Ion Exchange in Beet Sugar Factories -
JOHN W. MICHENER, BRYANT FITCH, AND ELLIOTT J. ROBERTS The Dorr Company, Denver, Colo. I o n exchange has now been applied on a commercial scale in sugar beet factories to purify second carbonation juice, green sirups, and molasses. Favorable reports have been given for the first two, and the operation on molasses seems to have been very profitable during the years of sugar shortage. Use of ion exchange at other points in the process has been considered. In the sugar recovery process the earlier the ion exchange treatment is applied, the greater the apparent potential advantages. However, operation ahead of a defecation step involves problems relating to the elimination of colloidal impurities. Operation on green sirups, where only a portion of the juice is treated, minimizes the amount of adaptation required in the remainder of the process and has proved profitable. Advantages of ion exchange purification of sugar beet juices include: greater recovery of white sugar, extractions up to 9394 being reported; better color removal; production of low ash white sugar; crystallization of two or three strikes of white sugar instead of one; elimination of evaporator and pan boilouts; production of edible molasses, and greater potentiality for by-products.
D
URING the 1948 beet sugar campaign (crop year) four
factories operated commercial scale ion exchange installations, each for their second year. Initial operating difficulties have been largely overcome, and much headway is being made in integrating this new unit process into sugar technology. Therefore it seems of interest to survey the subject as a whole and to outline current practice and development. The theory of deionization in general, and as applied to sugar beet juices in particular, has been amply covered in the literature (7, 13). Although the word “demineralization” has often been used to designate an operation involving successive treatment of a solution with cation and anion resins, the removal of organic substances, notably nitrogen compounds, is a highly important function of the ion exchange operation in sugar juice processing. Therefore the term “deionization” is preferred. It is ions, actually, and not minerals as a class, that are being removed. Since presentation of this paper, a t least two excellent surveys (8, 19) dealing with aspects of the same subject have been published.
filterable. The filtrate is further carbonated to remove as much as possible of the calcium remaining in solution and is again filtered. These operations eliminate not only colloidal impurities but also a substantial, amount of other impurities, both by precipitation as insoluble calcium salts and by adsorption in the calcium carbonate precipitate. The resulting solution is called “second carbonation” juice. 3. Second carbonation juice is treated with sulfur dioxide t o control its pH and to improve the color of the sugar produced. Itsis then evaporated to produce a concentrated sirup, or “thick” juice. Thick juice is filtered, sometimes after treatment with an adsorbent material such as activated carbon. 4. Successive crops or “strikes” of sugar are crystallized by further evaporation of the thick juice. Only the first strike of sugar in a standard (nonion-exchange) plant is taken as production. Succeeding strikes, usually two in number, are substandard. They are therefore “melted” or redissolved, and recycled for recrystallization to some point in the process ahead of the first strike. Intermediate mother liquors are called “green” siru s, and the final mother liquor, after all the sucrose feasible has teen crystallized, is molasses. 5. I n the Steffens process, molasses is further treated with lime to recipitate tricalcium saccharate, which is returned in place of yime to the defecation step. The final barren solution, called Steffens filtrate, has a very low sucrose content. I n some cases i t is processed for recovery of monosodium glutamate and other amino compounds. An old rule of thumb tells us t h a t each pound of nonsugars present in a juice prevents crystallization of 1.4 pounds of sugar. I n the past, any economical means of increasing the purity (percentage of sucrose in dissolved solids) of the process juices or sirups by one degree has been thought a good plant investment. Deionization for the purification of sugar beet juices has now reached its majority, and on a commercial scale is doing a better job by some five to ten times. For example, in one plant the average increase in purity when treating second carbonation juice was from 90.8 to 98.0% (6). Such an increase in purity and the correspondingly high removal of nonsugars mean many pounds of sugar for marketing instead of in molasses. APPLICATION OF DEIONIZATION
Ion exchange has been tried or proposed for treating the following process liquors: diffusion juice, second carbonation juice, green sirups, molasses, and Steffens filtrate. DIFFUSION JUICE.Early in experimental work it was found that an ion exchange process, in addition t o removing ionizable impurities, could also serve in place of the standard liming and carbonation steps to coagulate colloidal impurities. These are flocculated at the low p H resulting from cation exchange. The column of cation exchanger serves to filter out some of these coagulated colloids and suitably complete removals can be obtained by filtering the acid effluent from the cation cell before i t passes to the anion cell. Deionization of raw diffusion juice thus offers a n apparent simplification of the process. By purifying at this point, liming and the lime kiln are eliminated, as well as both carbonations and one filtration. Further application of deionization to diffusion juice results in a number of advantages shared with the operation on carbonation juices, which will be considered subsequently. I n either case, the thin juice is free of calcium, so there is no scaling in
STANDARD SUGAR PROCESS
For the convenience of those unfamiliar with sugar beet processing, the standard process for recovering sugar from beets is outlined in the following: 1. Sugar, along with impurities, is leached from sliced beets by counterrurrent extraction with hot water. The resulting impure dilute sugar solution is called “diffusion” juice. 2. Diffusion juice is heated and limed to precipitate the colloidal impurities, and then carbonated t o remove excess lime. Essentially complete removal of these pectinlike colloids is necessary to prevent gelling of the sirups during subsequent processing and to avoid production of off-color sugar. Actually this defecation step is carried out by adding a substantial excess of lime and then carbonating back to the pH optimum for precipitating the colloids, in order to obtain a precipitate that is
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
evaporators or pans. Quite important savings can be attributed to the corresponding lack of boilouts, shutdowns, and increased steam efficiency, although these are hard to evaluate closely in terms of dollars and cents. dlso, the thick juice has a purity of 987, or better; this permits several strikes of high puiity sugar as well as the economies achieved tiv elimination of the reboiling step. Treatment of rav.7 diffusion juice has been tried (9) and to date has not proved economical. First, the ion exchange load is substantially greater when tieating raw diffusion juice than d e n treating defecated juice. The liming process removes enough ionizable constituents so t h a t after defecation about one third mole juice can be treated through a given pair of exchange columns per cycle. Secondly, the acid-coagulated colloids are difficult to filter. Costly amounts of acidproof filtering equipment, of filter aid, and of labor are required. Thirdly, the colloids are foaming agents of astonishing potency, and special precautions are necessary in handling the juice through the cation cell and the filters. Also, the foam has an aggravating tendency t o float the resin out of the cells on backwashing. As an alternative t o the difficult interbed filtration, the colloids may be iemoved from the juice by a simple defecation step either following or preceding the ion exchange. Predefecation with lime is being widely considered. It offers the advantage of keeping the colloids out of the exchanger columns and also of reducing the load on the ion exchange station. Some of the anionic impurities are precipitated by the lime and are made up in the juice by alkalinity, whereas the increase in cationic impurities which might be expected from uptake of calcium is largely compensated for by precipitation of magnesium as the hydroxide. The resultant predefecated juice has only a slightly greater ionic load than second carbonation juice, by virtue of its higher calcium content. From the ion exchange standpoint it may be considered as essentially equivalent to second carbonation juice. Therefore, to be economically feasible, the defecation step must be cheaper than the standard carbonation steps which cost in the neighborhood of 30 cents per ton of beets. Thus far filtration of the precipitate obtained by lime predefecation also has proved so difficult and expensive that the process has not yet appeared preferable t o conventional carbonation. A further and relatively less impoi tant disadvantage of predefecated juice, as compared to second carbonation juice, is its higher calcium content. Economy dictates the use of sulfuric acid as a cation exchange regenerant. JVith high calcium juices, calcium sulfate tends to precipitate in the exchanger during regeneration. This mag plug the bed completely, but even failing this, it is detiimental to bed capacity and to purity of effluent. The potential advantages of treating diffusion juice appear to be many, and the problems encountered, particularly when preliming is contemplated, do not seem insurmountable. The problem of calcium sulfate precipitation is commonly encountered in the water treatment field, and expedients are known for overcoming it. Several individuals and companies are working on the filtration problem, and there is little doubt that it nil1 be solved. It seems likely that deionization will be applied successfully to diffusion juice in the near future. SECONDCARBONATION JUICE,Following conventional carbonation operations, the juice is free of the colloids which cause trouble in ion exchange. Also, following second carbonation, it is relatively low in calcium, and existing factories have facilities for carrying out the carbonation steps. Therefore, second carbonation juice appears a logical material on which to start ion exchange operations a t the present stage of development; during the 1948 campaign all full scale deionization installations operating in beet sugar factories worked on this material. The over-all process advantages of operating on second carbon-
Vol. 42, No. 4
ation juice are essentially the same as for operating on diffusion juice. The carbonation steps act essentially only as a rather elaborate defecation system when used in conjunction with dvionization. The magnitude of t'he benefits actually realizetl in operation will be apparent from the data presented. GREENSIRUPS. Another point a t which deionization (>au work to the sugar man's advantage is in the treatment of greeii sirups. This has bean reported by Barry and Gaddie ( 1 ) . -It Utah-Idaho Sugar Company's SVest Jordan, L'tah, factory i t deionization unit was set,up to treat green sirup from the high rancentrifugals. Sirup was diluted t o 30" Brix with sm.eet,a-ateror factor>.thin juice and deionized by passing through two cationanion units in series. The treated sirup was added t o the evaporator feed and no attempt was made to raise the purity to over RO%, which in this factory is normal t,hick juice purity. The installation was large enough t o treat only 25% of thc, available sirup. Operating in this fashion, t'here is a minimum of adaptation required in the rest of the house, while much of the potential advant,age of ion exchange can still be realized. One inherent advantage of working on a green sirup is that inversion is decreased as compared t o similar operation on thin juices. Hydrogen cxchangers act as a solid acid to catalyze inversion of sucroso. The quant,ity of invert formed is proportional to t,he quantity of sucrose passed through the exchangers, and in green sirups palt of the sucrose has been removed by crystallization. It might be assumed that the dilution introduced into the sirup in sweetening on and sweetening off the exchanger cells would be greater when treating the thicker or more concentrated material. On a percentage basis this is true, but on a total quantity basis: the difference seems to be negligible. I t takes but a little more water to sweeten off a cell which has been operating on a, 30" Brix sirup than is required after operating on thin juice. The quantity of resin to be sv-eet'ened on and off per day dependh on the quantity of nonsugars to be adsorbed and not, on the sugar concentration. The total quantity of adsorbable nolisugars present has been relatively unaffected by evaporation and boiling out pure sugar. Therefore, although the percentage dilution is greater when operat'ing on green sirup as compared to operating on thin juices, the actual addit,ional water to be evaporat,ed is not significantly different. By postponing deionization, the advantages of clean heating surfaces in t,he evaporators and pans have been aut,omat,ically lost. The simple three-boiling system with recycling of deionized green sirup such as practiced a t SI-est' Jordan would require modifications to treat, t,he entire flow of sirup, because noncrystallizable sugars and unadsorbable impurities would build up to an interfering level in the cycle. In the aut'hors' opinions the greatest advantages of trea.ting green sirups are realized in a part-scale operation, and as an intermediate step between straight house operation and full scale ion exchange treatment. ~IOLASSES. The fourth point of application of deionization is the treatment of molasses. This has not been applied to improve the yield of sugar, but. rather to produce a highly refined edible grade molasses. During sugar rationing, this product was in great demand and highly profitable. The economic soundness of such an operation depends on the price spread between molasses and the refined sirup produced. Operating costs are the same as when treating second carbonation juice and most advantages are lost. STEFFENS FILTRATE.The final point a t which deionization may have a place in the beet sugar factory is in the recovery of by-products from Steffens filtrate. Glutamic acid is the most obvious and one which i t is profihble to obtain; recovery of betaine has also been proposed (IO). In Table I an attempt has been made t o summarize graphica'lly some relative advantages of the alternative processes. Straight house operation is used as the basis of comparison. The data
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1950
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OF ALTERNATIVE OPERATIONS~ TABLE I. COMPARISON
Reduction
2nd psrbonation juice Green sirup Molssses
Yes
Increased
Improved
Decreased
Edible
Slight
Process Steps Eliminated Carbonation a n d part of sugar reboiling P a r t of sugar reboiling
No
Unaffected Unaffected
Possible Possible
Very slight 0
P a r t of sugar reboiling None
NO
Decreased Decreased (potentially) Not affected
Inediblea Edible
Steffens filtrate
Increased Increased (potentially) Not affected
Not affected
Possible
0
a
of
Scaling Yes
No
Extraction Increased
Sugar Purity Improved
Molasses Quantity Decreased
Molasses Quality Edible
Sugar Lost by Inversion Slight
By-products Recovery Most advantageous Possible
Material Treated Diffusion juice
Sugar
Not affected
None
As operated at West Jordan: total deionization of green sirups without recycling would give edible molasses.
show t h a t greater potential advantages exist when deionization is applied early in the refining process. POTENTIAL BY-PRODUCTS
I n at least two of the commercial installations, some provisions have been made for the future recovery of by-products from the ion exchange operation. Of most immediate importance is the recovery of spent regenerants for fertilizer. I n most of the factories, sulfuric acid and ammonia are used as rrgenerants. The sulfuric acid regeneration of the cation cell displaces into the effluent organic nitrogen compounds and cations including potassium and trace elements. The spent anion regenerant retains all its ammonia nitrogen and contains in addition organic nitrogen eluted from the exchanger. Thus together the spent regenerants contain most of the minerals originally in the beets, considerable organic nitrogen, plus large amounts of ammonium sulfate. The fertilizer value of this material is obvious. The total spent regenerants constitute a relatively dilute solution of the order of half normal total concentration. While the solution might be applied, as is, to the fields, perhaps through addition to irrigation water, i t will probably require evaporation t o reduce its bulk and facilitate transportation. I n the Hardin, Mont., plant of the Holly Sugar Company the spent regenerants are being ponded for solar evaporation and subsequent recovery. A number of the impurity compounds present in beet juices are potential by-products. A few possibilities are pectin, betaine, and glutamic acid. Of these, the most immediate prospect for profitable recovery is glutamic acid (6). This compound may be present in the juice in three forms: as glutamic acid, as its half amide, glutamine, and as pyrrolidone carboxylic acid. The first two are removable by a cation resin and can readily be recovered from it, relatively free of ash cations, by selective elution with ammonium hydroxide, Pyrrolidone carboxylic acid is adsorbed by the anion exchanger but cannot be isolated from accompanying anions as expediently. Exposure t o the heat and high p H of conventional carbonation steps converts the glutamine into pyrrolidone carboxylic acid, in which state i t is more difficult to isolate from accompanying impurities. Therefore, as indicated in Table I, recovery of glutamic acid as a by-product of exchange operations would appear most advantageous when treating diffusion juice. PLANTS TREATING SECOND CARBONATION JUICE
PIONEER PLANT.The pioneer installation of ion exchange for purifying sugar beet juices was a t the Mount Pleasant, Mich., plant of the Isabella Sugar Company. It was operated during 1941 by Vallez ( 1 4 ) . Second carbonation juice was treated, and it is reported t h a t as many as five strikes of white sugar were obtained from the treated juice. Many of the process expedients for handling the treated juice which are being rediscovered in current operations were employed by Vallez in this early operation. Among them are sulfuring of treated juice and careful control of the p H of the treated juice.
The Isabella operation was not a success economically. Its failure is attributed primarily t o the lack of stability of the anion exchangers available and used at that time. Although exchangers of today are enormously improved and completely outclass those used a t Mount Pleasant, the maintenance of anion exchange capacity is still recognized as an important problem. PRESENT-DAY PLANTS. Three full scale ion exchange installations operated on second carbonation juice during the 1948 campaign. These are the Twin Falls, Idaho, plant of the Amalgamated Sugar Company, the Hardin, Mont., plant of Holly Sugar Corporation, and the Layton, Utah, plant of the Layton Sugar Company. The principal features of these installations are given in Table 11. I n genoral all the ion exchange installations ran smoothly during the past campaign and gave technically good results. Table I11 shows purification results reported from the three factories. The most immediate problem encountered during the first campaign operation had been in boiling the deionized juice. The essentially colorless juices obtained by ion exchange treatment turned a very dark color during further processing. hiore than one strike of truly white sugar could not be obtained, and also it was found difficult to get proper crystallization in the low purity strikes.
TABLE 11. PRINCIPAL FEATURES OF EXCHANGE INSTALLATIONS Twin Falls Layton Hardin Average daily slice, 2650“ 1190 1807 1948 cam aign, tons beetsFday 2200 b 2700b 1640 Cation resin, total cubic feet Anion resin, total 2200 1650 1640 cubic feet Push button Manual Push button Type of operation Cation regeneration HtS04 (%stage) HzSOa (2-stage) HzSor (3-stage) NHaOH Anion regeneration NHaOH XaOH NHaON 4b 46 4 Pairs of cells Size of cation cells, 12 x 12 10 X 14 10 x 10 feet Size of anion cells, 12 x 12 10 x 11 10 x 10 feet a Impurities returned in saccharate from Steffenizing 100 tons/day of molasses were added to juice and hence to ion exchange burden. b Figures do not include water softeners used for preparing soft water for use i n making up regenerants.
+
TABLE111. AVERAGEPURIFICATION OBTAINEDIN ION EXCHANGE OPERATION Twin Falls, Layton Hardin 1948 1947 1948 1947 1948 Av. purity“ second carbona92.6 93.8 92.7 90.8 89.2 tion juice % Av. puritya’deionized juice, % 97.1 98.6 97.2 98.0 97.1 626 78 65 80 75 Av. apparent removal of nonsugars % ~ v nitrdgen . removal, % 51.6 45 Av. ash on sugar, % 0.0645 0.’003 0.0008 a Purities here reported are “apparent purity” which is a n approximate value determined instrumentally; i t is the common control analysis in augar factories. b Steffens process operations here increased quantity of impurities present which are not removable b y ion exchange.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
By the 1948-1949 campaign the color problem was well under control and no difficulty was found in working the low purity sirups. Two and three boilings of white sugar were obtained, and the molasses from ion exchange juices were reported to be running lower in true purity than straight process molasses. Three means were employed t o prevent color formation: First, the juice was boiled at low temperatures. Instead of operating the pans a t a temperature of above 90" C., they were boiled at as low as '70" C. Thick juice filtrations Tere carried out at as low a temperature as feasible, and considerable reduction in temperature was possible because the deionized juice had a lowered viscosity. Secondly, high p H was avoided during boiling. It has been customary in many factories to boil at a fairly high pH, about 8.8, because this decreased the sulfite content of the finished sugar. I n the presence of invert sugars, such a p H leads t o rapid color development. Thirdly, the juice was sulfured either before and/or after treatment. It has been found in practice that sulfites do inhibit color formation and also improve the workability of the juice. The color fors u m a b l y caused ,Z+ U95 by reactions of the invert sugar produced through contact with the 1.0 cation exchanger. Invert sugars may react with the 0.8 amino compounds present in t h e juice to form in0.6 t e n s e l y colored and flavored products. Par0.4 ticularly a t higher pH's and temperatures the invert will caramelize. The benef i c i a l e f f e c t s of sulfur dioxide or 5 6 1 8 ' 4 1 0 s u l f i t e additions PH h ave been reFigure 1. Development of Color for ported by RawDeionized Juice of Various pH's lings ( 1 2 ) . The effect of p~ was investigated in this laboratory. Typical results are given in Figure 1 which shows the effect of heating deionized juice t o approximately 96' C. for various times a t various pH's. iZnother type of problem which came sharply into light during early operations was a progressive blocking or poisoning of the anion resins, unless steps are taken t o purge it of the poisonous impurities ( 6 , 11). The poisoning was absent when operating on green sirups and using caustic soda for anion regeneration ( 1 ) . There has been considerable experimental evidence that the capacity of anion resins can be maintained through intermittrnt treatment with acid and that the capacity of a cation resin for removing nitrogen compounds is likewise maintained by a periodic treatment with alkali. DENSITY
(400x1
TWIN FALLS OPERATION
The amount of juice processed through the ion exchange station during the 1948-1949 campaign at Twin Falls was limited by the amount which could be cooled for treatment. The coolers originally intended for use in the ion exchange plant were those in the Steffens process. The Steffens process ran
Vol. 42, No. 4
this year, and a flash cooler was assembled from materials at hand to cool the juice for ion exchange. This flash cooler was not put into operation until after the start of the campaign, and during much of the time handled about 65% of the total juice flow. Toward the end of the campaign i t was developed to handle over 90% of the juice. At Twin Falls sulfured second carbonation juice was fed through the ion exchange station and a certain amount of sodium suIfite was added t o the treated juice ahead of the evaporators. The juice was boiled a t pH 7 or less. The color stability obtained was remarkable. Even when deionizing only about half the juice, excellent white sugar was obtained for two boilings. During this time a total of four strikes was made to produce a molasses with a true purity of around 557,. During several days of the campaign the true purity of the molasses produced was below 50%, and it is expected that with total deionization a final molasses purity of around 52y0 can reasonably be expected. LAYTON OPERATION
At the Layton factory the entire flow of juice was deionized throughout their campaign. The Layton ion exchange plant is characterized by large cells in relation t o the juice flow and by manual operation. At Layton the juice was boiled a t a fairly high pH, but especial attention was directed to keeping the temperature low throughout the system. Three strikes of sugar were obtained; when blended, these passed the standard for whiteness. B total of six or seven strikes T T ~ Smade to obtain a final molasses with a true purity which averaged 57.55YC,but which was a t times substantially 10x5er. Since the plant was run completely as a deionization house, a clear picture of the economics of such operation for this factory was obtained. Results and economics were reported in gratifying detail by Ellison ( 5 ) . He attributes to ion exchange an extra 9.47, of sugar production worth $103,810. The reported operating profit was reported as 833,549 excluPive of plant amortization and carrying charges, but Ellison states his calculation of profit to be very conservative. This profit was obtained a t a time when the price of molasses was veiy high as compared to sugar and since the largest debit against ion exchange operation is the molasses not made, profit will increase rapidly as the price of molasses, relative to sugar, decreases. Ellison, as do other sugar men, expects to further increase profits by marketing soft sugars, which cannot be made from nondeionized sugar beet juices. HARDIN OPERATION
At the Hardin plant of the Holly Sugar Corporation about half of the juice was treated through ion exchange during the 1948 campaign. Because of poor beets which gave the relatively low original purity of the juice, as indicated in Table 111, and a high color, only one strike of white sugar was obtained from the combined deionized and nondeionized fractions of the juice. The standard three-boil system was used, and no trouble mas encountered in processing the juice. The flow through the ion exchange station a t Hardin was limited to about half of the total juice because of a mechanical plugging of the underdrain system. This was aggravated during much of the campaign by use of extremely muddy water t o wash and rinse the cells. The source of the plugging was eliminated before the 1949 campaign. At Hardin the juice was sulfured after ion exchange treatment. They too boiled the juice at about p H 7 and held temperatures low through the boiling operation. Although the color in the juice was high all the way through the operation, it was fairly stable and did not increase unduly in the boiling.
April 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY BIBLIOGRAPHY
(1) Barry, E. F., and Gaddie, R. S., Proc. Am. SOC.Sugar Beet Technol., 1948, pp. 674-80. (2) Diokinson, B. N., Chem. Eng., 55, No. 7, 114 (1948). (3) ~ l l iH.~E., ~ presented ~ , before the ~ i ~of sugar i ~Chemistry, i ~ ~ 115th Meeting of the AMERICAN CHEMICAL SOCIETY,San Francisco, Calif. (4) Ellison, H. E.,Proc. Am. SOC.Sugar Beet Technol., 1948, pp. 557-62. (5) Fitch, E. B., and Michener, J. W., Ibid., 1948,pp. 696-704. (6) Haagensen, A. E., Ibid., 1948,pp. 690-5. (7) Haagensen, A. E.,Sugar, 41,36 (1946). (8) Jacobs, R. T., and Rawlings, F. N., IND. ENQ. CHEM.,41, 2769-75 (1949).
647
(9) Maudru, J. E.,Proc. Am. SOC.Sugar Beet Technol., 1947, pp. 161-7 1. (10) Nees, A. R.,and Bennett, A. N. (to Great Western Sugar), U. S. Patent 2,375,165(May 1, 1945). L.s.,prOc.Am. SugarBeetTechnol., 1948,PP. 714-21. (11) (12)Rawlings, F. N.,Jacobs, R. T., and Cole, E. B., 7th Intern. Congress Agric. Ind., Paris, France (May 1948). (13) Thompson, R. B., and Roberts, E. J., Chem. Eng. Progress, 43, No. 3,97(1947). (14)Vallez, A. H.,U. S. Patept 2,388,194(Oct. 30,1945). RECEIVED August 9, 1948. Presented as a part of the Symposium on Ion Exchange Application before the Division of Water, Sewage, and Sanitation CHEMICAL SOCIETY, Chicago, 111. Chemistry, 113th Meeting of the AMERICAN Revised 1949 to include data. from 1948-1949 campaign.
*
Treatment of Rice Water
n
CHARACTERISTICS AND LABORATORY STUDY HOVNANESS HEUKELEKIAN New Jersey Agricultural Experiment Station, Rutgers, N . J .
T h e waste water produced from the preparation of Minute Rice is carbonaceous and deficient in nitrogen. The solids are i n finely divided, i n colloidal, and in soluble forms. The average B.O.D. of the composite waste is around 1000 to 1100 p.p.m. with wide variations. Laboratory tests show that plain sedimentation results in only 30% B.O.D. reduction with accompanying large volumes of sludge. Lime treatment of settled liquor (1000 to 4000 p.p.m.) produced a n additional 15 to 40% B.O.D. removal. The anaerobic digestion of the raw rice water gave consistently satisfactory results. With B.O.D. loadings of 0.1 pound per cubic foot digestion capacity per day and a detention time as low as 1.2 days, a B.O.D. reduction of 92% was obtained. Without lime neutralization and with only small amounts of ammonia added for nutritional purposes, the efficiencies were as high as with neutralization, but the loadings were lower. The aeration of the raw waste with suitable seed material for 24 hours and sufficient quantities of nitrogen for nutritional purposes produced an effluent with 25 to 50 p.p.m. B.O.D. and reductions of more than 90%.
are 35 to 1. These ratios indicate that for biological treatment the nitrogen content is somewhat inadequate and has to be supplemented, whereas the phosphorus content is ample. The waste contained 1200 p.p.m. of starch and 70 p.p.m. of reducing sugars. On the basis of 0.6 to 0.7 part of 5-day B.O.D. for each part of starch and sugar, these two ingredients alone ahcount for 70 t o 80% of the total B.O.D. Five hundred and thirty pounds of B.O.D. and 730 pounds of solids are produced per ton of raw rice handled.
TABLE I. CHARACTERISTICS OF COMPOSITE RICEWASTE 4.2-7.0 1460 20.6 610 10.8 30 30
PH Total solids p.p.m. % Suspended Ash in totafsolids, solids, p.p.m. Ash in suspended solids Yo Total nitrogen (N), p.p:m. Phosphates (PI, p.p.m. B.O.D.. o.u.m. Starch,'p.p.m. Reducing sugars, p.p.m.
1 ne5 . ___
1200 70
T R E A T M E N T OF WASTE BY SEDIMENTATION
I
N T H E preparation of Minute Rice large volumes of wastes
are produced from soaking, cooking, and washing processes. The volumes of waste produced from the different processes are: Soaker Cooker Drain belt Drain tank Total
Gal./Ton 8,400 8,400 24,000 20,000 60,800
On the basis of 30 tons of raw rice handled per day, the total waste volume is about 1,800,000gallons. CHARACTERISTICS OF WASTE
The average analyses of a number of composite samples are given in Table I. The p H values, which varied from 4.2 t o 7.0, are affected by changes during shipment of samples. The total solids were 1460 p.p.m. and the ash in the solids was 20.5%. The suspended solids were 610 p.p.m. with an ash content of 10.8%. The waste had a nitrogen and phosphorus content of 30 p.p.m. each. The average B.O.D. of 20 samples was 1065 p.p.m., with a minimum of 400 p.p.m. and a maximum of 1590 p.p.m. The B.0.D.-nitrogen and B.0.D.-phosphorus ratioa
Plain sedimentation gave the following results:
a
Total solids Suspended solids B.O.D. 1-hour sedimentation.
Before Settling, P.P.M.
Aftera Settling, P.P.M.
Reduction,
1816 753 1380
1446 31 979
20.5 96 29
%
The rather low removal of B.O.D., despite the high removal of suspended solids, indicates that most of the B.O.D. is in the form of colloidal and soluble materials. This is substantiated by filtration of the waste through a Gooch filter, which gave a removal of only 25% of B.O.D. The sludge formed by sedimentation was thin and variable in volume, averaging 13.0% of the total volume of waste. I n view of the low B.O.D. removals and high sludge volumes, plain sedimentation is not a suitable method of treatment. LIME TREATMENT
Settled composite waste was treated with various quantities of lime, stirred gently for 20 minutes, and allowed t o settle. The average results of four tests were:
