INDUSTRIAL S X D E S G I S E E R I S G CHEMISTRY
February, 1927
of pressure which would oppose the general fall of pressure produced by the main course of the reaction. It appears to be generally conceded a t presentlo that ionization does not play a primary role in explosive reaction or flame propagation. It has been shown here that in the ionized oxidation of methane the presence of an antiknock does not retard but rather accelerates the reaction, probably by taking part in it through enhancing the absorption of the energy of alpha-radiation, May we assume that the function of the antiknock in ordinary combustion is a similar one under the influence of some other type of radiation, possibly infra-red? This was the original theory entertained by Midgley, though he was employing it to explain retardation rather than acceleration. Symposium of the Faraday Society on "Explosive Reactions in Gaseous Media," London, June, 1926. 10
233
The writers are not aware that any direct evidence exists that the antiknock does actually reduce the velocity of flame propagation. The idea has been recently expressed" that it does the opposite, by facilitating and in making the initiation of flame more instantaneous and uniform. This would appear to be more in accord with the present results as far as they are comparable, and also with a suggestion of one of the writerP that non-selective absorption dependent on the absolute density of the gas mixture may be an important factor in flame propagation just as it is in the reaction proceeding under the influence of alpha-radiation. 1 1 Charch, Mack, and W o o d , THISJOURNAL, 18, 338 (1926); also H. S. Taylor, private communication. 12 Lind, J. Chem. Sac. (London), 126, 1867 (1924).
Some Chemical Characteristics of Sewage Sludge' By S. L. Neave with A. M. Buswell STATE WATER SURVEY
DIVISION, U R B A N A , ILL.
T
HE bacterial digestion of sewage sludge under anaerobic conditions has received considerable attention in recent years, partly because it is a necessary step in the production of an inoffensive, rapidly drying product, and partly on account of the economic value of the combustible gases evolved during the process. Very little is known of the chemistry or the bacteriology involved, though the interesting work of Rudolfs2 in this country and of I m h ~ f fB , ~a ~ h S, ~ i e r ~and , ~ Groenewege6 on the Continent has already shown something of the complexity of the problem. From the viewpoint of the plant operator we need first a simple method of determining wheri a given sludge is "ripe," or sufficiently digested to be run onto the drying bed. Rudolfs has recently shown a relation between the biochemical oxygen demand of the sludge and its course of digestion. At the experimental plant of the Illinois State Water Survey Division, the writers have been following the volatile-matter content of dry sludge as a similar index. The ratio of volatile matter to fixed carbon is known to decrease in passing from wood through peat to coal (Table I). Table I'I
FIXEI)
VOLATILE MATTER ~
Wood Peat Lignite Anthracite a
Per cent 7 5 to 79 i o . 06 60.67 6.18
CARBON ~~~
~
Per cent 21 to 25 29.94 39.33 93.8%
Parr, Illinois Geol. Suruey, Bull. 3.
Consideration of the data in Table I suggested the probability that raw sludge would contain more volatile matter and less fixed carbon than digested sludge. If this were true and the variation proved to be sufficiently wide and consistent, the determination of volatile matter and fixed Presented before the Division of Water Sewage and Sanitation at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. * New Jersey Agr. Expt. Sta., Bull. 427 (1925). * Eng. News-Record, 91, 512 (1923); 93, 585 (1924). 4 Bach and Sierp, Cent?. Bakt. Parasitenk., I I A b f . , 69, 1 (1923); 60, 318 (1923). 6 Tech. Getneindebl., 27, 213 (1924); Gas Wasserfach, 68, 773 (1925). 6 Mededeel. Geneeskund. Lab. Wetlevreden, 1920, 163. 1
'
VOLATILEMATTER
hf A T E R I A L
Freshsolids Direstedsludge
SLUDGE A5 SAXPLED
FIXED
ASH-FREE BASIS
Max
Min.
Av.
Max
Min
Av.
%
c/o
R
70
%
70
70.9 61.2
46.5 4.5 9
59 3 97 0 8 3 . 9 9 0 . 8 54.9 92.7 86.2 89.5
Max. Min. Av.
70% 9.6 2.2 8.8 3.8
% 5.5 6.4
The use of the volatile and fixed carbon determination to distinguish between fresh and digested sludge does not appear to be feasible. It is a useful test in a research study of the character of sludge and there is still a possibility that the data so obtained may be correlated with the ripeness of the sludge. 7 Parr, "The Analysis of Fuel, Gas, Water, and Lubricants," p. 146, (1922). 8 Rather, THISJ O U R N A L , 10, 439 (1918).
INDUSTRIAL AND ENGINEERING CHEMISTRY
234 Grease
On most of the samples of this series, grease was determined by extraction with petroleum ether in a Soxhlet apparatus. This test also failed to show a marked difference between fresh solids and digested sludge (Table 111). Table 111 MITZRIAL
Fresh solids Digested sludge
PETROLEUM ETHER EXTRACT
Max.
Min.
Av.
P E Ycent 41.6 39.1
Per cent 11.2 21.6
Per cent 29.2 80.2
The extracted grease consisted of nearly equal amounts of lime soaps and unsaponified fats. The bulk of the fatty acids were of animal origin, mainly palmitic and stearic. Cholesterol was present in appreciable amounts, but phytosterol could not be detected. Small quantities of aluminum and iron soaps, and resin acids were present, and only 3 per cent of the total extracted matter was mineral oil. Investigations on the fats are not yet completed; so no statement can be made a t present regarding the changes that they undergo during sludge digestion. Nitrogen The nitrogenous components likewise are still incompletely determined. The Kjeldahl determination shows an average total nitrogen content in the undigested sludge of 3.01 per cent. Hydrolysis with 20 per cent hydrochloric acid liberatas half this nitrogen aa amino acids and urea, the relative amounts of each being still somewhat uncertain. Neither has the origin of the urea been ascertained. It may arise, like the amino acids, from protein hydrolysis, or it may occur as such either adsorbed on the sludge or chemically attached to it. Likewise, the other half of Figure 1-Loss in W e i h t of D Sludge the total nitrogen rewhen Extracted for 18 &ours bysuffered quires investigation. Solutions of Varying pH Value, at 2 5 O C. We would expect uric acid to be almost completely precipitated in the hard waters of the Middle West as the calcium or magnesium salt. Small amounts of other nitrogenous excremental substances are probably also deposited. Definite color reactions have been obtained for the purine and indole nuclei, but the oomplexity of the sludge mixture makes their origin and identification diflicult. Carbohydrates The carbohydrates have as yet received little attention. The soluble members of the group, of course, only enter into the problem as intermediary steps in the degradation of higher polymers, and are probably utilized for bacterial food as fast as they are produced. The formation of humic acids during the digestion of cellulose has not been worked out, but the few results which are available to date on pyridine-soluble humic acids show that they definitely increase during sludge digestion. The cellulose content of the solids seems to decrease very slowly, though such comparisons require a correction for shrinkage in solids during digestion and the meager data do not permit of such calculations.
Vol. 19, No. 2
The values are given, however, to show the general magnitude of these figures (Table IV). Table I V MATERIAL
PYRIDINE-SOLUBLE HUMICACIDS CELLULOSE
Per cent 6.2 19.1
Fresh solids Digested sludge
Per cent 16.9 19.5
The current belief that methane arises from lower fatty acids produced during carbohydrate degradationJg adds t o the attractiveness and economic importance of this phase of the problem. Peptization Since peptization, with or without hydrolysis, ia undoubtedly the first stage in sludge digestion, liquors of different pH values when in contact with sludge solids should show different rates of peptization. The following tesh were made with this in mind: Freshly settled solids were dried a t 103' C., the grease extracted with petroleum ether, and approximately one-gram portions of the resulting dry material placed in weighed Gooch crucibles. Onto the solid were poured 20-cc. portions of Clark's phosphate buffer solutions, and the crucibles placed in dishes of the same solution to maintain the liquor level. After standing 18 hours at 25" C. the solids were sucked dry, washed with three 10-cc. portions of cold water, dried, and the percentage loss determined. Table V and Figure 1 show deviations, mainly owing to the difficulty in wetting the solids when once completely dried. The curve as drawn, however, represents the arithmetic mean of successive points to within 0.04 per cent, while a least-squares solution of the residuals (in the sense observed value minus curve) gives the probable error of a single determination as 0.27 per cent loss in weight. Table V INITIALWEIGHT
Grams 1.0298 0.9814 0.9612 0.9999 0.9985 0.9609 0.9986 0.8305 0,9904 0.9006 0.8110 1.0287
Loss I N WEIGHT Grams 0,0497 0.0476 0.0532 0.0505 0.0583 0.0647 0.0659 0.0556 0.0628 0.0622 0.0556 0.0721
Per cent 4.83 4.85 5.57 5.06 5.92 6.72 6.60 6.68 6.34 6.90 6.86 7.01
PH VALUE
6.2 6.6 6.8 7.0 7.2 7.4 7.6 8.4 8.6 8.6
9.0 9.8
The amount of material extracted increases with increase of pH up to pH 7.4 after which the curve is relatively flat. The nature of the extracted material has not been ascertained, but the filtrates showed an apparent isoelectric point a t a pH value of 4.6 to 4.8. This, however, gives no information concerning composition since many proteins and a t least one of the humic acids show an isoelectric point near this value. Further work is being done on the nitrogen content and biochemical oxygen requirement of these extractable materials. 9 Groenewege, Med. Alg. Proefsfa. Landb. Depl. Landb. (Dutch East Indies), 18, 1 (1923).
Change of Address Members should note that the office of our Associate Editor
in New York and of the Advertising Department is now at 419 Fourth Avenue, this change having been made during the month of January. The telephone number remains as heretofore, Madison Square 5940.
