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T H E J O U R N A L OF INDCSTRIAL A N D ENGINEERTNG C H E M I S T R Y
shop coat is almost always torn off in the rough handling i t gets. I t costs more t o get on a coat of paint in the shop t h a n it doe5 in t h e field. Linseed oil gives protection for four or five months, which is as long as i t is wanted, a n d has given very good results except in one or t w o cases. 320 FIFTHAVENUE,NEW YORK
DETERMINATION OF THE BIOCHEMICAL OXYGEN DEMAND BY THE SALTPETER METHOD IN STOCKYARDS, TANNERY AND CORN PRODUCTS WASTES By ARTHURL E D E R ~ R ? Received April 13, 1915
The saltpeter method described b y me in t h e M a y (1914)issue of t h e Journal of Infectious Diseases a n d in a paper presented a t t h e last December meeting of t h e American Public Health Association ( A m . J . Pub. Health, April, 1915)is based upon experimental work with domestic sewage a n d polluted river water. Briefly, t h e method depends upon t h e denitrification of a sod i u m nitrate solution by t h e sewage bacteria present. It was f o u n d t h a t the a m o u n t of saltpeter oxygen absorbed b y t h e organic m a t t e r on incubation is t h e same as if fresh water oxygen was used. I n preparing a n d adding t h e sodium nitrate solution t o t h e sewage i t was assumed t h a t five atoms of oxygen are available from t w o molecules of sodium nitrate, a n d t h e figures obtained on this basis checked very well with figures obtained by t h e dilution method. By t h e dilution method is meant t h e preparation of sewagewater mixtures in stoppered bottles with t h e addition of a definite quantity of methylene blue. T h e dilution m a y or may not be carried t o t h e point of absolute stability. Usually the mixtures are incubated for ten d a y s a t zoo C. T e n days’incubation sufficesfor all practical purposes. T w e n t y days’ incubation is preferable when t h e t i m e element is not important. T h e stability is expressed in terms of “relative stability.” Knowing t h e free oxygen content of t h e diluting water a n d the t i m e of decolorization, t h e biochemical oxygen demand of t h e sewage can easily be calculated, a n d expressed in milligrams of oxygen per liter of sewage or p. p. m. T h e principal objection t o t h e dilution method from a scientific standpoint is t h e impossibility of determination of intermediate points of deoxygenation as is possible with t h e saltpeter method, a n d from t h e working standpoint t h a t it is time-consuming a n d ill adapted for field work. During t h e incubation with t h e saltpeter solution I observe t h e sediment, t h e odor, a n d t h e gas formation. If t h e sediment becomes “septic” (i. e., black color) during incubation, t h e bottle with t h e next higher content of saltpeter is selected for t h e determination of t h e residual nitrate-nitrite oxygen. If the saltpeter is present in sufficient quantities there is no putrid odor. If active gas formation does not t a k e place, t h e presence of either free acid or caustic alkali or other germicides may be discovered. This brings me t o t h e subject of trade wastes. A municipal sewage may contain a considerable quantity 1 Read in Abstract at the 50th Meeting of the American Chemical Society, New Orleans, March 31, to April 3, 1915. 2 Chemist and Bacteriologist, The Sanitary District of Chicago.
Vol. y , No. 6
of trade waste without losing entirely t h e characteristics of a domestic sewage. I n such a case t h e saltpeter method can be employed without a n y modification. However, sewage or trade wastes occur containing caustic alkali or acid, or a germicidal or antiseptic substance. These are t h e wastes which I want t o discuss more closely. I n previous publications I have warned against t h e indiscriminate application of the saltpeter method in t h e trade wastes, for t h e reasons already given. I n trade wastes investigations carried on for T h e Sanitary District of Chicago under t h e direction of Langdon Pearse, I have h a d ample o p p o r t u n i t y t o s t u d y t h e application of t h e saltpeter method t o such wastes, including those f r o m t h e stockyards, tannery, a n d corn products industry. T h e modifications of t h e method required when working with some of these wastes are simple a n d do not complicate the application in t h e least. With t h e packing house waste mixed with domestic sewage, t h e method remains t h e same as with domestic sewage. This waste resembles somewhat a concentrated domestic sewage, with a high organic nitrogenous a n d carbonaceous content. When working with such a waste of unknown strength, I have employed 500, 1,000,1,500, a n d 2,000 parts per million of oxygen in t h e form of sodium nitrate. On t h e individual plant outlet higher concentrations might be required. Some concentrated effluents containing blood a n d other complex organic m a t t e r absorb as much as ~ j , o o o p. p. m . of oxygen. T h e biologic oxygen consumption of t h e mixed waste obtained from t h e stockyards a n d packing town, with domestic sewage, in Chicago a t Center Ave., fluctuates between goo a n d 1,300 p. p. m . of oxygen during the working period of t h e day. A little experience is t h e best guide t o t h e quantity of sodium nitrate required. It is useless t o a$d methylene blue t o these wastes as a n indicator on account of t h e adsorption which takes place in t h e presence of colloids. T h e appearance of a black color in t h e sediment or t h e elimination of t h e putrid odor after incubation are not reliable indices, as is the case with domestic sewage. Profuse gas formation takes place whether there is a sufficient quantity of sodium nitrate present or not. T h e bacterial content of t h e packing house a n d stockyards waste is always very high. Domestic sewage is nearly always mixed in varying proportion, roughly, a b o u t twenty-five per cent. T h e best index of accomplished denitrification is undoubtedly furnished b y t h e nitrites. For instance, if nitrites are absent or present in traces in t h e 500 p. p. m. oxygen bottle, after incubation, discard t h e bottle a n d select t h e one with t h e higher a m o u n t of oxygen for t h e actual determination of t h e residual nitrite-nitrate. Supposing we find t h a t on t h e fifth d a y of incubation with t h e highest concentration of sodium nitrate there is b u t a weak nitrite reaction ( 5 cc. of t h e liquid is all t h a t is required for this t e s t ) . we have t h e n reason t o assume t h a t we shall be unable t o obtain a n accurate oxygen demand figure unless we a d d some more saltpeter oxygen. This can be done probably without incurring a n appreciable error. A t
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a n y rate, i t is advisable t o obtain a n approximate figure rather t h a n t o lose t h e result entirely. T h e residual nitrite is determined b y t h e sulfanilic acidnaphthylamine method, t h e nitrate b y t h e aluminum reduction method. A t t h e conclusion of t h e aluminum reduction, a n aliquot portion of t h e liquid is directly nesslerized. It is clear, of course, t h a t a certain working error is involved in t h e determination of such large quantities of residual nitrite-nitrate, b u t t h e error should not exceed I O per cent, even in t h e hands of t h e inexperienced chemist. Undoubtedly, t h e employment of a more rapid method a n d less sensitive method t h a n t h e ones mentioned would be desirable, b u t such methods are not available. A question arises whether t h e oxygen consumption increases with the excess of sodium nitrate employed. An extended series of tests with domestic sewages indicates t h a t t h e oxygen consumption increases somewhat with t h e excess of saltpeter employed. b u t not t o a n extent sufficient t o interfere with correct conclusions. I have found t h a t t h e excess must be considerable before t h e oxygen consumption is increased b y I O per cent or thereabouts. T h e excess consumption is insignificant when compared with t h a t obtained b y employing fresh water dilutions as is done in t h e so-called English incubation test.' The smaller t h e excess t h e more accurate t h e result: i t is merely a question of adding t o t h e number of bottles; t h e additional labor involved is slight. T h e saltpeter method on stockyards waste checks well with t h e d i h t i o n method, as can be noted from t h e following table: TABLE ~-cOMPARISON
OF
DILUTION hIETHOD
A K D SALTPETER
METHOD ON
MIXEDSTOCKYARDS SEWAGE
Biochemical Oxygen demand, p. p. m. Serial No. Dilution method Saltpeter method 1 1130 1090 2 1200 1110 3 890 848 4 1100 1160 56 960 940 950 890 Average.. . . , . . . , . . , 1036 1009
T h e oxygen consumption during t h e first 24 hrs. a t C. amounts t o approximately 20 t o 30 per cent of t h e ultimate consumption-during t h e first five days, 7 0 t o 85 per cent. I n domestic sewage t h e oxygen consumption during t h e first 24 hrs. is likewise approximately 2 0 t o 30 per cent of t h e ultimate. It is of interest t o obtain t h e oxygen consumption i n t h e first 24 hrs., as this indicates what might happen i n t h e stream when t h e trade waste is discharged. Work on t h e substitution of sodium nitrite for sodium nitrate as a source of oxygen gave promising results with weak domestic sewage. T h e substitution would simplify t h e method, inasmuch as t h e residual oxygen would be present only in t h e form of nitrite a n d not nitrate as well. Closer studies proved, however, t h a t nitrites give results lower t h a n t h e nitrate. With weak sewages t h e differences are negligible, b u t in stronger sewages a n d in t h e mixed stockyards sewage, a n average of a very large number of results shows results j t o I O per cent lower t h a n those obtained with t h e saltpeter a n d t h e dilution method. With tannery waste, nitrite results were even 2 j per cent lower. Still, t h e 20'
1
Lederer. THISJOURNAL, 6 (1914), 882.
515
analytical part of t h e nitrite method is so simple t h a t in t h e case of t h e continuous control of a sewage settling plant i t m a y seem feasible t o disregard the small difference, or else a d d t o all of t h e results obtained a certain percentage of oxygen. This percentage could be elicited experimentally b y a comparison with t h e nitrate or dilution method I have also applied this test t o t h e combined waste from a large establishment producing cornstarch a n d glucose. There was t h e admixture of domestic sewage from t h e workmen in t h e plant, with consequent high bacterial content. Often t h e effluent would he slightly acid, on account of t h e presence of free sulfurous acid, b u t t h e acidity would quickly disappear on standing. E v e n though the effluent was distinctly alkaline to methyl orange, gas formation was not noted a t first. Checks were not obtained with t h e dilution method. It was then found t h a t t h e presence of carbohydrates resulted in a fermentation during t h e incubation, forming organic acids which inhibited denitrifiration. However. when a few cubic centimeters of a saturated sodium bicarbonate solution were added a t the start, t o t a k e care of the acids of fermentation, t h e method worked well. It is useless t o a d d methylene blue as a n indicator or t o observe t h e sediment a n d odor. It is nearly impossible t o apply t h e dilution method t o this waste. OR account of t h e adsorption of coloring matter even i n t h e higher dilutions. T h e presence or absence of nitrites furnishes t h e best index. The total oxygen donsumption varied between 400 a n d 1 2 0 0 p. p. m. T h e oxygen consumption during t h e first 24 hrs. was only about 7 per cent, a n d during t h e first 5 days approximately 60 per cent of t h e total. The presence of sodium bicarbonate apparently does not interfere with t h e results obtained. Considerable quantities were added experimentally without change in t h e oxygen demand figures, as c a n , b e noted from Table 11. TABLE 11-BIOCHEMICALO X Y G E N
D E M A N D OF DOMESTIC S E W A G E COSQUASTXTIESO F S A T U R A T E D S O D I U M BICARBON SOLUTION.RESULTS I N PARTSPER MILLION Biochemical oxygen demand of sewage containing Serial 90. 0.0 1 cc. 3 cc. 5 cc. NaHCOs 1 134 140 146 161 170 170 2 157 3 118 115 4 130 135 138 126 5 158 153 159 150 6 150 165 150 153
TAINING VARYIKG
ATE
-
During the course of t h e incubation, tests can be made for free acid a n d if acid should develop, sodium bicarbonate may be added at a n y time. The temporary lifting of t h e stopper has no influence on t h e progress of deoxygenation. I n dealing with such wastes, I have made i t a rule t o a d d a few cubic centimeters of a saturated sodium bicarbonate solution t o each bottle a t t h e s t a r t . Caustic alkali was not noted b y me, b u t i t should be tested for with phenolphthalein, a n d if present neutralized with hydrochloric acid. It is particularly likely t o occur i n tannery waste. These vary considerably in strength from time t o time. A mixed waste is frequently strong in caustic alkali. If this is t h e case, a d d dilute hydrochloric acid t o neutralize t h e
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free lime, using phenolphthalein as an indicator. Preferably t h e sample should stand for about 30 min. with a slight excess of acid a n d be tested again for free lime, inasmuch as t h e free lime in the sediment does n o t combine very rapidly with t h e acid. T h e effluent resulting from t h e liming process may contain such a n excessive quantity of lime sediment as ‘to make complete initial neutralization extremely ,difficult. My experience with these particular efAuents is t h a t they do not lend themselves t o biochemical demand determinations readily by either t h e saltpeter or t h e dilution method. When employing the dilution method adsorption of the methylene blue takes place in t h e majority of cases even in the higher dilutions. I n a mixed t a n n e r y waste, however, suspended lime is ordinarily not present in quantities sufficient t o interfere with the reliability of either mode of procedure. -4s a rule, the bacterial content is high, making unnecessary t h e seeding of the waste with sewage after neutralization. However, in order t o insure the presence of sewage bacteria, t h e waste may be seeded after neutralization by t h e addition of one cubic centimeter of domestic sewage or polluted river water for each 8-oz. bottle containing t,he waste. T h e wash water resulting from t h e chemical tanning process is likely t o be acid. If i t is desired t o test this waste separately, i t becomes necessary t o neutralize with sodium bicarbonate a n d t o seed with sewage. Although the t a n n e r y wastes are often strongly colored t h e dilutions required in employing the dilution method are as a rule so great t h a t t h e y do not interfere with the observations of the decolorization of the methylene blue. T h e dilution method has been found t o check well with t h e saltpeter method when employed on combined t a n n e r y waste with t h e precautions mentioned The average of 2 4 days’ results showed t h e dilution method not quite 3 per cent higher. Considering the unavoidable working errors involved b y either method, this is a n excellent check. T h e total oxygen demand varied appreciably during t h e da.y, namely, from 4 0 0 t o 1000 p. p. m. The oxygen consumption in t h e first 24 hrs. was about 7 per cent a n d in the first j d a y s 6 0 per cent of t h e total. As yet, I have not encountered other germicidal .or antiseptic trade wastes, although such waste can undoubtedly be found in t h e gas works industry. .Offhand, I should say t h a t in such waste t h e dilution m e t h o d will be preferably employed t o offset t h e germi,tidal effect, a n d t h e dilution method would probably b e desirable when determining t h e oxygen demand of a ,disinfected sewage. Cases are rare where a sewage .or waste contains germicides other t h a n free lime or free acid in quantities sufficient t o interfere with t h e application of t h e saltpeter method. If free lime or free acid is present in a n y waste, t h e procedure t o be tried should be t h e one which is described. Finally, I may say a f e w words t o clear up certain misconceptions regarding the meaning of the t e r m oxygen demand. As determined, the oxygen is entirely supplied b y t h e nitrate. But this does not mean t h a t the oxygen demand so determined will have t o
1‘01. 7 , XO. 6
come from the available oxygen in the stream into which t h e sewage is discharged. On t h e contrary, while most of t h e oxygen may be derived from t h e stream, t h e rest may come from t h e air b y absorption or from t h e plankton. N o definite rule can be given, for each particular case is a m a t t e r of individual study. Whether a11 of the oxygen must be supplied from t h e stream or not. the saltpeter method affords a reliable a n d simple comparison of t h e strength of a sewage or waste from the deoxygenating standpoint. This a n d the amount of settling suspended matter are t h e items most interesting t o the sanitary engineer or chemist. Of less value are t h e routine chemical determination of t h e constituents usually looked for in sewage. T h e great advantage of the saltpeter method lies in the fact t h a t t h e oxygen consumption can be determined after a n y desired interval in a much more reliable a n d comparable manner t h a n can be accomplished by methods involving fresh water dilutions. T o t h e sanitary engineer this is a m a t t e r of great importance. The method has also been employed by me for the past year t o determine t h e efficiency of sewage purification devices a n d t h e degree of pollution of rivers. For the latter purpose, somewhat different technique is required,’ t h e discussion of which is not within the scope of this paper. THES A N I T A R Y DISTRICTOF CHICAGO 700 KARPENBUILDING, CHICAGO
THE ACIDITY AND ASH OF VANILLA EXTRACT B y A L WINTON,A. R. ALBRIGHTAND E H. BERRK Received January 23, 1915
I n a paper entitled “ T h e Chemical Composition of Authentic Vanilla Extracts. together with Analytical 5Iethods a n d Limits of Constants,”2 Winton and Berry tabulate analyses of 7 7 extracts prepared in t h e laboratory from different varieties, grades a n d lengths of vanilla beans a n d 18 extracts employing different menstrua. T h e determinations made were vanillin, normal lead number, color value of t h e extract a n d of the lead filtrate and the color insoluble in amyl alcohol. I n addition t o the extracts made b y the direct treatment of the beans with t h e menstruum, second extracts were prepared from the residues a n d separately analyzed. Since this paper was published it occurred t o us t h a t determinations of acidity a n d ash, as well as the solubility a n d alkalinity of the ash, would be of value in the examination of suspected samples. It is indeed surprising t h a t such simple determinations should have been overlooked in the search for means of distinguishing genuine from imitation extracts especially when ash a n d ash constants have been regarded of such importance in t h e analysis of fruit products a n d various other classes of foods. T h e ash values would appear t o be useful on t h e one hand because t h e common ingredients of imitation extracts, namely, vanillin, coumarin, sugar, glycerine and alcohol, are practically free from ash a n d o n t h e other h a n d because t h e use of alkali in t h e manufacture of extracts from beans would not only increase A m . J Pub Heallh, May, 1916 Proceedings of the Assn. of Official Agricultural Chemists for 191 1, U S. Dept of Agric., Bureau of Chemistry, Bull. 162, 146-158 1 Lederer,
2
