Februiir!. 1933
INDUSTRIAL
A\\
D ENGINEERI\-G
tendency to agglomerate, as do starch-filled sugars, is materially lessened. The greater accuracy of measuring the free-flowing sugar filled with tricalcium phosphate has also been observed. Cases have been reported where sugar filled a i t h starch has become moldy and easily picked up foreign odors. It may be expected that the use of tricalciurn phosphate as a filler will prevent this. Preliminary field tests on the use of tricalcium phosphate as a filler in granulated sugars are promising; they point to a way of eliminating troublesome caking in bagged or bulk sugar held in storage or in transit. LITERATURE
CITED
( I ) Bloom, C. Paper presented before the General Meeting at the S3rd Meeting of the American Chemical Society, N e v Orleans, La., March 28 to April 1, 1932.
CHE3lISTRY
1.17
(2) C'albeck, J., and Harner, H. R . , ISD. E s G . CaE?d., 19, 58-61 (1927). (3) Hoppert, C. A., Dept. of Chemistry Kutrition and Home Economics, S a t l . Soft Wheat Millers Assoc., Bull. (-4ug., 1928). (4) LaMer, 1'. K. Paper presented before American iissociation for ddrancement of Science and Regional Meeting of American Chemical Society, Syracuse, S . T..June 23 to 25, 1932. (.5) Lorah, J. R., Tartar, H . V., Wood, L., J . :lm. ( ' h e m . Soc., 51, 1097-1105 (1929). ( 0 ) McCollurn, E. V., M e d . SeurchZight c f S c i . R7iIZ. VIII, No. 1, 0 (1932). ( 7 ) AIellor, J. IT., "Comprehensive Treat e on Inorganic and Theoretical Chemist,ry," Vol. 111, pp. 64-5, 903, Longnians, 1922. ( 8 ) Sherman, H. C., "Chemistry of Food and Sutrition," 4th ed.. Chapters XI and X I I I , Macmillan, 1'332. (9) Steenbock, H. H., and Jones, J. H., J . Bid. Chem., 56,375 (1932). RECEIVEDJuly 20, 1932. Presented before t h e Division of Agricultural a n d Food Chemistry at t h e 84th Meeting of t h e Ainerlcan Chemical SocietJ , Denver, Colo., August 2 2 t o 26, 1932
Mechanical Equipment for Continuous Fermentation of Fibrous Materials Ji.AI. BUSWELL ASD C. S. BORUFF, State m'ater Survey, Urbana, Ill.
N TWO p r e v i o u s papers (a, 3 ) the w r i t e r s h a v e
I
iln apparalus has been designed which o w Most of the earlier reports, ab dificulties in c o n ~ i r z u o u s ~\fell ~ as those of more recent date, the refer to the accumulation, durfermenting Jibrous materials, such as cornstalks, ing fermentation, of practicallJ. sewage screenings, Paunch nlanurej and h e like. all of the digesting cellulose or Gas (carbon dioxide and methane) recocery dafa fibrous material a t the top of the bottle or fermentation v e s s e l . and operating fechnic are given. T h i s type of tank should be applicable to the alcoholic, acid, They report that the mat Ivas held up by entrapped gasbubbles or acetonic fermenta f ion of Jibrous malerials. formed during the fermentation.
"'led a t t e n t i o n to the possibility of fermenting waste cellulosic materials to methane and carbon dioxide. The fact that these gases can berecovered from a mixed culture fermentation of organic matter containing crude fiber has been known since JIizuno (8) &signed a tank inthe early part of the eighteenth century. The early works of Onieliaiiski, Trecul Popoff, tended to overcome this difficulty. He filled his tank with Hoppe-Seyler, RIazB, Sohngen, Pringheim, Fowler and Joshi. inverted T'-shaped troughs. These held the cellulosic mateand many others on the anaerobic fermentation of cellulose and rial in the liquor but had no effect on the liberation of the cellulosic materials have been summarized by various authors entrapped gas bubbles. This author, reporting results (1, 5 , 12). All of the studies prior to those rep0rtc.d by the using rice bran, states that during the first three weeks after present writers are characterized as giving low rates of charging his tank he was unable to burn the gas. After gasification as well as low yields per gram of material fed to this period it contained 30 to 50 per cent methane. Since the fermentation vessel. I n most of the 10- to 60-day experi- rice bran contains mainly starch with very little cellulose ments some 50 per cent of the cellulose decomposed was and only small amounts of less easily digestible crude fiber, converted into a mixture of the lom-er fatty acids. 'To insure this author probably did not observe the accumulation even this degree of fermentation, it was necessary to add con- of undigested residue and made no provision for its removal. siderable river slime or sewage sludge as the inoculating mateT.ABLEI. COMPARATIVE GAS YIELD DATA rial. These extraneous materials undoubtedly produced (Carbon dioxide plus methane: batch experiments) a n appreciable amount of the products recovered. Earlier FOWLER AND BUSWELL ATD workers also added calcium carbonate to neutralize the acids JOSHI ( 7 ) a OMELIANSKI ( 1 0 ) BORUFFb ~IATERIA FE LD Time Yield Time Yield Time Yield formed. CC./O. cc./g. Cc./o. Although certain writers have called attentiori to the Daus fed Dnus fed Days fed possibility of utilizing fermentation for the production of Filter paper 30 15 135 267 30 676 Newspaper 30 2 5 . . , . . . 30 300 power and fuel gas from waste cellulosic materials, none of Banana skins and steins 30 .,. 30 360 41 , , ,, 186 c 40 300 those who have actually investigated the process has re- Flax straw Flax shives . . . . .. . ,. . 20 210 ported gas yields that are encouraging (9, 1 2 ) . The most Wheat straw .. .. ... ,.. 20 "45 , . .. .. , , . , 20 275-375 promising results were obtained by Fowler and Jiishi ( 7 ) . Cornstalks a Used large quantities of sludge as inoculum. Their best figures, however, show yields of only 15 to 41 cc. b Used small amounts of inoculum; gas d a t a corrected for eaa from inocuof gas per gram of material fed, as compared with 300 to 676 lum. c 22 t o 31% loss in weight: no gas data. cc. of gas as obtained in similar bottle (batch) experiments Rudolfs and Heisig (11 ) encountered mechanical difficulconducted by the present miters. These and other similar comparisons are given in Table I. Fowler and Joshi also ties while invest'igating the possibility of fermenting screenstate that "cellulose is not attacked when it is in combination ings a t the LIihaukee, Wis., sewage disposal plant. The with pectin, lignin, etc., which are always present in raw scum saturator which they used to break up the floating mat was found to be inadequate. These investigators obtained vegetable tissues."
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INDUSTRIAL AND ENGINEERING CHEMISTRY
from 5.1 to 5.7 cubic feet of gas per pound (319 to 356 cc. per gram), dry weight, of screenings added, thus illustrating the potential gas yields obtainable from such a material. They were unable to continue because all of the screenings added collected in a very thick, hard mat a t the top of the digester.
FERMENTATION OF CELLULOSIC MATERIAL I n their preliminary studies on the fermentation of cellulose and cellulosic materials, the present writers encountered the same mechanical difficulty referred to above. It was also noted that, if the mat was not broken up and the bubbles released, the entire fermentation had a tendency to become sour; that is, organic acids would accumulate to such an extent that the buffer capacity of the medium was overTO GASOMETER
CLAMP OPEN
CLAMP CLOSED
wup
CLAMP OPEN
CU)sED
TO GASOMLTER POSITION I
POSITION 2
ON
FERMENTATION OF FIBROUS MATERIALS
Vol. 25, No. 2
forated metal. Each end of the drum is provided with a seal ring which is adjusted so as to prevent the escape of material from within the drum into the outer portions of the fermentation compartment. The feeding end of the tank is provided nith a spout extending through an opening in the tank end \Tall within the circle formed by the seal ring. The material t o be treated may thus be fed directly into the open end of the drum adjacent to the feeding spout. A discharge opening is provided in the lower portion of baffle wall A to permit undecomposed material from the drum to pass out into the discharge compartment. bxaterial discharged into the compartmentis withdrawn in any suitable and convenient manner, The fermentation compartment is fitted with a gas-tight provided with a gas vent having a tight or removable hood resting in a water seal. The water seal prevents the entrance of air into the digestion compartment where the fermentation takes place, and also the escape of gas. It likewise prevents the building up of excessive pressures within the digestion chamber and tends to keep a uniform, slight pressure therein. A pipe from the collecting hood serves to draw the gas out into a suitable reservoir or any device in xhich the gas may be used or stored. The drum is rotated or inverted- a t least twice a day, or continuously if desired. This releases the entrapped gases and the tank contents are sufficiently mixed to prevent local accumulation of acids. The writers have found the turning over of the drum and the periodic feeding a t the front end of the tank to be sufficient to cause the fermented material to work itself out through the opening in the baffle into the residue end of the tank. Here it continues to ferment slowly, and again gas bubbles are entrapped and the material is brought to the surface where it can be removed with a hay or manure fork or by a continuous device if desired. The design and operation of this type of tank are further described in a patent (6).
taxed and the pH would drop to 6.5 or below. Buffering with phosphate or calcium carbonate seemed to aggravate rather than aid this sour condition. If, however, the mat was broken up, or a t least broken up twice a day, no such difficulty was e n c o u n t e r e d . It was further noted that violent stirring was not necessary, for mere inversion of the fermentation flask released the gas bubbles and broke up the floating mat. The following experiment was carried out to determine the effect of inversion of the flask on the rate of fermentation: A fermentation bottle was fitted with tubes so that cellulose could be added, and digested .material and gas withdrawn. In the u right position the gas was drawn from the top. xfter about 12 hours this gas outlet was closed, the bottle was inverted, and a similar gas outlet in the bottom, which was now upright, was opened (Figure 1). In a comparative run on the digestion of 10 grams of cornstalks, in 10 days there were collected 1500 cc. of gas from a stationary bottle as compared with 2400 cc. from a similar bottle that was fitted FOR FIBROUS MATERIALS FIGURE2. DRUMDIGESTER so that it could be inverted twice a day. This method of gas liberation was found effective in the fermentation of pure cellulose, extracted tubers, sewage screenThe circulation of tank liquor in and over the cellulosic mat, ings, stable manure, straw, bagasse, and some thirty or more other formed in a regular sewage-digestion tank being fed chopped cellulosic materials. cornstalks, in a manner as proposed by Buswell (4)and On the basis of the above experiments, the authors built successfully used by him and others to break up greasy scum three pilot units of essentially the design shown in Figure 2. in sewage digestion tanks, was found inadequate. The use The tank is of rectangular shape and provided with a trans- of motor-driven stirrers was also unsuccessful. By the use of versely extending vertical baffle, A , spaced from one end to the apparatus described above, however, all the mechanical divide the tank into two compartments: a relatively large difficulties previously noted have been overcome. The miters have constructed three pilot units according digestion compartment, and a smaller residue compartment. A cylindrical drum is mounted horizontally within the to the design shown in Figure 2. One 1287-gallon tank digestion compartment upon a shaft journaled in bearings (172 cubic feet, or 4.9 cubic meters) has been operating since carried by wall A and the end wall of the tank. The drum is June, 1930. Another 1376-gallon tank (184 cubic feet, or adapted to be rotated continuously or intermittently a t any 5.2 cubic meters) has been in use since November, 1930. suitable speed. The frame of the drum is covered with a These two tanks have been employed successfully on straw, cylinder of reticular material, such as wire screening or per- cornstalks, stable manure, extracted Jerusalem artichokes,
February, 1933
INDUSTRIAL AND ENGINEERING
CHEMISTRY
149
FERMEXTATION OF CELLULOSIC MATERIALS TABLE 11. PILOTUNIT DATAox CONTINUOUS (Monthly averages)
RATEFEDPER DAY*
MATERIAL FED
DURATION OF EXPT. Av. of total
Lb./1000cu. ft. (kg./cu. m.) 105 (1.68) 140 (2.24) . ,
,Max. for 1 month Lb./lO00 cu. ft. (kg.,'cu. m.) 128 (2.05) 175 (2.80)
Av. of total Cu. f t . / l b . (l./ko.) 4 . 0 (250) 2 . 5 1156)
Months 17 Cornstalks Straw 8 Stable manure: 3 . 3 (206) 8 116 (1.86) 175 ( 2 . 80) Cornstalk bedding Straw bedding 2 103 (1.65) 127 (2.04) 2 . 7 (169) 5 . 1 (319) 239 (3.82) Sewage ecreeninge 6 200 (3.20) a Dry weight. b Unit of volume either cubic feet per 1000 cubic feet or cubic meters per 1000 cubic meters.
and a combination of straw and undiluted whey waste. Another smaller unit of 92 gallons (12.3 cubic feet, or 0.35 cubic meter) has been operating since December, 1931. For 6 months it worked successfully on bar screenings from the Urbana-Champaign sewage plant. It is nom being operated on packing house screenings and paunch manure. Work in this laboratory, as well as elsewhere, has shown that the biological stabilization of sewage screenings is possible. Heretofore, however, it has not been found practical, because of the fact that the screenings collect in the top of the digester in the same manner as previously pointed out in this paper (11). By use of the above described apparatus (Figure 2) the present authors have been able to stabilize sewage screenings fed a t the rate of 200 to 239 pounds dry weight per day per thousand cubic feet of tank capacity with the production of 1.0 to 1.2 thousand cubic feet of gas per day (3.2 to 3.8 kg. of screenings per cubic meter of tank volume per day; production of 1.0 to 1.2 cubic meters of gas per day per cubic meter of tank volume). The average methane content of the gas has been 59 per cent. The residual material has been found inoffensive and it drains readily. RESULTSFROX PILOTUNITS A brief summary of representative data collected from these pilot units is given in Table 11. More complete data will be given in a Water Survey Bulletin (1). Attention is called to the fact that these data are not based on smallscale experiments but are monthly averages collected from pilot unit studies. During the 17-month run on cornstalks, over half a ton of this material was fed to one unit and almost 4 tons to the other. From the data given in TaMe 11 it is noted that, during the entire experimental period, the cornstalks were fed a t an average rate of 105 pounds per day per thousand cubic feet (21 kg. per cubic meter) of tank capacity. This figure, as well as all other average figures given, includes all experimental periods, even those when the tank was intentionally being fed below a normal rate. The maximum daily rate for any month a t which cornstalks were fed was 128 pounds per day per thousand cubic feet (2.1 kg. per cubic meter) of tank capacity. From this fermentation there was collected an average and maximum gas production of 420 and 555 cubic feet of gas per day per thousand cubic feet (0.42 and 0.55 cubic meter per cubic meter) of tank capacity, respectively. This gas contained an average of 52 per cent methane. The other data given in Table I1 are self-explanatory. The data given for stable manure are undoubtedly all low, for a t no time during the digestion of this material was the tank fed a t what might be considered a maximum rate. Additional data on the digestion of sewage screenings will be given in another paper. The rate of feeding of these digestion tanks, up to that rate which results in excessive acid formation, is regulated by the rate of gasification desired. The more material fed per day, the greater will be the amount of gas recovered per day but the lower will be that recovered per pound of material fed. If the tanks are fed too much per day for a number of
VOLUMEOF Gas PRODUCED DAYPER 1000 VOLUMES Av. CHI
PER
GASPRODUCED
O F T A N K CaP.4cITYb
Max. for 1 month Cu. f t . / l b .
COXTENT OF
GAS
Av. of total
Max. for 1 month
5 . 7 (356) 2 . 9 1181)
420 350
555 462
52 50
5 . 2 (325) 3 . 3 (206) 7 . 0 (438)
384 280 1022
465 315 1195
54 58 59
%
(Z./kg.)
days, organic acids start to accumulate. When they reach a concentration of 1000 to 1500 p. p m. as acetic acid, the feeding should be omitted for a few days, or a t least the amount should be reduced. Regulation of feeding while putting the tank into operation is essential. Periodic checking of the tank liquors for volatile acid and ammonium nitrogen content is advised. The authors have found that the ammonium nitrogen content of the tank liquor should be kept a t or above 100 p. p. m. Greater concentrations (up to 1500 p. p. m.) do not aid nor have they been found detrimental. As there is seldom any overflow liquor drawn, the only loss of nitrogen is with the residue that is withdrawn. Fresh cornstalks and straw contain only about 0.7 to 0.8 per cent by weight of total nitrogen but even this small amount has been found sufficient to maintain the nitrogen a t a suitable concentration, provided the original ammonia concentration of the tank liquor is 100 p. p. m. or greater. KO ammonia nitrogen or other chemicals need be added in the digestion of sewage screenings, stable manure, or packing house wastes. Nitrogenous wastes are readily decomposed, mainly to carbon dioxide, methane, and ammonium acid carbonate. The ammonium acid carbonate formed in this manner may serve the cellulose-decomposing organisms. In the fermentation and stabilization of sewage screenings, paunch manure, stable manure, waste cornstalks, etc., the humus formed by the decomposition of the nonfibrous materials becomes so mixed with the fibrous residue that it is carried through the drum out into the residue end, and hence to the surface where it can be readily removed. In the experiments conducted by the authors, no sludge or draw-off pipe was found necessary for the removal of digested nonfibrous residue. The optimum fermentation temperature for this process seems to be between 25" and 30" C. (77' and 86' F.), This temperature may be maintained in winter by passing hot water or steam through a coil placed in the tank or by piling decomposing residue or fibrous material around the tank. This has been found to heat and insulate the tank.
LITERATURE CITED (1) Boruff and Buswell, Illinois State Water Survey, Bull. 32 (in preparation). (2) Boruff and Buswell, IND. Ewo. CHEY.,21, 1181 (1929). (3) Boruff and Buswell, I b i d . , 22, 931 (1930). (4) Buswell, Ibirl., 21, 322 (1929). (5) Buswell and Boruff, Cellulose, 1, 108, 162 (1930). (6) Buswell and Boruff, U. S. Patent 1,880,772 (Oct. 4, 1932). (7) Fowler and Joshi, J . I n d i a n Znst. Sci., 3, 39 (1920). (8) Misuno, French Patent 571,967 (1924). (9) Nathan, J. Soc. Chem. I n d . , 42, 279T (1923). (10) Omelianski, Centr. Baht. Parasitenk., 11, 8, 353 (1902); 12, 33 (1904). (11) Rudolfs and Heisig, Sewage W o r k s J . , 1, 519 (1929). (12) Thaysen and Bunker, "Microbiology of Cellulose, Hemicelluloses, Pectin and Gums," Oxford Univ. Press, 1927. RECEIVEDAugust 29, 1932. Presented before the Diviaion of Water, Sewage, and Sanitation Chemistry a t the 84th Meeting of the American Chemical Society, Denver, Colo., August 22 t o 26, 1932.
