BacterialSlimeand Corrosion in by R. J. DeGray and L. N. Killian, The Standard Oil Co. (Ohio)
Bacteria encourage rust and make slimes, which hold rust in suspension, which encourages bacteria, which encourage rust and make slimes . ..
THE INTERRELATION of
petroleum
and microorganisms has been widely studied. The comparative paucity of publications on the microbiology of refined petroleum fractions is striking. Bushnell and Haas reported the presence of bacteria in the water bottoms of tanks containing gasoline and kerosine. Allen stated that bacterial action on gasoline results in precipitation of tetraethyllead and in the formation of peroxides and gums. Harris and Strawinski stated that bacterial action results not only in loss through consumption of the hydrocarbon by the bacteria, but also in the formation of hydrogen sulfide, gums, peroxides, acids, and colored substances. The most dra matic effect of bacteria is reported by Bakanauskas. Here the bac terial slimes which developed at the water-JP-4 interface caused opera tional difficulties in KC-97 and B-47 jet aircraft by clogging the fuel filters. The authors started their bacterial examination of water-petroleum frac tion interfaces as part of a broad study of gasoline sediment and clarity. The filamentous aspect of such interfaces suggested bacterial activity. A connection between 74 A
such filaments and slimes and the settling rates of sediments was easily postulated. Bacteria in Refinery Tanks
Samples obtained from waterpetroleum fraction interfaces of ac tual refinery and bulk terminal tanks contain a variety of bacteria. Table I shows the genera found. The permanent residents of the tanks are predominantly Bacillus species. However, all of the flora are normally present in soil and in ground waters, so if a strain dies out, subsequent reinoculation may be expected. Not all bacteria thriving in tank
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I.
Identification
No.
Species
1 2 3 4 5 6 7 8 ο 10 11 12
Pseudomonas sp. Bacillus sp. Flavobacterium sp. Bacillus sp. Cylindrogloea Bacterifera Sorangium sp. Bacillus Mycoides Bacillus Subtilis Bacillus sp. Bacillus sp. Bacillus sp. Pseudomonas sp.
bottoms need to utilize the petroleum hydrocarbons in their metabolic processes. Tank bottom waters in many cases appear to be as nutritious as the best diet that we can assemble in the laboratory. Even those spe cies that can use hydrocarbons as an energy source may not do so, if the aqueous layer offers more tasty foods. A study of bacterial activity in real-life tanks is beset with many uncontrollable and extraneous fac tors. One systematic variable, how ever, is pH. This changes as proc ess waters are carried over into blending and storage tanks. The highest bacteria population is found at a pH of 6.96, or practically 7.
Table II.
Bacterial G r o w t h o f Pond W a t e r
Bacteria Count per Ml. Stationary Rotating 50,000 120,000 Without Iso-octane 80,000 270,000 With Iso-octane Table III.
Bacteria Prefer Long Chains
Soil bacteria 48 hour test Hydrocarbon Count per Ml. Iso-octane Kerosine
18,100 410,000
Corrosion
I/EC
Petroleum Product Storage
Investigation of Bacterial Growth Table IV.
Effect of a Rust Inhibitor
Without inhibitor With 25 p.p.m. inhibitor
Count per Ml.
.! N:
Bacterial count in water bottoms below kerosine after 48 hours
SO 0 0 0 2,200 0 0 0
RUS
To learn what harm might be caused by such bacterial growth, the authors conducted laboratory experiments. As inoculants, pooled samples of refinery tank bottoms— but subsequently from "pond water" —were used. Its flora were practically identical with those of tank bottoms, except for the vagrant species that appear only infrequently in the bottoms. Table II illustrates the effects of rotation to simulate the roiling of a working tank. In time (48 hours in this case) at least some of the species in pond water learned to appreciate isooctane, especially when contact between water and hydrocarbon is facilitated, as by sloshing. A bacteria culture prepared from local garden soil gave the data of Table III. Some rust inhibitors appear to function as nutrients for the bacteria. At the normal level for such inhibitors (25 to 50 p.p.m.) in both gasoline and kerosine, stimulation of growth is found. Table IV gives data on a kerosine which is essentially the same as JP-4 fuel. Surface-active rust inhibitors may be expected to reduce the inter-
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