. To the best of our knowledge, the biodesulphurization approach indicated in the present study using R. erythropolis is being reported for the first time. The study revealed that a maximum desulphurization of 44.6% was achieved in shake-flask experiment using S80 concentration of 2% v/v. In the scale up bioreactor studies, 49.2% and 51.2% sulphur removal was achieved in 1L and 10L bioreactors respectively. The ultrasonication technique (upto 1 hour treatment) was observed to have a marginal effect, leading to only 6% enhancement in biodesulphurization when compared with the control. Mineralogical analysis of original and treated samples provided better insights into the structural and phase changes following microbial treatment in presence and absence of Span-80.
... 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.
... Efficiency of Span 80 in sulphur removal with varying concentrations80 ...
The rapidly increasing modern industrial world demands a huge uninterrupted energy supply, where high-quality coal (HQC) is one of the major sources of the required energy. In this regard, a gigantic amount of solid waste including ash and toxic chemicals, such as heavy metals, nitrate and sulphur, gases including NOx and SOx are emitted during the direct incineration process of low-rank coal. About 10 Gt of CO 2 and about one-fifth of total greenhouse gases in the world are emitted each year due to coal combustion in power plants, making it the single largest cause of climate change. The UN proposed that OECD countries stop producing electricity from coal by 2030 and the rest of the world by 2040. Herein, we discuss the development of modern technologies that can convert low-quality coal (LQC) into high-quality coal (HQC) to minimize the impact of fossil fuel burn, climate change, premature death of animals and all other related environmental hazards. Amongst the many established technologies, flotation pre-treatment is the most common and effective method used worldwide due to its lower energy input than other methods. In this review, we attempt to present an up-to-date understanding of the applications and utilities of surfactants in coal floating. We also demonstrate the possible modernization of this surfactant chemistry and its prospects.
... The importance of fossil fuel reserves, which has been diminishing as many years and significant investments will be required to expand the use of renewable and clean energy sources, will continue to increase day by day. Since this will increase the environmental problems exponentially, it is of great importance that fossil fuels are cleaned from harmful content, especially before combustion ( Aytav and Kocar, 2013 ;Cemil Koyuno ğlu, 2019 ;Karaca et al., 2019 ;Koyuno ğlu and Karaca, 2019a , b ;Mishra et al., 2018Mishra et al., , 2016Speight, 2020 ). ...
In this context, this study aims to reduce the harmful effects of coal combustion and to investigate the possibility of efficient use of Turkish lignite with high sulfur content. In this study, peroxide leaching process and accounts for approximately 35% of lignite reserves in Turkey total sulfur content of the garment was removed from lignite. For this purpose, the effect of H2O2 on 5%, 10%, 20%, and 30% solutions and H2SO4 on the sulfur removal using 0.05 N, 0.1 N, 0.15 N, and 0.2 N solutions separately and together were investigated. According to the results, increasing the H2O2 concentration from 5% to 30%, the total sulfur content of the coal sample was removed by approximately 75%. When 0.1 N H2SO4 and H2O2 were used together, about 93% of sulfur removal was realized. The originality of the study is that scenario 8 of 12 situations is both high standard chemical exergy value used for economic analysis, low CO2 emission value determined according to the life cycle assessment method used for environmental impact assessment, and 20-year operating cost calculated by current value estimation method. The lowest value indicates that 20% of H2SO4 is suitable for the establishment of the desulphurization plant with a yield of 63.2% from 200 kg of coal per hour. The highest exergy efficiency value was calculated as 8,01782E-06 for the 8th scenario. So the 8th scenario should be applied for the establishment of a desulfurization plant for E.L. Due to the results, this study is an economical method of sulfur removal. The addition of H2SO4 to H2O2 has a synergistic effect on sulfur removal. In this study, a new perspective has been developed by using exergy calculation and life cycle methods apart from conventional methods while determining the economy.
... It contains a variety of functional groups including carbon (C), oxygen (O), nitrogen (N) and sulphur (S) contents. The percentage of sulphur content in coal varies according to the rank of coal (Mishra et al., 2018). The sulphur content in coals varies substantially from 0.5 wt% to 2.0 wt% (Chou, 2012), but can rise up to and above 10 wt% (Maffei et al., 2012). ...
Sulphur content in the coal is the most notorious environmental contaminant, which produces sulphur dioxide (SO2) during combustion. In this study, the sulphur content of the parent coal samples reduced through biodesulphurization treatment and its influence on the SO2 emissions concentration in a power plant was monitored. Coal samples were screened to a particle size fraction of – 0.85 mm, – 2.30 + 1.00 mm, – 4.60 + 2.30 mm and +4.60 mm prior to biodesulphurization treatment. Data used in this study comprised of average 2 daily interval sulphur content and SO2 emissions concentrations for the period 0 to 20 Days. The finer fraction of – 0.85 mm showed a significant reduction of sulphur content from 1.45 wt% to 0.50 wt% which translate to SO2 emissions concentration reduction from 3716 mg/Nm³ to 1280 mg/Nm³. However, when the temperature was increased from 23 ± 3 °C to 30 ± 2 °C, further reduction of SO2 emissions to 1023 mg/Nm³ was realized. Biodesulphurization treatment demonstrated to lower SO2 emissions by 72.4% and reduce ash content by some 33%. Moreover, pyrite was observed in vitrinite and inertinite, both syngenetically and epigenetically. The current study offers the possibility of reducing SO2 emissions in South African power plants through biodesulphurization treatment.
... The generation of fly ash (FA) resulting out of coal burning is being increased up to a considerable extent owing to the extensive rate of usages of coal in thermal power sectors Mishra et al., 2018;Mishra et al., 2016). This leads to cause serious concerns in the environment in the context of the management of the large quantity of the FA generated, and hence, it urges to develop suitable technology for its safe environmental disposal (Dan et al. 2021). ...
The present investigation is intended to develop the stabilization and transportation behavior of fly ash slurry (FAS) using the mixture of the surfactants, namely, Sapindus laurifolia (S. laurifolia, natural) and sodium dodecyl sulfate (SDS, synthetic). In addition to the rheological study, an attempt has been made to remove the toxic and other trace metals through the leaching method to address the safe disposal of FAS for mining backfilling applications. The data obtained from the different rheological studies of ash concentrations in the range of 45–65.8% were fitted to the Bingham plastic model. Addition of synthetic surfactant SDS to natural surfactant S. Laurifolia does enhance the wettability of fly ash (FA) particles by decreasing the surface tension and increasing the zeta potential of the slurry. The effect of other parameters like temperature, mixed surfactant concentration, and FA concentration on the formulation, stability, and leachability of FAS was investigated and reported. The results from the present investigation revealed that the optimum dosages of surfactants for both leaching and transportation of FAS is 0.009 g/cc of saponin and 0.008 g/cc of SDS. The stabilization interaction and leaching mechanism were proposed considering the hydrophobic/hydrophilic property of FA, S. laurifolia, and SDS.
Abbreviations
CMC: Critical micellar concentration; S. laurifolia: Sapindus laurifolia; SDS: Sodium dodecyl sulfate; FA: Fly ash; FAS: Fly ash slurry; η: Dynamic viscosity; τ0: Yield stress; γ: Applied shear rate; ζ: Zeta potential; τ: Shear stress
... Some earlier studies have also indicated the use of Acidithiobacillus ferrooxidans towards oxidation of sulphide ores and concentrates for release of the associated gold (Komnitsas and Pooley 1990;Natarajan 1998). In addition, bioleaching has also been used to remove impurities such as sulphur from coal; this process is more specifically called as bio-desulphurization (Mishra et al. 2018a(Mishra et al. , 2018b(Mishra et al. , 2017Ye et al. 2018), removing iron from kaolin and quartz (Barnett, Palumbo-Roe and Gregory 2018;Giese et al. 2019;Jun et al. 2020) and dissolution of rare-earth elements from both primary and secondary resources (Fathollahzadeh et al. 2019;Panda et al. 2021a). The following sub-sections presents more detailed insights into the fundamentals and applications of this process. ...
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 observed that about 40% sulphur could be removed using Trametes versicolor. Similarly, in one of the recent attempts made by Mishra et al. [25], lignite samples obtained from Canakkale province of Turkey were tested for biodesulphurization using Leptosprillum ferriphilum DSM 14647, where the effect of ferrous iron, surfactant (Span-80) and ultrasonication was studied. It was concluded that at 0.05% v/v Span-80, 61% of total sulphur could be removed in shake flasks. ...
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.
... The microbial coal desulfurization studies were mainly focused on the removal of the sulfur present in inorganic form (pyritic) from the coal samples. In a recent study, iron-oxidizing bacterium L. ferriphilum has been used for sulfur removal from a Turkish coal sample (Mishra et al. 2018). This study was performed to remove pyritic sulfur present in the coal (lignite) sample. ...
The present work deals with the use of iron/sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans for the desulfurization of a coal sample from Assam, India. The coal sample contains 3.87% w/w of organic sulfur, 1.4% w/w pyritic sulfur, and 1.29% w/w of sulfate sulfur which altogether are contributing to its total sulfur content of 6.56% w/w. The microbial process followed the oxidative-desulfurization mechanism for the removal of sulfur from the coal sample. The bacterium performed cleavage of the sulfide bonds in pyrite to release the inorganic sulfur. Mass spectroscopic analysis revealed that the bacterial strain A. ferrooxidans performed oxidative desulfurization of a model sulfur-containing organic compound dibenzothiophene to 2-hydroxy biphenyl through the formation of dioxy-dibenzothiophene. A. ferrooxidans cells played the catalytic role to release the sulfur present in organic and inorganic form in the coal sample. The microbial desulfurization process conducted in a shake flask scale (500 mL) removed about 79% of total sulfur from the coal sample in 14 days.
... 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.
... 11 Several metal recovery techniques can be applied to PCBs, according to the metal content, including pyrometallurgy, hydrometallurgy and bio-hydrometallurgy. 12,13 Bio-hydrometallurgical techniques, such as bioleaching, are more suitable for metal recovery due to their eco-friendly nature, high selectivity for metals and lower operational costs. [14][15][16][17] Bioleaching has proven to be a successful method for dissolving metal sulfides (also successfully applied to secondary resources such as e-waste) owing the oxidative activity of certain chemolithotrophic microbes which are mainly sulfur and iron oxidizers; these microbes obtain their Table 1 Reported studies on bioleaching of metals from WPCBs by mesophilic acidophiles [18][19][20][21][22] Biological activity can be reflected by variation in redox (oxidation-reduction) potential (ORP) in leaching solution, and several attempts have been made to control ORP for efficient metal dissolutions (see Table 1). Maximal values of ORP can promote the interaction between bacteria and WPCB for metal recovery, 23 and this can be achieved by providing pH balance. ...
BACKGROUND: The waste printed circuit boards (WPCBs), today, offer a wide array of metals and are of great importance because their metal concentration is much more than that in the ores. Largely, studies have been devoted to Cu bioleaching from WPCBs because it has the highest ratio among all metallic elements ( ̴ 10-30%). In the present study, an intensified mixed meso-acidophilic bacterial leaching of multi-metals has been studied from WPCBs of spent mobile phones, with the system operating under high oxido-reductive potentials (HORPs). ICP-OES, XRD and SEM-EDX characterization indicated the sample to have recoverable contents of Cu, Al, Ni & Zn which were targeted for bioleaching.
RESULTS: Shake flask optimization studies, under HORP of >750 mV indicated dissolutions of Cu – 98.1%, Al – 55.9%, Ni – 79.5% and Zn – 66.9% under optimized conditions of 9 g/L Fe (II), 10% pulp density, 1.8 initial pH and 10% (v/v) as initial inoculum. Under these conditions, at ORP >650 mV, Cu – 97.3%, Al – 55.8%, Ni – 79.3% and Zn – 66.8% were achieved in bench scale (1L) bioreactor systems without any significant reduction in efficiency (compared to shake flasks) in 8 days of operation.
CONCLUSION: Variations in the co-relatable parameters, to metal leaching, 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 efficient way to leach multi-metals from WPCBs.
... The burning of coal, possessing large amount of sulfur during industrial operations has negative impact on natural environment due to release of large amount of SO 2 into atmosphere. The high sulfur containing coals have been treated by L. ferriphilum in order to minimize the content of sulfur (Mishra et al. 2018). The improvement in treatment methodology and bacterial strains employed would give a new dimension for large scale coal biodesulfurization to reduce sulfur emission from industrially used low grade coals. ...
In natural ecosystems, diverse iron oxidizing bacteria are of common occurrence. Basically, two different mechanisms have been proposed for catalysis of iron oxidation by bacterial metabolic systems which differ mainly at cytochrome and rusticyanin level. Biological iron oxidizers not only affect the cycling of iron but also efficiently minimize the concentrations of hazardous metals such as lead, nickel, copper, chromium, cadmium and cobalt. The ferric iron generated after biological oxidation forms complexes with metals/metalloids present in their vicinity. Ferric ions produced by biological actions also act as catalyst for oxidation of toxic metalloid such as arsenite (As III) converting it into less toxic form. Most importantly, bacterial iron oxidizers have commercially been employed in industrial bioleaching for the recovery of important elements and remediation of acid mine drainage water. Currently, heavy metal contamination has emerged as one of the prime concerns for the world and is posing serious threats to both environment and human health. Although varieties of physical and chemical techniques are currently being used to manage the metal contamination, treatment using biological iron oxidation approaches are convincing because of their ecofriendly nature and low sludge generation. In the present review we have tried to focus on the diversity of bacterial iron oxidizers, mechanisms of iron oxidation by bacterial species, and role of bacterial iron oxidizers in bioremediation of metal pollutants along with future research possibilities in this area.
In the current paper, detailed mechanism of zinc, copper, and antimony bioleaching from tetrahedrite-rich concentrate was investigated. The bioleaching experiment was carried out with mixed mesophilic and moderately thermophilic cultures in shake flasks. The sample was characterized for its chemical, mineralogical, and morphological properties using optical microscope, XRD, ICP, SEM, and EDS analyzers. The initial screening tests showed that bacterial leaching positively affected the extraction of metals from tetrahedrite-rich concentrate compared to the abiotic control test. The effects of different chemicals and factors such as graphite, silver nitrate, l-cysteine, pyrite, elemental sulfur, ferrous sulfate, and mechanical activation on the bacterial leaching of tetrahedrite concentrate were studied for the first time in detail. It was found that mechanical activation by planetary mill (grinding time: 40 min) and addition of 126 mg/l of silver nitrate strongly affect the biodissolution of metals. During optimum condition, bioleaching parameters such as pH, ORP, Fe3+ concentration, and bacterial population were reported and considered favorable for bioextraction of metals. The results showed that maximum extraction of copper (Rcu = 95.56%), zinc (Rzn = 86.88%), and antimony (RSb = 22.01%) could be achieved by moderately thermophilic bacteria in the presence of external energy sources.Graphical Abstract
Coal spontaneous combustion (CSC) has hindered the utilization of coal resources and the development of the global economy for centuries. At present, many materials are used for preventing and extinguishing CSC fires, and different types of materials have various sites of action. In this paper, research on CSC fire prevention and extinguishing materials is reviewed and proposed. The preparation schemes and effects of physical barrier materials, chemical inhibitors, composite materials, and other fields of fire prevention materials were discussed. The improved compounding schemes of CSC inhibiting materials were analyzed regarding the characteristics of base materials and material properties. It was found that in the field of fire prevention materials, plant extracts, hydrolyzed proteins, biomass, and other green recycling materials have gradually become the new trend in materials. The composite material has a synergistic physical barrier and chemical inhibition and has a good inhibitory effect on coal heat storage and group activation, which has become an inhibitory material that is highly concerning. CSC inhibiting technology involving microbial control has emerged and exhibits notable characteristics, including a green cycle and long action time, but its application still needs to control the coexistence of heterogeneous microorganisms and improve the environmental livability. High‐quality firefighting materials, which are used in preventing battery fires, fighting building fires, inert coatings of cotton fabric, and other fields, have potential applicational value for CSC prevention. This review aims to provide new ideas for the research of CSC fireproof materials.
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.
The present study was conducted to investigate the heavy metals removal and gaseous data simulation for the bio-treatment of the electroplating industrial effluents. The iron discharge was reduced to 165.9 ± 0.98 mg/L and 155.92 ± 0.77 mg/L from the initial concentrations of 12,657 ± 393.43 mg/L and 688.42 ± 3.17 mg/L in the respective electroplating effluents when treated at statistically confirmed conditions. Zn removal efficiency was significantly improved (~10.0%) in both the real undiluted effluents, over the diluted effluent (50% dilution). The particle size analyzer (PSA) distribution data recorded shows the smaller size particle formation of 242.1 nm and 319.85 nm during the effluent treatment. The size of the particle in the liquid components was further reduced to 45.32 nm (56.95% Intensity) and 276.1 nm (73.4% Intensity) during the effluents treated at the 50% dilutions. The hypothesis of acid and heavy metals stress was simulated by modified SWeibull models.
The oxidation of various sulfides in mining wastes and rock outcrops commonly leads to environmental problems. Therefore, surface weathering of metal sulfide has been one of the most concerned epigenetic processes. More and more geological facts and experiments indicate microorganism play crucial roles in these processes. Microorganism cells tend to attach onto sulfide surface and construct biofilms. In the interface microenvironment between mineral surface and biofilm, microbial oxidation and chemical oxidation mutually promote the decomposition of sulfides and intensively Erode the sulfide surfaces. The elements of the sulfide (e. g., S, As and Fe) experience complicate processes of electron transferring and step-by-step oxidation, and produce ferric sulfates and oxides finally as well as large amounts of acid mine drainage bearing various heavy metals. The microbial oxidation is generally influenced by factors, such as bacteria type, light and Fe ⁺ concentrations in solution. Therefore, the release of heavy metals due to sulfides oxidation commonly brings serious environmental harm, and the produced AMD leads to decomposition of carbonate minerals and thereafter influences the global carbon cycle. Meanwhile, the consumption of oxygen probably had slowed down the oxygenation of earth atmosphere in the Archean-Proterozoic eras. Although the understanding on the microbe-mineral interaction has been greatly promoted in last decades, there are plenty rooms for the studies on the mechanism at atomic level and the impacts of the microbial oxidation on the geochemical cycles at the global level, and thus it is imperative and urgent to employ in-situ measurement techniques and global geochemical models. The related studies also favor the development of biological metallurgical technologies.
In order to comprehensively utilize coal gangue, we present fluidized calcination as a new thermal technology for activating coal gangue and systematical study was conducted in comparison with static calcination. The calcined products obtained by different calcination methods under various temperatures were characterized by the means of X-ray diffraction (XRD), thermal gravimetry-differential scanning calorimeter (TG-DSC), Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS). Chemical and physical characteristics such as aluminium leaching rate, chemical oxygen demand and whiteness of calcined products were also investigated. The results show that aluminium leaching rate could reach to the maximal value 74.42% at 500 °C by fluidized calcination, while the maximal value of 66.33% could be reached at 600 °C by static calcination. Products by fluidized calcination obtained higher whiteness and lower chemical oxygen demand (COD) under the same calcination temperature. The well-crystallized kaolinite transform to amorphous meta-kaolinite under 600 °C and mullite presence under 1000 °C according to phase transformation, chemical bond variation and microstructure evolution analysis. Fluidized calcination was more efficiently for combustion of carbon/organic matter and dehydroxylation of kaolinite, which might applied in coal gangue industry in future.
In the present study, co-liquefaction potential of Elbistan lignite and Balikesir olive bagasse were investigated by direct coal liquefaction process. The olive bagasse is a cheap and abundant biomass, so it is used to decrease the cost of oil production from the lignite. The effect of blending ratio of the lignite and the olive bagasse on liquefaction conversion and oil yield were investigated. Characterization studies of the starting materials were done using XRD, FTIR, DTA/TG and elemental analysis. Elemental compositions of liquefaction products were also determined and the composition of the obtained oil was identified by GC/MS. DTA and TGA results indicated the synergistic effect of the lignite and the olive bagasse and maximum oil conversion (36 %) was obtained from 1:3 blending ratio of lignite: olive bagasse. The results showed that the obtained oil was paraffinic-low waxy oil with 22.5 MJ/kg of calorific value and 95 g/cm³ density.
Coal is the most abundant fossil fuel containing sulfur and other elements which promote environmental pollution after burning. Also the silicon impurities make the transportation of coal expensive. In this research, two isolated fungi from oil contaminated soil with accessory number KF554100 (Fusarium oxysporum FE) and KC925672 (Exophiala spinifera FM) were used for heterotrophic biological leaching of coal. The leaching were detected by FTIR, CHNS, XRF analyzer and compared with iron and sulfate released in the supernatant. The results showed that E. spinifera FM produced more acidic metabolites in growing cells, promoting the iron and sulfate ions removal while resting cells of F. oxysporum FE enhanced the removal of aromatic sulfur. XRF analysis showed that the resting cells of E. spinifera FM proceeded maximum leaching for iron and silicon (48.8, 43.2 %, respectively). CHNS analysis demonstrated that 34.21 % of sulfur leaching was due to the activities of resting cells of F. oxysporum FE. Also F. oxysporum FE removed organic sulfur more than E. spinifera FM in both growing and resting cells. FTIR data showed that both fungi had the ability to remove pyrite and quartz from coal. These data indicated that inoculations of these fungi to the coal are cheap and impurity removals were faster than autotrophic bacteria. Also due to the removal of dibenzothiophene, pyrite, and quartz, we speculated that they are excellent candidates for bioleaching of coal, oil, and gas.
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.
A chloride salts medium was evaluated in biodesulfurization processes of a Colombian coal (2.34% total sulfur: 1.34% as pyritic, 0.90% as organic and 0.10% from sulfates), employing a consortium of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The process was carried out at three pulp concentrations (9.09%, 16.67% and 23.08%) and was compared with assays under similar conditions but containing modified T&K medium. All the tests were determined by measuring changes in soluble iron, pH, redox potential and microbial populations approach. Original and treated coal was analyzed by scanning electron microscopy with an energy-dispersive X-ray (SEM-EDX). For bioassays with chloride salts medium, the results showed above 70% of pyritic sulfur oxidation after 12 days, regardless of pulp concentration in contrast with results obtained for bioassays with a T&K modified medium where pulp concentration had influence and the pyrite oxidation was lower (below 55%).
Background: Sulfur oxides released from the burning of oil causes severe environmental pollution. The sulfur can be removed via the 4S pathway in biodesulfurization (BDS). Immobilization approaches have been developed to prevent cell contamination of oil during the BDS process.
Objectives: The encapsulation of Rhodococcus erythropolis R1 in calcium alginate beads was studied in order to enhance conversion of dibenzothiophene (DBT) to 2-hydroxy biphenyl (2-HBP) as the final product. Also the effect of different factors on the BDS process was investigated.
Materials and Methods: Calcium alginate capsules were prepared using peristaltic pumps with different needle sizes to control the beads sizes. Scanning electron microscopy and flow cytometry methods were used to study the distribution and viability of encapsulated cells, respectively. Two non-ionic surfactants and also nano Ƴ-Al2O3were used with the ratio of 0.5% (v/v) and 1:5 (v/v) respectively to investigate their BDS efficiency. In addition, the effect of different bead sizes and different concentrations of sodium alginate in BDS activity was
studied.
Results: The 2% (w/v) sodium alginate beads with 1.5mm size were found to be the optimum for beads stability and efficient 2-HBP production. The viability of encapsulated cells decreased by 12% after 20 h of desulfurization, compared to free cells. Adding the non-ionic surfactants markedly enhanced the rate of BDS, because of increasing mass transfer of DBT to the gel matrix. In addition, Span 80 was more effective than Tween 80. The nanoƳ-Al2O3 particles could increase BDS rate by up to two-folds greater than that of the control beads.
Conclusions: The nano Ƴ-Al2O3 can improve the immobilized biocatalyst for excellent efficiency of DBT desulfurization. Also the BDS activity can be enhanced by setting the other explained factors at optimum levels.
Keywords:Immobilization; Nano particles; Alginate; Flow Cytometry; Optimization
Polycyclic aromatic hydrocarbons (PAHs) are toxic environmental pollutants that are known or suspected carcinogens or mutagens. Bioremediation has been used as a general way to eliminate them from the contaminated sites or aquifers, but their biodegradation is rather limited due to their low bioavailability because of their sparingly soluble nature. Surfactant-mediated biodegradation is a promising alternative. The presence of surfactants can increase the solubility of PAHs and hence potentially increase their bioavailability. However, inconclusive results have been reported on the effects of surfactant on the biodegradation of PAHs. In this work, surfactant-mediated biodegradation of PAHs is reviewed.
The kinetics of ferrous ion oxidation by Leptospirillum ferriphilum were studied in continuous culture with a focus on the effect of solution pH (pH 0.8–2.0), assuming that the effect of pH on cell metabolism can be independently studied of reactor context and other reactions common in bioleach heaps. A simplified competitive ferric ion inhibition model and the Pirt Equation were used to analyze the experimental data. The results showed that the maximum specific activity of L. ferriphilum has a symmetrical bell-shaped curve relationship with pH. The maximum specific ferrous-iron oxidation rate, q Fe 2 + max gave a highest value of 14.54 mmol Fe 2+ (mmol C h) − 1 at pH 1.3, and was described by a quadratic function. The steady state carbon biomass in the reactor and the apparent affinity constant, K′ Fe 2 +, also increased with increase in pH; however, a slight increase in the carbon biomass was observed beyond pH 1.6. The results also showed that ferric ion precipitation is significant beyond pH 1.3 and about 13% total iron from the feed was lost at pH 2.0. The maximum biomass yield increased linearly with pH, while the culture maintenance coefficient was significantly small in all experiments and was minimum at pH 1.3. The values are indicative of actively growing chemostat cultures. This study shows that microbial ferrous ion oxidation by L. ferriphilum may be sustained at pH lower than pH 0.8 as the microbial activity is much higher than reported values for common mesophilic acidophiles. This may have implications on how bioleach heap operations can be started-up to improve metal recovery.
Three different types of coal were taken for microbial desulphurisation experiments using isolated cultures of Thiobacillus ferrooxidans. The samples were milled and then sieved. The effect of various parameters on microbial desulphurisation of three different coals such as particle size, pH, pulp density, media composition and contact time was studied. The conditions were optimised for the maximum removal of sulphur (91.81 wt% for Rajasthan lignite, 63.17 wt% for Polish bituminous coal and only 9.41 wt% of Assam coal).
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.
Iron is a key element influencing bacterial growth, oxidation efficiency and precipitate formation for most industrial applications using bioleaching and biooxidation processes. In this study, iron oxidation by an enrichment culture dominated by Leptospirillum ferriphilum was studied in a simulated heap leaching solution containing (g/L); Fe2+ (20); Mn2+ (3); Mg2+ (4); Al3+ (0.1); Na+ (3.6); Ca2+ (0.6). Initially, studies were conducted in batch bottles at 25 °C in order to determine possible toxicity effect and settling properties of precipitates produced at different pHs. Settling characteristics including interface height, zone settling velocity and sludge volume index were determined. The precipitates had good settling ability. Thereafter, a continuous-flow fluidized-bed reactor (FBR) was operated at 37 °C. The percent iron oxidation in the FBR decreased gradually from 98.5% to around 60% within 20 d due to precipitate formation. After installing a gravity settler to the recycle line of the FBR, the iron oxidation rate increased from 2 to 4 g Fe2+/L·h within 15 d. The maximum Fe2+ oxidation rate was 10 g Fe2+/L·h at a HRT of 2 h and optimum oxidation performance was achieved at a loading rate of 10.7 g Fe2+/L·h. The oxygen mass transfer limited the Fe2+ oxidation corresponding to an oxygen transfer rate of 35 kg O2/m3·d. This study reveals that a FBR combined with a gravity settler in the recycle line has potential for Fe3+ regeneration in heap leaching of sulfidic minerals.
A native isolate, 9C, identified as Rhodococcus ruber (Genbank Accession number – KY029073) was studied for dibenzothiophene degradation and subsequent bio-desulphurization of three different sulphur bearing materials (NE coal containing organic sulphur; lignite containing pyritic sulphur and a calcined petroleum-coke) of Indian origin. The isolate could degrade 0.25 mM DBT through the 4S pathway within 7 days. Preliminary studies for sulphur removal using the 9C isolate indicated NE coal to be more amenable (29% sulphur removal) followed by Lignite (15.87%) and CPC (14.83%) respectively. Characterization through XRD and FTIR along with the proximate and ultimate analysis of all the samples provided more insights into the changes in calorific values as well as the chemical constitution of the samples following microbial treatment. Owing to the amenability of NE coal, the effect of time, size fraction and pulp density were optimized. The best bio-desulphurization conditions for NE coal indicated 36% total sulphur removal (organic–53%, pyritic–18% and sulphate sulphur–14% respectively). Analytical characterization studies confirmed that the energy value of the NE coal was not affected due to biodesulphurization, rather it contributed towards an increase in gross calorific value from 6698 cal/g to 6812 cal/g following microbial treatment.
Mineral contents in two Zhundong coals and PRB coal were determined by XRF (X-ray fluorescence), XRD (X-ray diffraction) and TG-DSC (thermo gravimetry–differential scanning calorimetry). Effect of ashing temperature was assessed by comparing ash element compositions and mineral patterns at three temperature levels. Element compositions of the ashes showed that Zhundong coals have higher slagging and fouling tendency than PRB coal. It was also found that quartz and kaolinite are main mineral patterns in Zhundong coals and PRB coal. Quartz barely changes with ashing temperature because of its high reaction and melting temperature. Kaolinite begins to dehydrate at ~673 K and then decomposes as temperature further increases. The mineral patterns strongly depend on ashing temperature because of the different reactions among minerals. Based on the mineral pattern and transformation analyses using TG-DSC, calcite was the main form of calcium in one Zhundong coal, while anhydrate was the main form of calcium in the other Zhundong coal and PRB coal.
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.
This is a review of hydrophobic agglomeration methods to be used for fine particles in water suspensions. The hydrophobic interaction as a consequence of the hydrogen-bonding energy of water molecules, in the vicinity of hydrophobic particles, is discussed. The pattern of the growth of agglomerates is essentially determined by hydrodynamic forces. The thermodynamic model of both the surfactant salts and the oil droplets adhesion is based on the free energy balances. The role of binding liquid in spherical agglomeration of natural hydrophobic minerals is described. The spherical agglomeration of salt-type mineral suspensions is achieved at the critical surfactant concentration, which corresponds to the precipitation and adhesion of surfactant salt. The solubility differences of surfactant salts permit the selective separation of barite from carbonate suspension.
The lignite coal collected from Shengli coalfield of Inner Mongolia Autonomous Region in China contains about 5.22% by mass total sulfur with a gross calorific value of 6329 cal g−1. In the present work, the coal sample was subjected to desulfurization by using a new bacterium isolated from the native coal mine site. The native bacterium was identified to be Sinomonas flava XL4 based on the 16S rDNA gene sequence analysis, and reported first time for the capability to remove about 44% of total sulfur from the lignite coal. The influence of various process parameters such as medium pH, incubation time, pulp density, particle size, incubation temperature on sulfur removal from the lignite after S. flava XL4 treatment was investigated, and the experimental results showed that the total sulfur content of lignite coal was reduce to 2.92% under optimum reaction conditions. In addtion, the calorific value of lignite coal after bacterium desulfurization increased from 6329 to 6678 cal g−1, and the ash content was eliminated. © 2015 American Institute of Chemical Engineers Environ Prog, 2015
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.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Microbe–mineral interactions are very pervasive in nature. Since coal is a chief source of nonrenewable energy and finds its application in a wide variety of sectors, the importance of microbe–mineral interaction is indispensible for developing a sustainable microbial coal biotechnology. The underlying necessity of microbe–mineral interaction is also linked with acid mine drainage that is a universal environmental problem in iron- and sulfur-rich environments. In the view of the fact that microbes act as a storehouse of several novel biomolecules or enzymes, they can be used for bioprocessing on an industrial scale incorporating innovative ideas and advanced technologies. The coal mines comprise of several synergistic interactions occurring between microbes and minerals which vary according to pH, temperature, mineralogy, and metal concentration, ultimately forming a viable microbial community.
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.
Dumping of low-grade chalcopyrite encompasses several environmental problems. Despite slow dissolution rate, meso-acidophilic bioleaching is preferred for the extraction of copper from such ores. In the present study, meso-acidophilic bioleaching of a low-grade chalcopyrite in presence of an acid-processed waste newspaper (PWp) is discussed for the first time. The study illustrated a strong catalytic response of PWp with enhanced bio-recovery of copper from acid-conditioned chalcopyrite. A maximum of 99.13% copper recovery (0.36% Cu dissolution/day) was obtained in 6 days of bioleaching in presence of 2 gL- 1 PWp in contrast to only 5.7% copper in its absence. FTIR analysis of bioleached residues revealed similar spectral patterns to the original acid-conditioned ore in presence of PWp, thus indicating less development of passivation layer which was also confirmed through a complementary raman characterization of the bioleached residues. Further, a reaction mechanism (chemistry) was proposed suggesting the possible role of PWp as the electron donor under oxygen limiting conditions which facilitated microbial reduction of Fe (III). The resulting biochemical changes provided an energy source for the bacteria, thus allowing free flow of electrons through the ore surface, thus contributing towards enhanced bioleaching of copper.
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.
Energy is an essential factor to achieve sustainable development. So, countries striving to this end are seeking to reassess their energy systems with a view towards planning energy programmes and strategies in line with sustainable development goals and objectives. As would be expected, the rapid expansion of energy production and consumption has brought with it a wide range of environmental issues at the local, regional and global levels. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases. Turkey is an energy importing country with more than half of the energy requirement being supplied by imports, and air pollution is becoming a great environmental concern in the country. On the other hand, Turkey's geographical location has several advantages for extensive use of most of the renewable energy sources. In this regard, renewable energy resources appear the most efficient and effective solutions for clean and sustainable energy development in Turkey. This paper provides an overview of global energy use and renewables for clean and sustainable energy policies in Turkey.
Thermal analysis, i.e. TGA/DTA is used to study the changes in the combustion behaviour of microbially treated coals. In view of their high sulphur content and industrial significance three samples are under consideration, i.e. one lignite and two subbituminous from different region in Bulgaria. The differences in burning profiles can be related to structural changes resulted from biological treatments. The overall biological treatment generates these changes probably due to the oxidation process. Concerning organic sulphur biodesulphurization there is no change in any drastic manner of the thermal characteristic parameters. In general, applied biotreatments provoke a complex influence on combustion coal behaviour. From one side a better ignition performance, a minor decrease in higher heating value and diminishing peak temperature of maximum weight loss rate for all biotreated samples are observed. From other side some decrease in the combustibility indicated by an increase in the combustion time and the end of combustion temperature are obvious. Also well determined decrease of self-heating temperature after biotreatments evolves high risk of spontaneous unmanageable coal combustion.
Meso-acidophilic bacterial leaching of ball mill spillage (containing chalcopyrite >80%) was carried out in an innovative two-step bioleaching method. The major drawback of meso-acidophilic bioleaching limiting industrial application is the passivation phenomenon over the ore surfaces in iron-sulfur rich environments. In the present study, we present a novel wash solution that efficiently removed the passivation layer. FTIR characterization of the bioleached sample indicated that the residues could be further leached to recover extra copper after wash solution application. XRD study indicated accumulation of sulfates (SO(4)(-)) of Na, K, Fe and oxy hydroxides of iron [FeO(OH)] in the form of jarosite outlining the passivation layer. SEM, FESEM-EDS studies indicated severe corrosion effects of the wash solution on the passivation layer. Two step bioleaching of the ore sample yielded 32.6% copper in 68days in the first interlude and post wash solution application yielded 10.8% additional copper.
Relationships of ultimate and proximate analysis of 4540 US coal samples from 25 states with gross calorific value (GCV) have been investigated by regression and artificial neural networks (ANNs) methods. Three set of inputs: (a) volatile matter, ash and moisture (b) C, H, N, O, S and ash (c) C, H exclusive of moisture , N, O exclusive of moisture , S, moisture and ash were used for the prediction of GCV by regression and ANNs. The multivariable regression studies have shown that the model (c) is the most suitable estimator of GCV. Running of the best arranged ANNs structures for the models (a) to (c) and assessment of errors have shown that the ANNs are not better or much different from regression, as a common and understood technique, in the prediction of uncomplicated relationships between proximate and ultimate analysis and coal GCV.
In this study, the lignite was improved oxidizing sulfur compounds by Thiobacillus thiooxidans and Thiobacillus ferrooxidans bacteria. Experiments in the batch reactors have been carried out 20% aqueous suspension of coal samples. Sugar beet molasses was used as the bacterial substrate. The maximum removal of combustible sulfur was obtained as 78.2% under the following conditions; addition 5% of T. thiooxidans and 5% T. ferrooxidans into coal suspension, 0.2 g molasses/g coal change, pH value of 3, at shaking rate of 70 rpm and at 40°C for 5 days.
Traditionally, the kinetics of microbial ferrous iron oxidation have been studied in continuous or in batch culture. Both methods have drawbacks: in continuous culture experiments have to be repeated at a number of dilution rates to cover the entire spectrum of ferrous to ferric ratios, which is time-consuming. Furthermore, experiments at very low ferric-to-ferrous ratios require high dilution rates which are close to or exceed those at which wash-out occurs. In batch experiments, on the other hand, the prevalent ferric to ferrous ratio rapidly changes due to substrate depletion while the microbial population continually grows, making determination of specific momentary rates difficult. The present paper describes initial work with a novel device, the Redostat™, which allows careful electrochemical control of ferric to ferrous ratio in a batch reactor. A culture of Leptospirillum ferriphilum was grown at 35 °C and 5 g dm− 3 total iron by maintaining the ferric to ferrous ratio at 0.17, 0.51 and 1.65 (corresponding to redox potentials of 419, 452 and 482 mV vs. Ag/AgCl), respectively. The correlation of data obtained from off-gas and current measurements was excellent, and fitted Monod kinetics with ferric inhibition. A hitherto unobserved effect indicates the onset of ferric iron inhibition at the low redox potentials employed here. It was also noted that the biomass concentration has an effect on the biomass specific ferrous iron consumption rate and the biomass yield on ferrous iron.
Due to the requirement of stringent rules for ultra-low sulfur content of diesel fuels, it is necessary to develop alternative methods for desulfurization of fossil fuel derived oil. Using appropriate oxidants and catalysts with the assistance of ultrasound irradiation, model compounds such as dibenzothiophene can be quantitatively oxidized in minutes. For diesel fuels containing various levels of sulfur content, and through the use of catalytic oxidation and ultrasonication followed by solvent extraction, removal efficiency of sulfur-bearing compounds can reach or exceed 99% in a short contact time at ambient temperature and atmospheric pressure. This simple approach can be the basis for obtaining ultra-low sulfur-containing diesel oil. GC-PFPD, GC–MS, and GC-SIMDIS were used to monitor the change of organic sulfur compounds and hydrocarbons in diesels during the process.
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.
Bioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non-sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.
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.
Many species of lactic acid bacteria (LAB) produce extracellular heterotype polysaccharides, the so-called heteropolysaccharides (HePS). Biosynthesis and secretion of the HePS from the LAB occur during different growth phases, and both the amount and type of the polymer is influenced by growth conditions. The total yield of exopolysaccharides produced by the LAB depends on the composition of the medium (carbon and nitrogen sources, growth factors, etc.) and the conditions in which the strains grow, i.e. temperature, pH, oxygen tension, and incubation time. It is never higher than 1.5 g of polymer dry mass per litre of fermentation medium. Whereas mesophilic strains produce maximal amounts of HePS under conditions not optimal for growth, the HePS production from thermophilic LAB strains is growth-associated, i.e. maximum production during growth and under conditions optimal for growth. The HePS degradation often takes place upon prolonged incubation of the HePS-producing LAB strains due to glycohydrolase activity. Primary, secondary, and tertiary modelling unravel the functionality of the HePS-producing LAB strains in a food environment. Finally, appropriate process engineering can lead to an industrial breakthrough of the HePS production and applications: a high and stable high-molecular-mass HePS production by appropriate feeding strategies through fed-batch cultivation on the one hand, and the application of a two-step fermentation process in yoghurt manufacture on the other hand.
Pyrite oxidation rates were examined under various conditions in the presence of A. ferrooxidans and L. ferriphilum, in which different pulp concentration, inoculation amount, external addition of Fe3+ and initial pH value were performed. It is found that A. ferrooxidans and L. ferriphilum show similar behaviors in the bioleaching process. The increasing pulp concentration decreases the leaching rate of iron, and external addition of high concentration Fe3+ is also adverse to leaching pyrite. The increased inoculation amount and high initial pH value are beneficial to leaching pyrite, and these changed conditions bring more obvious effects on leaching pyrite by L. ferriphilum than by A. ferrooxidans. The results also show that adjusting the pH values in leaching process baffles leaching pyrite due to the formed jarosite. Jarosite formed in leaching process was observed using XRD, SEM and energy spectrum analysis, and a considerable amount of debris with a crystalline morphology is present on the surface of pyrite. The results imply that the indirect action is more important for bioleaching pyrite.
A study of the kinetics of ferrous iron oxidation by a free suspended culture of the bacterium Leptospirillum ferriphilum in batch regime at moderate to high iron concentrations was conducted. A circulating bed airlift bioreactor was used in order to obtain reliable biokinetic data, unaffected by biofilm growth. The two major factors in consideration were the effects of the pH and the total iron concentration in the range of 5–40 g/L. The optimal pH was found between 1.05 and 1.80. In this range a strictly growth associated biooxidation with constant yield coefficient was proven, while at suboptimal pH values non-growth associated iron biooxidation was shown at pH as low as 0.4. This effect was taken into consideration for the derivation of a Monod-type kinetic model, derived on first principles from the electrochemical-enzymatic model for ferrous iron biooxidation. Our model shows a linear dependence between the apparent half-saturation constant (Kapp) and the total iron concentration in studied range of iron concentration.
A biodesulfurization process was carried out for two coals from the southwest of Colombia using a consortium of native microorganisms Acidithiobacillus ferrooxidans-like and Acidithiobacillus thiooxidans-like. Characterization techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM/EDX) and chemical analysis were used in order to establish the mineralogy of the process. The sulfur content in coals varies from 2.6% to 5.7%, and pyrite is the main sulphide present in the inorganic phase. Other minerals in the substrates include kaolinite, calcite, dolomite and quartz. An 85–95% reduction of pyritic sulfur and 31–51% of total sulfur in a period of 30 days were achieved, for a particle size of − 74 µm, 10% w/v pulp density and 30 °C.
Bioleaching is an economical method for the recovery of metals that requires low investment and operation costs. Furthermore, it is generally more environmentally friendly than many physicochemical metal extraction processes. The bioleaching of chalcopyrite in shake flasks was investigated with pure and mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, and Leptospirillum ferriphilum. The mixed cultures containing both iron- and sulfur-oxidizing bacteria were more efficient than the pure culture alone. The presence of sulfur-oxidizing bacteria positively increased the dissolution rate and the percentage recovery of copper from chalcopyrite. Mixed cultures consisting of moderately thermophilic L. ferriphilum and A. caldus leached chalcopyrite more effectively than mesophilic A. ferrooxidans pure and mixed cultures. The decrease of the chalcopyrite dissolution rate in leaching systems containing A. ferrooxidans after 12–16 days coincided with the formation of jarosite precipitation as a passivation layer on the mineral surface during bioleaching. Low pH significantly reduces jarosite formation in pure and mixed cultures of L. ferriphilum and A. caldus.
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.
Energy is one of the indispensable factors regarding the assurance of social prosperity and economic development of a country. The developing countries struggle to obtain energy sources reliable in the long term to complete their economic development, and the developed countries struggle to get them to keep their present prosperity levels. Coal seems to continue its indispensable position among the other energy sources for many years because of its production in more than 50 countries, the least effect it has from the price fluctuation and its usage lifespan of more than 200 years. The countries that are aware of it have investments in mining fields in the countries rich in coal reserves, and they continue investing considerable amount of money.In the projections of Turkey in 2020, the primary energy consumption is estimated to be 298Mtoe, the production is estimated to be 70Mtoe, the ratio of production to consumption will reduce to the level of 23.5%, and this situation will cause serious risks for sustainable development. In other words, Turkey will have to import 76.5% of the energy that it consumes in the 2020s. However, Turkey can reduce the rate of the external dependency to the level of 50% by using the hard coal reserve of 1.3 billion tons, the lignite reserve of 8.058 billion tons and renewable source of great potential.