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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE IV. CHEMICAL COSCENTRATIONS REQUIRED TO KILL” A PURECULTURE OF A LARGE SLIME-FORMING ORGANISM Concn., P.P.M., after Contact for 1 2 4 1.5 3.0 min. Chemical min. hr. hr. hr. Chlorine 11 7.5 6.0 3.5 2.5 Chloramine 29 20 13 8.7 5.9 Silver ion >3.5 Santobrite 4000 2350 1350 i96 460 a For comparison a reduction of 99.9% in bacteria count is used rather than a complete kiil. 48-hour culture used in all cases. Initial bacteria counts raried from 31,000 to 310,000 per ml.
Vol. 41, No. P
I n both units water treatment made it possible to maintain high throughput rates for prolonged periods. Production and operating data confirmed the heat transfer data. Restricted production or operating difficulties were encountered a t the times relatively high dirt resistances were indicated, and high throughput rates were possible at the times low dirt resistances were indicated. Production expcriences, plant observations, and bacteriological data all indicate the practicability of using plant heat transfer data for evaluating the efficacy of slime control procedures. I
ACKNOWLEDGMENT
feed chlorinator was operated one hour out of every four, and data as shown in Table Is’ indicated that free available chlorine is probably essential to optimum slime control. Free available chlorine and chloramine chlorine were determined by the otolidine-arsenite method ( 1 ) . The bacteria count in the cooling water system was practically zero a t times of chlorinator operation. Although there mas practically complete loss of free chlorine and about one third or greater loss of chloramine chlorine in passing through the cooling tom-er, the bacteria count never increased to more than a few hundred per ml. a t times of adequate chlorine dosage, The mechanism of control here is definitely that of bactericidal action. Chlorine dosage was not optimum during a large part of the period shown on Figure 5 . I n this unit slime accumulations apparently sloughed off and did not reform a t times when the water temperature was about 130’ to 135’ F. or higher. This observation was confirmed by the inspection of condenser tubes at times of shutdowns.
The authors wish to acknolyledge the assistance of C. H. Welker, E. J. Rollins, and J. G. Demann in obtaining and organizing the basic data. LITERATURE CITED
(1) Am. Pub. Health Assoc., “Standard Methods for Examination of Water and Sewage,” 9th ed., 1946. ( 2 ) Bowman, R. A., Mueller, A. C., and S a g i e , K. M., Trans. Am. SOC. Mech. Engrs., 62, 283-94 (1940). (3) Holmes, J. A., Proc. 3rd Ann. Water Cons. Engrs. SOC.West Penna., 1942, 61-7. (4)Martin, R. B., Trans. Am. Soc. Mech. Engrs., 60,475-83 (1938). (5) Martin, R. B., and Dobson, J. G., Paper Trade J . , 121,No. 15, 39 (194.3. -_, (6) Sanborn, J. R., J.Bact,, 48, 211-17 (1944). (7) Wattic, Elsie, Sewage Works J.,15, No. 6, 476 (1943).
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RECEIVED January 14, 1948. Presented as part of t h e 14th Annual Chemical Engineering Symposium of the Division of Industrial and Engineering Chemistry, AMERICAN CHEMICAL SOCIETY, Illinois Institute of Technology, Chicago., Ill., Other papers of this symposium appeared in June 1948.
of Soluble Organic ent Growths H. HEUKELEKIAN New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, AT. J .
A
process of aerating concentrated, soluble, nontoxic, organic wastes has been developed by returning to the raw waste the liquid i n which the biological growth is dispersed. Experiments, using the batch process, have been conducted to determine the importance of factors affecting the process and the extent of B.Q.D. reductions. The work was done with streptomycin and penicillin wastes.
HE activated sludge process with its modifications has become established as the main aeration method for biological treatment of sewage. It has been established that plain aeration of sewage does not bring about appreciable purification within practical detention periods. The tendency a t present is to pattern waste treatment closely after sewage treating processes. Among biological processes, activated sludge, trickling filters, and sand filtration have been successfully applied to diverse wastes. Certain wastes, however, are not amenable to treatment by such conventional processes because of the high concentration of organic matter. Other wastes may be more conveniently or economically treated by newer biological processes. Differences in chemical composition and concentration of certain wastes from sewage make the search for new biological methods imperative. Aeration in the absence of flocculent growths which develop characteristically from sewage, as a means of biological treatment of wastes, has not yet been studied.
Seeding is essential for high-rate biological activity. I n the activated sludge process this is acconiplished by returning a portion of the copious quantity of sludge formed. This procedure ensures a large number of organisms in a relatively small volume of seed material because the organisms are mainly aggregated in the sludge floc. It is conceivable, however, to treat certain wastes in which the growth is not so aggregated but is dispersed. The return of the liquor containing the dispersed growths may answer the purpose of seeding. Even if variable quantities of sludge are formed in some wastes, it may not be desirable to ieturn the settled sludge as seed. Either the settled liquor or the mixed liquor before settling may furnish the necessary amount of seed. Treatment by nonflocculent growths may be specially adapted to soluble organic wastes of high concentration. Such wastes would automatically produce much less sludge as result of aeration than would wastes of equivalent strength in colloidal OF settleable form. Furthermore, i t is difficult to produce flocculent growths from wastes containing high concentrations of soluble organic materials. Experiments are described to illustrate the importance of some factors and results to be expected when penicillin and streptomycin wastes are aerated in the absence of flocculent growths. Aeration was conducted in cylindrical glass tubes 2 5 inches in diameter and 24 inches long. Air was supplied through a diffuser bulb attached to the rubber stopper a t the bottom of the tube.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949
The seed material for treatment by dispersed growths was developed by adding a suspension of soil or sewage to the wastes. After aeration, the material was settled and a portion of the supernatant liquor was used to seed a fresh batch of raw waste. Whether sludge was produced or not, the seed material did not contain sludge. The efficiency of the process was judged by the reduction of biochemical oxygen demand (B.O.D.) after treatment ( 1 ) .
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I
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I
I
SEED DEVELOPMENT AND VOLUME
The question might be raised as to the time necessary to establish seed in a fresh soil inoculation and obtain maximum reduction of B.O.D. Table I compares some results on streptomycin waste inoculated with soil suspension and on the same waste with established seed. After three dosings, with an aeration period of one day for each dose, a 90.5% B.O.D. reduction was obtained by starting with a soil suspension, as compared to 93.0% reduction obtained with established seed. The following reductions varied between 86 and 90,5%, which are similar to those obtained from established seed material.
1.
I
I
I 0.7
15 . 1.9 CU. FT.AIR/GAL./
2.7
2.3 HR.
3.1
Figure 1. Effect of Rate and Time of Aeration on Percentage B.O.D. Reduction of Penicillin Spent Broth
of air up to 3.0 cubic feet per gallon per hour and B.O.D. reduction in 12 hours with a maximum of 6570 reduction. With 24 hours of aeration the reductions increased from a !ittle over 4001, with 0.7 cubic foot of air per gallon to 70% with 1.8 cubic feet per gallon. Increasing the rate of aeration beyond this value had TABLE I. COMPARISON OF B.O.D. VALUESOBTAINED IN AERAno additional effect. TION OF STREPTOMYCIN SPENTBROTHWITH ESTABLISHED DISSTRENGTH OF WASTE. The strength of penicillin spent broth PERSED SEEDAND WITH INITIAL INOCULUM OF SOILSUSPENSION" with an initial B.O.D. of 2160 p.p.m. was reduced by dilution Established Seedb Soil Inooulumb with water to one half and one quarter of its concentration. Dosing B.O.D., Reduction, B.O.D., Reduction, No. P. p. m. % p. P. m. % These are seeded with equal volumes of previously developed 69.0 275 1 115 seed (2 volumes of waste to 1 volume of seed) and aerated a t a 220 75.0 105 2 constant rate of 1 cubic foot per gallon per hour. Daily dosings 85 90.5 60 3 123 86.0 117 5 were continued under these, conditions for 1 week, and then the 90.0 112 90 7 113 87.0 8 100 B.O.D. of the aerated mixtures was determined a t the end of 6, 87 90.6 12 66 12, and 24 hours. Figure 2 shows the results. The percentage a Aeration period, 24 hours; B.O.D. of streptomycin broth before treatB.O.D. reductions in the undiluted spent broth were low after ment, 885 p.p.m. b One third of volume of treated material retained as seed. 6 and 12 hours of aeration, and reached a maximum of 85% after 24hour aeration. I n contrast, after dilution to one half to one fourth of the original strength, maximum reductions were ' The minimum quantity of seed to be retained compatible obtained in 12 hours of aeration; then the rate of reduction with maximum efficiency is important from the standpoint of the decreased. The maximum reduction was around 85'70 after capacity of the aeratlon tank required. Table I1 gives results 24hour aeration whether the waste was diluted or not. obtained with different volumetric ratios of penicillin spent Table I11 summarizes results of daily dosing of penicillin wash broth to seed. Reducing the volume of seed in relation to the water for 7 months, grouped on the basis of the B.O.D. of raw waste fed had little effect on the efficiency of purification. Subwaste. A maximum of 80.5% reduction was obtained when the sequent work showed that the seed volume could be even lower. strength of the waste was between 1000 and 2000 p.p.m. of B.O.D. For all the work to be described, a ratio of 2 volumes of waste The efficiency was not materially affected when the B.O.D. of to 1 volume of seed was used. the waste was between 2000 and 3000 p.p.m. with an average of 2725 p.p.m. The B.O.D. reductions dropped to 70.5% in the 3000 to 4000 p.p.m. group with an average of 3400 p.p.m., and TABLE 11. EFFECT OF VOLUME OF SEEDON B.O.D. REDUCTION decreased further to 46% when the average B.O.D. of the wash OF PENICILLIN SPENTBROTH^ AFTER AERATION WITH DISPERSED GROWTHS Ratio, Waste :Seed 0.4:l 0.6:1 0.8:1
a b
B.O.D., P.P.M. 1000 1030 1380
Reduotionb, yo
1.O:l 950 1.2:1 1200 B.O.D. of penicillin broth before treatment, 400 p.p.m.
100
77.5 76.5 68.5 78.5 73.0
After aeration for 24 hours.
80
z 2 c
60
0
EFFECT OF VARIABLES
pH. No differences in the B.O.D. reduction of penicillin spent broth treated at an initial pH value of 6.4 and one adjusted to a pH value of 7.2 could be detected. I n a number of experiments the pH rose above the neutral point during aeration. TIME AND RATE OF AERATION. Figure 1 illustrates the effect of time and rate of aeration on the percentage B.O.D. reduction of penicillin spent broth with an initial B.O.D. of 3800 p.p.m. The reductions were irregular and generally below 40% after 6 hours of aeration, irrespective of the rate of air input. There was a more direct relation between the quantity
3 0 W
40
ci m 9 8
20
0 0
6
I2
16
24
HOURS AERATION
Figure 2. Effect of Dilution on Progressive Percentage B.O.D. Reductions of Penicillin Spent Broth
INDUSTRIAL AND ENGINEERING CHEMISTRY
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water was 7290 p.p.m. I n spite of the decrease in efficiency of reduction, the p.p.m. B.O.D. reductions increased wjth higher concentrations of waste regularly (Figure 3). AIR CSED PER POUND OF B.O.D. REMOVAL
When wash water with an initial B.O.D. of 2160 p.p.m. was treated with air, controlled at 1 cubi,c foot per gallon per hour, the air consumption after 6-hour aeration was 665 cubic feet per pound of B.O.D. removed and 1430 cubic feet per pound of B.O.D. removed after 24-hour aeration. Spent broth with a B.O.D. of 3800 p.p.m. and reinoval of 70% after 24-hour aeration at the rate of 1.8 cubic feet per gallon per hour required 2000 cubic feet of air per pound of B.O.D. removed. The efficiencies calculated on this basis would be higher with 4000 lower rates of aeraI I tion a n d s t r o n g e r initial wastes. In the 3000 0 activatedsludge proc0 ess treating sewage a ZOO0 with a B.O.D. of 100 to 200 p.p.m., the air a? consumption per 1000 pound of B.O.D. rea' a' moved after 6-hour aeration varies from 0 500to 1500cubic feet. Such c o m p a r i s o n s Figure 3. Relation between B.O.D. may be misleading, of Penicillin Wash Water and however, because of P.P.M. pf B.O.D. Removal after 24the differences in Hour Aeration the character and strength of sewage and waste. On the basis of strength, the comparison is in favor of the activated sludge process of treating sewage since more air is needed to remove a pound of B.O.D. from the weaker material. But the treatment by dispersed growth represents complete removal by oxidation and not by adsorption and partial oxidation as is true in the activated sludge process. The coniparison on this basis is favorable to the dispersed growth treatment,
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SLUDGE FORlIATIOY
I n these experiments little if any sludge was produced from thP treatment of soluble organic wastes. Under certain conditions, however, sludge niay be produced. I n conical vessels with the aeration bulb a t the apex, the side walls may become coated with extensive biological growth, apparently because the air does not come in contact with the side walls. Eventually the growth sloughs off and appears as sludge. When the vastes are aerated in cylindrical vessels, there is no side growth and consequently no sludge is formed. I n larger tanks the area of wetted surface in relation to the volume treated would be small; therefore sludge formation from side growths, even if there were dead areas, would be comparatively small. It does not seem probable that the
TABLE111. B.O.D. REDUCTIOS OBTAISEDFROX XERATIOXOF PENICILLIN W A S H R'ATEIZ WITHOUT SLUDGEa
Average B.O.D. s o . of EffluEffluent Raw, ent, Reduction, Samples Samples p.p.m. p.p.m. % 1000-2000 8 21 1350 265 80.5 2000-3000 4 8 2725 632 77.0 3000-4000 7 16 3406 1012 70.5 7290 3940 46.0 4 8 4000-10,500 Total 23 53 a Aeration period, 24 hours; daily additions of 2 volumes of raw wash water to 1volume of aerated liquor.
B.O.D. Range In Raw Waste, P.P.bl.
KO. of
Raw Waste
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roughness of the tank walls as compared with glass surfaces would have an appreciable effect on the quantity of attached growths, provided spots of low velocity were avoided. Irrespective of whether sludge was formed or not, the results noted here were obtained without the recirculation of sludge but only with settled supernatant. DISCUSSION OF RESULTS
Bacteria normally grow in cult'ure media in a dispersed state as individual cells or in small groups wit,hout forming flocculent aggregates. Inoculations are made by transferring a small portion of the dispersed growths into fresh cult,ure media. Flocculent aggregations are normally produced by the aeration of dilute materials containing suspended as well as soluble materials. Suspended materials serve as focuses for the aggregation by actual biological growt,hs and accretion of residual suspended material removed horn the liquid. The oxidation of soluble wastes gives rise only to a biological residue. No other form of suspended organic mat'crial is formed. The biological residue produced from the aerat,ion of concentrated organic wastes is nonflocculent. These general observations suggest a process of aeration and Oxidation of such wasbes by returning, as seed, the liquor in which the organisms are suspended. I n this preliniinary paper amention is dircctcd to such a process of aerating certain strong, soluble, nontoxic, organic wast,es in t,he absence of flocculent growths. The seed consiPts of finely dispersed cells which normally do not settle. It is generally accepted that such wastes are not) amenable to the activated sludge type of treatnieiit because the sludge eit'licr disperses or bulks. Trickling filters have been used satisfactorily t o treat such strong wastes with recirculation. The re1at)ive merits and economics of aeration by dispersed growths and trickling filters remain t o be determined. However, if large scale t,reatment by this process bears out, the laboratory experience, there will be a decided advantage in disposing of sludge by aeration with dispersed growths. The process is simple and can be readily controlled. The volume of seed used and the p1-I of the waste added do not seem to be of critical importance. If t,lie seed should be lost, new seed can easily be developed. Foaming difficulties will be eiicountered with certain types of wastes, but. they can be ovcrconic mcchanically or by antifoam agents. Wastes deficient in nitrogen and phosphorus will require supplemental additions. I n spite of these aids, however, certain wastes, such as those containing toxic materials, may not respond to thij type of treatment. Other types of biological trcatmcnt will be similarly affected in such cases. The adaptability of a pal t8icularwaste to sue11 a process can easily be tested under laboratory conditions. Unless conditions in the stream warrant., this type of treatment cannot be used for complete treatment,. With strong wastes up t o 4000 p.p.m. o€ B.O.D., 70 to 80% reductions obtained would not produce efflueiits acceptable for most, streams. Cnder these Wnditions the process can be used as a "roughing" unit in conjunction with subsequent biological processes, such a s coarse or fine grained filters or activated sludge. By this combination a large proportion of the B.O.D. can be removed in the aeration tank, which is not upset readily by high loads; an effluent of relatively low B.O.D. is then left t o be treated by more sensitive conventional biological processes. With weaker wastes of not more than 1000 p.p.m., 90% efficiency of B.O.D. removal is obtained; with relatively high stream flows, this process may be sufficient treatment. There is a lower limit of B.O.D. below which it would not be economical to treat wast,es by this process. As a result of the growth of the organisms in a dispersed state, the turbidity of the waste is increased during treatment. I t has been common experience to start with a clear raw waste and end with a turbid liquor. The color of the waste is not reduced as a rcsult of treatment.
'July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY CONCLUSIONS
1. The seed material can be readily developed from soil, and within a few days maximum efficiencies can be obtained. 2. The volume of seed material returned does not appear to be critical. A ratio of 2 volumes of waste to 1 volume of seed material has been used successfully. 3. The pH of the waste does not seem t o be critical. Raw waste with a p H of 6.4 gave as high reductions a s one adjusted to 7.2. The pH increases during aeration. 4. The percentage B.O.D. reduction decreases with wastes above 3000 p.p.m. of B.O.D., but the p.p.m. of B.O.D. removal increases. B.O.D. reductions of 90% have been obtained after 24-hour aeration with wastes of less than 1000 p.p.m. of B.O.D.; about; 80% may be expected with wastes up t o 3000 p.p.m. of B.O.D.; wastes with higher B.O.D. give lower percentage reductions. 5. 0 timum results have been obtained with an aeration rate of 2 cufic feet per gallon of waste per hour for 24 hours or of 3 cubic feet per gallon per hour for 12 hours for a waste with an initial B.O.D. of 3800 p,p.m.. Weaker wastes give equivalent percentage B.O.D. reductlons in shorter time and consequently require less air than sfronger ones. A wash water with
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an initial B.O.D. of 2160 p.p.m. required 1430 cubic feet of air per pound of B.O.D. removed. Spent broth with a B.O.D. of 3800 p. p. m. gave 70% reduction of B.O.D. with an air consumption of 2000 cubic feet per pound of B.O.D. removed. 6. Sludge may be formed through the sloughing off of side wall growths. Normally the quantity of sludge formed is small. 7. The effluent will have a higher turbidity than the raw waste. 8. The process may be used as a pretreatment unit ahead of other conventional biological units t o remove a substantial portion of the B.O.D. and to enable the secondary oxidation devices to operate without difficulty. LITERATURE CITED
(1) Am. Public Health Assoc., "Standard Methods for Examination of Watar and Sewage," 9th ed., 1946. RECEIVED M a y 10, 1948. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 113th Meeting of the AMPXICAN CHEMICAL SOCIETY, Chicago, Ill. Journal Series Paper of New Jersey Agricultiiral Experiment Station.
Reactions of Ions in Aqueous Solution with Glass and Metal Surfaces STUDIES WITH RADIOACTIVE TRACERS JAMES W. HENSLEY', ARTHUR 0. LONG, AND JOHN E. WILLARD University of Wisconsin, Madison, Wis, Radioactive tracers are shown to afford a direct, sensitive and rapid means for studying the sorption of ions in solution on solid surfaces. Preliminary studies have been made of the effect of time of immersion, pH, temperature, and pretreatment of the surface on the sorption of sodium ions on soft glass. Tests have been made on sorption of sodium ions on fused silica, steel, aluminum, silver, and platinum, and of sorption of cesium and silver ions on soft glass. Determinations of apparent activation energy of sorption are used as a means of comparing sorption processes. Radioautographs produced by sorbed radioactive ions are suggested as a test for surface cleanliness.
A
GREAT deal of evidence indicates that glass surfaces are able t o take part in exchange and adsorption reactions with ions in aqueous solution ( 5 ) . Somewhat similar reactions may occur also a t metal surfaces. I n general, however, the methods by which evidence on such sorption processes has been obtained are indirect and tedious. (Sorption as used in this paper indicates any type of process by which ions from solutions may adhere to solid surfaces.) The authors have explored the possibility of using radiotracers as a tool to study such phenomena more effectively. The method consists simply of immersing small flat samples in a solution of thc radioactively tagged ion or molecule, removing, rinsing, and drying the samples and determining the intensity of the radioactivity on each with the aid of a GeigerM;iller counter. The pretreatment, of the sample, and the time, temperature, and pH of immersion were varied t o study the effects of these factors. Initial results, reported here, show that the method is direct, rapid, and sensitive, and is applicable to the study of processes which could not be studied by any other method, such as the exchange of sodium ion in solution with the 1 Present address, Research Department, Wyandotte Chemicals Corporation, Wyandotte, Mich.
sodium in a glass surface. Such studies may contribute to a fundamental understanding of surface phenomena and may be of practical importance. in connection with problems in such fields as those of detergent action, electroplating, mirror formation, glass electrode operation, and the catalytic effects of surfaces. Because the work of this paper is exploratory i t deals with the determination of the major effects of different variables rather than the quantitative evaluation of the effects. The results indicate that amounts of sodium ion ranging from approximately 0.01 monolayer to 10 monolayers are' picked up in the course of a few minutes or hours of exposure of soft glass, Pyrex, fused silica, steel, aluminum, or platinum to sodium nitrate or sodium carbonate solutions. [For the purposes of this paper a monolayer is arbitrarily defined as the number of ions required to cover the macro surface area of the sample if each ion covers an area equal t o the square of its ionic diameter (S).] The sorption of sodium ion on soft glass increases with time of immersion, with pH, and with temperature. It varies with the pretreatment of the glass but for two types of pretreatment, giving quite different rates of sorption, the rates show approximately the same temperature dependence, giving an apparent activation energy of about 10,000 calories per mole. The rate of loss of the radiosodium from the glass t o a water rinse solution is slow. The sorption on quartz decreases with increasing temperature in contrast to the effect with glass. Silver ion reacts with soft glass a t a rate similar to sodium ion, and reaction has been observed also with cesium ion. The sorption of carbonate ion by both the glass and metal surfaces tested is less than 0.01 monolayer. EXPERIMENTAL PROCEDURE
Radioactive Materials. Table 1 lists the radioactive isotopes which were used in this work, with their half lives, the chemical form in which they were used, the energy of the beta particle
