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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
cover after a year or two that such duties offer no prospect of advancement, and add very little t o their knowledge of engineering. In one case, after spending some years at the testbed of a firm of steam turbine builders, an ex-student had not even learned the essential differences between a reaction and an impulse turbine. Such matters were not included in the curriculum of his college at the date of his graduation, and he added little or nothing to this ignorance by his years of testing.” With some of this we cannot agree, for no matter how poorly t h e laboratory may serve t h e purpose of profitable improvement, as is undoubtedly t h e case in m a n y instances, a n d no matter how little m a y be t h e value of testing work t o engineering graduates or t o their employers, i t does not follow t h a t such considerations greatly restrict t h e applicability of organized research work in t h e field of mechanical engineering or in a n y other branch. The distinction here rests again o n names; laboratories as generally understood are not essential t o some very useful research nor is t h e existence of a testing department proof of t h e doing of research work. Forces of men m a y spend their lives making consumption tests of turbines, strength tests of metals or determining calorific powers of fuels i n well equipped laboratories a n d improve related industries not one bit, a n d yet one m a n with no laboratory whatever m a y stroll leisurely through a few establishments or sit a t his desk a n d evolve a n improvement t h a t m a y materially advance several industries a t once when developed, though before getting i t i n shape for commercial use experimental development work is almost universally required. Depending on t h e case, this work may be most profitably done i n laboratories, in shop or in t h e field, b u t i t must b e done. T h e International Harvester Company has added more t o improvement of agricultural conditions b y i t s machine a n d implement developments t h a n a n y organization i n t h e world, b u t i t has n o research laboratory, though maintaining testing a n d development departments. This does not mean t h a t it does no research, for such results could not be produced without research, only i t would be obviously absurd t o t r y t o develop standard plows, a n d tractors t o pull t h e m , suitable for every soil in t h e world b y a n y laboratory tests; t h e machines must be planned, built a n d then tried a n d studied everywhere, then returned t o t h e shops, changed t o correct faults a n d tried again. T h e real research men here are those who plan and s t u d y operation i n t h e plowing field, t h e only place where i t c a n be studied, a n d who then analyze faults a n d plan again; these men spend most of their time in railroad trains rather t h a n in laboratories; in t h e true sense their laboratory is t h e plowing field, as i t should be. Americans cannot agree with t h e idea t h a t t h e fore-
f
m a n or superintendent or engineer, whose primary function is t h e production, at lowest cost, of goods of proper standard quality, is t h e best m a n t o carry on research or development work; quite t o t h e contrary, in f a c t he is t h e very worst. This is because, first, scheming always occupies t h e mind t o t h e exclusion of executive routine, which is his main business, a n d second, but vastly more important, t h e type of mind a n d training t h a t best fits for one is destructive, or exclusive, of t h e other. N o m a n well adapted t o pushing routine economic production can possibly discover faults a n d remedies with efficiency, a n d certainly t h e creative mind t h a t can, becomes impatient with production routine a n d so neglects it. RESEARCH AND THE PROFESSOR
“Experience in research work is often made a sine pia non for the holding of a professional chair at certain of our universities, and if the word ‘research’ be interpreted in a sufficiently liberal and comprehensive manner, the condition is, we think, a wise one. In many cases, however, the conduct of a few experiments on lubrication or on elastic moduli will be counted as research, though the experimenter may have displayed no deep knowledge of engineering and physical principles, and be quite incapable of giving material aid to the advancement of the art. He would, however, on the above basis, be preferred to a competitor who had never made a laboratory experiment in his life, but had been in responsible charge of, say, the bridge department of a large firm. “On the other hand, there are men of exceptional ability in really original research who have not the gift of commending themselves to students and who fail accordingly t o teach anything to any but a few exceptional men. A t the same time they may do such good work in the study as to more than outweigh their class room deficiencies so far as the world at large is concerned, unfortunate as matters may be for the average student. It is important that work of this character should be done, but the difficulty is t o reconcile the claims of abstract technics with the not unnatural demands of the average British parent. A University should certainly promote the former, but as teaching is also one of its functions, undergraduates have a right to demand that their interests shall not be wholly sacrificed to the claims of research.”
It is t r u e t h a t a great m a n y directors of engineering schools have insisted on a research record for newly appointed men without knowing just what they meant b y t h e requirement, a n d while some still do i t , times do change a n d so do standards. Few enlightenedschools now fail t o recognize t h a t both teachers a n d investigators are absolutely necessary on t h e staff] and while i t most commonly happens t h a t ability i n one line is inversely proportional t o strength in t h e other, yet we know of quite a number of men who possess this dual C. E. LUCKE power.
ORIGINAL PAPERS THE BIOCHEMICAL OXYGEN DEMAND OF SEWAGES By ARTHUR L E D E R E R ~ Received September 26, 1914
This paper represents t h e result of a s t u d y of a test t o determine t h e biochemical oxygen demand made 1
Chemist and Bacteriologist, the Sanitary District of Chicago.
Vol. 6, KO. I I
I
b y a subcommittee of t h e laboratory section of t h e American Public Health Association. Interest i n this subject has recently been revived through t h e adoption of standards of permissible stream pollution b y t h e English Royal Commission on Sewage Disposal, embodied i n a n appendix of t h e 8th report of
Nov., 1914
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
the commission. T h e test recommended by the commission will be hereafter referred to as t h e “English Incubation Test.” Before I go into t h e details of this test, i t seems well to discuss briefly its meaning a n d importance. As t h e title of the paper indicates, t h e oxygen referred t o here is t h a t utilized by microorganisms which take part in t h e decomposition of sewage. T o what extent t h e reaction taking place is of a purely biological or chemical or physical nature is unknown. T h e process is most probably a combination of all three forces. I n designating properly a test, which gives expression t o t h e demand for oxygen such as is present in streams, one can hardly be criticized for using t h e expression “Biochemical Oxygen Demand.” T h e danger of introducing the t e r m “Oxygen Demand” alone is t h a t i t would be somewhat confusing with the time-honored expression “Oxygen Consumed.” We know t h a t “oxygen consumed” indicates the permanganate oxygen required for t h e oxidation of a small portion of t h e organic carbonaceous matter. This oxidation is a purely chemical reaction a n d bears no relation whatsoever t o t h e “biochemical” oxygen demand. T h e biochemical oxygen demand of a sewage a s a rule is much higher t h a n t h e permanganate oxygen consumption a n d t h e figures bear absolutely no relation t o each other. I n certain cases t h e biochemical oxygen demand m a y be low a n d t h e permanganate oxygen consumption high. This may occur with trade wastes containing organic carbonaceous preservatives. T h e principal value of a test for t h e determination of t h e biochemical oxygen demand in a sewage lies in the fact t h a t it is t h e best indicator of what may be called t h e “strength” of a sewage. Anyone who has ever employed one or t h e other of such tests is quickly convinced t h a t none of t h e routine chemical determinations heretofore in use can furnish t h e same information. From the standpoint of stream pollution i t means very little t o t h e sanitary engineer a n d chemist t o know how much organic nitrogen or “oxygen consumed” or chlorine a certain sewage will a d d t o t h e stream. T h e y are interested in t h e amount of oxygen t h a t will be absorbed in t h e stream, particularly during t h e first stretch after discharge. Of t h e chemical constituents t h e suspended matter is of interest because of its relation t o t h e aesthetic features of sewage disposal by dilution, a n d on account of its relation t o t h e formation of mudbanks. Some instances of comparing the “strength” of certain sewages from t h e standpoint of t h e routine chemical analysis a n d the biochemical oxygen demand are indeed surprising. T h e writer has in mind one instance in particular, in which a certain sewage when compared t o another from t h e standpoint of the routine chemical tests was twice as strong a n d when judged by t h e biochemical oxygen demand a b o u t f o r t y times as strong. Personally, I do not advise chemists t o disregard chemical determinations in sewages altogether; we surely want t o know whether a sewage is alkaline or acid for instance. M y principal plea is t o subordinate the routine determinations of t h e chemical constituents t o the determination of t h e oxygen-consuming capacity of a sewage.
883
The laboratory section of t h e American Public Health Association has recognized t h e importance of standardizing such a test a n d for some months past a subcommittee has devoted its attention t o this question. T h e members of t h e subcommittee are: F. Bachmann, Chicago; R. H. Brown, New York City; J. W. M, Bunker, Cambridge, Mass.; Frederic Bonnet, Jr. Worcester, Mass.; W. M. Cobleigh, Bozeman, Mont., John R. Downes, Plainfield, N. J.; F. E. Hale, Brooklyn, N . Y . ; C. B. Hoover, Columbus, 0 . ;A. Lederer, Chicago; T. W. Melia, Brooklyn, N. Y.; F. W. Mohlman, Urbana, Ill.; John F. Norton, Boston, Mass.; E. B. Phelps, Washington, D. C.; a n d S. T. Powell, Baltimore, Md. A. Lederer is chairman of the subcommittee. The following sanitary engineers have been kind enough t o give the subcommittee on various occasions the benefit of their valuable opinion: H. C. McRae, Baltimore, Md. ; Langdon Pearse, Chicago, Ill.; a n d W. L. Stevenson, Philadelphia, Pa. T h e standardization of a biochemical test differs from t h e standardization of a purely chemical test in various respects. One chemist might be put t o work out a chemical method a n d his results would be of equal value anywhere. This is not the case with a biochemical test. Two sewages may be alike with reference t o their chemical constituents a n d yet they may differ vastly in their biology. Rarely will two sewages be exactly alike in this respect. N o biologic procedure can be expected t o furnish ready formulae which would work out with mathematical precision everywhere a t all times. Even if we h a d such a procedure a t our disposal we would still have such factors t o account €or as obstructions in a stream, differences in velocity a n d temperature, influence of sunlight, absorption of oxygen by mud banks a n d other factors which of necessity are not represented in a laboratory procedure. It seemed evident, therefore, t h a t in proposing a n d adopting a standard procedure we would have t o confine ourselves for the present t o methods furnishing fairly accurate, consistent results, comparable with each other. It could not be expected in the present state of our knowledge of self-purification of rivers with reference t o oxygenation a n d de-oxygenation, t h a t we should be able t o work out a procedure which could tell us with certainty how much sewage i s . t o be permitted in a stream t o maintain a certain degree of purity further downstream. This could be done only if rivers in all parts of the country were alike with reference t o temperatures, velocities, obstructions, etc. Any deeper s t u d y of de-oxygenation a n d oxygenation in a particular stream will apply only t o another stream very similar hydrographically. With these conceptions in mind it seemed most advisable t o standardize a procedure which would permit t h e expression of “total biochemical oxygen consumption” a n d t o leave t h e practical application of this test for t h e purpose of controlling stream pollution t o individual local study. I n order t o compare t h e applicability of a standard procedure in various localities it is important t o experiment with as many sewages a s possible. Such tests were made with t h e sewages of Chicago, Ill.,
I
884
T H E J O U R N A L O F I N D U S T R I A L A N D E,TGINEERINC C H E M I S T R Y
Plainfield, N. J., Champaign, Ill., Lawrence, Kan., New York City, Washington, D. C. a n d Worcester, Mass. Since the number of results obtained with Worcester a n d New York City sewage are too small, these sewages are not considered in connection with this study. A method of determining the actual strength of putrescible material is given in the last edition of t h e “Standard Methods of Water Analysis.” The method consists in making various dilutions of the putrescible material with aerated tapwater, adding methylene blue as a n indicator, a n d calculating t h e oxygen demand from the “relative stability” figures obtained. T h e method is undoubtedly very useful a n d simple. It will be retained in t h e next progress report of t h e committee in a f o r m elaborated upon by Prof. Phelps. The possible objections t o this method are t h a t t h e relative stability figures obtained are based upon empirical findings a n d t h a t intermediate points of de-oxygenation, if such are desired, cannot be obtained. T h e method proposed by the Royal Commission of Sewage Disposal contained much .which seemed worthy of a s t u d y by American chemists. Briefly, the English procedure is as follows: A definite volume of sewage or effluent is completely aerated by shaking. It is then mixed with a larger definite volume of t a p water a n d t h e mixture again aerated. T h e dilutions recommended for raw sewages a n d settled sewages are about 9 9 t o I a n d 49 t o I , respectively. The intention is to adjust the ratio of t h e aerated water t o the sewage under test SO t h a t during the test only about j o or 60 per cent of t h e oxygen in the diluting water will be used up. It is stated t h a t if less t h a n 30 per cent of the initial oxygen is absorbed the error of the experiment becomes large, but if more t h a n 60 per cent is absorbed the error is even greater. A large dilution reduces t h e food supply of t h e bacteria a n d thus retards deoxygenation. T h e prepared dilutions are carefully put into 4 clean glass-stoppered bottles holding 11 t o 1 2 ounces. T h e bottles are left unstoppered for 5 minutes t o give t h e entrapped air a t the shoulder a chance t o escape. Stress is laid on t h e importance of having all the liquids in t h e mixture and even the bottles a t incubation temperature before beginning t h e incubation. T h e incubation temperature recommended is 6 5 O F. (18.3’ C . ) , this representing the maximum summer temperature of even the most sluggish English streams. T h e j-day incubation temperature has been found t o give a smaller experimental error t h a n longer incubation periods. Two of the bottles are tested for oxygen a t once; t h e other z bottles are tested for oxygen a t the end of incubation. The determination of t h e free oxygen was made by t h e Winkler method as modified by Rideal a n d Stewart. The principle of the modification consists in the oxidation of t h e organic matter a n d t h e nitrites b y the addition of permanganate in acid solution followed b y the addition of I cc. of potassium oxalate previous t o the addition of t h e standard reagents employed in t h e Winkler method. T h e English standard for sewage effluents
Vol. 6 , No.
II
is one t h a t absorbs less t h a n 20 p. p. m. of ox-ggen in j days a t 6 j O F. I t is not the purpose of this subcommittee t o concern itself with the adoption of standards for sewage effluents but solely t o fix a laboratory procedure which will give uniform results. It is thought t h a t such a procedure will be a valuable aid t o t h e sanitary engineer in establishing standards of .permissible stream pollution. There mere a number of features in the original English test for the determination of t h e biochemical oxygen demand which did not appeal t o t h e collahorators, a n d after considerable correspondence i t was finally decided t o do some comparative work with the method, employing, however, a n incubation temperature of 2 0 ’ C., a n d t o extend t h e incubation period to I O days in order t o study t h e oxygen consumption from d a y t o day. T h e assumption was t h a t the oxygen consumption a t t h e end of I O days would be practically I O O per cent. It was also decided t o work with three different concentrations simultaneously, so t h a t the influence of concentration upon oxygen consumption could be studied. An ideal experimental series was t o show oxygen absorptions of less t h a n 30 per cent, between 30 and 60 per cent, a n d over 6 0 per cent, respectively. T h e preparation of t h e mixtures previous t o incubation differed from t h e English procedure in t h a t we employed aerated distilled water instead of t a p water a n d 8-ounce bottles were used instead of 11-ounce bottles. T h e sewage was not aerated before mixing it with the distilled water, but t h e mixture was brought t o the incubation temperature previous t o incubation. T h e sewage was settled in the laboratory before the mixtures were prepared, for t h e reason t h a t unevenly divided suspended matter might have introduced serious discrepancies in t h e final results. The original Winkler method was employed for the determination of t h e free oxygen. Later on, during t h e tests, it was recommended t o employ Hale a n d Melia’s modification of the Winkler method. Professor Phelps employed Rideal a n d Stewart’s modification in t h e latter part of his series. A number of blue-printed record sheets were mailed t o the co-workers in order t o facilitate the compilation of t h e results obtained. I t was suggested a t the start t h a t each collaborator should obtain a t least I O ideal series, b u t the time a n d labor involved was so great t h a t it was impossible t o live u p t o it. Unless one has worked with t h e same sewage for a considerable period it is almost impossible t o prepare dilutions which will allow reductions of oxygen simultaneously to 30 per cent, t o between 30 a n d 60 per cent a n d over 6 0 per cent. A great deal of time in such work is always lost with preliminary tests. I n order t o obtain a n ideal series one has to incubate a t least 3 0 bottles a n d preferably more in order t o check doubtful results. I n his series, N r . I l o h l m a n recorded in addition to t h e oxygen consumption figures, Phelps’ velocity coefficient “ K ” for each day. A subsequent calculation of K on all of the results obtained by the various collaborators gave some interesting information. The
T H E J O U R N A L OF ILVDUSTRIAL A X D E N G I N E E R I N G C H E M I S T R Y
Nov., 1914
885
TABLEI-PERCENTAGE OF TOTAL OXYGEN ABSORBED A N D PHELPS'VELOCITY COEFFICIENT, K , AFTER 24 HOURSA N D 5 DAYSINCUBATION AT 20" C . Total Oxygen Consumption Compared with Initial Available Oxygen after 10 Days Incubation 30 t o 60 PERCENT hfORE THAN 60 PER CENT LESS T H A N 30 PERC E N T
-
- --
-
c
7
24 hours 5 days K Average -h_ Date of sampling 7cp of 10 days 7c0 1914 abs'd K abs d K incubation SERIES: Phelps. S O U R C EScreened : Washington Sewage April 2 1 . . , 22.. . . 0,00031 75 0,00020 0,00020 24 . . . . 23 0,00026 61 0,00016 0,00018 28 . . . . 28 29.. . . 3 0 , . , . 38 0,00031 84 0,00015 0,00017 0,00016 22 0,00018 88 0,00016 80 0.00016 0.00017 20 0.00018 May 1 . . , . 8 . , . . 17 0.00018 65 0,00016 0.00016
24 bours
7c0
5 days
700
K 24 hours 5 days Average ,-----%0 of 1 0 d a y s 70 0 K abs'd K incubation asb'd
abs'd
K
abs'd
K
23 26 29
0.00026 0.00026 0.00037
67 80 77
0,00015 0,00019 0,00021
0.00017 0.00019 0,00022
33 32 25
85 77 75 86 75 81 88 90
0,00020 0.00019 0.00021 0.00030 0,00019 0.00020 0.00021 0.00024
0,00018 0.00019 0,00021 0.00029 0,00019 0.00017 0.00023 0.00025
79 89 77 83 71 79
0.00028 0.00030 0.00024 0.00028 0,00020 0.00025
0.00028 0.00027 0.00023 0.00024 0.00021 0.00021
51 67 65 77 76 52 90
0.0012 O.OOOi9 0.0016 0.0046 0.0027 0.0017 0.0023
0.0020 0.000i9 0.0022 0.0054
.
12 . . . . 13 . . . .
18 17
0.00018 0,00013
52 60
0,00013 0.00012
0.00014 0.00011
14 . . . .
i!15
47
0,00039
63
0.00010
0.00016
15 . . . . 16....
28 41
30
0,00031
86
0.00010
0.00018
0,00034 0.00037 0.00030 0.00043 0.00042 0.00015 0,00042 0.00045
27 23 26 23 20 21
0.00043 0.00035 0.00034 0,00034 0,00024 0.00028
23 . . . .
.
., 26.. .. 28.. , . 25.,
SERIES: Poung and Bruckmiller. M a y 2 3 . . . . 25 2 6 . . . . 27 27 . . . . 14 June 9 . , . .
io. . . . 11 . . . .
28 29
0.0015 0.0034
SOURCE.Settled Sewage-Lawrence, Kansas 0.0015 0.0060 69 51 0.0016 0,0013 50 74 51 0.00094 0.0058 29 45 33 77 0.0020 0,0018 38 41 58 0.00096 0.0016
SERIES:Downes. SOURCE:Screened Sewage-Plainfield, N.J. May 2 . . _ . 18 0.0011 66 0,00075 0.00087 15 . . . .
0.0011
84
0.00082
..
37
0.0014
84
0.00066
0.0005i
37
0.0012
86
0.00060
0,00059 45
SERIES. Moblman. Septic April 2 1
SOURCE,Crude and Septic Sewage-Champaign,
0.0012
84
0,00050
Crude May
...
0.00058
30.. ..
15 17
0.0016 0,0013
56 58
0.0014 0.0010
0.0014 0.0011
...
38 28 17 26
0.0045 0.0036 0.0017 0.0060
76 66 65 61
0,0017 0,0021 0,0015 0.0031
0.0020 0.0021 0.0016 0.0036
34 28
0.0058 0.0079
60 55
0.0020 0.0032
0.0025 0.0040
0.00051
0.00047
0.00032
0.00036
5. 5. 9. 11. 14.
SERIES: Lederer and Bachmann. A p r i l 2 0 . , . . 26 0.0012 18 0.00059 2 1 . . . . 28 0.0011 26 0.00070 2 2 . . . . 10 0.00036
..,
24
0.0011
28 . . . .
41 35 22 24 44
0.0011 0.00069 0.0007 1 0.00056 0.0016
23.
29.. 30. May
..
... ..
33
0.0010
4. ... 6. ...
29 41
0.0016 0.0016
1..
27.
...
28.. . , June 4 . . . .
30 30 35 41
0.00071 0.00039 0.0012 0.0011
0.00052 0.00031
78 76
0.00030 0.00027
0.00032 0.00025
34
0,00064
76
0.00037
0.00040
34 36 36 46
0.00054 0.00056 0.0005i 0.00071
84 85 80 92
0.00037 0.00035 0,00033 0.00038
0.00036 0.00036 0,00036 0,00039
0.0020 0.0016
0.0018 0.0020
81 89 79 73 70
0,00072 0.0011 0.00070 0,00099 0.00062
0.00068 0.0010 0.00077 0.0011 0.00075
0,0013 0,0014 0,0013 0.0015 o;ooii 0,0012 0,0015
0,0013 0.0015 0.0014 0.0014
63 53 59 38
23 68 80 87 0.0024 0.0060
44 57 44 28 41
0,0020
Ill.
21 . . . . 25
34 23
30 61
0.00086 0.0014 0.0010 0.00094
0.00080
1 . . .. 6.... 12 . . . .
26.. June
26
K Average of 10 days incubation
S O U R C ECrude : Sewage (Settled)- -Chicago, 111. 78 0.00084 0,00088 16 0.00046 80 76 0.00052 0.00049 72 0.00057 0,00069 37 0.00074 74 78 0.00045 0.00046 78 0.00068 0.00055 11 66 0,00036 22 0.00043 81 66 0.00063 0.00062 30 0.00086 70 33 0.00075 76 91 0.00047 0.00049 25 0.0005 1 75 91 0.00041 0,00039 71 0.00044 0.00050 68 0.00032 0.00036 83 0.00066 92 0.00077 31 42 79 84 0.00059 0.00058 24 82 26 82 79 0.00089 0.00084 29 90 0.00088 26 94 0.00080 76 31 94 60 0.00031 0,00040 24 79 78 0.00022 0.0002 1 65 0.00047 0.00075 90 0.00055 33 91 0.00050 0.00053 24 0.00059 88
factor K is part of a formula developed b y Prof. Phelps a n d Col. Black during an investigation of the pollution of New York harbor in 1911. The method employed b y Phelps a n d Black consisted in t h e incubation of suitable mixtures of t h e sewage with
34 27 25 18
0,0020 0.0021 0.0014 0.0013
25 18
0.0017 0,0010
81 75 80 76 64 72 86
25 22 25 14
0,0014 0.0035 0.0072 0.0049
82 61 73 58
0,0014 0,0026 0.0052 0,0025
0,0015 0.0028 0.0053 0,0031
33
0.00089
93
0.00067
0.00061
33 19
0.00096 0.00047
81 83
0.00075 0.00070
0.00065 0.00066
14 o.ooio
0.ooii
0,0012 0,0011
0.00043 0.00040 0.00045 0.00039 0,0003i
0,0005 1 0.00023 0.0005 1 0,00059
0.0004i 0.00050
aerated mater for a specified time, say 24 hours. T h e oxygen is determined a t t h e start a n d a t t h e end of incubation. Considering t h e reaction between the organic matter of t h e sewage a n d t h e oxygen dissolved in t h e water, t h e following relation is said t o hold:
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
886 log
0’
0
=
KCt*
O’ represents
the
the
final a m o u n t of oxygen present. C expresses t h e concentration of t h e sewage, t the duration of t h e incubation in hours, a n d K t h e velocity constant of t h e reaction t o be determined. Knowing t h e form of t h e reaction curve, one computes first K a n d then b y extrapolation t o a n extended period t h e total oxygen demand of t h e organic matter in t h e sewage. Originally it was claimed t h a t K is independent of t h e extent of dilution. This, however, was found later t o be not quite correct. It was m y experience
Vol. 6 , No. I I
a t t h e highest concentration of t h e sewage. After 24 hours, K is much higher t h a n after days and i t decreases (this does not show in t h e tables given) continuously up t o t h e last d a y of incubation. However, after the fourth or fifth d a y the differences are b y no means as marked as t h e y are during t h e first few days. I n many cases, K is fairly constant after 5 days. K after 5 d a y s of incubation coincides quite well with t h e average of t h e I O days period. These results are given without comment or recommendation, for t h e reason t h a t t h e formula is now undergoing a very comprehensive study in connection with
TABLE11-PER CENT RELATION OF “MG. OXYGEN ADDED TO 1 LITER OF SEWAGE” TO “MG. OXYGEN ABSORBEDPER LITER OF SEWAGE“
AFTER 24 HOURS, 5 DAYS AND 10 DAYS INCUBATION AT Z O O C. Mg. 0 Mg. 0 Per added PER CENT 0 ABSORBED IN P e r added PERCENT 0 ABSORBEDIN cent to 11. r cent t o 11. I dilu- sew- 24 hours 5 d a y s 10 d a y s dilu- sew- 24 hours 5 days 10 d a y s DATE COLLABORATOR tion age DATE COLLABORATOR tion age Av. Av. Av. Av. Av. Av. 7 35 23 43 31 M a y 14 Mohlman 0 . 2 5 3488 10 10 20 20 36 36 April 20 Lederer and Bachmann 3 . 0 280 287 11 23 Young a n d Bruckmiller 0 . 3 6 21 11 5 14 21 21 280 10 9 28 29 36 37 26 2111 2 . 5 18 24 May 6 282 28 66 80 26 2111 5 14.5 20 April 21 Mohlman 21 68 87 276 27 2111 2 . 5 5 18 21 276 15 70 82 June 10 2111 2 . 5 18 24 30 21 69 68 84 83 275 21 11 2111 7 4 9 13 22 21.5 May 5 40 40 47 21 47 352 21 5 Mohlman 0 . 5 0 1680 9 . 5 26 34 2 Downes 43 54 9 1512 15 35 57 15 19 4 . 0 252 55 69 225 11 1580 18 51 70 26 30 54 63 226 14 1688 16 15 26 3 4 45 51 June 1 28 2 Downes 2132 3 10 16 6 66 90 230 26 43 51 15 2080 3 5 3 11 10 13 15 12 26 65 225 23 M a y 21 Young a n d Bruckmiller 0 . 7 2 1055 20 20 46 April 22 Lederer a n d Bacbmann 210 9.5 36 44 35 45 26 1055 20 26 40 23 215 15 202 9 22 28 27 1055 21 28 42 M a y 27 210 15.5 43 48 June 9 1055 19 42 55 28 202 12 12 46 3 6 52 43 10 1055 21 32 55 June 4 224 6 20 27 11 1055 24 21 37 31 41 4 6 . 5 April24 Phelps 6 M a y 26 Downes 1.00 938 7 16.5 20 28 222 16 25 7 224 959 7 7 16 16 18 19 30 June 1 16 16 25 4 217 856 8 31 55 May 8 April 30 Molhman 4 30 854 7 24 41 12 13 25 210 12 4 38 57 13 May 5 884 22 221 219 8 11 ij.5 5 836 9 34 51 , 14 9 728 18 50 82 15 221 14 826 24 15 50 38 86 62 16 228 April 20 Lederer a n d Bachmann 870 7 21 26 16 219 26 15 20 April 28 Lederer a n d Bachmann 5 . 0 166 21 890 6 168 17 22 30 22 870 2 168 16 24 May 1 23 890 6 55 166 13 14 4 28 870 6 6 . 0 150 12 16 26 Downes 29 860 3 . 5 94 146 17 20 June 12 30 880 8 59 May 1 880 6 17 M a y 6 Lederer a n d Bachmann 135 4 870 8 22 28 April 24 Phelps 147 146 6 860 8 20 20 28 147 .. 12 29 27 840 4 148 6 24 28 870 7 13 20 30 146 11 28 33 June 4 840 6 6 13 16 14 19 May 1 139 5 .. 26 April 20 Lederer a n d Bachmann I.5 573 5 20 25 5 21 586 6 5 . 5 17 18 21 23 8 146 11 27 35 141 13 27 35 1.8 422 5 0 73 79 13 M a y 23 Young a n d Bruckmiller 26 422 46 59 87 14 143 13 30 48 144 14 .. 49 27 422 47 64 80 15 144 11 32 42 June 9 422 26 61 70 23 38 10 422 21 63 71 23 10 37 28 44 141 10 11 38 49 11 422 45 39 57 63 73 77 27 Lederer a n d Bachmann 7 . 0 111 116 31 77 94 2 Downes 2.0 530 9 27 40 28 78 111 17 19 74 63 9 0 15 512 12 1 0 . 5 22 24 3 0 35 June 4 8 . 0 107 13 38 50 April 21 Mohlman 429 20 55 73 M a y 8 Phelps 101 17 49 57 21 409 14 58 75 12 102 6.5 36 44 46 70 13 25 372 11 109 18 41 45 30 430 17 15 48 52 67 71 14 58 73 103 25 22 Lederer a n d Bachmann 425 3 . 5 21 32 15 108 10 36 51 23 435 9 6 22 21 31 31 25 53 104 11 14 42 43 53 3 0 Phelps 422 2 8 25 10.0 87 25 56 72 May 5 437 1 1.5 , . 8 i i 11 April 21 Phelps 69 8 2 . 5 16 52 April 2 8 Lederer a n d Bachmann 2 . 5 340 9 25 27 22 82 26 64 76 29 336 7 20 30 M a y 26 83 26 62 72 28 30 28 30 344 9 60 75 80 27 344 8 34 28 May 1 72 4 340 1 1 . 9 33 26 3 6 31 28 80 32 25 65 6 0 70
..
..
t h a t K decreased as t h e concentration increased, a n d t h e results obtained in Tables I a n d I1 bear this o u t uniformly. T o meet this objection, Phelps recommended t h a t C i n his formula be effected b y a concentration exponent %, which would have t o be determined for each particular sewage b y a study of a series of dilutions. I n making a s t u d y of K, obtained in t h e experiments of t h e collaborators, t h e following facts present t h e m selves very strikingly. K is almost invariably lowest
the work of t h e U. S. Public Health Service on the self-purification of t h e Ohio a n d Potomac rivers. Possibly, t h e results obtained i n connection with t h e investigation of t h e English iincubation test will be of some service t o t h e students*of the formula. Before discussing t h e results obtained b y t h e collaborators a n d giving their comments, t h e results are compiled in Table I. I n some cases, as can be noted, t h e number of determinations was rather small, a n d in such cases one
Nov., 1914
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
is hardly justified in drawing a n average. T h e heading “ P e r Cent of Total Oxygen Absorbed” serves t o indicate t h e per cent ratio of absorption, assuming t h a t it is I O O per cent after I O days. For instance, t h e column “ P e r Cent Oxygen Absorbed in 24 Hours” indicates t h e per cent ratio between t h e oxygen absorbed in 2 4 hours a n d I O days. Table I1 shows t h e per cent of oxygen absorbed after I , 5 a n d I O days incubation. Table I shows very strikingly t h a t t h e rate of absorption in certain dilutions with certain sewages is fairly uniform b u t t h a t there is n o uniformity whatsoever i n this respect when comparing different sewages with each other. I n other words, one might incubate a certain dilution of a certain sewage for 24 hours a n d assume with fair certainty t h e approximate oxygen consumption in 5 d a y s a n d I O days, provided he has once established t h e relation i n preliminary tests. This, of course, implies a good deal of work which t h e busy works-chemist is not always in a position t o do. I n all of t h e experiments, t h e number of mg. of oxygen absorbed per liter of sewage was lower t h e higher the concentration. T h e percentage of oxygen absorbed b y t h e sewage increased with t h e concentration. Some experiments were omitted in t h e tabulation, for t h e reason t h a t there was a discrepancy in t h e results which apparently seemed illogical. Such discrepancies were noted in nearly all of t h e series. There is no doubt t h a t some of these discrepancie-s are not merely analytical errors b u t due t o reasons which still lack satisfactory explanation. It often happened t h a t t h e oxygen consumption would suddenly increase o n one day, t o drop down Bo a logical figure on t h e next day. T h e greater part of t h e consumption has been reached as a rule b y t h e fifth day. T h e consumption belween t h e fifth a n d t e n t h d a y amounted t o a b o u t 2 0 t o 2 5 per cent of t h e total. On t h e whole t h e concentration did not m a t t e r greatly when comparing t h e per cent oxygen absorbed in 24 hours a n d j d a y s (Table I). When t h e incubation was such t h a t less t h a n 30 per cent a n d between 30 a n d 60 per cent of t h e initial oxygen was consumed, t h e “per cent oxygen absorbed in 24 hours” was a b o u t 30 per cent (variation 17 t o 46), a n d t h e “per cent oxygen absorbed in j days” a b o u t 7 5 per cent of t h e total (variation 58 t o 81). When more t h a n 60 per cent of t h e initial oxygen was absorbed, t h e ratio of absorption was somewhat higher. For t h e I-day period t h e ratio was on the average 3 5 per cent (variation 2 2 t o 51) a n d for t h e 5-day period, a b o u t 80 per cent of t h e total per cent consumption (variation 73 t o 86). T h a t this method furnishes only approximate figures a t t h e best is apparent. Some of t h e collaborators have given a more detailed opinion o n t h e result of their tests, excerpts of which are given herewith. Mr. Mohlman, who employed Jackson’s bulb pipettes as seals for t h e bottles during incubation, states t h a t A number of runs were spoiled b y variations i n incubation temperature.” Instead of preparing t h e required dilutions for each individual bottle, Mr. Mohlman prepared a larger quantity of t h e desired mixture
