96 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 22, No. 1

A non-Steffen molasses was treated with sufficient barium hydrate to raise the pH from about 7.0 to 9.0. Besides ad- justing the pH to the desired value, this treatment removed some of the sulfates present, thus preventing their crystalliza- tion on concentration. The viscosity of this molasses was determined a t 50" and 60" C. and over a concentration range from 76 to 80 per cent. The pH was then reduced to 7.2 by means of hydrochloric acid in one portion and sulfur dioxide in another. The viscosity of these two samples was deter- mined over the same range. The results are given in Table IX.

Table IX-Effect of pH on Viscosity of Molasses VISCOSITY

Poises Poises Poises At 50° C.

PH 76% D. S.O 78% D. S. 80% D. S.

9 .0 7 , 2 with HC1 7 . 2 with SOP

9 . 0 7 . 2 with HCl 7 . 2 with Son

2.04 3 .50 6 . 3 4 2 . 0 7 3 .53 6 .41 2 . 0 8 3.55 6 . 5 0

At 60' C. 1.14 1 .85 3 .15 1 .15 1 .89 3.21 1.18 1 .90 3.27

D. S. stands for dry substance.

It is seen that there is an apparent slight increase in the viscosity as the pH is lowered. The effect is small and is practically within the limit of error of the determination. It might well be accounted for by small errors in the determina- tion of the dry substance.

Discussion of Results

The viscosity of sirups made from a non-steffenized molasses is lower than the viscosity of a pure sugar solution of the same dry substance. This difference increases as the concentra- tion increases and as the temperature decreases. This low- ering in viscosity is due to the inorganic impurities present and is partially counteracted by the raffiose, which has a greater effect on viscosity than does sucrose.

Sirups made from a steffenized molasses, as a rule, are higher in raffinose and lower in ash than are non-Steffen sirups. Consequently their viscosity is somewhat higher, but nevertheless it is lower than that of a pure sugar solution of the same concentration and temperature.

Molasses resulting from the barium process for recovering sugar is extremely high in raffiose and correspondingly low in ash. Its viscosity is appreciably higher than that of either of the other types and is also higher than that of a corre- sponding pure sugar solution. In general, it can be said that the viscosity increases as the raffinose increases and as the in- organic constituents decrease.

The viscosity of saturated solutions at a given temperature increase as the purity of the sirup decreases (Tables I1 and V). This is because the solubility of sugar increases rapidly with decreasing purity.

The viscosity of saturated solutions shows a decided mini- mum at some definite temperature, depending upon the purity of the sirup. Solutions of pure sugar show the minimum a t about 70" C., 75 purity sirups at 55" C., and 60 purity sirups at 45" C.

Literature Cited

(1) Bingham and Jackson, Bur. Standards, Sci. Paper %98. (2) Brown, "Handbook of Sugar Analysis," p. 310. (3) Brown, Sharp, and Nees, IND. ENG. CHEM., 20, 945 (1928). (4) Burkhardt, Z . Rubenzuckerind., 1874. (5) Fischer, 2. angew. Chem., 84, 153 (1921). (6) Fischer, Chem.-Ztg., 44, 622 (1920). (7) Gibson and Jacobs, J. Chem. Soc., 117, 473 (1920). (8) Green, Ibid., 98, 2023 (1908). (9) Hosking, Phil. Mag., 49, 274 (1900).

(10) Kucharenko, Sucr. Belge, 46, 222 (1927); 47, 244 (1928). (11) Kucharenko, Planter Sugar Mfr. , May, June, July, 1928. (12) Ladenburg, Ann. Physik, 28, 9 (1907). (13) Orth, Bull. assocn. chim. SUCY. dist. , 29, 137 (1912). (14) Paine and Balch, IND. ENG. CHEM., 17, 240 (1926). (15) Powell, J. Chem. Soc., 105, 1 (1914). (16) Roubinck, Z. Zuckerind. Bbhmen, 38, 578 (1914). (17) Sheppard, J. IND. END. CHEM., 9, 523 (1917).

Thermophilic Digestion of Sewage Solids'*' I-Preliminary Paper

Willem Rudolfs and H. Heukelekian

NEW JERSEY AGRICULTURAL EXPERIMENT STATION, NEW BRUNSWICK, N. J.

HE role and importance of temperature in the digestion of sewage solids has been repeatedly emphasized T during recent years. Attention has been called to

the advantages of maintaining the temperature of digestion tanks a t approximately 20" C. during the winter months. The optimum temperature for digestion has been found t o be nearer 26-28' C., and higher temperatures up t o 37" C. have not shown further acceleration of the digestion.

The bacteria known as thermophilic organisms have an optimum temperature range of 50" to 60" C. The group contains a variety of organisms some of which may grow a t both 37" and 55" C. (facultative thermophiles), while others only a t 55O.C. (obligate thermophiles). The bacteria that have an optimum growth range between 20' and 37' C. will ordinarily not be active a t 50-60" C. but they are not neces- sarily killed.

1 Received May 20, 1929. Presented before the Division of Water, Sewage, and Sanitation at the 77th Meeting of the American Chemical Society, Columbus, Ohio, April 29 to May 3, 1929.

*Journal Series Paper of the New Jersey Agricultural Experiment Station, Department of Sewage Disposal.

The effect of high temperatures on the digestion of sewage solids has not been fully investigated. As early as 1875 Popoff (2) measured the rate of gas production from canal mud with temperatures as high as 50-55' C. He found that a t the thermophilic range 38-55' C. the rate of gas production was faster than a t 16-22' C. When material incubated a t 50-55" C. was later digested a t 20-25" C., the evolution of gas stopped for 4 days. Coolhaas (1) studied the decomposition of salts of fatty acids and carbohydrates by thermophilic bacteria. At 60' C. a great number of salts of fatty acids were converted to methane and carbon dioxide when inocu- lated with canal mud. The minimum temperature for the thermophilic decomposition was found to be 45' C. and the maximum 69" C. The organisms were spore-forming types and were not the same as those active a t lower temperatures. Cabbage leaves inoculated with feces and incubated a t 60" C. gave more methane than a t 26" C. Out of 20 grams of dry cabbage leaves, 5.3 liters of methane were produced in 20 days.

I n view of these results, it was considered of interest to

January, 1930

INCUBA- TIOK

D a y ~ 7 8 9

11 13 20

Total

INDUSTRIAL AND ENGINEERING CHEMISTRY

450 c. 50' C. 550 c. cot C H I COa CH4 COa CHI

% CC.5 % CC." % cc.a % cc.5 % CC.0 % CC.5 . . . . . . . 2 7 . 2 7 9 . 0 6 1 . 4 1 7 8 . 0

20:2 7 5 . 0 65:O l8b:O . . . . . . . . . . 2 3 . 4 1 5 . 2 6 6 . 0 4 2 . 0 2 3 . 1 1 6 . 0 6 9 . 0 4 8 . 0 . . . 2 3 . 0 1 5 . 3 7 0 . 0 4 6 . 7 2 0 . 6 3 6 . 4 7 3 . 2 1 2 9 . 0 24: 7 6 4 . 0 66:7 l72:O 1 9 . 7 2 6 . 0 64 .7 86.0

. . . . . .

2 2 . 3 3 2 . 0 7 0 . 4 1 0 0 . 0 2 6 . 6 3 3 . 8 6 7 . 9 8 6 . 0 2 2 . 2 2 0 . 7 6 9 . 5 6 5 . 0 76 .5 1 5 1 . 0 1 4 . 1 5 0 . 5 8 1 . 0 2 9 0 . 0 1 6 . 3 3 5 . 4 8 2 . 5 1 8 1 . 0 1 7 . 3 _- -- __ __ 3 5 . 3 -_

194.7 6 1 3 . 0 1 4 8 . 3 548 .0 191 .6 597 .7

97

digest sewage solids a t the thermophilic range and to obtain information as to the rate of digestion and the quantity and composition of the gas evolved.

Methods

Fresh solids and ripe sludge were obtained from the Plain- field plant, seeded in a ratio of 1 ripe sludge to 2 of fresh solids on the basis of volatile matter, and digested in con- stant-temperature incubators. Daily gas measurements were made, and solids and ash were determined both a t the beginning and a t the end of digestion. The gas was analyzed for carbon dioxide, oxygen, and combustible gases. pH values were determined during the course of digestion on a set of duplicates.

Thermophilic Digestion Experiments

FRESH SoLIDs-Unseeded fresh solids were incubated a t 37", 45", and 55" C. for 5 months. Digestion a t 37" C. was included for the pur- pose of compar ison . A moderate amount of gas was produced a t 37" C., but a t 45" and 55" C. very little gas was produced through- out the period of incubation. T h e p H va lue of these materials had reached the n e u t r a l p o i n t within a month, but still gasification did not take place. Within a month volatile-matter re- ductions of 21 and 10 per cent were obtained for the materials incubated a t 45" a n d 5 5 " C., respectively. This reduction might be at- t r i b u t e d to liquefaction. Since there was no advan- tage to be derived from the

period of initial inactivity a t 45" and 55" C., on the other hand, would indicate a period of biological adjustment in which the organisms typical of sludge digested a t lower temperatures were giving way to thermophilic organisms. Once such a flora was established in the decomposing ma- terial, gasification proceeded rapidly and digestion was com- pleted in 18 to 20 days. The slightly more rapid rate of gasi- fication a t 55" C. indicates that the optimum temperature for thermophilic digestion is nearer 55" C. than 45" C. The yield of gas per gram of volatile matter in the fresh solids a t 37", 45", and 55" C. was 804, 930, and 810 cc., respectively.

The pH value of the seeded mixtures was a t no time below 7.1.

In another series similar to the one just described] the re- sults reported above were checked.

SLUDGE PRODUCED UKDER THERMOPHILIC CONDITIONS FOR SEEDING-The above experiments indicated that with the

Odors were a t times very strong.

Sewage solids, both seeded and unseeded, have been digested at thermophilic temperatures in order to obtain information as to the rate of digestion and to the quantity and composition of the gas evolved.

It has been shown that the digestion of fresh sewage solids at temperatures of 45-55' C. is feasible. The time required for the digestion of seeded solids at this temperature range is materially shorter than at the optimum (28' C.) for lower temperature digestion, provided the seeded sludge has been produced under thermophilic conditions. Unseeded solids do not digest rapidly in the thermophilic range. The yield of gas per gram of volatile matter is higher with ther- mophilic digestion, probably because of a greater destruction of organic matter. The composition of the gas was 70 per cent combustible and 22 per cent carbon dioxide, which corresponds to the gas composi- tion produced at lower temperatures.

incubation of fresh solids a t such high temperatures, attention was directed to the digestion of the seeded mixtures.

tion from the decomposition of seeded mixtures a t the three temperatures indicated above are presented in Figure 1. At 37" C. gas evolution extended more or less uniformily over a period of 3 weeks, after which it decreased. At 45" C. gas was evolved a t a very slow rate for 2 weeks, after which it increased rapidly, reaching a peak within 22 days and drop- ping to a low value again within 34 days. Incubation a t 55" C. gave similar results as a t 45" C., except that the process was hastened a few days.

The protracted gas evolution a t 37" C. would indicate that this temperature was beyond the optimum for non-thermo- philic digestion and not high enough for the thermophilic range-hence its intermediate character. The prolonged

FRESH SOLIDS AND RIPE SLUDGE-The rates Of gas produc-

ordinary ripe sludge there was an initial period of in- activity due to the establish- ment of the proper thermo- philic flora. It was thought that if a sludge produced under thermophilic condi- tions was used for seeding, the initial period of retarda- tion, and thereby the total time of digestion, could be ma te r i a l ly reduced. Ac- cordingly, to the sludges ob- tained from the previous ex- periment a definite quantity of fresh solids was added (1:2 on basis of vo la t i l e m a t t e r ) and the mixtures were reincubated a t t h e temperature a t which the sludges were produced.

The rate of gas evolution per gram of raw volatile

matter per day is given in Figure 2. T i e materials incubated a t 37.5" C. had not gasified to any extent during the 19 days of digestion. The large amount of gas recorded for the first day is due to the expansion of the air in the bottles and expansion of the gas already entrained in the sludge. Apparently 37" C. is above the optimum for the lower range of digestion temperature and not high enough for the thermophilic range. Digestion a t both 45" and 55" C. was completed within 18-19 days, although gasification reached the peak 3 days earlier in the mixture incubated a t 55" C. The initial period of re- tardation was reduced from 15 days to 5 days by the use of sludge produced under thermophilic conditions. The total time of digestion was reduced similarly from 30-34 days to 18-19 days.

The reduction of volatile matter of the fresh solids a t 37", 45", and 55" C. was 36.0, 51.5, and 58.0 per cent, respectively.

Per gram volatile matter.

98 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 22, No. 1

These figures give further proof that a t the termination of the experiment (19 days) the digestion at 37" C. was not complete while at 45" and 55" C. substantially greater reduction of volatile matter had taken place.

SEEDING WITH SLUDGE SUBJECTED TO SECOND THERMO- PHILIC DIGEsTIoN-8ince the subjection of ordinary sludge to digestion under thermophilic conditions improved its seeding value, i t seemed that a further improvement might be obtained by a second passage. It was thought that an en- richment of the numbers of the thermophilic organisms and intensification of their activities might be induced by using the same sludge in digesting successively several different batches of fresh solids under thermophilic conditions.

in this series, since no seed material produced at this particular temperature was available. The time required for complete digestion was the same as for the two other mixtures, although the peak of gas production came somewhat later.

These results indicate that there is no well-defined optimum point of digestion a t the thermophilic range, but rather a range of 10" C. between 45" and 55" C. There are indi- vidual characteristics a t the various temperatures, but the total time of digestion is not materially affected. The differ- ences in the type of digestion might be caused by the types of organisms active a t the different temperatures. It is further probable that the retardation observed a t 50" C. was caused b s the difference in the temDerature a t which the seed sludge

cw7 Figure I-Gas Production from Sewage Solids a t Different

Temperatures

Accordingly, the sludges from the previous experiment were used for seeding a new batch of fresh solids. The sludge pro- duced a t 45" C. was mixed with fresh solids and reincubated at 45" C. The one produced a t 55" C. was mixed similarly; half of it reincubated a t 55" C., the remainder a t 50" C. It was considered of interest to include the digestion at 50" C. in order to determine more accurately the optimum tempera- ture within the thermophilic range. The digestion of 60" C. was omitted because it was considered to be beyond the optimum range.

mrs Figure 2-Gas Production from Sewage

Solids Inoculated with Material Produced under Thermophilic Conditions

In Figure 3 are represented the daily gas-production values from materials incubated a t 45" and 55" C. The digestion of the mixtures seeded with sludge that had been subjected to thermophilic digestion a second time did not proceed faster than when the sludge has been digested once under thermo- philic conditions. The digestion was completed in 19 or 20 days, as in the previous series. The initial lag period was not reduced beyond 5 days. At 45" C. the peak was attained in 11 days, whereas a t 55" C. it was more suppressed and pro- longed. The highest gas production in any given day was 95 CC. per gram volatile matter. The gas-production curve for the material incubated a t 50" C. is not directly comparable

w& produced and at which-the new mixture was incubateud. The yield of gas per gram of volatile matter in the fresh

solids is generally higher in the thermophilic range than a t the non-thermophilic range, as will be seen from the figures given below: Temperature, C. 20-30 45 50 55 Gas, cc. per gram raw volatile matter 550 877 750 850

The somewhat lower yield at 50" C. might be explained in the light of the suppositions made above.

The carbon dioxide and combustible gases produced during the active period of gasification are given in Table I. The percentage of carbon dioxide was high (26 to 27 per cent) in the beginning and decreased gradually to about 15 per cent. Combustible gases, on the other hand, were comparatively low (60 to 65 per cent) in the beginning and increased to 75-80 per cent towards the end of digestion. The average percentages were practically constant-namely, 22.2 to 22.3 per cent for carbon dioxide, and 70.0 to 70.5 per cent for com- bustible gases. The percentage nitrogen, as determined by difference, was 7.2 to 7.8 per cent. There are, therefore, no differences in the composition of gas produced a t the different temperatures. The relationship noted above as to the decrease of carbon dioxide and increase of methane with the progress of digestion is identically the same as in the digestion a t lower temperatures. The average composition of the gas produced a t thermophilic range is also comparable with that a t lower temperatures.

Discussion

It has been shown that the digestion of fresh sewage solids a t higher temperatures (45-55" C.) is feasible if certain con- ditions are fulfilled. In the f i s t place, it is best to start

Figure 3-Gas Production from Sewage Sludge Reseeded with Material under Thermophilic Conditions

wherever possible with ripe sludge produced under ordinary temperatures, because fresh solids alone digest slowly, even a t high temperatures. It has been further shown that a "thermophilic" sludge is better for seeding than a sludge pro- duced at lower temperatures. With a sludge produced under thermophilic conditions the total digestion time is 18 to 20 days. Within this period about 50 per cent reduction of

January, 1930 INDUSTRIAL A N D ENGINEERlNG CHEMISTRY 99

volatile matter takes place with a higher yield of gas than would be obtained a t lower temperatures. The composition of the gas is not materially changed a t the higher tempera- tures.

At about 28” C., which is considered to be the approximate optimum for lower temperature digestion, the time required to complete the digestion processes from a practical stand- point is about 30 days. If gas production is taken as an index and when it is considered that for practical purposes from 80 to 85 per cent of the gas is given off within 25 or 26 days so that a longer digestion period would be uneconomical, this number of days might also be used for comparison with the number required a t higher temperatures. The time required for complete digestion a t 45-55’ C. is from 18 to 20 days, whereas the time required for a gas production of 85 per cent of the total would under these conditions be from 14 to 15 days. The reduction in time is therefore considerable, but whether such a reduction would be economical depends upon several factors and local conditions. For instance, if in the neighborhood of a sewage plant factories are present which have an ample supply of exhaust steam which can be utilized a t practically no cost, the temperature of rather concentrated sludge could very well be raised. It should be kept in mind, however, that when the time of digestion is decreased an increase in the intensity of odors can be expected, because the same amounts of odor-producing substances must be decom- posed in this shorter time. This necessitates, even more than under ordinary circumstances, adequate means of collecting and burning the gases.

It might be expected that the heat loss from tanks operating

a t the higher temperature per unit of time and per unit of exposed surface is larger than from tanks operated a t lower temperatures. There are, however, two main factors which govern the economy of digestion in general-insulation of tanks and size of tanks. Insulation of digestion tanks is a problem for engineers which will be solved eventually, but if the insulation of low- and high-temperature digestion tanks is the same, the size of the tanks required for high- temperature digestion is materially less than for low-tempera- ture digestion, because the digestion time a t 28” C. is a t least 30 days and a t 45-55’ C. about 15 days. This means that the size of the tanks can be cut in half while the total amount of gas produced is the same. Thus, even if the radiation is greater and the temperature required higher, sufficient gas is available to take care of these conditions. A more complete discussion of the digestion capacity required and economy of high-temperature digestion will be presented in a paper dealing with the digestion of daily additions of fresh solids.

The early work of Popoff (.2) has been checked. The re- sults are also in conformity with Coolhaas’ statement (1) that 45” C. is the minimum for thermophilic digestion, but his maximum temperature of 69” C. has been found too high. The yield of gas in 20 days per gram of dry cabbage leaves is reported to be 265 cc. Sewage solids are a much richer source of gas than material like cabbage leaves.

Literature Cited

(1) Coolhaas, Cenlr. Bakt , Parasitenk., II Ab:. , 75, 161 (1928). (2) Popoff, Arch ges. Physiol. (Pfluger’s) , 10, 113 (1876).

A Chemical Dictionary. Containing the words generally used in chemistry and many of the terms used in the related sciences of physics, astrophysics, mineralogy, pharmacy, and biology with their pronunciation based on recent chemical literature. BY INGO W. D. HACKH. 790 pages. 100 tables. 232 illus- trations, P. Blakiston’s Son & Co., Inc., Philadelphia, 1929. Price, $10.00.

The scope of this work is defined by the author as follows: A chemical dictionary should state clearly and precisely the theories,

laws, and rules; describe accurately the elements, compounds, minerals, drugs, vegetable and animal products; list concisely the important reac- tions, processes, and methods; mention briefly the chemical apparatus, equipment, and instruments; and, finally, should note the names of the in- vestigators who have built up the science. As chemistry reaches into nearly every branch of human endeavor it should not forget to bring in the collateral vocabulary of physics, astrophysics, geology, minetalogy, botany, zoblogy, medicine, and pharmacy and, also, the pertinent jargon of industry, mining, and commerce.

Only continued use of the book will enable one to decide how well the author has carried out this series of postulates.

The author also states that the terminology of Chemical Abstracts was taken as standard; yet we notice almost consistent use of such words as “chlorbenzene,” “iodaniline,” etc. ; and the abbreviation a for asymmetric, s for symmetric, and rfor racemic; the symbols for ortho, meta, and para are given as roman instead of italic letters. etc. It is unfortunate that this work, published in America, should not have adopted throughout the usage of Chemical Abstracts, which is being more and more recognized as the standard for chemical nomenclature.

It seems to the reviewer that the author has misunderstood the meaning of certain radicals; for example, he states that chlorobutyryl is the same as butyryl chloride : strictly speaking, chlorobutyryl should be the radical CH CH CH CO, containing a C1 in place of one of the H atoms. The same mistake is made with chlorocinnamoyl.

One interesting feature of the work is the pronunciation of the words defined. While it may seem that this is carried to the extreme, in that such words as “fuel,” “fruit,” etc., have their pronunciations indicated, yet this will be of great value for the large number of words which always prove a stumbling block for the beginning student in chemistry, as well as for some of us who are supposed to be well versed in the subject.

The author admits the possibility of errors of fact, omissions, etc. One such noted was the formation of chlorobutyrone by distilling butyrone with phosphoric anhydride.

In spite of the above criticisms, the author has produced a book which represents many laborious hours of searching the literature and many more in attempting to re-state and re-define in simple modern terms the phenomena of science. The work will prove of invaluable assistance to many students and scien- tific workers 3s a source of definitions of many obscure terms and many of the modern terms which have come into more or less general use without having been clearly defined, or, if defined, in a place not easily located. The author is t o be congratulated on the results of his labors and it is to be hoped that all who use the book will cooperate with him in making i t possible to correct errors of fact, omissions, etc., in a future edition.-C. J. WEST

Sparking of Steel. BY E. PITOIS. Translated and enlarged by JOHN D. GAT 89 pages. Chemical Publishing Co., Easton, Pa., 1929. Price, $2.00. The translation consists of two chapters and three appendixes.

Chapter I sets forth the applications and technic of the art. It contains drawings and descriptions of the author’s apparatus for producing sparks under constant grinding pressure. Chapter I1 is devoted to verbal and photographic illustrations of the charac- teristic spark streams of carbon steels of varying degrees of hard- ness, cast irons, and alloy steels. In each plate is an insert free- hand drawing by the author of typical sparks, or “bursts” as he terms them, several times magnified. Each kind of spark stream is vividly described, and the author frequently rises to poetic flights of imagery that are as scintillating as these fireflies of steel and emery.

Appendix I gives the author’s method of spark photography. Appendix I1 shows phctcgraphs of incrustations formed by the impinging of spark-stream fragments on photographic plates. Appendix I11 treats of spark streams fcrmed in gases other than air

The translator supplies Appendix IV, on “Spark Testing as It Is Conducted in the United States,” crediting his data to John A. Houtz. There are 24 pages of thoroughly practical details for grading steel by sparking. A portable grinder weighingonly 8 pounds, which is especially valuable in scrap classification, is il- lustrated.

This novel book is cordially recommended to those interested in sparking.-CHARLES MORRIS JOHNSON