Treatment of Liquid Wastes from the Textile Industrv J
C. R. HOOVER Wesleyan University, Middletown, Conn.
This review outlines methods of treating textile wastes. The examples given and the advantages and disadvantages discussed are based largely on observations made during several years’ study of the wastes from thirty plants for the State Water Commission of Connecticut.
The introduction of a few terms in this table, not commonly used by the industrial chemist, may serve to emphasize the point that waste treatment information and technique are largely in the field of the sanitarychemist and engineer. The industrial chemist must familiarize himself with this technique if he is to approach waste treatment problems in the most effective way. The nature or degree of dispersion of textile waste particles is an important property, since it can be expected to have some relation to the degree of purification that can be effected by various means. From seventy-two determinations of suspended solids and B. 0. D. equivalents in typical textile wastes in Connecticut and North Carolina (15) and certain assumptions, it can be estimated that 20 per cent of the oxygen demand of an average textile waste is due to suspended matter. From ultrafiltration of dye-waste components with graded pore-sized membranes it is found that approximately 25 per cent of the combustible matter is in the form of particles held in suspension or emulsion, 45 per cent in the general colloid range, and 30 per cent in molecular solution (4). Much information is available regarding the need of treating textile wastes, the general nature of the problem, and specific suggestions regarding possible processes of treatment and recovery. These were summarized in a report by Geyer and Perry ( 3 ) , and an extensive bibliography was included. More recent progress in textile waste treatment and recovery was discussed by Snell (11).
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EXTILE manufacturing and finishing plants produce wastes of a solid, liquid, and gaseous nature, but the liquid or water-borne wastes are the most important in quantity and effect. In general, the object of liquid waste treatment is to convert these water-borne wastes into solids and disseminative gases. The liquids draining from a dyehouse, textile-finishing plant, or a diversified textile-manufacturing process differ decidedly in appearance from pure water, but in chemical composition they usually average from 99.8 to 99.95 per cent water, or are as pure in their polluted state as many solid industrial products are in their refined state. This statement may serve to draw attention to the economic difficulties of textile waste treatment, and especially to the limitations of profitable by-product recovery. Special operations in textile manufacture such as wool washing, silk degumming, kier boiling, mercerizing, and rayon-pulp steeping produce wastes containing from 1 to 3 per cent of organic matter; it is from such wastes that by-products of value can be looked Methods of Treating Textile Wastes for most hopefully. Another important and frequently discussed characteristic of textile wastes is the wide variation DILUTION.This expedient is the first recourse and last in composition from plant to plant and in the same plant resort in all waste disposal. It is the only ultimate solution For a t least some part of most water-borne wastes; but it is from time to time. This indicates that the design and operation of treatment processes and by-product recoveries cannot be readily standardized and that each waste is a new problem requiring T.4BLE I. OXYGEN DEMAND AND POPULATION EQUIVALEXT OF chemical and engineering investigation as a TEXTILE PLANT COMPOSITES AND TYPICAL VARIATIONS basis for a satisfactory solution. Approx. &Day Gal. of Table I illustrates some of the points just No. of B. 0. D., Wastes Population Nature of Process Workers pH p. p. m. per Day Equivalenta mentioned. The variations shown may repreCotton thread (bleach, kier, oil, dye) 150 3.3 550 40,000 1,093 sent recurring conditions or changed condi9.0 378 19,000 357 tions due to manufacturers’ efforts to improve Finishing cotton piece goods (bleach, 120 9.6 605 274,000 8,239 kier, dye, print) 6 . 9 420 180,000 3,745 plant effluents. The number of employees 478 438,000 10,405 Finishing cotton piece goods (bleach, 220 9.8 and the waste analyzed are for the whole tex5,635 7.6 315 360,000 kier, mercerize, print, dye) 1983 220,000 21,682 Cotton webbing (bleach, kier, dye, 750 11.1 tile plant and not merely for the dyehouse or 6.3 245 80,000 974 impregnate) finishing department. The average 5-day bioSilk (degum, bleach, dye, print, weave) 2500 4.6 462 1,200,000 27,554 7 . 0 360 700,000 3,578 chemical oxygen demand (B. 0. D.) for this Rayon (knit, bleach, dye, size) 250 7.0 1920 125,000 11,928 selection of wastes is 618 p. p. m., and on this 2.5 183 115,000 1,046 basis these wastes have an average oxygen Wool (scour, weave, dye, finish) 200 11.7 936 120,000 5,582 8 . 1 540 120,000 3,221 requirement of 12.7 times the number of Felt from scoured wool 100 1.5 138 30,000 206 persons employed in the plants. That is, the 5.3 370 75,000 1,379 wastes have a greater polluting effect than the Basis: 5-day B . 0. D . of 0.167-lb. oxygen requirement of domestia sewage from one entire population of many typical one-industry person for 24 hours. textile towns. fi
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not technically controlled, and present trends in waste treatment indicate that it must decrease in the future. Its discussion is a special problem involving stream classification, local requirements, and standards of purity (18). SEGREGATION.Separation of strong and weak wastes is the obvious first step in recovery operations, but it cannot always be assumed that purification treatment of a concentrated waste is the most efficient. Furthermore, retaining strong wastes for treatment and discarding weak ones may not be satisfactorily controlled, and accidental discharges of strong wastes is a cause of much stream damage and popular disapproval.
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solid surfaces, changes in solubility, and evaporation while passing a gas through or over a solution containing typical waste. Various catalysts have been suggested for bringing about chemical oxidation (IS,16), but negative results have also been published (14). It has been reported that as much as 70 per cent oxidation of textile wastes can be brought about through solution aeration which involves both biological and chemical action ( 5 ) . Subsequent work with a sterile nonreducing waste in all-glass apparatus shows that not over 10 per cent oxidation is accomplished by vigorous aeration with catalysts over a period of 72 hours. Aeration is a cheap useful process, but it is most effective when carried out under conditions allowing for combined physical, c h e m i cal, and biological action.
M i x i n g or compositing of wastes from a complete cycle of p l a n t operations, allowing opportunity for dilution, reguMECHANICAL OR lation of flow, and PHASE SEPARAmutual reactions TIONS. Such sepasuch as neutralirations may inzation and precipiclude a number of tation, is so simple useful p r o c e s s e s and cheap to carry ranging from sediout and is so frementation to elecquently helpful trodialysis. T h e that i t should be sedimentation inconsidered an escidental to equalis e n t i a l p a r t of LAGOONS 24 HOURSAFTER SLUDGE DISCHARGE, AND PART OF TREATMENT zation and storage textile manufacPLANT SHOWN IN FIGURE 4 should be carried t u r e . Eaualization has an imout in some form of basin having a portant bearing on reasonably smooth bottom so that solid deposits can be overcoming opposition to admission of textile wastes to removed periodically. The nonputrescible nature of most sewage-treatment plants and makes possible the maximum textile waste solids makes it possible to retain sedimented utilization of dilution effects. material in a basin for relatively long periods of time. STORAGE.This step necessarily accompanies equalieaSeparations by screens are chiefly effective in removing tion, involves surface aeration, and brings about more complete mutual reaction and precipitation of suspended solids. loose fibers. American manufacturers are apparently not Tests in the laboratory and in treatment plants indicate that, as much interested in removing such fibers, especially wool and hair, as the British, who make extensive use of in addition to the removal of the bulk of suspended solids, mechanically cleaned “floc and fibre catching machines”. other objectionable properties such as caustic alkalinity and Separations by commercial supercentrifuges are used in a oxygen demand can be decreased from 5 to 10 per cent by well-known process of grease recovery from wool scour. the first 24 hours of storage in layers 1 foot deep, or with air stirring in deeper layers. But what is more important, Passing oily textile wastes through a supercentrifuge a t 16,000 r. p. m. before chemical treatment increases the wastes appear to be partly stabilized and a 2-day B. 0. D. degree of purification. may be decreased as much as 40 per cent. Storage of textile Separation by dialysis has made possible what appears to wastes also serves to bring about cooling which is necessary be the most profitable recovery process in textile manufacture for the best results with many chemical and biological treat-that is, the recovery of caustic from the steep liquor of ment processes. I n this connection it may be suggested that rayon plants (17). Laboratory dialysis has been applied more textile plants might well follow the practice of laundries to spent kier liquor, which is generally considered to be the and install heat interchangers on effluent lines. AERATION. The chemical and physical effects of intimate most difficult textile waste to treat. With a six-section contact between textile wastes and air are important as disparchment tube dialyzer 50 per cent recovery of a caustic solution containing approximately 5000 p. p. m. of alkalinity tinguished from biological oxidations. Storage and equalizwas secured (6). The residual kier liquor is easier to treat ing effects are accelerated, emulsions can be transferred into chemically and biologically, and it would seem that with the removable scum as in the King and Imhoff processes for more efficient industrial equipment both kier liquor and waste recovery of wool grease (I), floc formation aided, and reducing mercerizing liquor could ell be treated by dialysis to cheapen effluents oxidized. Increasing use of this fundamental process disposal costs, although the operation may not be profitable should be made in industrial waste treatment. Tests as to in itself. I n the case of a segregated single-dye waste like the method of applying air, both for oxidation and neuindigo or alizarin, which forms relatively coarse dispersions tralization of textile wastes, indicate somewhat better efficiency with fine bubbles than with liquid sprays or mechanical when acidified and aerated, dialysis of the acidified waste with air stirring gives a pure product in a relatively short time. aerators. The distinction between chemical and biochemical Electrodialysis and ordinary electrolysis with carbon elecoxidation is largely academic as far as the results with textile trodes both appear to be worthy of further consideration in wastes are concerned. It is difficult to create and maintain dye recovery. sterile conditions and to eliminate effects of adsorption on
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COAGULATION. Treatment of liquid textile wastes with soluble substances designed to form large adsorbing surfaces is generally described as chemical precipitation, but the direct addition of finely divided adsorbing solids may also be included under coagulation. Critical and unprejudiced comparison of more than twenty suggested coagulants with textile wastes has led to certain general conclusions. One can probably demonstrate that for a certain waste every coagulant or regulating chemical suggested shows certain advan-
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an excellent color remover and effective in reducing oxygen demand. It is useful with relatively weak wastes and as a supplement to partial chemical coagulation. The chief objection to its use is its cost. Certain other effects of a typical coagulant are shown in Table 11. This particular waste was a difficult one to treat but illustrates the effect of changing pH; for example, oxygen demand reduction is frequently a little better a t low pH’s while color removal is better a t higher values. The figures in the fourth column may serve to draw attention to the different methods of evaluating oxygen requirements of textile wastes. Summarizing experiments with a large number of comparisons, no one method or single determination can be explicitly relied upon. T o secure a real evaluation of the total probable effect of a waste on natural bodies of water, biochemical oxygen demand tests incubated for a t least 20 days are necessary. The almost insuperable difficulties experienced with very concentrated industrial wastes, especially those containing much suspended matter, have caused a preference for the direct oxygen adsorption method of B. 0. D. determination with such samples. The best chemical method available appears to be the chromic acid wet-combustion determination. The standard or, more notably, the concentrated permanganate oxygen-consumed method is convenient and rapid for comparisons of similar materials and for preliminary evaluation, but i t is not reliable for pollution evaluations or for many comparisons. TABLE 11. TYPICAL CHEMICAL TREATMENT OF A RAYONFINISHING WASTE %
FIGURE 1. COMPARISON OF EFFECT OF COAGULANTS AND PH ON SYNTHETIC COMPOSITE TEXTILE WASTEOF 400 P. P. M. OXYGEN DEMAND
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tages, but for the combined effects on the essential factors in successful treatment (that is, the lowering of oxygen demand, the removal of color, suspended solids, and toxic materials, the regulation of pH, and the cost of construction, operation, and chemicals) the substances considered may be arranged as follows: ferric and ferrous sulfates; aluminum sulfate and combinations with ferric sulfate; chlorinated copperas and ferric chloride; activated carbon; and sodium aluminate, clays, and sodium silicate, in order. The acidifying reagents in order of preference are sulfuric acid, chlorine, and sulfur dioxide. As an alkalizing reagent lime has no rival. Calcium chloride is a useful source of the essential calcium ion in alkaline or neutral wastes. Figure 1shows typical effects of four materials on B. 0. D. reduction. Lime and sulfuric acid were used to regulate the pH. I n general, ferric sulfate acts best in neutral or slightly acid wastes and gives an effluent with a favorable pH. Ferrous sulfate cannot be used effectively below pH 8 and gives a relatively large volume of sludge, but it is the cheapest chemical coagulant and is easy to handle in small treatment plants. Compared to iron sulfate flow, aluminum sulfate floc appears to be inferior in rate of settling and in reduction of oxygen demand except in the case of waste containing chiefly soap, where it is found that this coagulant, combined with calcium chloride, gives excellent results. The amounts of coagulants indicated in Figure 1 were chosen because, when combined with the necessary regulating chemicals, the average cost of treatments was approximately equal with the exception of kaolin. Clays, even in heavy dosages of 20 to 30 pounds per 1000 gallons, seldom equal the effects shown for chemically precipitated coagulants. Activated carbon is
Treatment Lb. 1000 G$1. F e ~ & h ) a Lime Original
pH 6.7
On Consumed,a p. p. m. 380
Reductionin % % 0 2 Con- Sludge Color sumed (1 Hour) Reduction
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Determined by using a permanganate solution ten times a8 concentrated of Water and Sewage”.
as called for in ”Standard Methods for the Analysis
With composite textile wastes, addition of metallic salts, followed by lime, generally produces better lowering of oxygen demand than the reverse order. If floc formation is slow, the addition of lime first is beneficial. Electrophoretic studies of waste-treating concentrations of ordinary ferric sulfate solutions indicate an isoelectric point for hydrated ferric oxide micelles and floc at pH 6.1 (9). Passing from lower to higher pH’s causes this dispersion to change from positively to negatively charged particles, making it favorable for action with both negative and positive waste dispersion particles. I n this connection improved results have been secured with certain wastes such as those containing soluble oils or soaps by a two-step or two-pH coagulation process. The first step may consist of strong acidification with chlorine or sulfuric acid in the presence of clay; the second step would be pH increase and clarification with chemical coagulants or activated carbon. The solution method of feed of metallic salts gives a more uniform and concentrated dispersion of hydrated iron oxide micelles than dry feed, especially a t neutral or high pH’s. I n practical operations solution feed seems to be more efficient than dry feed, a t least for relatively high concentration of coagulants.
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Stirring coagulating mixtures with air appears to improve the effluent slightly if the operation is continued beyond 30 minutes and ferric salts are used. It appears to be less effective than mechanical stirring with aluminum sulfate, copperas, and powdered activated carbon. The general impression that slow mechanical stirring is superior seems borne out, but not a t the start of the coagulation process. At this point stirring should be thorough, and propellerblade-tip velocities of 250 feet per minute do not appear to interfere with floc formation. The relative merits of fill-and-draw operations us. continuous treatment call for the application of engineering economics. For small plants the discontinuous-treatment tank may also serve as an equalizer, and for such plants the filland-draw method has been almost universally chosen; but for large plants and those with equalizing basins, mechanically operated continuous-treating equipment may offer economies. Processes designed to prepare coagulants from iron by flue gas and air or waste sour are not generally economical with present labor, equipment, and chemical costs. Acid felting of wool is a process which produces an exceptionally strong acid waste, and on a laboratory scale the continuous preparation of iron sulfate solution from the segregated strong acid waste and scrap iron appears interesting. However, a combination of high- and low-magnesia limestone is still being used to neutralize the excess acid from a felt plant in Connecticut. The disposal of the sludge from coagulation is a major problem, so difficult that one plant has been known to carry out a successful coagulation operation and then discharge the sludge into the adjoining stream along with the decanted liquor. Two hours should be sufficient time to settle a chemical floc in a vessel 10 feet deep to 2 or 3 per cent of the volume of waste treated. An acre of undrained earth lagoon will care for the sludge from 150,000 gallons of waste per day; an acre of underdrained sand beds is adequate for 500,000 gallons. The general practice appears to consist of reducing the sludge to approximately one tenth its volume on a drying bed, when it can be removed to a dump and further drying and weathering carried out. In some cases the partly dried sludge has a sufficient heat of combustion to make it possible for it to be burned with solid fuel. The sludge discharged from a treatment tank can be dewatered to 60 per cent moisture on a continuous vacuum filter. The conditioning required may consist of 20 pounds of lime and 5 pounds of ferric sulfate per 1000 gallons. After air drying and weathering for some weeks, over 80 per cent of the
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iron content of a sludge can be recovered by treatment with sulfuric acid. However, the over-all cost of the effectively recovered ferric sulfate appears to offer little saving over the cost of new chemical. The retention of sludge in fill-and-draw treatment tanks is practiced in some plants with certain wastes. This practice is illustrated in Figure 2, where a 30 per cent saving in chemical dosage is indicated. This percentage figure was arrived a t after a study of varying dosages of new chemical coagulant. After four or five re-uses of sludge, the efficiency falls off and consequently i t is well to withdraw from 20 to 25 per cent of the total sludge after each treatment.
TABLE111. SCREENING FILTERS reduction in 0 2 consumed at:
' 6 0 0 gal./cu. yd./day
1000 gal./cu. yd./day 2100 gal./cu. yd./day Av. capacity to clogging gal./cu. yd. AT. total oxidizable matter removed, lb./cu. yd.
Coke Breeze
Coal Ash
48-82 34-79 22-64 26,210 18.05
37-77 30-79 19-58 29,610 17.06
Steam Coal 52-84 42-77 19-55 12,780 5.19
BIOLOGICAL ACTION. The application of biological processes to textile waste purification was shown to be possible in work begun over thirty years ago a t the Lawrence Experiment Station. It is extensively used in Great Britain but has been less recognized in this country. The most effective method of providing the contact of air and waste necessary for aerobic action is by means of bio-aeration or intermittent or trickling filters, which are familiar in domestic sewage treatment. Textile wastes differ fundamentally from domestic sewage, and failure to recognize these differences has placed biological processes in unmerited disrepute. An undiluted textile waste carrying nonputrescible suspended matter cannot be applied directly to an intermittent sand filter a t the usual rates without clogging it within a few months. Filters of sand or coke breeze discharge an effluent with a decreased oxygen demand under these conditions, but examination of the filter ballast indicates that much of the organic matter present in the original waste is still in the filter. Straining or screening filters of coke breeze, bituminous steam coal, and bituminous coal ash of approximately equal size particles, 4 feet deep, have been tested with both composite and special process wastes such as those from print rooms, wool washers and cotton kiers. Some average results are shown in Table 111. There is no indication of nitrate formation in such filters, and no difference in effect was noted when the filters were completely flooded as compared to ordinary trickling operation. This (4 seems to indicate that aerobic action plays 3 '4 a minor role. Coke ballast appears to be slightly more efficient than coal ash, but its 8 B chief advantage would seem to be that i t h can be disposed of with its adsorbed waste by burning under a factory boiler. With c, segregated oily and soapy wastes, Snell b secured more than 80 per cent reduction in oxygen consumed values on a coal ash n; filter 3 feet deep ( l a ) . He reports that K some chemical, action of salts in the ash as well as filtration is involved in the process. Simple filtration may provide all the treatment necessary for special wastes, but NUMBER T/M€S FLOC US€B with composite wastes it seems better suited FIGURE2. RE-USEOF COAGULATED FLOC WITH 70 PERCENTNEWDOSAGE to preliminary treatment which is to be
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The effect of different proportions of a Connecticut textile waste on gas evolution during separate sludge digestion on a laboratory scale IS shown by Figure 3 (7'). The sludge mixtures used were obtained by compositing raw domestic sewage and textile waste in the proportions shown over %hour periods and settling for 4 hours. No seeding was used in the control digestion or in the lower textile waste percentage mixtures.
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Figure 4 is a diagram of a cotton piece-goods waste treatment plant. Equalizing and cooling of wastes in a concrete receiving basin are fol4 lowed by treatment with copperas and lime to 2 pH 8.3 in wooden tanks. The cycle of operations in one tank can be carried out in 4 hours. $ After the supernatant liquid is siphoned from the treatment tanks through an aeration channel, DRYS 0 10 20 SO 40-50 bO 70 80 90 ZOO 110 120 130 140 I50 Zbo 170 the sludge is withdrawn by gravity from the conFIGURE 3. EFFECT OF TEXTILE WASTEON GAS PRODUCTION FROM SEWical bottom of the tanks and run to lagoons with AGE SLUDGE DIGESTION AT 30" c. sand bottoms. Rain water and supernatant (2) Control (sanitary sewage) liquid are run back to the receiving basin. (3) 5 0 7 sanitary-50% active seed The normal capacity of the plant is 250,000 (4) 5 0 8 mixed (75% sanitary-25% textile waste)-50% active seed 15-4) 25 textile w a s t e 7 5 % sanitary sewage gallons in 24 hours. The average cost of chemi15Bj 15 textile w a s t e 8 5 o sanitary sewage cals used is approximately 3 cents per 1000 ( j c j 10 textile weste-gog sanitary sewage gallons of waste treated. The owners have estimated that the total annual charges against followed by chemical coagulation or true bio-aeration filtrathe plant are 5000 dollars when it is operated a t half cation. Mixed with 80 to 90 per cent of domestic sewage, i t pacity. This indicates that it costs 13 cents to treat each has been shown repeatedly that trickling filtration will purify 1000 gallons of waste. However, by combining engineerconcentrated textile wastes satisfactorily. On a laboratory ing estimates of the cost of the plant and the company's scale it has been found that if a complete textile plant waste operating expense, a cost of 10 cents per 1000 gallons is effluent of the usual alkaline reaction is equalized to secure indicated. At normal capacity a cost of 8 cents per 1000 maximum neutralization and good precipitation, strained gallons is calculated. and aerated by simple filters (with recirculation if necesFigure 5 shows a layout of a chemical precipitation plant sary), diluted to a concentration equivalent to domestic for the treatment of rayon-finishing wastes. This plant has sewage, inoculated by mixing with the amount of domestic a rated capacity of 300,000 gallons per day, and 10,857 dollars sewage produced by t h e workers in a typical diversified textile factory, and applied to a trickling filter, an over-all purification of 90 per cent can be reasonably expected at a cost comparable with that of treating domestic sewage. It has been shown recently that sulfur dye waste, one of the most concentrated and difficult dye wastes to treat, can be WASTE L I N E purified by the active sludge processes when I ~ e l diluted l with domestic sewage (8). As an example of the possibilities of anaerobic biological action, experiments have been carried out with equal parts of domestic sewage and of woolen and hat factory wastes. These wastes contained so much hair and wool fiber that satisfactory operation of an Imhoff tank was prevented. With slow surface stirring and thermophilic digestion a t 55' C., the fibers and hair were completely destroyed and normal sewage sludge was produced. Rudolfs and his co-workers in New Jersey carried out extensive experiments on the effect of industrial waste on sludge digestion (IO). These experiments indicate that TAIL RACE M textile waste retards but does not prevent sludge digestion. Pales gave a summary of the effects of industrial wastes on sewage FIGURE4. COTTON PIECE-GOODS FINISHING WASTETREATMENT PLANT treatment ( 2 ) .
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STORAGE -OVERFLOW
90.0oOGALS.
+POST INDICATOR
FIGURE 5. RAYON-FINISHING WASTETREATMEXT PLANT
were expeincled on construction. Ferric sulfate and lime costing from 3 t o 5 cents per 1000 gallons are used in the treatment tank, and after this treatment the effluent waste is discharged to a secondary settling and equalizing basin a t a pH of 6.6. The treated effluent is allowed to run from the secondary basin a t a constant rate for a period of 24 hours. The company estimates that a t one third of rated capacity it costs from 10 to 12 cents to treat 1000 gallons of waste; operated a t rated capacity, the entire cost should be 9 cents per 1000 gallons.
Conclusions Although it is realized that the natural-fiber textile industry is not notably prosperous, that it is not expanding, and that it is highly competitive, nevertheless, waste treatment must be considered a legitimate part of the manufacturing process if general enforcement of stringent regulation of all waste discharge is to be avoided. The textile manufacturer has a legitimate claim upon his community for assistance in the disposal of his wastes, provided he will equalize discharge rates and concentration and will apply sufficient treatment
in the plant to make them comparable in concentration and ease of treatment to domestic sewage. How far a community should attempt to modify conventional domestic sewage treatment processes to accommodate industrial waste is a question that must be faced more generally in this country. Technical advisers to the textile industry may well give increased attention to (a) the simple and cheap treatment methods of equalization, aeration, and mechanical separation, (b) application of biological action, (c) cheapened and improved use of chemical coagulation, and (d) development of recovery processes in order to reduce pollution rather than increase profits. Manufacturers may profit by consideration of the following general suggestions : 1. Careful study of plant processes with the object of eliminating or decreasing objectionable wastes. 2. Securing of sound chemical and engineering advice in plant construction and waste treatment, realizing that no magically simple and cheap method of purifying textile wastes is likely t o be found; with proper advice, however, it can be expected that improvements and special ‘modifications of the undamentally sound methods of treatment can be adapted to a particular problem.
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3. Cooperation with trade organizations and pollution control agencies endeavoring to solve general waste treatment problems for industry, rather than attem ting to avoid waste treatment, employing homemade rnakes&fts, or buying off lower riparian objectors. 4. Removal of waste from natural waters, not only to benefit recreational and domestic water users, but also other industrial users and ultimately all industry.
Literature Cited (1) Buswell, A. M., Alexander’s “Colloid Chemistry”, Vol. IV, p. 693, New York, D. Van Nostrand Co., 1937. (2) Fales, A. L., Sewage Works J . , 9, 970 (1937). (3) Geyer, J. C., and Perry, W. A., “Textile Waste Treatment and Recovery”, Washington, Textile Foundation, Inc., 1936. (4) Goodrich, R. B., master’s thesis, Wesleyan Univ., 1938. (5) Hoover, C. R., State Water Commission Conn., 5th Biennial Rept., 1934.
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(6) Hoover, C. R.. Aaronson. H. J., and Deitch, M . , Div. Water, Sewage, and Sanitation Chemistry, A. C. S., Rochester, 1937. (7) Hoover, C. R., Phelps, I. K., and Jones, L. G., Ibid., Milwaukee, 1938. (8) Miles, H. J., and Porges, R., Sewage Works J., 10, 323, 856 (1938). (9) ‘Raab, E. L., master’s thesis, Wesleyan Univ., 1937. (IO) Rudolfs, W., and Setter, L. R., Sewage Works J.,9, 549 (1937). (11) Snell, F. D., Am. Dyestus Reptr., 26, 730 ,1937). (12) Snell, F.D., Iwn. ENG.CHEM.,29, 1438 (1937). (13) Spoehr, H. A., J . Am. Chem. Soc., 46, 1494 (1924). (14) Theriault, E. J., Butterfield, C . J., and McNamee, P. D., Ibid., 55, 2012 (1933). (15) Trice, M. F., Industrial Waste Survey, State Board Health, Raleigh, N. C., 1931. (16) Urbain, 0, M., U. S. Patent 1,967,916 (1934). (17) Vollrath, H. B., Chern. & Met. Eng., 43, 303 (1936). (18) Weston, R.s., J. Boston Soc. civil Eng., 16, 358 (1929); IKD. ENG.CHEM.31, 1311 (1939).
Wastes Problems in the Nonferrous Smelting Industry ROBERT E. SWAIN Stanford University, Calif.
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ONFERROUS smelting operations have traditionally been accompanied by a great waste of by-products. These have embraced many substances, both metallic and nonmetpllic, which because of their relatively small quantity or their high degree of dispersion in enormous volumes of exit gases, of slag, or of refinery slimes, were long regarded as beyond the bounds of economic recovery. But that day is passing, as even a superficial survey of the advances of recent years cannot fail to reveal.
Sulfur Here sulfur must take first place. It is not only a waste product which is stupendous in the gross amount discharged from smelting operations the world over, but it is probably the world’s greatest trouble maker for the metallurgical industry. It takes first place in smelting progress in the last ten years as a result of developments through which i t is being recovered from waste gases of high dilution and sent into useful channels. We are actually in a new era so far as the sulfur problem in the smelting industry is concerned. This remarkable attack upon the problem found its initial impulse in a recognition by the industry a t large that here was a menace to agriculture and forestry which must be put under control. In more recent years, the great economic loss being suffered and the possibility of the profitable recovery of sulfur dioxide in waste gases have spurred efforts to meet the situation. This is now a dominant motive in countries like Germany with no native sulfur, little iron pyrites, and an urge toward national sufficiency. Like every other movement it passed slowly through many initial stages. As far back as 1910 sulfuric acid was produced on a large scale from the smelters a t Ducktown, Tenn., as a remedial measure, and soon afterward a sulfuric acid plant was installed a t Anaconda, to be followed by similar installations a t other points. Yet the surface was hardly scratched by these developments, for two dominant reasons.
One was a limited market for sulfuric acid, especially in the great western smelting areas. The other was the fact that many smelting operations, especially with lead ores and to a degree with copper ores, did not yield sulfur dioxide in concentrations sufficient to permit economic recovery. The prevailing concentrations of 0.5 to 2 per cent in enormous volumes of waste gases were not regarded as recoverable, even in the wildest flights of the imagination. Thus the problem stood practically up to the threshold of this decade. Then two new ideas took shape, one the outgrowth of the other. The first was to strip the sulfur dioxide from these dilute gases by means of absorbents, then to release it and make it available in more concentrated form. The other was to produce elementary sulfur from the concentrated sulfur dioxide and thus to tap a much wider market. It is impossible here to give an adequate review of the work done in these directions during the last seven or eight years when the major developments have taken place. Many of the investigations upon which they are based are superb examples of the application of physical-chemical principles to a complicated problem. From this work three outstanding processes have emerged; all of them are today in successful operation on a large scale on waste gases from smelting operations. At the great lead and zinc smelter a t Trail, Canada, the Consolidated Mining and Smelting Company has developed and put into successful operation a process in which a solution of ammonia is the primary absorbent. The waste gases are sent through scrubbing towers, where the absorption of sulfur dioxide is continued until a strong solution of ammonium bisulfite, with some normal sulfite, results. This is then treated with sulfuric acid to form ammonium sulfate and release pure sulfur dioxide, the former being sent to the fertilizer by-product plant. The sulfur dioxide is then sent through reducing furnaces, fired with coke, to produce elementary sulfur. This plant has a production capacity of nearly 200 tons of sulfur per day. The recovery of sulfur dioxide from the gases treated is practically
