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cules would still be looped around those molecules which take part in the fibering. These other molecules also would have their spirals (or zigzags) stretched out but would have no opportunity to align themselves accurately so that they would not contribute to the fiber structure. They would, however, make possible the forces necessary to reestablish the tangle after the external forces of stretching are removed. It is assumed, of course, that the ends of the molecular complexes would stretch out rapidly but that the straightening out of the tangle would require more time, so that reasonably perfect alignment will occur only after a time lag. Such a picture is apparenty consistent with a mass of other data in the literature (see literature references a t end of citation 1). The picture may appear to be open to the objection that the size of the loops in the tangle may be too small to allow the overstretched ends just to release the strain of overstretching. This difficulty may be met if we assume that, as a rule, there is more length available in the tangle than is required to release the strain of overstretching. The relaxing of the ends would then take place until the secondary valence forces have a chance to tie adjacent molecular complexes together into a fiber structure which would persist during the rest of the stretching period. I n the case of certain fibers it is likely that there may not be enough untangling to relieve the overstretched ends. This would result in torn fibers resulting in turn, in the failure of Hooke’s lam, racking, and
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finally in tearing. The chemical reactivity of torn molecules (or complexes) might conceivably account, too, for the combined effect of cyclic and aging mentioned under section C.
ACKNOTVLEDGMEKT The writers are greatly indebted to C. W. Scliarf of the Bell Telephone Laboratories, Inc., and to W. F. Busse of the B. F. Goodrich Company for samples of rubber, and to the General Electric Company, Schenectady, N.Y., for making available equipment without which the work would have been extremely difficult, if not impossible. The authors are also grateful to W. F. Busse, A. T. hlcPherson, and L. F. Curtiss for their kindness in examining the data and conclusions during the preparation of the manuscript.
LITERATURE CITED (1) Acken, M. F., Singer, W. E., and Davey, \V. P., IND ENQ. CHEM., 24, 54 (1932). (2) H a u s e r , E. A., Gummi-Ztg., 40, 2090 (1926); IND.ENG.CREM, 19, 169 (1927). (3) K a t e , J. R., C h e w - Z t g . , 49, 353 (1925). (4) S a u t e r , E., 2. physik. Chem., 21, 161 (1933). RECEIVED November 22, 1933. Abstracted from the theses submitted by J. D. Long and W. E. Singer t o the Graduate School of The Pennsylvania State College in partial fulfillment of the requirementa for the degree of doctor of philosophy in physical chemistry and chemical physics
Nitrification in Sewage Mixtures EMERY J. THERIAULT AND
PAUL
D.
hlCNA4MEE
U. S. Public Health Service, Stream Pollution Investigations, Cincinnati, Ohio PREVIOUS publication ( 8 )has shown that the adjustment of the various factors which may affect the rate and extent of a biological oxidation in a sewage mixture is not critical when observations are restricted to the first or carbonaceous stage of this purification process. Ample indications were obtained, however, that the specifications should be far more rigid in studies extending to the second or nitrification stage of a bacterial oxidation. In the first instance the work of oxidation is carried out by mixed cultures which, taken collectively, are adaptable to wide variations in pH adjustments and other factors affecting bacterial growth. I n the subsequent stage of nitrification the oxidation process depends on the activity of highly specialized groups of organisms whose cultural characteristics must be carefully considered. Essentially, therefore, any study of nitrification even in such a heterogeneous mixture as sewage, becomes a “pure culture” problem with all of the difficulties attending such work. Among the variables which may affect a nitrification process are the nature and concentration of the mineral salts. the carbon dioxide tension, and the dissolved oxygen content. Except for conditions either of extreme deficiency or of abnormal concentration, these variables may be regarded as secondary in influence to the more important factor of pH. The discussion which follows will accordingly be limited largely to the effects of pH adjustment and control on the nitrification process.
A
EXPERIMENTAL PROCEDURE The general plan of experimentation mas to inoculate sewage mixtures buffered a t various p H values, generally pH 6.0, 7.2, and 8.2, with nitrifying organisms acclimated to one
or the other of these pH values. The sewage mixtures were prepared by diluting ordinary domestic sewage with the Clark-Lubs phosphate buffer solutions, suitably diluted, as described in previous work ( 7 ) . The cultures of nitrifying organisms were obtained by the repeated transfer of actively growing organisms to appropriate media buffered a t selected pH values. While this procedure is not expected to give a pure culture in the bacteriological sense, it does assure a preponderance of nitrifying organisms acclimated to a particular pH value. Cultures of nitrifying organisms which were satisfactory at pH 6.0 were also obtained from the activated sludge plant a t Rockville Center, where the pH value of the raw sewage is around 6.0.
LABORATORY EXAMINATIONS The pH value of the experimental solutions was determined colorimetrically with frequent comparisons against the quinhydrone electrode. The course of nitrification was followed by determinations of nitrogen present as ammonia, nitrites, and nitrates, using more or less standardized procedures. The methods used in the determinations of dissolved oxygen and oxygen demand have been fully presented elsewhere ( 7 ) . The Rideal-Stewart or permanganate modification of the Winkler method was used throughout. Of the numerous analytical precautions to be observed, mention should be made of the necessity for using ammoniafree water for dilution purposes. Ordinary distilled water, especially where the chloramine process of water sterilization is used, may readily contain 0.2 or 0.3 p. p. m. of oxidizable nitrogen. Applying a factor of 4.6, this minute trace of nitrogenous impurity will lead to a huge error in the oxygen demand determination. The difficulty may not be aroided
INDUSTRIAL AND ENGINEERING
548
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by the c u s t o m a r y e x p e d i e n t of prolonged storage unless mineral salts and a g r o w i n g culture of nitrifying organisms are also present. The presence of free c h l o r i n e in distilled water may be expected under various conditions. The removal of t h i s objectionable constitue n t i s r e a d i l y assured by the passage of t h e r a w w a t e r t h r o u g h a filter of a c t i v a t e d carbon prior to distillation. Starting with raw sewage as a potential s o u r c e of nitrifying material, erratic Eesilts may be obtained if a series of highly diluted subsamples is examined a t the very onset of the nitrification stage. The difficulty here presumably arises from the paucity of the original seeding or from an actual diminution during the long period of inactivity which precedes the nitrification stage. Very satisfactory agreement between duplicates is obtained by seeding, as in the experiments reported in this paper, or by pooling and redistribution of the subsamples around the sixth day of incubation or just prior to the onset of nitrification. Resort to this artifice is also permissible as a means of reaerating the subsamples in cases where the total disappearance of dissolved oxygen is indicated. If undertaken prior to the establishment of anaerobic conditions, this apparently heroic treatment is without effect on the rate and extent of oxidation during the first stage (8). Following the general procedure which has just been described, the course of n i t r i f i c a t i o n was followed using sewage mixtures buffered at pH 6.0, 7.2, and 8.2. These mixtures were inoculated with a culture of nitrite-forming organisms which had
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p r e v i o u s l y been shown to be active a t pH 8.2. The pH value of the sewage was 7.2 and, as it was not sterilized, nitrification was also to be expected a t that p H value. The results are shown in Figure 1 where the oxygen demand and the nitrite data are plotted against the period of incubation in days a t 20” C. The oxygen demand results are somewhat the same during the first 7 or 8 days prior to the onset of nitrification. T h e r e a f t e r the most v i g o r o u s o x i d a t i o n was obtained at pH 8.2, although the results a t pH 7.2 are but slightly lower. At p H 6.0, however, nitrite f o r m a t i o n h a d n o t proceeded to any appreciable extent after 20 days of i n c u b a t i o n a t 20” C. This is in line with the repeated observation that the nitrifying organisms in sewage may not adapt themselves to such a relatively small change as one p H unit, even in the course of 10 to 20 days of incubation. These experiments were repeated under identical conditions, except that the inoculation consisted of a nitrite culture growing actively a t pH 7.2 instead of 8.2. The sewage used in this experiment was collected from another source and possessed a pH value of 8.0. As s h o w n in Figure 2 the results are again in reasonably close accord during the first or carbonaceous stage of oxidation. After 7 or 8 days, however, nitrification was in active progress and all agreement ceased. The most v i g o r o u s o x i d a t i o n was obt a i n e d a t p H 7.2, corresponding to the pH value of the actively growing culture added as an inoculum. T h e nitrification process w a s some-
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May, 1934
I N D U S T R I A I, A N D E N G I N E E R I i?i G C H E M I S T R Y
what delayed a t p H 8.2 and it proceeded still more slowly at p H 6.0. These peculiarities of the oxygen demand curves (upper curves) are reflected in the direct observations on nitrites which are shown in the lower part of Figure 2. The formation of nitrates was greatly delayed in this experiment. I n completion of these observations on the effect of pH on nitrification, a third series of experiments was undertaken in which the inoculum consisted of a mixed culture of both nitriteand nitrate-forming organisms which has been acclimated to pH 6.0. I n previous experiments no attempt was made to add nitrate-forming organisms. The pH value of the sewage itself was 7.2. I n other respects the experirnental conditions were unchanged. As shown in Figure 2 the agreement in oxygen demand results was excellent during the first 8 or 10 days of incubation. Beyond the tenth day the interpretation of results is complicated by the fact that the production of nitrates and nitrites proceeded simultaneously a t pH 6.0 and 7.2. At p H 8.2 nitrate formation was delayed until the fourteenth day. The nitrite figure a t pH 8.2 accordingly reached a higher value than a t 6.0 or 7 . 2 . The expectancy that the rate of nitrification a t pH 6.0 would be as high as a t 7.2 was only partly fulfilled in this experiment. It is significant, nevertheless, that nitrification did proceed a t pH 6.0 a t a satisfactory rate whereas, in other experiments a t the same pH value, nitrification was either practically nil, as in Figure 1, or else greatly retarded, as in Figure 2. A further point of interest is that nitrate formation, under the influence of the added inoculum, did proceed at all three pH values in sharp contrast with the results presented in Figures 1 and 2.
DISCUSSION OF RESVLTS There is nothing in the early part of the deoxygenation curves presented in Figures 1-3 to indicate the wide variations in oxygen consumption which may occur after 8 or more days of incubation under standardized conditions. With a knowledge of the pH values of the sewage itself, of the dilution water, and particularly of the inoculum, the results are readily interpretable, proper allowance being made for the inoculation present in the sewage. The p H value of the dilution water should be suitably adjusted if concordant results are to be expected in studies of biological oxidations which extend into the nitrification stage. It is noteworthy that the addition of nitrifying organisms in active growth did not induce nitrification from the start but only after an incubation period of a week or more a t 20’ C. The delay in nitrification, therefore, is to be attributed not to a lag occasioned by the presence of attenuated cultures, or even to a scarcity of nitrifying organisms, but to the welldefined effect first clearly demonstrated by Adeney (1) for sewage mixtures and later generalized by Kendall (3) as the “sparing action of carbohydrates.” Carbon, as carbon dioxide, nevertheless appears to be an essential ingredient in the diet of nitrifying organisms. I n work with a simple medium, using ammonium chloride as the sole source oCfood, it was found necessary to prepare a buffer solution from potassium phosphate and sodium carbonate instead of the customary phosphate-hydroxide buffer. This precaution becomes unnecessary in work with raw sewage, as carbon dioxide is always present in relative abundance as a result of the preliminary oxidation of carbonaceous materials which invariably precedes the nitrification stage.
549
as correctives for the troublesome “bulking” of activated sludge. Thus, Donaldson ( 2 ) has controlled bulking a t Tenafly, N. J., by the addition of lime to maintain a pH value of 8.6 to 8.8 for 6 to 12 hours, while Mieder and Viehl (4) a t Leipzig, Germany, have obtained good results by maintaining a pH value of 6.5 with hydrochloric acid. On the basis of other results reported by Viehl (10) and of the data presented in this paper, it must be concluded that nitrification should be impeded by such measures if the normal pH value of the sludge-sewage mixture is around 7.5. I n effect, the supply of dissolved oxygen should be temporarily increased and, as claimed by Townsend (9) and others, the settling characteristics of the sludge should improve. The further experimental test of these views is now in progress using a small activated sludge plant. There is warrant for suggesting improper pH adjustments as a reason for the discordant results reported in well-sponsored investigations of the oxygen requirements of sewage plant effluents. Such an explanation would seem particularly applicable to cases where comparisons have been made of the effect of various dilution waters on the rate and extent of oxidation of partly nitrified effluents or of effluents which are just entering the nitrification stage. I n this connection it is tempting to suggest that extraordinary claims for reductions of 50 p. p. m., and more, in the oxygen requirements of samples treated with 1or 2 p. p. m. of free chlorine, may be due either to the absence of nitrifying organisms in the seeding which must necessarily be added, or to the use of a dilution water adjusted to a pH value which does not permit the growth of the added inoculum. This double hazard should also be encountered in examinations of effluents partly sterilized by the recently revived processes of chemical precipitition. Other discordant or patently improbable results with partly purified effluents might profitably be examined from this angle. These experimental difficulties in the evaluation of the efficiency of sewage treatment processes are due primarily to the extension of the oxygen demand test into regions far removed from its original use as a measure of stream pollution. I n tests of raw sewages which are restricted to the customary 5-day period of incubation, it must be concluded with Mohlman (6) that “a careful study of the results will indicate that the discrepancies are usually due to sampling errors, errors in the technic, or the presence of germicidal substances in the sample.”
SUMMARY Sitrification in sewage mixtures, even with an inoculum of known nitrifying organisms, does not proceed to a n appreciable extent until after approximately a week of incubation at 20’ C. Erroneous results may be obtained in evaluating the performance of sewage treatment processes if complete reliance is placed on the limited seeding of nitrifying organisms normally present in raw sewage, especially in partly sterilized or chemically treated samples. The p H value of the dilution water should be roughly adjusted to that of the established optimum for the prevailing nitrifying organisms when partly nitrified effluents are examined. A possible reconciliation is suggested for the apparent conflict in claims regarding the use either of acid or lime as correctives for the bulking of activated sludge. LITERATURE CITED
APPLICATION T O SEWAGE TRE.4ThlENT Phelps et al. (6) call attention to the seemingly contradictory claims for the beneficial effect of either lime or acid
(1) Adeney, W. E., Sci. Trans. Roy. Dublin SOC.,5, 539-620 (1895). (2) Donaldson, W., Sewage Works J.,4 , 283 (1932). (3) Kendall, A. I., Chem. d Met. Eng.,24, 56-60 (1921). (4) Mieder, F., and Viehl, K., Wasser, 5, 236-58 (1931).
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INDUSTRIAL AND ENGINEERING CHEMISTRY
( 5 ) Mohlman, F. W., Sewage Works J.,4, 899-900 (1932). (6) Phelps, E.B., e t al., Zbid., 5, 579 (1933). (7) Theriitult, E.J., Suppl. Pub. Health Repts. 90 (1931). (8) Theriault, E. J., MoNamee, P. D., and Butterfield, C. T., Pub. Health Repts., 46, 1084-1116 (1931); Pub. Health R e print 1475.
Vol. 26. No. 5
(9) Townsend, D.W., Munic. Sanit., 3,18 (1932). (10) Viehl, K., Zentr. Bakt. Parasitenk., II,86, 34-43 (1932). RECEIVEDJanuary 22, 1934. Presented before the Division of Water, Sewage, and Sanitation Chemistry e t the 85th Meeting of the American Chemical Society, Washington, D. C.. March 26 to 31, 1933.
Porter's Rule Graphical Analysis of Viscosity-Temperature Data for Solutions of Electrolytes A. M. RENTEAND F. E. SEUFFERT, Wayne University, Detroit, Mich. HE viscosity of liquids and solutions is an important fate a t 43" C., start at the isoviscoidal temperature of 43" and factor in the flow of fluids. Important as it is, the ex- follow the dotted line to B. At this point the viscosity of the istent data concerning viscosity of solutions of elec- potassium sulfate solution is the same as that of pure water at trolytes are meager. I n this paper it is proposed to extend 52" C. Therefore, the intersection point of the 52" C. temPorter's method for estimating unknown viscosities of solu- perature line of pure wat,er with curve A will determine the tions a t a given temperature when the viscosity is known a t viscosity in poises of the potassium sulfate solution at 43" temperature. some other temperature. To develop the statement that "the isoviscoidal lines for a Duhring's rule (1) states that, when the temperature of one substance is plotted against the temperature a t which a second series of concentrations of a certain substance are straight s u b s t a n c e h a s the lines," the viscosity data of fifteen electrolytes have been f-9 same vapor pressure studied. It is realized that fifteen electrolytes are not enough :.0/6 $ as the first, the result to establish a positive generalization, yet they are sufficient 60e will be practically a to indicate a characteristic trend. I n all cases the data have %2 straight line. This been taken from a reliable source (2). Also, the plotting of all graphical charts was done on a very large scale, 1" C. being ? 404 rule applies both to kOO8 pure l i q u i d s and to measured by a distance of 25.4 mm. (1 inch). z r ~ g solutions of electroThe isoviscoidal lines for the fifteen substances investi$ 2 lytes. Porter (3) ap- gated are straight lines, and with but six exceptions these 0 plied this idea to or- lines meet in a common point. Further, this point often 20 40 60 80 g a n i c l i q u i d s a n d lies on, or near, the diagonal Y = X . One of the six excepT E M R O f WATER OC showed that viscosity tions-potassium chloride-gives four lines that may be said FIGURE1. DIAGRAM OF PROCEDURE could be substituted to intersect a t (25, 25). A fifth line (for the concentration FOR DETERMINING VISCOSITY for vanor Dressure. and the result, as before, mould be a straigdt line. Since isoviscoidal means equal viscosity, the name "isoviscoidal lines" will be given to u' 60 0 these Porter lines. It will be shown that the isoviscoidal lines 2'40 4 for a series of concentrations of a particular 0 electrolyte in water are straight and that in v) 20 most cases these lines meet in a common point. Lc Whenever this common point can be located, it 0 0 may be used to locate any number of lines of different concentrations of the same salt. It $-Z0 is necessary to know merely one point on the k! unknown isoviscoidal line; by joining this point -EO 0 20 40 60 -40 -20 0 20 40 to the common point, the line is determined. This line, then, indirectly expresses the relationship between temperature and viscosity for 60 that concentration of the solution it represents. 640 This method is only approximate, but is graphi0 40 cal and should be sufficiently accurate for engi$2 0 neering calculations. 4 0 20 The procedure used for determining viscosity Y O is i l l u s t r a t e d in Figure 1 and is the same method as that described by Walker, Lewis, 4j 0 -ZO and McAdams (4). A is the viscosity us. temperature curve of pure water (2). The righte-40 $ -2 0 hand ordinate represents the temperature a t which a solution must be in order to have the -20 0 20 40 -20 0 PO 40 60 same absolute viscosity as pure water a t some ZSOV/SC O/DAL T E M ~ , ~ . IS OV/SCO/DAL JEMR, OC. particular temperature. For example, to determine the viscosity of 0.979 N potassium sulFIGURE 2. GROUPINGS OF ISOVISCOIDAL LINES
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