March, 1926 1-Animals of oxygen. 2-.4nimals and saved by 3-Animals
I N D USTRIdL A-TD ENGINEERING CHEMISTRY killed immediately by carbon monoxide and lack brought out unconscious from carbon monoxide fresh air or oxygen treatment. brought out unconscious from carbon monoxide
291
poisoning and revived by air or oxygen only to die later of pulmonary edema due to nitrous fumes. 4-Animals brought out seemingly but little affected at the time, but which die later of pulmonary edema due to nitrous fumes.
Effect of Temperature on Rate of Deoxygenation of Diluted Sewage',' By R. E. Greenfield a n d A. L. Elder STATEWATERSVRVEY LABORATORY, URBANA, ILL
Biochemical oxygen demand in sewage diluted with aerated distilled water a n d incubated a t from 2' to 6' C. shows a lag phase during the first few days, followed by a fairly rapid rise in t h e rate of deoxygenation. The duration of this lag phase decreases with t h e increase of sewage concentration. Evidence is presented which indicates that this lag phase is due to t h e necessity for t h e development of a sufficient number of low-temperature tolerant bacteria t o carry on a measurable deoxygenation. On account of t h e lag phase a n d slow r a t e of oxygen consumption at t h e lower temperatures, t h e commonly accepted formulas connecting rate, time, a n d concentration d o n o t adequately represent t h e rate of deoxygenation in sewage under these conditions. The total a m o u n t of oxygen used u p in sewage dilutions a t lower temperatures seems to be equal to, or possibly
greater than, t h e total a m o u n t used by similar dilutions at higher temperatures providing sufficient time is allowed. In general, t h e r a t e of deoxygenation of sewage dilutions incubated a t 14' a n d 20' C. corresponds fairly well with t h e formulas developed by Theriault, Streeter and Phelps, a n d others. Biochemical oxygen demand curves such as reported by Theriault for Ohio River water, indicating two stages of oxidation, were n o t obtained when diluted sewage was used. Such curves were obtained, however, from samples of Illinois River water. These results indicate t h a t t h e second stage is not so m u c h a nitrification process, as suggested by Theriault, b u t rather is caused by a n increase of putrescible m a t t e r resulting from t h e death of plankton.
............
A
SUITABLE dissolved oxygen content in a stream is necessary for the support of a normal flora and fauna. Investigations as t o the oxygen-absorbing capacity of polluting wastes introduced into natural water courses have become increasingly important. This oxygen-absorbing capacity is often called "biochemical oxygen demand." For the most part, these investigations have been carried out a t temperatures approximating normal summer temperatures-i. e., 20" to 37' C., with the assumption, either implied or stated, that such summer conditions represented the critical conditions encountered in a polluted stream. Some winter investigations made in 1924-25 by the Illinois State Water S ~ r v e y in , ~ which low oxygen concentrations were encountered under the ice a t points where higher oxygen concentrations had been found during the summer months, indicated the desirability of having more information as to the rate of oxygen utilization under low temperature conditions. With the exception of experiments made by Pleissner4 a t 7' C., and later experiments reported by Theriault6 at 9" C., practically no information was found in the literature on this subject. I n this paper will be presented experiments on the rate of deoxygenation of sewage samples diluted with aerated distilled water a t temperatures ranging from 2' to 20" C. Received October 29, 1925. of a thesis submitted t o the Graduate School of the University of Illinois in partial fulfilment of requirements for the degree of master of science. Illinois State Natural History Survey, Bull. 15, Art. 7 (1925). 4 Arb. kais. Ccsundh.. 34, 230 (1910). 6 "Rate of Deoxygenation of Polluted Water" presented a t the convention of American Society of Civil Engineers, Cincinnati, Ohio, April 22 to 24, 1925. 1
* Abstract
*
Experiments with Diluted Sewage The water used for diluting samples in these experiments was prepared as follows : Double-distilled water was aerated by bubbling air through it for several days. After standing for 2 to 3 weeks it was again aerated at the temperature to be used in the experiment. I n this way water was obtained which upon incubation showed no decrease in dissolved oxygen concentration. The necessity of bringing the dilution water to the incubation temperature before dilutions are made has been mentioned by others,617 and was confirmed by some preliminary experiments. At the lower temperatures, if the water is not brought to the incubation temperature and reaerated, the resulting solution is subsaturated with oxygen. This is not desirable because it does not correspond to natural conditions in streams. On the other hand, if water is aerated a t low temperatures and incubated at higher temperatures, the resulting solution is supersaturated with oxygen. Supersaturation causes the escape of gaseous oxygen around the stoppers of the bottles. This was shown in some cases to amount to as much as 0.51 p. p. m. in 24 hours. Certain published data examined in the course of this investigation seem to be affected by this error. All dilutions used for each series of experiments (here reported in each separate figure) were made up from one sample of sewage. The samples were collected from the sewerage system of a city of 15,000 population, in which there were no important industries furnishing trade wastes. The sewage samples were allowed to settle one hour and the supernatant liquid was taken for the dilutions. The dilutions were made in bulk, thoroughly mixed, and siphoned into 250-cc. glassstoppered bottles. These bottles were completely filled 6
7
Report of Royal Commission, Eng. News, 68, 1159 (1913). Theriault, P u b . Hcalfh Rpts., 31, 1087 (1920).
INDUSTRIAL AND ENGISEERISG CHEMISTRY
292
and precautions were taken to see that no air bubbles were entrapped under the stoppers. I n order to prevent the entrance of atmospheric air, the bottles were always incubated entirely immersed water. Numerous experiments indicated that, even when the water used for immersing the bottles contained considerable organic matter, in no case was sufficient sealing water sucked into the bottles to cause any discrepancies in the results. It is suggested that this method Series I 3 14 16 17 19 2 0 Temperoture 2' 2' 20'20' 14' 14' Dtlution / % 2 % / %2% 19'' 2%
8
7
Days Figure 1-Rate
of Deoxygena$on of 1 and 2 Per c e n t Sewage Dilutions a t 2 , 1 4 O , a n d 20° C.
of incubation of bottles is considerably more convenient than the rubber-collar seal and other devices described in the l i t e r a t ~ r e . It ~ ~is~ ~also ~ ~ suggested that the incubation of bottles in a constant-temperature water bath is often more convenient and accompanied by less variation than if carried out in an incubator. Even if an incubator is used, immersion in a vessel of water tends to minimize the temperature fluctuations encountered in such devices. With the exception of the 6" C. experiments, which varied sometimes as much as 2" C., all temperatures were controlled t o within *lo c. I n all the experiments a large number of duplicate bottles were made for each dilution, the initial dissolved oxygen was determined immediately, and the residual dissolved oxygen
-u 7
1
38 3:
Series
Temperal,ure 2' Dilution I%
2 22
I
n
0
8
Figure 2-Rate
40 41 42 6' 20' 20' 2%
I% 2%
1 1 1
I
I
I
I
/6
24
Days
I
I
32
40
I 48
I 56
I
64
of Deoxygenation of 1 a n d 2 Per c e n t Sewage Dilutions a t 2O, 6'. and 20' C.
determined a t intervals throughout the incubation period. The dissolved oxygen was determined by use of the RidealStewart modification of the Winkler method." Jackson and Horton,THISJOURNAL, 1, 329 (1909). Ibid., 6, 325 (1914). 10 Mohlman, Am. J . Pub. Ncalfh, 15, 10 (1925). 11 "Standard Methods for the Examination of Water and Sewage," b y the American Public Health Association, IQBS. 8
* Buswell,
T'ol. 18, No. 3
The results of one of the typical experiments are shown in Figure 1. The amount of oxygen used up in p. p. m.-that is, the difference between the initial dissolved oxygen and the residual found a t any time, t-is plotted against the time in days. Curves are given for 1 and 2 per cent sewage dilutions incubated at 2", 14", and 20" C. The curves show that the rate of deoxygenation is highest at 20" C., somewhat lower at 14' C., and much lower a t 2" C. Deoxygenation does take pIace at 2" C., although there is a distinct lag phase of a few days during which little oxygen is absorbed. Figure 2 shows another typical series of experiments a t 2", B o , and 20" C. The curve for the rate of deoxygenation a t 6" C. lies, as is to be expected, between the 2" C. curve and the 20" C. curve. At 6" C. the lag phase is of shorter duration. Deoxygenation at 20' C. is practically complete a t the end of 16 to 20 days. The 2" C. experiment,. represented in Figure 2, was carried on for 58 days, Temperature 20" and at the end of that time as much oxygen had been absorbed by the 1 per cent dilution as by the corresponding dilution at 20" C. Although no 20" C. experiments were carried on for 58 0 8 /6 24 32 days, the fact that Do ys t,here was very little Figure 3-Rate of Deoxygenation of deoxygenation f r o m Illinois River Water a t 20" C. Showing the twentieth to the Two-Stage Reactions forty-fifth day (Figure 1) indicated that no additional absorption would take place from the forty-fifth to the fifty-eighth day. These curves, at least at higher temperatures, are regular and have the general form of exponential curves. The follon-ing general formula has been developed by Streeter and PhelpsI2 and ~ t h e r s to , ~ fit such curves:
where
L
= total biochemical oxygen demand
X = biochemical oxygen demand for t days K = a constant for any given temperature
K defines the rate of deoxygenation and varies with temperature, as can be seen from Figures 1 and 2. From all the experiments a t 20" C., about twelve in number, we derive the value for K equals 0.11 * 0.01 when t is expressed in days and the biochemical oxygen demand in parts per million. The 14' C. experiments, six in number, gave K equals 0.075 * 0.005. This agrees very well with the data published by Phelps and StreeterI2 for the Ohio River. At lower temperatures, however, application of this formula is not of much value at the present time-first, because of the lag phase found in the lower temperature experiments, which is not represented in the genera1 formula; and second, because at these low temperatures with such low rates of deoxygenation the total biochemical oxygen demand is more of a fictitious than a real figure, and is therefore practically a second empirical constant. If an empirical equation with two or more constants is to be employed, it is quite probable that another equation could be developed which would better represent the results of the lower temperature experiments. Theriault's6 curves for Ohio River water,are of a somewhat different shape than those shown in Figures 1 and 2, in that two stages of deoxygenation are indicated. The first stage follows the general formula and general shape of the 15" and 13
Pub. Hcalfh Bull. 146 (1925).
I N D U S T R I S L d N D E S G I S E E R I S G CHE.IfISTR1'
March, 1926
20' C. curves in Figures 1 and 2, this stage lastmg about 15 days. I n the second stage deoxygenation is somewhat more rapid than is to be anticipated from the equation. Theriault agrees with Adeney13 that this difference may be explained on the basis that the first stage represents carbonaceous oxidation, and the second, nitrification; and he seems to assume that it is a general phenomenon to be encountered in all such de-
JI Series 33 34 35 36 Temperature 2' 2' 2" 2' I d 29. 3% 42
IO 9 -u
8
QJ
w 7
3
c6
gng
3
0 4
z 3 c 2 I
0
16
24
32
Days Figure 4-Effect of Concentration of Sewage on Duration of Lag Phase in 2' C. Deoxygenation Experiments
oxygenation experiments. I n Figures 1and 2, although these experiments were carried out in one case for 45 days, no second stage appears.
293
Study of Lag Phase
In all the low-temperature experiments there was a definite lag phase, and as the duration of this lag phase was not constant, further study was made of this phenomenon. I n Figure 4, 2-degree experiments are shown for 1, 2 , 3, and 4 per cent dilutions. From these curves it is seen that the duration of the Iag phase decreases with increase in concentration of sewage. This indicates that the bacteria involved in the deoxygenation either required time for acclimatization or that the organisms capable of growing a t these low temperatures were so few in number that time was needed for development of a sufficient number to produce a measurable reaction. The first explanation, that of acclimatization, would hardly explain why the duration of the lag phase decreased with increase in concentration of organic matter, unless the acclimatization was more readily accomplished under conditions of increased food supply. If it is assumed, however, that the lag phase represents the development of a sufficient number of low-temperature organisms, then a heavier initial seeding would lessen the time of development of this minimum number of organisms. Figure 5 gives the result of one experiment on 4 per cent sewage, samples of which were examined for the first 96 hours a t 12.hour intervals. I n this figure, where the scale is somewhat more extended than in the previous ones, it is seen that this lag phase consists of a gradual rise in rate of deoxygenation, followed by the more abrupt rise noted in the other figures. The fact that the rate increases gradually 8 7 6
/
Experiment with Illinois River Water
Since the experiments carried out using diluted sewage did not give results simiIar to those reported by Theriault using Ohio River water, one experiment was carried out using Illinois River water. The results of this experiment, as presented in Figure 3, show two distinct stages of deoxygenation. This phenomenon seems to be one encountered in river water, but not always in sewage dilutions. It is probable that these two stages, rather than being carbonaceous oxidation and nitrification, represent, first, the decomposition of the dead organic matter contained in the river water, and second, the decomposition of what a t the e., time of collection of sample are living organisms-i. plankton-which subsequently die and constitute another biochemical oxygen demand. Some Illinois River water, collected under summer conditions, cooled to 2' C., and incubated a t that temperature, failed to have as large an oxygen demand during a limited length of time as that of a sewage dilution with the same 20° C. demand. No doubt the plankton were rendered dormant by the low temperature but did not. die and become oxidized as they did at the higher temperature. Furthermore, preliminary experiments on the rate of death of plankton in the dilutioxi bottles tend to confirm the theory that the second stage of oxidation is due to the decomposition of plankton forms which have recently died." Further work along this line is to be done in this laboratory. Trons. Roy. Dublrn SOL, N. S.,5, Pt. 6, 539 (1895). Data on this rate of death of plankton were obtained from S. t. Neave of the Illinois State Water Survey. (Unpublished at time of publication of this paper.) '3
14
0
24
f8 72
96
I20 144
16%
192 216 240
Hours Figure 5-Rate of Deoxygenation of Dilute Sewage at 2 O C. during t h e First Few Hours of Incubation
indicates that it is a development of organisms rather than an acclimatization. To confirm this point, counts were made from a series of 2 per cent dilutions incubated for varying lengths of time at 2" C. The samples were plated on standard nutrient agar" and incubated a t 8" C. for 5 days. The results of one set of these experiments are shown in the accompanying table. Effect of T i m e on Rate of Growth of Bacteria i n Sewage Dilutions Incubated at 2 O C. Bacterial counts Days per CC. 1 940 2 2.140 3
4 5 6
$;Go
12,000 38.000 Over 100.000
The number of organisms developing a t 2' C. is a t first very limited, increasing slowly on the second and third days and more rapidly on the fourth and fifth days. The rate of bacterial growth during the first 4 days is thus similar to the rate of deoxygenation as shown in Figures I, 2, 4,and 5 .
ISDCSTRIL4LA S D ESGIA%ERISG CHEXISTRY
294
It is probable, therefore, that the lag phase is due to the necessity for the deyelopment of a sufficient number of bacteria capable of gron-ing at this low temperature.
5’01. 18, s o . 3
Further work on this point and on the nature of the bacteria entering into the reaction will be carried out in this laboratory.
Fractionating Column Calculations’ Relations between Height of Theoretical Plate, Radius of Packing Rings, and Nature of Liquids under Distillation in Packed Fractionating Columns By T. S. Carswell BATSSCHEMICAL C o , LANSDOWNE, PA
X THE packed type of column there is no one definite plate upon which the vapor and liquid approach equilibrium before passing to the succeeding plate. Instead, the interchange between vapor and liquid takes plnce gradually as they flow past each other in opposite directions. A definite length of packing is therefore required t o produce the same effect as one perfect plate, and Peters2 has termed this length the “height of the equivalent theoretical plate” (H.E.T.P.). This length Peters has shown t o vary with the liquid to be fractionated and with the radius of the packing rings. The manner in which the variation takes place may be mathematically analyzed in the following manner: Complete equilibrium between liquid and vapor is secured only when actual physical contact is obtained between the two phases. Therefore, the efficiency with which equilibrium is reached in any one section of the column will vary directly as the surface into which the backflow is broken up and indirectly as the volume of the space through which the vapor ascends. Consequently, the H.E.T.P., which represents the length of column in which perfect equilibrium is reached, will vary indirectly as the surface of the packing and directly as the \yolume of the vapor space, or
I
H.E.T.P.
v
= C-
(1) S where c = constant of proportionality V = volume of vapor space S = surface of paclung As is well known, the most efficient column packing is secured when the height of each packing ring is equal to its diameter, since in this case there is most chance for even distribution of the packing and least chance for channeling. I n these calculations it will be assumed that the packing rings fulfil this condition. The surface S for one H.E.T.P. is the sum of the surfaces of each ring plus the surface of the column wall in that section, or S = 8 nrzm s (2) where r = mean radius of packing ring m = number of rings in one H.E.T.P. s = surface of column wall in one H.E.T.P. Ordinarily, s is negligible in coinparison with 8ar2m,and therefore (2) may be simplified to
-+
S
=
8+tn
(31
The volume of the vapor space in one H.E.T.P. is the total volume of that portion of the column included in the H.E.T.P. less the space occupied by the solid portion of the packing rings, or V =vR2 (H.E.T.P.) - w ( r l z - r z z ) m (4) where R = inner radius of the column rl = outer radius of one ring r2 = inner radius of one ring 1
3
Received October 9, 1925. THISJ O U R N A L , 14, 476 (1922).
In dropping into the column the rings assume an irregular position, so that the radius of any one ring projected upon a line perpendicular to the axis of the column will vary between r and
d%,with an average radius of r(l?-).
De-
note this average radius by @. Then the average number of rings in one H.E.T.P. is R Z(H.E.T.P.) m =
Q3r3
Substituting this value of m in Equations 3 and 4,and then substituting the values for S and V thus obtained in Equation l, we have
L -J When the packing has thin walls, as is usual, the term rl2- ry2 in Equation 6 becomes negligible, and Equation 6 Q 37 simplifies to H.E.T.P. = Cr (7) where the constant C includes all the multiplying constants. This equation means that for the same liquids and the same pressure of distillation, the height of the equivalent theoretical plate varies directly as the radius of the packing rings. Peters has indicated this relationship graphically, and from his data the following values of the constant C have been calculated for acetic acid-water mixtures. Mean radius of packing
Table I H.E.T.P. found Cm.
0.64
10 14 25 63 132
Cm. 0.16 0.32
1.58
2.54
C 62
44
Av.
40 39 52 47
It will be noted that the agreement between the values of C is quite satisfactory, with the exception of the first case, where T = 0.16. Here the radius is so small that the term
”*, neglected
112Q37
in Equation 7, has an appreciable magni-
tude, and its neglect introduces an error. The fact that the term R, the radius of the column, drops out during the derivation of Equation 6 indicates that under ideal conditions the G.E.T.P. is independent of the radius of the column. That this must actually be the case follows from the consideration that the number of rings in the column, and consequently the total surface exposed, varies directly as the volume of the column. Consequently, the ratio V:S must be constant and independent of the radius of the column. Peters also points out that the H.E.T.P. varies with the nature of the liquids that are under separation, and states
