Persistence of Oily Wastes in Polluted Water under Aerobic Conditions MOTOR OIL CLASS OF HYDROCARBONS 'F. L.
LUDZACK AND DIANA KINKEAD
Robert A. Taft Sanitary Engineering Center, U. S. Department o f Health, ,fducafion, and Welfare, Public Healfh Service, Cincinnati 26, Ohio
This work reports the effect o f common variables related to stream pollution on the rate of oil destruction b y microorganisms. Organisms capable of biochemical destruction of oily waste in water (except for a trace o f stable and odorous material) are abundant in nature. Oxidation o f oil was not observed at low temperatures; at summer water temperatures the half life of the oil was approximately one week. Biological stabilization was associated with the sedimentation of oil emulsions, and frequent reseeding was necessary to maintain biological activity. This work i s a guide to understanding the behavior of streams that are polluted with oily wastes, the nature of oil decomposition, and its effects on water quality.
IL Contamination of surface water originates from a variety of common operations. Oil refineries and drilling operations are obvious, large contributors. The transportation services, including rail, pipeline, boat, and automobile, are widely distributed sources of oil waste. Each industrial operation contributes a variable quantity of oil due to processing or use of lubricants, cutting oils, solvents, or associated materials. This is a major problem for pollution control agencies. Their standards generally contain a limit for oil, which may be expressed as a maximum concentration of oil in the effluent or in terms of the prevention of films, emulsions, or sedimentary deposits in the receiving water. The objectionable features of oil contamination that are detectable by sight, smell, or touch are well known. They eventually disappear from polluted water. Other effects and the behavior of oil in water are not so well understood. Ruchhoft and others ( 4 )showed that hydrocarbons were associated with the taste and odor of water. Coe (3)found t h a t refinery wastes inhibited purification by activated sludge. ZoBell's review ( 7 ) included the following observations: Hydrocarbons were attacked by many species of organisms under aerobic or anaerobic conditions, heavy metals, hydrogen sulfide, oxidase inhibitors, or toxic substances affected the rate of selfpurifications of oil, and biochemical decomposition of oil occurred primarily a t the oil-water interface. Many data have been obtained on the behavior of oil in water, but they do not provide a basis for predicting the behavior of oil as a stream pollutant, Most investigations of oil-water systems have employed a physical or biological feature as an index of activity. Stone, Fenske, and White ( 6 )observed the emulsification of oil by bacteria. Coe ( 9 ) adopted the electrode potential. Carbon dioxide production, respiratory coefficients, bacterial count, and production of acids or other degradation products were reported in the review by ZoBell ( 7 ) . These were useful measures, but did not describe the system adequately. This investigation was designed to show the degree of biochemical oxidation of oil under specified conditions.
0
February 1956
The biochemical oxidation of oil was followed by infrared analysis ( 3 ) and by the determination of the principal oxidation product, carbon dioxide. The combination pr0vide.d data on the oil concentration, intermediate products, end products, and biological activity a t any given time. A medium grade commercial motor oil was used for all investigations.
Oxidation System The apparatus for aerobic oxidation of motor oil was arranged as shown in Figure 1. The oxidation bottle (5-gallon or 4 l i t e r )
was filled with B.O.D. dilution water ( 1 ) containing emulsified commercial motor oil, and suitably inoculated. Air was introduced a t a rate which would maintain a t least 60% oxygen saturation in the sample. A carbon dioxide absorption system was provided for effluent gas. Oil loss from the liquid could occur by oxidation and sedimentation. Air recirculation was provided in order to limit sedimentary effects. The carbon dioxide recovery system consisted of three absorbers in series containing barium hydroxide solution. Strength of alkali was adjusted so that not more than 50% of the alkali in the first absorber was neutralized by normal production of carbon dioxide in 24 hours. The carbon dioxide production per day was calculated from the difference in titration with standardized hydrochloric acid of an initial and a final sample of alkali. Exposure to room air was maintained reasonably constant for each titration. Under these conditions the first absorber trapped approximately 90% of the carbon dioxide absorbed by the three units. The second trapped most of the remainder; the third unit invariably picked up some carbon dioxide. Normally only the first unit was titrated each day, while the second and third were moved up one position, so that the fresh absorber was last in the line. A significant figure for carbon dioxide required careful control of several factors in operation. These included the absence of
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leaks in the system, loss of carbon dioxide during seeding or sampling, careful regulation of aeration rates, freedom from air line obstructions, and equilibrium of carbon dioxide in air and liquid. Inadequate control resulted in low values for carbon dioxide. Destruction of organic material added during inoculation resulted in higher carbon dioxide production than that calculated from oil loss. A good material balance between carbon from the oxidized oil and that appearing as carbon dioxide was obtained when these factors were properly controlled. It was not possible to obtain a theoretical balance. A reasonable approach was considered to be recovery of 80% of the carbon dioxide anticipated from the infrared data on oil loss. This amount was accepted as proof that the oil loss was due to oxidation rather than t o physical disappearance. The infrared data were more precise (5), but did iiot provide a continuous daily record. Carbon dioxide data were used only when backed by infrared data and a reasonable carbon balance. inoculation
Biochemical oxidation requires the presence of an adequate mixture of active organisms. The literature indicates that many species are capable of attacking oils. This investigation was not concerned with particular species, but evidence of the general distribution of such organisms in surface water n-as highly desirable. Mixed cultures for inoculation were therefore collected from several sources, including soils from the Ohio River bank a t points with and without visible oil contamination, oil-contaminated soils a t a refinery, refinery cooling tower effluent before treatment, and freshlj settled sewage. Seed activity was checked by B.O.D. technique (1)on freshly prepared octadecane emulsions. The emulsions were seeded with a t least two concentrations of the selected inocula and the results were discarded if they did not check within 10% or if the seed correction was insignificant. The relative degrees of attack on the hydrocarbon as a result of the various seed additions are shown by the corrected oxygen depletions in Table I. Comparisons in Table I are possible only between columns of a given series, as the concentration of hydrocarbon was not constant for all series. Sewage was more effective than any of the inocula tried. Parallel tests on 4-liter oxidation bottles showed similar behavior. Organisms suitable for the biochemical oxidation of oil are widely distributed. Surface water receives an ample supply from sewage and surface drainage to promote thc self-purification of oil waste.
Table I.
Series No.
1 2
Corrected Oxygen Depletion of Octadecane Suspensions with Various Seed Sources
Fresh Settled Sewage 2.14 2.63 2.13 1.59 4.04 3.32 4.36 4.22 3 30
(P.U.m., 5 days a t 20' C.) ~ ~ f iOhio ~ River ~ Silt ~ ~ No Cooling Tower Oil e\-ident Effluent saturated oil 1.94 1.59 2.23 .. 1.91 1.67 1.34 0.50 .. 3.66
4 18 4 40 3 06
2,52
, .
3 90 2.84
4:ofi 3.02
Soil , from Refinery Crude
hTaplithaoilsaturated saturated
1.31 1 80 4 : 60
3.54 3.67
1 83 1 87 2 02 1.23 3.14 3.46 3 06 , .
3'08
..
The effect of a single application of 10% by volume of settled sewage on oxidation of a motor oil emulsion a t 25' C. is shown in Figure 2, in which carbon dioxide production is plotted against time in days. hnalytical data for oil concentration and loss are included. Each week the system was analyzed and oil added to provide a new initial of approximately the same range.
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The curve shows that there was an increase of carbon dioxide production until the middle of the second week and a decrease thereafter. There was little activity at the end of 28 days, when reseeding was started. It was necessary to add 1% by volume of settled sewage per day to restore activity to 50% loss of hydrocarbon per week. t- C 0 2 - F R E E
[-(ALKALI
I F O R P R O T E C T I O N OF T H E AERATOR F R O M REVERSE A L K A L I FLOW DURING A I R FA IL U R E )
,
OXIDATION
Figure 1.
AIR
WASHED)
R E C l R C U L A l' I O N PUMP BOTTLE
Aerobic oxidation system for motor oil in water
The authors are indebted to C. M, Palmer, Biology Section of this laboratory, for a series of microscopic observations to account for the described behavior. The sample, similar to that of Figure 2, was examined after 4 weeks without reseeding, then for several successive days after daily reseeding. The examination included observation of the abundance and type of organisms but not specific species. The results of Palmer's examination showed that rotifers were abundant in the infrequently seeded system, while other active organisms a ere not detectable. Rotifers and inactive protozoan and algal cysts, minute oil globules, and amorphous aggregates were evident in all samples before and after seeding. A Monas type (free-saimming flagellate) and eubacteria (minute rods and spheres) appeared after the first day of sewage addition. Peranema, filamentous bacteria, and mold spores were noticeable after the third day. Ameba was detected on the sixth day, but not thereafter. S'erticella was noticed after the eighth day; mold hyphae and nematodes were noted on the ninth, A sample of the surface scum of the oxidation system after 6 days of reseeding revealed rotifers, Monas type, mold hyphae, and spores. The scum appeared to be flee of bacteria and was composed primarily of oil globules apparently held together by an invisible film. There appeared to be no close relationship between oil globules and other microscopic objects, except with the amorphous aggregates in the sediment. A mixed system of organisms appeared to be associated vrith the appearance of smaller oil globules. It was ~ this was due t o some peptizing action or to not known ' i hether other factors. This information s h o w a marked difference in the population variety of the system, depending upon the frequency of seeding. It appears that rotifers were more adaptable to oil than other organisms and dominated the system for a short time when reseeding was stopped. The oxidation of motor oil waq ncgligible in the absence of a suitable culture, and frequent reseeding was found necessary t o maintain active biochemical oxidation of oil under the conditions investigated. The data in Figure 2 show good correlation of oil disappearance and carbon dioxide production. Complete oxidation of octadecane would result in 3.12 mg. of carbon dioxide for each milligram of the hydrocarbon. This ratio shows relatively small change for any hydrocarbon above Clo in the paraffin series, hence is it reasonable approximation for motor oil. The total loss of oil during the Pweek period was 244 mg.; carbon dioxide equivalent
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STREAM POLLUTION PROBLEMS 70
6o 50
I
t
I
I
I
I
I-
i
The two systems in Table I1 were continued for 2 months with sewage addition and another month without it. At the end of 90 days, extracts of two mixtures were dissimilar with respect to odor. The sewage extract had a mild odor with no marked distinction; the oil extract had a pronounced resinous odor. This indicates that the odor components of the oil were more persistent than the nonodorous constituents, a small percentage of stable odor-producing foreign substance remained in the system, while the oils were oxidized, or the metabolic products were different in the two systems. I n any event, the effect upon the water supply would be identical. Infrared or chromatographic separation with alumina (3') failed to distinguish the odor components from hydrocarbons; therefore the odor apparently was not due t o oxygenated material. Recirculation
0
I
5
0
I
I
I
I
10
I5
20
25
30
TIME IN DAYS
Figure 2.
Carbon dioxide production in aerobic motor oil system (without reseeding)
yoLoss
Mg. Initial Hydrocarbon 104
1 st week 2nd week 3rd week 4th week
COZProduction per W e e k 282 323 226 135
Hc/Week
64 81 59
99 103 115
31
was 3.12 X 244 or 760 mg.; 966 mg. of carbon dioxide were collected during the interval, or 206 mg. in excess of that calculated from oil disappearance. The oxygen demand of the sewage seed as determined by B.O.D. technique was 220 mg. The anticipated and observed carbon dioxide were in good agreement, showing that carbon dioxide was the principal end product of oil oxidation. It was shown by Coe ( 2 ) that oil inhibited the self-purification of sewage. Table I1 verifies this conclusion, These data were obtained from two oxidation bottles a t 25' C.; one was seeded daily with 1% by volume of settled sewage, the other with the same amount of sewage in the presence of motor oil. If the carbon dioxide production from sewage was the same in both systems, the sum of rows 1 and 4 should be equivalent to row 2. This was true of the first week only. The amount of inhibition varied with oil concentration and with age of the system. After the fourth week, the production of carbon dioxide from sewage was greater than from sewage plus oil 75% of the time. This behavior made it difficult to decide on a control technique. The B.O.D. of the sewage seed was determined and a weighted average calculated for each week; this served only to indicate a limit, but did not provide a suitable measure of sewage oxidation in the presence of oil.
Table II. Row 1 2 3 4 5 6
Carbon Dioxide Production in Control and Motor Oil Oxidation System
Sewage, COz prod., mg. Sewage oil, Con prod., mg. Loss of oil mg. COz equivhent of oil loss. mg. Total of row 1 row 4 Difference, row 5 - row 2
+
February 1956
+
1st Week 169 252 25 78 247 -5
2nd Week 282 278 20 62 344 66
3rd Week 214 276 33 99 313 37
4th Week 260 247 18 56 316 69
Stone, Fenske, and White (6) regarded the agitation or interface area of the oil-water system as a critical factor. This was checked by observing carbon dioxide production and oil loss with and without air recirculation (6) on a seeded oxidation system. Figure 3 shows the results. No figures on oil loss are presented from 25 to 40 days because of an accidental spill. Figure 3 shows that 47% of the oil disappeared during the first 13 days; 73% during the next 12 days. Air recirculation time was the principal difference. Carbon dioxide data were more informative. Air recirculation for 2 hours per day increased carbon dioxide recovery on the sixth d a y with no additional oil. Increased carbon dioxide after reseeding on the 13th day was insignificant compared to that after continuous recirculation. The abrupt drop after recirculation of air was stopped on the 27th day shows a radical decrease in activity. The decreased activity without recirculation was partially due to carbon dioxide retention in the system and to a lower pH (5.2 to 6.0 without, 6.5 to 6.8 with recirculation). Stratification was another factor. Part of the minute oil globules rose to the top as a surface scum, but most of t h e organisms settled with the detritus and oil globules to the bottom. Although good contact of organisms and oil was possible in the sediment, oxygen and carbon dioxide transfer was questionable. Agitation was necessary to correct these factors. The preceding investigations established the operating procedures for the investigation. Oxidation system requirements were: frequent addition of suitable seed, agitation, production of a uniform emulsion before the system was started, and frequent check for tubing or apparatus leaks. Requirements for the analytical technique and calculation of results were: homogenization of the material in the oxidation bottle before oil sampling, determination of extractable material in the seed, and inclusion of one determination for oil plus oxygenated materials, another limited to hydrocarbons. Comparisons of carbon dioxide and oil loss checked better when the first determination was used. The second was more specific. Results of Persistence Investigations
Table I11 shows the results of oxidation of motor oil a t 25' C. Except for numbers 4 and 5, which were affected by low air recirculation, the oil loss was between 50 and 80% per week. I n each of the values, oil oxidation was established by at least 80% recovery of carbon dioxide as calculated from oil loss, and by the nature of the infrared curves. Most of the oxidation occurred during the first 4 or 5 days and resulted in curves similar to that of Figure 3 from the 17th t o the 25th day. The physical behavior of the system provided an interesting development in this series. The oil was introduced as an oil-inwater dispersion; many of the oil globules were visible only under X430 magnification. After 1 or 2 days in the active system, the turbid suspension separated into three zones when air recircula-
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n
70
60 v)
U =I
50
zr
X
N
U W
L
40
c)
W
0
3
n 30
2 h r . /24 hr,l_RECIR
N O RECIR-1-RECIR.
C O N T I N U O U S _(-NO
T I N I T I A L H c 121Mg.
47 To LOSS OF H c
-1I
"
0
5
7 3 % LOSS O F H c
15
IO
I N I T I A L Hc 130 Mg.
1
25
20
TIME
Figure 3.
1I -_
I N I T I A L Hc 144Mg.
30
35
40
IN D A Y S
Effect of recirculation of air on carbon dioxide production
Biochemical oxidafion of rnofor oil of 25' C.
Table HI.
hY0.
1
Biochemical Oxidation of Dispersed Motor Oil in Water at 25" C. Initial Oil 4-L. Vol., Mg.
121 33 104 4s 111 5Q 2 29 6 76 7 72 8 142 9 104 a Low air recirculation r a t e
2 3
Interval. Days 9 6 8 9 14
7 7 7 7
Reduction
of Oil,
%
SO
62 76 38 64
::
81 65
tion was stopped. 4 top scum, a clear liquid zone, and a settleable sludge separated within 1 hour of sedimentation. A suspended solids content of 100 mg. per liter was adequate to promote separation of oil concentrations from 10 to 100 mg. per liter. KO oil film was detectable as a result of this separation, 80% of the total oil was found trapped as oil globules in the settleable organic material. The separation did not occur upon addition of 300 nig. per liter of Dicalite; hence it was not strictly a surface action phenomenon. A'o separation occurred if seeding was omitted for several weeks. Oil oxidation a t 4 O C. was not measurable. Emulsion characteristics, infrared curves, and oil concentrations were unchanged after 60 days' observation. Carbon dioxide recovery was negligible. An increase in temperature to 10" C. resulted in an increase in carbon dioxide recovery and a corresponding oil loss. The separation of emulsion that required less than 2 days' contact with the
266
active organisms at 25" C. appeared after 1 week a t 10' C. Oil analysis showed 20 t o 30% oil oxidation per week. Table IV shows the average results of four replicate 5-gallon oil oxidation systems a t 20' C. The initial oil concentration was close t o 100 mg. per liter; on the 2Ist day oil was added t o increase the concentration to 33 mg. per liter.
Table
IV.
Aerobic Oxidation of Motor Oil at
20" C.
(Sewage seed, averages of 4 replicate systems reported) Loss (HC co2 co2, HC Susp. Absorbed, % of Loss, Solids, PH Interval Mg. % Mg. Theory % Mg./L. Range 86 . . 7.2-8.9 2325 First two weeks 1495 82 50 246 51 62 6.0-7.5 Third week 1 6 5 42 1266 47 94 5.8-6.0 Fourth week 236 36 1615 220 F i f t h week 140 3 0 916 218 36 95 5.7-5.9 145 41 995 220 30 88 5.9-6.3 Sixth week
ox)+
The loss of oil on the basis of hydrocarbon plus oxygenated products was 30 to 50% per week; it was slightly higher on the basis of hydrocarbon. The percentage loss of hydrocarbons decreased throughout the observation period. Almost 2000 mg. of oil were oxidized during the first 5 weeks; the residual oil was 7.3 mg. per liter. Concentration or relative stability of the oil frartion could have been responsible for the decrease. During the first 2 weeks, the yield of carbon dioxide was low when compared Jvith oil loss, and the pH of the system was high. The sewage seed was not entirely responsible for the high pH, a4 two units had a maximum p H of 7.6 and one had a maximum of 8.9. The accumulation of bound carbon dioxide during the early period was demonstrated b y 50% recovery of theoretical carbon dioxide during the first 2 weeks, more than 200% after the p€I
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STREAM PQLLUTIQN PROBLEMS
decrease. Total carbon dioxide collected was 81% of that calculated from oil loss during the 6-week period after the correction for seeding had been estimated. Table V shows the data on oil oxidation at 20' C. using a mold Fusarium oxusporum as the seed culture. Wm. Bridge Cooke, mycologist in this laboratory, provided the culture and the exploratory work. H e found that F u s a r i u m increased in numbers to a greater extent in the oil oxidation system than in sewage and was present in the oil oxidation system in greater numbers than the combined total of other molds and yeasts.
Table V.
Oil Oxidation System at 20" C. (Fusarium culture seed)
Interval Firsttwo weeks Third week Fourth week Fifth week Sixth week
Loss (HC r' ox) Mg. % 340 49 60 18 29 165 110 31 30 13
COB Absorbed, Mg.
1010 288 235 437 269
COz,
% of Theory 80 154 46 130 270
HC
Loss.
%
pH Range
57 63 20 48 51
6.6-7.3 8.4-6.6 6.4-6.6 6.1-6.6 6.1-7.2
The system was not maintained as a pure culture and some difficulty was experienced in maintaining a suitable nitrogen balance (third week). F u s a r i u m was added twice during the 6 weeks, at 0 and 14 days. Oil loss varied from 13 to 31% per week during the 6-week period. The F u s a r i u m count increased threefold during the first 2 weeks. More favorable conditions should stabilize and increase the oil oxidation rate. Sewage-seeded oil oxidation systems may owe much of their activity to molds. Discussion
The oxidation of oil was demonstrated by the infrared determination of oil, the appearance of intermediates in the infrared curve, and the recovery of carbon dioxide t o account for a major part of the carbon in the feed materials. Data were rejected if a serious imbalance was found. Many intermediate oxidation products-including peroxides, alcohols, diols, aldehydes, acids, ketones, ethers, and esters-are possible in the biochemical oxidation of hydrocarbons. Esters and acids were the only intermediates isolated and identified by group reactions in this investigation. Other compounds were undoubtedly present, as shown by general absorption in the infrared curve, but the concentrations of this mixture were such that isolation and identification were not attempted. The intermediate compounds in turn were oxidized to carbon dioxide and water. The infrared carbonyl absorption (characteristic of > C = 0) of the acids and esters was important as a rate indicator for biochemical oxidation of oil. During the first 2 t o 4 weeks in the simulated system, carbonyl absorption gradually increased; later a n equilibrium was established, where carbonyl absorption would remain relatively constant until a rate-changing factor such as temperature or seeding was altered. The estimation of carbon dioxide from sewage oxidation gave ambiguous results. Therefore, seeding was held a t a minimum, BO that the carbon dioxide from seed was relatively small compared t o that from oil oxidation. Infrared data were corrected for the extractable seed materials. The remaining approximation for carbon dioxide from seed was based on the seed oxygen demand and the concentration of oil in the system and in the seed. A good balance of carbon dioxide and oil disappearance was obtained, as shown in Figure 2 and Table V, where seeding was infrequent. Seed correction on a daily basis could not be estimated precisely. The upper limit of the estimated range for seed corrections was used.
February 1956
A summary of biochemical oxidation of oil per week a t t h e temperatures investigated shows: At 25' C. 200 c. 100 c.
40
50 t o 80% 1
c.
30 to 50% 20 to 30% No apparent action
High water temperatures are favorable for the biochemical oxidation of oil. The effect of temperature on oxidation was reinforced by a corresponding effect on the separation and sedimentation. Loss in oil from surface water should be relatively rapid in summer, very slow during winter temperature conditions. The conditions of oxidation were adopted in a n attempt t o secure a maximum oxidation rate for oil. It is not likely that oxidation in surface water will approach the rate in the simulated system a t the same temperature. The effects of sedimentation in surface water probably would be much greater than those of oxidation. Biological growth and silt would promote sedimentation. The net effect would tend toward more rapid loss of oil from surface water than in the simulated system where sedimentation was inhibited. The characteristics of sewage-seeded oil oxidation systems resembled those of activated sludge in odor, color, solids build-up, and settleability. The extent t o which this information applies t o the stream must await confirmation under stream conditions. Many variables were not investigated and conditions in the oxidation system were not exactly like those encountered in a stream-for example, the extent of oxidation of oil in sediment was not investigated. Certain algae were able t o grow rapidly in the presence of oil and light. Algae appeared t o have no effect on the oxidation rate but may have influenced sedimentation. Concentration of the oil and age of the system may have influenced oxidation rates, because new systems frequently showed higher activities. The following conclusions indicate the significant observed results. Common microorganisms in surface water are capable of biochemical oxidation of motor oil. Continuation of biochemical oxidation depends upon reinoculation with fresh organisms under the conditions investigated. Oil contamination of water presented a two-phase problem; persistence of the oil in water, and inhibition of the oxidation of other wastes in the water. The reduction in number and type of organisms in the presence of oil in the system was associated with both. Predators were the last t o be affected. Greater oil-water interface area increased the oxidation rate. The temperature of the oxidation system is a major variable. At 4 ' C. oil content was apparently unaffected by oxidation and sedimentation in the simulated system. The extracts of oxidized motor oil systems were characterized by increased odor. The principal end product of oil oxidation is carbon dioxide. The most prominent intermediate compounds are organic acids and esters. literature Cited
Public Health Assoc., New York, "Standard Methods for Examination of Water and Sewage," 9th ed., 1946. (2) Coe, R. H., Sewage and I d . Wastes 24, 731 (1952). (3) Ludzaok, F. J., and Whitfield, C. E., Anal. Chem 28, 157 (1956). (4) Ruchhoft, C. C., lliddleton, F. M., Braus, Harry, and Rosen,
(1) Am.
A . A., IND. ENG.CHEM.46, 284 (1954). ( 5 ) Setter, L. R., Brittingham, W. E., and W'essels, R. F., Sewage and Ind. Wastes 25, 798 (1953). (6)
Stone, R. W., Fenske, M. R., and White, A. G. C., J. Bacterid. 44, 169 (1942).
(7) ZoBell, C. E., Bacterid Reus. 10, 1 (1946).
RECEIVED for review June 20,
1955.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTED September 21, 1955.
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