1012
Vol. 19, No. 9
INDUSTRIAL A N D ENGINEERISG CHEMISTRY
Discussion of Results The results seem to support the theory advanced to explain the behavior of the 1,6 acid-namely, that the conversion of any of the naphthalenesulfonic acids to others involves hydrolysis and subsequent resulfonation. Like the 1,6 acid the 1,5 acid undergoes hydrolysis directly to naphthalene in the lower concentrations of sulfuric acid and it is converted into the other isomers in the higher concentrations. At any temperature where the 1,6 acid is converted into isomeric acids the 1,5 acid is converted into the same isomers, the 2,6 and 2,7 acids. In the case of the 1,s acid, however, the conversion also takes place under conditions which do not produce such a change in the 1,6 acid-that is, a t lower temperatures and in less concentrated sulfuric acid. This, of course, indicates that the 1,5 acid is less stable and is either more readily hydrolyzed or more susceptible to intramolecular rearrangement. If it is a case of intramolecular rearrangement and we find it possible for the 1,s acid to rearrange its sulfo groups into the 1 and 6 positions, we would expect that where the 1,6 acid is stable and the 1,s acid unstable the latter would be transformed into the former. Table I11 shows that a t 140' C. in 73 per cent sulfuric acid the 1,5 acid is converted into the 1,6 acid and a trace of the 2,7 acid. Under identical conditions the 1,6 acid was partially hydrolyzed, but no other isomers were obtained. A t 140" C. in 77 per cent sulfuric acid, however, where the 1,6 acid showed similar stability, the 1,5 acid has been completely replaced by the 2,7 acid. Thus we see that, although the 1,5 acid can be converted into the l,6, it is not always so converted under conditions in which the 1,6 acid is stable. Hence the reaction is apparently not a rearrangement. The most
probabIe expIanation is resulfonation of the naphthalene produced by hydrolysis. The factor which determines the products in that case is the course of the reaction between naphthalene and sulfuric acid under the existing conditions. This is satisfied in every case, for wherever the initial acid is sufficiently hydrolyzed new isomers appear and they are a h a y s the ones that would be produced by the sulfonation of naphthalene under identical conditions. Table III-Products* Obtained by Heating Naphthalene-1,5-nisuIf o n i c Acid w i t h Various Concentrations of Sulfuric Acid at Different Temperatures HzSO4
STRENGTH 100' C. 120" C. 140' C.
c;;c1
...
...
...
J
...
...
9
. .
22
...
... ... ...
. . 1,s
42
...
1,s
64
...
1,s
69
..
73
1,s
7i
1,s
2,7
1,s
...
85
CioHs
13
CioHs l,5 ClOH8
1,s
CioHa
1,6
2,7b CioHs
160' C. 180' C. 200' C. 220' C. 1,5 1,5 CioHs CioHs 1,s 1,s CiOH8 CioHs l,5 1,s G O H B CioH. 1.5 1,5 CioHs CioHs 1,s 1,s ClOH8 CioHa 1,s l,5 CloHs CioH,
2,6 2,7 SOzb CioHs 2,6 2,7 SOib CioHs
... ...
1,5 CioHa CioHa CioHs 1.5 CIOH8 1.5 CioHa CIOH 8 C~OHR . . .
...
...
l,5 CioHa
so2
...
...
...
...
...
...
...
...
1,5 is naphthalene-l,5-disulfonic acid; 1,6 is naphthaIene-1,6-disulfonic acid; 2.6 is naphthalene-2,6-disulfonic acid; 2,7 is naphthalene-2,7-disuIfonic acid; and CloHa is naphthalene. b Trace.
Fate of Grease in Sludge Digestion' By S. L. Neave with A. M. Buswell STATEWATERSURVEY, UNIVERSITY or' ILLINOIS, URBANA, ILL.
H E scarcity of literature on the bacterial degradation of fats and soaps indicates a need for further investigation. O'Shaughnessyz pointed out that a little over one-third of the fatty matter is lost during digestion of sewage sludge, while the laboratory experiments of Bach and Sierp, on the anaerobic digestion of various foodstuffs, showed as high as 50 per cent decomposition of the fats. I n a recent paper the present writers4 have shown that the percentage of "grease" (using this term loosely t o include oils, fats, and soaps extractable by petroleum ether) is the same in freshly settled sewage solids and in the digested sludge; consequently, since about 30 per cent of the solid matter is liquefied during digestion, a corresponding decrease in grease must occur. Fat-splitting bacteria have been reported in the Imhoff tank flora by Hotchkiss and Murray,6 though Rudolfs6 reports no decomposition of grease during sludge digestion. Some of the tests in this laboratory have indicated that, whereas sodium and potassium soaps, which would predominate in a soft-water region, strongly resist bacterial action, the calcium soaps of our hard-water sewage are readily decomposed. This point is receiving further study t o see whether
T
1 Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 to 16, 1927. 2 J . SOC.Chem. I n d . , 33, 3 (1914). 1 Centr. Bakt. Parasitenk., II A b f . , 62, 24 (1924). 4 THIS JOURNAL, 19,233 (1927). 6 Am. J. Pub. Healih, 13, 562 (19231. 8 N. J . Agr. E r p l . Sla., Bull. 427, 64 (1926).
the predominant cation may not explain the reported variability in grease digestion. The present paper reports experimental evidence that grease not only can digest, but also may serve as an important source of methane. Experimental Procedure Sewage solids were obtained from a settling tank operating on a purely domestic sewage from a combined system. A thoroughly mixed sample of the soIids was divided into thirteen 1-liter portions, one portion being used for the initial analysis and the other twelve being placed in bottles fitted for gas collection. No initial seeding was used. Each week one bottle was removed and the contents analyzed. After 3 weeks, when gas evolution had nearly ceased, three of the remaining bottles received 5 grams of lime each to bring the p H from 5.0 back t o 6.8, and then digestion was allowed to proceed for comparison with the untreated ones. ANALYTICAL hkTHon-The solids were drained on a Buchner funnel using suction, and the resultant cake, containing about 7 2 per cent water, was dried to constant weight a t 100" C. On the filtrate were determined pH, free amino nitrogen, total amino nitrogen after hydrolysis with 33 per cent sulfuric acid, ammonia, urea, total nitrogen by Kjeldahl digestion, volatile fatty acids by steam distillation, and lactic acid by vacuum distillation. On the dry cake were determined total dry weight, ash, grease (including soaps), cellulose, and total nitrogen; also a &gram sample was hydrolyzed with 33 per cent sulfuric acid and the nitrogenous com-
INDUSTRIAL AND ENGIYEERING CHEiMISTRY
September, 1927
ponents were determined as humin-x, amid-N, amine-N, purine bases, and total nitrogen by Kjeldahl digestion. Some of these data relate to an independent study of the nitrogen cycle and are omitted in the present discussion. Results
Table I summarizes the analytical results on the initial solids and on the digesting sludges a t weekly iiitervals. Results for the eighth week are averages of two bottles, the duplication being thought desirable to check both analytical ac-
curacy and uniformity in the digestion processes; the deviation was:too slight to justify tabulating both. Figure 1 shows the decrease in total weight of solids in the bottles and Figure 2 the decrease in organic content of the solids. The curves indicate that lime increases the rate, rather than the extent, of digestion, though this drop in organic matter (Figure 2 ) may be:due only t o increased solubility in the more alkaline liquor, as noted before.4 This variation in solubility with pH is receiving further study, so that the apparent digestive processes may be corrected for it. The proteolytic flora is largely suppressed in this acid digestion and more than 80 per cent of the loss in organic matter can be accounted for as grease digested. The degradation of grease (Figure 3) seems to be more complete in the limed series, though here again it may be only a solubility effect. The second peak in gas evolution following liming (Figure 5) cannot be taken as a criterion of increased liquefaction, becauSe the gas originates from substances already in abundance in solution. Also, the peak in the lower fatty acid production following the addition of lime (Figure 4) may indicate merely the formation of soluble or peptized calcium salts of these acids. Observations to date indicate that a pH of 5.0 is too acid for the most rapid digestion of grease, though the writers are now building u p an acid-digesting flora, by a procedure analogous to that followed in obtaining the usual alkaline flora, to see whether this method of removing the bulk of the acid-producing components may be an economical step Table I-Acid TOTAL
TIME
SOLIDS
li-eeks
Gvams 47 9 43 8 41 0
40 38 38 38 37 36 37 35 39
4 1 6 4 8 7 4 4 0
ORGANIC
ASH
Grams 12.5 11.8 11.3 11.5 10.2 12.5 11.1 11.0 10.6 12.6 9.9 13.7
SOLIDS Grams 35.4 32.0 29.7 28.9 27.9 26.1 27.3 26.8 26.1 24.8 25.5 25 3
GREASE Grams 12.4 6.8 5.3 4.9 4.0 3.6 5.1 4.6 4.6 2.7 3.8 2.7
1013
prior to a final alkaline period to remove obnoxious nitrogen compounds. Another series of experiments is directed toward methods for controlling the acidity. I n addition to liming and to utilizing the buffer value of a large excess of alkaline sludge, slight aeration seems to offer interesting po-sibilities. T o the writers’ knowledge this has not been attempted in sludge digestion, though the industrial processes for cellulose fermentation make use of restricted aeration, and in the activated sludge process the sludge neither becomes acid nor has the greasy nature of settled sewage solids. Oxygen increases the pH by converting acetic acid into carbon dioxide and water, and thus oxygen may be considered as a base. For example, one of the liquors, having a pH value of 5 2 , received roughly 0.02 cubic foot of air per gallon (145 cc. per liter) per hour and in 18 hours had reached a pH of 7.2. This change, like the acidity of a digesting sludge, is slightly dependent upon carbon dioxide, but an actual decrease in volatile fatty acids from 211 mg. to 80 mg. per liter was observed. The origin of methane in digestion-tank gases has never been conclusively determined. Since paper pulp is a known component of sewage solids, and since cellulose fermentation can give methane, it has been assumed that sewage-tank methane also arises from cellulose. The writers’ experiments do not support this assumption. Accurate gas measurements \$ere obtained only on the limed serieq, though the gis 11‘1 1
9
the same composition in both series. I n the weeks the limed bottle had evolved 2860 cc. of gas of the following oomposition: CH4 75.8, C o n 16.9, H, 3.6, Nz3.7 per cent. This volume is equivalent to 80 cc. per gram of organic matter or 275 cc. per gram of organic matter digested. Acetic acid has been shown by Groenewege’ and others t o be a precursor of methane in cellulose fermentation, and the “acetate sludge” of Bach and Sierp* points to a similar mechanism in sludge digestion. Groenewegeg has further shown that calcium forMededeel. Alg. Proefsta. Landb. Dept. Landb., N i j ~ d . Handcl, 13, 1 (1923). 8 Centr. Bakt. Parasilenk., I I Abt., 60, 318 (1923). Mededsel. Burgerlijk. Geneeskund. Dienst Xedevland-Indi8, 1920, No. 1, p. 75. Digestion Da ta PH OF LIQUOR 6.9 5.4
5.0 5.0 5.0 6.0 5.0
5.0 5.0 6.4 5.0 6.4
I,OWER FATTY ACIDSIX LIQUOR Grams 0.2 1.4 1.9 2.8 3.8 5.2 3.6 3.7 4.1 3.2 4.2 2.7
TOTAL SOLIDS Grams 1.39 1.23 0.99 0.93 0.87 0.89 0.82 0.72 0 80 0 56 0.72 0.51
SITROGEN
LIQUOR Grams 0.07 0.12 0.15 0.28 0 37 0.41 0.33 0.61 0.37 0.58 0.47 0.70
CELLULOSE Grams
I N D UXTRIAL AND ENGINEERING CHEMIXTR Y
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Vol. 19, No. 9
writers’ laboratory tests, though not yet completed, have so far failed to show methane in the gases from the following when seeded with sludge liquor: inulin, starch, dextrin, raffinose, maltose, sucrose, lactose, salicin, glucose, fructose, dulcitol, mannitol, adonitol, and glycerol-all of which, however, give hydrogen. The analyses for cellulose (Table I), using the common Schweitzer’s reagent extraction of greasefree samples, show that no large decrease in amount has occurred. This, of course, does not cover the alkaline range, but even there, if we consider the relatively brief period in the digestion tank as compared with the months commonly required by cellulose cultures, i t seems unlikely that any appreciable amount of methane arises from this source. I n the last limed bottle. after 9 weeks, a piece of newspaper showing no signs of degradation, was found, the small type being still legible. Relation of Gas Production t o Grease Content
OO
/
2
3
4 5 6 7 7hiC /N f l U € K S .
8
9
mate, calcium butyrate, and salts of higher fatty acids having a n even number of carbon atoms can produce methane. Since acetic acid is the predominant fatty acid in the digestions described herein, it is not surprising that evolved methane nearly accounts for the loss in weight of free fatty acids, thus: Grams Loss in grease containing 12.5 per cent Ca (as soaps) = 9 . 7 or on an ash-free basis Free f a t t y acids remaining in liquor L o s s in free fatty acids Acetic acid equivalent of the methane evolved
8 5
2 7 5 8
5.3
If methane arises chiefly from de-carboxylation of acetic qcid, thus: CHsCOOH = CHI
+ COz
we would expect to find a 1 : l molecular ratio of CH4:COz. Actually, without obtaining that portion of the carbon dioxide which was combined with ammonia and calcium, but correcting for that in simple solution, the ratio was 1:0.4. A different experimental technic would be desirable to establish this ratio. It should be noted that fatty acids, hence acetic acid and methane, can arise not only from cellulose, starch, etc., and from grease, but also by de-amination of the amino acids. Theoretically, therefore, methane may arise from carbohydrates, fats, or proteins, or from all three. I n acid digestions the protein degradation is slight; indeed, that is why the resultant sludge is not well digested. The lower carbohydrates, being soluble, are not present to any appreciable extent in the sludge, though traces of starch, pentosans, and glycoproteins may be found. It is probable that the small amount of hydrogen evolved early in digestion is a fair indication of the quantity of available carbohydrates, since they usually ferment anaerobically to carbon dioxide and hydrogen. The
As a further test on the relation of gas production to grease content, digestion experiments were set up with a series of dry sludges of varying grease content, the highest being a dried scum containing 73 per cent grease. One-gram samples were added to tubes of liquor drained from a digested sludge and the tubes stoppered for gas collection. Figure __ 6 s h k s the total gas IL1 evolution in 10 days, the relative v o l u m e s being roughly propor90 tional to the percentage of grease. The mechanism of the fatty acid degradation is now under study; it seems to be 70 primarily a hydrolysis on the b e t a c a r b o n 2 a t o m resembling the b Fiq. 6 familiar beta oxidation a Rela f i v e Volumes of fats. of Gas f v o l v e d i n Summary
i[ I,
lo h j s from sfudqes in varyin9 grease
I-In the acid type con ten f. of sludge digestion, a 2 r a p i d destruction of g r e a s e a n d calcium soaps occurs with the p r o d u c t i o n of lower fatty acids. 2-Some of the lower /O fatty acid f e r m e n t s further to givemethane. 73% 3-Proteolysis is h i n d e r e d bv the low pH and, as a“ result, the sludge is not well digested. 4-The rate of fermentation, as measured by gas production, is roughly proportional to the grease content of the solids, a scum high in grease being the most vigorous gas producer. 5-Cellulose is believed to undergo little, if any, digestion during the ordinary sludge-digestion period.
German “Oil from Coal” Assured Trade Commissioner William T. Daugherty, of Berlin, states that Generalkonsul Bruckmann, head of the A . G. fur Industrie und Technik, which lastkyear traded its control of Bergius coal hydrogenation patents t o the German Dye Trust, recently advised the company’s stockholders that beginning next year the I. G. would produce enough oil from coal to meet one-half of the local demand.
