T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
July, 1 9 1 4
to that resulting from the aeration of sewage. It is free from offensive odor and comparatively stable. Partial analyses of this sludge, made during March, gave the results appearing in Table 11. TABLE 11-PARTIAL ANALYSESO F ACTIVATEDSLUDGE (PERCENTAGES) DRY COMPOSITION OP DRYSOLIDS DATE ORGANIC MINERAL FATS 1916 MOISTURE SOLIDS ~. 33.9 7.3 1.21 66.1 March 5 . . , , , , , , , , , 98.79 9.1 28.9 1.42 71.1 98.58 IO., ,, , ,.,, 9.4 72.3 27.7 1.84 18 . . . . . . . . . . . . 9 8 . 1 6 11.6 74.8 25.2 2.30 27 . . . . . . . . . . . . 9 7 . 7 0 ~
,.
T h e increasing percentage of dry solids, organic matter, and fats in the accumulating sludge is worthy of note. The analyses in Table I1 were made o n sludge resulting from 2 hrs.' sedimentation. T h a t there is a wide difference in the volume of sludge after different periods of sedimentation is shown by Table 111. AFTER DIFFERENTPERIODS TABLE 111-VOLUME OF ACTIVATEDSLUDGE OF SEDIMENTATION IN MEASURING GLASSES
Sedimentation Periods
(Hrs.).., . . . . . . . . . . .
Sludge (per cent of sample) . . . . . . . . . . . .
'/a
S/a
1
11/t
2
3
4
18
2 5 . 0 2 2 . 0 2 0 . 7 1 8 . 6 16.6 1 4 . 7 1 3 . 3 1 2 . 8 1 1 . 3
PERIOD OF SEDIMESTATIOS REQCIRED
T h e amount of suspended matter remaining in the aeration tank liquor after different periods of aeration on April 6, 1916, gave the results noted in Table IV. IN AERATION TANK LIQUOR DIFFERENTPERIODS OF SEDIMENTATION Period oi Sedimcntation, 1io:ir; . . . . . . . . 1 I : : I 2 1 8 Suspended .\latter i i i Supernatact Liquor. 260 86 6 ; 5 ) ,31 2: Reduction ?I? C;edimc:itation in Succecdinz Period.,, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 22 14 18 10 Reduction per H o u r . . . . . . . . . . . . . . . . . . . . . . . . 696 44 14 9 2.5
TABLE IV-SUSPENDED MATTER(P. P. M.) AFTER
Though a very large proportion of the suspended matter was removed by 'I2 hr.'s sedimentation considerable fine suspended matter continued t o settle after that. Undoubtedly mass action in a large tank would bring about more rapid sedimentation. AMOUNT O F AIR REQUIRED
Considerable trouble has been experienced from frothing due to the soapy character of the wastes aerated and caused principally by the necessity of discharging some w-ool-scouring liquors into the wastes channel without degreasing until certain improvements in the degreasing plant have been completed. This trouble has necessitated cutting down the air supply to the minimum which will furnish sufficient agitation. At a rate as low as 0 . 2 5 cu. it. per hr. of air per gal. of wastes aerated, 20 hrs.' aeration was insufficient to produce stability. There are indications t h a t double this rate of applying the air will be more economical. Even a t the higher rates of application of air the aeration-tank liquors show only about 15 per cent saturation of dissolved oxygen after 20 hrs.' aeration. It is hoped that the period of aeration may be materially shortened as the tests progress. T h e effect of a n increasing proportion of activated sludge, of reduction in the temperature of aeration, and of variation in the depth of liquor aerated remain to be studied, 14 BEACONSTREET,BOSTON
TREATMENT OF PACKING-HOUSE SEWAGE BY AERATION IN T H E PRESENCE OF ACTIVATED SLUDGE By PAULRUDNICKA N D G L. NOBLE
Chief Chemist and Chemist, Armour & Company
This paper is a brief account of experiments with the activatedsludge process1 on sewage from the plant of a r m o u r & Co., a t Chicago. An idea of the extreme variation in the nature and composition of the different kinds of sewage involved may be obtained 1 G. J. Fowler, E. Ardern a n d W.T. Lockett, J . SOC.Cham. I n d . , 3 1 (1912), 471; E. Ardern a n d T1'. T. Lockett, I b i d . , 33 (1914). 523 and 34 (19151, 937; E. Bartow and F. W. Mohlman, THIS JOURNAL,7 (1915), 318 and 8 (1916). 16; T . C. Hatton, Eng. r e v s , 74 (1915). 134 a n d Eng. Rec.. 72 (1915), 481.
4.51
from the following list of the more important departments where this sewage originates: Hog, beef and sheep abattoirs, power plant, lard refinery, oleomargarine, meat-canning, meatcuring and sausage departments, rendering tanks, fertilizer plant, several other smaller departments, a n d t h e domestic sewage of 10,000 employees. This sewage is much more concentrated than domestic sewage, containing approximately four times as much suspended solids. Averages of recent analyses, including analyses of night and holiday sewage, show the composition in Table I. The suspended solids consist largely of organic material. The high content of inorganic matter is caused to great extent by the deep-well water used in many departments, the total solids of which is more than 2 , 0 0 0 parts per million. TABLE.I-SOLIDSI N R A W SEWAGE: PARTS PER MILLION Organic suspended solids.. . . . 425 Organic.. . . . . . . . . . . . . . . . . . 560 Inorganic, . . . . . . . . . . . . . . . . . 2990 Inorganic suspended solids. 75
.. -
~
Total..
. . . . . . . . . . . . . . . . . . . 3550
Total suspended solids.. . . . . . 500
Sewage from each of the three main outlets is pumped into a weir box, which also acts as a small grit chamber. From this the sewage passes into a n aerating tank I O ft. by 2 0 ft. by IO ft., where it is aerated for I O hrs. A partition is arranged so -that the path of the flow is about 40 f t . long. Sludge containing 9 9 . 5 per cent water, which has been aerated for 3 hrs., is introduced into the aerating tank a t the same point as the raw sewage a t the rate of 30 per cent of the raw sewage flow. The aerating tank is fitted with underflow and overflow baffles, and the air is distributed by means of 3./4 inch pipes perforated with l / p ~ in. holes, z in. apart and staggered, t h e pipes being placed a t 4-it. intervals a t right angles t o the line of flow. Sfter leaving the aeration tank the sewage is allowed to settle 40 t o 60 min. in a separate chamber. The sludge is siphoned continuously into the sludge storage and the effluent continuously flows over the edges of the settling chamber. T h e air is measured by means of a n orifice and differential manometer: 3 cu. ft. of air are required per gal. of sewage. This includes the air used for siphoning the sludge from the settling chamber t o the sludge storage and from the sludge storage to the aerating tank for inoculation. T h e effluent is fairly clear and practically odorless. T h e methylene blue test1 shows that it is nonputrescible for a t least 4 days. Typical sanitary analyses of the effluent are shown in Table 11. TABLE11-NITROGEN CONTENTSOF EFFLUENT: PARTSPER MILLION Albuminoid 2.40 7.40 3.00 4.10 2.50
Ammonia 23.80 16.20 31.20 27.90 28.60
Nitrite 0.60 0.07 0.25 0.15 Trace
Nitrate None None None None None
The change in the composition of the sewage caused by the aeration process is concisely shown in Table 111, which gives the percentage of decrease of certain constituents. TABLE111-APPROXIMATE PERCENTAGE REDUCTIONOF CERTAIN CONAlbuminoid nitrogen 96
STITUEKTS BY AERATION Ammonia Total organic Total organic nitrogen nitrogen matter 71 66 70
Suspended solids 95
A very important factor in the decomposition of the sludge is its high content of moisture and the difficulty of dewatering it in large quantities. A summary of a series of analyses of TABLE I\'-ANALYSES
SLUDGE:RESULTSIN PERCENTAGES AMMONI,A(~) NITROGEN(U) F A T (.a ,) Number of analyses 12 18 18 17 M a x i m u m . . . . . . . . . . 99.70 7.84 6.46 9.36 3.60 2.96 1.98 M i n i m u m . . . . . . . . . . 99.10 5.57 4.59 5 . 54 Average. . . . . . . . . . . . 99.48 ( a ) Calculated t o a commercially d r y (10 per cent moisture) basis. OF
AMOISTURP,
sludge obtained from the experimental unit is given in Table IV, which shows also the limits which may be expected for the fertilizer value and the fat content of the dried sludge. 1 Am. Pub. Health Assoc , "Standard Methods for the Examination of Water a n d Sewage," 2nd E d , 1912, 63.
6j 2
T H E JOCRjVAL OF I N D U S T R I A L A N D ENGILVEERING CHEMISTRY
The dry sludge contains very small proportions of phosphoric acid (approximately z per cent calculated as PzOs) and potash (approximately o . 4 per cent calculated as K20) and its fertilizer value therefore lies entirely in its content of nitrogen. Much work has been done to find some practicable means of dewatering the sludge so t h a t i t may be obtained in a form in which it can be dried in the driers regularly used for handling fertilizer materials. The moisture content of the wet sludge coming from the settling chamber must be reduced from 9 9 . 5 to j o per cent if possible. The importance of this problem is brought out much more clearly when i t is considered t h a t such reduction involves the removal of almost 99 per cent of the weight of the wet sludge as i t comes from the settling chamber Filter pressing in the ordinary type of filter press and in the newer forms, such as Kelly or 3,veetland presses, has proved entirely unsuccessful. The filter cloths are very rapidly clogged. A special type of F.lter press may be developed for this purpose and experiments in t h a t direction are under way. Centrifuges of the imperforate-bowl type have also been tried, b u t i t will be difficult to construct a machine of sufficient capacity t o bring the cost of installation t o a nonprohibitive amount. After the sludge has been reduced to a j o per cent moisture content it can be readily and cheaply dried in the usual driers employed for drying organic ammoniates for fertilizers. As available space is a n important consideration. a n investigation into the possible depth of aerating tanks was made. Two pipes 14 in. in diameter vvere erected, one 36 f t . and the other 18 it. high The air, which was discharged through perforated pipes, mas allowed to pass into each unit in equal amounts. The sewage used for t h i ~experiment came from the beef abattoir. Samples were taken a t regular hours covering several days and the albuminoid, ammonia, nitrite and nitrate nitrogens, and the putrescibilitp were determined.. d s the results in either pipe were practically identical i t was concluded that a n aerating tank of any depth to 36 ft. \vi11 produce a.s good results as a more shallow tank in respect to purification of sewage. Economy in consumption of air should also be considered in this connection. The bacteriological data are too meagre t o warrant conclusions, but two facts are apparent: ( I ) three or four hours' aeration of the sludge from the settling chamber increases the number of organisms, but further aeration reduces them somewhat; ( 2 ) the organisms grov better a t 20' C. than a t 37 O C. as might be expected, Throughout the records there seems to be a correlation between warm sewage temperatures above 75 F. and inactivity of the organisms, which results in a n inactive sludge. This may be an obstacle t h a t will prevent the placing of a disposal plant close to the abattoir where the sewage temperature may suddenly change from cold to hot or vice xnu. The results of the experimental work warrant the belief t h a t this process offers more promising possibilities than any of the other methods of disposing of packing-house wastes hitherto proposed. The relatirely small area required for installation, the comparatively high nitrogen content of the sludge, the comparative clarity and stability of the effluent, and the relatively short time of treatment are perhaps the most important features of the proccss. C I I E ~ C Si,riBon.kTonY, I~ Amrocn b Conp.mr L-IIOK STOCK TARDS, CHICAGO
CHEMICAL OBSERVATIONS ON THE ACTHVATEDSLUDGE PROCESS AS APPLIED TO STOCKYARD SEWAGE By AKTAURLEDERER Chemist, Sanitary District of Chicago
The Sanitary District of Chicago began experiments xyith the activated-sludge process of sewage purification on the sewage of Stockyards and Packzingtown in April, r g r j . The operation on the fill-and-draw plan \?-as conducted in two zoo-gal.
T'ol. 8 , No. 7
galvanized iron tanks well into the cold season, being discontinued when the contents of the tanks froze. Certain observations can be explained by the effect of low temperatures on the process. These observations xere substantiated on the larger +unit installation of the Sanitary District designed to treat 30,000 t o IOO,OOO gals. a day on the continuous-flow basis. This installation was put into operation early in 1916 under the direction of Langdon Pearse. The object of this paper is to elaborate certain chemical and biological facts, which have presented themselves in the course of operation, and not to furnish any prescription for the treatment of the stockyard waste. The features of opcration now being worked out will require much time and experience before final recommendations can be made. Economically the continuous-flow proccss seems preferable, but it has certain disadvantages TThich the fill-and-draw plan aroids. Experience from our OTT'I~ experiments and those of others will probably indicate the solution. Like other sewage-treatment processes, this is governed primarily by the composition of the waste. The process, being largely biological in nature, is greatly influenced by the temperature of the sewage. In this respect the stockyard waste lends itself readily t o the process, the tcmperature T-arying between 60' and 90' F . throughout the year a t the Center Avenue outlet. The fall of tempcrature in the plant is only a ferv degrees in the coldest winter weather. By far the greater percentage of the sewage treated is packinghouse waste. The -variation in discharge and composition between day and night waste is extremely marked. The frce oxygen demand is approximately 8 to I O times greater than t h a t of the domesik sewage oi Chicago. The changes of the nitrogenous constituents during the aeration process have been carefully studied. Our experience has coincided, so far as I a m avare, with the experience of other observers. During the warmer season a decrease of ammonia nitrogen t o about I or z parts per miliion and a n increase of nitrife nitrogen to 5 or I O parts per million indicate complete oxidation and clarification. \Then colder weather set in, however, this ceased to be the condition with the small galvanized iron tanks, which were easily affected by changes in temperature ol' the air. Absolute stabilities were reached in cold days with ammonia nitrogen actually increasing several hundred per cent and n4th little, if any, change in the nitrite and nitrate nitrogen. The reduction of the organic nitrogen was just as marked as in summer. Clarification was very satisfactory. The results mentioned are those noted when the effluent showed a relative stability of IOO or thereabouts. \X7ith the small galvanized iron tanks, in which the warm sewage quickly chilled, i t took longer in cold weather t o obtain such high stability, but the chemical results were consistently as noted. It is clear t h a t the mechanical features of the process outweighed the biological features. The higher putrescible colloids have siniply been whipped out of suspension by the continuous agitation. Repeated obser\-ations indicate t h a t the mere mechanical removal of the colloidal matter from sewage brings about a n improvement far out of proportion t o the actual percer,tage of substance removed. There is n o doubt, however, t h a t there is some biologic activity e w n in a liquid near freezing; otherwise the persistent increase in ammonia nitrogen could hardly be explained. Various active protozoa, such as infusoria and trachelomonas, also were noted in the sludge a t ali times. More highly developed animal or plant orgallisms vvere not found. Our work indicates t h a t the tempcrature of the liquid treated will be a controlling factor. On a large scale changes in temperature wiil probahly be much srnaller than cn the rery small scale of zoo-gallon stcei tank. exI)osed to weather. During cold Txeathrr, remoral of colloidal matter was the only immediate indication of accomplished oxidation. Determina-
