Aortite inflammatoire au cours de la maladie de Horton : à propos de 4 cas

Fuel 158 (2015) 572–581

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Petrological and biological studies on some fly and bottom ashes collected at different times from an Indian coal-based captive power plant Binoy K. Saikia a,⇑, James C. Hower b, Madison M. Hood b, Reshita Baruah c, Hari P. Dekaboruah c, Ratan Boruah d, Arpita Sharma a, Bimala P. Baruah a a

Coal Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat 785006, Assam, India University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, USA c Bio-technology Division, CSIR-North East Institute of Science & Technology, Jorhat 785006, Assam, India d Department of Physics, Tezpur University, Tezpur 784001, India b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Petrological and biological aspects of

Indian coal-derived fly ash are addressed.  The petrology of coal-derived fly and bottom ashes is dominated by glass and spinel.  The deposition of coal fly ash over the plants leaves reduces the photosynthesis rate.  Coal-derived fly ash affects the stomatal conductance in plants leaves.

a r t i c l e

i n f o

Article history: Received 11 January 2015 Received in revised form 29 May 2015 Accepted 3 June 2015 Available online 10 June 2015 Keywords: Indian coal fly ash Petrology of fly ash Biology of fly ash Power plant Photosynthesis

a b s t r a c t India has about a tenth of the world’s coal reserves, much of it with high mineral content. These coals produce a large amount of fly ash, which can affect human health and environmental quality aspects during utilization. In this paper, the petrological and biological aspects of some industrially important Indian coal fly ash (CFA) from a coal-based captive power plant are addressed. The petrology of the CFAs is also studied for the samples collected in different times. The study has revealed that the CFAs contain mainly glass fragments, spinel, quartz, and other minerals in lesser quantities. Fly ash carbons were present as chars, possibly from the incomplete combustion of the coals (bituminous and/or subbituminous) used in the power plant. The deposition of CFAs over the leaves of different plant species reduces the photosynthesis rate by about 95% within a period of 2 h. The CFAs also show minor effects to some test microbes. This investigation will be useful in assessment of the environmental impact of a coal-based power plant. Ó 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (B.K. Saikia). http://dx.doi.org/10.1016/j.fuel.2015.06.007 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved.

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Fig. 1. Area illustration of the coal-based power plant.

1. Introduction There are about 88 coal-based power plants in India, which form the major source of fly ash in the country. The generation of fly ash from coal-based power plants in India was 131 MT/year in 2012–13 and, with the commissioning of new thermal power plants and with the increasing use of low-grade coal of high ash yield, the production of ash is likely to go up to 300– 400 MT/year by 2016–17 [1]. The coal-derived fly ashes pose serious environmental and ecological problems if present in sufficient quantities [2–5]. However, fly ash can be either an industrial waste material and ecological nuisance or a valuable raw material [6]. A large number of technologies have been developed for gainful utilization and safe management of this fly ash under the concerted efforts of ‘‘Fly Ash Mission’’ of the Govt. of India since 1994. For all these purposes, characterization needs to be done before their further processing [7].

Coal combustion ash consists of two distinct products: bottom ash (CBA) and fly ash (CFA). Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all Indian fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata [8]. Fly ash is a potential substitute for cement, the most common form of fly ash utilization, and other industrial and agricultural applications [9]. Fly ash contains trace elements such as Zn, As, Se, and Pb [10]; adsorbs Hg from the flue gas stream; and also has also been considered as a source of base metals, Ga and Ge, and rare earth elements [11–18]. The aspects of mineralogical studies of coal-derived fly ash are very much important for minimization of their environmental pollution. Thus, pre-characterization of coal fly ash may lead to better environmental management. In this paper, we describe the petrological characterization of some CFA and CBA from an Indian

Table 1 Chemical characteristics of feed coal and coal fly ash (as received basis; wt.%). Samples

Ash

M

VM

FC

C

H

N

Stotal

O

Feed coal Fly ash

43.00 89.6

5.5 1.72

13.5 –

38.0 –

81.3 6.0

4.49 0.36

0.86 –

1.37 0.15

11.98 –

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

Others

60.12 62.76

26.66 25.53

4.24 3.41

3.73 0.90

1.27 0.60

0.76 0.13

0.86 0.05

2.36 6.62

Feed coal Fly ash

M: Moisture, VM: Volatile Matter, FC: Fixed Carbon, C: Carbon, H: Hydrogen, N: Nitrogen, Stotal: Total Sulfur, O: Oxygen.

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2.2. Coal fly ash (CFA) and bottom ash (CBA) samples

Table 2a Petrology of coal fly ash (v%). CFAs

FA 1 1 Jan 13

FA 1 2 Jan 13

FA 2 1 Jan 13

FA 2 2 Jan 13

FA 3 3 Jan 13

FA 3 4 Jan 13

FA 3 7 Jan 13

Glass Mullite Spinel Quartz Sulfide Sulfate Oxidized fragment Rock fragment Isotropic coke Anisotropic coke Inertinite Unburned coal

68.0 0.0 8.0 0.8 0.0 0.0 0.0

84.0 0.0 8.4 0.8 0.0 0.0 2.0

66.4 0.0 8.0 2.8 0.0 0.0 0.0

84.8 0.0 6.0 0.0 0.0 0.0 2.8

84.8 0.0 5.6 0.0 0.0 0.0 4.4

71.6 0.0 11.2 0.8 0.0 0.0 2.4

69.2 0.0 10.8 0.8 0.0 0.0 3.2

0.0 17.2 2.0

0.4 2.8 0.8

0.0 11.2 4.4

0.4 4.4 1.2

0.0 2.0 1.6

0.4 8.4 3.6

0.0 5.6 7.2

4.0 0.0

0.8 0.0

7.2 0.0

0.4 0.0

1.6 0.0

1.6 0.0

3.2 0.0

coal-based thermal plant as one tool in understanding their quality for further utilization. We also discuss their biological effects as an incentive to their possible environmental issues with special attention to key aspects indicating the photosynthetic effects and toxicity of the materials. Another objective of this study is to understand how coal fly ash (CFA) that settles from the ambient air on leaves might damage them. The biological toxicity testing on the fly ashes was also conducted to predict the potential risks to the ecological systems around the coal power plant.

2. Materials and method 2.1. Feed coal characteristics The feed coals (approximately 20 mm in size) used in the power station were from Raniganj coalfield (West Bengal) during our sampling periods. The Raniganj measures coal has special characteristics containing the best type of non-coking coal reserves in the country. The proximate analysis of the feed coal sample was done in the ‘Proximate Analyzer’ (Model: TGA 701; Leco Corporation, USA) by following ASTM method [19]. The carbon, hydrogen and nitrogen were estimated by using ‘Elemental Analyzer’ (Model: Perkin–Elmer 2400) and total sulfur by ‘Sulfur Analyzer’ (Leco Corporation, USA) by following ASTM methods [20,21]. The percentage of oxygen was calculated by the difference. The ash analysis of the feed coal as well as the fly ash samples was carried out by using chemical methods [22,23].

Table 2b Petrology of coal bottom ash (v%). CBAs

BA 1 1 Jan 13

BA 1 2 Jan 13

BA 2 1 Jan 13

BA 2 2 Jan 13

BA 3 3 Jan 13

BA 3 4 Jan 13

BA 3 7 Jan 13

Glass Mullite Spinel Quartz Sulfide Sulfate Oxidized fragment Rock fragment Isotropic coke Anisotropic coke Inertinite Unburned coal

79.0 0.0 2.5 8.0 0.0 0.0 0.0

95.0 0.0 0.0 2.0 0.0 0.0 0.0

91.0 0.0 1.0 4.0 0.0 0.0 0.0

86.2 0.0 0.5 3.0 0.0 0.0 0.0

85.5 0.0 3.0 3.0 0.0 0.0 0.0

81.0 0.0 1.5 8.0 0.0 0.5 0.0

80.0 0.5 2.5 5.0 0.0 0.0 0.0

0.5 1.5 5.5

0.0 0.5 2.0

1.5 0.5 2.0

3.4 0.5 3.9

1.0 2.5 2.5

0.0 1.0 5.0

1.0 0.0 7.5

3.0 0.0

0.5 0.0

0.0 0.0

2.5 0.0

2.5 0.0

3.0 0.0

3.5 t

The CFA (FA 1, FA 2, and FA 3) and CBA (BA 1, BA2, and BA 3) samples at different time intervals were obtained from a coal-based captive power plant of NTPC-SAIL Power Company (P) Ltd, West Bengal (Fig. 1). This plant generally supplies power to the steel plants at Durgapur, West Bengal (India). At present, about 160 Mt of CFA per year are produced by NTPC coal-based thermal plants and the amount may reach to 600 Mt by 2030. The coals from the Eastern coalfields (Raniganj) are usually used in this NTPC-SAIL power plant. Fly ashes from this plant are mainly locally used for cement and brick making. Seven representative CFA samples were collected from pre-emission control hydroelectric device sampling point. In the same way, CBA samples were also collected in the same time period. 2.3. Petrological characterization The coal fly ash petrology was performed on epoxy-bound particulate pellets prepared to a final 0.05-lm-alumina polish. Reflected light microscopy with a Leitz Orthoplan microscope, using a 50-x reflected-light oil-immersion objective yielded the petrographic information of the samples. The petrology followed procedures outlined by Hower [24]. 2.4. Photosynthesis experiments Effect of the fly ash on net photosynthesis, leaf temperature, and stomatal conductance were tested on five different tree species: Dimaru (Ficus hipida), Kadam (Anthocepalus kadamba), Modhuri (Psidium guajava), Teak (Tectona grandis), and Thekera (Garcinia pedunculata). The measurements were carried out using CIRAS 2 (NUTECH, USA) from 10 to 14 h with the following accessory and internal adjustments: Photosynthetic Leaf Cuvette (PLC6 U) 18-mm diameter insert, leaf area 2.50 cm2, cuvette flow 200 ml/min, CO2 concentration (Cref) 425 ppm, H2O reference 100%, PAR 1000 lmol m 2 s 1, and temperature of cuvette environment 25 °C. The chosen leaves were then enclosed in the cuvette. A minimum of three leaves were recorded for each plant. The recordings were taken before and after spraying the leaves with the fly ash until all the leaves get entirely covered by fly ash. The leaves were completely covered by CFA in order to draw a conclusive response of their photosynthetic activity. 2.5. SEM analysis Scanning electron microscopic analyses were also performed on the control and treated leaves to know the effect of CFAs on the net photosynthesis. For scanning electron microscopic (SEM) analysis, leaf sections were prepared from the samples, which were critical point dried, fixed to metal stubs with carbon conducting double sided adhesive tape. The samples were coated with platinum by Auto Fine Coater (JFC-1600; JEOL, Tokyo, Japan) and examined in a scanning electron microscope of model No. JSM-6390LV; JEOL. Observations and photographs with the SEM were made at 20 kV with a working distance of 11 mm and spot size 36. 2.6. Antibacterial activity of CFA (Toxicity test) Antibacterial activity of the CFA and CBA samples were tested against six pathogenic bacterial strains: Bacillus subtilis, Staplylococcus aureus, Proteus vulgaris, Pseudomonas syringae, Escherichia coli, and Mycobacterium abscessus. This was done by direct spotting (up to 20 mg) of each sample onto the media plates with 100 lL of each strain spread uniformly. The plates were then

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Fig. 2a. Anisotropic coke in bottom ash samples (reflected light).

Fig. 2b. Anisotropic coke and char in bottom ash samples (reflected light).

incubated at 30 °C for 24 h and zone of inhibition was measured in centimeters [25]. 3. Results and discussion 3.1. Coal and fly ash characteristics The feed coal characteristics as well as the representative fly ash chemistry are shown in Table 1. The coal contains medium sulfur

with high ash yield of 43.0%. Carbon content in our representative fly ash sample is about 12.0%. In general, the coal fly ashes studied were dominated by the presence of SiO2, Al2O3 and Fe2O3 (Table 1). The low C concentrations in the fly ash samples indicate the nearly complete combustion of the coals in the power plant. Furthermore, the production of Fe was also observed to be high in the fly ash, which is also evident from the higher amounts of spinel in some of the CFAs of the plant. Considerable amounts of oxides of Ca, Mg, and K are also observed in the CFAs.

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Fig. 2c. Inertinite, spinel, and coke in bottom ash and fly ash samples (reflected light).

Fig. 2d. Partially melted rock fragment (left) and quartz in the bottom ash samples (reflected light).

3.2. Petrology of CFA and CBA The petrology of the CFA and CBA collected at different times is shown in Tables 2a and 2b. Fly and bottom ash petrology is dominant by glass, which is mainly derived from the melting of clay minerals, and partially vitrified rock fragments derived from the incomplete melting of clays [26]. As determined by petrological analysis, the carbons in the fine minerals, at or below the optical limit of detection, are likely to

be present within the glass. Carbon forms, dominated by anisotropic coke, are more abundant in the CFA than in the CBA samples. The most abundant constituent in the CFA samples was found to be glass (Table 2a), with partially-vitrified rock fragments (Fig. 1A), spinel (Fig. 2e), and quartz (Fig. 2d) while other minerals present were found in lesser quantities. Fly ash carbons were present as chars (Fig. 2b), possibly from the incomplete combustion of the low-rank coals, identified as isotropic coke (Fig. 2b), inertinite (Fig. 2c), and anisotropic coke (Fig. 2a). The isotropic and

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Fig. 2e. Spinel with metal (upper left image) and spinel in glass in the bottom ash samples (reflected light).

Table 3 Effect of fly ash treatment on net photosynthesis and stomatal conductance of five tested plants. Name of the plant

Dimaru (Ficus hispida) Madhuri (Psidium guajava) Thekara (Garcinia pedunculata) Kadam Anthocepalus kadamba Teak Tectona grandis Gomari (Gmelina arborea) LSD

Net photosynthesis (lmol m 2 s 1)

Stomatal conductance (lmol m 2 s 1)

Before treatment

After treatment

Before treatment

After treatment

19.5 ± 0.2

0.13 ± 0.02

107.1 ± 1.8

101.7 ± 2.1

11.8 ± 0.3

0.3 ± 0.01

79.3 ± 2.1

31.7 ± 2.4

3.8 ± 0.1

2.2 ± 0.01

82.7 ± 2.2

68.3 ± 2.3

3.5 ± 0.4

3.9 ± 0.02

81.1 ± 1.5

64.3 ± 1.3

6.4 ± 0.1 5.6 ± 0.1

5.8 ± 0.01 0.1 ± 0.01

61.5 ± 2.3 93.1 ± 2.3

90.1 ± 1.5 61.3 ± 2.1

1.8

0.1

5.6

6.1

Data were mean of minimum five records of individual plants with six replication; ± = standard error (SE) means of six observation, LSD significantly different from each observation within the column according to Tukey’s test.

anisotropic cokes represent the melting of vitrinite and re-polymerization of the thermoplastic melt, a carbon form typical of the combustion of bituminous coals. 3.3. Difference in petrology between CFA and CBA As noted above, the CFA and CBA petrology is dominated by glass. The CFA samples contain around 84.8% of glass, whereas CBA contain a maximum of 95%. The spinel content is greater in

CFA than in that of CBA whereas quartz is more abundant in CBA than CFA. Isotropic coke is found to be more abundant in CFA particles while the inertinite concentration is similar in both CFA and CBA. However, the significance of these changes may vary with the type of feed coal, particle size of samples, and the time factor of both CFA and CBA sampling. 3.4. Change in Petrology of CFA with the time of sampling The CFA samples (FA1 and FA2) collected from the power plant in a time interval of around 24 h were dominated by glass and isotropic coke with significant amounts of spinel in the coarser fractions (Table 2a). The carbon content in CFA usually decreases with a decrease in particle size. Thus, the increase in glass content is coincident with the decrease in the carbon content in CFA. The time of sampling particularly is also found to be important. It is observed that that about 85 vol.% of the fly ash of the power plant was found to be inorganic constituents after an interval of 24 h (see Table 2a). The glass and spinel contents in FA1, FA2, and FA3 varied with the time of sampling as described in Table 2a. The FA3 samples were collected intermittently over the course of 24 or 48 h, which shows the decrease of glass contents with increasing time interval. The spinel contents in FA1 and FA3 increase with the sampling time, whereas spinel decreases in FA2 with sampling time. The amount of quartz in all the CFA samples collected in different time interval is seen to vary from 0% to 2.8% (Table 2a). The concentrations of isotropic coke are found to be 17.2% in FA1 sample (collected 1 Jan 13) followed by FA2 (11.2%). However, it decreases with the time interval in both FA1 and FA2 samples (2.8% and 4.4%), but in case of FA3, collected at intervals over 24 h, it

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Table 4 Toxicity effect of the CFA samples against six bacteria strains. Amounts (mg)

a

Strains used-inhibition zone (cm) Bacillus subtilis

Staplylococcus aureus

Proteus vulgaris

Pseudomonas syringae

Escherichia coli

Mycobacterium abscessus

20

0 0

0 0

0 0

0.8a 1.0a

1.4a 1.1a

0 0

20

0 0

0 0

0 0

1.2a 1.3a

1.3a 1.5a

0 0

There was just a slight reduction in the number of colonies.

Fig. 3. Photographs showing the six different strains with fly ash samples spotted.

increases to a higher value (8.4%) than that of previous sample with (2.0%). But, it is found to be further decreased to 5.6% in the sample (FA3) collected in the time interval of 96 h. The anisotropic coke and inertinite contents decrease in both FA1 and FA2 samples of the power plant with the time of sampling. However, FA3 sample shows an increase in anisotropic coke and inertinite with the time of sampling. Other inorganic constituents in CFA samples do not show any significant change with the sampling time (Table 2a).

3.5. Change in petrology of CBA with time of sampling The petrographic compositions of the CBA (Table 2b) indicate their variation with the time of sampling. The glass content in BA1 increases with the sampling time (from 79% to 95%). The BA2 and BA3 samples show the decrease of glass contents with increasing in time intervals (from 91%, to 86.2% and 85.5%, to 81% and 80%). The amount of mullite is found to be less in BA3

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Fig. 4a. SEM micrographs (secondary electron images) showing coal fly ash deposition and deformation of trichrome of Dimaru (Ficus hispida); (A–C: Control leaves; D–F: coal fly ash treated leaves).

Fig. 4b. SEM micrographs (secondary electron images) showing blockage of stomata in Madhuri (Psidium guajava) by coal fly ash deposition (A–B: Control leaves; C–D: coal fly ash treated leaves).

sample collected at intervals over 96 h. Spinel content also decreased with an increase in sampling time in all the CBA samples. The isotropic carbon contents in CBA are less than CFA, which is seen to decrease with increasing sampling time (Table 1). However, anisotropic carbon contents in CBA are more or less similar to that of CFA. The inertinite contents are also observed to be unusually varied with different sampling time (Table 2b).

3.6. Effect of CFA in Photosynthesis Table 3 shows the effect of fly ash treatment on net photosynthesis and stomatal conductance of six plant species, namely Dimaru, Kadam, Modhuri, Teak, Thekera, and Gomari. Pair-wise comparison found that there was significant effect of fly ash treatment on net photosynthesis on the tested tree species due to the

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interruption of receiving light source. Significant reduction in net photosynthesis occurred in Teak followed by Kadam > Thekera > Gomari > Madhuri, respectively. Like net photosynthesis, a reduction in transpiration was also observed in the trees except Modhuri and Teak. The contrasting effect of fly ash on net photosynthesis and transpiration in Teak plants attributed to the functional role played by trichrome. Trichomes contribute to the control of transpiration and temperature of the organ on which they occur. They affect transpiration rate by influencing the water diffusion boundary layer of the transpiring surface by blocking air flow across the leaf surface [27]. Moreover, they can also alter heat loss from a plant, and act in storage and secretion of secondary metabolites. The variation of stomatal conductance in different plants leaves are due to smooth surface of trichrome. The exceptionally higher stomatal conductance might be due to dense trichrome. Inhibition of normal transpiration and photosynthesis in the plants due to the dusting of fly ash were also earlier reported by Gupta et al. [28]. Similarly, Mishra and Shukla [29] reported that dusting of fly ash causes a reduction in pigment content and dry matter. They reported that the dusting of fly ash causes an excessive uptake and accumulation of associative metal and alkalinity, which is caused by soluble salt on the surface. It is also found that CFA distorted the nature of trichromes and mostly affect the physiological behavior of trichrome (Fig. 4a). It is observed that in Dimaru, the CFA were mostly deposited on the trichrome and the net photosynthesis was distorted (Fig. 4b). On the other hand, CFA closed the stomata in the leaves, thereby reduces the stomatal conductance. 3.7. Toxic Effect of CFA against microbes Toxic effect of the CFA samples was assessed against six test organism; of which three are gram positive (B. subtilis, S. aureus, M. abscessus) while three are gram negative (P. vulgaris, P syringae, E. coli) (Table 4). It was found that the 20 mg of fly ash inhibited the growth of E. coli and P. syringae, while for the others no inhibition is seen at this amount (Table 4 and Fig. 3). However, at higher concentration, the CFA samples affect the total microbial count. Studies reported that, in general, fly ash showed less effect on overall inhibition and microbial activities of soil [30–32]. Facultative anaerobes E. coli form a part of the normal gut microbiota of humans and warm-blooded animals, providing beneficial vitamins to their hosts. This is necessary for stimulation of development and activity of immune system and for protection against colonization and infection by pathogenic microbes [33]. CFA as well as CBA may enter into the bodies of coal workers exposed to high amounts of pulverized coal ash through inhalation [34,35]. Thus, CFA may pose as a risk to human immune system, resulting in diseases such as gastrointestinal infections. 4. Conclusions The petrology of the fly and bottom ashes from the NTPC-SAIL power plant is dominated by glass, followed by spinel. Partially-vitrified rock fragments and quartz were also present while the other minerals are found to be less abundant. The fly ash carbons (isotropic coke, inertinite, and anisotropic coke) present as chars are derived from the incomplete combustion of the low-rank coals. The isotropic and anisotropic cokes represent the melting of vitrinite and re-polymerization of the thermoplastic melt, a carbon form typical of the combustion of bituminous coals. The power plant uses a blend of subbituminous to bituminous coals. The petrology of CFA as well as CBA considerably varies with the time of their sampling indicating the use of different types/ranks of coals. There was significant reduction in the

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