INDUSTRIAL AND ENGINEERING CHEMISTRY
1132
It is apparent that the gelling power of ammonium salts a t both 8' and 25' C. is not entirely due to acid formed by hydrolysis, as gels are formed a t a p H only slightly less alkaline than the p H of the sodium silicates themselves. This ability of ammonium salts to form sols and gels is probably due to the formation of slightly ionized, heavily hydrated, insoluble gelatinous salts. The data are in agreement with the theory most widely accepted a t the present time conccrning the structure of silica gels. According to this theory, a silica gel consists of heavily hydrated interlaced fibrillar or brush heap structure of very large polysilicic acid molecules with the spaces filled with water or dilute silicate solutions. These chains are formed by the condensation of molecules of simpler silicic acids or hydroxides forming water and high Dolvmeric Dolvsilicic acids. If we assume that eelation is due to a reaction of this type, fastestgelation should and probably does occur near the p H of least ionization where there -
I
-
I
Y
Anaerobic
Vol. 43, No. 5
is a minimum of repulsive forces between similarly charged silicic acids or hydroxides. LITERATURE CITED (1) Baylis, J. R., J . Am. W a t e r W o r k s Assoc., 34, 1397 (1942). ( 2 ) Baylis, J. R., w o r k s & Sewerage, 83, 469 (1936). (3) Hay, H. R., U. S. P a t e n t 2,444,774 (July 6, 1948). (4) H u d C. B.9 C'hem. Rezs.1 221 403 (1938). (5) Hurd, C. B., and Barclay, R. W., J . Phys. Chem., 44, 847 (1940). Hurd, C, B,, and hIlller, p. s,, 36, 2194 (1932). (7) Hurd, C. B., Pomattl, R. C., Spittle. J. H., and iiloes, F. J., J . Am. Chem. Soc., 66, 388 (1944). (8) Merrill, R. C., IND.ENG.CHEM.,40, 1355 (1948). (9) hIerrill, R. and Bolton, z,, Chem. Progress, No.1, 27 (1947). (10) PIerrill, R. C., and Spencer, R. W., J . Phys. $. Colloid Chem., 54, 806 (1950). RECEIVED July 7, 1950. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 117th Meeting of the AVERICAVCHEMICAL sOCIETY, Detroit, Mioh,
water
c.,
sistence of o-Cresol
enol
111. B. ETTIKGER, W. ALLAN MOORE, AND R. J. LISHKA Federal Security Agency, Public Health Service, Environmental Health Center, Cincinnati, Ohio Factors bearing on the resistance of phenolic materials to destruction by natural agencies are of importance because of the difficulty which the presence of trace amounts of such materials causes in the production of a safe palatable water from surface water supplies. Phenol and o-cresol are observed to undergo complete destruction under anaerobic conditions similar to those that might be encountered in polluted streams or waste lagoons. The end products of such decomposition are presumed to be carbon dioxide and methane. The over-all
persistence of the phenolic materials studied under anaerobic conditions was found to be significantly greater than the persistence noted for such materials in polluted aerobic waters. Microorganisms are responsible for the chemical changes observed. This work indicates that controlled storage may be satisfactory as a means of destroying the phenol content of wastes under certain circumstances. Phenolic material will be transported farther with a minimum loss in a deoxygenated stream under ice cover.
I
was used. A 5-gallon carboy was preferred because the smaller size made possible fairly effective mixing by manual shaking. To prevent photosynthesis, the carboys used were given several coats of a heavy black paint and placed in the laboratory where they received no direct sunlight. Incubations were carried out a t both room temperature and a t 4" C. I n the latter case, the entire apparatus was placed in a 4' C. incubator. In making a run, the carboy was Bled with a mixture of sewage and a selected diluent. Diluents used have consisted of up to 95% of tap water, formula C dilution water (S), or various surface waters. The mixture was allowed to stand until oxygen-free on the basis of the Winkler test ( 2 ) . The phenolic material was then introduced through the thistle tube. The holding bottle was shaken thoroughly. Samples for examination were withdrawn through the siphon tube. When required, air was pumped through the deoxygenating train into the bottle to maintain nitrogen pressure in the system slightly greater than atmospheric pressure.
N AN earlier series of investigations, the factors governing the persistence of phenolic materials in surface waters were studied in Borne detail (5). This study is a natural sequel. It represents an attempt to determine some of the principal factors which govern the persistence of phenol and 0-cresol under anaerobic conditions such as might be encountered in badly polluted surface waters or waste lagoons. The scope of the work has been limited to: (1) a qualitative evaluation of some of the most important factors involved, and (2) making sufficient observations to permit qualitative comparison of the anaerobic persistence of phenol and o-cresol with the aerobic persistence of these materials in polluted waters previously reported. Tarvin and Buswell ( 7 ) have shown that phenol and a number of other aromatic compounds will undergo anaerobic decomposition, with the carbon involved appearing in the end products as carbon dioxide and methane. The extended series of investigations reported by Buswell and his coworkers ( 1 ) make it evident that the anaerobic diesimilation of phenol reflects the metabolic activity of microorganisms. METHOD O F INVESTIGATION
The apparatus illustrated in Figure 1 was used t o make this series of investigations. According to the need of a particular experiment, either a 5gallon or 10-gallon carboy of accurately known total capacity
*
In setting up the deoxygenation train, it was found desirable to stagger the levels of the alkaline pyrogallol as indicated by Figure 1. In practice it was found that while the apparatus was standing the first several bottles of the washing train would remove some oxygen from the quiescent gas above them. This set up vacuum conditions which resulted in sucking back of the pyrogallol solution toward the inlet end of the train. In order to avoid this difficulty, particularly because some experiments were run for several months, the system of filling the washing bottles was used as indicated in Figure 1. Determinations of phenol and 0-cresol were made using the
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1133
EXPERIMENTAL RESULTS Thistle Tube
FIGURE I
APPARATUS USED FOR ANAEROBIC PERSISTENCE STUDIES
In Table I are given some features of the results of eight different studies of the persistence of approximately 1 p.p.m. of phenol in anaerobic solutions a t room temperature. No substantial lag factors were encountered in this work. I n almost all cases, the removal of the last half of the added phenol was much slower than the removal of the first half. In Figure 2 are shown graphs of the detailed persistence data of three of the experiments. The lag in phenol dissimilation during the first two days shown by curve 2 was the longest lag noted in any of the anaerobic persistence studies of phenol a t room temperature.
Slop C o c k
TABLE I. PERSISTENCE OF 1 P.P.M. ADDITIONS OF PHENOL AT LABORATORY TEMPERATURE
5 t a l l o n Carboy
Glass Sloppertd G a l Woihlng Bott1eo Containing Alkaline Pyrogallol
Conioining Sludge
Initial Composition of Anaerobic Mixture
% c
modification of the Gibbs reaction described by Ettinger and Ruchhoft (4). In general, the analytical results are consistent. In some cases, because of difficulty in mixing, the results obtained immediately after the addition of phenolic material to the anaerobic solution were out of line. In these cases, calculated rather than observed values were used. I n actual practice, surface waters which contain no dissolved oxygen would be encountered only in heavily polluted streams. The most probable persistence of septic conditions would be in streams under ice cover. The experiments were designed to correspond, in some measure, to these conditions. With one exception, the anaerobic solutions studied had a relatively high initial
B.O.D.
Sewage 10 7.5 10 10 10 5 5
1
I"
2 2 1 2 2 3 6 5
17
16
a
10 10
15
11
22
Two observations of the anaerobic persistence of o-cresol a t room temperature are shown in Figure 3. One other observatioli was made on 0-cresol, and this is discussed below in detail. A comparison of the graphs of Figure 3 with those of Figure 2 indicates that the initial rates of attack on phenol and o-cresol are
FIGURE 4
IO00
ANAEROBIC PERSISTENCE OF PHENOL A T ROOM TEMPERATURE (1)
Diluent Formula C water Great Miami River water Tap water Tap water plus 50 p.p.m. NazSOl Tap water Great Miami and Ohio River waters Great Miami and Ohio River waters Synthetic media
Days Required to Obtain Indicated Reduction of Phenol ._ 50'% 100%
ANAEROBIC PERSISTENCE ,D
lnlO%Sswoge intap water
OF PHENOL AT 4'C.
800
1 B
f
600
4
t p
400
* 8
200
0 iR
1oooL
0
2
4
8
6
Day6
Slow6
5
10
I5
20
Days Stored
Days Stored
10
I4
16
25
30
35
40
1134
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 5
FIGURE 6
1
FIGURE 7 1000
ANAEROBIC PERSISTENCE OF SERIAL PHENOL ADDITIONS AT ROOM TEMPERATURE
NAEROBIC PERSISTENCE F SERIAL ADDITIONS F PHENOL AT 4'C.
800
(In5% Sewage In polluted river water)
-
lIn10%So*oqe I " f 0 I r n " l G c"va1sr)
m
2 600 B 1
P400 ?.
P ::200 0 5
0
IO
26
20
IS
35
40
45
Days S l o r e d
very similar. Although the data are too meager to serve as a basis for definite conclusions, it would seem that at room temperature the persistence of o-cresol is less than the corresponding persistence of phenol. Figures 4 and 5 show the results of studies of the anaerobic persistence of phenol and o-cresol at 4" C. The rates of disappearance of phenol a t 4' C. are more rapid than would be anticipated from $he general knowledge of the effect of temperature on anaerobic digestions. In the case of the 4" C. data (Figure 5 ) , the complete disappearance of o-cresol within 10 days is surprising. A comparison of Figure 5 with Figure 3 suggests that lowering the temperature to 4" C. had a relatively small effect on the 0-cresol dissimilation, only slight lags and a relativelv small in-
crease in total persistence time being attributable to the lower temperature. A somewhat surprising factor shown throughout the observations is the absence of lags of any extended duration. This suggests that the microorganisms responsible for the chemical transformation noted must be extremely plentiful in the solutions which were studied. The implication is that sewage normally contains many microorganisms or groups of microorganisms capable of decomposing phenol and o-cresol anaerobically. Many of the data presented in tabular or graphic form have represented only the first stage of a series of feedings. I n all, nine serial feeding experiments were made, including a t least two experiments each a t 4" C. and a t room temperature for phenol and 0-cresol: In most instances, after the first feeding of 1000 parts per billion or the second feeding at that level, subsequent additions were increased to produce higher levels of phenol or: o-cresol in the substrate. Four graphs showing results obtained with each chemical under each set of conditions are presented in Figures 6 to 9. Figures 6, 8, and 9 represent a somewhat unorthodox type of graphical presentation. I n order t o combine the range advantages of multitier semilog paper with the ability to present a zero observation graphically, a small constant is added to each ob-
XI
FIGURE 8
n
4NAEROBIC PERSISTENCE OF S E R I A L 0 - C R E S O L 4DDlTlONS AT ROOM TEMPERATURE ( I n 5% Serape tn P o I I u v e d r i v e r w a t e r )
FIGURE 9
ANAEROBIC P E R S I S T E N C E O F S E R I A L o.CRESO1 ADDITIONS AT 4'C. (I"
IO% s w a g e in Dollutad r i v e r w o l e r )
n
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1135 FIGURE I1
FIGURE IO
ATYPICAL ANAEROSIC PERSISTENCE OF PHENOL AND o-CRESOL AT ROOM TEMPERATURE
-m
(I) Phenol in
t
10%
Sewage in formula
EFFECT OF pH ON ANAEROBIC PERSISTENCE OF PHENOL AT ROOM TEMPERATURE (1) 1000 Partsper blillon in 10%Sewage a t r o o m temperature Initial p H 4.5.
”c’ water
40
0 0
5
IO
15
20
25
30
35
50
60
70
80
Days Stored
D O Y S Storod
1
1
servation and the graph of the sum is presented. The basic shape of the semilogarithmic curve is preserved unless the observation is of the same order of magnitude as the added constant. At the same time, a zero observation does not have to be visualized a t some imaginary location. The results of serial feeding studies, taken collectively, indicate that a previous history of acclimatization tends to promote the further removal of phenol or 0-cresol under anaerobic conditions, although exceptions were noted. It was also found possible to develop anaerobic substrates in which- 50,000 p.p.b. of o-cresol were dissipated (Figure 8) with reasonable facility. The same sort of experiment was carried out with phenol, although the detailed data on this particular experiment are not presented graphically. The development of inocula and substrates able to decompose fairly large quantities of phenol or o-cresol was not particularly surprising. From the work of Tarvin and Buswell (7) it would be inferred that much higher concentrations of phenol than those used in the present work undergo anaerobic decomposition. In a few experiments, it has been observed that after an initial attack on the phenolic material there were subsequent static periods in which the phenolic material was not attacked. In some of the serial feeding studies, the rates of attack observed were highly inconsistent. Thus, after the second addition of ocresol shown in Figure 8, there was a lag of 3 days. After the lag, the dissipation of the o-cresol apparently was substantially slower than that of either the preceding or the following additions. In Figure 10 are shown two observations of essentially similar nature, in which after the initial attack further dissipation of phenolic material was extremely slow and incomplete when depletion of the substrate brought the experiment to an end. The data are definitely atypical. However, they demonstrate that in the course of an anaerobic attack on even a relatively dilute substrate, conditions will develop which will greatly retard further anaerobic action. This is not a totally unexpected observation. For instance, in the digestion of fresh unseeded sewage solids, the normal course of the digestion leads to the development of acid conditions followed by an extended period in which further transformation is exceedingly slow. In general, supplying alkali to neutralize an anaerobic mixture which has become acid will not cause an immediate resumption of fermentation. I t is not the intention of this paper to examine exhaustively the factors that may tend to retard or halt anaerobic fermentations. It is sufficient to recognize that such factors exist and that anaerobic fermentations may develop conditions or products of biological activity which cause such retarded action. The results of the two experiments graphically presented in Figure 10 are definitely unusual. In fact, they represent the only two sets of observations in which the phenolic material was
not exhausted when the experiment was halted. Unfortunately, observations of the pH or other auxiliary data which might have offered some explanation of the retarded rates were not obtained. To demonstrate that a low pH alone is sufficient to greatly impede the anaerobic dissimilation of phenol, one experiment wag set up in which the pH was adjusted to 4.5 before the substrate became septic. The results of this experiment, presented graphically in Figure 11, demonstrate the relatively great retarding effect that a low pH may have on the anaerobic dissimilation of phenols. SIGNIFICANCE OF DATA
The implications of these data are fairly clear. The over-all persistence of the phenolic materials studied under anaerobic conditions was significantly greater than the persistence found for such materials in polluted aerobic waters (6). This statement would seem to hold regardless of the temperature. Accordingly, phenolic material would be expected to show greater persistence in travel in a septic stream than in an aerobic stream. It may be predicted that phenolic material would be transported farther with a minimum loss in a deoxygenated stream under ice cover. The observations suggest that lagooning or extended storage might provide adequate treatment for phenolic wastes under certain circumstances. Aerobic attack on relatively concentrated phenolic wastes is currently practiced as a means of phenol removal (6). It appears that under favorable anaerobic conditions, even a t low temperature, up to 50 p.p.m. of phenol may be dissimilated completely in approximately 2 weeks. If controlled storage will reduce the B.O.D. of a waste to a low level, the Bame operation should also result in a very substantial reduction or a complete removal of phenol and 0-cresol. LITERATURE CITED
(1) Buswell, A. M.,et aE., Ill. State Water Survey, Urbana, Ill., Bull. 32. (2) American Publio Health Association, New York, “Standard Methods for the Examination of Water and Sewage,” 9th ed., p. 129,1946. (3) Ibid., p. 140. (4) Ettinger, M. B., and Ruchhoft, C. C., Anal. Chem., 20, 1191 (1948). (5) Ettinger, M. B., and Ruchhoft, C. C., IND.ENG.CHEM.,41,1422 (1949). (6) Harlow, I. F.,and Powers, T. J., Ibid., 39, 572 (1947). (7) Tarvin, D.,and Buswell, A. M., J. Am. Chem. SOC.,56, 1751 (1934). RECIUIVIUD September 13, 1950. Presented before the Division of Water. Sewage, and Sanitation Chemistry a t the 118th Meeting of the AMERICAN CHEMICAL SOCIETY, Chioago, Ill.
