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Biodesulfurization of Turkish lignites: 2. Microbial desulfurization of Mengen lignite by the mesophilic microorganism Rhodococcus rhodochrous
ELSEVIER
Fuel Vol. 76, No. 4, pp. 341-344, 1997 © 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0016-2361/97 $17.00 + 0.00
PII: S0016-2361(96)00237-2
Biodesulfurization of Turkish lignites 2. Microbial desulfurization of Mengen lignite by the mesophilic m icroorga n ism Rhodococcus rhodochrous TLilay Durusoy, Tijen 0zba Bozdemir, Evrim Erincin and Yuda Y0r0m* Hacettepe University, Chemical Engineering and *Chemistry Departments, Beytepe, 06532 Ankara, Turkey (Received 26 May 1996; revised 20 September 1996)
The effects of substrate type in the growth medium, mixing time of lignite into the growth medium and the biodesulfurization time on sulfur removal were studied. Biodesulfurization experiments were carried out with Mengen lignite under optimum growth conditions of Rhodococcus rhodochrous. The highest reduction of organic sulfur forms was 27.1% when sodium acetate was the substrate. Sulfate sulfur could be totally reduced when lignite was added to the culture medium 24 h after incubation. Compared with sodium acetate, glycerol yielded higher sulfate sulfur reduction rates when lignite was added at the time of incubation. The highest organic sulfur removal rates were found when sodium acetate was the substrate. © 1997 Elsevier Science Ltd. All rights reserved. (Keywords: lignite; biodesulfurization; Rhodococcus rhodochrous)
Today it is imperative that natural resources are utilized most efficiently without polluting the environment. Fossil fuels constitute an important fraction of the natural fuel sources. Sulfur oxides evolved during the use of fossil fuels are the focus of attention as a result of the volume released and scope of the damage they cause 1. Post-combustion desulfurization processes are inconvenient and expensive. Physical, chemical and biochemical techniques are available for removing or reducing the sulfur content of the coal before combustion. In addition, removal of sulfur from coal before combustion has some superiority over other methods 2. Certain bacteria, fungi and mixed cultures have been used in removing sulfur from coal in considerable levels. There are many reports on Thiobacillusferrooxidans and Thiobacillus thiooxidans, which have been quite successful in decreasing pyritic sulfur though not so successful in removing organic sulfur 3. In contrast, a thermophilic bacterium, Sulfolobus acidocaldarius, has been observed to remove fractions of pyritic and organic sulfur contents equally weU4. Another Sulfolobus variety, S. solfataricus, is also being studied currently to investigate sulfur removal from lignites 5-7. Early results indicate that high sulfur removal and organic sulfur conversion rates can be attained with this bacterium. A new microorganism that is efficient in the removal of the organic sulfur is Rhodococcus rhodochrous. There are some previous studies with this bacterium using model organic compounds and petroleum 8-11. The purpose of the current study was to investigate sulfur removal from a very high-sulfur lignite under the
predetermined optimum growth conditions of Rhodococcus rhodochrous 12. For this purpose, various growth and process parameters such as substrate type of the growth medium, mixing time of lignite into the growth medium and biodesulfurization time were investigated. EXPERIMENTAL Bolu-Mengen lignite from the Western Black Sea area in Turkey was used in this study. Biodesulfurization experiments were conducted with the microorganism cultured at its optimum growth conditions. The coal samples were prepared for desulfurization runs by the procedure described in the previous study 12. RESULTS AND DISCUSSION Biodesulfurization experiments were carried out at the optimum growth temperature, initial pH, shaking rate and inoculum concentration of Rhodococcus rhodochrous 12. Each experiment was performed by adding 2 0 g L -1 of Mehgen lignite to the growth medium containing 20 mM sodium acetate as substrate. Lignite samples were added to the media in two different ways. In the first group of experiments, sterile lignite was included as soon as the growth medium was incubated with the microorganism (t = 0 h). Sulfur removal runs lasted 4 days. Sulfur types and levels of the samples were monitored by periodic sampling from the culture media. The biodesulfurization time variation of total, sulfate, pyritic and organic sulfur contents of the lignite is plotted
Fuel 1997 Volume 76 Number 4
341
Biodesulfurization of Turkish/ignites." T. Durusoy et al.
14 ,-. 12
T S P 0
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96
Biodesulfurization time (h)
Figure 1 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite when lignite was added to the culture medium containing sodium acetate at the time of incubation (t = 0 h)
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Biodesulfurization time (h)
Figure 2 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite when lignite was added to the culture medium containing sodium acetate 24 h after the incubation (t = 24 h)
in Figure 1. As is seen, all sulfur types decreased with increasing biodesulfurization time. To investigate the effect of mixing time, lignite was added to the culture 24h after the incubation of the growth medium with the microorganism (t = 24 h) in the second group of runs. In this case, the experiments lasted for 1 week and the sulfur content was determined by periodic sampling of the lignite from the culture medium. The results are given in Figure 2, where all sulfur forms are again seen to decrease with increasing biodesulfurization time. The highest reduction rate for total sulfur was 33.4% at 167 h in the second group of experiments. It is interesting that sulfate sulfur can be totally removed when lignite is added 24 h after incubation. The effects of the sample addition time to the culture medium on the degree of reduction of total sulfur and sulfur forms for Mengen lignite at 72 h of biodesulfurization are shown in Figure 3. It is seen that there is not much change in the total sulfur content. The highest
342
Fuel 1997 V o l u m e 76 N u m b e r 4
100
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.-. 80
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Figure 3 Comparison of the effects of lignite addition time to the culture medium on the total sulfur and sulfur forms removal percentages of Mengen lignite at 72 h of biodesulfurization
Biodesulfurization of Turkish lignites." T. Durusoy et al.
14 12
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Figure 4 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite with glycerol as substrate when lignite was added to the culture medium at the time of incubation (t = 0 h) 100 80
0
•
60
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[ ] Glycerol
E
~ 40 20 0 Total
Sulfate
Pyritic
Organic
Figure 5 Comparison of removal of total sulfur and sulfur forms obtained for both substrates at 72 h of biodesulfurization at the same lignite addition time (t = 0 h)
reduction level for organic sulfur, 27.1%, was obtained at 72 h in the experiment in which the lignite was added at the time of incubation. However, the pyritic sulfur reduction was smaller under the same conditions. In the second phase of the study, glycerol was used as the substrate. In these experiments lignite was added at the time of incubation, in accordance with the findings of the first phase of experiments, where organic sulfur reduction was found to be the highest. The initial glycerol concentration was 40mM in all runs. Microbiological sulfur reduction results are given in Figure 4. The highest extents of sulfur reduction were recorded at 48 h. The highest degree of organic sulfur reduction was recorded as 17.6% at 48 h for glycerol. Figure 5 shows the degree of reduction of total sulfur and sulfur forms obtained for the two substrates at 72 h of biodesulfurization at the same lignite addition time (t = Oh). Compared with sodium acetate, glycerol yielded higher reduction in sulfate but lower pyritic and organic sulfur reduction. CONCLUSIONS The most striking advantages of R. rhodochrous are that
it has an optimum growth temperature of 28°C and has the ability to remove organic sulfur forms as well. The highest reduction of organic sulfur was recorded as 27.1% at 72 h of biodesulfurization when sodium acetate was the substrate (t = 0). After 48 h of reduction there was not much change in the total and organic sulfur contents. Sulfate sulfur could be totally removed when lignite was added to the medium 24h after incubation. However, there was not much change in the pyritic and organic sulfur contents. Glycerol yielded a higher degree of sulfate sulfur reduction than sodium acetate; however, the highest degree of organic sulfur removal was recorded with sodium acetate as substrate. ACKNOWLEDGEMENT This research was supported by T O B I T A K under Project No. MISAG 62.
REFERENCES 1 2
3 4 5
6 7 8 9
Elliot, R. C. (ed.), Coal Desulfurization Prior to Combustion. Noyes Data Corporation, Park Ridge, NJ, 1978, pp. V-VI, 33-42, 141-153. Wheelock, R. A., Coal Desulfurization. Chemical and Physical Methods, Symposium Series 64. American Chemical Society, Washington, DC, 1977, pp. IX-XI, 101-120. Kargl, F., Enzyme and Microbial Technology, 1982, 4, 13 Kargt, F. and Robinson, J. M., Applied and Environmental Microbiology, 1982, 44, 878. Gfillfi, G., Durusoy, T., 6zba~, T., Tanyolaq, A. and Yfirfim, Y., in Clean Utilization of Coal and Coal Structure and Reactivity, Cleaning and Environmental Aspects, ed. Y. Yfir/im, NATO ASI Series C: Mathematical and Physical Sciences, Vol. 370. 1992, pp. 185-205. Durusoy, T., 6zba~, T., Tanyolaq, A. and Yiir~m, Y., Energy and Fuels, 1992, 6, 804. Ozba~,T., Durusoy, T., Tanyolag, A. and Yfirfim, Y., Fuel Processing Technology, 1993, 33, 61. Kilbane, J. J. and Bielaga, B. A., Chemtech, 1990, 747. Sorkhoh, N. A., Ghannoum, M. A., Ibrahim, A. S., Stretton, R. J. and Radwan, S. S., Environmental Pollution, 1990, 65, 1.
Fuel 1997 Volume 76 Number 4
343
Biodesulfurization of Turkish lignites: T. Durusoy et al.
10 11 12
344
Olson,E. S., Stanley, D. C. and Gallagher, J. R., Energy and Fuels, 1993, 7, 159. Gallagher,J. R., Olson, E. S. and Stanley, D. C., FEMS Microbiology Letters, 1993, 107, 31. Ozba~ Bozdemir, T., Durusoy, T., Erincin, E. and Yiiriim, Y., Fuel, 1996, 75, 1596.
Fuel 1997 Volume 76 Number 4
NOMENCLATURE O P S t T
organic sulfur content (wt% db) pyritic sulfur content (wt% db) sulfate sulfur content (wt% db) mixing time of lignite in the growth medium (h) total sulfur content (wt% db)
Fuel Vol. 76, No. 4, pp. 341-344, 1997 © 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0016-2361/97 $17.00 + 0.00
PII: S0016-2361(96)00237-2
Biodesulfurization of Turkish lignites 2. Microbial desulfurization of Mengen lignite by the mesophilic m icroorga n ism Rhodococcus rhodochrous TLilay Durusoy, Tijen 0zba Bozdemir, Evrim Erincin and Yuda Y0r0m* Hacettepe University, Chemical Engineering and *Chemistry Departments, Beytepe, 06532 Ankara, Turkey (Received 26 May 1996; revised 20 September 1996)
The effects of substrate type in the growth medium, mixing time of lignite into the growth medium and the biodesulfurization time on sulfur removal were studied. Biodesulfurization experiments were carried out with Mengen lignite under optimum growth conditions of Rhodococcus rhodochrous. The highest reduction of organic sulfur forms was 27.1% when sodium acetate was the substrate. Sulfate sulfur could be totally reduced when lignite was added to the culture medium 24 h after incubation. Compared with sodium acetate, glycerol yielded higher sulfate sulfur reduction rates when lignite was added at the time of incubation. The highest organic sulfur removal rates were found when sodium acetate was the substrate. © 1997 Elsevier Science Ltd. All rights reserved. (Keywords: lignite; biodesulfurization; Rhodococcus rhodochrous)
Today it is imperative that natural resources are utilized most efficiently without polluting the environment. Fossil fuels constitute an important fraction of the natural fuel sources. Sulfur oxides evolved during the use of fossil fuels are the focus of attention as a result of the volume released and scope of the damage they cause 1. Post-combustion desulfurization processes are inconvenient and expensive. Physical, chemical and biochemical techniques are available for removing or reducing the sulfur content of the coal before combustion. In addition, removal of sulfur from coal before combustion has some superiority over other methods 2. Certain bacteria, fungi and mixed cultures have been used in removing sulfur from coal in considerable levels. There are many reports on Thiobacillusferrooxidans and Thiobacillus thiooxidans, which have been quite successful in decreasing pyritic sulfur though not so successful in removing organic sulfur 3. In contrast, a thermophilic bacterium, Sulfolobus acidocaldarius, has been observed to remove fractions of pyritic and organic sulfur contents equally weU4. Another Sulfolobus variety, S. solfataricus, is also being studied currently to investigate sulfur removal from lignites 5-7. Early results indicate that high sulfur removal and organic sulfur conversion rates can be attained with this bacterium. A new microorganism that is efficient in the removal of the organic sulfur is Rhodococcus rhodochrous. There are some previous studies with this bacterium using model organic compounds and petroleum 8-11. The purpose of the current study was to investigate sulfur removal from a very high-sulfur lignite under the
predetermined optimum growth conditions of Rhodococcus rhodochrous 12. For this purpose, various growth and process parameters such as substrate type of the growth medium, mixing time of lignite into the growth medium and biodesulfurization time were investigated. EXPERIMENTAL Bolu-Mengen lignite from the Western Black Sea area in Turkey was used in this study. Biodesulfurization experiments were conducted with the microorganism cultured at its optimum growth conditions. The coal samples were prepared for desulfurization runs by the procedure described in the previous study 12. RESULTS AND DISCUSSION Biodesulfurization experiments were carried out at the optimum growth temperature, initial pH, shaking rate and inoculum concentration of Rhodococcus rhodochrous 12. Each experiment was performed by adding 2 0 g L -1 of Mehgen lignite to the growth medium containing 20 mM sodium acetate as substrate. Lignite samples were added to the media in two different ways. In the first group of experiments, sterile lignite was included as soon as the growth medium was incubated with the microorganism (t = 0 h). Sulfur removal runs lasted 4 days. Sulfur types and levels of the samples were monitored by periodic sampling from the culture media. The biodesulfurization time variation of total, sulfate, pyritic and organic sulfur contents of the lignite is plotted
Fuel 1997 Volume 76 Number 4
341
Biodesulfurization of Turkish/ignites." T. Durusoy et al.
14 ,-. 12
T S P 0
0
tO
0
•
•
•
•
•
•
•
0
0
0
0
O3
4
0
a
I
0
,
1
24
i
48
0
I
I
72
96
Biodesulfurization time (h)
Figure 1 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite when lignite was added to the culture medium containing sodium acetate at the time of incubation (t = 0 h)
14 T
d
S
12 o
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o
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I
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96
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120
|
I
144
168
Biodesulfurization time (h)
Figure 2 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite when lignite was added to the culture medium containing sodium acetate 24 h after the incubation (t = 24 h)
in Figure 1. As is seen, all sulfur types decreased with increasing biodesulfurization time. To investigate the effect of mixing time, lignite was added to the culture 24h after the incubation of the growth medium with the microorganism (t = 24 h) in the second group of runs. In this case, the experiments lasted for 1 week and the sulfur content was determined by periodic sampling of the lignite from the culture medium. The results are given in Figure 2, where all sulfur forms are again seen to decrease with increasing biodesulfurization time. The highest reduction rate for total sulfur was 33.4% at 167 h in the second group of experiments. It is interesting that sulfate sulfur can be totally removed when lignite is added 24 h after incubation. The effects of the sample addition time to the culture medium on the degree of reduction of total sulfur and sulfur forms for Mengen lignite at 72 h of biodesulfurization are shown in Figure 3. It is seen that there is not much change in the total sulfur content. The highest
342
Fuel 1997 V o l u m e 76 N u m b e r 4
100
¢ / i , ¢1/.~ ¢ / / s
.-. 80
E
60
_
~-;;:
It=Oh
¢ / / I ¢ ]
I
]
~
i / / ,
#.
40
r / / / f / f /
O3
20
Total
Sulfate
Pyritic
Organic
Figure 3 Comparison of the effects of lignite addition time to the culture medium on the total sulfur and sulfur forms removal percentages of Mengen lignite at 72 h of biodesulfurization
Biodesulfurization of Turkish lignites." T. Durusoy et al.
14 12
•
10
•
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S
0
P
•
0
81 • Q
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48 72 Biodesulfurizationtime (h)
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0
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i
l
,
96
I
120
Figure 4 Effect of biodesulfurization time on total, sulfate, pyritic and organic sulfur contents of Mengen lignite with glycerol as substrate when lignite was added to the culture medium at the time of incubation (t = 0 h) 100 80
0
•
60
Sodium Acetate
[ ] Glycerol
E
~ 40 20 0 Total
Sulfate
Pyritic
Organic
Figure 5 Comparison of removal of total sulfur and sulfur forms obtained for both substrates at 72 h of biodesulfurization at the same lignite addition time (t = 0 h)
reduction level for organic sulfur, 27.1%, was obtained at 72 h in the experiment in which the lignite was added at the time of incubation. However, the pyritic sulfur reduction was smaller under the same conditions. In the second phase of the study, glycerol was used as the substrate. In these experiments lignite was added at the time of incubation, in accordance with the findings of the first phase of experiments, where organic sulfur reduction was found to be the highest. The initial glycerol concentration was 40mM in all runs. Microbiological sulfur reduction results are given in Figure 4. The highest extents of sulfur reduction were recorded at 48 h. The highest degree of organic sulfur reduction was recorded as 17.6% at 48 h for glycerol. Figure 5 shows the degree of reduction of total sulfur and sulfur forms obtained for the two substrates at 72 h of biodesulfurization at the same lignite addition time (t = Oh). Compared with sodium acetate, glycerol yielded higher reduction in sulfate but lower pyritic and organic sulfur reduction. CONCLUSIONS The most striking advantages of R. rhodochrous are that
it has an optimum growth temperature of 28°C and has the ability to remove organic sulfur forms as well. The highest reduction of organic sulfur was recorded as 27.1% at 72 h of biodesulfurization when sodium acetate was the substrate (t = 0). After 48 h of reduction there was not much change in the total and organic sulfur contents. Sulfate sulfur could be totally removed when lignite was added to the medium 24h after incubation. However, there was not much change in the pyritic and organic sulfur contents. Glycerol yielded a higher degree of sulfate sulfur reduction than sodium acetate; however, the highest degree of organic sulfur removal was recorded with sodium acetate as substrate. ACKNOWLEDGEMENT This research was supported by T O B I T A K under Project No. MISAG 62.
REFERENCES 1 2
3 4 5
6 7 8 9
Elliot, R. C. (ed.), Coal Desulfurization Prior to Combustion. Noyes Data Corporation, Park Ridge, NJ, 1978, pp. V-VI, 33-42, 141-153. Wheelock, R. A., Coal Desulfurization. Chemical and Physical Methods, Symposium Series 64. American Chemical Society, Washington, DC, 1977, pp. IX-XI, 101-120. Kargl, F., Enzyme and Microbial Technology, 1982, 4, 13 Kargt, F. and Robinson, J. M., Applied and Environmental Microbiology, 1982, 44, 878. Gfillfi, G., Durusoy, T., 6zba~, T., Tanyolaq, A. and Yfirfim, Y., in Clean Utilization of Coal and Coal Structure and Reactivity, Cleaning and Environmental Aspects, ed. Y. Yfir/im, NATO ASI Series C: Mathematical and Physical Sciences, Vol. 370. 1992, pp. 185-205. Durusoy, T., 6zba~, T., Tanyolaq, A. and Yiir~m, Y., Energy and Fuels, 1992, 6, 804. Ozba~,T., Durusoy, T., Tanyolag, A. and Yfirfim, Y., Fuel Processing Technology, 1993, 33, 61. Kilbane, J. J. and Bielaga, B. A., Chemtech, 1990, 747. Sorkhoh, N. A., Ghannoum, M. A., Ibrahim, A. S., Stretton, R. J. and Radwan, S. S., Environmental Pollution, 1990, 65, 1.
Fuel 1997 Volume 76 Number 4
343
Biodesulfurization of Turkish lignites: T. Durusoy et al.
10 11 12
344
Olson,E. S., Stanley, D. C. and Gallagher, J. R., Energy and Fuels, 1993, 7, 159. Gallagher,J. R., Olson, E. S. and Stanley, D. C., FEMS Microbiology Letters, 1993, 107, 31. Ozba~ Bozdemir, T., Durusoy, T., Erincin, E. and Yiiriim, Y., Fuel, 1996, 75, 1596.
Fuel 1997 Volume 76 Number 4
NOMENCLATURE O P S t T
organic sulfur content (wt% db) pyritic sulfur content (wt% db) sulfate sulfur content (wt% db) mixing time of lignite in the growth medium (h) total sulfur content (wt% db)