Determination of Biochemical Oxygen Demand - Analytical Chemistry

Sulfamic Acid Modification of Winkler Method for Dissolved Oxygen ... Mary Kirk. Industrial & Engineering Chemistry Analytical Edition 1941 13 (9), 62...
0 downloads 0 Views 508KB Size
Determination of Biochemical Oxygen Demand Comparative Study of Azide and Rideal-Stewart Modifications of Winkler Method O. R. PLACAR AND C. C. RUCHHOFT U. S. Public Health Service, Stream Pollution Investigations Station, Cincinnati, Ohio

liberated iodine on a volume of solution equivalent to 200 ml. of the original sample immediately with 0.025 N sodium thiosulfate, using starch indicator. Alsterberg. The sodium azide used is combined with the alkaline iodide reagent. Alsterberg used 5 grams per liter. Barnett 8 grams per liter. Add 2 ml. of manganous sulfate and 2 ml. of the alkaline iodide-azide solution to the sample and shake for 20 seconds. Allow the precipitate to settle and acidify the sample with 2 ml. of concentrated sulfuric acid. Complete the titration as above. Modified Azide. Add 0.7 ml. of concentrated sulfuric acid to the sample as in the Rideal-Stewart procedure, followed by 0.8 ml. of a 2 per cent aqueous sodium azide solution. Stopper the bottle, mix the contents by shaking, and allow the bottle to stand for 10 minutes. Add 1 ml. of manganous sulfate and 3 ml. of alkaline iodide, and complete the determination exactly as stated in the Rideal-Stewart procedure.

THE determination of dissolved oxygen by the Winkler the azide modification for the destruction of nitrites has recently occasioned great interest. In a previous

INmethod,

paper (6) a comparison was drawn between dissolved oxygen (D. 0.) determinations made with the azide and the RidealStewart modifications. No results on biochemical oxygen demand (B. 0. D.) were reported at that time. The azide, in the previous study, was used separately in acid medium— that is, it was simply substituted for the potassium permanganate and oxalate used in the Rideal-Stewart procedure. Since then Barnett and Hurwitz (2) have recommended returning to the original Alsterberg procedure (1, S)—that is, adding the azide with the alkaline iodide reagent. This method is now used by the Sanitary District of Chicago (4). Either technique has an advantage in time required and simplicity over the Rideal-Stewart procedure. The background of the method has been ably reviewed in the previous papers and merits no further discussion here. Meanwhile, considerable data relative to the use of the various azide procedures and to the determination of B. 0. D. by the azide modification have accumulated in the authors’ laboratory; they present excellent confirmation of the value of this worthwhile method.

Comparative B. O. D. Determinations Azide and Rideal-Stewart

Comparisons were made at two laboratories. The samples from the upper Ohio River were analyzed on the laboratory boat Kiski, stationed at Dam 29 near Ashland, Ky. The Ohio River tributaries included in this area are the Scioto, Kanawha, Guyandot, Little Sandy and Big Sandy Rivers, and Tygert Creek. The remainder of the samples were examined at the main laboratory in Cincinnati. These included samples from the Cincinnati section of the Ohio River and the following tributaries: Little Miami, Great Miami, Turtle Creek, Todd’s Fork, Kentucky, Whitewater, South Licking, and Licking. The sampling period included an interval of 11 months. The data obtained have been divided into three groups corresponding to the B. O. D. ranges 0 to 2, 2 to 4, and above 4.0 p. p. m., and are presented in Table I. This classification was undertaken to determine the effect, if any, of increasing

Rideal-Stewart. To the sample in a 300-ml. bottle add 0.7 ml. of concentrated sulfuric acid followed by enough permanganate solution (6.32 grams per liter) to obtain a violet tinge which persists for 5 minutes after shaking. Destroy the excess with a minimum amount of a 2 per cent potassium oxalate solution. When perfectly colorless add 1 ml. of manganous sulfate solution (480 grams of manganous sulfate tetrahydrate per liter) and 3 ml. of alkaline iodide solution (500 grams of sodium hydroxide and 150 grams of potassium iodide). Shake the sample for 20 seconds, allow the precipitate to settle and then acidify with 2 ml. of concentrated sulfuric acid. Titrate the

Table I.

B. O. D, Range

Comparative Dissolved Oxygen

Source of Samples

Ohio River above Dam 29° Ohio River below Dam 29& Ohio River Cincinnati poolc Tributaries Cincinnati aread Tributaries Ashland area6 Average of all in B. O. D. range Ohio River above Dam 29 2.01 to 4.00 Ohio River below Dam 29 Ohio River Cincinnati pool Tributaries Cincinnati area Tributaries Ashland area Average of all in B. O. D. range Ohio River above Dam 29 Above 4.00 Ohio River below Dam 29 Ohio River Cincinnati pool All tributaries Average of all in B. O. D. range 0 to 2.0

Average of all samples in entire range °

6 c

d 6

by Modified Methods

and

B. O. D. Data

and azide modifications upon 1396 Ohio River and tributary samples) Deviations, Azide minus Mean Dissolved Oxygen Rideal-Stewart B. O. D. Final Number Initial Final Initial RidealRidealof RidealD. O. B. O. D. D. O. Azide Stewart Azide Azide Stewart Stewart Samples P. p. 771. P. p. m. P. p. m. P. p. m. P. p. m. P. p. m. P. p. m. P. p. m. P. p. m. 0.11 0.02 1.07 0.13 7.17 1.09 8.24 7.28 253 8.37 0.06 0.13 0.07 1.13 1.07 7.21 7.14 8.34 8.21 310 0.15 0.05 1.64 0.20 1.69 7.02 6.87 85 8.71 8.51 0.12 0.03 1.02 0.15 7.04 1.05 7.16 269 8.21 8.06 0.12 0.01 1.16 1.15 0.13 7.46 112 8.61 7.58 8.74 0.11 0.04 0.15 1.15 1.11 7.24 7.13 1029 8.24 8.39 0.10 0.07 2.20 0.17 2.27 7.84 5.74 5.64 16 8.01 0.16 0.18 0.02 2.36 2.20 5.61 7.99 7.81 5.63 29 0.13 0.09 0.22 2.66 2.57 5.79 8.58 8.36 5.92 129 0.16 0.26 0.10 2.58 2.42 5.56 5.46 37 8.14 7.88 0.23 0.09 0.32 2.93 2.84 5.68 5.45 83 8.61 8.29 0.10 0.24 0.14 2.67 2.57 5.63 294 8.44 8.20 5.77 0.45 0.16 -0.29 4.35 3.41 4.50 1 7.46 3.12 7.64 0.46 -0.24 0.22 4.24 4.48 3.47 2 7.95 3.93 8.17 0.30 4.39 0.25 -0.05 4.67 3.59 3.64 13 8.28 8.03 0.27 0.18 0.09 4.81 4.90 3.69 3.51 57 8.59 8.32 0.12 0.14 4.72 0.26 4.84 3.67 3.53 73 8.51 8.25 1396

8.41

8.23

From 6 sampling points in a 55-mile stretch of river. From 6 sampling points in a 57-mile stretch of river. From 3 sampling points in a 20.4-mile stretch of river, From 14 sampling points distributed among 6 tributaries. From sampling points distributed among 8 tributaries. 12

6.75

6.63

1.66

1.60

0.18

0.12

0.06

January 15, 1941

ANALYTICAL

Figure

1.

EDITION

Frequency

amounts of B. O. D. on the comparative results. A study of the mean values obtained shows a deviation varying from 0.04 p. p. m. in the lower range to 0.12 p. p. m. in the highest. Apparently the deviation in 5-day B. O. D. between the two methods is not an absolute deviation, but involves an extremely small portion of the B. O. D. in the higher ranges. However, this discrepancy is so slight, all mean results being within or just outside the experimental limits of error, that it possesses little real significance. An over-all average, involving 1396 samples, reveals a deviation of 0.06 p. p. m. in the 5-day B. O. D. A frequency curve, Figure 1, confirms the conclusions drawn from the mean results and shows the range of the deviations. The most probable deviation is seen to be 0.05 p. p. m. It is obvious that the azide method and the Rideal-Stewart modification are equally satisfactory in determining the 5-day B. O. D. on samples from streams such as the middle and lower Ohio and its tributaries or for use in comparable work. Determination of the 5-day B. O. D. by the modified azide and Rideal-Stewart modifications was also studied on the Scioto River. The Scioto, a small stream, carries a proportionately greater pollution load than the Ohio. Above Shadeville, it receives the effluent from the Columbus Sewage Treatment plant. At the Pennsylvania Railroad Bridge (two miles below Circleville) it received, during the period studied, the untreated sewage of the City of Circleville and waste from the strawboard plant located there. Samples collected at Kilgore contain the effluent from the primary treatment plant at Chillicothe and wastes from the two paper mills located there. Stream flow varies widely even over shorttime intervals. Nitrites are always found in the stream, varying with the point of collection and the season from a few hundredths to several parts per million. The Scioto constitutes a more stringent basis of comparison than the Ohio. The mean results, presented in Table II, are similar to those obtained on the Ohio, but of slightly greater magnitude. The greatest deviation occurs at the Pennsylvania Railroad Bridge sampling station. On occasion the 5-day B. O. D. was as high as 30 p. p. m. at this

of

13

Deviations

Table II.

of Comparative Study Rideal-Stewart Methods

Summary

of

Azide

and

(Determining 5-day B. O. D. of Scioto River samples) Deviations, Miles Number Mean B. 0. D. of RidealRidealColumbus Samples Azide Stewart Stewart Sampling Point Shadeville 7.44 13 30 7.53 + 0.09 Circleville 8 33 2.59 2.52 + 0.07 21 5.14 35 4.85 Pennsylvania R. R. + 0.29 Chillicothe 61 3.53 3.50 30 + 0.03 67 36 3.21 3.12 Kilgore + 0.09 29 4.57 4.51 76 Higby +0.06 All samples 154 4.60 4.50 + 0.10

point, necessitating dilution of the samples before incubation. This introduces a new factor. Any difference between the two methods, strictly speaking, is shown only by the deviations in the amounts actually incubated or in the differences between actual titrations. This deviation is then magnified mathematically in calculating the B. O. D. by the dilution factor as follows: Deviation in B. O. D. dilution factor X deviation in actual titration =

This is a difficulty inherent in any dilution method. If the deviation of 0.29 p. p. m. obtained at the Pennsylvania Railroad Bridge, for example, is recalculated on the basis of actual titrations, it is reduced to 0.18 p. p. m. Similar reductions could be expected at other stations. These results indicate that the azide and the Rideal-Stewart modifications of the Winkler method are in remarkably close agreement in determining the biochemical oxygen demand on river samples. mean

Comparison of Preliminary Acid-Azide Treatment with Alsterberg Procedure When the sodium azide modification for the destruction of nitrites is used, the original technique may be varied by adding the azide as a separate solution in a preliminary step

INDUSTRIAL

14

AND

ENGINEERING

after acidifying the sample. This method was employed in the foregoing study. The comparative reliability of these two methods was investigated on samples from the Ohio River and its tributaries in the Cincinnati area. Table III.

ment

(On

a

or Preliminary Acid-Azide TreatAlsterberg Procedure

Comparison with

series of 184 Ohio River and

tributary samples. Initial Dissolved

Preliminary acid-azide treatment Alsterberg procedure

Oxygen P. p. m. 7.43 7.42

Mean values) Final Dissolved 5-Day B. O. D. Oxygen 5.47 5.45

1.95 1.96

A total of

184 samples were analyzed in duplicate and the summarized in Table III. The mean results exhibit a remarkable agreement, the deviation being only 0.01 p. p. m. in the initial dissolved oxygen, 0.02 p. p. m. in the final dissolved oxygen, and 0.01 p. p. m. in the 5-day B. O. D. Evidently from the standpoint of reliability in ordinary work there can be no choice between the two methods. For routine work where difficulties are not likely to be encountered, the Alsterberg procedure must be recommended, combining as it does both shortened time and simplified manipulations. The greater flexibility of the preliminary acid-azide treatment, on the other hand, must be understood in any evaluation of the scope of these two methods. In any case when the period of alkalinization must be shortened or the technique of the so-called “short Winkler” method is employed, the preliminary acid-azide treatment is recommended. It appears also to have merits in delayed titrations. It has been observed that a 2 per cent sodium azide solution is a very stable reagent. Solutions that have been kept for one year in the authors’ laboratory have given results in complete agreement with freshly prepared azide solutions when used on duplicate samples.

results

are

Use of Azide to Prevent Oxidation

of Samples

during Storage

In making dissolved oxygen determinations, it is frequently convenient or expedient to delay the titration. As the azide method showed some promise in this contingency, an investigation was undertaken to demonstrate its value for this purpose.

CHEMISTRY

Vol. 13, No.

1

The mean values of the data obtained are presented in Table IV. An inspection indicates the value of the azide in delayed titrations. It is immediately apparent that, even after 5 hours, the samples dosed with azide check very closely with the initials run, these deviations being only 0.04, 0.06, and 0.08 p. p. m. The samples dosed with acid, on the contrary, while showing close agreement on the 10 per cent sewage, show deviations of 0.30 p. p. m. using trickling filter effluent and 0.22 p. p. m. using activated sludge effluent. Complete treatment shows a considerable deviation, 0.22 p. p. m., with the trickling filter effluent, but close agreement on the sewage and the activated sludge effluent. When the data relative to the longer time interval, 21 to 29 hours, are examined, these deviations become more pronounced. Agreement is closest on the 10 per cent sewage samples, the complete treatment and acid giving deviations of 0.18 and 0.15 p. p. m., respectively, as compared with 0.10 p. p. m. for the acid-azide treatment. When trickling filter effluents are used, the deviations are more marked, 0.69 p. p. m. and 0.98 p. p. m., respectively, for the complete treatment and acid dosage, and only 0.25 p. p. m. for the acid-azide treatment. Similarly, with activated sludge effluents these deviations are 0.34 and 0.81 p. p. m. for complete treatment and acid dosage, and 0.26 p. p. m. for acid-azide treatment. These deviations calculated to a percentage basis are given below to emphasize further the general superiority of the acid-azide treatment as a preservative during periods of sample storage preliminary to dissolved oxygen determination: Percentage Deviation after Storage for 21 to 29 Hours

Complete

treatment

10%

raw

Trickling filter effluent

15.5

Activated sludge effluent

Use of

acid-azide treatment

2.4 21.9 14.5

2.9

sewage

Preliminary treatment

6.0

Preliminary Acid-Azide Treatment in Field Work

During the course of a study of the Scioto River, the feasia preliminary acid-azide treatment of dissolved oxygen samples, to be performed by the sample collector, was studied. Duplicate samples were collected, one being dosed with acid and azide in the field and the other being brought to the laboratory undosed. Here the azide determination was completed and the other sample was analyzed by the Rideal-Stewart method. The time in transit averaged about 2.5 hours varying between extremes of 1 and 5 hours. The mean values for dissolved oxygen (p. p. m.) obtained from 63 samples are: preliminary acid-azide treatment in field by Winkler procedure completed in laboratory, 8.44; RidealStewart procedure in laboratory, 8.21; deviation, 0.23. These results agree very closely with observations previously reported (6). The mean deviation of 78 samples

bility of

The materials selected for this experiment were a 10 per cent mixture of sewage in dilution water, the effluent from an experimental trickling filter, and the effluent from an experimental activated sludge unit. This latter effluent was aerated to inThe results on these samples concrease the oxygen content. stitute a more severe test than would ordinarily be encountered in stream pollution studies. Ten series of tests were made on each material, all determinations being made in triplicate. In each series twenty-one bottles were put up. Three of these were dosed comTable IV. Use pletely, using the azide method, and titrated to obtain an initial dissolved oxygen. The remainder were divided into three groups of six each. The first group was dosed completely through the final acidification and stored; the second was treated with acid and azide and stored; the third was dosed with acid only and stored. This storage period, at room temperature, was divided into two intervals, a fairly short one of 2 to 5 hours, 10% raw sewage Trickling filter effluent designated as A, and a longer one varying Activated sludge effluent from the from 21 to 29 hours start, designated as B. Then, A hours later three samples from each group were taken and the determination 10% raw sewage was completed when necessary, and titrated. Trickling filter effluent Activated sludge effluent After B hours this procedure was repeated with the remaining samples.

of

Azide

to

Prevent

Oxidation

after Interval of After complete AcidInitial azide azideDissolved Winkler treated Oxygen treatment sample P. p. m. P. p. m. P. p. m. Interval A 6.25 6.31 6.25 4.46 4.24 4.42 5.58 5.50 5.50 Interval B 6.21 6.31 6.13 4.21 4.46 3.77 5.32 5.58 5.24

Storage

Acidtreated sample P. p. m.

6.24 4.16 5.36

6.16 3.48

4.77

during

Storage

Dissolved Oxygen Loss

after Period of Storage by Indicated Treatment AcidAcid Complete azide P. p.

m.

P. p.

m.

P. p.

m.

0.06 0.22

0.06 0.04

0.08

0.07 0.30 0.22

0.18

0.10 0.25 0.26

0.15 0.98 0.81

0.08

0.69

0.34

ANALYTICAL

January 15, 1941

reported at that time, on samples having a dissolved oxygen content over 7.0 p. p. m., was 0.31 p. p. m. These observations were obtained on duplicates dosed in the laboratory. It is apparent that in this particular set of data there is no advantage in a preliminary acid-azide dose performed in the field, probably because the B. O. D. of these samples was very low. With samples in higher B. O. D. ranges this procedure probably w'ould be of value in field work or where samples have to be transported for a considerable distance for laboratory examination. It has long been known that various substances interfere with the Winkler procedure. Modifications have been devised to overcome these difficulties, one such being the azide modification for the destruction of nitrites, discussed in this paper. These modifications themselves possess limitations and should not be used indiscriminately. Certain examples of interference have been noticed. Some of these have been confirmed; others are indicated by preliminary data and merit further investigation. The azide method is not recommended for the determination of dissolved oxygen in suspensions of river mud (5), or in the presence of ferrous and/or ferric iron, or in raw undiluted sewage. Tentatively, pending further investigation, the azide method is not recommended in the presence of considerable amounts of copper or of sulfite wastes or for any industrial waste containing reducing or oxidizing materials.

Summary The azide and the Rideal-Stewart modifications of the Winkler method are equally efficacious for the determination of B. O. D. in river pollution studies. Either may be expected to give reliable results. The azide reagent may be added in a preliminary step following acid or it may be added in combination with the

EDITION

15

alkaline-iodide Winkler reagent. The first method affords greater flexibility, while the latter has manipulative advantages for routine work. The authors’ results on samples from a 267-mile stretch of the Ohio River, extending from 265 to 532 river miles below Pittsburgh, and from tributaries in the area, indicate that these methods will be in complete agreement. A preliminary treatment with acid and azide, whenever it may be necessary or convenient to store a sample for a short time, is advantageous in preventing oxidation. Such a procedure is superior to a complete Winkler treatment through the final acidification, when the titration is delayed. A preliminary acid-azide treatment will probably be useful in the determination of dissolved oxygen when the samples are to be transported for a considerable distance to a central laboratory.

Acknowledgment The authors wish to acknowledge the cooperation of W. W. Walker and . E. Ettinger in the analytical work upon which this paper is based.

Literature Cited (1) Alsterberg, G., Biochem. Z., 159, 36-47 (1925). (2) Barnett, G. R., and Hurwitz, E., Sewage Works (3)

(4) (5) (6)

J., 11, 781-87 (1939). Brandt, H. J., Gesundh.-Ing., 60, 557-9 (1937); Sewage Works J., 10, 377-80 (1938). Poindexter, G. GIbid., 11, 1025-9 (1939). Ruchhoft, C. C., and Moore, W. A., in press. Ruchhoft, C. C., Moore, W. A., and Placak, 0. R„ Ind. Eng. Chem., Anal. Ed., 10, 701-3 (1938).

Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 99th Meeting of the American Chemical Society, Cincinnati, Ohio.

Determination of Levulose in the Presence of Dextrose and Sucrose. A Ferricyanide Method H. C. BECKER AND D. T. ENGLIS, Noyes Chemical Laboratory, University of

there are only slight differences in the rates of dextrose and levulose with most oxidizing agents, the determination of one sugar in the presence of the other presents a much more difficult problem than the determination of total reducing sugar.

reaction of BECAUSE

At the present time, the only chemical method for levulose in general use is Jackson and Mathews’ (S) modification of the method proposed by Nyns. In this procedure, it is necessary to introduce a factor to correct for the reducing action of the dextrose that is present. Fischl (ß) described a procedure which uses a reagent composed of cupric sulfate, Rochelle salt, sodium carbonate, and disodium phosphate. He reported that, under the conditions specified, levulose has a reducing action 167 times as great as dextrose, although no analytical results are given to substantiate this. A method developed by Strepkov ((?) was reported several years ago; the reagent used is a 0.005 Af solution of potassium ferricyanide containing 80 grams of disodium phosphate per liter. It has been impossible, however, to confirm his finding that dextrose has no reducing action at all under the specified conditions.

A previous publication (1) reported the results of a study of the effect of temperature and the concentration of sodium carbonate and disodium phosphate in the ferricyanide reagent upon the rates of oxidation of the two sugars. Further con-

Illinois, Urbana, III.

sideration of the reaction has shown that the basis for calculation and expression of the results of the previous paper is somewhat misleading. It was believed that a near-stoichiometric relationship prevailed between the reactants. As a consequence, when ferricyanide was in excess, it was assumed that the quantity of sugar oxidized was proportional to the amount of reagent reduced. The fact that the amount reduced reached a maximum and constant value after the mixture had been heated on a steam cone for 10 minutes caused this value to be assigned as that of 100 per cent oxidation for the quantity of sugar taken. However, as will be shown, the equivalent relationships of the reactants change considerably with change in the composition of the reagent and the conditions of the reaction. Hence, the values in the previous paper for per cent of sugar oxidized are only “apparent” but the results as expressed show a correct relationship of the various effects, since the apparent per cent oxidation is directly proportional to the amount of reagent reduced. As the previous paper has shown, the reaction was very rapid at boiling temperature, and no great selectivity could be obtained. At 50° C., however, the reaction was slower but showed a much greater difference in the oxidation rates of levulose and dextrose. Since a temperature of 50° C. was