Determination of Oxygen-Consumed Values of Organic Wastes A Comparative Study
of Methods
W. ALLAN MOORE, F. J. LUDZACK, AND C. C. RUCHHOFT Environmental Health Center, Public Health Service, Cincinnati, Ohio
Anal. Chem. 1951.23:1297-1300. Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/23/19. For personal use only.
During the past few
years several methods have been proposed for the determination of oxygen consumed in organic wastes. In order to evaluate the proposed methods a comparative study was made. When silver sulfate is used as a catalyst in conjunction with the Moore procedure, higher oxidation values are obtained than with the other methods studied. This
is especially true on straight-chain acids, which are not attacked by the ordinary methods. Statistical evaluation of the data indicated that the Moore acid dichromate method is applicable to a larger variety of wastes with advantages in precision and reproducibility. It also has advantages in ease of manipulation and time required.
the past few years several methods have been prorun at the same time when the iodic acid method was used. In each case an equal number of blanks were run, except when the check oxygen consumed in organic wastes. The shortcomings of the American Public Health Assoresults on blanks assured that a smaller number would be sufficiation’s permanganate method are well known and there is a cient. Tests were run by each method on various sample volumes definite need for a better method for determining oxygen conwithin the range permitted by the amount of available oxidizing sumed in stream sanitation and industrial waste studies. In order to evaluate the variTable I. Statistical Comparison of Methods for Determining Oxygen Consumed ous proposed methods, a comCoefficient parative study was made by of No. of Standard Confidence Compound or Waste % of Sample b Theoretical No. and Method Used Variation this laboratory. In addition Detns.® Mean Range Deviation Limits, 1 to the permanganate or standOrganic dye waste 0.041 Iodate® 223 39.4 110 99 960 ard method (1), the methods 166 0.064 591 73.6 96 Ingols 1,153 211 466 0.306 Madison 99 690 1,184 studied included the dichro75 0.072 98 463 169 33.3 Permanganate6 36 0.013 mate method proposed by InMoore 100 113 15.9 1,183 2 o-Cresol gols and Murray (4), the di0.024 Iodate® 99 575 79 14.0 39 91.4 chromate method of Madison 0.024 86.3 543 80 12.9 29.1 98 Ingols Madison 459 174 30.5 68.9 0.066 72.9 99 (6), the iodic acid method of 0.051 443 100 22.8 51.5 70.5 99 Permanganate6 as modified 11.6 0.01 Moore 530 31 5.1 84.2 100 Dzyadzio (2) by 3 Oil refinery caustic waste Johnson, Halvorson, and Tsu0.045 Iodate® 49 50,900 8,182 2,274 6,322 chiya (5), and the dichromate 0.019 50 874 46,000 1,976 Ingols 3,680 0.088 Madison 50 2,838 32,200 19,360 6,413 method proposed by Moore, 50 0.046 29,100 10,040 1,232 2,784 Permanganate6 of and Ruchhoft 347 0.007 Moore 50 783 (7) 48,400 1,843 Kroner, 0.013 29 742 Moore-Ag2S04 57,500 3,230 1,676 this center. Shortly after the 4 Textile dye waste was the use of study started, Iodate® 20 0.060 27,477 6,674 1,634 4,543 20 0.016 569 35,209 1,285 Ingols 2,313 silver sulfate as a catalyst as 20 461 0.006 Moore 786 204 36,599 Muers was (8) proposed by Moore-AgzSOid added to the modifications 5 Glycocoll
DURING posed for the determination of
used. EXPERIMENTAL
In the present study, four organic compounds which are typical of those that might be found in sewage and industrial wastes, and four industrial wastes, were used. Industrial wastes were selected that would be stable over the period necessary to carry out the comparison. Ten replicates at a time were run by each of the methods studied, except that only five replicates could be conveniently
Iodate®»e
10
Ingols Moore
20 20 20
417 592 607
76
20
356 344 902
38
20
20 20 20
1,320 1,336 1,356
Moore-AgsSO* 6
7
Distillery
waste
Ingols Moore Moore-AgzSO* 2-Amino-8-naphthoI-6sulfonic acid/ Ingols Moore Moore-AgíSOí
20
18.3 4.5 4.5
41.4 10.2 10.2
0.044 0.008 0.007
19 24
14.8 6.0 5.3
33.4 13.6 11.9
0.041 0.018 0.006
52 25 35
13.8 6.1 10.3
31.1 13.9 23,4
0.010 0.005 0.008
19
20
65.2 90.8 94.8
79.4 80.4 81.8
Sodium lauryl sulfate® 0.012 71.8 20 62 16.9 38.1 1,436 Ingols 0.010 76.4 20 68 15.3 34,9 Moore 1,527 90.7 20 0.013 106 23.0 52.0 1,812 Moore-Ag2S04 a Ten replicates were run on all methods except iodate, where five replicates were run. 6 95% confidence limits of single determination. c American Public Health Association standard method. d Silver sulfate could not be used as a catalyst on this waste, resulted in 40 to 60% lower value than regular procedure. 6 Replicate determinations varied from 45 to 133 p.p.m. and less than 10% of theory was obtained. / Technical grade. 0 Technical grade, probably a mixture of lauryl sulfates. 8
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CHEMISTRY
ANALYTICAL
1298
Table II.
Ninety-Five Per Cent Confidence Limits of Mean
Number of Replicates Indicated in Table I
on
'__±95% Iodate
Sample
Organic dye waste o-Cresol Oil refinery canstic waste
Textile dye Glycocoll
Distillery
waste
waste
2-Ainino-8-
naphthol-6-
sulfonic acid Sodium lauryl sulfate
3.3 894 1016
Ingols 6.2
2.9
Confidence Limits of Mean_ PermanMoore Madison ganate AgaSOt 10.4 4.1 2.8 4.0 3.4 1.6 927
282 287
394
111 103
311
9.2 7.5
2.3
7.0
3.1
5.2
8.5
7.8
11.6
3.1
2.3 2.6
agent. Over one half the samples were so tested in order to check the effect of sample size. The effect of different reflux times on the oxygen-consumed values was evaluated.by the Moore method to determine whether the specified 2-hour period could be shortened. The iodic acid method was checked by adding various amounts of distilled water to the reaction mixture before refluxing, to determine the effect of the volume of the reflux mixture (with a constant sample volume) on oxygen-consumed results. RESULTS
Table I presents the statistical data obtained on all samples. On the first two samples 100 replicates were run by each method. Because of accidental factors which gave results not representative of the method or sample, a few determinations were discarded and statistical data were calculated on the basis of the remaining replicates.
indicated an oxygen-consumed value of near])’ the same magnitude for both the Moore and Ingols procedures. However, the range of results of the Ingols and particularly the Madison method was excessive. Although the standard deviation of the permanganate method places it second on this sample, the order of magnitude of its coefficient of variation indicates that it is inferior to all the methods except that of Madison. On sample 2 the iodic acid method gave the highest percentage recovery, although in reproducibility it was inferior to both the Moore and Ingols methods. As with the first sample, the order of magnitude of the coefficients of variation places the permanganate method fourth, only slightly better than the Madison proSample
1
cedure. On sample 3 the iodate method again gave the highest oxygenconsumed value of all except the Moore procedure using silver sulfate as a catalyst. The reproducibility of the iodate procedure was very poor, poorer reproducibility being shown only by the Madison method. The coefficients of variation on this sample were in the same order as with the previous two samples.
The data on confidence limits included in Tables I and II are 95% confidence limits, which means that either the single determination or the mean as indicated in the table will be within the limits stated 19 out of 20 times. On the basis of the data assembled on the first three samples, the Madison and permanganate procedures were dropped and another procedure, the basic Moore method modified by the addition of silver sulfate in the reflux mixture, was added to the list of methods given further study. As a result of this work, it was judged feasible to decrease the number of replicates for each method to 20 for the remainder of the study with each group of five or ten replicates obtained on different days. This made it possible to use industrial wastes which were not stable enough to be used over the long period of time required for the greater number of determinations used in the first three samples.
With sample 4 (Table I), the iodate method resulted not only in very poor reproducibility but also in a lower oxygen-consumed
value. The use of the Moore procedure, modified by addition of the silver sulfate, on this waste, resulted in a reduction of oxygen consumed of 40 to 60%. Definite signs of incompatibility between catalyst and sample were noted as soon as refluxing began. The iodate method oxidized sample 5 from 5 to 20%, whereas the dichromate methods resulted in uniform high oxidations. With two different standard solutions of iodate, the results on sample 5 ranged from 45 to 133 p.p.m. of oxygen consumed. A similar situation was evident in a filtrate from a waste containing naphtholsulfonic acid. On the latter material, the iodate method would not give a consistent oxygen-consumed value, whereas the dichromate methods yielded consistent results on the order of 60,000 p.p.m. As this sample changed from day to day, it could not be included in this study. After the work on these samples, the iodate procedure was dropped from the study. A distillery waste, sample 6, was high in organic acids such as acetic, propionic, and lactic. Hence, the silver sulfate method responded very well from the standpoint of both recovery and reproducibility. The results obtained with samples 7 and 8 indicate no definite superiority for any of the dichromate reflux methods used.
The minimum safe number of replicates (3), required to produce mean (95% confidence limits) within 2% of the mean of a large number of determinations on the same sample, is given in Table III. The data presented in Table III were calculated according to the following formula: a
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