Article

Effect of Span-80 and Ultrasonication on Biodesulphurization of Lignite by Rhodococcus erythropolis: Lab to Semi-pilot scale tests

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Abstract

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.

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The floatability of lignite is usually known to be very poor. Generally, surfactants are applied to improve its hydrophobicity in the flotation process. This research focuses on the adsorption performance of a nonionic surfactant, sorbitan monooleate, on the lignite particles with different densities, including −1.45 g/cm³, −1.80+1.45 g/cm³, and +1.80 g/cm³. From Fourier transform infrared spectroscopy results, it was obvious that organic oxygen functional groups determined the surface properties of lower density lignite, whereas inorganic Si-O determined the surface properties of higher density sample. Qualitative similarities are found in the curves of the surface electrokinetic potentials versus pH values. Points of zero charge of the samples were measured to be at pH values of 2.3, 3.0, and 3.0, respectively. Hence, organic oxygen functional groups are similar to Si-O on the coal surface in adsorbing OH– and H⁺ in electrolyte solution. The X-ray photoelectron spectroscopy results show that the lower density lignite particle has stronger adsorptions of sorbitan monooleate. In other words, organic oxygen functional groups have the priority over inorganic Si-O in adsorbing sorbitan monooleate. In addition, polar groups of the surfactant have different adsorbing abilities with organic oxygen functional groups. Interestingly, the oxygen content of +1.8 g/cm³ lignite nearly does not change after the pretreatment by sorbitan monooleate solutions. Therefore, the sorbitan monooleate molecule almost cannot adsorb on the mineral surface.
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In this study, low-rank lignite coal sample collected from Jining coalfield of Shandong province in China was subjected to desulphurization by using a new bacteria and Acidithiobacillus ferrooxidans isolated from the native coal mine site. The molecular identification of the 16S rRNA gene showed that the new native bacteria was Pseudomonas sp., denoted as NP22, and it is reported for the first time for the capability to remove about 46% of total sulphur from the lignite coal. In the present study, the effects of various parameters such as medium pH, incubation time, pulp density, particle size, incubation temperature on desulphurization from lignite coal with the Pseudomonas sp. NP22 and Acidithiobacillus ferrooxidans were investigated. Analytical characterization indicated that total sulphur content of lignite coal was reduced to 2.76% and 3.23% by using two microorganisms. Also, the calorific value of lignite coal was not affected adversely after two microorganisms' desulphurization but rather its calorific value increased from 6219 cal/g to 6406 cal/g and 6315 cal/g, however, the ash content of the lignite coal was eliminated.
Article
Microorganisms in a biofilter play important roles in the gas contaminants treatment process. In this study, thermophilic desulfurization bacteria were inoculated in a thermophilic biofilter for SO2 treatment after acclimation and enrichment. Molecular biology techniques were applied to detect temporal variation of microbial population during acclimation and biofilter start-up period. The acclimation temperatures were 50, 55, and 60 °C. Desulfurization bacteria dominated the enrichments. During acclimation, desulfurization bacteria and thermophilic bacteria increased from 36.84% to 78.95%–52.94% and 88.24%, respectively. In addition, the microbial diversity indices of these enrichments decreased with time. Substrate species and acclimation temperature influenced the microbial structure of the enrichments. The thermophilic biofilter inoculated with enrichments could achieve a rapid start-up, and over 80% of removal efficiency could be obtained within two weeks. The maximum elimination capacity was 38.71 g m−3 h−1 at 152 mg m−3 inlet concentration. The total sulfur bacteria proportion increased obviously during the start-up period. Moreover, desulfurization bacteria that originally existed in inocula, e.g., Pseudomonas putida, Bacillus thioparans, Microbacterium sp., and Thermoanaerobacteriaceae, were abundant in the thermophilic biofilter for SO2 removal.
Article
Atmospheric pressure-temperature programmed reduction coupled with on-line mass spectrometry (AP-TPR/MS) is used for the first time on microbiologically treated coal samples as a technique to monitor the degree of desulfurization of the various sulfur functionalities. The experimental procedure enables the identification of both organic and inorganic sulfur species present in the coal matrix. A better insight in the degradation of the coal matrix and the accompanying processes during the AP-TPR experiment is obtained by a quantitative differentiation of the sulfur. The determination of the sulfur balance for the reductive pyrolysis gives an overview of the side reactions and their relative contribution in the total process. The volatile sulfur species are unambiguously identified using AP-TPR off-line coupled with gas chromatography/mass spectrometry (GC/MS). In this way, fundamental mechanisms and reactions that occur during the reductive pyrolysis could be quantified, explaining the differences in AP-TPR recoveries. Therefore, this study gives a clearer view on the possibilities and limitations of AP-TPR as a technique to monitor sulfur functionalities in coal.
Article
For an efficient operation in biodesulfurization of petroleum and related fuels, the aqueous solubility of insoluble or very slightly soluble sulfur compounds contained in the petroleum products has to be increased. In this study, polyoxyethylene nonionic surfactants were used in order to enhance the aqueous solubility of insoluble or very slightly soluble sulfur compounds contained in the bunker-C oil and the solubilized sulfur contents in the aqueous surfactant solutions were measured by X-ray sulfur spectrophotometer. The most hydrophobic surfactant used during this study showed the maximum solubilization capacity for sulfur compounds contained in the bunker-C oil and the solubilization of sulfur compounds was found to increase with temperature and to be abruptly increased at above 5 wt % surfactant concentrations. It was found that Tergitol series surfactants showed higher solubilizing capacity than Neodol series surfactants presumably due to the disruption of the regular packing in the hydrocarbon region of the surfactant micellar aggregates and that the addition of a cosurfactant and/or an electrolyte increased the solubilization of sulfur compounds in the bunker-C oil. It was also shown that partitioning phenomena were shown to be significant with a hydrophobic surfactant especially at high temperature and pH of the Tergitol surfactant solution did not affect the solubilization of sulfur compounds. The growth of M6 sulfur-reducing bacteria was not greatly affected by the addition of both nonionic surfactant and cosurfactant. Desulfurization experiments with M6 sulfur-reducing bacteria showed that the biodesulfurization rate of bunker-C oil was enhanced with addition of nonionic surfactant and these data suggested the potential applicability of surfactant to the actual biodesulfurization system.
Article
Studies on the desulfurization of three or more ringed-compounds, which are considered to inhibit biodesulfurization of crude oil, are rare. In this paper, desulfurization of a three-ringed compound benzo[b]naphtho[2,1-d]thiophene (BNT) by an isolated strain Gordonia sp. IITR100 is described. The bacterium mediates desulfurization of BNT and utilizes the released sulfur for its growth. The reaction is accompanied with the formation of metabolites BNT-sulfone and BNT-sulfinate, in addition to the reported BNT-hydroxide. Recombinant E. coli cells, harboring DszC or DszA, were also able to mediate the metabolism of BNT to BNT-sulfone, or of BNT-sulfone to BNT-sulfinate, respectively. Desulfurization of BNT, both by IITR100 and E. coli-DszC cells was strongly inhibited in the presence of dibenzothiophene. The results are discussed in the context of the biodesulfurization of petroleum fractions where several organosulfur compounds are present together.
Article
Microwave heating has been used in desulfurization of coal. Removal of organic sulfur and organic sulfur forms alterations of Xishan (XS) coal and Yunnan (YN) coal was investigated under microwave and ultrasonic irradiation. The results showed the optimum conditions for desulfurization were 50 min and 560 W for microwave and ultrasound for both coals. The desulfurization rate was maximum 23.53% for XS coal and 76.58% for YN coal. The effect of combining microwave and ultrasonic irradiation on desulfurization was stronger than simple microwave irradiation. The content of sulphone sulfur in coal was increased from the XPS after microwave and ultrasonic co-enhanced oxidative desulfurization.
Article
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.
Article
Organic sulfur components of the petroleum are too resistant to be removed by the conventional desulfurization processes. This study aimed to investigate the removal of dibenzothiophene (DBT) as an organic sulfur compound, from the oily phase by a bioprocess employing the immobilized cells.Rho-dococcus erythropolisR1 cells were encapsulated in calcium alginate beads by considering factors such as the alginate concentration, size of the beads, the concentration of surfactants andƔ-Al2O3nano particles for optimizing biodesulfurization (BDS) via Taguchi approach. The impact of two cofactor precursors (nicotinamide and riboflavin) on the long term BDS efficiency was also examined. The results indicated that the optimum factor levels for the bigger is better criterion could be achieved at 20% (w/w) ofƔ-Al2O3 nano particles, alginate beads size equal to 1.5 mm, 1% (w/v) of the alginate and 0.5% (v/v) of span 80. The related statistical analysis showed that the concentration ofƔ-Al2O3nano particles was the most sig-nificant factor in the BDS process. Moreover, the addition of nicotinamide and riboflavin significantly decreased the biocatalytic inactivation of the immobilized cells system after successive operational steps enhancing the BDS efficiency by more than 30% after four steps. It can be concluded that a combination of the nanoƔ-Al2O3particles with alginate immobilized cells could be very effective in biodesulfurization process.
Article
Acid leaching is an alternative to the conventional stabilization of ash by carbonatization or polymer induced coagulation/flocculation [1-3]. It has also been suggested that ash can replace limestone in biohydrometallurgical processing [4, 5]. Dissolved metals can be recovered from the effluent in the downstream stages of a bioleaching process. Metals extracted at delocalized units, i.e., in separate acid leaching processes, precipitated and shipped to the main biohydrometallurgical plant as hydroxides or sulfides. The above scenario is threefold beneficial: (i) it saves limestone in the hydrometallurgical processing of sulfidic minerals, (ii) it recycles metals and (iii) it creates an inert solid ash residue. All three come with economic as well as environmental gains. The acid consumption in ash/water slurries (pH 1.0, initial S/L ratio 1:10) starts at a modest 5 L 1 M H2SO4 per kg dry peat fly-ash and reaches 15 L /kg for bottom-ash from the combustion of wood chips and 18-24 L/kg for ash from lignites [4, 5]. Mn and Mg are regularly leached to near unity, but the yields of other dominant elements - K, Na, Al and Fe - vary, probably due to the presence of stable oxides. The current work shows the time dependencies of acid consumption and elemental compositions in the aqueous phase for four ashes and the kinetics of acid consumption of an additional 10 coal-ashes and whole coals. Time dependent studies can link acid consumption to the dissolution of major ash components and correlate trace element extraction to the destabilization of certain major phases [6]. This is the topic of a subsequent paper [7]. The current work forms a platform to
Article
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.
Article
Control of air pollution originating from sulfur oxide emissions has gotten increasing attention in Turkey during the past decade. Consequent upon serious episodes of air pollution in the capital city, Ankara, and in several other Anotolian cities, it is now clear that the prime cause of pollution is the burning of high-sulfur Turkish lignites for space heating. Furthermore, the Transboundary Air Pollution Control International Act stipulates that sulfur oxide emissions from power plants must be lowered drastically as we approach the end of the century. One method of controlling sulfur oxide emission is by desulfurization of coals prior to combustion. Among the methods available, bacterial desulfurization prior to coal combustion seems promising for the future in many respects. The common method of testing microbial desulfurization is by using shake flask cultures. Several factors are reported to affect the rate and extent of bacterial desulfurization.
Article
Modes of distribution of sulphur have been determined in eleven lignite samples from major reserves in Turkey. Total sulphur contents have been found to vary 0.91%–10.32% on dry basis. The lignites contain relatively high amounts of organic sulphur. Distributions of sulphur have been determined in chars from the pyrolysis of lignites at 440 °C. Reductions in combustible sulphur contents have been found to vary 15.7%–72.0%. No correlation has been found between the extent of desulphurization by pyrolysis and the relative amounts of forms of sulphur in the parent lignites.
Article
The extractive desulfurization of four high sulfur coals from China were promoted with ultrasonic and microwave in tetrachloroethylene organic solvents. It was shown that the joint promotion with ultrasonic and microwave had an active effect on extractive desulfurization. The rate of desulfurization increased with the increase of time in ultrasonic field as well as with the power of ultrasonic, but declined with the increase of the particle size of coal. The rate of desulfurization was not identical for different coal, which was perhaps related to the existed forms of organic sulfur in coal.
Article
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.
Article
The effects of surfactants on dibenzothiophene (DBT) degradation by Corynebacterium sp. ZD-1 were investigated in hydrocarbon aqueous biphasic (O/W) systems in shake flask. Among Brij-35, Tween-80, Triton-100X and β-cyclodextrin, Tween-80 was a suitable surfactant to improve the desulfurization rate of dibenzothiophene. The amount of 2-hydroxybiphenyl (2-HBP) formed with Tween-80 present was about 50% more than that formed without surfactant. The results demonstrated that Tween-80 could improve the mass transfer of DBT between organic and aqueous phases, and could be used in dibenzothiophene biodesulfurization systems.
Article
Short-term water solubility characteristics of bottom ashes and fly ashes from two important Turkish lignites were investigated in association with the concentrations of some heavy metals. For this, the alkaline ashes were interacted with acidic rain water and dilute acidic solutions for leaching times changing from 10 min to 2 days to assess the mobilization potential during ash–water interactions. The concentrations of leachable trace elements such as chromium, lead, cadmium, zinc, and nickel were determined in leachate using Atomic Absorption (AA) Spectrometry. Iron concentrations were also investigated since it plays a critical role on trace element enrichment mechanism. The mineralogical and structural identification of the parent ash samples were carried out by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. The extent of the mobility of the ashes was identified regarding the physical and chemical properties of the ashes. Concentrations of the trace elements in leachates were compared to the several guideline values regulating the maximum contaminant levels in drinking water and irrigation water as well as the regulatory threshold concentrations in leachate.
Article
Bioremediation processes based on biofilms are usually very effective. The presence of (bio)surfactants in such processes can increase bioavailability of hydrophobic pollutants in aqueous phase. However, surfactants can affect the biofilm as well as individual microbial cells in different ways. Biosurfactants produced by a microbial population can be involved in the final structure of biofilm. An external application of synthetic surfactants or 'foreign' biosurfactants often results in partial or complete destruction of the biofilm and their high concentrations also have a toxic effect on microbial cells. Finding a suitable surfactant and its concentration, which would minimize the negative effects mentioned above, would allow to construct effective bioremediation processes using the benefits of both the biofilm and the surfactant. In this context, G(+) bacterium Rhodococcus erythropolis, which has a wide potential for biodegradation of aromatic compounds, was studied. High surface hydrophobicity of its cells, given mainly by the presence of mycolic acids in the cell envelopes, allows formation of stable biofilms. Three synthetic surfactants (Spolapon AOS 146, Novanik 0633A, Tween 80) and rhamnolipid isolated from Pseudomonas aeruginosa were used. Changes in initial adhesion and biofilm formation caused by the surfactants were monitored in a flow cell equipped with hydrophilic/hydrophobic carriers and analyzed by image analysis.
Article
Artificial neural networks procedures were used to predict the organic and inorganic sulfur reduction from coal using mixed culture consisted ferrooxidans species extracted from coal washery tailings, for pyritic sulfur, and Rhodococcus species, extracted from oily soils, for the organic sulfur removal. The particle size, pulp density, initial pH, shaking rate, leaching time and temperature, in pyritic sulfur removal prediction, and pulp density, shaking rate, leaching time and temperature, in organic sulfur removal prediction, were used as inputs to the network. Feed-forward artificial neural networks with 4-8-4-1 and 3-5-6-1 arrangements, were capable to estimate organic and inorganic sulfur removal, respectively. The outputs of the models were percentage of organic and inorganic sulfur reduction. It was achieved quite satisfactory correlations of R2 = 1.00 and 0.98 in training and testing stages for pyritic sulfur removal prediction and R2 = 1.00 and 0.97 in training and testing stages, respectively, for organic sulfur removal prediction. The proposed neural network models accurately estimate the effects of operational variables in organic and inorganic desulphurization plants and can be used in order to optimize the process parameters without having to conduct the new experiments in laboratory.
Article
The raw coal from the Çayirhan mine, Beypazari basin, Turkey contains an average of 28.5% mineral matter, consisting up to 80% zeolites. The coal seam is split by a 1-m-thick tuffaceous siltstone into the upper, first (Tv) and lower, second (Tb) seams, which contain essentially different zeolites. The first seam contains Ca-rich zeolites (clinoptilolite/heulandite) whilst the second seam contains Na-rich zeolites (analcime). Experimental work has shown that a Na-rich activation solution will produce Na-rich zeolites when the original volcanic glass is Na-rich, but will produce Ca-rich zeolites when the volcanic material is Ca-rich. It is thought that a Na-rich activation solution, derived from contemporaneous volcanics in the Beypazari basin, reacted with volcanic tuffs of different chemical composition to produce the vertical variability in the mineral matter of the two seams. Trace element analyses of the raw coal showed that they are enriched in As, B, Cr, Ni and Zr when compared to world-wide averages of coal. They are also enriched in the major elements Na and K. These elements are probably also derived from a volcanic source. Barium and Sr show a clear affinity for analcime, whilst Li, Cr, Ni, Cu, Zn, Co and Ga show a clear affinity for clinoptilolite/heulandite. Trace elements showing a positive correlation with the organic matter are Mn, B, Be, Ge, Y, Zr, Nb, Hf, W and U. Manganese, U, Th, Sc, Ge and HREE (heavy rare earth elements) show correlations with phosphate. Trace elements showing correlation with both Fe and S contents are Co, Mo, Ta, Pb and IREE (intermediate rare earth elements). Arsenic and V seem to have mixed affinities with sulphides and zeolites, and organic matter and zeolites, respectively. Although a proportion of the As, B and S are retained in the ash during coal combustion, due to the sorption mechanism of CaO derived from the clinoptilolite/heulandite decomposition, significant emissions of these elements may arise from the Çayirhan thermal power station due to the anomalously high concentrations of these elements in the Beypazari coal. The high total alkali metal content of these coals exceeds the recommended maximum for steam coal, but it is believed that sodium occurring in a mineralogical form such as analcime is not as likely to contribute to boiler fouling as organically-associated sodium.
Article
Arthrobacter sp. P1-1 was isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated site in Hilo, HI, USA. This strain can degrade approximately 82% of dibenzothiophene (DBT) (40 mg l−1) and 57% of carbazole (CBZ) (40 mg l−1) in 14 days incubation. Dibenzothiophene-5,5′-dioxide was formed from sulfur oxidation of DBT. Dibenzothiophene diols that were transformed from 1,2- and 3,4-dioxygenations of DBT underwent ortho- and meta-ring cleavages to produce benzo[b]thiophene-2,3-dicarboxylic acid and hydroxyl-benzo[b]thiophene carboxylic acid, respectively. These products were converged into benzo[b]thiophene-2,3-diol, which was further transformed to 2,2′-dithiosalicylic acid via 2-mercaptobenzoic acid. These results indicate that strain P1-1 has diverse lateral dioxygenase systems and subsequent metabolic enzyme systems. The five detected CBZ metabolites by strain P1-1 were 4-(3-hydroxy-1H-indol-2-yl)-2-oxobut-3-enoic acid, 2-(2-carboxy-vinyl)-1H-indole-3-carboxylic acid, pyrido[1,2-a]indole-6,10-dione, indole-2,3-dicarboxylic acid, and 2-aminobenzoic acid. The results suggest that CBZ degradation underwent 3,4-dioxygenation followed by ortho- and meta-ring cleavage.
Article
The distribution of trace elements in the lower Eocene coal seam mined in the Yeniceltek, Kucukkohne and Ayridam coal mines from the Sorgun Basin was investigated in relation to ash content and maceral composition. The coal seam is mainly composed of huminite. In the present study, 35 samples from five seam sections were collected on the basis of megascopic characteristics. Results were determined using an energy dispersive polarised X-ray fluorescence (EDP-XRF) spectrometer on a whole-coal dry basis. Most of the major and trace elements studied are enriched in high-ash samples, while Ba, Br, Mn and W show relative enrichments in low-ash samples. Most of elements studied, such as Ga, Ce, La, Th, Nb, Rb, Zr, V, Cu, U, Pb, Sb, Cs, Sn, Cr, Se, Y and Zn, are primarily associated with mineral matter (clay minerals). Arsenic and a part of Zn, Se and Sb are probably concentrated in pyrites in the samples. Element concentrations show statistically significant negative correlations with many macerals and positive relationships with only attrinite that is mainly mixed with mineral matter (clay minerals and small quartz grains) in the samples. Nine trace elements (As, Cr, Mn, Ni, Pb, Sb, Se, Th and U), considered as potentially Hazardous Air Pollutants, are present in low to moderate concentrations. The mean values of trace element concentrations display relative enrichments in Se (2.8 ppm), Th (21 ppm) and W (26 ppm) in the investigated samples in comparison with other coals in the world.
Article
Coal mining and processing activities in Russia result in the generation of huge quantities of wastes containing elevated concentrations of residual S (Sdt=2.1–9%), C (Cdo > 12%), heavy metals and other hazardous elements. These wastes which are usually piled or dumped without specific care close to mining sites and processing plants are subjected to adverse climatic conditions and in most cases cause severe impacts to various receptors. The worst impacts, in Russian mining and disposal areas, are due to the oxidation of the residual sulfide phases and the generation of coal mine drainage, with pH often ranging between 2.5 and 4. These acidic leachates contaminate severely soils, surface- and groundwater; therefore the risk for humans and ecosystems in these sites is considered as extremely high.The present paper examines the feasibility of thermal treatment of high sulfur coal wastes, in particular those containing elevated content of carbon, kaolin and iron, in order to reduce environmental risk at the disposal sites and produce saleable by-products. Carbon reduces substantially fuel consumption while kaolin and iron assist the formation of secondary products. Parameters studied include temperature and air excess ratios, up to 1400 °C and 1.4 respectively. Coal wastes were subjected to thermal treatment (a) as such, in order to study the removal of sulfur and the production of saleable products (sulfuric acid, various construction materials, products with high magnetic susceptibility, aluminum sulfate) and (b) after mixing with calcium carbonate in order to study the fixation of sulfur in multi-mineral phases possessing binding properties. Prior to implementation of laboratory experiments in order to assess the potential of thermal treatment, thermodynamic calculations were performed to determine optimum operating parameters and possible phase transformations.
Article
Biodesulphurization experiments were carried out with Tunçbilek lignite, characterized by high sulfur content (2.59%) by using Trametes versicolor ATCC 200801 and Phanerochaete chrysosporium ME 446. At fungal biomass studies, the effects of various parameters on fungal desulphurization of coals such as pH, temperature, pulp density, incubation time, and sterilization were investigated for both microorganisms. The maximum desulphurization (40%) was observed after 6 days of incubation at 35 °C for T. versicolor. The optimum pH was measured at 6, and the agitation rate was fixed at 125 rpm. The pulp density was found as 5% (w/v) for the high extent of desulphurization. Also, calorific value did not change during this experiment. However, the ash and metal contents of coal were eliminated.
Article
Sulfur emission from coal combustion presents many environmental problems. It is believed that the best method to limit the amount of sulfur oxides emitted into the atmosphere is to reduce the amount of sulfur in coal before combustion. The techniques used 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 coal biodesulfurization processes is reviewed. The barriers for biodesulfurization processes to scale up to commercial applications are highlighted. In addition, the future needs of research for the development of efficient biodesulfurization processes are included.