Jan., 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
The effluents obtained from t h e tanks during this 6-hour cycle were not all stable, yet t h e average improvement was so great t h a t t h e conclusion was reached t h a t activated sludge may be built up b y changing sewage a t frequent intervals without complete nitrification of each dose of fresh sewage. A considerable degree of purification is also obtained from t h e beginning of t h e operation, and t h e time for building up adequate sludge for t h e process is cut down very decidedly. A later experiment with t a n k C showed t h a t satisfactory activated sludge could be built upon a 6-hour cycle. D I F F U S I O K A R E A REQUIRED-The bottom Of t a n k contains 3 sq. f t . of Filtros plates as described above; the bottom of tank D contains I sq. ft. These tanks were p u t in operation July 6th and t h e sewage was changed every 6 hours. There was a noticeable difference in t h e working of these tanks. C gave some stable effluents after 5 days; D did not give stable effluents in 18 days. The sludge from C was of good appearance, while t h a t from D was not as flocculent a n d at times had a septic odor. During t h e comparative experiment a n average of 450 cu. ft. of air per 400 gallons of sewage was used with C and of 360 CU. ft. of air per 400 gallons of sewage with D. The amount of air given D was always sufficient t o keep the sludge mixed with the sewage. I n fact, the sewage in D was agitated much more violently t h a n t h a t in C. We have concluded t h a t I sq. ft. of Filtros plate per I O sq. f t . of floor area is hardly sufficient. Of t h e four tanks, C, with 3 sq. ft. of Filtros plate per I O sq. ft. of floor area, has given t h e best results. We have noted t h a t it is quite essential t h a t t h e plates be as nearly as possible a t t h e same level. A variation of in. in level will cause uneven air distribution. The distribution seems t o become more uniform t h e longer t h e plates are used. Q U A L I T Y O F EFFLuENTs-The quality Of t h e effluents has usually depended more on t h e strength of t h e raw sewage t h a n upon any other variable. The tanks, when operating on a 6-hour cycle, were filled a t 9 A.M., 3 P . M . , 9 P.M., and 3 A . M . The strength of t h e raw sewage, estimated b y t h e free ammonia values, averaged for t h e 9 A.M. sewage between 20 and 2 5 parts per million, for the 3 A . M . sewage between 3 and 1 2 parts per million. Nearly all of the 3 A.M. sewages have given stable effluents, b u t t h e strong morning sewages have quite frequently given putrescible effluents. Unless the sludge is in good condition, a n d well nitrified, a strong sewage cannot always be purified in 4 ’ / 2 hours even b y increasing t h e air to 800 cu. f t . per 400 gallons. I n t h e normal working of t h e plant t h e sludge will usually regain its “activity” if 800 cu. ft. of air is applied for several periods after t h e strong sewage has been added. At times, however, with a succession of strong sewages, it is necessary t o increase t h e time of aeration in order t o obtain good effluents. Ardern and Lockett’ noted in their first paper that if t h e aeration was stopped before t h e sewage was well nitrified, t h e activity of t h e sludge would be inhibited. When strong sew-
c
1
J . SOC.Chern. Ind.. 33, 623-39.
I7
ages are t o be treated a definite cycle of operation cannot be established without provision for longer aeration of the sewage or separate aeration of t h e sludge. I n order t o keep t h e sludge in its most active state, complete nitrification of each sewage is necessary. Effluents are usually stable if 50 per cent of the free ammonia is removed, and 2 t o 3 parts per million of nitrogen as nitrates are present. A completely nitrified effluent is neither necessary nor economical. The greatest efficiency in air consumption will be obtained when enough air is used t o make t h e sewage non-putrescible and t o keep t h e sludge activated. The operation of t h e plant during six months has suggested t h e advisability of studying more carefully such other features of t h e process as t h e amount of sludge formed, t h e building up of nitrogen in t h e sludge and the composition of t h e effluent gases. STATE WATBRSURVEY U N I V E R S I T Y OF ILLINOIS. URBANA
FERTILIZER VALUE OF ACTIVATED SLUDGE’ By
EDWARD BARTOW AND W. D. HATFIBLD
Activated sludge is a n essential material a n d a n important product in a new method of sewage disposal, which was first described by Ardern and Lockett12 of Manchester, England, in 1914. At present, September, 1915, experimental plants are being operated at Baltimore, Md.; Chicago, Ill.; Cleveland, 0.; Houston, Tex.; Milwaukee, Wis.; New York City; Regina, Saskatchewan; Urbana, Ill. ; and Washington, D. C.3 At Baltimore a modified Imhoff t a n k is t o be operated with continuous flow. At Milwaukee both fill and draw and continuous flow processes are being operated on a n experimental scale, and a z,ooo,ooo gallon plant is under construction. At Cleveland a I,OOO,OOO gallon plant is t o be built. At Urbana a n experimental plant of 6,000 gallons capacity is being operated on t h e fill and draw system. As in other sewage disposal processes, t h e ultimate disposal of t h e sludge is of great importance. Near t h e seaboard it is possible t o carry this sludge out t o sea, but in t h e interior, t h e problem of sludge disposal is often very serious. I n the experimental plant at the University of Illinois, in Urbana, we have tried t o study all phases of t h e process14 a n d have paid especial attention t o t h e sludge. The amounts of sludge formed a n d its chemical corhposition evidently vary with t h e concentration of the sewage, a n d with temperature conditions. The sewage treated in t h e experimental plant during rainy weather contains large amounts of diluting water, which reduces t h e amount of sludge per unit of water. The diluting water carries considerable dirt from the streets which reduces t h e nitrogen content of t h e sludge obtained. Also during warm weather, bacteriological action is more rapid, and, 1 Presented a t the j l s t Meeting of t h e American Chemical Society, Seattle, August 31-September 3, 1915. * J. SOC.Chsm. I n d . , 33 (1914). 523, 1122. a Eng. News, 74, 164-70 4 THIS JOURNAL, 7 (1915), 318.
T H E J O U R N A L OF IIVDUSTRIAL A N D ENGINEERING CHEMISTRY
18
apparently, t h e a’lllount of sludge is considerably reduced. The sludge obtained in t h e process is flocculent, resembling a freshly formed precipitate of ferrousferric hydroxide. I t separates easily from t h e clarified water, a n d after one hour’s settling contains from 96 t o 98 per cent of moisture. On further standing, about one-half of this water can be removed. The remaining material can be dried by filter-pressing or by drying on beds of sand and evaporating over steam baths. Experiments with t h e worms found in t h e wet sludge’ have proved t h a t they are not essential to t h e purification process. Nitrifying bacteria, and bacteria which have t h e power of destroying organic matter have been isolated from t h e sludge. The nitrifying bacteria alone will not purify sterile sewage. A combination of t h e nitrifying bacteria with t h e other varieties will purify sterile sewage very satisfactorily. This work carried on with R . Russell will be described in another article. The disposal of the sludge can be most easily accomplished if it has manurial value. T h a t activated sludge has manurial value is shown by its chemical composition, by its reaction with various soils, and by its effect on the growth of plants. Specimens of sludge obtained at t h e experimental plant have varied in nitrogen content from 3 . 5 t o 6 . 4 per cent. The lower values were obtained during periods of high water. Street wash was getting into t h e sanit a r y sewers and since no grit chamber was provided t o remove t h e grit, t h e nitrogen value of t h e sludge was greatly lowered. The tests of the fertilizer value have been made on t h e richer specimens which were first obtained. Through the courtesy of Mr. Paul Rudnick, chief chemist, Armour & Company, Chicago, t h e availability, according t o alkaline permanganate method as used by the Kew England states, was shown t o be below jo per cent (44.7per cent), and the sludge would be classed as a n inferior ammoniate, but the availability according t o t h e neutral permanganate method which has been adopted by t h e southeastern states was shown t o be above 8j per cent ( 8 9 per cent), and would therefore be classed as satisfactory. Tests have been made by Professor C. B. Lipman, according t o a method described by Lipman and Burgess,2 in which a fertilizer and a soil are incuba-ted for a month. The amount of nitrogen changed into nitrate is then determined. This amount is a n index of t h e availability of the nitrogen with respect t o t h e soil used. The results obtained were reported by Professor Lipman, as follows: “The activated sludge used contained 6 . 2 per cent total nitrogen and no nitrate. The hundred grams of soil in every case contained nitrate as follows: Anaheim soil, 1.0 mg. N. Davis soil, 0.3 mg. N.
Oakley soil, 0.1 mg. pu‘.
The amounts of nitrate produced in one month’s incubation from the soil’s own nitrogen and from the nitrogen of the sludge 1
THIS JOURNAL, 7 (1915),319.
2
Univ. of Calif., Bull. 261 (1915).
Vol. 8, S o .
I
mixed with the soil in the ratio of one part of sludge per hundred of soil is as follows: Milligrams nitrate produced Without sludge W t h sludge Anaheim.. . . . . . . , , , , , , . 6 . 0 10.0 Davis.. . . . . , . . . . , , , . , , 4 . 2 14.0 Oakley ......... 2.2 4.0 SOIL
.
The Davis soi best nitrifying soil of the three, especially for high-grade organic material. Anaheim is next, and the Oakley by far the poorest. Indeed, the last named does not nitrify the nitrogen of dried blood at all in a period of a month in the incubator. These figures indicate that the general tendency is to make available the nitrogen of sludge in type soils at about the same rate that nitrogen is transformed into nitrate in such organic nitrogenous fertilizers as fish guano. While it seems to hold a medium position, it nevertheless resembles very much more closely in its general characteristics, so far as available nirrogen is concerned, the so-called high-grade organic nitrogenous fertilizers, dried blood and high-grade tankage, etc., rather than the low-grade nitrogenous fertilizers, steamed bone meal, cottonseed meal, garbage tankage, etc.” Although the chemical tests and t h e nitrification tests with soils indicate t h a t the activated sludge has a h’gh fertilizer value, t h e final test must be its effect on plant growth. Pot cultures, using wheat, were started in March, 1 9 1 5 ,under ~ She general direction of Professor C. G. Hopkins and with t h e assistance of Mr. J. C. Anderson. The contents of t h e pots in which the wheat was planted were as follows, in grams: Pot No.
I...
,
,
White sand 19,820
Dolomite 60
19,820
60 60
4.. . . . 19,820
ActiBone Potassium vated meal sulfate sludge 6 3 0 6 3 0 6 3 20 6 3 0
Ex-
tracted sludge 0 0
Dried blood 0.0 8.61 0.0
20
0.0
Each pot contained a n equivalent of j tons per acre of dolomite, l/2 ton per acre of bone meal, and 500 lbs. per acre of potassium sulfate Pot I, t h e check pot, contained only the 60 mg. of nitrogen which were added in the bone meal: this small amount was without significance since the same amount was added t o t h e other pots. Pot z contained a n equivalent of 1 2 0 lbs. of nitrogen per acre added in the form of dried blood. Pots 3 and 4 contained a n equivalent of 1 2 0 lbs. of nitrogen in the form of dried activated sludge (one ton of sludge) per acre. The sludge used analyzed as follows in percentages: Total nitrogen 6.3
Phosphorus (P205)
ETHERSOLCBLE 3 hrs. extraction 16 hrs. extraction
2.69
4.00
11.8
Thirty wheat seeds were planted, z seeds in each of I j holes, in each pot. I n 4 days t h e plants were up in each pot and in I O days were j in. high. At the end of 18 days t h e plants were thinned t o 1 5 of t h e best in each pot, in most cases leaving one plant t o each hole. I n 2 0 days from date of planting there was a marked showing in favor of t h e plants in Pots 3 and 4. I n 2 3 days the plants in Pots 3 and 4 (see Fig. I ) were growing far ahead of those in I and 2 . The plants in Pot 2 fertilized with the same amount of nitrogen grew much more slowly than those in 3 and 4. The reason for t h e poor showing of the plants in Pot 2 is not known. I n 30 days a slight brown mold appeared on t h e 1
Twrs JOURNAL. 7 (1913,318-320.
T H E J O U R N A L O F I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Jan., 1916
larger plants, which may have been due t o t h e dark, d a m p weather. Powdered sulfur was used t o fight
it.
,
During the fifth a n d sixth weeks the plants in t h e pots fertilized with t h e sludge, which had grown fully three times a s large in height and in t h e amount of foliage as those in t h e pot fertilized with dried blood, began t o yellow. About half of t h e foliage died,
19
The surprisingly rapid growth of the wheat fertilized by the sludge must be due for t h e most part t o nitrogen present in a very available form. It may be due in part t o the phosphorus (2.69 per cent) which is present in t h e sludge. At t h e time of making the pot cultures we did not consider t h e phosphorus since it was present in such a small quantity. The growth may be due in part to the organic matter
r
1
FIG.I-WHBIT
Ssaizs I. 23 DAYSAS~TBI
Fm. 11-WHEAT
PLANTINO
SBIIBS I. b3 DArs APTSR PLANTINO
FIG 1 1 1 - w ~S~m ~ m s~ 11, 35 DAYSAPTBR PLANTING
Each pot contained pure white s n d to which the same amounts of plant food (crcept nitrogen) had heen added below: No. I , the check. matnincd pr~cticnlly00 nitrogen To each of the other pots WBS added the nitrogen rquivaleot of 20 mems of dried aetlvatcd ilvdge In the form indiented below: Nor 2 ood 13 No. 3 No. I No. 5 No. 7 No 9 Sodium Ammooium 2 0 g. Dried Activated Sludge 20 g. Drisd Aetivafcd Sludge Dried 20 g. Dried Nitrate Sullatc Extrnefed with Ligroin Extracted with Ether Blood Activated Sludge
leaving two healthy stalks t o each plant. The plants possibly grew so fast, a t first, t h a t all the foliage which had started could not develop. The remaining stalks immediately grew stronger a n d of a deeper bluegreen color. After 9 weeks t h e plants were strong a n d healthy (see Fig. 11). In 14 weeks the plants in Pots 3 and 4 began to head a n d in 1 5 weeks there were about 20 good heads in each. The plants in Pot I were very weak, while those in 2 were just beginning t o develop heads. When it was first noticed t h a t t h e plants fertilized with sludge were-growing much better than those fertilized with dried blood, in order to confirm t h e results, a second series of pot cultures was started. In this series t h e sludge was compared with dried blood, nitrate of soda, ammonium sulfate a n d gluten meal. This series contained 14 pots: 2 check pots, 6 containing nitrogen equivalent equal to a n application of 20 grams of sludge, and 6 nitrogen equivalent to 30 grams of sludge. The plants in this series grew faster t h a n those in t h e first because of better weather. They showed exactly t h e same characteristics t h a t t h e plants in t h e other series showed. The plants fertilized with sludge were t h e best. The results confirmed t h e results obtained in t h e first series. At the end of j weeks striking differences were noticeable (see Fig. 111). The pots containing t h e equivalent of 30 grams of sludge gave no better results than those with a n equivalent-of -20 grams. When the wheat matured i t was carefully harvested and calculations made t o determine t h e yield per acre. The results are shown in Table I. TABLB I-AMO~NTS 01 WIIBAT AND STRAW OBTAINBD IN THE h ~ s SrB I ~ S S YIELD OP S B B m YlSLD OF ST**W Pot N O No Grams Bu. per A. Av. stalk S e a r Ton$ per A.
No. bends reeds I...I4 85 2
..
189 3 . . 22 491 4 . . . 23 518 The mntml series 15
weds (ealet8l*ted) Length (in.) ~ r n m s(enleulatcd) 2.38 5.29 13.748 14.501
6.2 13.6 35.9 37.7
rcIyit3 corre.pooding
19.4 23.0
2.25 8.25
0.18 0.68
35.4 36.1
26.75 26.21
2.23 2.18
to
tho= of the first -des.
KO. I I
Gluten Meel
present in the sludge, since.the sand used contains no organic matter. The cause of t h e molding of t h e leaves has not yet been determined. I t was quite noticeable that the mold appeared chiefly on t h e leaves of rapidly growing plants. I n t h e first series i t attacked only plants fertilized with sludge. I n t h e second series i t also attacked the plants fertilized with gluten meal. The rapidly growing leaves are
I
1 naturally more tender t h a n those which grow slowly and consequently are more easily attacked by mold spores. The mold evidently does not come from t h e sludge because t h e extracted sludge surely would be sterile. and plants fertilized with i t showed the same mold. Plants fertilized with gluten meal also had the mold' The sludge causes such a rapid growth of wheat t h a t i t should be valuable to truck gardeners for rush-
T H E J O U R N A L OF IiVDUSTRIAL A N D EiVGINEERIXG C H E M I S T R Y
20
ing spring crops. T O test its value t o the inarket gardener, three plots each z ft. X 3 ft. were laid out in a field. One plot was not fertilized, one was fertilized with a n equivalent of 126 lbs. of nitrogen, one t o n of sludge per acre, and the third with an equivalent of extracted sludge. On April 24, 191j , two rows of radishes and lettuce were planted in each of t h e three plots. The plants in t h e plot where the extracted sludge was used came up first. a little ahead of those in the plot where t h e unextracted sludge was used. A t t h e end of z weeks t h e lettuce and radishes of the treated plots appeared t o be twice t h e size of those in the untreated plot. At t h e end of 4 weeks t h e plants were thinned. The roots of the radishes from the treated plots were already red and quite rounded near the tops while those from t h e untreated plots had not yet started t o s n d and had not become red. The lettuce plants from the treated plots were nearly twice as large as those from t h e untreated plots. On June I , 38 days after planting, t h e six best plants of lettuce and radishes were taken from each plot and are shown in Fig. IV. T h e differences in size are very marked. COMPARISOX OF THE LETTUCEAXD RADISHESPROM UNFERTILIZEDA N D FERTILIZED PLOTS Plot Treatment Wt. of lettuce Wt. of radishes l , . . . . . . . None 4 . 5 g. 2 3 . 4 g. 2 . . . . . , . . , Sludge 6 . 3 g. 6 3 . 0 g. 3 . . . . . . . . Extracted sludge 6 . 8 g. 6 8 . 0 g. I
The increase in weight, due t o t h e sludge, is 40 per cent in t h e lettuce, and Ijo per cent in t h e radishes. T h e radishes from t h e sludge pots, when cut open and eaten, were found t o be very crisp and solid, a n d t o have a good flavor, These pot cultures and gardening experiments show t h a t the nitrogen in “activated sludge” is in a very available form and t h a t activated sludge is valuable as a fertilizer. STATE WATERSURVEY UNIVERSITYOF ILLINOIS, URBANA
EQUILIBRIUM RELATIONS AMONG AROMATIC HYDROCARBONS PRODUCED BY CRACKING PETROLEUM’ By W. F. RITTMANAXD T. J. TWOMEY Received October 15, 1915
The results of several series of experiments on t h e cracking of petroleum in the vapor phase have served t o furnish evidence as t o t h e course a n d mechanism of t h e cracking reaction. I t has been indicated t h a t decompositions occur with two general effects: ( I ) decrease in size of molecule, and ( 2 ) decrease in saturation. A study of t h e relations among classes of hydrocarbons2 has shown t h a t certain conditions of temperature and pressure are favorable for t h e production of low-boiling aliphatic compounds, certain others for aromatics and still another set for t h e formation of carbon and gas: viz., u p t o 500’ C. for aliphatic formation, from j o o o t o 800’ C. for aromatics, and above 800’ C. for carbon a n d gas. A special study3 has dealt with t h e field of gas pro1
Published with the permission of the Director of the Bureau of
Mines. 2
3
Rittman, THISJOURNAL,7 (1915), 945. Whitaker and Rittman. Ibid., 6 (1914), 383, 472.
Vol. 8, S O .I
duction. and work has been done also t o determine conditions obtaining in t h e temperature range favorable for aromatic formation. One section of this work1 dealt with transformations in which pure aromatics were used as starting out material and cracked under carefully regulated conditions of temperature and pressure. The results described in t h e present communication approach t h e same end in a different manner. Here petroleum has been subjected t o cracking and, by t h e careful analysis of products, important relations have been discovered among the degrees of formation of certain aromatic compounds. THE 0 R E T I C4 L
I n the other experiments of t h e present general series t h e effects of temperature and pressure have been studied with care. I n t h e present study it has been necessary t o minimize the importance of these factors on account of experimental conditions which will receive discussion later. I t has been assumed t h a t t h e extent t o which cracking proceeds is in a general way proportional t o t h e specific gravity of t h e recovered oil or t a r . T h e absolute t r u t h of this assumption may be open t o some question but of its general correctness there is little doubt and it affords a convenient method of combining in one function t h e effects of the several variables in t h e cracking reactiontemperature, pressure, rate of feed and contact surface. The scheme followed has been to note t h e variations, with specific gravity of cracked oil, of t h e percentages of five hydrocarbons : benzene, toluene, xylene, naphthalene and anthracene. These five have been selected, partly on account of their scientific and commercial importance and partly because convenient analytical methods are available for their estimation. I n connection with a n y series of experiments i t is of importance t o consider a n y indications which may appear on t h e basis of previous knowledge. For the cracking reaction in general i t is possible t o make clearcut predictions as t o t h e effects of temperature and pressure. By calculating approximate equilibrium constants according t o t h e Nernst formula it is possible t o discover how t h e course of reaction varies with temperature. For t h e effect of pressure it is t o be noted t h a t increase in this variable is favorable in accelerating t h e cracking reaction up t o such a velocity t h a t equilibrium may be attained in the time allotted. Beyond this point increase in pressure is favorable or unfavorable, according as t h e reaction proceeds with decrease or increase of total volume. For t h e work here described i t may be noted t h a t all indications point toward t h e fact t h a t equilibrium was approached only remotely. The effect of pressure upon reaction velocity is therefore the one of importance. I n t h e present experiments primary consideration has not been given t o t h e effects of temperature and pressure, b u t instead t o t h e relative amounts of t h e various hydrocarbons produced under each set of cracking conditions. Temperature conditions were of course as significant as ever, b u t owing t o mechanical 1
Rittman, Byron and Egloff, THISJOURNAL, 7 (1915), 1019
