Carbon Monoxide in Underground Atmospheres The Role of Bacteria in Its Elimination G. W. JONES AND G. S. SCOTT Central Experiment Station, U. S. Bureau of Mines, Pittsburgh, Penna.
Tests are described showing that certain types of bacteria or microorganisms are present in anthracite gangway waters, sewage, and surface materials which have the ability of readily consuming hydrogen and carbon monoxide from gaseous mixtures. The reactions appeared to consist largely of oxidation of the carbon monoxide to carbon dioxide and oxidation of the hydrogen to water. In the tests in which oxygen was present in the atmosphere, the carbon monoxide did not combine with the hydrogen to give methane and water vapor. Under favorable conditions certain anthraoitemine bacteria or microorganisms remove carbon monoxide a t a rapid rate; for example, a gangway
water from one anthracite mine contained enough bacteria to remove 1.7 volumes of carbon monoxide per volume of the water during a 20-day exposure period. The type and character of the bacteria that cause elimination of the hydrogen and carbon monoxide have not as yet been identified, but work on this phase of the investigation is now under way. Because of these findings it is no longer safe to assume that anthracite-mine fires are extinguished when the atmospheres in sealed fire areas contain no carbon monoxide. Bacteria or other living microorganisms may be present which are able to eliminate the carbon monoxide as fast as it is generated by the fire.
D
URING an investigation by the Bureau of Mines of combustible gases and explosions in underground chambers, manholes, and conduits it was observed that certain gases lose part or all of their hydrogen and carbon monoxide contents on passing through certain soils, especially those containing organic and sewage materials. The action was thought to be due to microorganisms. A study by the Bureau of Mines, now in progress, has confirmed the suggestion that microorganisms found in the water and sludge from certain manholes consume both carbon monoxide and hydrogen a t a rapid rate; and they may eliminate these gases from manufactured gas within 10 to 30 days, depending upon the rate a t which the microorganisms multiply while in contact with the gas. Some time ago the authors investigated a rather extensive underground fire in one of the anthracite mines of Pennsylvania. The fire area, which comprised some 6 million cubic feet of space, m7as sealed; a complete record of the atmosphere behind the seals was obtained by taking samples of the atmosphere a t frequent intervals and a t different locations. A plot of the composition of the atmosphere against the time elapsed after sealing showed that the carbon monoxide content, although rather high 2 days after sealing, dropped rapidly and had disappeared tvithin 20 days after sealing. The final disappearance of the carbon monoxide was determined by testing the atmospheres at the seals in the mine with a micro carbon monoxide indicator capable of indicating concentrations of 0.002 per cent of carbon monoxide. Although calculations showed that some leakage took place in the sealet area it could account for only part of the carbon monoxide that had disappeared in the 20-day period.
Two suggestions were offered for this high rate of carbon monoxide disappearance : (a) The carbon monoxide was oxidized a t temperatures below 150' C. by either the anthracite or its ash (tests on many anthracites have shown that a t temperatures above 150' C. carbon monoxide is liberated in the oxidation products when air is passed through it) ; (h)the carbon monoxide was consumed by microorganisms in the sealed area, as indicated in manhole surveys, if carbon-monoxide-consuming bacteria were present in the gangway water, on the decaying timber, or on the coal itself. In many anthracite mines in Pennsylvania conditions are favorable for the harboring and growth of bacteria. Surface water containing various types of bacteria often passes through fissures and broken areas from the surface into the mine workings; various types of bacteria will be present in and around stables and along the gangway over which the mules travel; and there are microorganisms associated with the decay of mine timber. That bacteria might be the cause of the carbon monoxide elimination in the area was indicated by Graham (8) who made oxidation experiments on wetted shavings from old pit props and found that the residual gas remaining after the experiments did not contain even a trace of carbon monoxide; however, he found that if zinc chloride was added to kill any bacteria that might be present, the oxidation was accompanied by the formation of carbon monoxide. These experiments showed that microorganisms may be instrumental in the elimination of carbon monoxide when wood is oxidized. Haldane and Makgill (3) conducted an investigation to determine why carbon monoxide is absent in concentrated black damp from old workings. When they confined dry coal 775
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dust in a flask a t 104' F. (40" C.) until the oxygen in the atmosphere disappeared (after 17 days), carbon monoxide was produced, and the quantity increased steadily as the oxygen was absorbed. The percentage of carbon monoxide liberated was 0.32 at the end of the experiment, but in similar tests on wetted coal dust with pure oxygen substituted for air a sample taken 20 hours after the start of the experiment contained
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Effect of Bacteria on Carbon Monoxide The disappearance of carbon monoxide in the particular sealed anthracite area was a t first thought to be due to its absorption by the coal a t temperatures below 150" C. A sample of 900 grams of 8-14 mesh anthracite was confined in a mercury-sealed bell jar containing 8.6 liters of an atmosphere with 1.10 per cent carbon monoxide for 5 months at laboratory
d
FIGURES1 (left)
AND
2 (right). REACTION VESSEILFOR STUDYING THE ACTIVITY OF MICROORGANISMS ON
0.36 per cent carbon monoxide; on the third day the percentage had risen to 0.55 per cent, on the fourth day it had fallen to 0.41, and after 14 days the carbon monoxide had disappeared. These investigators suspected that bacterial action might be hastening the oxidation of wet coal and causing the disappearance of carbon monoxide; but further experimentation with a solution of mercuric chloride of 1 part in 1000 instead of pure water showed that the carbon monoxide disappeared after a time. As a result of these and numerous other tests they concluded "that bacteria did not cause the elimination of carbon monoxide, but that the disappearance of the carbon monoxide is due to the oxidizing action of the substance which is a t first found in the coal when it takes u p oxygen from the air . . . . and that if coal is wet when air is slowly passing over it, the carbon monoxide formed in its oxidation will disappear completely, so that we can thus easily account for the absence of carbon monoxide in the black damp issuing from old workings where the coal is nearly always wetted by water." The experiments to be reported here show that in mine-fire atmospheres containing high percentages of carbon monoxide and hydrogen, both gases may be removed by microorganisms (bacteria) and that even when the atmosphere was not in contact with coal, the carbon monoxide was entirely eliminated and the hydrogen almost completely eliminated before the oxygen content of the atmosphere in contact with the microorganisms was reduced to zero. The results presented here indicate that bacteria may play a major part in the consumption of carbon monoxide and hydrogen in anthracite-mine fire areas, underground soil areas, and manholes used by utilities for power, light, and other services. The authors have made no attempt as yet to identify the type of bacteria that causes the reactions a t ordinary temperatures; however, enough selected and diverse materials have been tested to show that such carbon-monoxide-consuming bacteria are widely distributed and may perhaps be present in bituminous and other mines.
GASES
temperatures. The slight decrease in the carbon monoxide content was insufficient to account for the disappearance of carbon monoxide in the sealed-mine fire area. Atmospheres containing various percentages of carbon monoxide were passed through charges of anthracite a t temperatures ranging from 150" C. to ordinary room temperatures to determine whether the carbon monoxide reacted catalytically with the heated coal or any of the mineral constituents in the coal ash; the results showed little if any reaction of the carbon monoxide. As a preliminary experiment to determine the effect of bacteria on carbon monoxide, a Sam le of surface drain water from a storm sewer at the Central Experiment Station a t Pittsburgh was placed in a test apparatus of the type shown in Figure 1. Reaction vessel a, previously sterilized at 100' C., was filled with distilled water by assing the water from leveling bulb b through cock c into the %ottle. The connection between bottle a and mercury sampling bottle e was broken at and a gas mixture containing 0.52 per cent of carbon monoxi!: was added as the water was withdrawn completely from the reaction chamber. Three hundred cubic centimeters of the sewage were then run into the vessel from leveling bottle b, and the gas displaced by the liquid was allowed to escape t o the air. The cock above manometer d was then closed, and samples were withdrawn through cock h for analysis at the end of 8 and 20 days, by means of sample bottle e and leveling bottle f.
The following change in composition of the gas mixture was observed (in per cent): Days after start of teat Carbon dioxide Oxygen Hydrogen Carbon monoxide Methane Nitrogen
0 0.03 17.50 0.00 0.52 0.00 81.96
'
8 2.30 15.54 0.00 0.43 0.00 81.73
20 3.28 14.59 0.00 0.28 0.00 81.85
The above results indicated that bacteiia caused a very slow elimination of carbon monoxide and that other reactions caused the production of more carbon dioxide than would be
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produced by reaction of the bacteria with the carbon monoxide to produce carbon dioxide. These results were encouraging enough to try further experiments in which numerous types of bacteria would be present. A mixture of rotted wood, toadstools, fungi, and manure (materials that may be present in an anthracite mine) were stirred together in distilled water. A 800-cc. portion of the liquid and solid mixture was placed in reaction vessels of the type shown in Figure 1in contact with an atmosphere made by the oxidation of anthracite with stir at elevated temperatures. After 11 to 14 days the three atmospheres were analyzed and the following results were obtained (per cent by volume) : Original
Carbon dioxide Oxygen Hydrogen Carbon monoxide Methane Nitrogen
Gas Mixture 1.1
17.4 3.3 2.7 0.6 74.9
-Composition of Gas after:11 days, 13 days, 14 days. bottle 3 bottle 1 bottle 2 18.7 20.5 24.3 0.2 0 0 0 0 0 0 0 0 0.5 0.3 0.5 79.0 75.4 80.6
Reactions were taking place in these mixtures even during the first day of test because of the reduction of pressure inside the bottles as indicated by the mercury manometers. I n 11 days or longer the gas mixture which originally contained 3.3 per cent of hydrogen and 2.7 per cent of carbon monoxide contained no hydrogen or carbon monoxide, the oxygen had been entirely consumed, and large percentages of carbon dioxide had been produced. Although these tests showed that bacteria had removed the hydrogen and carbon monoxide, they did not give evidence as to whether the hydrogen and carbon monoxide were removed before the oxygen had been eliminated. This is an important factor because in most mine-fire areas oxygen is always present. The high percentage of carbon dioxide in the final mixtures indicated that a t least part of this gas was produced by the solid matter in the liquid.
Effect of Solid Organic Material Tests were next made in which all solid matter was filtered out and only the liquid was used. They were made to determine whether organic matter, such as decaying wood, and
TABLE I. ACTIONOF BACTERIA ON Days from Start of Test 0 2 5 10 17 33 37 44 51 65 86 0 50
Temp.,
c.
23 24 22.5 24 23 24 25 24.5 24 25 25 27 25
Total I'ressure, Mm. 754 720 706 710 705 683 677 667 662 660 675 733 736
Relative Vol. 1.000 0.952 0.938 0.938 0.938 0.898 0.894 0.879 0.875 0.879 0.890
cot 3.5 3.5 3.9 4.1 4.8 10.6 11.7 13.8 15.2 15.3 15.4
A
ON A GASEOUS ATMOSFIGURE 3. ACTIONOF BACTERIA PHERE CONTAINING HYDROGEN AND CARBON MONOXIDE
blank test made under similar conditions, except that one part of mercuric chloride was added per 1000 parts of liquid to kill any bacteria present and thus to show whether bacteria caused the reactions. As Table I and Figure 3 show, the hydrogen was completely consumed in 10 days. During the first 17-day period there was little change in the carbon monoxide content. However, after 17 days the elimination of carbon monoxide began, and this gas had disappeared a t the end of 51 days. No methane was formed in these tests; therefore the microorganisms caus-
GASEOUS ATMOSPHERE CONTAINING HYDROGES AND CARBON MONOXIDE Gas Analysis, 5% by Vo1.Hz CO CH4 9.2 4.1 11.6 0 8.0 0.3 12.0 0 7.4 0.1 12.2 0 7.2 0 11.5 0 6.9 0 11.4 0 4.2 0 5.9 0 3.8 0 4.5 0 2.4 0 2.0 0 2.0 0 0 0 1.6 0 0 0 1.7 0 0 0 0 1
Blank Test, Bacteria Killed with HgClz 1 .a00 2.1 11.3 2.0 1.010 2.3 11.2 1.8
solids were necessary to cause elimination of hydrogen and carbon monoxide. A liter of the decanted liquid was placed in a 19-liter vessel (Figure 2) in contact with a gas mixture made by :passing air through incandescent anthracite. About 50 per cent of this gas and 50 per cent of air were introduced into the vessel holding the liquid containing the bacteria. The atmosphere was analyzed periodically to determine the reactivity of the bacteria on the gaseous mixture. The results a.re summarized in Table I; data are included for a
10.0 10.0
0 0
Nz
71.6 76.2 76.4 77.2 76.9 79.3 80.0 81.8 82.8 83.1 82.9
-------Calcd. Relative Vol., % by V 0 1 . p COz Oz Hz CO CH4 Nz 4.1 0 3.5 9.2 11.6 71.6 3.3 11.4 0.3 0 7.6 72.5 11.4 0.1 0 3.7 6.9 71.7 0 0 3.8 6.7 10.8 72.4 0 4.5 6.5 10.7 72.1 0 0 9.5 0 3.8 71.2 5.3 4.0 10.5 0 0 3.4 71.5 2.1 12.1 0 0 72.0 1.8 13.3 0 0 0 1.7 72.5 1.4 13.5 0 0 0 73.0 1.5 13.7 0 0 0 73.8
74.6 74.7
ing the elimination of hydrogen and carbon monoxide are not of the same type as those mentioned by Fischer, Lieske, and Winzer (1). They found that certain bacteria cause hydrogen and carbon monoxide to combine in the absence of oxygen to form methane: CO 3Hz = CHd HzO
+
+
They proposed this method for the removal of carbon monoxide from illuminating gas to render the gas nontoxic.
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VOL. 31, NO. 6
TABLE 11. ACTIONOF MINE BACTERIA ON G A ~ E O U ATMOSPHERES S CONTAINING HYDROGEN AND CARBON MONOXIDE Mine No. 1
Sample No. 1
2
2
Water from gangway
2
3
Water from gangway
2
4
2 3
Compn. of Gas Mixt., % by Vol.
Contact Time, Days 0 30
coz
0 1
HL
co
0.4 7.0
11.3 4.7
14.3 1.6
12.3 7.6
0 40 0 40
0.9 5.3 0.9 5.1
9.5 3.3 9.5 2.1
7.8 2.2
15.9 13.6
0 0.3
7.8 1.0
15.9 13.5
0 0
65.9 75.3 65.9 78.3
Water from slope
0 40
0.9 1.6
9.5 7.8
7.8 5.8
15.9 15.8
0 0.1
65.9 68.9
5
Slime from inactive abandoned section of mine
0 40
0.4 0.7
11.3 11.1
14.3 12.6
12.3 10.2
0 0
61.7 65.4
6
Water from gangway
0 40
0.4 7.6
11.3 2.6
14.3 3.3
12.3 9.0
0 0
61.7 77.5
Remarks Water from gangway fire area
The nitrogen content of the mixture increased with the time of contact of the gas with the bacteria, and the increase was due to a decrease in the volume of hydrogen and carbon monoxide. When corrections are made for the change in volume of the test mixture, as given in Table I, the carbon dioxide is produced by oxidation of the carbon monoxide and the decrease in oxygen content of the gas mixture is due largely to oxidation of the hydrogen to water and the carbon monoxide to carbon dioxide. Thus, in these tests the following reactions appear to have taken place: 2H2 2co
+
0 2
+
0 2
= =
2H20 2c02
(1) (2)
The reason for the delayed reaction of the carbon monoxide with oxygen is not clear. The results show that solid organic matter is not required in the reaction, that hydrogen is more reactive than carbon monoxide in this particular media, that the reaction takes place in atmospheres in which free oxygen is present, and that the reactions are due to living organisms. A control test which was made a t the same time and in which mercuric chloride was present showed virtually no change in the composition of the original gas mixture after 50 days of contact.
Bacteria in Water and Slimes A further step in the investigation was the determination of whether gangway water and slimes from stagnant and other regions in various mines in the anthracite region contained bacteria of a type that would consume carbon monoxide and hydrogen. Six samples of liquids and slimes were collected from three different mines, and tests were conducted in reaction vessels of the type shown in Figure 1. The results obtained are given in Table 11. The samples of water from mines 1and 3 showed a considerable elimination of hydrogen and carbon monoxide from the gas mixtures after 30 or 40 days of contact with the liquid, while one sample from mine 2 showed practically no change in carbon monoxide concentration after 40 days and the other three only a slight reduction. Sample 1 was of special significance because it came from the mine-fire area in which the carbon monoxide content of the air had decreased rapidly a few days after the area was sealed. The liquid from the 30-day test was given further treatment in the 19-liter reaction vessel shown in Figure 2. A gas containing hydrogen and carbon monoxide was made by passing air through incandescent anthracite, and a mixture containing about 40 per cent of this gas and 60 per cent of air was prepared. The final mixture contained 9.4 per cent of carbon monoxide (Table 111). At the end of 20 days the bacteria had entirely eliminated the carbon monoxide, and only 0.5 per cent of hydrogen remained in the atmosphere.
C H4 0 0
N2 61.7 79.1
At the end of 40 days the carbon dioxide content had increased slightly and the oxygen content had fallen as shown; however, the major reactions had taken place during the first 20 days. The test was therefore stopped a t the end of 60 days. I n this test small strips of sponge (i, Figure 2), sterilized a t 100" C. in an oven for 12 hours, were suspended in the reaction vessel to increase the surface contact between the liquid and the gas. An approximate estimate of the amount of carbon monoxide that was eliminated by the mine water can be obtained from the decrease in carbon monoxide content over the 20-day exposure period and from the volumes of the gas mixture and the mine water containing the bacteria. The data show that for an exposure of 20 days 1volume of the mine water eliminated approximately 1.7 volumes of carbon monoxide. TABLF, 111. CHANGE IN COMPOSITION OF A MINE-FIREATMOSPHERE CONTAINING CARBON MONOXIDE AND HYDROGEN IN CONTACT WITH A GANGWAY WATERCONTAINING BACTERIA^ Days from start of test 0 20 40 60 Carbon dioxide 2.4 12.8 14.5 15.2 Oxygen 11.0 3.7 1.4 0.5 Hydrogen 0.5 0 0 1.3 0 0 0 Carbon monoxide 9.4 0 0 0.1 Methane 0 Nitrogen 75.9 83.0 84.1 84.2 a One liter of liquid in contact with 18 liters of gas mixture at start of test.
The rate of elimination of carbon monoxide is ample to account for the elimination of the carbon monoxide in the rninefire area discussed at the beginning of this report. These results show conclusively that some waters and sludges in anthracite mines carry unidentified bacteria or microorganisms; under favorable conditions they react rapidly with carbon monoxide to produce carbon dioxide and with hydrogen to produce water vapor, and thus cause the disappearance of these gases in sealed areas.
Acknowledgment Acknowledgment is made to R. D. Currie, of the Safety Division of the Bureau of Mines, who collected the samples of liquids and slimes reported in Table 11.
Literature Cited (1) Fischer, Franz, Lieske, R.. and Winzer, K., Brennst0.f-Chem., 11. 452-5 (1930). (2) Graham, I., -!Z'ran8. Inst. Mining Engrs. (London), 79, 92-111 (192940). (3) Haldane, J. S., and Makgill, R. H., Ibicl., 85, 172-85 (1933). PRESENTED a t the 96th Meeting of t h e American Chemical Society, Milwaukee, Wis. Published b y permission of the Director, U. 8. Bureau of Mines. (Not subject t o copyright.)
