TEXTILE INDUSTRY _ _
. .
veloped during the Past sixty to out the of the waste-sewage W 9e% remOV6d from the fibers in preparation years along lines found suitmixture so it m y be successfully purified in the municipal able for the treatment of dofor dyeing and 6nishing, toplant. Treatment problems may he simplified by reducmestic sewage and wastes gether with the chemifrom other industries, N~ ing the waste discharge within the mill or modifying the o.&ssddeterpiogstsused or remsrktextile pmcesses. Where wastes must be treated in millin thp scourinE_ DIy)cesm, . able- devices have developed owned disposal plants, equalization and chemical pmipiWool acoving waste is a tation are most ~ommonlyused. Whneoessary, pmyellowish-brown, tbickly turM panaoew for the textile dpitation isfouowd by meehanieal or hiologieal filtration. bid, greasy liquid, strongly manufactmm' Pollution d s culties. Aswithotherwastes, alkaline, high in organic matthe methods used do not alter, and readily putrescible. ways prduce the degree of treatment that might be desired and Characteristics of this waste are shown in the folloaing table. often cost an m o u n t which seriously hinders progress toward which summarizes the results of some hundred analyses (9): wider construction of disposal plants. P ~ r tp s r Million by Weight The fact that textile waste treatment is relatively expensive MSXim"m Minimum A"e.aW3 and often difficult cannot be attributed to a lack of research. creme 25.800 3 000 8,65Q 30,300 2:400 11,520 Excellent experimental work has gone on from time to time in all ~ y ~ & d & ~ t ~ $ 7,400 398 1 830 textile producing areas. That carried out in North Carolina Alkalinity 29,400 3,430 6:780 * Oxygen absorbed in 4 hours from I/* N permaupnate at 90° F. under the BusDiCes of the Textile Foundation is OutstsndinK. Various groups- of investigators at the University of North Cotton kiering w a t e watera contain the vegetable fats, waxes, C a r o b worked continuously for more tbm ten years compiling resins, boll fragments, starch, and sizing materials removed from data on waste characteristics. assembling information on existing the fiber by boiling under preasnre in B strong solution of caustic practice, and performing an nnpressive amount of research on the soda, soda ash, and smdl amounts of oils and other chemicals. nature and behavior of textile wastes and on methods for purifyBoil-out wastes are similar, but, since pressure is not used, the ing these wastea separately and in combination with domestic amount of materisl removed from the fiber is lesa. Wet-out sewage (f, 9,4, 6-10), wastes, produced by detergins at lower temperatures, are less Textile wastes, notorious for t h e r variety, range from heavily heavily polluted. In any case the natnre of the waste depends on polluted, o h e m i d y strong dischargesfromdetergingoperationsto the amount of material removed from the fiber and on the amount relatively uncontaminatedrinse waters. They are as vari-colored of rinse water used. The boil-out and wet-ont processes are beas the goods produced. When the combined wastes from a m i ! : ing generdly replaced by kiering as a step toward simpliseation must he treated, the wide variations in character force almost uniof textile mill operation. versal adoption of separation of the worst wastes from the weakest, The amount and nat$re of kier wastes are indicated by the foland the blending of those that require treatment before discbarge lowing averages for wastes from several mills where the one boil to the municipal sewer or treatment in a mill-owned plant. method was in use (9): Whenever possible, textile wastes should be combined with Quantities per 100 Lb. Goods domestic sewage for treatment in the municipal plant. This Kier Rinse TOtd method of disposal is simpler and costs less, and the control of 8a 116 33 GsillOns the treatment processes is usually better. When mills must pro4.78 4.11 8.89 Total solids, lb. 0.79 1.60 Bioche+cal oxygen demand. Ib. 0.81 vide their o m plants, equilization or averaging followed by Domestla emage equiv.. pelsons 4.82 ' 4.84 9.66 chemical precipitation and settling is generally used. If a high degree of treatment is required, the precipitation process is folS,& degumming liquor, a thick brown mapy liquid which m y lowed by either mechanical or biological filtration. The cast of have almost jellylike cousistenCyy,contaiW the sericin or gum precipitation and settling textile wastes is usually in the range of removed from the fiber and the soap and sodium dicate or other 10 to 20 cents per 1OW gallons. detergents used in the process. The degree of degumming varies from the removd of part of the sericin, or soupling, to complete TEXTILE WASTES boil-off. The character of the waste varies accordindv. Liquid wastes produred in textile milL fall into t w o broad The Sorth Carolina Hedth Dcparimrut rrporta ldlcrwing rlassfieations, dctcrpjng or scouring w a s i s , and dyeinK W S W . values fur a plant employing t w o waahcs after the boil-out (91: The former class, aj r c p t w e n d by FWI aeonring, cotton kicriny, Quantities per 100 Lb. ailk degumming, aud h x retting wasiw, are highly pdlutcd and Good* d i e d 1 to handle in treatment plants. Dye watts. on the other Uallona 850 Total solide Ib. 3J.7 hand, generally carry Lrss organic and mineral matter i h t is Vvlarlle mlih. Ib. 22 7 3.7 Supended aodda, Ib. d a u p j n g to stream and, except lor a few !)pea, ran bc arrtiaB.O.U.. Ih. fartorily treated at lesa cxpcnrr. Pop"Ie.,iYo equiv.. r.creons
it?
653
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. !
Figure 1. Diagram of a Plant Designed for Batch Treatment a n d Filtration of Textile Wastes (2) Flax retting is the process of steeping and fermenting the 0ax straw to remove pectose from the fihers. The waste is heavily loaded with highly putrescible organic matter. The retting process is usually carried out at the h x farm where wastes are ponded until they have undergone sufficient decomposition t o permit their safe discharge into streams. Wastes produced by bleaching and souring cotton EIC often similar to Eer or boil-out wa8tes but carry less polluting material. The exact nature of the waste depends on the process used and on whether bleaching is combined with the !&ring operation. Characteristiw of the combined waste from the latter treatment are about as follow8 ( 8 ) : Qusntities per 100 Lh. Goods 976 19 66 6 60
Gallotla Total solids. Ibs. Population equlv.. persons
Wastes from chlorine or peroxide bleaching only are much less heavily polluted than those given. They present no special problem when combined with other mill wastes. DYE WASTES
The large volumes of highly colored dye wastes have a wide range in character with regard to both their damaging effect on streams and the ease with which they may be treated. The discharge from direct dyeing, acid dyeing, and basic dyeing processes,
Table I. Wastes'of Cotton Textile Industry (12) PTO.yyI Slaaher (siring waste) Delalng
Kienng Bleaching S0"hg
Eer and bleaoh Direot dyeing Sulfur dyeing Vat dyeing
Wastes per 100 Lb. Goods, Gal. 6
110 174 115 336 1150 640 545 1890
5-Dar B.O.D. P.P.M: 820 1750 1240 300 72 120 220 1300 140
Population Equivalent er 100 LE. Gooda 0.2 9.6 10.8 1.7 1.2 7.1 7.1 a5.7 12.9
although not SO polluting as the sulfur and vat dye wastes, may have a higher oxygen demand than domestic sewage. These wastes contain, in addition to the spent dye, large amounts of neutral sodium salts used to drive the color into the fibers. Complete decolorization of wastes from direct, basic, and acid dyeins is often difficult because of the high solubility of the dyestuffs. Sulfur dye wastes are slkdine and strongly toxic. The wastes contain considerable quantities of sodium sulfide in addition to the dye. All sulfur dye wastes are damaging to streams and difficult*to treat separately, and interfere with the operation of municipal plants unless mixed with other wastes and proportioned into the domestic sewage. The nature of the waste from sulfnr dyeing is as fallows (2): Gallom per 100 ib. goods Total alkalinity,P . P . ~ . Popul~tionequw., per 100 ib. goods
545 1511 35.69
Vat dyes are dissolved and applied to the fiber in an a l U e bath containing a strong reducing agent. The color is subsequently fixed by oxidation in air or in a solution of an oxidizing agent, The wastes are alkaline and have a high initial or chemical oxygen demand because of the presence of the reducing agent. The nature of the waste is indicated by the following table (2): Galiona of waste per 100 lb. goods Total alkalinity. P . P . ~ . Popul&tionequiv. per 100 lb. goods
1800 1675 12.86
Wastea from other types of dyeing and from printing operations may differ from those described here, but they are usually less heavily polluted and can ordinarily be treated by methods which will handle those described. The United States Public Health Senice has reported the quantities mpresentative of wastes produced in the cotton textile industry (Table I) and %hoserelative to characteristics of the textile plant composites (Table 11). WASTE REDUCTION AND RECOVERY
Both proc~sscasts and the expense of waste treatment may sometimes be cut down by reducing the amount of liquid waste produced in textile mills. PwihiLities in this direction include (a) the we of wastes from one operation to make up baths or
May 1947
INDUSTRIAL A N D ENGINEERING CHEMISTRY
solutions used in another, (b) the muse of relatively clean wash waters to make up more concentrakdsolutions in the same prow, (c) the use of countedow equipment which continuously discharges a waste that is s d l in volume and uniform in character, (d) the retention of spent baths and reuse after making up to str&ngth,and (e) changes in type of processes used to eliminate those that produce large volumes of w a s h or wastes that are difficult to treat. The opportunities for recovery of wastes or the production of useful by-products appear to he confined to the strong chemical wastes. Dialysis is now used extensively to recover strong caustic solutions used in the manufacture of rayon. Both dialysis and evaporation have been used to recover caustic from the meroeri% ing wastes. In the viscose rayon industry spent acid baths are reconditioned by filtration to remove solid impurities, by evaporation to remove excess water, and by crystallization to remove the exeesa salts (11). The heavy pollution load carried by wool scouring wastes can be reduced by removal of the grease and dirt before the wool is washed. Two methods are used: solvent extraction of the grease followed by beating and dusting to remove the dnt, and the freeaing process in which the grease is hardened and removed with the dirt in a single beating operation. Lanolin is a by-product of both these operations. When the wool is subjected to the usual scouring without these treatments, grease has been removed from the waste by soid cracking, evaporation, centrifuging, and by treatment with hypochlorites ( 1 A ) . Because of the high dispersion of dyes in spent dye solutions aud rinse waters, the recovery of dye chemic& has usually been found to he impractical. However, the waste of dyes within the plant has been greatly reduced by saving spent baths and ma% them up to strength or by using continuous dyeing equipment from which the strong dye bath is never removed. Indigo was formerly recovered in some cases, but, since the wastes from modern indigo machinas consist only of relatively dilute rinses, the recovery proms is no longer attractive.
Table 11. Textile Plant Composite )Wastes (12) Waate Gallon& per day Cotton thread (bleaoh. kier. oil, dye) Finishing cotton pieoe goods (bleach,
kier, dye, print) Fiojahmg cotton piece goods (bleach. hie.. mercerize. print. due) Cotton webbing (bleaoh, kier, dye) ' Cotton denim (dyeing) Cotton (desire, her, bleaoh, dye. print. memarise, finish) HOsierp Knit good8 Indigo dyeing
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. . I ' , . .
. .. .
Diagram of a Phnt' for &otinuous Treaturent of Textile Wastes (2)
mow
5-Day
B.O.D., P.P.M. 550
:2g:
i
378
274,000 180 ooo
605
420 478 315
438:000
360,o~)
2
1983 ~
244,000
~
! ~ 245
220
800,000
460
244.000
zao
128,ooo .30,000
300 000
Population E uiv/lCOo &I.iDsy 27
19 30 21 24 16 98 ~ 12 11 28
15 11 30
TREATMENT OF TEXTILE WASTES
.
Figure 2.
655
The methods used for handling and treatment of textile wastes at independent mill owned plants include separation, eqnalieation, coprecipitatiou, chemical precipitation, filtration, and biological purification. The mast common combination of treatments encountered is equalization followed by chemical precipitation and settling. Satisfactory disposal of the precipitated impurities or sludge is an essential part of any process and may at times present problems as severe as the primary.job of removing polluting mater& from the liquid. Equalieation by combining and mixing various wastes from different parts of the mill is a.necessary preliminary step designed to provide a mill effluent of uniform character. Operation of a k e d installation using either ohemieal or biological treatment would be impossible without thorough blending of the diverse and sudden dischargee from the ditIerent departments in a textile mill: In continuous-flow plants. tanks capable of holding the full %hour discharge are desirable and are Often provided.-The minimum holding time is probably around 2 or 3 hours, except in, fill-and-draw plants where batches are accumulated, mixed, tested, and precipitttted in the same tank. Where strong alkaline aud acid wastes are produced in separate processes, it may be possible to combine these or portions of them to bring the pH to the isoelectric point. The copreoipitation thus produced m a y materially reduce the expense of further chemical treatment. Ordinarily the highl? alkaline deterging and bleaching wastes can be partdly'neutralieed by combining them with souring, carbonizing, and acid dye wastes. Occasionally these alwine wastes have been neutralized by the acid wastes from near-by industries with mutual ljenefit to both concerns. Chemhal precipitation is the most widely used method of treating textile wastes. Coagulants used in this country me lime, sulfuric mid, ferrous and ferric sulfate, aluminum sulfate, ferric chloride. and calcium chloride; Of these, ferrous sulfate and lime usually work the hest and so me the mast economical. Treatment plants are designed to operate by either batch or continuous method. Batch or W-and-draw plants are cheapest and glve best r d t s when the amount of waste ta be treated LS not greater than 2 or 3 hundred thousand gallons per day. Simplicity in operation usually dictates selection of a continuous-flow plant when daily flows exceed this volume. A bntch trcatment plant usually consir.: of two circulxr tanks, each capable uf holding at least 2 or 3 huurs' dischare. Each tank iU equipped with a motor-driven stirring device. \Vslice is III.L.Umulat~iuonerankwhileth~I,atchin rheotheristreawd. When a tank is full it L firat thoroii&Iy mixed. A sample is tbru taken, and jar It614 arc made to determine the correct dose of rnagulant for the partieulxr batch. Char& provide fhe operator with ready meam of interpreting jar tests in t e r m of puunds of chemical to be added. The chemical is weighed out and fed into the t m k . Stirring is continued for 15 to 30 minutes and then stopped, and time is allowed for the pwripitaw to mttle. 'Khe supemtant or
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IN 9 U S.TA1.AL A N D ,.EN,GI N.E-E R.IN G ..C.RE MI 8 T R Y
tioning . the priliminrtry t r i a t i e n t involve separation of wastes at the mill and neutralization, precipitation, or aeration of those that are strong or toxic. . The North Buffaloplant at Greensboro, N. C. (Figure 3), is an outetandiug example of B .municipal sewage works designed to handle large volumes of textile wastes (3,6). This plant tEs,te a aewage-wastemixturecontainingabout15 to zO%of textile wastea derived from complete processing of cotton into finisbed go&. Kiering and sulfur and indigo dyeing processes predominate. The wastes are collected and equalized at the mill and are discharged in proportion to the flow, in the municipal outfall sewer. The B.O.D. of the .sewagGwaste mixture after neutralization . This is reduced to about 180 with acid is about 350 p. some 80 P.P.W. of alum. The .p.p.m. by preeipibtion settled Sewage is then treated in activated sludge tanks in which suspended solids are carried at ahout 2000 p.p.m. and ahout 1.75 cubic feet of air are used per gallon of sewage. The activated sludge settled f n m the noration rank effluent nceivee 12 h o w reaeration before it is returned to the process. The effluent has a B.O.D. of about 15 p.p.m. and a suspended solids content of about 10 p.p.m., and it retainsa slight blue tint. ,
treated liquid is withdrawn through a moving-arm decanting device for discharge to the stream. It is often beneficid to leave a considerable volume of "the sludge in the tank to assist in the cosgulation process. When sludge is withdrawn it is d l y lagooned or dried on sand beds.. The dried sludge is used for 6U or is hcinerated; Sludges from most textile waste plants do not decompose readily and wnsemently seldom create nuisance problems. In continuowflow plants theseparate devices provided for each step in the treatment include equalization tanks; chemical feed machines, flash mixere, flocculatora, settling tar&, and sludge handling and d i s p d equipment. When theprecipitatedand aettled waste liquor requires further treatment before diecharge, it is fdtered through either a mechanical fdter of the raoid sand tvne .. or a biolo&d trickliog.fdter. Means for chlorinating the effluent are wmrlimes provided. Tho two n h t s described below utilize what is believed to be the best prictice in the treatdent of textile wastes in sepata d - o w n e d plants: The plant shown in Figure 1 treats the composite waste from silk degumming and from dyeing and finishiog of the silk, wtton, rayon, and wool hosiery. The operation of this till-and-draw plant is BS described. C h d d requirements are w u u d 100 pounds of lime and 25 pounds of chlorinated wpperas per 25,000 gnllons of water. The decanting arm in the settling tank operates a switch which shuts off the effluent pump when the tank is drawn down to the sludge line. Sludge is left in the settlers until it builds up t o n point where it interfere with settling; it is then withdrawn to coke drying beds. The supernatant liquor is passed through preeaure fdtera of the water purification type before dischmge t o the stream. The plant shown in Figure 2 treats the waste from cotton kiering, dyeing, printing, and finiehing. During operation for 8 hours per day, alum m added at 25 pounds per hour, lime at 10 pounds per hour, and chlorine at 10 pounds per hour. The average discharge during this period w& MI0 gallons per hour. ENT WITH MUNICIPAL SEWAGE
and plnces the treatment under skillad supervision. However,
Vol. 39, No. 5
. mgy
IITEB*TUBE CITED
(1) Chriaao. H.F., White.A. M.. andBaity, H. G., Sewwe Wwka J., 5, 674 (1933). (1A) Faber, H. A., ZbiJ., 19. 248 (1947). (2) Geyer. J. C., and Perry, W. A,. "Textale Waste Treatment and RBoovery", Textile Foundation, Washington,D. C., 1936. (3) Horton, R. K., andBaity, H. G., TwtileReseorch, 11,321(1941). (4) Horton, R. K.,Porgee. Ralph, and Baity, H. G., S-E Wwh J.. 14,818 (1942). (5) Mengel, G. W., &4il Ew., $0,2437 (1840). (6) M~les,J. H., and Porgea. Ralph, S-e Wmka J., 10, 322, 856 (1938); 11, 1038'(1938). (7) Porpes, Ralph, Hortoh. R. K., and Baity, H. G., Ibid , 11, 828 (1939). (8) Porgea, Ralph,Sorton, R. K., andGotaas, H. B., ZbiJ., 13, 308 (1941). (9) I M . . 14, 685 (1943). (10) Porw, Ralph, Miles, H. J.. and Baity, H. G., Ib*l., 12. 601 (1940). (11) Roetman, E.T., Warn Wmka & Smrwe, 91,265,295 (194.4). (12) U. S.Public Health Service, Appendix V of Suppl. D to Pt. 2 of Ohio River Pollution Control Survey. House of Repmsentativffl Documeqt 268 (1943).
