Studies were made on the treatment of wastes from the laundry for contaminated clothing at Los Alamos. Thf wastes contained soap, synthetic detergents, citric acid, and lint. The 5-day B.O.D.’s of the wastes varied from about 200 to 600 p.p.m. The alpha activity from plutonium was relatively low, averaging about 1500 counts per minute per liter, but maxima of 20,000 counts per minute per liter were observed, The objective i n treatment was to reduce the plutonium activity in the discharged effluent to 70 counts per minute per liter or less. A reduction in the B.O.D. was desirable but of secondary importance. Experiments indicated that biological treatment was superior to chemical treatment. Chemical treatment (carrier precipitation) might not be entirely successful because of coagula-
tion difficulties caused by complexing agents. Activated sludge treatment was not feasible on detergent wastes because of excessive foaming. When the waste was deficient in biological nutrients, ammonia and phosphate were added to the laundry waste prior to biological treatment. The single-stage pilot trickling filter was ineffective in B.O.D. or plutonium removal with recirculation ratios of 8 to 1 or less. With recirculation ratios of 15 to 1 and higher, analytical results indicated nitrification, 90% or more B.O.D. removal, and satisfactory plutonium removal. The work indicates that the plutonium removal objective can be attained either chemically or biologically. Simplicity of operation and volume of sludge to be disposed of seem to favor biological treatment.
John F. Newell, C. W. Christenson, and E. R. Mathews U. S. ATOMIC ENERGY COMMISSION, LOS ALAMOS, N. M.
C. C. Ruchhoft
H. L. Krieger and D. W. Moeller
U. S. PUBLIC HEALTH SERVICE, CINCINNATI, OHIO
U. S. PUBLIC HEALTH SERVICE, LOS ALAMOS, N. M .
Laboratory Studies on Removal of Plutonium from Laundry Wastes T
HE primary function of a laundry a t any atomic energy installation is the removal of radioactive material from garments and equipment. A secondary and almost equally import a n t function is the actual removal of ordinary types of soil. At Los Alamos the laundry operation is very similar to t h a t of the ordinary commercial laundry. However, because of the decontamination requirements, the washing operations require large quantities of synthetic detergents, and more washing and rinsing per operation cycle. Starching, ironing, and finishing operations are absent. Materials used in the laundering operations include soap and synthetic detergents, ammonium citrate, ammonium fluosilicate, and occasionally some phosphates. The resulting waste has a 5day biochemical oxygen demand (B.O.D.) ranging from 100 t o 600 p.p.m. and which will average about 350 p.p.m. The total solids average about 700 p.p.m. The suspended solids average about 100 p.p.m. of which about 60 p.p.m. are settleable. The B.O.D. is substantially lower than the oxygen consumed value run by the procedure described by Moore et al. (9). The reason for this is t h a t the wastes contain a synthetic detergent resistant to biochemical oxidation but readily oxidized chemically. The detergent in question is Igepal CA Extra which is a polymerized ethylene oxide. Plutonium 239, a n alpha emitter with a half life of about 24,000 years, is the only consequential radioactive material in the waste. The plutonium content of the waste will average about 1000 counts per minute per liter with minimum t o maximum variations from 100 t o 20,000 counts per minute per liter. (One microgram of plutonium is equivalent t o about 70,000 counts per minute.) The higher concentrations which have been of infrequent occurrence, presumably resulted from the laundering of highly contaminated materials following extraordinary operations. It is imperative t h a t the hazardous and toxic materials be re moved from the wastes before they are discharged. The primary objective for treatment of this or any other radioactive waste is the removal of the radioactive contaminants. For other obvious public health reasons an important secondary objective in treating
the laundry wastes is the removal of the B.O.D. Over the past years the various public health agencies have established standards for permissible B.O.D. levels t h a t may be discharged into receiving streams; however, since the atomic energy industry is in its infancy, these agencies do not as yet have the necessary information for the establishment of permissible levels of radioactivity which may be discharged. The Atomic Energy Commission and its contractors have established tentative permissible discharge levels or tolerance values for various types of radiation, It is obviously desirable to develop an economical liquid waste treatment process which will more than comply with minimum tentative standards. On this basis the ultimate objective of one thousandth of’ a microgram per liter was tentatively selected as the maximum desirable concentration of plutonium in the treated waste. B t the time this goal was established this quantity was well below the tentative permissible plutonium concentration in drinking water. One thousandth of a microgram of plutonium is equivalent to about 140 disintegration per minute per liter. Since the counting equipment has a 50% geometry the 140 disintegrations are recorded as 70 counts. For conversion t o curies it should be remembered that 1 curie is equivalent t o 3.7 X 1O’O disintegrations per second. At present the laundry wastes are discharged into a series of two open gravel beds. The gravel beds were designed t o function very much like a slow sand biological filter. I n practice, however, these beds have become clogged with soap curds and lint resulting in very little percolation of the laundry effluent through the sand. The laundering operation must be designed t o have a maximum of success in dissolving or suspending and dispersing the plutonium content of the materials processed. This naturally results in a waste containing agents which are efficient in holding the plutonium content in solution or stable dispersion. Accordingly, it would be anticipated t h a t the laundry wastes would be more difficult to treat than the laboratory wastes previously discussed by Christenson et al. (1).
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Chemical Treatment
Biological Processes
The success of ordinary precipitation operations with lime and iron or alum in removinB plutonium from distilled water or ,laboratory wastes naturally resulted in the investigation of similar processes for application to the laundry wastes. At this point, it may be noted before discussing the results obtained in these flocculation experiments that all the work included rapid mixing while the reagents were added, followed by a half hour of gentle agitation before further steps were undertaken. The first attempts to use precipitation methods on samples of this waste resulted in dismal failure. Extensive experimentation failed to yield any method which gave a good coagulation using alum. Ordinary dosages of ferric chloride (up t o 100 p.p.m.) also failed to give satisfactory results. It was possible to get a consistently satisfactory floc which would remove plutonium and settle and filter well only with a large dose of iron and lime followed by p H adjustment to 11.5 and higher with sodium hydroxide. Later, the addition of about 100 p.p.m. of calcium chloride assisted in tying up the complexing agents and resulted in some improvement in coagulation. As a further step, 20 p.p.m. of activated sodium silicate were added prior to the addition of the iron giving further improved flocculation. The effect of the order of addition of the chemicals was investigated and after some experimentation it was found that best results were produced without lime and by adding the other chemicals in solution or suspension as follows: 300 p.p.m. of calcium chloride, sodium hydroxide to p H 12.0, 20 p.p.m. of activated silica, and finally 60 p.p.m. of iron as ferric chloride. This is the procedure currently used, and with the samples encountered up to the present time it has effected satisfactory plutonium removal. The initial plutonium values were run on straight wastes. The treated values were run on samples filtered through Whatman No. 2 fluted filter paper.
The study of biological processes was started a t substantially the same time as the flocculation studies. Previous reports by Ruchhoft (6) and Newell ( 4 ) had indicated that plutonium in low concentrations could be removed from solution by the use of the activated sludge process. The presence of relatively large quantities of soaps and other surface active agents in laundry waste would cause foaming in any process employing bubble aeration. This difficulty ruled out the activated sludge process. Consequently, the biological trickling filter which contains biological active floes similar to activated sludge and which requires no aeration was selected for study. In addition, it was anticipated that the operation of a trickling filter would produce lower volumes of waste radioactive sludge than a chemical precipitation process. To inaugurate this phase of the investigation, a single stage trickling filter was constructed adjacent t o the laundry waste discharge. The filter consisted of two 55-gallon drums, mounted in an upright position, one on the other, and filled with stones varying in diameter from 1 to 4 inches. A collection pan was attached beneath the lower drum t o discharge into a cylindrical 5gallon settling tank. A perforated metal plate was placed on the top surface of the rock. A tilting bucket of about 1-liter capacity was constructed and mounted on the top rim of the barrel. This tilting bucket provided intermittent dosing of the waste and discharged on the perforated plate which provided good distribution of the small flow over the entire surface of the filter. . Laundry waste containing about 10% by volume of secondary sludge from the Los Alamos municipal sewage treatment plant was applied to the filter starting on June 9. The rate of application was 200 ml. per minute, corresponding to about 1.25 million gallons per acre per day. Formation of the initial slime nas slow; 3 weeks were required for the development of a sparse growth. Although microscopic examination of the slime indicated a normal biological flora, laboratory measurements of results of operation were unfavorable. Recirculation of the filter effluent from the settling tank back through the filter a t a ratio of 2 parts of effluent to 1 part of laundry waste was started on July 6. The application rate of the raw laundry waste was not changed. Operation results for this period were not favorable, analytical data showing less than 20y0 removal of the B.O.D. and no removal of plutonium. On August 9 a stirring mechanism was installed in the settling tank to retain the sludge in suspension. The introduction of nitrogen and phosphorus into the laundry waste was started on August 19. The nitrogen and phosphorus additions were varied as follows:
Table I.
Max. Min. Av.
Removal of Plutonium from Laundry Wastes by Chemical Treatment (Period of observation, Maroh 9 to June 9) Plutonium Concentration, " ~ : ~ ~ ~ , l e Counts/Min./Liter Suspended Solids Initial Treated P.p.m. % ash Ml./Liter 966 83 120 3185 665 150 29 20 176 4 384 50 58.5 600 87
The results of plutonium removal by chemical treatment are listed in Table I. The suspended solids figures represent determinations performed on the mixed liquor after addition of the chemicals and flocculation. The settleable solids represent the amount of wet sludge to be expected from this treatment process. This figure indicates that the wet sludge volume will be about 5.85% of the total volume of wastes to be treated. During the period in which these observations were made the plutonium concentration in the waste was somewhat lower than the average previously reported. This fact is not too significant, however, because the original plutonium concehtration in the wastes, within the limits observed, has not in itself influenced the success or failure of the treatment process. Unsatisfactory plutonium removals resulted from poor coagulation caused by complexing agents and not because of plutonium concentration. Since the treatment procedure described above has been adopted, no failures have occurred in the removal of plutonium to the desired goal. Therefore, it is reasonable to assume that the chemical precipitation method will provide an effective treatment process as far as plutonium removals go. It should be pointed out, however, that the settleable solids contain the radioactivity which has been removed from the waste. The problems involved in handling and disposing of radioactive sludge suggest that other processes should be considered for treatment of these wastes.
Date 8/19-8/31
8/31-9/8 9/8 4 / 2 7
Nitrogen and Phosphorus Additions 7 p.p.m. ammonia nitrogen: 7 p.p.m. nitrate nitrogen; 14 p.p.m. phosphate 14 p.p.m. ammonia nitrogen: 14 p.p.m. nitrate nitrogen: 14 p.p.m. phosphate 30 p.p.m. ammonia nitrogen as ammonium hydroxide, I5 p.p.m. phosphate
The dosage rate and recirculation ratio remained unchanged. Operation results showed slight improvement as indicated by B.O.D. removals but the plutonium removal remained zero. . From August 29 to November 4 the recirculation ratio was increased to 4 t o 1. The nitrogen feed was increased to 60 p.p.m. of ammonia nitrogen fed in the form of ammonium hydroxide. The phosphate feed was kept a t 15 p.p.m. of phosphate which maintained phosphate in the effluent. On November 9 the recirculation ratio was increased to about 8 to 1. The increased recirculation was obtained by reducing the amount of raw waste applied, first to 0.6 million gallons per acre per day and then to 0.3 million gallons per acre per day. In spite of low temperatures (about 45" F.) the B.O.D. removals increased to the 60 to 70% range. At this time the soluble plutonium began t o indicate response t o treatment, showing about 20% removal.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 43, No. 7
Fol1oR'ing a freeze of the filter on December 9 operation of the unit was suspended. Thereafter the filter unit was moved to a heated building and a second stage filter similar to the first was added. growth Was On both by feeding tap water containing 10% by volume of secondary sludge from the municipal sewage treatment. plant, 150 p.p.m. of flour, 50 p.p.m. of dextrose, and 200 p.p.m. of soap. Supplementary nitrogen and phosphorus were added in slight excess of the following ratios:
performance. In preparing the data of Table 11, the last six to fifteenobservations to a fixed mode of operation have been It is felt that these observations, preceded by an adjustment period of at least 2 w&s in most cases, are representative of might be expected from a given mode of operation. A t certain periods in the early stages of the work it was noted that extraordinarily good plutonium removal coincided with the appearance of large quantities of nitrate in the effluent, I n order 1 part of n i t r o g e n to 20 parts of B.O.D. in the waste t o increase the nitrate in t,he effluent the amount of ammonia 1 part of phosphorus to 80 parts of B.O.D. in the waste. added with the raw feed was deliberately increased for several proThese ratios have been previously reported by Huekelekian ( 2 ) tracted periode of operation as is shown by the data of Table 11. as the minimum amounts of these elements which will provide a The two highest figures for nitrate content of the e'ffluent are shown by the table to have occurred in the periods April 7 to balanced food for the growth of microorganisms. The soap, flour, and sugar were gradually decreased and increasingly larger April 24 and June 21 to July 10. The plutonium residue in the filtered effluent during the corresponding periods represents the amounts of laundry wastes were added. lowest average values of plutonium residue attained. First Stage Second Stage Some of the variation in the result's obtained may be due to factors other than Holding Trickling Settling Trickling Settling Sand those of application rate, ammonia feed, Tank Filter Tank Filter Tank Filter or recirculation ratios and arrangements. These uncontrolled factors include: 1, the Raw 50 ml./m. 50 ml/m. Laundry variable nature of the waste in the matter Waste I of mineral and organic content; 2, variation in the amount and biological quality of the filter slime; 3, temperature variaRecirculation: 6: I Recirculation:6: I tions. It may be noted from Table I1 that in Figure 1. Flow Diagram of Pilot Plant for Laundry Waste Disposal many cases the B.O.D. redubtion produced by the second stage was exceedingly small. Xithin 1 week, an active growth was evident in both filters. In any normal sewage plant trickling filter installation, it would Beginning January 16, 1950 the filters were placed in operation as be absurd to operate a second stage to reduce the B.O.D. of an a series, two-stage unit with a 15 to 1 recirculation ratio. Ameffluent from 9 to 4 or from 26 to 3. However, these relatively monia and phosphates were added to the laundry waste to provide inconsequential B.O.D. reductions are accompanied by very subnecessary nitrogen and phosphorus. For the first time analytical stantial reductions in the plutonium residue of the final effluent. results showed nitrification of the waste, and a t this time the Accordingly, a second stage is obvlously desirable from the standB.O.D. removals increased to the 904; range and plutonium was point of the particular problem contemplated because it docs also removed. show this plutonium removal. In terms of percentage removal Over a period of 6 months the two filters were operated with of the original plutonium content of the waste, the removal in various combinations of flow patterns and recirculation ratios. A tht: second stage may be small. However, in terms of absolute flow diagram of one type of operation and recirculation arrangeplutonium content of the waste discharged, this removal is highly ment investigated is presented in Figure 1. Throughout this 6significant. month period the raw feed was maintained constant a t 50 ml. per Throughout this work the phosphate feed was kept constant at minute corresponding to an application rate of 0.3 million gallons 15 p.p.m. of phosphate. At times the amount of phosphate enterper acre per day on the primary filter. This amounts to about 150 ing the system was substantially larger than this because of the pounds of B.O.D. per acre foot per day on the basis of the volume intermittent usage of phosphate in the laundry. However, the of the primary filter only. 15 p.p.m. added to the feed resulted in a final effluent which never failed to show a substantial phosphate content. Although this Those observations made during a period of adjustment to a indicates that the phosphate requirement is satisfied, in view of new operation pattern are less likely to reflect a true picture of
Table 11. Plutonium Removal from Laundry Wastes by a Two-Stage Trickling Filter. data for the period from February 1 to July 10) B.O.D.6 Nitrogen Plutonium!, Ammoniad Nitrate0 Counts/Min./Liter Duration ObaervaNo. Sec. P.p:m. of Experition of Raw to pri. Sec. Pri. Seo. Pri. Sec. Pri. See. rnent Period Obs. feed sec. Raw eff. eff. Raw eff. eff. Raw eff. eff* Raw eff. eff. 2 / 1 --2/24 2/15-2/24 6 1 ,. 335 22 12 26 0 0 0 7 10 731 140 103 2/28-3/20 3/9 -3/20 6 1 18.0 406 56 18 32 3 0 0 2 5 450 192 134 3/22-4/24 4/7 -4/24 7 1 22.0 380 26 3 67 10 3 0 16 38 638 146 37 4/24-6/9 5/1 -6/9 15 1 , .. .,. 6.4 22.0 213 9 4 17 0 0 0 9 16 325 120 80 e/!?- -7/10 6/21-7/10 8 1 .,, ,.. 6.0 6.0 236 7 2 34 0 0 0 32 38 190 66 46 a These d a t a show average B.O.D. iemovals, nitrogen utilization, and results of plutonium assays for the indicated observation periods and recirculation patterns. b Values listed are ratio of volume recirculated to raw feed t o primary filter. Recirculation is from bottom of settling tank. Raw feed maintained a t 0.3 million gallons per acre per day. c Raw values are on straight wastes. Primary effluent and secondary e 5 u e n t values are obtained from samples filtered through Whatman N o 2 fluted filter paper. d Direct nesslerization method. e Phenoldisulfonic methqd. f Raw values are on straight wastes. Primary effluent and secondary e 5 u e n t values are obtained from samples filtered through Whatman No. 2 fluted filter paper. (Summary of selected Recirculation Patternb Pri. Sec. Pri. to to to sec. pri. pri. 6.6 6.6 ,,. . .. 1 2 . 0 ,. , ,. 6.4
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July 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
other features of the process there seems to be no need for seeking the minimum phosphate level. The relationship between the nitrate and plutonium content of the effluent has already been pointed out. A nitrogen balance on the trickling filter system has never been possible. At least two factors may enter into this situation. First, there is the storage of nitrogen by the filter microflora and fauna in the form of organized protoplasm. As a corollary t o this storage factor, it may also be expected t h a t due to periodic discharge of biological floc in the cycle of the filter, more nitrogen might be d'ischarged in the effluent at times than entered the filter in the feed. These factors alone are sufficient to preclude the possibility of working out a nitrogen balahce on the system. A possible mode for the dissipation of nitrogen lies in the well-known Van Slyke reaction-i.e., under certain circumstances ammonium nitrite may decompose with the formation of gaseous nitrogen and water. Any nitrogen lost in this way could not be accounted for. The possibility that substantial amounts of nitrogen may leave the system in the form of organic nitrogen has been investigated. Organic nitrogen determinations were made on the effluent and the amount of organic nitrogen leaving the system in this way is relatively small in relation to the discrepancy between the nitrogen fed in the form of ammonia and the nitrogen discharged in the form of nitrate. From examination of the data it has been observed t h a t in all the studies where B.O.D. removal was good and high recirculation ratios used, almost all of the ammonia nitrogen was converted to nitrate in the primary filter. The individual observations have indicated both the storage of nitrogen and releases of nitrogen by the system. The secondary filter does not differ from the primary filter in this respect. Very little nitrite has been noted in either the primary effluent or the secondary effluent a t any time. Apparently with these high recirculation ratios and low loadings the nitrite is almost completely oxidized to nitrate as fast a s it is produced. I n this connection it might be well t o point out t h a t during the course of the operation of the filter there have been occasional periods when high nitrates were produced in the effluent during a period of relatively low nitrogen feed. It was in fact, the observation of these accidental periods which lead t o the investigation of increased ammonia feed as a factor in plutonium removal. I n the application of a trickling filter system t o the treatment of laundry waste there will be two points of removal of plutonium. First, a certain amount of plutonium will be carried out with the settleable solids that are removed ahead of the filter. It is, of course, possible and may be desirable, t o eliminate this step by stirring or mixing the waste before sending it to the trickling filter system. The second point a t which the actual plutonium removal will occur is in the suspended solids in the secondary effluent. It is impossible t o contemplate this system without either removing the solids from the secondary effluent by very perfect sedimentation or by filtration. I n the pilot studies reported long periods have occurred in which the suspended solids have been very low (10 p.p.m.). However, for any sustained operation it is obviously necessary to assume that substantial amounts of plutonium may carry through the system in this fashion. This suspended material may be readily removed by filtrations. During operation of the two-stage trickling filter for the past &month period the settleable solids have been very low, less than 0.2%.
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These solids have been recirculated with the effluents over the filters. This mode of operation did not cause a build-up of settleable solids in the system during the period of study. It is reasonable that sustained operation will cause some increase in the settleable solids in the filter.
Conclusions Comparative studies of the chemical precipitation process and of the trickling filter process for removing plutonium from laundry wastes show the following: 1. Either process will effectively remove plutonium from the wastes. 2. The volume of sludge produced by the chemical process will be in the order of 25 t o 30 times the volume produced by t h e trickling filter process. This factor is extremely important since the sludge will contain the plutonium; and handling radioactive sludge is hazardous and complicated. On this basis the trickling filter process appears the more attractive. 3. A trickling filter plant design should provide the following features: ( a ) A holding tank to allow continuous application of the laundry waste t o the filter system at a constant rate. (b) A two-stage trickling filter system with provisions for varied recirculation ratios. Present data indicate t h a t series operation with a recirculation of 6 to 1 or more over each filter will effect the desired plutonium removal. However, it may be necessary t o recirculate a t a rate a8 high as 15 t o 1 while placing the filter system into operation. ( c ) Extremely low rates of application of the raw laundry waste with respect t o volume and B.O.D. The data show that desired plutonium removal may be effected at an application rate of 0.3 million gallons per acre per day with a B.O.D. loading of about 150 pounds per acre-foot per day, based upon the primary filter. ( d ) Facilities for adding supplemental nitrogen and phosphorus t o the laundry waste before it is applied t o the primar filter. The nitrogen may be added in solution as ammonium sugate and the phosphorus may be added in solution as trisodium phosphate. The amount of nitrogen in t h e waste should be sufficient and the mode of operation such as to ensure t h a t the final effluent will contain a relatively high concentration of nitrates. (e) The secondary effluent should be filtered t o ensure removal of any suspended matter carried over. Exploratory studies indicate that a n ordinary rapid sand filter will be effective. The filter backwash should be returned to the laundry waste holding tank.
Acknowledgment The work upon which this paper is based was performed at Los Alamos, N. M., by cooperation of The University of California, United States Public Health Service, and United States Atomic Energy Commission.
Literature Cited (1) Christenson, C.
(2) (3) (4)
(5)
W.,Ettinger, M. B., Robeck, G. C., Hermann,
,E. R.,Kohr, K. C., and Newell, J.F., IND.ENG.CHEM.,43, 1509 (1951). Huekelekian, H., Sewage and I n d . Wastes, 22, 87-93 (1950). Moore, W. A., Kroner, R. C., and Ruohhoft, C. C., Anal. Chem., 21, 953 (1949). Newell, J. F., U. S. Atomic Energy Commission, Technical Information Division, Oak Ridge, Tenn., AECD-2712 (1950). Ruchhoft, C. C.,Sewage Works J., 21,877-83 (1949).
RECEIVED November 24,1950.
