Methods for Removing Detergents from Waste C. A. BRUI'~ER, U.S. Department of Heakh, Education and XWelfare; Public Health Service; Division of Water Supply and Pollution Control, Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio Abstract

L a u n d e r e t t e wastes, on the o%er h a n d , oftqn have ABS eonen o f 50 rag/liter and several hundred r a g / liter is not uncommon. [n addition, launderette wastes c o n t a i n eonvn o f phosphate a n d of suspended m a t t e r t h a t are as high as several h u n d r e d rag/liter. Because o f differences in the over-all composition and the volun'm o f the two waters, different t r e a t m e n t methods have been suggested f o r each. I n d u s t r i a l wastes art another source o f detergent pollution, especially nonionics. These wastes are extremely variable in n a t u r e . In m a n y eases their beh a v i o r with respeet to detergent r e m o v a l is similar to that of nnmicipal waste water.

A n u m b e r o f processes have been investigated or are b e i n g investigated f o r r e m o v a l o f alkylbenzene sulfonate (ABS) from waste waters. These can be divided into processes applicable to launderette wastes and processes applicable to municipal waste w a t e r although there is overlap. Launderette waste t r e a t i n g methods include, floeeulation, flotation, adsorption on activated earbe.n or ion exehange mateNMs and filtration. In munieipal waste w a t e r t r e a t m e n t any ABS removal method must be ve~T inexpensive. Two methods t h a t have been used to remove most of the residual ABS a f t e r conventional sewage t r e a t m e n t are foaming and a d d i n g of cationic detergents. Both methods are capable o f renmving ABS down to levels of 0.5 p p m or less. A n u m b e r of o t h e r t r e a t m e n t methods t h a t will remove organics, including ABS, from municipal wastes are being studied. Their costs are, in general, too high to make t h e m applicable f o r ABS removM alone. Processes u n d e r s t u d y i n c l u d e adsorptior~, chemical oxidation, ion exchange, electrochemical degradation and e v e n distillation.

Methods for Treating Launderette Wastes A n u m b e r of p r i v a t e companies have designed l a u n derette waste-treatment equipment (1). Beem~se it is desirable f o r this e q u i p m e n t to remove phosphate and suspended m a t t e r in a d d i t i o n to ABS, a n u m b e r o f operations usually are r e q u i r e d . These i n e l u d e floeo eulation, adsorption o r absorption, ion exchange, filt r a t i o n and flotation. A n excellent discussion of a n u m b e r o f systems is g i v e n by Flym~ a n d Andres (2). The most efficient o f these f o r ABS r e m o v a l is eap~)le o f r e d u e i n g the ABS eonmt to less t i t a n 3 rag/liter. T h e t o t a l cost (d t r e a t m e n t i n c l u d i n g amortization o f equipmm~t, o p e r a t i n g costs a n d w a s t e eone o r residue disposal is likely to be somewhat more than $1.00/ 1000 gal. In some cases, chemical eos/~ alone are more t h a n $1.00/1000 gal. It might a p p e a r t h a t t r e a t i n e n t f o r only ABS renmvaI would be considerably ehe~tper. This is not necessarily t r u e , however, because processes would still be r e q u i r e d t h a t would Mlow the waste residue containing the removed ABS to be coned to a small volume. Small-scale processes tl~at aeeomplish this are costly.

Introduction created a n u m b e r o f w a t e r q u a l i t y problems. The nmst obvious, as f a r as the public is concerned, is the aesthetic p r o b l e m of f o a m formation on ~a~terways and in ground w a t e r as a result o f waste-water pollution. IZoamhlg is also a p r o b l e m at, m a n y munieipal waste-water t r e a t m e n t planls. Until r a t h e r recently there was little positive evidence t h a t more readily degrad~d)le detergmlt m a t e rials would be devdoped. The c h i e f solution to ~ke p r o b l e m of detergent foaming appeared to be t r e a t ment processes t h a t remove detergents from waste waters. A n u m b e r o f process development studies were undertaken in this a r e a . It now appears, however, that " s o f t e r " o r more degradable detergents will be avail. able and will be widely used in this country. While lhis will no doubt greatly alleviate the detergent p o l l u tion problem, most probably it will not solve it completely. Detergent r e m o v a l methods may very like]y still be necessary a t some locations.

Methods of Treating Municipal Waste Water for ABS Removal Since l/he amt of .ABS in eompletely t r e a t e d munieip a l waste w a t e r is o f t e n less than 1% o f the t o t d contaminants a n d less t h a n 10% o f the organic contamin a n t s , any r e m o v a l m e t h o d f o r ABS None must b e very inexpensive in contrast to launderette waste t r e a t m e n t . Costs o f a few t e n t s o r less/thousand gM are all t h a t might be tolerated. Only a few methods a t present can be eonsidered. These i n c l u d e a d d i t i o n of eationie detergents, biodegradation o f the ABS on soils and foaming. The use o f cationic detergents f o r removM o f ABS has been studied by SamNes (3). MateriNs sneh as a n alkyl d i m e t h y l benzyl ammonium chloride r e a c t with ABS to produce a precipitate. Removal of the p r e c i p i t a t e by ~.um floeeulation followed by filtration o r even b y filtration a l o n e results in ABS cohen of ca. 1 rag/liter o r less. F o r the p a r t i c u l a r secondary efflue n t studied it was f o u n d t h a L in a d d i t i o n to ABS, onehalf or n:mre of the t o t a l organic pollution as measured by chemicalo x y g e n d e m a n d ( C O D ) also was removed. B a s e d upon present prices, the cost o f cationic det e r g e n t f o r this process is ca. $0.006/1000 g d f o r each mg of ABS/liter of waste water. F o r nmst municipal wastes, this represents a rain chemical cost o f ea.

Detergent Pollution in Waste Water Two waste w a t e r sourees t h a t have been suflieiently important contributors to detergent pollution f a r rem o v a l studies to have been u n d e r t a k e n are municipal waste t r e a t m e n t plants and launderettes. On a nationwide basis, the volmne o f launderette waste is i n s i g nificant in comparison to the volmne of municipal waste, b u t there are locations such as Suffolk County, N.Y., where launderette waste causes intensive l o c a l pollution problems by mixing with the g r o u n d w a t e r used as the source o f drinking water. The ABS cohen (as determined by the methylene blue analysis) of municipal w a s t e w a t e r is o f t e n ca. 5 rag/liter a n d is seldom raueh above 10 mg/Iiter.

813

814

THE ,JouRNAL

OF TIlE ASIERI(~AN OIl~ ( lIE.lISTS

TABLE I Foaming of Secondary Effluent ~ olume of air/n'~ass of ABS in feed (liter/rag)

~,BS e(men of product uater (mg/|iter)

1.0 20 3.0

~)57 0.:~6 0.~9

$0.03:1000 gal. The t o t a l operating cost o f the t r e a t . mere method a p p a r e n t l y would be barely within the r a n g e o f acceptability. T h e I)riee o f the cationic det e r g e n t might decrease significantly, however, if the material were widely used. The process would then be nmre attractive. T h e use o f soils t(~ remove organics from waste w a t e r has been known and practiced f o r some time. Robeek e t al, (4), recently made a detailed lysimeter study of the ability o f s a n d y soils to remove ABS and o t h e r organic eontaminants from domestic waste water. By a p p l y i n g tile w a t e r intermittently so as to mainlain aerobic conditions in the soil, they f o u n d that ABS could be biologically degraded to a 0.5 rag/liter level even when the ABS eonen h a d been artifieally increased to levels h i g h e r than usually f o u n d in waste effluents. Radioactive t r a c e r tests with Sas tagged ABS indicated that much o f the ABS degraded f a r enough to produce s u l f a t e ion. Most of the t o t a l organic material fed was actually removed. Alth(mgh this t r e a t m e n t method is technically promising, it has the disadvantage of requiring large infiltration area~. Based on the lysimeter s u r f a c e area used, the r a t e of applieation was, a t most, 3.5 g p d / f t ~. A t this rate ca. 60(1 level acres of suitable soil might be r e q u i r e d f o r the waste w a t e r of a city of 500,000 population. The cost o f ABS r e m o v a l by spreading the waste w a t e r on soil would certainly depend upon the cost of l a n d . In addition, there would be cost f o r bed p r e p a r a t i o n and maintenance o f the s p r e a d i n g and poauibly any undcrdrain system required. T h e t o t a l cost is di~cult to estimate a t present, but might be reason~ able in some areas, Foaming o f m u n M p a l waste w a t e r f o r ABS r e . moval has been investigated and is presently being used in several t r e a t m e n t p l a n t s as a supplementary proeess a f t e r secondary o r biological treatment. The s m ess of the method results from adsorption o f surfactants to the water-air interface. When bubbles o f air are blown through the w a t e r a large amt of interface is produced, w h i c h is conveniently removed as foam. Table I shows average results from continuous laboratory runs in which secondary effluent samples from
Other Processes Capable of Removing ABS from Municipal Waste O t h e r processes f o r more complete removal of contaminants from waste w a t e r than is possible with the

SOCIETY

VoL. 41

present conventional l reatment methods a r e u n d e r study by tim Advanced Wash, T r e a t m e n t Research Program of the tLS. Public Ilealth Service. Although most of these processe~ will remov(! A B e , the gross removal of organics, inorganies or both, is lheir primary function. Those that remove ABS include adsorpliou on activated carbon, chemical oxidation, distillation, reverse osmosis and solvent extractiou with seeondary amines. These t r e a t m e n t nmthods are, in general, too expensive to be considered f o r ABS removal almle. Adsorptinu, which is very promising f o r r e m o v a l of many organics, can be carried out with g r a n n l a r or powdered carbon. Ca. 0.75 Ib of g r a n u l a r carbon/1000 gal is required. The exhausted carbon must be reactivated for eeonomical opcration. The total eost f o r t r e a t m e n t of secondary effluent to produce w a t e r having a maximum ABS conch o f 0.5 rag/liter might be less than $0.10/1000 gal f o r plants t r e a t i n g 10 mgd. Chemical oxidation with hydrogen peroxide o r ozone can also be employed f o r removal o f organic materials. In the process, ABS appears to be oxidized p r e f e r e n . tially; cohen of less than 0.5 rag/liter are achieved. The cost of the process a p p e a r s to be g r e a t e r than the cost of carbon adsorption, however. Distillation removes nearly all the contaminants from waste water. With care to prevent f o a m c a r r y . over, ABS can bc reduced to negligible levels at (,osts probably comparable with those f o r sea w a t e r conversion. Reverse (~smosis is a relatively new t r e a t m e n t method that effects removals eomparable to those o f distillation. Ill the process, w a t e r is freed from impurities by being f o r c e d through a special type of membrane t a m e r high pressure. F o r waste-water t r e a t m e n t , preliminary results suggest t h a t operating costs may be competitive with those for distillation. Like distillation and reverse osmosis, the solvcm extraction process referred to here is capable o f separ a t i n g both organic and inorganic materials from waste water. W a t e r molecules f o n n a loose complex with certain amines. By raising the temp of the (.omplex, the w a t e r can be sel)araled and recovered. I:'urity of the p r o d u c t w a t e r is not as high an in distillation. ABS removal down to ca. 1 rag/liter is all that is usually obtained. O p e r a t i n g costs can not yet be p r e . dieted with any degree o f accuracy.

Future of Advanced Waste Treatment Processes After Use of Degradable Detergents Becomes Widespread Municipal waste w a t e r that has been given conventional prilaary and secondary t r e a t m e n t contains an average of ca. 3()0 rag/liter mor~ dissolved organic and inorganic material than does tile w a t e r supplied to the c i t y . The waste w a t e r frma a lmmderette contains, besides ABS and certain u t h e r materials, large amt of various forms of s o d i u m phosphate. ]n addition, both waste waters contain suspended matter. Obviously this t o t a l amount o f material added d u r i n g use, not just the. ABS, wmfld have to be removed if manmade pollution were to be eliminated. In a closed system with continued reuse of the w a t e r f o r an indefinite period, complete r e m o v a l of the contaminants added d u r i n g each use would be necessary. Even with the degree of reuse presently practiced, removal of a t least a fraction of the added contaminants is desirable. Any process, therefore, t h a t removes a significant amt of organic o r inorganic material could be of v a l u e now and shouhl be of g r e a t e r v a l u e in the future when increased reuse wilI be necessary.

DECE.~BE~, 1964

B R U N N E R : METItODS FOR REMOVING D E T E R G E N T S

All the processes discussed here remove significant amt of impurities o t h e r than ABS. They might, theref o r e , be used whether or not ABS were present. Most of the processes would, in f a c t , operate more efficiently if ABS were not present. Foaming is a possiMe exception. The synergistic action between small amt of ABS and o t h e r organic materials in waste w a t e r is, in many instances, very effective in producing stable foam. I I o w strong the foaming tendency of waste w a t e r might be in 1he absence o f the presently used ABS is not well known. A reduction in foamability would eertahdy be expected. This might be overeoro~ partly by ehanges in the design o f foaming equipment. It might also be possible t o add small amt of foaming agents to produce a more stable foam. Products and environmental patterns change with time. W e cannot expect to tailor waste t r e a t m e n t f o r each new p r o b l e m compound l h a t comes along. W a t e r reuse considerations will demand that only a very

815

h)w level o f many eontamilmnts be allowed to remain in water. W e need a n arseHM of highly efficient t r e a t meat methods to cope wilh all types of contaminants. There is no question t h a t o u r technology can develop such methods. W e nmst provide the t r e a t m e n t m e a n s if the clean w a t e r needed and demanded by the public is 1o be available. REFERENC~ES 1. Anon., Chem. Eng. News 40, 48 (Oct. 29, 1962). 2. Ylynn, J. M., and B. Andres, Water Pollution Control Federation, 5ournM SS. 783 (1963). 3. ramifies. W. R., I b i d . a4, 1070 (1962). 4. Robeek, G, G,, a. M. Cohen, W. T. Sugars and R. In. W~mdward. Ibid. gS, 1225 (1963). 5. Public Health Service Publication No, 999-~.VP~5, "0ontaminant Removal from Sewage P l a n t Efliuents by Foaming," A~WTR.5 (1963). 6, Sharmin, S. H., W. R~ Seixuett, D. Kyriacou and W. A. Swesney. "Foam Recycle: A ~et~hod for Improved Removal of Detergents from Sewage," pre~ented at the 147th ACS ~eeting, Phi]adelphla, Pa. April, I964. [Received June 17,

]964~Aecepted October 22, 1964]

Performance of Straight-Chain (LAS) in W. A. S W E E N E Y and A. (2. O L S O N ,1 California Research Corporation, Richmond, California Abstract Tile foamability (dishwashing and washing ma. t h i n e ) and detergmiey of L A S in heavy-duty detergents is directly emnpared with polypropylene ABS ( P P A B S ) a t various reel wt, Cohen, w a t e r hardnesses and t e m p . In every case a peak in performance is obtained in the Cn to C17 side chain r a n g e . The peak is shifted to l o w e r reel wt as w a t e r hardness is hmreased, especially a t low detergent cones. L A g opt performanee is generally e q u a l to P P A B S , except in dishwashing foam in soft water. The I~AS peaks, however, are shifted to ca. one carbon l o w e r m(fl wt than the PPABS. Therefore, best eve>all performaIme is obtained f o r L A S whose average reel wt corresponds to a 3.2.5 carbon side chain, whereas P P A B S is best with a n average 13.5 carbon side chain. Dishwashing foamability is markedly different f o r the different isomers contained in LAS. When the phenyl g r o u p it attached to the middle o f the alkyl c h a i n , surprisingly high results are obtained. This dishwashing difference is g r e a t enough to be noticeable when the i s o m e r d i s t r i b u tion ehanges in whole products made u s i n g different alkylation catalysts. Detergency a n d washing machine f o a m are not affected enough to see dif~ ferences between whole alkylates. L A S solubility is g r e a t e r than P P A B S a n d is influenced by i s o m e r distribution.

Introduction reports on various aspects performance o f detergents containing t e t r a ABS since it has been the roost Mdely used synthetic anionic s u r f a c t a n t f o r m a n y years. In the last few y e a r s the performance of some o f the commercial polypropylcne alkylates has been improved b y IIERE ItAVE BEEN* m a n y

of the T propy/ene

Present address: W, Reg Res. Lab., USDA, Albany. Calif.

raising the average moI wt to equal about a 13.5 carbon side chain (1). There ha~'e m)t been m a n y r e p o r t s on performance o f LAS. Gray et al. (2,3) p r e p a r e d several pure compounds arid obtained w e t t i n g time, detergency and f o a m d a t a . B a m a g a r t n e r (4) p r e p a r e d and tested a n u m b e r o f dodeeylbenzene isomers. Koelbet and coworkers (5) reviewed the literature on t h e effect o f s t r u c t u r e on properties of a n u m b e r o f straight-chain and branched-chain alkylbenzcne sulfonates a n d o t h e r anionies. Most of the d a t a are on physical properties, sueh as s u r f a c e tension and eritieat mieelle eoneentration (CMC). Recently, Stanberry e t al. (6) presented some d a t a on perfomnanee of L A S vs. moI w t , but the L A B source was not specified and no direct comparison with polypropylene products was given. Therefore, the question o f how L A S performs in heavy-duty formulas in "praetieal-type" tests in direet comparison with P P A B S has not previously been answered. The present report comes to b e a r on this question and on w h e t h e r there is a n opport u n i t y to tailor straight-chain alkylbenzene s h i r e n a r e s t o obtain the s u p e r i o r properties o f the h i g h e r reel wt polypropyleue products. The dishwashing foam test is o f p a r t i e n l a r interest because it was folmd t o be a sensitive test f o r showing the improvement as reel wt was bmreased in the polypropylene ease. U n f o r t u n a t e l y , polypropytene alkylbenzene sulfonate has become generally known simply as "ABS." Therefore, to avoid a n y confusion between materials and to emphasize the considerable difference between polypropylene and straight-chain products, we will refer to Ghe l a t t e r as LAS, standing f o r linear alkylate sulfonate, The polypropylene p r o d u c t will be called PPABS.

Experimental

PreparaHo~ of Materials. The alkylbenzenes used in this work originated from several sources as summarized in Table I. They were bateh sulfonated with