Courtesy, Northwest Paper Company
BEATERR O O U SHOWIVG
B E 4 T E R S , AY'D SIZE, A L L X , 411) SIXSH
STOCK
TAYKSO V
THE
DEX
The Cooking Process VII. Cooking Wood with Sodium Hydroxide and Trisodiurn Phosphate S. I. ARONOWKYAND Ross AIKEN GORTNER,Minnesota
W
Agricultural Experiment Station, St. Paul, Minn.
ATER alone ( I ) and aqueous solutions of sodium sodium hydroxide was employed in quantitie:, equal to 15.1 carbonate @), sodium sulfate ( 3 ) , sodium thio- and 30.2 per cent of the weight of oven-ciry wood, equivalent, sulfate (4, sodium sulfite ( 5 ) , and sodium sulfide on the sodium basis, to 20 and 40 per cent sodium carbonate, (6) have been used as cooking agents in this series of in- respectively. The wood used in these cooks (100.0 gram5 air-dry equals 90.0 grains ovenvestigations. dry) was aspen sawdust from S o d i u m h y d r o x i d e is the +-ispensawdust i m s tooked for 2 arid 12 hours the same b a t c h descrilied in cooking ingredient of the soda at 170" and 186" 0'. icith f5.1 and 30.2 per cent previous reports. process l i q u o r s and the main sodium hydroxide (based on thr ocen-dry wood)'), Two 2-hour cook? were run at ingredient, in quantity, of the equicalent, on the sodium basis, to 20 arid 41) sulfate or Kraft process liquors. 186" C. u s i n g 47.8 and 95.6 The effects of sodium hydroxide per cent trisodiurn phosphate per cent sodium carbonate, respectiiiely. The as a cooking agent is the main (Sa3PO4.12H?O),e q u i v a l e n t , residual liquors contained more total organic on the sodium basis, to 20 and theme of this report. matter, volatile organic acids (as acetic), pentoSince phosphates play such 40 per cent sodium carbonate, sans, and lignin (72 per cent sulfuric acid a n i m p o r t a n t role in t h e respectively. The a n a l y t i c a1 method) than were f o u n d in the residual liquors of biological d e c o m p o s i t i o n of results given are the averages of a t l e a s t t w o d e t e r m i n a sugars, it was t h o u g h t that the corresponding water cooks. Light brown to they might have special effects tions. brown residues, partially to completely pulped, u p o n t h e cellulose of wood were obtained. The p u ' p yields were lower than and upon the s u g a r s formed RESIDVAL rJrauoKs those f o r the corresponding water cooks. The during t h e c o o k i n g process. The residual liquors from the sodium hydroxide pulps contained less lignin The r e s u l t s of c o o k i n g w i t h sodium h y d r o x i d e cooks were sodium phosphate are included and more pentosans. Cooking with 30.2 per reddish brown and clear when in this r e p o r t since o n l y two cent caustic soda or with water alone resulted in hot, a n d h r o WII - b 1a c k when cooks were m a d e w i t h t h i s similar Cross and B e z m cellulose yields, while cold. They were all alkaline salt. 15.1 per cent sodium hydroxide yielded larger to l i t m u s paper. T h e y conEight cooks were made with tained very small a m o u n t s of quantities of this constiiuent. Sodium hydroxide s o d i u m h y d r o x i d e a t 170" easily dispersible, dark brown and 186" C. for 2 or 12 hours hindered the hydrolytic action of water on the solid matter. T h e y f o a m e d of c o o k i n g . A c a u s t i c soda alpha-cellulose. Sodium hydroxide is a strong p r o f u s e l y but the foam dissolution, containing 114.0grams pulping agent. Cooking aspen sawdust with appeared quickly. per l i t e r s o d i u m h y d r o x i d e trisodium phosphate yielded results similar to The residual liquors from thc and 3.2 grams per liter sodium sodium phosphate cooks were those obtained with sodium carbonate. c a r b o n a t e , was u s e d . The 220
February, 1934
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
orange-brown to reddish brown when hot, and dark brown to brown-black when cold, the liquor with the higher concentration of the salt being darker. Both liquors were turbid. The liquor obtained by cooking with 47.8 per cent sodium phosphate was slightly acid to litmus paper, R hile the okher was slightly alkaline. Small amounts of brown, easily dispersible solid matter separated out upon standing. Shaking these liquors caused but little foam formation. TOTAL ORGANIC MATTER. The quantities of total organic matter found in the residual liquors of the sodium hydroxide cooks were larger than those obtained by cooking with water only, as shown in Table I and Figure 1. They were approximately equal to those obtained with sodium sulfide (5). The organic matter increased with increasing amounts of sodium hydroxide and with temperature of rooking. The increased time of cooking a t 170" C. resulted in larger yields of organic matter, while a t 186" C. no appreciable differences were noticed. The maximum yield of total organic matter was about 45 per cent of the original dry wood, equal to the maximum obtained with sodium sulfite (6) but lower than the sodium sulfide maximum yield. The yield of pulp of this particular cook (91) was only 40 per cent of the oven-dry mood. The yields of total organic matter of the residual liquors from the trisodium phosphate cooks are also shown in Table I. They were approximately equal to the quantities of organic matter obtained by cooking with sodium carbonate under similar conditions ( 2 ) . The total organic matter mas determined by multiplying the total organic carbon contents of these liquors by the same factor that was used in obtaining the organic matter of the sodium sulfite and sodium sulfide liquors-namely, 2.0. DISTRIBUTION OF SALTS. The distribution of sodium hydroxide and sodium carbonate in the original and residual liquors is given in Table 11. The quantities of these components in the residual liquors were determined by titrations, made on the liquors before and after precipitation of the sodium carbonate -.ith barium &loride, itll acid, using phenolphthalein and methyl orange as the indicators, The sodium hydroxide was almost, completely used up or changed to the carbonate in those cooks in XI hich 15'1 per cent caustic added. In the Other cooks the increase in time and temperature of cooking caused decreases in the quantities of sodium hydroxide, a i such, found in the residual liquors. The quantities of sodium carbonate formed increased with the larger amounts of caustic soda used but decreased somewhat a t the higher cooking temperature, with the exception of the values found for cook 93 (2 hours, 188" C., 30.2 per cent sodium hydroxide). The quantities of sodium carbonate found do not give a true index of the amounts of carbon dioxide formed in the cooking process. This is due to the fact that the sodium hydroxide combines with the woody material very early in the cooking process, and the production of carbon dioxide by decomposition of the wood begins, very probably, only a t or near the cooking temperature. It was found, using water a. the sole cooking agent ( I ) , that very little decomposition of the wood took place a t 148" C., while a t 170" C. and above, the losses of wood substance were rather large. It is likely, too, that in cooks 88 and 90 (Table 11) excess quantities of carbon dioxide were present. The small quantities of alkali reported, in the residual liquors of these cooks, as sodium hydroxide were probably sodium salts of weak organic acids which can be titrated to complete neutralization with phenolphthalein as the sole indicator. The quantities of sodium combined with the organic matter of these liquors were about equal to the values found for the sodium sulfite cooks, but somewhat less than those obtained
e
ldd
r)
Vda!,/e
221
o.ya"(cf%/f.r
2
L*nn
A shown in Table TI. LIGNIN. Larger quantities of lignin (72 per cent sulfuric acid-insoluble) were found in the residual liquors of the sodium hydroxide cooks than in those of the Corresponding water cooks (Table 111,Figure 1). With 15.1per cent sodium hydroxide used in cooking, the lignin yields in the residua1 liquors were higher than those found in the corresponding sodium sulfide residual liquors, but the reverse mas true at the higher salt concentrations. Doubling the quantities of qodium hydroxide added to the autoclave resulted in only slight increases in the lignin contents of the residual liquors, nhereas the amounts of lignin found in the sodium sulfide reqidual liquors were almost directly proportional to the quantities of this salt used in cooking. The increase in time and temperature of cooking had but little effect on the lignin contents of the sodium hydroxide residual liquors. The lignin contents of the residual liquors of the trisodium phosphate cooks are also given in Table 111. These quantities were larger than those obtained by cooking with water only, and about equal to those obtained in the corresponding
222
Vol. 26, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I.
RESIDUAL WOODS
YIELDS OF
AXD T O T A L ORGANIC
MATTER IN RESIDUAL LIQUORS" TOTAL ORQANIC MATTEBIN
REaIDuaL
COOK
NaOH ADDED
TEMP.
13 86 87
TIME Hour8 2 2 2
170 170 170
Grams HsO onlyb 13.6C 27.2d
16 88 89
12 12 12
170 170 170
Ha0 onlyb 13.6 27.2
61 8 5i 0
17 92 93
2 2 2
186 186 186
HzO only&
61 6 5%2
21 90 91
12 12 12
186 186
Ha0 onlyh 13.6 27.2
a
Weight Grams 6'3.7 5% 9 5'3 2
TO DIQEBTER
c.
186
% 70 94 65 44 59 11
MATERIAL UNACCOUNT~D FOR BY .kNALYsI8 On basis original oven-dry Weight wood Grams % 6 9 7.67 5.0 5.66 6 8 7.60
68.52 60 00 50 03
14 98 30.0% 37 02
16.65 33.38 41.16
13.0
68.60 60.22 49 89
16.31 29.78 40.60
18.16 33.09 45.11
11.9 4.5
13.24 6.69 5.00
50.0
60.69 55,55
.I6 0
40 OD
15.90 31.51 39 96
17.71 33.04 44.40
19.4 8.5 14.0
21.60 9.44 15.56
11.9 4.7
3.24 5.22 6.69
45 0
13.6 27.2
RESIDUAL LIQUOR (ORQANIC CARBONX 2) On basis original oven-dry Weight wood Grams % 19.211 21.39 26 Oi3h 28.90 29 96 33 29
\VOOD On basis original oven-dry wood
41 9 5%.5
Na,P0,,12HzO A D D E I J 17 2 186 HIO onlyb 61.6 68.60 lU.31 18.16 94 2 186 43.0' 65.5 72.78 19.80 22.00 60.7 65.22 95 2 186 86.01 2Fi 28 28.09 a 80.0grams oven-dry wood (100.0grams air-dry) were used in each cook. b 89.8 grams oven-dry wood (100.0grama air-dry) were used in cooking with water only. 0 15.11 of we/ght of oven-dry wood used and equivalent, on sodium basis, to 20% NazCOs (Hz0 3350 grams). d 30.22% of weight of oven-dry wood used and equivalent, on sodium basis, to 40% NasCOa (Hz0: 3350 grams). 6 47.78% of weight of oven-dry wood used and equivalent, on eodjum baajs, to 20y NazCOa (Hz0 3350 grams). 195.56% of weight of oven-dry wood used and equivalent, on sodium basis, to 40% NazCOa (HzO: 3350 grams). s Total organic matter in water cooks includes furfural from digester condensate. h Total organic matter in hydroxide and phosphate cooks was determined by multiplying total organic carbon content of liquors
sodium thiosulfate cooks (4). Doubling the quantity of sodium phosphate used in cooking resulted in a larger amount of lignin in the residual liquor. PENTOSES AND PENTOSANS. The quantities of pentoses and pentosans (calculated together as pentosans) in the residual liquors of the sodium hydroxide cooks were larger than those found by cooking with water alone, except in the 2-hour, 170" C . cooks. The pentosan contents of these caustic liquors were approximately the same as those of the sodium sulfite and sodium thiosulfate liquors. The increase in concentration of sodium hydroxide in the cooking liquors and the increase in time and temperature of cooking had, apparently, little effect on the pentosan contents of the residual liquors. The data are given in Table I11 and Figure 1. The pentoses and pentosans found in the trisodium phosphate residual liquors were approximately equal in amount to those obtained in the corresponding caustic soda cooks, as shown in Table 111. Doubling the salt concentration of the cooking liquor had no effect on the pentosan content of the residual liquor. REDUCINQ SUGARS.Owing to the alkalinity of the liquors, only traces of reducing sugars were found in the residual liquors of the sodium hydroxide cooks. Cooking with trisodium phosphate resulted in only slightly larger yields of reducing sugars. These low reducing-sugar yields were probably due more to the high pH, or alkalinity, of the liquors than to the action of the phosphate ions. VOLATILEORGANICACIDS. More volatile organic acids (calculated as acetic) were found in the caustic soda residual liquors than in those obtained by cooking with mater only.
6.0 8 0 6.0
t.0
14.50 6.62 8.84
by 2
The quantities obtaiued were about equal to the acid yields from the sodium sulfide cooks and greater than the corresponding yields found in the sodium sulfite residual liquors. The increases in time and temperature of cooking and in the amount of sodium hydroxide added to the autoclave tended to increase the yields of volatile organic acids. The data are given in Table I11 and Figure 1. The maximum yield of volatile organic acids obtained in this series of cooks was 12.4 per cent of the oven-dry wood (cook 91, 12 hours, 186" C., 30.2 per cent sodium hydroxide). The yields of volatile acids obtained by cooking with trisodium phosphate were higher than those found in the residual liquors of the corresponding water cooks (Table 111) and approximately equal to the yields obtained by cooking with sodium sulfite. Doubling the amount of trisodium phosphate used in cooking resulted in an increase in volatile organic acids.
DIGESTER CONDENSATES The condensate liquors of the sodium hydroxide cooks were water-white to light yellow in color, slightly turbid, and neutral to litmus paper, They had a slight odor reminiscent of wood distillate. No furfural was found in these liquors. The condensates from the trisodium phosphate cooks were water-white and similar in all other respects to those of the caustic soda cooks. RESIDUliL WOODS
The colors of the residual woods and pulps of the sodium hydroxide cooks mere light brownish gray to brown, about
OF SALTSIX ORIGINAL . ~ N DR E ~ I D U A LIQUORS L TABLE11. DISTRIBUTION
Total
-CHEMICAL8
COOK
TIME
.kDDED
TEMP.
NaOH
NarCOa
Grams 13.6 27.2 13.6 27.2
Grams 0.38 0.76 0.38 0.76
as NazO (1) Grams 10.76 21.52 10.76 21.52
13.6 27.2 13.6 27.2
0.38 0.76 0.38 0.76
10.76 21.52 10.76 21.52
Hours
C
86 87 88 89
2 2 12
170 170 170 170
92 93 90 91
2 2 12 12
186 186
SALT$.is SECH FOUNDI N LIQUOR NaOR Narc08 Grams Crams 0.88 5.09 12.08 5.72 0.38 "80 6.22 5.65
0.38 6.66 0.32 5.20
4.07 8.12 1.27 7.42
TOTAL 3ALTs Ad
NarO (2) Grams 3.66 12.71 1.93 9.88 2.68 10.50 0.99 8.37
Nan0 COMBINED WITE ORQANIC MATTER, (1) MINE8 (2) On basis original Weight Nay0 Grams % 7.10 66.0 8.81 40.9 8.83 82.0 11.64 54.1
8.08 11.02 9.77 13.15
75.1 51.2 92.7 61.1
Fez08 FOUNDIN LIQUOR Grams 0.13 0.22 0.17 0.37
0.13 0.60 0.15 0.40
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1934
223
midway between those of the pulps from the sulfite and sulfide cooks. The residue from cook 86 (2 hours, 170"C., 15.1 per cent sodium hydroxide) was not pulped. The moist residues from cooks 87 and 92 could be pulped by rubbing between the fingers. Semipulped residues were obtained from cooks 88 and 90, while those from cooks 89, 91, and 93 were completely pulped. These pulped residues were somewhat softer to the touch than those from the 0 14 7 194 sulfite and sulfide cooks. The residual wood or pulp yields obtained by cooking with sodium hydroxide are given in Tables I and IV and Figure 2. Smaller yields were obtained in these cooks than in the corresponding water cooks or in most of the sodium sulfite cooks (6). The residual wood yields were similar to those of the sulfide pulps a t the lower salt concentrations ( 6 ) , but they were lower when the amounts of chemical used for cooking were doubled. The pulp yields of the sodium hy14.7 droxide cooks decreased w i t h i n c r e a s i n g No, 5 N+S Co&.y L c -ZHF~ Cooh.ng ?imp -/86'C Cook,n9 -/2Hrs Cookmg Gmp. -186'C amounts of caustic soda used and with increasing time and temperature of cooking. WOOD AND ITS COMPONENTS FIGURE 2. YIELDS OF RESIDUAL It may be seen from the r e s i d u a l wood 411 d a t a based o n original charge of 100.0 grama air-dry (90.0 gram8 oven-dry) aspen a a u d u s t : zern per cent sodium sulfide represents results obtained b y cooking with water only. yields i n T a b l e s I a n d IT that in this series of cooks, as in the s o d i u m sulfite and sodium sulfide series, the rise in cooking temperature hydroxide concentration on the cellulosic constituents of from 170" to 186" C. is equivalent to an increahe of 10 hours the wood under the extreme cooking conditions used in this in cooking time a t the lower temperature. The pulp yield cook. The reddish brown colors of the residual woods from the two of cook 91 (12 hours, 186" C., 30.2 per cent sodium hydroxide) was 40.0 per cent of the original oven-dry sawdust, the lowest trisodium 'phosphate cooks were similar to that of cook 27 yield obtained in this series of investigations. (2 hours, 186" C., 20 per cent sodium carbonate), the wood The losses suffered by the original wood in cooking with from the cook run with 86.0 grams trisodium phosphate being sodium hydroxide were smaller than those which attended slightly darker. The residual woods were soft but not the cooks made with water as the sole cooking agent, as pulped. The yield of residual wood from cook 94 (43.0 shown in Tables I and V and Figure 3 . These losses were of grams trisodium phosphate) was greater than that obtained the same order as those obtained with sodium sulfide, but in the corresponding water cook, while the latter was larger they were, in general, somewhat higher than the lo,,sses ac- than the yield from cook 95 (86.0 grams trisodium phosphate). companying the cooks made with sodium sulfite. The in- These yields were larger than those obtained in the corcreases in concentration of caustic soda and of the time arid responding sodium carbonate cooks ( 2 ) . The losses of woody temperature of cooking resulted in increased 1oss~3of wood material sustained by cooking the aspen sawdust with trisubstance. The relatively large loss of material in cook 91 sodium phosphate were of the same order as those suffered by may be due to the destructive action of the higher sodiuni cooking with sodium sulfite, sulfide, or hydroxide under fa
sf0
T m e
TABLE
111.
YIELDS OF
TOTAL ORGANIC MATTER, LIGNIN,PENTOSANS, T'OLATILE TOTAL REDUCIKG SUGARS IN RESIDUAL LIQUORS To,raL ORGANIC
LIONININ RERIDUAL LIQUOR O n basis original oven-dry Weight wood Grams % 5.77 6.43 9.56 10.62 10.52 11.69
MATTER
COOK
~ I M E
IJours 2 2
TEMP.
c.
NaOH ADDED TO DIGEETER Gram8 H10 only 13.6 27.2
(ORGANIC CARBON x 2) Grams
19.21
>
170 170 170
12 12 12
170 170 170
Ha0 only
13.6 27.2
30.04
17 92 93
2
> 3
186
186 186
H10 only 13.6 27.2
21 90 91
12 12 12
186 186 186
HrO only
2
186 186
13
86 87
16
88 89
13.6
27.2
26.06 29,96
4.78
PENTOSELI AND
ORGANIC
PENTOSANS~ IN RESIDUALLIQUOR On, basis original oven-dry Weight wood Grams % 5.12 5.70 3.32 3.69 3.45 3.83
ACIDS, AND
VOLATILEORGANIC ACIDS(ASACETIC)
13 RESIDVAL LIQUOR
Weight Grams 1.77 6.65
7.38
On basis original oven-dry wood
%
REDUCING SUQABSb IN
RESIDUAL LIQUOR Gams
1.97
11.3:
7.39 8.20
11.33 14.37
0.60 3.07 2.65
0.67 3.41 2.94
7.84
1.76
9.58
8.71 10.64
2 35
12.93
16.31 29.78 40.60
4.95 11.46 11.97
12.73
5.51
0.75
0.83 3.93 2.90
1.34 7.48 8.79
1.49 8.31
4.47
15.90 31.54 39.96
1.78
2.83
11.34
11.12
14.98
4.29
10.20
37.04
13.30
5.10 8.12
3.54 2.61
5.68 9.02 12.60
0.54
2.35 3.84
0.60 2.61 4.27
5.51 6.00 8.89 0.2 gram
0.75 3.50 3.38
0.83 3.89 3.76
1.58
1.60
8.25
0.77 9.17
12.36
NaaPO+.12HzO ADDED 17 94 95 Calculated
>
186 together as pentoeans. 2
Ha0 only 43.0
86.0
16.31 19.80
25.28
b Calculated as glueme.
C
.
4.95 5.40 8.00 . .indicate
S The quantities of pentosans found in the CooLng -2Hrr C o o l r m p Grip. - /70'C. Cooking 7 ; r a - / Z H r r . CooCmg TInp -/70°C. trisodium phosphate residual woods were 100 greater than those found in the correspondAeo ing water-cooked woods and about equal to the pentosan contents of the correspond$ ing sodium sulfite residual woods. The losses e 60 of pentosans in t'hese two cooks were also of 2 the same order as found in cooking with 2'" sodium sulfite. $20 CELLULOSE. The quantities of Cross and Revan cellulose remaining in the residual woods of the sodium hydroxide cooks were ./. Na*S No,S larger than those found in the residues obCookmg -2Hrr CeoLm9 Zmp. -186.C. Cmkznj -fZffrs Cookvng Z m p - IBC'C tained by cooking water These FIGURE 3. PERCENTAGE OF ORIGINAL CO.MPO;YENTS OF W O O D DESTROYED data are given in Table IV and Figure 2. (NOT ACCOUNTED FORBY ANALYSIS)IN COOKING PROCESS The cellulose contents of the sodium hydroxZero per cent sodium sulfide represents results obtained by cooking with water only.
:::
~cel/Llc3,
t
fo
.
./o
7;m.
Tna
INDUSTRIAL AND ENGINEERING CHEMISTRY
226
cooking for 12 hours at 170' C. or for 2 hours a t 186" C. yielded equal quantities of cellulose a t the same concentration of sodium hydroxide. The percentage losses of Cross and Bevan cellulose are given in Table V and Figure 3. These data show that, a t the higher caustic soda concentrations, the losses of cellulose in these residual woods were equal or nearly equal to those sustained by cooking with water only. The destruction of Cross and Bevan cellulose depended to a great extent upon the pH of the cooking liquors, being greater with larger hydroxyl-ion concentrations. The residual woods of the trisodium phosphate cooks retained more cellulose than was found in the residues of the corresponding cooks made with water only or with any of the salts used in this series of investigations, except those made with sodium sulfite. The cellulose yields of the trisodium phosphate cooks were approximately equal to those obtained by cooking with sodium sulfite. ALPHA-CELLULOSE. The quantities of alpha-cellulose found in the residual woods or pulps of the sodium hydroxide cooks are given in Table IV and Figure 2. With 15.1 per cent caustic soda used in cooking, the yields of alpha-cellulose were greater than those found for the corresponding water cooks, but the reverse was true at the higher sodium hydroxide concentrations, except in the case of cook 91 (12 hours, 186" C.). The increases in time and temperature of cooking resulted in decreasing the quantities of alpha-cellulose in the residual woods of the caustic soda cooks. The alpha-cellulose contents of these pulps were generally higher than those of the sodium sulfite residual woods. They were higher than
Vol. 26, No. 2
the quantities of alpha-cellulose found in the sodium sulfide cooks at the lower concentrations of cooking chemicals, but lower when the amounts of chemicals used in cooking were doubled. The amounts of alpha-cellulose destroyed, or rendered soluble in 17.5 per cent caustic soda, in cooking with sodium hydroxide are given in Table V and Figure 3. It is apparent from these data that, while a certain hydroxyl-ion concentration of the cooking liquor is necessary to protect the alphacellulose against hydrolysis or transformation into betaand gamma-celluloses, an increase in the pH of the cooking liquors tends toward increased degradation of this constituent. The destruction of alpha-cellulose was greater when trisodium phosphate was used as the cooking agent than when water alone was used. Increasing the amount of salt used in cooking caused an increased destruction or conversion of the alpha-cellulose in the residual wood.
LITERATURE CITED (1) Aronovsky and Gortner, IND.ENG.CHEM., 22, 264 (19301 (2) Ibid., 22, 941 (1930). (3) Ibid., 25, 305 (1933). (4) Ibid., 25, 1260 (1933). (5) Ibid., 25, 1349 (1933) (6) Ibid., 26, 6 1 (1934).
RECEIVED August 12, 1933. Presented before the Divisioa of Cellulose Chemistry at the 84th Meeting of the American Chemical Society, Denver, Colo., August 22 to 26, 1932. Published with the approval of the director ae Paper No. 1202, Journal Series, Minnesota Agricultural Experimeat Station. 9.I. Aronovaky is the Cloquet Wood Produota Fellow, Univeraity of Minnesota; the fellowship waa established by the Northwest Paper Company of Cloquet, Minn
Prefiltration Treatment of Sewage Sludge F. W. MOHLMAN AND G. P. E D W A R D S , The Sanitary District of Chicago, Chicago, 111.
A
TREMESDOUS amount of research has been carried on in various sewage works laboratories in the past several years concerning the Drefiltration treatment of sewage sludge. Practically none of the results of these investiga-
A
Parious chemicals and filter aids w e used to condition sludge prior 1; fifiltration. A large number of such filter aids are tested with cornparatine data on rates Of filtration through Biichner $filters. T h e materials used are cornpared as to rates of filtration, economy, andpracticability used with various types of sludges, bofh undigested and digested.
been but they are in the files of various municipalities or concerns interested in the mechanical dewatering of sludge. Here are described briefly the results of some preliminary laboratory investigations made during the winter and spring of 1931-32 in the Main Laboratory of the Sanitary District of Chicago in which various chemicals and conditioning agents were added t o several types of sewage sludge followed by vacuum filtration on Buchner funnels. This work was augmented a t the time by tests on small Oliver vacuum filters, and later by operating results with a large &foot Oliver filter. This paper, hoxever, deals only with the Biichner tests, since a large variety of materials were studied and their value as conditioning agents determined. The outstanding value of ferric chloride as a conditioner for sludge was discovered by John Palmer, in the Calumet Laboratory of the Sanitary District of Chicago, in 1925, and reported by Mohlman and Palmer.' Since then ferric chloride has been used in practically all sewage works where sludge has been filtered on vacuum filters. In the past few 1
Enp News-Record, 100, 147-50 (1925).
years 'increasing efforts have been m a d e to find some augmenting or cheapening agent to l,Se with f e r r i c c h l o r i d e . Consequently many m a t e r i a 1s have been tried in conjunction with ferric chloride. Most of the tests were made on mixed activated and settled s o l i d s , a b o u t o n e t o o n e on the dry basis. Tests were also made with settled and activated sludges separately, Imhoff sludges, and sludges from heated separate digestion tanks. Although the differences in characteristics of these various sludges with regard to conditioning were studied during the Biichner tests, the main purpose was to test the use of various conditioners on undigested activated plus settled solids rather than to determine the ferric chloride requirements of various types of sludges. ~
TECHNIC OF TESTS Samples of sludge were treated with various amounts of conditioning materials, mixed, and poured on a Biichner funnel 9 cm in diameter. Whatman No. 1 filter paper was used, and the vacuum was held at approximately 20 inches (50.8 cm.) of mercury. The filtrate was received in a 250-cc. graduated cylinder, whereby the volume of filtrate could be read at frequent intervals. The end point, when the cake cracked from the sides and the vacuum broke, was noted. The tests in most cases included determinations of moisture contents of feed and cake, volatile matter, pH, and iron content. Altogether about two hundred tests were made, of which only a few representative data sheets are included here.
