N a y , 1916
T H E J O C R N A L O F I A ' D U S T R I A L A hi D E N G I N E E RI MG C H E M I S T R Y
OXYGEN DEMAND OF SEWAGES B y F. Vi. BRUCKMILLER Received December 6. 1915
During a recent investigation1 of t h e sewage disposal plants of t h e s t a t e , t h e nitrate method for oxygen demand was used in preference t o t h e modified English dilution method. for t h e following reasons: I-It is more easily manipulated. 11-It lends itself better t o field work. 111-It is not open t o a n y great errors in manipulation. T h e modified English dilution method2 consists in making dilutions of t h e sewage in question with aerated distilled water, incubating at 20' C. for I O days, determining the residua1 Oxygen, and>from that dilution in which between 30 t o 60 per Cent of t h e oxygen is used UP, t h e oxygen required for the sewage is calculated. Since each sewage is different from every other one, t h a t dilution which will work for one sewage will not always work for another. *4 Preliminary series of dilutions must, therefore, be made on each sewage in order t o determine t h e proper dilution. This requires time and equipment, both of which were lacking in t h e work under discussion. Furthermore, considerable laboratory apparatus is required t o make t h e dilutions as well as t h e oxygen determinations, all of which must be made in t h e field where t h e sample is collected. The nitrate method3 on t h e other hand adapts itself to field work. No are necessary which, as has been previously shown, are a great source of error in t h e English m e t h ~ d . I~n a n unknown sewage, Lederer5 advocates t h a t varying quantities of NaNOa (equivalent t o 100, 1 3 0 , 160, 190, 2 1 0 a n d 240, p. p. M. 0.) be added t o a constant quantity of sewage a n d t h a t t h e sample which remains sweet a n d free from sediment be taken as t h e one containing t h e proper quantity of oxygen. From t h e residual nitrate a n d nitrite present, t h e oxygen equivalent can be readily calculated. At most, this procedure requires 6 bottles, Instead of adding varying quantities of NaN03, a n excess can be added to one bottle a n d t h e presence of nitrate be indicated b y methylene blue. This w& t h e procedure adopted in our work, after we h a d satisfied ourselves t h a t t h e excess S a X O a h a d no effect on t h e biological action during incubation. T h e results obtained were quite gratifying. N o determinations need be made in t h e field. After incubation, t h e samples can be chloroformed a n d sent to t h e laboratory for examination. This in itself is a great feature in favor of t h e nitrate method for oxygen demand in field work. Because of t h e manipulations through which t h e sewage must go in t h e English method, it is open to many grave errors. In t h e first place, in making t h e dilutions, aeration results unless great care is exercised. Oxygen is lost during incubation through leaky stoppers. Gases invariably collect under t h e glass stoppers a n d escape when t h e stopper is removed Under the direction of the S t a t e Chemical Research D e p t . a n d Sanitar? Engineering Dept.. of Kansas. THISJOURNAL, 6 (1914). 884. J . Infect. Dis., 14, 482. THISJOCRNAL, 6 (1914), 886. J . Infect. Dis., 14, 485..
403
t o introduce reagents. T h a t oxygen is lost in this way has been shown b y a number of investigators.' Only when t h e dilution is such t h a t t h e same percentage of oxygen is used u p in each sample do t h e results coincide very well. T o get this dilution each time is rather difficult a n d constitutes one of t h e greatest objections t o t h e dilution method. Lastly, errors in t h e oxygen determinations are possible. Unless all t h e organic matters and nitrites are removed, accurate results are not possible. T h e simplicity of t h e nitrate method eliminates any due to manipulations. great souqce of lies in the determination of large quantities of nitrites and nitrates, An in the determination of t h e latter is of more concern t h a n in t h e former, since the former are seldom present in quantities greater t h a n 5 P. P. l(1. An error of I P. P. M. in t h e nitrite therefore, not seriously affect t h e results, producing, as it were, in oxygen equivalent, a n error of only 1.7 P. P. M.of oxygen Ivhich is well on sewages that demand 3oo within limit of P. p. M. of oxygen. By making the dilutions jcarefully with respect t o t h e nitrates a n d using t h e phenoldisulfonic acid method for their determination, reasonable accuracy can be assured. Because of these considerations, the nitrate method was used in all the oxygen demand determinations connected with our sewage investigations. The sewages vr,ith which T~,eworked were all domestic sewages from small towns. Partial analyses of a few typical sewages are given in Table I, TABLE I-RESULTS EXPRESSED IN
P A R T S P E R MILLION NITROGENOxygen Chlo- Oxygen
---SOLIDS-F r e e Or- consumed rine NO. T o t a l Volatile Suspended N H ~ganic 120 172 2o 70 3o 80 ,. ,. , 7o 88
7;:
$68
demand 220 142
317 528 572
974 482 814
344 304 546
376 58 96
5 16 8
3.5 50 25
700 112 220
105 72 68
297 63 75
407
1638
992
476
16
35
650
230
89
A t w o weeks' s t a y was made a t each town.
-3,
Portable laboratory Permitted t h e estimation of oxygen consumed, chlorine a n d oxygen demand, together with a number of engineering observations. Cornposite samples were sent t o t h e laboratory at Lawrence, where t h e solids a n d t h e nitrogen content were determined. AS only one man made t h e trips it was necessary t o simplify t h e work as much as possible. This factor more t h a n a n y other led u s t o use t h e nitrate method in preference t o t h e dilution method for oxygen demand; not, however, until we convinced ourselves b y experiments herewith related and also b y those of others t h a t t h e results from t h e nitrate method could be depended upon. Fo? nitrate procedure we filled a 2 j 0 - C C . bottle through a funnel with settled sewage: overflowing half in order t o get rid of all t h e air in t h e bottle. T h e nitrate solution was of such a strength t h a t z cc. were equivalent to j o o P. P. L f . of oxygen. T h e samples were incubated a t z o o for I O days. Such a quantity Of Sewage was taken for estimation Of nitrates t h a t a reading of about 30 on t h e colorimeter was always obtained. 1 Lederer, A m . J . Pub. Heallh, 5, 3 5 5 ; also Lederer, (1914). 887.
THISJ O V R W A L , 6
T H E J O L - K X A L O F I N D U S T R I A L A N D E-VGINEERIIVG C H E M I S T R Y
404
I n general, we secured consistent results.
Once in
a while anomalies would occur; t h a t is n-e would ob-
tain results which were entirely out of harmony with t h e other values. These errors were mostly plus in character and were attributed t o an ununiform mixing of t h e sample of sewage. Rarely was a determination lost and then only due t o carelessness or technical errors. Some samples went foul the third or fourth d a y when experience had shown t h a t they contained enough nitrate t o keep them sweet a t least I O days. These "freak" results were also attributed t o poor mixing of t h e sample, or t h e presence of a n undue amount of organic matter in suspension. In general, however, t h e method worked quite smoothly a n d gave consistent resu rs all through the work. Before t h e investigation began, some preliminary work in t h e laboratory mas done, t h e results of which strengthened t h e conclusions above noted. I n connection with other collaborators of D r . Lederer bn t h e English method, we endeavored t o find t h e best dilution and also a value a t j days from which t h e absolute value of oxygen demand could be calculated. This we found not t o be feasible. The results in Table I1 show no agreement whatsoever in t h e carious dilutions. One would expect t h e error in a I per cent dilution not t o be a n y more t h a n twice as large as t h e error in a z per cent dilution. Our experience, as the table shox-s. has been contrary t o this supposition. X method whose results 1-ary so with each dilution employed requires. in our judgment; some further study in order t o determine the reason for t h e deviations. T A B L E 11-EFFECT
O F VARYING
Incubation a t 20' C.
-
P PI ..cent . . ...
nuvppn --~, ----
DILUTIONS OF S E W A G E 7 6 P P I f Oxygen a t S t a r t
Ratio
Sewage IncuAbsorbed in of Oxygen in bation Diluted Sewage Absorbed in Mixture D a y s P. P.&I. P e r cent 5 : 10 d a y s 0.4 5.55 0 36 0.00 0.0 i.90 0.6 0 6 7.90 ii Per cent 1 1 14.42 I .4 18.40 21.05 1.h 8 21 " 0 5 1.6 21 . 0 5 9 1.6 10 21 .0.i 1.6 1 21.05 1.00 1.6 21.05 1.6 21.05 .. 1.6 21.05 1.6 ?1,05 51 Per cent 1.6 28.94 2.2 2.2 28.94 .. 2.6 34.21 9 2.6 .. 34.21 .. 10 3.1 40.79 50.00 3.8 2.00 6 0 . 5 2 .. 4.6 67.10 ., 5.1 J 1 71.05 43 P e r cent 5.6 73 68 76.31 .. 5.8 76.31 .. 5.8 J 8 . 34 .. i. 8 76.94 .. 6.0 10 i8.94 6.0
Oxygen Absorbed (Basis of Sewage) P . P. Lf. P e r cent 111.1 5.25 11l.i 2,25 166.6 i .89 166.6 7.89 305.5 14.47 51 1 . 1 24.20 58'4.0 27.66 584.0 27.66 584.0 27.66 584.0 27.66 222.2 10.54 222.2 10.54 222.2 10.54 222.2 10.54 222.2 10.54 14.47 305.8 305.8 11.47 361.3 11.20 361,3 17.20 20.40 431.0 10.00 211.0 12.10 255.5 13.43 283,2 14.20 299.5 14.72 310.3 322.2 15.56 15.56 322.2 15.56 322.2 333.5 15.80 15.80 333.5
Using a known sewage, comparisons of both methods of procedure of t h e nitrate method were made. The results contained in Table I11 confirm those published b y Ledeyer.' Those in Method A were obtained b y adding varying quantities of SaN03 t o the sewage, a n d noting the one which just remained sweet. Those in Method B were obtained by adding an excess of N a N 0 3 and 0.4 cc. methylene blue t o just one bottle of sewage. All determinations n-ere made after I O 1
J , Infect D i s . , 14, 485.
5'01. 8 ,
NO.j
days' incubation a t zoo C. in zjo cc. glass stoppered bottles. T A B L E 111-OXYGEN
A-By B-By Trial No. Method A , . . . . . . . . Method B . . . . . . , , ,
DEHAYD
(P. P. M.)
adding excess iYaNOs adding 10 cc. N a N O s 1 2 3 4 300 265 250 310 310 270 248 308
BY N I T R A T E M E T H O D
(26.56 g. per liter) 5 6 8 7 287 326 297 269 290 320 300 265
9
307 310
IO 278 275
The agreement in Table 111 shows t h a t t h e excess of S a S 0 3does not affect the biologic process upon which the loss of oxygen depends. From this we decided t h a t the addition of excess N a S 0 3 t o t h e sewage would give us as reliable results as t h e use of varying concentrations would. I n order t o see whether t h e two methods, t h e excess nitrate and. t h e dilution method, gave results of close agreement, the two were tried on a known sewage. For t h e dilutions! aerated distilled water with a temperature of 20' C. Tvas used: 2jo cc. bottles were filled t o overflowing and 3 cc. of sewage added near t h e bottom of t h e bottle. After mixing t h e y were incubated for IO days a t z o o C. The Rideal and Stewart' procedure was used. Thirty-five per cent of the oxygen was absorbed a t the end of I O days. T A B L E I ~ ~ - c O M P , A R I S O N OF O X Y C B N DEXAND (P. P . 31.) BY T H E N I T R A T E AND T H E DILUTIONb 1 E r H O D S . I N C U R A T I N G AT 20'
c.
Trial h-0. 1 7 3
26 h
9 10
Dilution Method 305 298 301 310 302 285 297 289 300 294
Trial Dilution KO. Method 11 293 12 298 13 307 14 290 15 310 288 296 18 298 19 302 20 289
Nitrate Method 301 285 299 312 304 283 294 285 298 291
;$
Nitrate
Method 298 296 303 285 306 295 300 293 299 294
A%sidefrom the fact t h a t t h e nitrate results are consistently lower t h a n t h e dilution results, t h e t w o determinations agree fairly well. In fact, they agree well enough for all practical purposes, and strengthened us in our decision t h a t the nitrate method would give satisfactory results in t h e field; also they are i n strict accord viith those obtained b y Lederer.2 Furthermore, our experience has confirmed this decision, and after a year's trial, we conclude t h a t t h e nitrate method is far better adapted t o field work t h a n t h e modified English dilution method. WATZRAND SEWAGE LABORATORY KANSAS.L.4WRENCE
U N I V E R S I T Y OF
A COMPARISON OF THE PERMANGANATE METHODS FOR THE DETERMINATION OF REQUIRED OXYGEN By
JOHN
H. SACHS
Received December 3, 1915
As t h e determination of required oxygen is of very great3 importance in t h e examination of waters, i t was thought t h a t it would be well t o look into t h e methods in use for t h e same and t o choose from among t h e m t h e one t h a t seemed t o give the best results. I t was realized a t t h e start t h a t the method is not quantitative, and t h a t t h e results obtained are only comparative. On t h e other hand, were a large number of waters examined in exactly t h e same way, t h e 1 Analyst,
a6 (1901), 141. czt a Fleck, Z. angew. Chem.. 1889, 580. 2 LOC
