INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1929
161
Biochemical Oxygen Demand of Certain Substances' G. E. Symons with A. M. Buswell STATE WATERSURVEY DIVISION, URBANA, ILL.
H E biochemical oxygen demand test offers one of the most accurate methods of determining relative strengths of sewage, effluents and trade wastes. It is also invaluable as a criterion of pollution in streams. Of the methods available for this determination the dilution method is a t present standard procedure. It is cumbersome and has its limitations, most notably that the information obtained is delayed for a period of days. It has been suggested that, with the newer improvements in combustion apparatus such as are used in the steel industry, the constituents of a sewage or sludge could be determined by (,ombustion and the oxygen demand calculated stoichiometrically from the composition. One difficulty probably to be met in this method would be the low concentrations. Obviously, however, the point of attack on this problem lies in a comparison of the calculated oxygen demand with the determined biochemical oxygen demand of pure substances. If these two bear any definite relation to each other, then the possibilities of the combustion method are worth further investigation. With this point in view the experiments reported here were undertaken.
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Methods Used In the study of pure substances the dilution method for determining biochemical oxygen demand and the RidealSteward modification of the Winkler method for the determination of dissolved oxygen were used essentially as outlined in Standard Methods for Water Analysis(J).* The newer improvements in these determinations as reported by Theriault ( 4 ) and Mohlman, Edwards, and Swope(2) were embodied in the procedures except in regard to seals and dilution water, when the suggestions of Greenfield, Elder, and McMurray(1) were followed. The oxygen demand of the following substances was studied: lactose, starch, cellulose (filter paper, Whatman No. l), sodium palmitate, peptone, and urea. With the exception of the peptone, the theoretical oxygen demand was calculated from the equation for complete oxidation of the substances. The oxygen demand of the peptone (Bacto-peptone, Difco Brand) was calculated from its analysis as furnished by the Digestive Ferments Company of Detroit, Mich. The control method of analysis was used; i. e., the pure substances were added to a synthetic dilution water containing a certain percentage of filtered sewage. This oxygen demand of sewage was calculated from the oxygen consumed value (by potassium permanganate) to require 1mg. of oxygen per liter (3). Experimental Amounts of the pure substance were added that were calculated to demand 4 mg. of oxygen per liter. A series of bottles of the control was incubated a t 20" C. and series of bottles filled with the control plus the pure substance were incubated at the same temperature. Dissolved oxygen determinations were made a t different times during a 30-day period. The oxygen demand of the control and that of the control plus the pure substance were determined by com1
Received February 18, 1929.
* Italic numbers in parenthesis refer to literature cited a t end of article.
parison of the dissolved oxygen with the original blank. These values were plotted and curves drawn through the points. By subtracting the curve for the oxygen demand of the control from the curve for the oxygen demand of the control plus the pure substance, the curve representing the oxygen demand of the pure substance was obtained. The difficulty of this procedure appears between the fifth and seventeenth day, in which period nitrification proceeds in the control series but not in the other series. This is to be expected according t o the two-stage theory of oxidation, that nitrification begins when carbonaceous material has all been fermented. Obviously there is less carbonaceous material in the control series, so that the reactions would not be expected to follow the same course during this period. However, after nitrification begins in the series containing the pure substance, the procedure for determining the oxygen demand of the pure substance becomes applicable, and values obtained a t the end of the determination can be said to represent the biochemical oxygen demand of the pure substance. Urea, which undergoes only nitrification, does not suffer from this difficulty, for nitrification begins a t the same time as i t does in the control series; hence the reactions follow the same course. Fiqure I
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O a y q m Demand of 1 Starch Sodium kblmtfote oid U r w
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If the points obtained for the oxygen demand of the substance during this period of nitrification in the control are neglected, and a curve is drawn through the values obtained in the first 5 and last 13 days, the curve is found to fit the equation Log L = Kt L-x total biochemical oxygen demand determined, not calculated X = biochemical oxygen demand for t days K = a constant for a given temperature, T (0.1at 20' C.)(P)
where L
=
Results Peptone shows two-stage oxidation, the first of which fits the above equation. Urea does not give a curve which fits this equation, but appears as the second-stage oxidation curve of ordinary sewage. Figure 1 shows the oxygen demand of the pure substances, starch, sodium palmitate, and urea, as determined by the procedure discussed above. An inspection of the data in Table I shows that up to 30
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ANALYTICAL EDITION
162
days the total biochemical oxygen demand for carbonaceous substances is not equal to the theoretical oxygen demand of the substance. Urea, however, shows complete oxidation. Table I-Comparison of Biochemical Oxygen Demand with Theoretical Oxygen Demand of Pure Substances PER CENTOF THEORETICAL OXYGEN SUBSTANCE DEMAND I N 30 DAYS AVERAGE Lactose 82.5, 69.0, 80.5, 67.5 75.0 Starch 87.5, 78.7 83.0 Cellulose (Elter paper Whatman KO. 1) 78.0, 69.0 71.0 Sodiumhalmitate 75.0, 81.0 78.0 82.5 Peptone" 100.0 Urea 76.0 Sodium oleate (20 days)a a Unpublished data of E. L. Pearson, of this laboratory.
Conclusions
Oxygen demand Of carbonaceous substances in 30 days is equivalent to from 70 to 85 per cent
Note on the Recovery of Platinum' G . J. Hough BUREAU OF CHEMISTRY AND SOILS, %'ASHINGTOZI, D.
1
Received February 27, 1929.
of the theoretical oxygen demand depending on the substance. 2-The biochemical oxygen demand of urea in 20 days is equivalent to the calculated theoretical oxygen demand. 3-The rate of deoxygenation of a sample containing any of the carbon compounds studied follows the equation of a first-order reaction. 4-Compounds containing both carbon and nitrogen show two-stage oxidation, the first of which fits the above equation. Urea, showing no carbon oxidation, gives a curve which appears as the second-stage oxidation curve. Literature Cited (1) (2) (3) (4)
Greenfield, Elder, and McMurray, IND. EKG.CHEM.,18, 1276 (1926). Mohlman, Edwards, and Swope, [bid., 20, 242 (1928). Standard Methods for Water Analysis, 6th ed., 1925, A. P. H. A. Theriault, U. S. Pub. Health Service, Pub. Health Bull. 173, App. 111, p. 163 (1927).
determinations and seven to eight recovery treatments, was found to have lost only 200 mg. of platinum. Consequently, the loss of platinum in each determination was less than onefourth of a cent.
c.
H E following method for the recovery of platinum and alcohol from the filtrates and residues obtained in methods involving the use of platinic chloride for the determination of potassium has been in use in the soils laboratories for several years and has proved very convenient and satisfactory. In order to recover the platinum and alcohol in the filtrates, obtained from washing the chloroplatinates, about 1 gram of ammonium chloride crystals is added to each 300 cc. of filtrate, the mixture stirred well, allowed to stand until clear, and filtered. If the 80 per cent alcoholic solution with the platinum were allowed to stand before the addition of ammonium chloride, a slow reaction with the formation of platinum black and acetone would occur and render the alcohol unfit for use and difficult t o purify. Hence, precipitation should be made a t once after filtering. The alcoholic solution may be allowed to accumulate until a suitable quantity for rectification is obtained. If it is distilled to one-fourth of its original volume, the distillate will consist of 83 to 85 per cent alcohol suitable for re-use. The ammonium platinic chloride obtained above, together with the chloroplatinate residues from the potassium determinations, is dissolved in hot water, and a few cubic centimeters of hydrochloric acid (1:2) are added. The solution is heated nearly to boiling, and magnesium powder is added gradually until a slight excess is present. After the platinum salt has been completely decomposed, concentrated hydrochloric acid is added slowly to dissolve the excess magnesium, the solution is boiled several minutes, and the platinum black filtered off and washed well. The recovered platinum is transferred to a porcelain dish, dissolved in aqua regia, and evaporated to a thick paste. The paste is treated three times with hydrochloric acid and evaporated nearly dry after each addition of acid; finally, it is taken up with hot water and a few drops of hydrochloric acid, filtered, and made up to the volume employed in making determinations. Experience has shown that the loss of platinum by this method of recovery is very small. A solution of platinic chloride after two years' use, involving more than two hundred
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Vol. 1, No. 3
Simple Graduated Wash Bottles' Earle R. Caley PRINCFTON UNIVERSITY, PRINCETON, N. J.
investigations it is sometimes desirable to know IThisNtheanalytical amount of fluid employed in washing precipitates. is, indeed, necessary where a given precipitate exhibits a slight solubility in the washing medium used. I n such cases a fairly accurate measure of the amount of wash liquid used must be made in order t o apply the necessary correction for the slight amount of precipitate lost in the washing operation. Two simple forms of graduated wash bottles, which the writer has found to be serviceable for this purpose, are shown in the illustration. The one, constructed from a suitable-sized graduate, is most convenient in those cases where a cold washing fluid is employed; while the other, constructed from a large test tube which has been calibrated and etched, is necessary where a hot washing medium must be used. In the latter case a turned wooden base is provided in order to maintain the apparatus upright on the working table.
