IiYD USTRIAL A N D ENGINEERING CHEMISTRY
1154
T'ol. 23, No. 10
Sludge-Digestion Capacity'" E. L. Pearson and A. M. Buswell ILLINOIS STATE WATERSURVEYURBANA, ILL.
EPARATE sludge-digestion tanks have been built with per capita capacities ( S , 4 ) ranging from 1 to 9 cubic feet (0.03 to 0.27 cubic meter). Recent installations, however, probably fall within the narrower range of from 1 to 5 cubic feet (0.03 to 0.15 cubic meter) per capita. The minimum capacity, consistent with satisfactory operation, has not been extensively studied, probably partly because other considerations, such as winter storage of sludge and, until recently, lack of methods of controlling scum and foaming, have been influential in determining the capacity provided. With the present heated tanks and improved mechanical and hydraulic methods of control, and in the advent of more speedy methods of disposal of the digested sludge, capacity information would be of considerable value.
S
Operation of Digestion Unit
A digestion unit was used having a total capacity of 1330 gallons or 0.9 cubic foot (5054 liters or 0.027 cubic meter) per capita. Connections were made for circulating liquor over the scum. The tank was filled with liquor and sludge from another experiment. The total volatile matter introduced as seed was 105 pounds. Thereafter it was fed with fresh sludge from a nidus tank three times daily a t an average rate of 13.5 pounds (6.04 kg.) (of volatile matter) per day. Table I shows the composition of this material. The average maximum digestion time was 10.7 days, based on the following calculation: Five scum and sludge measurements (made a t intervals during the experiment to determine the amount of sludge to be drawn) indicated the presence of an average of 113 pounds (51.3 kg.) of volatile matter. A total of 1560 pounds (707.6 kg.) of volatile matter was fed and 930 pounds (421.8 kg.) of gas collected. In a previous experiment (2) it was calculated that the digestion of 1 pound (0.45 kg.) of volatile matter produced 1.25 pounds (0.567 kg.) of gas. On this basis the 930 pounds (421.8 kg.) of gas account for 744 pounds (337.4 kg.) of volatile matter digested, indicating a reduction of 47.7 per cent of the volatile matter fed. The daily charge of 13.8 pounds (6.26 kg.) would then produce 7.2 pounds (3.27 kg.) of digested sludge. Assuming the rate of digestion to be constant over this period, the mean weight of one day's charge in its course through the tank would be 10.5 pounds (4.77 kg.). Thus, the daily charge is equivalent to 9.3 per cent of the tank contents representing, therefore, a detention period of 10.7 days. T a b l e I-Fresh
was maintained a t 27" C. by means of steam coils submerged in the sludge. The population equivalent of the sludge added is based on the FeTvage flow. The data in Table 11,however, further confirm this, in that the grams of solids per capita fall within the limits of the solids collected a t other installations. This table also indicates that about 10 cubic feet of gas per pound (600 cc. per gram) of volatile matter added to a digestion unit is the average gas production. In this connection it is of interest to calculate the highest possible yield of gas from digesting volatile matter. Of the important constituents of organic matter, carbon, hydrogen, oxygen, and nitrogen, carbon is the element governing the quantity of gas available. Hydrogen and oxygen are found in the gas in significant amounts only in combination with carbon as methane and carbon dioxide. The maximum yield of gas would, therefore, be obtained if the volatile matter consisted entirely of pure carbon. I n this case a gram molecule of carbon would produce 22.4 liters of gas. One gram would produce 1870 cc., and one pound, 29.9 cubic feet. A yield in excess of 1870 cc. per gram of digested volatile matter has been reported in
9t?
'0O
g 500 &*O
S l u d g e F e d a n d G a s Produced
_________SOLIDS
MONTH November December January February
Sludge volume Cu. m. 4.5 5.95 7.1 5.46
Total weight
% 4.9 3.8 3.7 3.9
Ash,dry Crease, Raw basis dry basis sludge % % pH 6.5 24.4 35.3 6.4 33.7 21.4 6.4 23.3 34.8 6.3 22.2 27.2
GAS Cu,n. 4.7 12.8 18.4 16.8
The interval between sludge withdrawals averaged 5 days. Liquor was circulated over the scum for from hour to 2 hours twice daily except during the foaming period when the circulator was run for from 15 t o 20 hours. The temperature 1 Received May 11, 1931. Presented before the Division of Water. Sewage, and Sanitation Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931 2 This work was carried out with the assistance of funds furnished by the Chemical Foundation.
Figure 1-Data
on Volatile Acids, S l u d g e , a n d Gas
the literature ( 5 ) ,but since sewage solids are not pure carbon, the actual yield must necessarily be considerably less than the theoretical maximum yield. For sewage grease which has been shown ( I ) to be an important source of gas, the maximum yield would be approximately 20 cubic feet per pound or 1200 cc. per gram of grease digested. However, since grease is not the only constituent of volatile matter, and since all of the volatile matter does not gasify, the yield in practice as indicated in Table 11 is in the neighborhood of 10 cubic feet per pound (600 cc. per gram) of volatile matter added.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1931
Table 11-Sludge
PLANT Antigo. W i s . Plaintield. N. J. Marion, Ohio Rxpt. Plant Exlit. Plant
S o l i d s a n d Gas Yield per Capita
....
a
GAS YIELD Per gram volatile matter added L8lers 0.73 1.13
SOLIDSPER VOLATILE MATTER Per CORRECTED POPULATIONCAPITA PER CAPLTA capita Grams Grams Liters 5,600 84.7 25.0 18.2 45,500 28.3a 33.F, 40,000 37.5 200 i!8 ’ ii:05 200 42 32 17.0 31.3 19.8 200 40.2 40.000 45 .... 7,000 64 35’ ’ .... 28.0 7,000 h4 6 55 37 .... 130.000 22.5 44.5 4 400 .... 40.000 74 ....
.... ii‘
sludge)
1155
.
1
.
.
0.53 0.41 0.495
....
REFERENCE
P u b l i c W o r k s , 69, 134 (1928) I b i d . . 58, 342 (1027) I b t d . , 67, 350 (1026) Water Survey, Bull. 29 Seamage W o r k s J . , 3 (April, 1931) P u b l i c W o r k s , 67, 343 (1926)
. .. .
Sewage W o r k s J . , 2, 30 (1930)
. ...
Sewage W o r k ;
0.333 ,... 0.505
P u b l i c W o r k s 6 1 24 (1030) J.,’1, 173 (1929) Zbid., 2, 404 (1930)
Estimated, 1931.
Foaming
(5.34 cc. per gram) of volatile matter added. Daily analysis of the gas showed the average composition t o be as follows: methane, 65.8 per cent; carbon dioxide, 30.9 per cent; hydrogen, 1.2 per cent; and nitrogen, 1.9 per cent. Figure 1 shows the concurrent rise of volatile acids with increasing rate of gasification, and a falling off of volatile acids after the average gas rate has been established. It is interesting to note that the daily gas production in 20 days equaled or exceeded the total tank volume (178 cubic feet). SLUDGEDRAwN-Table 111 gives the characteristics of the digested sludge. The average biochemical oxygen demand is below the limit (1500 p. p. m.) set by Rudolfs and Fischer (6) for a digested sludge stable enough to be drawn. On only two occasions was this limit esceeded. The average ash content, 36.4 per cent, shows considerable increase over that of the fresh solids (22.8 per cent). The sludge had good draining qualities as measured by the drainability test ( 3 ) , was gray, and had an inoffensive tarry odor. On a sand bed it dried to a moisture content of 65 per cent in from 20 to 30 days, but remained of a gummy consistency and did not crack. The drying beds, however, were indoors and the humidity was always high owing to escaping steam. Further drying of samples in the laboratory resulted in large cracks and a tough fibrous cake that would not lend itself to easy removal from a bed.
The daily gas-production curve (Figure 1) indicates that nornial digestion was under way by the thirtieth day. On the thirty-second day (two days after the increase in gasification) foaming became very pronounced. The shaft on the pump was so worn that, when run continuously, the packing would leak air. On several occasions when the pump was run overnight with no one on duty, air was drawn into the system and foaming became so aggravated that considerable material was forced out through the water seal. A few hours after the air leak was stopped, the foaming would again he under control. The foam was very light and stable, having the characteristics of a good soap lather. This aggravation of foaming by air could not have been a mechanical effect, because the liquor first struck a splashboard in the top of the tank and was sprayed over the top of the scum. After the air leakage had been permanently stopped, the foaming and scum were effectively controlled by the routine circulating schedule. Measurements showed an average of from 4 to 6 inches (10.2 to 15.2 cm.) of light soft scum. Discussion of Results
Sludge-level measurements indicated that there was in the tank an average of 260 gallons (985.4 liters) of sludge. Except for the small amount of scum, the remainder of the volume (about 75 per cent of the total) was occupied by sludge liquor. It is not unreasonable to predict that much of this volume could be utilized for sludge space, whereby with the same capacity-namely, 0.9 cubic foot (0.027 cubic meter) per capita or 10 cubic feet per pound (600 cc. per gram) of fresh solids added per day, a longer detention period would be provided which, as will appear in the discussion on the digested sludge, would be necessary to produce a sludge which could be readily handled on a drying bed. Secondary digestion would berve the same purpose. With mechanical thickeners for the digesting sludge, with adequate scum and foaming control, and barring troublesome industrial wastes, 0.5 cubic foot (0.015 cubic meter) per capita or 5 cubic feet per pound (300 cc. per gram) of raw solids per day should be sufficient digestion space for a 10- to 12-day digestion schedule. This would permit recovery of practically 90 per cent of the gas and produce an inoffensive but not a well-drying sludge. Since most modern digestion units are equipped with sludge thickeners and scum-control devices, there would be no added cost on that account. However, a limited capacity would require closer supervision and probably more frequent operation of the scum- and foam-control mechanisms, and a means of storing or disposing of the sludge as it was digested. GAS PRODUCTION--FOr 3 months following the initial lag of about 30 days, the gas production averaged 10.6 (corrected for nitrogen) cubic feet per pound (636 cc. per grain) of volatile matter fed, or 0.70 cubic foot (0.021 cubic meter) per capita per day. The total production was 8.90 cubic feet per poind
of Digested Sludge AVERAGE MAXIMUM MINIMUM Solids, % ’ 4.1 5.6 1.2 Ash, % 36.4 41.5 30.1 Volatile acids, p. p. m. 373 696 91 7.0 7.0 0.0 PH 24-hour B. 0. D., p. p. m. per % volatile matter ( I ) 1180 1810 850 24-hr. gas, cc per gram volatile matter ( I ) 72 123 42 Moisture drained in 7 hours, 81.1 96.2 71.0 Table 111-Analysis
Literature Cited (1) Buswell and Neave, State Water Survey, Bull. SO (1930). (2) Buswell and Pearson, “Further Observations on Rapid-Stage Sludge Digestion.” Seu’age W o r k s J . , 3, No. 2 (Aptil, 1931). (3) Buswell and Symons, Ibid., 2, 378 (1930). (4) Fuller and McClintock, “Solving Sewage Problems,” McGraw-Hill, 1926. (5) Heukelekian. Sewage W o r k s J.,2, 224 (1930). (6) Rudolfs and Fischer, P u b l i c W o r k s , 67, 171 (1926).
u
U. S. Supplies China with Large Amount of Old Newspapers The United States supplied 97 per cent of the over-issue newspapers imported into Hong Kong, China, during the fiscal year ended April 30, 1931, total receipts of which amounted to 26,545 short tons, according t o a report received in the Department of Commerce. Most of these over-issue newspapers are reexported to the coast ports of South China, and from there find their way into the interior towns. Over-issue newspapers are in demand in China by the manufacturers of firecrackers, by the poorer classes as a substitute for window glass. and bv small shoDs to wraD purchases. This latter use i s b y far the most important.
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1156
Vol. 23, No. 10
Distribution of Ether Extractive in Slash Pine' E. F. Kurth* and E. C. Sherrard3 FOREST PRODUCTS LABORATORY, MADISON. WIS.
The extractive in young slash pine trees that appear been generally reported ( 2 , 1 1 , to contain only sapwood is not uniformly distributed for its primary object 12, 14). Owing to the many throughout the trunk. Some sections of the trunk a determination of the methods used by these invesrun very high in material of an oleoresinous nature, resin distribution in the saptigators, no definite concluwhereas other sections run relatively low in this mawood of turpentined and unsions can be drawn regarding terial. The distribution of the extractive in all the trees turpentined slash pine, Pinus the effect of seasoning on studied, however, follows certain definite rules. caribaea M o r e l e t . Slash the solubility of the extracThe separation and characterization of the conpine is of special i n t e r e s t tives. The s u b s t a n c e s exstituents composing sapwood extractive is a long procbecause it is an important tracted are of such chemical ess. It can, however, be definitely stated from the res o u r c e of naval stores and nature that they are very sults of this investigation that the extractive contained is becoming of increasing insusceptible to the action of in the sapwood differs in character from that conterest to the pulp and paper light, heat, air, and chemical tained in heartwood or from the gum oleoresin formed industry. reagents. by wounding the tree. The difference between the sapThe distribution and comwood extractive and the heartwood extractive may be position of the extractives in Description of Stands caused by a greater dilution of the resin acids in the young conifers have not been sapwood by esters than in the heartwood. Similarly, The slash pine used for this thoroughly studied. I n fact, gum oleoresin may differ from both heartwood and sapstudy was collected from four in many instances no distincwood extractive by the presence of a larger portion of separate stands by B. H. Paul,, tion has even been made beesters and unsaponifiable material in the latter two. silviculturist, F o r e s t Prodt w e e n sapwood and heartThe composition of the extractive in the sapwood of ucts Laboratory. Stands 1 wood extractives, a l t h o u g h slash pine cannot be regarded as uniform, but is and 4 are on low, moist sites. the resin content of sapwood transitional, changing with the age of the wood. This Stands 2 and 3 are on areas is very much less than that of is further demonstrated by a preliminary investigation having a somewhat higher heartwood. of the unsaponifiable portion of the ether extracts, elevation than is common for G o m b e r g (6) has deterwhich reveals that the outer rings of the sapwood conslash pine. mined the amount. of ethertain appreciably larger quantities of sterols. Stand 1, which is near Cogsoluble material in turpendell, Ga., consists principally tined and untumentined trees of longleaf pine containing a large proportion of heartwood. of young slash pine trees of rapid growth, ranging from 8 The ether extractive present in certain specimens of maritime to 18 years of age. The trees are distributed irregularly pine has also been investigated (4, IS). Filipovich and over the area and have large spreading crowns. The diameVuisotzkii (5) state that the resin of Pinus silvestris varies in ters of the trees range up to 10 inches, breast high. Stand 2 is on old pasture land near Waresboro, Ga. The composition according to the season and to the height in the tree, the amount of unsaponifiable material increasing with forest land is about as high as the surrounding cultivated height from 7.34 per cent a t the level of the ground to 9.7 fields but it is not far distant from a typical slash pine-cypress swamp. The trees logged from this stand were young and per cent at a height of 8.34 meters. The most satisfactory method of obtaining the crude resin thrifty, and were rather openly spaced. They varied in age from the wood of the conifers is by extracting it with inert from 16 to 24 years, and in diameter from 8.7 to 11.0 inches, solvents. Ethyl ether, gasoline, and petroleum ether all breast high. yield light-colored extracts. Acetone, methanol, ethyl alcoStand 3, which is also near Waresboro, Ga., is a rather dense hol, and benzene-alcohol mixtures show greater extractive second-growth stand of slash pine growing on an old field. powers. The extract, however, is darker in color and usually This stand borders a small water course which contained turbid. Ethyl ether, being a pure compound and thus hav- practically no water a t the time the trees were cut for this ing a definite boiling point, was the solvent chosen for this study. The trees logged stood about 100 feet from the investigation. It dissolves both hydrocarbons and oxygen- water course on land said never to have been covered by high ated compounds, but very little of the water-soluble con- water. The trees on account of crowding were growing slowly a t the time of cutting The trees ranged in age from 25 to stituents. The ether extractives of the genus Pinus consist primarily 30 years, and in diameter from 7.3 to 8.7 inches, breast high. of resin acids, essential oils, fats and fatty acids, and un- A few loblolly pine trees were scattered throughout the stand. saponifiable or inert matter. They, therefore, differ in comStand 4,which is near Lake City, Fla., is of the cypressposition from the gum oleoresin from longleaf and slash pine slash pine forest type. The stand is rather closely stocked obtained by wounding the tree, which is generally regarded with trees of 30 to 35 years of age. The diameters of the as a solution of resin acids in turpentine. Schorger (9) has trees at breast height range from 2 to 10 inches. reported an analysis of slash pine leaf and twig oil, the comThe color of the wood in the center of the older trees (25position of which differs from that of gum turpentine (3) 35 years) was of a deeper shade than the adjoining wood. and also of crude wood turpentine (8). The contrast in color was noticeable in several instances only A decrease in the resin and fat content with seasoning has after the cut end had been exposed for several days. The 1 Received April 6, 1931. Presented before the Division of Cellulose wood in this area was not in all respects true heartwood, but Chemistry at the Slst Meeting of the American Chemiral Society, Indianappeared to be in the transitional stage from sapwood to apolis, Ind., March 30 to April 3, 1931. heartwood. Figure 1 shows representative specimens of 9 Junior chemist. slash pine. Principal chemist.
T
HIS investigation had
