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suction pit for the pumps. X screen with vertical bars spaced with 3,’-in. openings prevents coarse material from reaching t h e pumps. A grit chamber 3 4 f t . long with z compartments, each one foot wide, was provided t o catch the heavy material. This was later discarded, owing t o modifications in the plant which will be described later. The sewage flows from the grit chamber into t h e aeration chamber, a ELECTROCHEMICAL LABORATORY, HAVEMEYER HALL, rectangular concrete t a n k 17 x 36l,’* f t . in plan and COLUMBIA Uh-IVERSITY, h’EW Y O R K C I T Y g l , ? ft. deep. A greater depth would have been desirable, but using an old t a n k , it was impossible easily t o obtain it. The aeration chamber, after allowances PURIFICATION OF SEWAGE BY AERATION IN THE are made for baffling and sloping bottom. has a capacity PRESENCE OF ACTIVATED SLUDGE-111’ of 36.000 gallons. It is dil-ided longitudinally by 3 B y EDWARD BARTOW The results obtained in experiments on t h e purifica- baffles into 4 compartments through which the sewage tion of sewage by aeration in t h e presence of activated flows a distance of about 1 4 0 ft. The lower part of sludge a t t h e Sewage Experiment Station of the Illi- each compartment has sides sloping toward the cenin. xide and 4 in. deep, and nois State n’ater S u r l e y a t t h e University of Illinois, tral part t o a channel the length of the compartment. Above the have been given in previous articles in THISJ O U R K A L .extending ~ channel, Filtros plates are supported on T-bars emT h e removal of ammonia, and the development of bedded in concrete. The channel belon- the Filtros nitrate nitrogen have been discussed. The process plates was divided into sections for six Filtros plates has been shown t o be essentially bacteriological. By each, with the expectation t h a t each set of plates analysis of t h e sludge, and by cultures of wheat, the would be separated from all the others and t h a t the sludge has been shown t o be valuable as a fertilizer. Exsupply of air t o each set could be regulated by an air periments in concrete t a n k s operating on t h e fill-anddraw plan h a r e shown t h a t sludge can be built up pipe and valve. I t was. however. found impossible t o rapidly without seeding from other sludges. During regulate independently the air for each set of plates. The aeration chamber was calculated t o treat 1 4 4 , 0 0 0 the building-up process t h e increase of the nitrogen gallons of sewage and sludge daily, if aerated during and phosphorus content of the sludge is very rapid. The necessity for oxygen has been shown b y t h e in- a period of 6 hrs.. I;O,OOO gallons if aerated j hrs.. and crease of carbon dioxide and the decrease of oxygen 2 1 6 , 0 0 0 gallons if aerated 4 hrs. From ; o , o o o t o 8 5 , in the effluent air. Since t h e previous articles were ooo gallons of sludge were puniped back into t h e aerawritten, a large amount of experimental work has tion chamber, for each I O O , O O O gallons of sewage added. been done in many plants in this country and in The calculation for the capacity of the chamber was, England. I t would be impossible t o mention them therefore, reasonably accurate. From the aeration all in an article of this length, so t h a t we shall confine chamber, the mixed sewage and sludge passes t o a ourselves almost entirely t o t h e work done a t t h e settling chamber 6 X 1o1I2ft. in plan and 11 ft. deep, Sewage Experiment Station of t h e Illinois State K a t e r a t its lowest point, having a capacity of 3>700gallons. If t h e sewage and sludge flowed through all parts of Survey a t the University of Illinois. t h e settling chamber i t would have a retention period COKSTRUCTION A S D OPERATIOS OF COKTINUOUS-FLOW of 24, 31 and 37 minutes, with a flow through t h e PLAKT In aeration chamber of 4 j j and 6 hrs., respectively. The continuous-flow plant which was put in opera- order t o assist the settling of the sludge t h e liquid tion during the summer of 1916 was expected t o handle passes down into the center and up around the edge of a 2 0 0 , 0 0 0 gallons of sewage and sludge per day and TTas hollow frustrum of a pyramid and overflom-s into built in a septic t a n k designed b y Prof. A. N. Talbot drains which entirely surround the settling chamber. in 1897 for t h e City of Champaign. The t a n k was reFrom the settling chamber the effluent flows over a constructed for t h e activated-sludge process. The weir and is either returned t o the sewer or discharged plant contains a screen chamber and pumping p i t , a into a pond, formed by two dams thrown across t h e grit chamber, a n aerating chamber, a settling chamber, abandoned bed of a stream. This pond covers about a blower room and a laboratory containing sludge- o I of an acre and has a maximum depth of 3 ft. drying apparatus (see Fig. I ) . A sludge-drying bed The sludge is withdrawn from the settling chamber and a pond into which t h e effluent from t h e process by an air-lift and can be discharged a t t h e place where may be discharged are also provided. The sewage is the raw sewage enters t h e aeration chamber or be drawn from t h e main outlet sewer from t h e City of diverted for experimental purposes or discharged into Champaign. The daily flow is estimated t o be from the sewer. Air is supplied for aeration and for the I , O O O , O O O t o I , joo,ooo gallons, though in wet weather, air-lift b y a rotary positive pressure blower, having owing t o seepage into the sewers, t h e amount of flow a rated capacity of 300 cu. ft. per minute, driven by is greatly increased. The manhole nearest the septic a 15-H. P. electric motor. The air is filtered through t a n k was modified t o serve as a screen chamber and cheesecloth spread over a box having sides of wire 1 Read at the Buffalo Meeting of the American Institute of Chemical netting, and is measured through a lTenturi meter. Engineers, June 20, 1917 The plant was operated from May 2 5 t o June 1 1 , 2 THISJOURNAL, 7 11915). 3 1 8 , 8 (1916), 15, 1 7 , and 646.
111-The increased corrosion a t the anode raises the current efficiency a t the cathode, particularly with rolled nickel anodes. IY-Corrosion in general with direct current or with superimposed A. C. is markedly affected by the mechanical nature of t h e metal. V-Alternating current alone has but slight corrosive effect a t the anode.
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1916, when it was shut down t o repair leaks due t o faulty concrete work. Much care should be taken in order t o make t h e concrete air-tight, or cast-iron or metal frames as used a t Milwaukee and Cleveland should be used. The plant was again put in operation on July 1 1 , and operated continuously until October 2 2 . The amount of sewage added during weekly periods varied from 61,000 t o 177,600 gallons per day. Approximately 2 cu. ft. of air per gallon of sewage was necessary t o obtain stable effluents. Undoubtedly better results could be obtained with increased settling capacity, and a steeper slope from t h e vertical sides t o t h e extreme bottom of t h e chamber. The actual period of flow through t h e settling chamber as determined by tests with fluorescein and with salt when t h e rate of pumping was 133,900 gallons per day, was found t o be 2 0 minutes instead of 34 minutes as calculated. A large chamber, or two chambers possibly, with a n arrangement for aeration between them, would undoubtedly increase t h e capacity of t h e plant. For further experiments t h e plant was modified by cutting out t h e grit chamber and inserting a short box, into which t h e sewage was pumped, The box is 4 f t . g in. X 1 1 in. in plan and I O in. deep and has a V-shaped weir a t t h e end for measuring t h e sewage. One-quarter of t h e aeration chamber was cut off from t h e remainder for a sludge-aerating tank. This decreased t h e length of flow in t h e aeration chamber t o 1 0 5 f t . The plant was again started January 17, 1917, and has been in operation continuously until t h e present time, June 1 2 , 1917. COMPARISON OF M E T H O D S OF AIR DIFFUSION
An important feature of t h e activated-sludge process I n t h e original experiments air was introduced into t h e sewage in bottles through small glass tubes. The relatively large bubbles delivered by this method made it appear feasible t h a t better air diffusion t o break up t h e air stream into smaller bubbles might be productive of increased efficiency, and t h u s become a n important feature in reducing t h e cost of t h e process. I n t h e first continuous system experiments conducted a t Manchester by Ardern a n d Lockett,’ a series of perforated pipes placed a t 4 in. intervals and fixed a t a depth of 1 2 in. below t h e surface was used. I n subsequent experiments Ardern and Lockett used porous tile similar t o those used by Fowler and Mumford in connection with other work on t h e clarification of sewage by means of specific organisms. Ardern and Lockett reported t h a t a comparison of t h e results with those obtained with pipe diffusers showed advantages in favor of porous tile. This was demonstrated in three sets of experiments using (I) an excessive amount of air on a strong sewage, ( 2 ) a n average amount of air o n a dilute sewage, and (3) a minimum amount of air o n a dilute sewage. At Salford2 a roughing filter was converted into an activated-sludge t a n k and t h e air ’pipes of t h e filter were used for diffusers. The outlets, I in. in diameter, were placed 8 in. apart on t h e t o p
is t h e method of air diffusion.
1 2
J . SOC.Chem. I n d . , 33 (1914). 523-39, 1122-4. Surveyor, 46 (1914), 681-2; J . SOC.Chem. Ind., 33 (19141, 1124-30.
Vol. 9, No. g
and sides of t h e pipes. Effluents within t h e requirements of local conditions were obtained. Fowler1 described an arrangement devised originally by Jones and Atwood, which consists of a series of nozzles, one in each square yard of t h e aeration t a n k . T h e scheme was not satisfactory because deposits of sludge formed around each nozzle. I n this country, Filtros plates were first used for air diffusion in a small t a n k in the laboratory of the Illinois State Water Survey, and have since been used rather generally in America. Much has been written and various opinions expressed regarding kinds of air diffusers. Hammond,Z in April 1916,after visiting five working plants, stated t h a t air distribution troubles had been rather general and t h a t he believed t h a t pipe grids were more satisfactory t h a n porous diffusers. Hammond states t h a t t h e use of porous diffusers has been largely from theoretical rather t h a n practical reasons. Hatton,s after various experiments, reports t h a t Filtros plates were t h e most satisfactory medium he has found for air diffusion, b u t t h a t they should be of uniform porosity, should be properly installed, and all oil and dust should be excluded from t h e air passing through them. Wooden-block diffusers give good diffusion with least frictional loss. The bubbles are smaller t h a n those obtained by Filtros plates. T h e experiments, however, are insufficient t o warrant their adoption for working-scale installations. Furthermore, t h e deterioration is apparently rapid. Pearse and Richardson, in a recent report* on t h e activated-sludge process for handling Packingtown trade waste, state: “At t h e present time Filtros plates offer t h e most satisfactory air distribution. Although t h e cost of maintenance may be somewhat higher t h a n t h e perforated-pipe grids, we believe t h e distribution is better and t h e size of air bubbles is much smaller with consequent increase of efficiency. The basswood plates, now being tested in Milwaukee, produce a remarkably fine air bubble, insuring a considerable reduction in t h e use of air. The life of basswood plates is a t present very uncertain because of possible decay.” The statements by various authorities concerning t h e use of diffusers were so decidedly a t variance t h a t we were led t o make some comparisons of different diffusers in service under identical conditions. The four reinforced concrete tanks used in former experiments and described in a previous paper6 were remodelled and each fitted with a different air diffuser (see Fig. 11). The tanks operate on t h e fill-and-draw system and are 3 ft. 2 in. square and 8 f t . deep. At eac; filling 3 5 0 gallons of sewage were added. One t a n k ( A ) was fitted with a system of perforated pipes having perforations one-twenty-fifth of an inch in diameter placed 2 in. apart and staggered a t an angle of 4 j O from t h e t o p of t h e pipes. There were about 40 holes in the pipes or 4 t o each square foot of surface J . Inst. Sun. Engrs.. March and April, 1916. Eng. News, 76 (1916), 798-801. 3 Eng. and Contr., 46 (1916), 104-8. 4 “The Activated-Sludge Process for Handling Packingtown Trades Wastes,” Sanitary District of Chicago, 1917. 1 2
8
LOG. c i t .
Sept.,
1917
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
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FIG I - ILL h 0 ' 5 STA'E AATc'R W R V E Y SEWAGE EXPERIMENT STATION
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FIG II
UNIVERSITY OF ILLINOIS
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SCALE IN FEET
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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
Vol. 9 , NO. 9
TABLE1-SUMMARY OB RESULTS(PARTS PER MILLION)OETAINED IN THE COMPARISON O B EFFICIENCY O F METHODS O F AERATION MEASURED IN TERMSOF AMXONIA NITROGEN. NITRATEAND NITRITE NITROGEN, OXYGENCOXSUMED, TURBIDITY AND THE ACCUMULATION OB SLUDGE AMMONIA NITROGEN NITRATE AND TITR RITE N I T R O G ~OXYGEN N CONSUMED TURBIDITY PER CENTSLUDGE Sew- ---EffluentsPERIOD Sew- --EffluentsSew- -Effluents-Sew- --Effluents---Effluents1917 a g e 9 B C D age A B C D ageA B C D age A B C D A B C D Mar. 27 to Apr. 1 ....... 21 17 17 18 17 0 . 9 1.2 4 . 0 3.9 3.9 58 26 19 20 22 282 48 39 46 46 9 8 S 7 Apr. 1 to 6 . . . . . . . . . . . . . 17 17 16 16 16 4 . 7 3.9 4 . 7 6.1 6.3 46 21 18 15 14 317 9 6 6 6 14 14 12 12 Apr. 6 to 12 . . . . . . . . . . . . 16 11 9 8 9 5 . 1 4 . 9 4.5 5.9 7.2 50 26 24 19 26 190 9 5 5 5 18 21 18 18 Apr. 12 to 1 7 . . . . . . . . . . . 26 30 29 0 0 0 . 3 0.4 0.3 6 . 8 10.2 55 32 26 25 16 248 7 5 5 5 26 29 25 28 Apr. 17 t o 22 . . . . . . . . . . . 21 21 21 0 0 1 . 2 0 . 3 0.0 15.0 16.9 . . . . . . . . . . 306 5 5 5 5 29 35 34 31 . . . 25 24 23 0 0 1 . 0 0 . 2 0 . 1 25.8 26.0 . . . . . . . . . . 309 5 5 5 5 38 37 44 39 Apr. 2 2 to 27 . . . 22 30 20 0 0 4 . 5 0 . 3 0.0 23.8 24.7 268 5 5 5 5 35 33 36 33 Average Reduction . . . . . 21 20 19 6 6 2.5 1.7 1.9 12.6 13.6 Si io i9 274 13 10 1 1 11 . . . . . . . . or Percentages . . . . . . . . . . 5 10 71 71 . . . . . . . . . . . . . . . . . 60 58 6 2 63 . . . 95 96 96 96 . . . . . . . . Results A p r i l 12-30 after A c t i v a t e d S l u d g e w a s Formed ,. 24 24 23 0 0 1.7 0 . 3 0 . 1 1 7 . 8 1 9 . 4 55 32 26 25 16 283 5 5 5 5 38 37 44 39 or Percentages . . . . . . . . . . 0 4 100 100 . . . . . . . . . . . . . . . . . 41 53 54 70 98 98 98 98 . . . . . . . . A, tank with perforated pipes; B, wooden blocks; C, fine Filtros plates; D coarse Filtros plates.
ii ii
...
area. The bottom of t h e t a n k is sloped from t h e cen- 1 5 , 20, and 3 j days, respectively. Each of t h e tanks ter a n d sides a t a n angle of 4 5 O , thus forming two was operated in three aeration periods daily of 5 1 0 , V-shaped channels of equal size, I ft. in depth, running 300, and 2 7 0 min. with a a-hour allowance between entirely across t h e t a n k . t h e periods for settling, emptying and filling. T h e The bottom of t h e second t a n k ( B ) was hoppered same amount of air as measured by ordinary gas from all four sides and a concrete container for wooden- meters was added t o each t a n k . All conditions were block air diffusers was placed i n t h e b o t t o m of t h e maintained as nearly identical as possible. T h e hopper. The container was patterned after one de- sewage was pumped from t h e main sewer just outside signed by Nordelll a n d used a t Milwaukee in t h e t h e city limits of Champaign and accordingly was Nordell aerating t a n k . T h e container is a one-piece fresh. It mas a fairly strong, domestic sewage with casting 2 ft. 8 in. long, I ft. 89/16in. broad, and j in. no trade wastes. N o activated sludge was added thick with a receptacle for t h e blocks I ft. 39/16 in. by t o t h e tanks a t t h e beginning of any of t h e series of tests. 2 ft. 3 in. in plan, 3 / 4 in. deep a t t h e edge, and I ’ / ~ Samples of sewage were taken as t h e sewage was in. deep at t h e center. T h e wooden blocks rest upon a series of thirteen ridges, I’/* in. wide a n d 1/4 in. high being pumped into t h e t a n k s a n d samples of effluents t h a t run across t h e receptacle, leaving a 1/4 in. space were collected a t t h e close of each aeration period underneath for t h e air t o circulate. The surface of after t h e sludge had been allowed t o settle for 30 mint h e container was cast on a curve so t h a t t h e tendency utes. The methods of analysis were those given in of t h e wooden blocks on swelling would be t o wedge t h e 1 9 1 7 edition of “Standard Methods for t h e Exthemselves more firmly into position. T h e basswood amination of Water and Sewage of t h e American blocks used in our experiments were very kindly fur- Public Health Association.” nished us by T. Chalkley H a t t o n . They were l/z in. The third series of tests, which lasted 3 j days, thick, 6 in. long a n d 2 1 / 8 in. wide. At first difficulty was t h e most satisfactory (see Table I ) . There was was experienced in keeping t h e blocks in position be- no sludge present a t t h e beginning and, owing t o t h e cause of t h e excessive swelling t h a t took place when length of t h e test, a t times some of t h e excess of t h e they were placed under water and also because they accumulated sludge was wasted. N o accurate combecame soft a n d spongy. Many of t h e blocks be- parison of t h e sludge accumulation a t t h e end of t h e came so curved a n d twisted t h a t they were discarded. series can be made. T h e maximum amount of sludge I t was found necessary t o place strips of heavy gal- was reached last in t h e t a n k with perforated pipes. vanized iron on edge between each row of blocks Removal of turbidity a n d oxygen-consuming capacity for reinforcement a n d t o close up certain joints with was practically t h e same in all tanks. Measured in oakum. terms of removal of ammonia nitrogen and in proFiltros plates of different porosity, kindly furnished duction of nitrate nitrogen t h e tanks with Filtros b y t h e General Filtration Co., were placed in two of plates were decidedly superior. Ammonia nitrogen t h e tanks ( C and D). Three plates were used in each was entirely removed in t h e t a n k s with Filtros plates t a n k , covering one-third of t h e area and forming t h e after 1 7 days. Owing t o rains, nitrate nitrogen was bottom of a trough with sides sloping a t a n angle present in t h e raw sewage during t h e early p a r t of t h e of 45’. T h e plates of t h e third t a n k (C) were marked series and continued t o increase in t h e tanks contain“fine,” because on t h e basis of dry rating these plates ing Filtros plates, reaching about 2 5 p. p. m. Pracpassed 5 . 8 cu. f t . of air per minute per square foot tically all of t h e nitrate nitrogen disappeared from t h e under a water pressure of z inches. When saturated other tanks. The poor results from t h e t a n k with with water and passing 2 cu. f t . of air per minute wooden blocks were probably caused by t h e developthey showed a resistance on a water gauge of 1 1 . 4 ment of a hole in t h e t a n k , which prevented t h e format o 1 1 . 8 in. The fourth t a n k ( D ) was equipped with tion of finely divided bubbles. The stability t o methylplates marked “coarse” which, on t h e same basis, ene blue was tested on and after t h e eleventh day passed 1 2 cu. ft. of air per minute per sq. f t . When a n d all effluents from t h e tanks containing Filtros passing z cu. f t . of air per minute these plates regis- plates were stable for I O days at z o o C. Most of t h e tered a resistance of 8 . 8 t o 9 . 6 in. of water pressure. effluents from t h e other tanks were unstable. Nearly T h e t a n k s were operated during three periods of 30,000 gallons of sewage were treated in each t a n k with 3 . z cu. f t . of free air per gallon. T h e sludges in 1 Annual Report of Sewerage Commission of Milwaukee (1916).
Sept., 1917
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 CHEMISTRY
t h e t a n k s with Filtros plates settled better and after removal a t t h e end of t h e series, h a d specific gravities of I . 013 and I . 0 2 2 , compared with I . 006 for t h e sludges from t h e other tanks. The results obtained from these comparative tests indicate t h e superiority of Filtros plates as air diffusers over perforated pipes, such as were used in our tests under t h e conditions maintained. The wooden blocks were difficult t o handle though this was caused in part b y t h e faulty design of our containers. Even in t h e time t h e y were used, there was evidence of considerable deterioration. From t h e results obtained we could distinguish little, if any, difference between t h e coarse a n d fine grades of Filtros plates. With air free from dust and oil there should be little trouble experienced from clogging of plates. D E W A T E R I I i G O F ACTIVATED SLUDGE
Satisfactory purification of sewage has been obtained b y us a n d by many others, b u t before t h e method can be considered a n unqualified success a practical and economical method of drying t h e sludge must be found. Various methods have been tried b y different investigators, b u t we have a t t h e risk of duplication experimented with many of these methods. Although drying on sand-beds h a d been tried at Cleveland, and we h a d ourselves tried i t , we thought wise t o repeat t h e experiments on better constructed beds t h a n were used in our previous work. The experiments were not successful. Owing t o t h e large amount of moisture in t h e sludge, 98 t o 99 per cent, t h e solid matter obtainable from a foot depth of sludge would be only from one-quarter t o one-half a n inch, according t o t h e residual moisture content. It was also difficult t o separate t h e sludge a n d sand. T h e fertilizer obtained was more or less impure a n d of decreased value. The sand beds used were one-hundredth of a n acre in area a n d divided into five compartments. Underdrains were overlain with I O in. of coarse gravel and 8 inches of sand. The beds were provided with a canvas cover supported on a framework so t h a t they could be protected during storms. One compartment was allowed t o dry after a single filling, another after tn7o fillings, a n d another after three fillings. I n no case were t h e results sufficiently satisfactory t o warrant t h e use of sand beds for t h e drying of t h e sludge a n d t h e production of a commercial fertilizer. Experiments with a filter press with leaves in, square operating on a fairly concentrated sludge were also unsatisfactory. It has t h u s far been impossible for us t o obtain a cake of good consistency. Further experiments are t o be tried with t h e hope t h a t better results can be obtained. Through t h e courtesy of t h e Koering Cyaniding Company, of Detroit, a rotary filter was placed a t our disposal. This style of filter is used satisfactorily in filtering slimes in extracting gold a n d silver by t h e cyaniding process. The apparatus consists of a cylinder of Filtros plates supported on a perforated steel cylinder outside of which, a t a distance of about one inch, is a solid steel outer shell. The material t o be filtered is forced into t h e interior of t h e cylinder of
849
Filtros plates, t h e cylinder is revolved and a cake of sludge is built u p on t h e inside of t h e plates. The liquid filters through t h e plates into t h e space between t h e cylinders. Air pressure can be exerted from t h e interior t o dry t h e cake, and from the exterior t o loosen it. The plates can be cleaned b y back-flushing with water. The first trial mith a comparatively heavy a n d not very fresh sludge did not give satisfactory results. The quick-opening door could not s t a n d t h e pressure. Another trial will be given as soon as t h e door can be replaced. Mohlman' reported experiments with two small centrifuges, one of t h e low-speed basket type and t h e other of t h e high-speed bottle type. The basket of t h e low-speed machine was 8 in. in diameter and 6 in. deep. The periphery was perforated with numerous holes '/E in. in diameter. When t h e holes were covered with a strip of muslin cloth, approximately one gallon of 98 per cent moisture sludge was p u t into t h e centrifuge and after I j minutes, 700 g. of 91 per cent moisture sludge were obtained. T h e high-speed bottle-type machine reduced the moisture from 98 t o 9 2 per cent in 3 minutes. Mohlman stated t h a t in order t o be economical there should be a n automatic arrangement for removing the cake. The most successful apparatus of this t y p e is t h e Schafer-ter Meer centrifuge described b y Hammond.2 This machine is said t o be very efficient b u t was too expensive for us t o obtain for experimental work. At Cleveland, P r a t t a n d Gascoigne3 used a laundry centrifuge with a 2 6 in. basket, lined with a ' / 4 in. wire mesh inside of which was a canvas bag. I n t h e best run, when t h e basket revolved a t about 1 2 0 0 r. p. m., 6 0 gallons of 97.5 per cent moisture sludge was added in about 2 j minutes a n d in 2 hours t h e moisture cont e n t was reduced t o 84 per cent. The time required would seem t o make this process impracticable. Working on t h e assumption t h a t t h e principle used in drying of china clays or t h a t used in t h e cream separator might be applicable, a modified basket-type centrifuge and a modified cream separator were tired. T h e holes of a n 8-in. basket-type centrifuge were covered with a strip of rubber packing. The best results were obtained with 1 5 0 0 r. p. m.. which was t h e limiting speed of t h e machine. This would seem t o indicate t h a t t h e process would give efficient results if carried on a t a n increased speed, b u t would yield a n effluent t h a t must be returned with t h e sewage t o t h e aeration chamber. A series of tests was made with a cream separator, t h e bowl of which was modified, b y removing t h e inner disks and discharging t h e clarified liquid about a n inch from t h e center of t h e bowl a t t h e top. The sludge added a t t h e t o p dropped t o t h e bottom of t h e bowl, and t h e liquid was thrown out over t h e rim. Sludge cakes containing from 8 j t o 86 per cent of moisture were obtained b y t h e cream separator in 6 t o 8 minutes, which encouraged us t o obtain a special machine for further experiments. A specially designed centrifuge was purchased from 1
Thesis, University of Illinois, June, 1916.
* Eng. News, 75 (1916), 800.
* I b i d . , 76 (1916),
1124.
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 t h e Tolhurst Machine Works, of Troy, New York. This machine is 1 2 in. in diameter, 91/2in. high and a t a speed of 1800 r. p. m. exerts a centrifugal force of 550 lbs. According t o its concentration, from I O t o 2 5 gallons of t h e sludge are added and I O lbs. of cake obtained. The sludge cake contains about 88 per cent moisture. The space underneath t h e rim contains 0.158 cu. ft. Owing t o t h e small size of t h e machine and t o t h e fact t h a t t h e material must be scraped out, t h e time of cleaning is longer t h a n would be required for a l u g e r machine with an opening in the bottom, so t h a t a large machine could undoqbtedly have been filled and emptied more rapidly t h a n the small laboratory machine. We have found it entirely possible t o fill and empty t h e small machine 4 times in one hour. Calculating t h a t t h e same rate could be used with a 40-in. machine having 46 times t h e capacity, we could obtain in each filling 460 lbs. of sludge of 88 per cent moisture, equivalent t o 5 5 pounds of dry material. One 40-in. machine would, therefore, deliver t h e equivalent of 2 2 0 0 lbs. of dry material in a working d a y of I O hrs. On the supposition t h a t one-half ton of dry material will be obtained from I,OOO,OOO gallons of sewage, one machine would dewater t h e sludge from 2,000,000 gallons of sewage per day. The cost of t h e 40-in. machine a t present is only $ 7 5 0 and t h e power'to run it is small enough t o make t h e process appear practical for preparing sludge cake for a dryer. T h e actual cost of dewatering will depend upon t h e amount of water t h a t can be removed by t h e centrifuge, t h e size of dryer and t h e amount of coal required for removing t h e residual water. A drying test using 2 2 0 lbs. of 88 per cent sludge cake made by t h e John P. Devine Co. indicates t h a t t h e dewatering process can be made practical. The author desires t o acknowledge his indebtedness t o t h e members of t h e staff of t h e Illinois State Water Survey, and especially t o J. F. Schnellbach, F. L. Mickle, W. D. Hatfield, and E. Greenfield for their interest and assistance in carrying out t h e experimental work. STATB WATERSURVEY UNIVERSITY OF ILLINOIS. URBANA
THE ANALYSIS OF SULFATED OILS B y RALPHHART Received July 19. 1917 INTRODUCTION
The present methods for t h e analysis of Turkey-red oils have proven t o be inadequate for the routine work of this laboratory where several such analyses have t o be made every day. The determinations of importance in such products are t h e percentages of total f a t and of combined sulfuric anhydride. The methods usually employed for total fat are (I) t o extract with ether, or (2) t o decompose with acid and t o measure t h e volume of t h e oil which separates. Both methods were found unsuitable for our purposes; besides other reasons, t h e former was too tedious, and the latter consumed too much time. The present method for t h e determination of combined sulfuric anhydride requires two gravimetric
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analyses, and, because of its length, its application for factory control is limited. It was noted, however, t h a t this determination afforded a n excellent means of judging and controlling the manufacture of sulfated products, as is illustrated by t h e following case. A commercial Turkey-red oil, which was a t first passed as satisfactory, was found on analysis t o contain 40 per cent less bound SO3 t h a n it should have. As a result, the oil was retested in a practical way, and found t o be faulty in many respects. The cause of the trouble was later traced t o hot weather, which caused the temperature of t h e unwashed sulfated oil t o rise during t h e night. T o insure uniformity in shipments, this laboratory has made it a practice t o estimate t h e amount of f a t bound as soap, and t h e amount present as free f a t t y acids; t h e former was determined by titrating a water solution of t h e sample with H2S04 in presence of methyl orange, and t h e latter by titrating t h e alcoholic solution with NaOH in presence of phenolphthalein. It occurred t o t h e writer t h a t it might be possible t o saponify completely t h e rest of t h e f a t by ordinary means. A few experiments proved t h a t such was t h e case, and this fact was utilized t o develop a new method for t h e determination of f a t . A short method for combined so3 and ammonia was also worked out a t t h e same time. By our new procedure, we are able t o determine, within a reasonable length of time, not only total fat and sulfuric anhydride, b u t also ammonia a n d caustic soda. Furthermore, this method makes it possible t o estimate from t h e d a t a obtained for t h e other tests t h e amount of f a t present as soap, as free f a t t y acids and as esters, lactones, etc.; t h e only additional test required is for free f a t t y acids, which is determined as mentioned above. PRESENT
METHOD F O R FAT
The technical procedure1 for t h e determination of f a t in Turkey-red oils, Monopole oils, Sulfo Textol oils, etc., is t o decompose with acid a sample contained in a special flask having a long neck graduated in cc., a n d t o boil t h e contents until t h e oil is clear. The latter is then brought within t h e graduation on t h e flask by pouring in a saturated salt solution. The per cent fat is then calculated from t h e volume of t h e oil and its specific gravity which is assumed t o be 0.945 a t room temperature. This method presents many difficulties; for example, during the heating, the oil which spreads on t h e surface of t h e water prevents the latter from boiling freely, and, unless the flask is vigorously and constantly agitated, t h e contents are likely t o spout out. Holde' says: "A disadvantage of t h e method is t h e fact t h a t t h e layers do not completely separate, t h e deviation in results being as much as I per cent." Another source of error is t h a t t h e contraction of t h e contents in t h e flask on cooling leaves behind a film of oil which is not taken into account, Finally, it has lately been almost impossible t o obtain a flask of this type t h a t will not break on heating. A modified method is t o heat t h e contents of t h e 1 "Examination of Hydrocarbon Oils," D . Holde, 1915 edition, pp. 409 and 410. English translation by E. Mueller.
