I X D U S T R I A L A S D ENGINEERING CHEMISTRY
January, 1931
quent digestion processes, but would probably be an advantage. This heating is an engineering problem and requires further study. The dewatering of sludge, which is preferably discharged continuously, could best be accomplished by a mechanical filter. Even if sludge is discharged several times a dav, a mechanical filter would be better than sand filters, and probably more economical. A thermophilic digestion unit would therefore make it possible to do away with sand beds.
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For larger plants fresh solids would be charged continuously, possibly preheated, kept in the tanks for probably24 hours, dewatered on mechanical filters, and carted away to dumping grounds or sold. Literature Cited Heukelekian, S e ~ , a g eWorks J., 2, 219 (1930). (2) Heukelekian, Ibid., in press. (3) Rudolfs and Heukelekian, IND. ENG. CHEM.,22, 96 (1930).
A Study of Tannery Effluent I-Effect of Various Gases upon the Nitrogen Distribution' Edwin R. Theis and Philip Kratz2 DEPARTMENT OF CHEMICAL ENGINEERIXG, LEHICHUNIVERSITY, BETHLEHEM, PA
T
HEIS and Lutz (1) made a preliminary study of the effect of nitrate oxygen upon tannery soak water and showed that treating such water with 1000 p. p. m. of sodium nitrate gave a rapid evolution of gas which was largely nitrogen, a rapid reduction of the added nitrate to nitrite, free ammonia, and free nitrogen. They also showed that the sulfur compounds were acted upon to produce hydrogen sulfide. During the past year this work has been expanded to cover the effect of varying pH of the soak-water effluent and the relation of this effluent to pH under the influence of nitrate oxygen. T/mr
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medium of air; therefore it was desirable to know just what effect would be produced when hydrogen or oxygen was used in place of air. A definite amount of effluent was placed in an apparatus, as shown in Figure 2, so arranged that any ammonia or hydrogen sulfide evolved could be collected and determined quantitatively. The gases were bubbled through the effluent for 7 days, at the end of which period more of the same effluent was placed in the apparatus and the gases again passed through the system for 7 days. This passage of gas was continued for about 4 weeks. At the end of each 7 days the amounts of ammonia and hydrogen sulfide evolved were determined. In the residual effluent nitrogen-distribution determinations were made consisting of the determination of total nitrogen, protein nitrogen, free ammonia nitrogen, formaldehyde titration, and amount of volatile fatty acid formed (these acids would be formed through the deaminization of various amino acids). Figures 3 to 7 show the results obtained from such experiments. Discussion
I
\
When the pH of the sewage-nitrate system was varied, it was found that during the first 24 hours of incubation (Figure 1) the solutions having a pH of 1 to 5 produced goodly quantities of gas, while those solutions of higher pH not only did not produce gas but actually adsorbed gas; in other words, from pH 1 to 5 the pressure was positive but above 5 it was negative. In all the cases tried soak-water effluent produced quantities of gas under acid environment but not in alkaline solution.
Experimental Procedure
It vas decided to determine just how much gas was produced when the hydrogen-ion concentration was varied. The gas produced was measured by determining the pressure in small bottles fitted with manometer tubes. In the bottles were placed 100 ml. of the effluent, the pH of which had been adjusted, the system was brought to 37' C., enough sodium nitrate added to give a solution of 1000p. p. m., the manometers attached, and readings taken a t given intervals. The pH of the samples was varied from 1 to 10. Figure 1 shows the results obtained. It was further desired to find the effect of various gases upon the effluent in question. In the activated-sludge process of sewage treatment, activation is brought about through the Presented before the Division of Leather 1 Received October 27, 1930. and Gelatin Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September S to 12, 1930. 2 Hunt-Rankin Leather Company research fellow, Lehigh University.
Figure 2-Apparatus for D e t e r m i n i n g Effect of Various Gases on Soak-Water
When gases were passed through the effluent, it was found that oxygen caused ammonia to be produced and evolved during i; passage through the sys(em. Upon the other hand, oxygen produced no hydrogen sulfide beyond mere traces. Hydrogen used in place Of air or oxygen caused the
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vol. 23, No. 1
Showing Amounts of Ammonia and Volatile S u k h idel Evolved d u r l y
Sewage ---- Raw Hydrogen
of Dayyen ondffydrayen t4rorqrl €ff/uenf
Por,oge
- - - - --.Osypen
t
II Time (in Weeks) I Sho wdnq Ammonicd Compounds
in R e r i d u d .Cff/uent
Fiq 5
---
ShowinyAmunf Compdundsh'eos tiny wifh f o r m d d e h y4r /n Reriduo/ Eff/uenf forma/ T i ' f r s fi'n
Row Sewage
Hydrogen On y p e n
Row Sew098 Hydroqen
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4
Time (Weeks)
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Shown Vo/oiile Fof t y A c i d os B u f y r ~ Acd Foun%dunny Passage o f Yoribus Gases
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Hydrogen RawSewuge Oxygen
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e _ -, .-_____ ___ __ --* __---.-5--.+-,-=-
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Time (wee&.
production of much volatile sulfides but little ammonia (Figure 3). During the first 7 days oxygen caused the production of 300 per cent more ammonia than did hydrogen under the same conditions. As the raw, untreated effluent stood and was allowed to degenerate, hydrogen caused almost as much ammonia to be evolved as oxygen, but the ammonia evolved by both oxygen and hydrogen was probably preformed by standing, as indicated in Figure 3 during the third week. Figure 4 shows the total nitrogen in the residual soakwater effluent after the passage of the gases for each weekly period. It also shows the changes occurring in the raw untreated sewage overthese periods. Figure 5 shows the ammoniacal compounds present in the residual effluent after the
passage of the gases and also in the raw untreated sewage. Figures 4 and 5 indicate that in the case of oxygen during first and second weeks of digestion the tendency is to evolve a goodly amount of ammonia, but not during the third and fourth weeks. The ammoniacal compounds may be changed into other non-volatile compounds of more complex structure by the passage of oxygen. When hydrogen is used, this condition is not noted. Physically the two effluents become entirely different shortly after the passage of the two gases. The oxygenated effluent becomes very colloidal with little tendency to form a precipitate, while the hydrogenated one does not become colloidal and after a short time a heavy precipitate forms. Figure 6 shows the compounds existing in the residual effluent which react with formaldehydeammonia, amines, and similar compounds. Figure 7 shows the extent of deaminieation under the two different types of gaseous environments. In the case of oxygen and the raw untreated effluent the amount of volatile fatty acids decreases rapidly during the first week, whereas in the hydrogen environment, such is not the case. It would appear that hydrogen is activated to some extent and acts as a reducing substance, causing an apparent deaminization and thus the higher volatile fatty acid content. The volatile fatty acid content of the residual effluent does not materially decrease until the end of the third week, when the acids decrease to about the same extent as those of the untreated and oxygen-treated effluent. It is possible that in oxygen environment there is a deaminization of amino acid with liberation of ammonia, followed by an oxidation of the deaminized acid. In this case there would be little or no volatile acids present in the residual
January, 1931
I N D USTRIAL L4Y D ENGIATEERIIYGCHEMIX T R Y
effluent. I n the hydrogen environment no oxidation of the deaminized acids would be expected, thus giving volatile acids in the effluent. Summary The work outlined is of a preliminary nature indicating some of the reactions that occur when tannery effluent is treated with oxygen and hydrogen. It is pointed out that oxygen promotes formation of ammonia, indicating deaminization of the amino acids, causes the effluent to become very
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collodial in character, and retards formation of volatile sulfides. It is further shown that hydrogen environment furthers the formation of hydrogen sulfide, causes deaminization with subsequent reduction, and finally causes the formation of volatile acids, which are not found in the oxygentreated effluent. The work is being extended to include the effect of hydrogen-ion concentration with relation to the gaseous environment. Literature Cited (1) Theisand Lutz, IND.ENG.CHEM.,21, 763 (1929).
Diastatic Activity of Some American HoneyslB2 R. E. Lothrop and H. S. Paine BUREAU OF CHEMISTRY A N D SOILS, WASHINGTON, D. C.
In view of objections raised in Germany to the low diastatic activity of various importations of American honey, an investigation was made of the diastatic activity of a large number of samples of unheated American honey of a great variety of floral types. The results indicate that the natural diastatic activity of most types is sufficiently high to meet the German requirements i n this respect. Honeys of certain floral types, notably those of darker color, show characteristically high diastase values, whereas a few, among which alfalfa and orange are the best examples, generally show low diastase values. A considerable variation in the diastatic activity of various samples of the same floral type was found, however, so that careful attention to the diastase content of honeys intended for export (to Germany) should be observed in the future. The effect of even moderate heating of honey is to lower the diastatic activity somewhat; hence, great care should be exercised in the heating of honey when the preservation of its natural diastatic strength is de-
sired. The diastase is probably derived from pollen. The activity of honey diastase is greatly affected by variations in hydrogen-ion concentration, the optimum activity being attained a t a pH of about 5.3. Methods for determining diastatic activity of honey which are in vogue in Germany do not take this factor fully into account. Gothe’s method is objectionable i n that large differences in pH exist between the contents of the comparison tubes in a given determination. For honeys of medium diastatic activity Gothe’s method furnishes fairly satisfactory comparative values, since the pH values of the significant comparison liquids are near the optimum. In the case of very low or very high values, the method does not yield comparable results. A modification of Gothe’s procedure is described in which the pH of the various liquids in a comparison series is kept constant a t the optimum point for diastatic activity. The use of this modification is recommended when a higher degree of accuracy is desired.
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N CONNECTION with a comprehensive investigation
of the composition of gmerican honeys in relation to the suitability of honeys of different types for various industrial uses which has been undertaken recently by the Carbohydrate Division, considerable attention has been given to diastatic activity. The practical importance of a study of the diastase value of American honeys has arisen from the fact that during the past few years a number of shipments of American honey to Germany have been penalized by the German importers because of low diastatic activity, this action being based upon the position taken by the German food authorities that all genuine honeys which have not been overheated should show a t least a specified minimum diastatic activity. Diastase Value in Relation to Exportation of American Honey Since Germany has been the largest foreign consumer of American honey during recent years, this situation has seriously affected exports of honey from this country. Of some 20 million pounds imported into Germany annually, approximately one-third is American honey. This represents 1 Received September 22, 1930. Presented before the Division of Sugar Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930. Contribution 98, Carbohydrate Division, Bureau of Chemistry and
Soils.
more than half of the total quantity of honey exported (3) from the United States, Great Britain being the next largest consumer. American honey exporters have built up a substantial business during recent years, and have gained an excellent reputation for their honey, which has tended to wean the Germans away from the use of L‘Kunsthonig”and cheap marmalades as “spreads” in place of honey. It was therefore important to determine whether or not American honey of certain types is naturally deficient in diastase, or whether the diastase is partially destroyed or inactivated as a result of overheating during extraction or subsequent processing. A large proportion of the honey shipped to Germany from the United States originates in California, and a portion of this in turn comes from the Imperial Valley. The high temperatures prevailing in the Imperial Valley, especially during the summer, suggest the possibility that prolonged exposure of extracted honey to atmospheric temperature in that region, especially in direct sunlight, might cause an appreciable reduction in diastatic activity. As a rule, little attention has been given to diastatic activity in conjunction with chemical examination of honey in the United States, although in Germany (also in France and Switzerland) the subject of enzymes in honey has been studied rather extensively for a number of years. Erlenmeyer and von Planta ( 4 ) were the first to report the pres-
