BEET SUGAR INDUSTRY BRUCE M. MCDILL ’
I
Ohio Department of Health, Columbus, Ohio
four major liquid wastes, aggregately large in volume and high in organic ocntent. Wastes fmm processing 1000 tons of beets m a y represent a population equivalent load of 126,000 to 230,000. A review of manufacturingprocesses, of waste characteristics, and of experiaees in the treatment of these wastes leads to practical eonolusions relative towastes disposal, embracing (1) waste elimination, (2) waste separation, (3) waste modi6eation for recirculation and re-use, and (4) treatment and/or storage of redud volumes for controlled discharge tn receiving streams.
A
5 I N so many food processing procedures, theextractionof sugar from the beet results in liquid wastesaf high organic
content which are difficult of disposal. Successful solutions of the waste disposal problem have been most troublesome. At present there are eighty-five or ninety beet sugar factories in t h e United States. T h w are located in seventeen states, the principal areas being California and the Paci6c Northwest, the Rocky Mountain states, and the states adjacent t o the Great Lakes. Ohio is the most easterly state supporting the industry. California and Co!orado together produce about 43% of the total United States beet sugar output; Idaho, Nebraska, and Utah, about 25% equally divided, Michigan about 11%, and’Ohio about 3%. Other states in the geceral areas indicated produce the remaining 17%. Ohio has four well established and successful factories, and it is of interest t o note that Only about 4% of the suitable beet growing area in, the state is being utilised. ,Mthough no de&& estiumte can be given, it is t o be assumed that the other states likewise have large areas which, though adapted t o beet p w t h , are unused for this p u r p w . . During 1935 to 1941, inclusive, about 32% of the world sugar supply was obtained from beets. During this period the United States produced from this souroe 17% of the sugar consumed. Present conditions are indicative not only of a revival of beet sugar prw duction to normal but of a program of material expansion by the industry. MANUFACTURING PROCESSES
Beet sugar manufacture is a seasonal operation. I n Ohio and the Great Lakes area, harvesting of beets starts about the-first of October and continues far the next 60 t o 90 days, the rate depending on storsge and slicing capacity of t h e factory. The factory will operate for virtually the same period, although storage facilities m y permit the campaign t o extend a little longer. It seldom lasts over 90 t o 100 days. The capacity of the plant is expressed in terms of tons of beets sliced per day. Generally, capacities range from 750 t o 2000 .tons. Of the four plants in Ohio, two are rated a t 1000 tons and two at 1200 tom. There are two distinct phases t o sugar extraction from the beeGnamely, the straight house operation. and the S M e n s process. The straight house operation is common to all plants
657
and is capable of recovering 80 to 85% of the sugar removed from the beet. The S M e m prooess follows t h e straight house operation and can r a v e l ‘ an additional 10% (approximate) of sugar. I n general, the processes for the manufacture of sugar from beets are about the same in all fwtoriea, and there are only minor variations in equipment and in methods of operation. Descriptions based on Ohio practices are believed t o be, for the most part, typical of all plants. Figure 1 is a flow sheet of the beet sugar manufacturing process. STRnram HOUSE OPERATION. After the beets have been weighed and tared, they are delivemj to the y d where they are stored overoradjacenttoaeystemofconcretech~e~usual?yrefeRed t o as flumes (Figure2). Lateral flumesteminate in aflume header which extends to the plant proper. AB needed, the beets arefloated hymeansofwatertotheplant (Figure2). Justaheadof the plant they are floated over a bar grating through which Stonea a d some sand and earth may fall for collection into a depraased section of the flume. This may best be referred t o as a stone catcher. Beyond the stone catcher is a weed catcher to remove parts of beet tops, weeds, and light vegetation. This latter e q u i p ment frequently comprises b traveling rake mounted on an endless chain. The forks of the rake sldm the surface ef the flume water in a direction advem t o the flow and thus intercept the vegetation. At this point a wheel elevates the beets to a washer. The flume water, having served ita purpose, passes on through the wheel t o the plant sewer. Water is supplied t o the washer which, by agitation, removes the dirt and.debris. This wash water discharges to the flume water sewer, where= the beets are moved hy a horizontal conveyor m o s s a p i c b g table to an elevator which moves them to the top of the p h t building. Here,they am weighed in a hopperahaped container and thence dumped into slicers. I n the slicers the beets are pressed against sets of rotating knives which cut them into long narrow rihbons, V-shaped in cross section, called “cossettes”. The cossettes then are transferred t o diffusion batteries (Figure 3), which comprise a series of cylindrical tanks or “cells” with valve openine at top and hottom. . Sugar is extracted by p w h g hot water (55’ or 65” C.) through the cells charged with cossettes. An important procedure is t o introduce the new or f m h water into the cell which has been under diffusion the longest, whereas the richer juices are introduced progressively into cells that have been charged for the shorteat time. Hence the juice just before dmwoff d l have been in contact with a cell charged with freshly cut cossettas. I n this way, by time, temperature, and volume adjustments it is possible t o extract all hut a small fraction of the sugar. T w o products result from this prm-usion juice or “raw” juice with sugar content of 10 to 13% and exhausted caaeettes or “beet pulp” with sugar content of about 0.2% based on weight of beets. The pulp is washed out of the cells, screened over B slotted screen (Efanger screen) with openinge of about 1 mm., and introduced into presses to remove 88 much water 88 -le before drying. Figure 4 shows the appearance of dry pulp. The raw juice from the dHusion batteries is delivered t o one of
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two carbonization tanka operated in seriea (Figure 5). In the first unit, milk of lime is added in suitable proportion and carbon dioxide, produced in a lime kiln from limestone and coke, is bubbled through the limed juice. The reaction precipitates calcium carbonate which drags out suspended solids and nonsugars wagdated by the mixture of lime and raw juice. The mixture is then filtered in presses or through Oliver filters to remove the sc-ealled lime cake and to produce the first press juice. The latter is then introduced to the second Carbonization unit in which more carbon dioxide is applied to precipitate the re msjning lime. The filtering of this mixture produces the second press juice and more lime cake. After the second filtration the juice is treated with sulfur dioxide to adjust its akalinity -md pH. The lime cake resulting from both fitrations is watered to a slurry, filtered, and washed t o remove the last trrtces of sugar. The h a l lime cake is a waste containing about 0.2% sugar based on beet weight. The thin juice (10 to 13% sugar) is conoentrrtted in multiple-effect evaporators to an evaporator thick juice of 55 to 65% sugar cantent. The pH of the thick juice may again be adjusted in accordance with tbe practices of the particular plant by the application of sulfur dioxide and t o it is returned certain melted sugar from a later process. Activated carbon may or may not be added for decolorization before the thick juice is subjected t o careful fitration. At this stage the juice is referred to as blow-up thick juice or pan sirup. The latter is boiled in vacuum pans (Figure 6) until crystals of the d&ed sire begin to form. The mixture of sirup and crystab, called “white massecuite”, is i n t m d u c d t o high speed centrifugal machines (Figure 7) in which the sugarcrystals are retained on a wire screen or basket, while the sirup is thrown through the screen. The last traces of sirup wded through the screen with hot water, and the wet sugar goes to the granulator’for drying, cooling, and screening. Automatic machines packzge the h a l product. The first sirup which leaves the chtrifuges is designated as high green, the second sirup as high wash. The latter, of higher purity, is fitered and returned to the vacuum pan near the end of the boiling operation. The’high green sirup is boiled again and centrifuged to obtain a second crop of crystals, high raw sugar. The mother liquor from this operation is boiled once more and, after centrifuging, res u l k in a third crop of crystals, low raw sugar. Both high and low raw sugars are remelted, returned~tothe evaporator thick juice before vmum pan concentration, and eventually recovered as white sugar. The mother liquor from the centrifuging of the low raw sugss is h o w u as molasses. It is so low in purity that no more sugar can be extracted profitably by crystdlimtion. STEPFENE F’ROOE~S.The molasses from the straight house operation, sugar content about 50%, is diluted t o a sugar e o n c e n t d o n of about 7%. Screened diffusion-battery wash
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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
water is frequently used for this purpo>e. T o t1iL cold solution i, added finely pulverized lime \\-hiell combines with tlie sweetCareful con.j to form calcinm triwcc1iar:ite. results in less than 1rC sugar renxiiniiig in tlie molasses. The misture is filtered through Oliver filters, arid the calcium trisaccharate c a f e is delivered to the carbouization tank and there added to t,lie difiuxion juice along with lime: the sugar recovercd from this stage is described in the straight house proch so-called hot Steffens process can lie used t o recover slightly mGre sugar. This comprises the addition of more pulverized lime to the cold process filtrate under steam pressure. The economy of the hot process is questionable, and it has not been practiced a t Ohio plants. Recently the market value of molasses as such has not justified the Steffens house operation a t all. FIXALPRODVCT. This represents the purest food produced, virtually 100n, digestible. The following foreign matmerialcontents are typical: moisture, 0.0257,; mineral ash. 0.0095; sulfates, less than 5 parti: per million; organic nonsugars, trace. BY-PRODUCTS
The beet pulp nashed from the diffusion battery cells, usually p r e w d and dried, represents a valuable by-product which, in the earlier periods of development, was thrown aviay n-ith other witst(' n-aters. The recovery of this material has not only represented a definite step in improved wastes disposal, but resulted in placing on the market a nutritious aninial feed. As previously indicated. the mol from the straight house operation reccnt1)- has had greater niarl~etvalue a s a by-product than as a sourre of additional sugar. \T-hetlier this condition continues is someivhat problematical. \-aluable c o n 4 t u e n t s of the molasses are sugar, proteins, from which amino acids can be 01)tained, and potash for use in fertilizers. Current report? are that the molasses have been rather generally used in the protluction of yeasts. Prior to 1942 Steffens n-astes from the Ohio and some of the Michigan plant,s were used for the manufacture of monosodium glutamate, a condiment or t a s k intensifier for canned soups anti other foods. Recovery of constituents of Steffens n w t e for ingredients of commercial fertilizer is reported by Eldridge (31 as successful during Korld \Tar I when prices of potash and nitrogen 1w-c a t high levels. His analyses indicated that, for each ton of beets sliced, Steffens waste liquor contained 3.6%, of potaih, 1.5 pounds of nit,rogen, and 12 pounds of organic matter. The characterijt>ics of the ingredients of straight house 1x10Insre? and Steffens wastes, in case this process is profitable, .seem to offer a field of continued research by which recovery of va1uaI)lc hy-pro~luct~s may be obtained. LIQUID WASTES
Combined wast'es from beet sugar ni:tnufitcture zire large in volume and are concentrated from the standpoint of organic solids contents. The straight house operation prcsmta three major sources of liquid n-aste-namely, flume xater, procc~swater, and lime cake slurry. Evaporator condeming water is a source of process water giving leaser concern, but it cannot tip c~ritirelyneglected in the analyses of 1)-aste disposal problems. The fourth major source of liquid waste is the end liquor resulting from the Steffens process and designated as Steffens waste. Figure 1 gives a diagrammatic indication of n-aste sources. FLunrE WATER. This v a t e r comprises that used in floating beets from the storage piles to the factory proper, together lvith that used in the beet washer. The volume usually amounts to 2200-2400 gallons per ton of beets sliced. By nature of the specific operation the waste contains large quantities of mud, sand, and debris, and hence is high in suspended solids. This particular characteristic depends considerably on the conditions
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under \vhicli t hc hects wxre harwsted and storcd, whether the on n-as w-et or dry, and h ~ \ vmuch soil clings to the beets. eeds, pieces of beet, tops. tails, and vegetation are present to a certain extent. 1Iechanical means of topping the beets and of loading thr,m in the fields tends to in se tl-ie dirt and foreign niaterial handled and is reflected in flunie wafCr characteristics. Broken and imperfect beets and beets daniagtd by frost impsrt organic solids \\-hich will be reflect,ed in the cisygen demanding properties of the wastes. The biochemical rlsygen tienland of this n-astr is not so high as wastes from other sources, but ihe over-all pollution load is significant, as \vi11 be indicated later. Thc equipment (stone catcher anti weed c a t c h t ~ j !noriiially introd u c ~ din ilic? flume tcni ahead of thc beet n-asher, i pl,iniarily to cs~iniinate to about I50 gallons per t o n of beets sliced. Drainage from continuous flow-through settling ponds is probably about 75 gallons. The drag-out of inipurities from t>he raw juiecs is reflected in the organic characteristics of t,his waste. STEFFESS\T*.AsTE~. The liquor remaining after the removal of all but a small percentage of sugar from s ~ r a i g h thouse moffens house operation constitutes the most con 'entratecl 'iv:tst~and the most difficult of modification and disposal. This iraite is extremely high in total solids, most, of which are in solution, :xiid i- extremely high in osygen demmding properties. The volume of this waste vnrie.; from 120 to 200 gallons per tlm of beetr sliced. COSDESSISG \\-.\TER. Evaporator condensing Lvater, as a rule, lins iiot heen considered as industrid vaste. The amount of \'apor etiti'ninmerit n-liich n.ill occur n o doubt will depend considcrnhly on the efficiency of equipment and on operation techniques. The volume of' this water required per ton of beets sliced amounts to : i h u t 1400 gallons. ht one plant studied it \vas estimated t h t conc!eii~ed vapors iiicreaserl tlii. volume tO about 1720 galloiii. Thi- \\-:iter is discharged :it :I relativcly high teniper:itnre 111 effect on the receiving stream nliicli c:uiiiot be eiitiw1)- overlooked. \\-.AS TI< I-OLLXJX. On the In-ii of no rwiti1iz:ition of ivastt's, the ngprepate volume from mijor iutlividual sources amowit,- to approsim;itely 3000 gallons per ton of l m t s sliced or 3,000,000 g ~ l l o n rper day for a factory of 1000-ton capzrity. &iddingto this the water used for eondenbing purposes, the totnl volume of waste for R factory of this capacity is about 4.4 million gallons per day. -1ctunl measurements of n x t e f l o ~ from s factories reflect witer conservation. \TASTE - ~ S A L I - S I S . From the standpoint of analyzing tlie wastes for modification and disposal and of evstluating pollution loads, solids contents (total, suspended, ant1 dissolved) and bio-
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Figure 3 (aboue). A Battery Cell Being Charged with Fresh Cossettes
Figure 4 ( r i g h t ) . Beet Pulp as Dried for .ininla1 Feed
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INDUSTRIAL AND ENGINEERING CHEMISTRY
cliemical oxygen demand (5-day B.O.D.), are of greatest value. Other constituents, such as nitrogen, alkalinity, etc., cannot be neglected in tlie detailed studies of waste modification. Solids and 13.O.D. for the several malor irn,tea vary considerably, depending on conditions under which the beets are handled and upon operating techniques in the different f:ictorieF. I n discwsing operating procedures with technicd pcrronnel of the industry, it ap11~ars that improved efficiencies for minimizing sugar losses may l i e refiectcd in wahte analyses. Urifortunritely, fen. recent analyses of w:ihtes I)>- specific classifications havc heen made because ( a ) supervi.-ion of industrial a.n-tes di>posnl during 1942 to 1945, iriclucivr, rieces-:u.ily had to lie neglectrd ; and ( h ) industry in efi'orts to reduce I)ollution 11:~sused v:iriou> methods of wihte rccirculation a i d re-u.e, nrid it is lielice difficult or impractical to obtain reprebentative samplrs of w:i& ified. Compositioiis of beet sugar factory wastes, as publislied by Eldridge (3) Elre considered typical nnd are given in Table I. Table I1 comparpr: these wastes from the standpoint of pollution lontl.
Table I.
Table 111. Analysis of Factory W a s t e of Buckeye S u g a r
C o m p a n y , I n c l u d i n g Condensing W a t e r (1925) Flow, million gallons per day &day B.O.D. (20" C.), p.p.m. Total solids p.p.m. Total volatiie solids. p . p , m . Suspended solids, p.p.m. Population equivalent o n B.O.D. Total volatile solids, tons Total suspended solids, tone
7-olume per ton of beets, gal. 5-day B.O.D. Total solids suspended solids Dissolved solids
Process Water
Lime Cake Drainage
2200 200 1580 800 780
660 1230 2220 1100 1120
75 1420 3310 450 2850
WASTE TREATMENT
Steffens Waste 120 10,000 43,600 700 42,900
Table 11. C o m p a r i s o n of Wastes (per Ton of Beets) Waste Flume water Process water Lime drainage Steffens Total
Volume % Gal./day 72.1 2200 660 21 6 2 4 75 120 3.9
B.O.D. Lb./day 7" 3.70 17.6 6.77 31.7 0.70 3.4
-
__
10 01
47.3 __
3055
100.0
21.18
100.0
Population Equivalent 22 40 4 60
-~ 126
Correlation of these d a t a with studies of the respective wastes at Ohio plants indicates that, under conditions where no waste treatment or re-utilization is practiced, the population equivalents per ton of beets may range from about 126 t o an extreme of 230. Elimination of the Steffens house process will reduce the pollution load by at least 50yGand in some instances by probably 75%. Analyses of factory wastes at the plant of The Buckeye Sugar Company, Ott'awa, Ohio, were made December 2, 1925, prior t o the time the company had made any effort toward waste elimination except for ponding of lime cake slurry and Steffens wastes. Included with the discharge of factory wastes was the condensing water. Results of these analyses (Table 111) hold interest from the standpoint of accomplishments to date. It was estimated a t the time of this study that, including the tn-o n-astes ponded for tlie duration of the campaign, the over-all pollution load of the factory was represented by a population equivalent of 130,000. A series of analyses of raw Tvater supply a t the river iiitalce and of condensing water a t the point of diecliarge to the plant sewer, respectively, of this Ohio plant are indicative of entrainment of organic solids. The average contents obtained on four surveys during 1939 and 1940 follo\r:
:E,%, Flow.
Intakeriveruater Condensing water
(20' C , ) ,
M , G , D . P.P.hI. 1.4 4.9 1 . 72 94
Solids, P.P.11. n - ~ ~ SusB . 0 D., Suspended Total pended Lb. Solids, Lb. 662 28 57 327 771 51 1347 731
These analyses :ire indicative of a definite increase in pollution load represented by 1200 pounds of B.O.D., equivalent to a population of 7720 or a population equivalent per ton of beet.? sliced of
3.16 409 6,164 1,260 5,056 64,500 16.6 66.6
about, 7.7. The inereme in suspended solids is of someuliat less significance, amounting to 404 pounds. Corroborating the extreme concentrations of Steffens wastes a s bet forth in Table I ( S ) , average contents of a series of four analyses of 24-hour composites from the plant of The Buckeye Sugar Company were: 5-day B.O.D. (20" C.), 17,500 p.p.m.; total solids, 39,500 p.p.m.; suspended solids, 348 p.p.m.
Composition of Vastes (in P.P.M.) Flume Water
66 1
~
Factors definitely affecting the treatment and disposal of beet sugar wastes are: the extremely large volumes of wastes of variable characteristics, high organic contents of wrtstes, seasonal operation of beet sugar manufacture, normally low sta,res of stream flows during the beet sugar campaign, and high costs of waste treatment processes capable of degrees of waste modification sufficient to meet many stream requirements. I n many localities water conservation, if not essential t o the industry from the standpoint of cost, is most desirable in the advancement of tile social and economic welfare of the citizens. The beet sugar industry is a community activity affecting the farmer, employmont of local labor, and factory managing personnel. The economic advantage of the industry to the community must be considered in the approach to the waste treatment and disposal problem, but the responsibilities for stream pollution abatement are no less essential. Elimination of wastes by changes in manufacturing processes, and reduction in volumes of waste by modification and re-use of waters and by recovery and reutilization of by-products merit much study in an endeavor to reduce the cost of satisfactory industrial waste treatment and disposal. The general history of beet sugar waste treatment and tile problems inherent t o the disposal of these wastes is well covered by Eldridge (3). Serious efforts were first necemary in the European areas. Germany, for instance, conducted research and experimentation before the problem became acute in the United States. It was early determined that separation of wastes from the major sources with individual treat,ment was the most logical approach. A German treatise on industrial wp.ste treatment by Boehm ( 2 ) discusses early methods, including re-use of flume water after removal of sediment and the double-fermentation Hildeshein method of treating process mater in pondh, combined with sand filtration or brond irrigation. .inother German article by Nolte ( 7 ) refers to the Salawedler method of process water treatment'. This comprised a controlled fernientation-septization process in a series of three ponds. The process reportedly vas effective in the destruction of organic solids. POSDING AND LAXD IRRIOATION. By renson of tlie large volumes of wastes incident to beet sugar niariuf:xture and of the characteristics of the flume Kater (virtually three fourths of the volume of the whole), sedimentation in relatively large ponds hrzs been given first consideration. Settling ponds oi the flow-through type piwide reasonably effective clarification for the first two or three weeks. However, decomposition of accumulated organic solids soon give rise to gas product'ion, hydrogen sulfide odors,. and lifting of solids. Before the campaign has progressed far, a pond effluent contairis polluting characteristics ~ ~ - h i cmay h be even worse than the raw 11-astes. Long period storage, applying principles of fermentation and septization, 'offers complexities of control and has the disadvan-
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Start Crystallization
t,age of producing serious odor nuisances. Infiltration- t'hrough . and .breaks of earthen embankments present hazards relative to the escape of concentrated wastes a t inopportune times. Constant attention to the maintenance of pond embankments is essential. Ponding of lime slurry in a relatively small unit for the extent of the campaign with drawoff of supernatant to the stream at times of high river flow has been reasonably successful in many instances. To maintain effective pond capacities, the lime sludge must be removed annually. Factory management has depended rather generally on use of t,his material by the farmer for its fertilizing and soil building properties. Ponding of Steffens waste for the extent of the season has in the past been rather general practice. Because of its high organic content the discharge of this waste t o a stream must be controlled carefully; the amount of oxygen
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INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1947
Land irrigation even with screening and presettling requires large areas. This method of disposal has not been considered practical in this country. FLUME TT-ATER CLARIFICATION.Reasonable clarification of flume xvater can be accomplished by screening, grit removal, and sedimentation. These units may be typical of those used in modern sen-nye treatment, Screeni of the slotted, drag, or rotary t'ypes are applicable. inch have been used successfully in the drag Slot openings of type screen. Rotary screens with openings of l / ~X 3/4 inch and a capacity of about 1 square foot per 800 gallons per hour maximum rate of flow have been recommended by Eldridge (3). Irregular rates of f l o ~or surges 'n-ithin the flume system affect the size of screens. Cleansing of screens by water jet and screeninqs disposal present no particular problem. Grit chambers should preferably be provided in multiple units and should have continuow grit-removal equipment. Practical design calls for a velocity of flow of 1 foot'per second. The elimination of grit materially improves subsequent settling and sludge dispoial. The organic matter n-liich is carried d0Tv-n with the grit does not decompose readily and offers no particular disposal difficulty. For flexibility, multiple sedinientation units of the clarifier type are preferable. The design of settling tanks should provide a detention period of a t lea5t 1 hour and preferably 1 1 / * hours. Details of the design should be typical of selvage treatment practice. Efficiencies that may be expected (3) are suspended solids removal of about 92y0 and B.O.D. removal of about
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have been carried o n by the .\lichignn Engineering Experiment, Station, East Lansing, llich., with the cooperation of the Farmers and Beet Sugar Manufact,urers Association and of the llichigan Stream Control Commission. The work was supervised bl- E . F. Eldridge, research associate, vhose reports have been published ( 4 , 5 ) . These experiments, including pilot plant studies, led to the installation of a full scale waste treatmerit plant for The Monitor Sugar Com1,any a t Bay City, Mich. The treatment facilities were constructed t o modify factory wastes. This factory hnd n capacity of 2000 tons of beets
427,.
Coagulation of flume water results in improved removal. However, a t pre>ent it does not appear that the additional removal obtainable just,ifies the cost of chemicals. Chemical treatment of flume waters recirculated in closed systems warrants further study.
PR 0 CESS
w
A TE R
c L.4R I FI C A T I O N.
Process v a t e r (diffusion battery n-ater and pulp press water) containing organic solids largely in solution and in the colloidal state requires coagulation with lime (500 t o 600 p.p.m. CaO) for effective clarification by sedimentation. Here also equipment applicable to sewage treatment practice is suitable. Facilities for quick mix should be followed by a coagulation for 20 to 30 minutes (3). Sedimentation in a unit of the clarifier type is capable of removing about 937, of the suspended solids and about 47% of the B.O.D. ( 3 ) . A clear liquid is obtained. FacrroRY ITTASTE C L A R I F I C 1 T I O S . From present information the most extensive studies and experiments on beet sugar tvastes in the United States
Figure 7. Upper Photo Show-s Centrifuge in Operation with Crystallization .4ccelerated (Sirup Spun Off). Lower Photo Shows Retention of Sugar Crystals i n Centrifuge (Sugar Goes to Granulator)
..=,
..-
Condenser W
Flumes-
lid per day with a t o h l waste flow of about 5.0 million gallous per day. The facilities, comprising rotary acreen, grit chamber provided with continuous grit removal, mixing trough, c o a g n b tion tank equpped with mechanical a&ation, and rectangular settling units equipped with straight line sludge removal mechan-, were deagned for a flow of 0.0 d o n gallous per day. Pertinent features of individual equipment were 88 follows: mreen, 5.0 feet in diametm and 9.5 X ‘I8inch; grit chambers, 40 feet long, providing a flow mixing trough,SO inches wide, 2 with slope of about 10 inch-; miputadetention; and fonrsettlingunifa, eaoh20.0 X 10.0 X 9.5 feetd e @ ,p r o v i a a detention period of 80 tninutes. S M e m waste added to the effluent of the grit chamhers m factory proportion proved ta have coagulating power. Operations for 1939 were reported by Eldridge (6). The e5mency b a d on
o v e r 4 suspended solids removal was 91.4% and on over-all B.O.D. removal, 61.2%. The B.O.D. of the final effluent for the period of the campaign averaged 358 p.p.m. h t e r operating data of thia plant have not been made available, but I t is understood from a statement of the plant management that the Steffens p r m has been discontinued during the past few years due t o the market value of molasses and that the plant bas been operated for cla&cation of t h e flume water only, the process water being ponded. Although coagulahon of factaiy waste with Steffens waste results in considerahle reduction both of solids and B.0 D. of this waste and of the SteEem waste, the application is limited by reason of the relatively high organic content of the effluent. Such effluent will not meet the reqnuements of many streams. SLUDGEDISPOSU..Sludge from the clarification of %umewater and process water, separately or combined, may be pouded with reeaonable success in relatively small ponds; 1.0 t o 1.5 acres, 6.0
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INDUSTRIAL AND ENGINEERING CHEMISTRY
feet deep, is atwut tlie Pize required ior sludge from efrectively 01)erated sedimentation a t a factory slicing 1000 tons of beets per day. The relatively small quantity of supernatant may be disposed of hy controlled discharge to the receiving stream a t times of high flows, and the sludge can be removed Tt-ithout too much difficulty for return to farms. Return of supernatant to sedimentation units may, in instances, be advisable for a coagulating effect but this will depend on whether it may interfere n-ith waste recirculation. Experiments of Eldridge (3,&, 5') definitely indicate feanibility of vacuiim filtration. This is a much more positive method of disposal. Flume v-ater sludge requires preconditioning by lime, 60 to 70 pounds per 1000 gallons. Process iyater coagulated wit'h lime does not' require preconditioning. The filter rate recommended is about 100 gallons per square foot per 24 hours. The sludge handles easily and can he piled in tlie yard for later disposal or can be hauled immediately to farms. Dilution and ponding are rather uniLnm CAKEDISPOSAL. versally used to dispose of lime cake. Much is to be said for avoiding the "making" of a liquid wabte by arranging to handle the cake as filtered. This cake, containing about ij070 moisture, can be handled hy belt conveyor or other mechanical means. The older factories are so arranged that installation oi such equipment may tje difficult. I t seems desirable, that this feature be given consideration in new factories and in changrs made in old ones. Another method of disposing of lime slurry which has heen proposed by represeritatives of the industry is that of spray drying. It is understood t,hat the heat wasted :It n beet sugar plant might well be used for some such purpose. Kliere ponding oi lime slurry is practiced, it is preferable to confine it to a small pond area sufficient in capacity to hold the ~ e a ~ ~flow. n ' s In such case lime drainage can receive controlled discharge as stream conditions wvarraiit. Sludge should be removed annually. STBFFESS IT'ASTEDISPOSAL. Favornhle market value of molasses from straight house opernt,ions eliminates the Steffem Taste. In case the recovery of the ndditionnl sugar again prove5 profitnhl?, the most logical method of disposal is by evaporation and utilization of the valuable con5tituents contairied in tlie waste. For plants in the Ohio-Xcllignn aren one definite outlet is assured to The .%mino Producth Cumi)niiy a t Rossford, Ohio, n-lirre it i p drhired for use in the recovery oi glutamic acid. Holyevrr, tliis focuses an extremely difficult x\--n>tedisposal problem nt a single location unless the recovery of other constituents of the liquor provei: practical or iinle+ tlie v w t e cnn be n.liolly disposed of by evnporation. B I ~ L ~ GTREATMXT. I~AL By reason oi the short campaign and of the srnioii of tlie campaign, biological treatment of wastes is not generally practiced and is not verl- efficient. I n cases xhere waste voliimes can be materially rrduced I-,>- reatilizntion or by process changes or both, costs of biological treatment might he justified in some fex instances to meet stringent stream requirements.
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flushing exhausted cossettes from the battery cells but for re-use in the juice extraction process, has proved promising. It is rather common practice to re-use a portion of the process waste for flushing erhausted coiiettes from the cells, but relatively few factories in this country have yet attempted clarification of the combined diffusion-battery viash water and pulp press wat.er nith return of it or a portion of it to the cells fclr juice extraction. The Buckeye Sugar Company has followed this procedure, a t least in part, for the pait seven or eight years with rensonalile success. ?*lacDonald (6) reported on a successful recirculation of proct:ss waste within the battery system. He states that definite benefits are derived from the Conservation of sensitive heat and from the conservation of organic matter as sugar, ai pulp, or as molrisses. T o prevent organic decomposition, he recommended adju4ment of p H to about 7 and sterilization of the return wastes by heat,ing to about 90" C. just before addition to the batteries. I n favor of re-use he reported gains of 0.08% additional sugar in t.he bag, o.1470 additional molasses, and 0.4570 increase in dry pulp, all based on weight of beets. Bachman (1) reported favorably on the re-use of process wastes by the Wintzell-Lauritson method. I n this process diffusion water and pulp press mater are condit'ioned separately by screening through a rotary drum of metal gauze (Babrowski filter'). The pulp press water after screening is acidified to a p H of about 3.2 in order t,o coagulate albumin and is then united with diffusion n-ater, and the combined waters arc returned to the battery as fresh water. Albumin is mixed wit,h pulp in animal feed prcparation. I t is indicated that thij process has been used with no loss in sugar yicld and with a gain in solids recover>-. Corrosive .action of the acid characteristics on metal eqiiipment has heen an objection to t,heprocess. I t seems to be indicated that perhaps (ent,irely successful operation by this process requires the construction of equipment with acid-resisting metals. Certain English authorities have for sonic time proposed tliffusion bat,teries of the continuous type instead of multiple-c:ell batteries for elimination of process m:tstes. Thi; equipment comprises a circular drum, presumably 9 or 10 fect i n diameter and about SO or 85 feet long, set a t a slight angle rrith the horizontal. Cosset,tes introduced continuously at the bottom are kept moving by propellcr mechanism against the flow of water introduced a t the top. The cossettes are removed from the top, and the pulp press wat,er is re-used in the diffusion proceduro t,o avoid losse- oi sugar. Ohjections of the sugar industry to this type of diffusion have been: (a)more impurities in the juice, (b) increased lo-ws of sugar, and (c) high costs of revamping existing factorivs for the installation of the equipment. T h a t attention has been and is being given to changes in operating procedure and to changes of process equipment for re-utilization of waste n-ater and for additional recovery of valuable ingredients, offers considerable encouragement tcl waste elimination as one approach to t'he beet sugar waste disposal problem. Ecoiiomies of changes weighed against the treatment of wastes for satisfactory diaposal represent the real criterion.
WASTE RE-UTILIZITION
Re-utilization of flume water and process viater in circuits of the respective processes has considerably more merit than it has hitherto been given credit for. This practice not only conserves water but materially reduces the stream pollution problem. Experience in Oliio indicates that' flume water effectively clarified can be maintained in a closed system or a t least virtually so. Organic build-up, n-ith use again and again, takes place but tor fluming purposes this need not give too much concern during the extent of the campaign. Pond facilities should be available to receive emergency overflows from the system and to store the contents of the system a t the end of the season pending a propitious time for ultimate disposal to the receiving stream. Likewise, clarification and re-use of process yater, not only for
PRESENT PRACTICES O F WASTE TREAThIENT
Efforts tolvard \Taste modificat,ion and disposal vary considerably in details of methods used and in accomplishments. It :ai)pears that, particularly among the more easterly plants, some reutilization of wastes for fluming is rather generally pract'iced. Ponds are probably more generally used for settling the factory wastes prior to recirculation for fluming. Lime sludge is either settled in a separak pond or is discharged to the pond system receiving excess factory wastcs. Figure 8 is a flow sheet for the plant of the Great Lakes Sugar Company a t F'remont, Oliio, and is reasonably typical of popular procedures. At this plant a vibrating screen is used for the removal of detris from the flume water prior to its discharge to the pond system. This unit has
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~,..~,..~ ,,,~ ,..". slotted openings of sbout''/s x 2 inches. Considerable accomplishment has been realized from the standpoint of reducing the pollution load on the receiving stream. The result has been some reduction of volume with long period storage for excess waste flows. Pond ares. necessarily is large to hold accumulated wastes during the extent of the campaign. Several plants have installed or are proposing treatment equipment comprising screens, grit chambers, and settling tanks designed in accoordanoe with accepted sewage treatment practice for the positive removal of solids from flume water. Two of the plants in Ohio have provided screens and sedimentation units, the sludge being dispwed of by ponding. Future programs for both plants include the installation of grit chambers preceding the settling tanks. All of the Ohio plants are reusing a'part of the process waste for flushing exhausted cossettes from the hatterycells, but onlyone has endeavored to clarify and recirculate this water for diffusion purposes with m y approach toward maintaining a closed system. The efforts of one company in this respect are set forth in the subsequent paragraphs. The Buckeye Sugar Company has made sufficient progress in
Vol. 39, No. 5
waste modification, re-utilization, and disposal to merit special comment. This factory equipped with both straight house and Steffem house facilities has a cspsoity of 1000 tons of beets per day. Water consumption on the basis of no re-utilization of wastes would average 4.3 to 4.4 million gallons per day. The major portion of water is obtained from the Blsnehard River, and wastes are returned to the river a t a point well below the intake. Monthly river flows as low 8$, 5.5 cubic feet per second have occurred during the season of the sugar campaign, and the minimum daily flow has on occasion approached 1.0 cubic feet per second. Water conservation is important at this plant, and likewise the stream pollution problem has been acute. WASTEMODIFICATION A N n DISPOSAL improvements of waste disposal were initiated in 1937 and placed in operation in 1939. These comprised: (1) a Screen of drag type and clarification unit for flume water treatment recirculating the water for fluming beets; (2) arrangements for coagulation and clarification of process water and the recirculation of this water for flushing exhausted cossettes from battery cells and for juice extraction in battery cells; (3) the installation of a spray pond for cooling condensing water prior to dischirge to the stream; (4)the pro-
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mion of total storage facilities for flume water chri6er sludge, for lime d w y , and for Steffens waste, respectively; (5) t h e provision of ditches around these ponds to receive seepage and to conduct it to sumps for return to ponds by permanently installed sump Pumps. Figure 9 is a p h of the flume wakr settling tank. Figure 10 presents flow charts of flume water oiroulation and of p~oceg4 water circulation, respeetively. Figure 11 is a flow sheet of the condensing water, cooling system, and ultimate water disposal. FLWMECmmrr. The water usdd in washing beets is regularly chlorinated with d c i u m hypochlorite solution. The practice bas been to apply chlorine at the rate of about 5 p.p.m., one third t o the beet wash water and two thirds to the flume water beyohd the washer. The opinion of the superintendent of thia factory is that the chlorine application has a value in controuing odors in the vicinity of the beet washer. Ita value within the system as a whole is considered relatwel~inaigoifioent. Flume water screened through a drw-type unit with L/ipineh slatted opening8 flows t o a receiving well from which it is l i t e d by a 3ooogallon-per-minute pump to the settling tank. Temporary flume stoppagas by beets in the flotation operation gives rise to surges; hence an emergency overflow hae been maintained from the receiving well. The settling tar&, capacity 88,400gallons, provides a detention of 30 minutes at the maxirnum pumping rate of 3000 gallons per minute. On th;e basis of a d f o r m rate of 1700 gallons per minute (2.4 million gallons per day), the detention would he 52 minutes. A pump of the plunger type,delivers sludge to the pond. T o date the circuit has not been comletelv . . closed hv reason of overflows ta thc plant sewer cawed by s w g w in vxeess of the raw Bum? WI)ter pump rapacity, hut the volumes of Bume water discharged M thc sircam have t n r n materially redured. l'FLDCE55 Wwrm CIRCUIT.Most of this w m t e is wuscd (Piaure lo), but some is utilized for diluting lime cake, and in if Steffenahouse operation some can he employed for diluting molasses. Battery wash water and co888ttes from the cells are received in a pit from which they are pumped to the E f w screen or pulp fanger, a slotted screen of 1-nun. openings. The water is conducted into a receiving tank, and the pulp is introduced by endleea flight conveyor to the presses. Pulp press water is returned to the pit receiving coasettes to mist in tlmting them to
the pump. From the receiving tank the combined water, except for the portion which goes t o the lime cake scroll for dilution, is pumped t o two Babrowski filters, &mesh metal drum screens. Screenings from this operation are discharged to the lime sludge system and the effluent to a hafled, cylindrical, conical-bottomed reaction and clari6cation tank. Milk of lime is added with the wa-te water for coagulation and clari6cation The effluent ia drawn off a t one, two, or three levels through a oonstan6hm.i chamber toatreated-waterreeivingtankfromwhichitispumped to the diffmion bsttery juice circuit. Sludge from the clarifier tion tank is drawn to the lime sludge system. Afresh water connection controlled by float maintain^ the proper level in the trested-water recei+irig tank. A t ~ m p e r a t u r eof 65" C. is maintained m this tank t o avoid fermentation. Any emergency overflows from equipment are connected to t4e lime sludge disposal system. By the method outlined, discharge of this waste to the stream is eliminated. CONDENSINQ WATER COOIXNGSYSTEM. From the condenser seal tanks the condsssing water is discharged t o a receivmg raservoir in the yard. From thia reservoir it is pumped through spray nozzles for aeration, eooluig, and collection in a second pond which normally overtlnws to t h e plant sewer. T h e primary purpose of this procedure has been to avoid the disaharge of big4 temperature water t o t h e stream and t o avoid heavy clouds of vapor at the sewer outfall. Connsctlon from the system to the Bume water system is m a i n k e d for make-up purposes. During a t least three camoaigns, the last being 1946,river flows b v e been so low that cooled condensing water has h e n returned t o the Dlant water sumlv t o e n s u e sufficientwater for olant use. .. . svstem . STEPPEXSWASTEDiwosAi.. If BteRens house Qpcrationa we resumed, it ia anticipated that thi. waste will be stoml in a Mcalled Stetlens waste pond of sufficient caparity to bold this waste accumulation for the extent of the campaign. It is likely that after the campaign it will be coneentratedin&aigbt house &POrators and sold to The Amino Products Company. There will he no direct discharge of this wsste t o the stream d e a f it is controlled at times of high river flows. OPEBATION RESULTS. Based On f0W andySe5 Of %-hour Conpcaite saSnples eallected on s m y s during the interim 1939 to 1941, inclusive, the efficiency of the flume water settling tank based on suspended solids removed was 75.3%; on B.O.D. re-
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1947
‘rnble 17.’. Analyses of Pollution Load
Dare 10124-25/39 11/7-8139 11/?0-21139 1212-3/41
Flow, 1I.G.D. 3.09 2 80 8 04 2.43
5-Day B.O. n.
(200 C.),
P.P.hI. 168 181 217 112
Solids, P.P.11. Total SusTotal volatile pended 942 316 196 1020 276 214 1000 360 144 808 312 40
Population Equivalent on B.O.D. 25,900 25,200 32.900 13,600
nioired, 16.0rc. S o material putrefaction of flume miter has occiirred during the period of the campaign. The organic build-up has not led to obiectionable conditions. 1,imited sampling and analyses duriug the 1939-41 period has indicated that sludge removed from the tank has contained 3 to 7 5 solids. Sludge concentration Lyill depend, however, on frequency of pumping and periods over which the sludge pump is operated. There has been no opportunity for obtaining recent operating r e d t s of the waste treatment and diqposnl facilities. Based on a series of four surveys of the 1939-41 period, including the collection of 24-hour composite samples. the pollution load as contributed by wastes discharged from the factory was analyzed as shown in Taille IV. The survey of operations in 1911 showed a marked improvement over the first year of operation, 1939. Also there has been a material rcdriction in pollution load over that experienced prior to the efi’orts of t h e company ton-arc1 stream pollution abatement. By compai%on with Tahlc 111, the 1941 operation indicates a B.O. I). populntion eqliivalent reduction of 7 9 7 , a volatile solids reduction of goc;, and a siippended solids reduction of 9 9 7 over the operation of 1925. By reason of the limited studies these data should not be accepted as absolute criteria of accomplishments, but they are indications of improvements that have lieen made in the disposal of liquid wastes a t this plant. Flows from the plant sewer in excess of about 1.72 million gallons per day (condensing water) roughly represent the overflow from the flume water recirculating system. The low flows which occur in the receiving stream, and which must lie expected to occur from time to time during the beet sugar campaign, require further efforts toward waste improvement if satisfactory conditions are to be assured continuously. Analytical control features of the operation of process water recirculation are not available. These, however, are closely related to manufacturing procedures. That the elimination of this waste is feasible without detriment to the product has been definitely indicated by operating personnel at this plant. . ~ D D I T I O N A L CORRECTIVE ~IEASURES. Other improvements to e s i h i g facilities are definitely suggested by the efforts of wade modification, re-utilization, and disposal a t this plant. They include an increased vet-well capacity for raw flume water, duplicate pumps for raw flume water, modern grit removal equipment, increwed sedimentation capacity for flume !rater, and flume water tem drawoff established from settling tank effluent rather than from raw flume water wet well. In addition, attention should he given to over-all operation and housekeeping methods to reduce contamination of condensing water. For a longer range program, consideration should be given to facilitating sludge handling by means of vacuum filtration and to lime cake handling by mechanical means. SUMhIARY
The waste disposal problem of the beet sugar factory is complicated 1,- \Tastes of large volume and of high solids and organic characteristics, produced during a short period of the late autumn and early ninter months. The degree of treatment, the ex-tent of waste elimination and. in many cases, the combination of these are dependent on the requirements of the receiving stream. Since the satisfactory treatment and disposal of the wastes produced must he charged as a production cost, the industry may well consider changes in processes and elimination of features
Total Volatile Total Solids, Su-pended Tons Solids, Tons 4.07 2.52 3.22 2.50 34 .. 51 66 o1 . 48 12
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n.hich will permit economies of Ivaste disposnl. For instance, the difficulties of disposal of Steffens \Taste as such will n.arrant tlie weighing of returns from the additional sugar produced against the cost of sati*factorv disoosnl. together nitli the return ihat may Ii’r expected from the sale of straight house molasses. Stefi‘ens vraste if produced ehoulcl lie processed for va1uat)le liy-
paration of !Tastes for individment, re-utilization, and disposal is the most logical approach to the !Tastes disposal problems. \Taste treatment methods following present practices in the primary treatment of sewage apply t,o bpet sugar wastes. Sedimentation alone isted by coagulation is cnpable of good performance based on e percentage:$ of solids anti of B.O.D. removed. Coagulation of straight house factory waste by the Steffens waste is a special application; it?,merit depends (1) on no better method of Steffens waste disposal and (2) on the ability of the stream to receive and to absorl-1 a large volume of waste effluent of oxygen demanding properties equal to or greater than an average municipal sewage. In fact, effluents from primary treatment devices are not suitable for diqcharge to many streams. Biological processes though capable of improving beet sugar waste, are not productive of the best performances because of the short campaign during the season when weather conditions are adverse to maximum biological activity. Furthermore, t’his type of secondary treatment is costly unless waste volumes car be materially reduced. Ponding of total waste volumes seldom can lie entirely satisfactory because of the large unn-ieldy areas required, of the odors produced, of unsatisfactory effluentp, and of the difficult features of maintenance and control of the e facilities. Kell constructed and maintained ponds of relatirel. small capacity may well have an application for long period storage if combined in a well planned program of wastes elimination, modification, and recirculation. The perfection of facilities for separate modifications and for separate recirculating system? for flume water and process waste, respectively, has merit. Esperiences in Ohio indicate that the pollution load can be materially reduced and that waste volumes can be so reduced as to encourage saticfactory methods for treating any residual waste, either by long qtorage ponds or by other means. Positive removal of solids and the positive disposal of sludge lend to improved n-aste disposal and to improved conditions a t the factory site. Disposal of lime cake as cake in contrast to disposal by slurry t,o ponds definitely warrants consideration. As tlie industry finds it feasible to do so, rearrangements of factories to provide mechanical means for handling this material seems most desirable. The beet sugar industry has taken cognizance of its waste d.isposal problem. Much effort has been made toward the abatement of stream pollution. HoTvever, the necessity of additional corrective measures is imminent. The scientific approach may well be the elimination of waste by improved processes and equipment, linked with a program of x-aste modification for re-utilization. ACKSOB~LEDGIIENT
I n the preparation of this paper valuable assistance nm :received from J. H. Bass, Ohio Department of Health, in the preparation of charts, and from J. S. Eckert, The Buckeye Sug:ar Company, for furnishing photographs and informative data re:iative to beet sugar factory processes and to his. experiences with waste modification, treatment, and diyposal. LITERATURE CITED
(1) Bachman, d., Intern. SUQWJ . , 47, 7 2 (1945). (2) Boehrn, B., “Gewerblich Ahvasser”, pp. 156-222 (1939), tr. by -&. E. Kimberly. ( 3 ) Eldridge, E. F., “Industrial WaQte Treatment Piactice”, pp. 84114 (1942)., (4) Eidridge, E. F., Mich. Eng. Expt. Sta., Bull. 51 (1933); 60 (1934) : 67 and 71 (1936) ; 78 (1936). (5) I W , , 87 (1939). (6) MacDonald, J. C.,Intern. S u g a r . J , , 46, 208-10 (1944). (7) S o l t e . Ernst, “Yon Kasser”. \-ol. 11, pp. 272-80 (1928), tr. by A. E. Kimberly. ( 8 ) Rogers, H. G., Rept. of Tech. Corninittee, Upper Miss. Board of Sanitary Engrs., Fell. 5 , 1947. PRESESTED before t h e Industrial Waste Symposium ,%.t t h e 111th hIeeting of t h e A M E R I C A ~CHEMIC.AL V Q o c i r i Y , .itlantic City, S . J.
