Foaming a t Northeast Works in Philadelphia w h e n sewage was aerated without many solids in t h e tank. F o a m is n o w controlled b y carrying mixed liquor solids of around 8 0 0 to 1200 p.p.m.
A t
STAFF REPORT Ν
Effect of Detergents on S e w a g e a n d W a t e r Treatment Since the first mountain of f o a m mystified operators of sewage a n d w a t e r treatment plants, detergents h a v e been investigated as the culprit. A symposium organized by the Division of W a t e r , S e w a g e , a n d Sanitation Chemistry summed up recent results 1072
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alleged in t h e field to arise from t h e increasing use of syndets, a n d others showed the effect of detergent residuals on water treated for re-use. Although all detergent solutions eventually g o down the drain, it takes a large quantity of a n y water-soluble material, no matter h o w active, t o constitute a waste disposal problem. T h e fact that this symposium was held indicates the rapid growth of t h e detergent industry during recent years. In 1940, sale of synthetic detergents amounted to only 1 % of those of soap—in o n e decade, this figure jumped to 4G9o and quantity-wise exceeded o n e billion pounds. It is thus evident that if problems arise a s a result of t h e introduction of detergents into s e w a g e and water treatment plants, temporary o r marginal measures to solve them will not suffice.
Foam has been the cause of a number of the reported difficulties in treating plants. T h e Mt. Penn eruption, previously referred t o , was probably t h e first serious case of s e w a g e treatment plant trouble. Mt. Penn is located adjacent to the city o f Reading, Pa., and has a population o f approximately 5 0 0 0 persons. The area i s primarily residential and is served b y a separate sewage system with a mechanical type activated sludge plant for complete treatment of domestic s e w a g e . On a Friday in 1947, a large m a n u facturer o f a household nonionic detergent canvassed the entire area distributing o n e ounce samples of a nonionic syndet. T h e next morning, sewage plant operators noticed large volumes of foam or suds o n top of t h e separators. B y Monday m o r n ing, the foam, 2 to 5 feet in depth, c o m -
Participants in Symposium o n W a t e r a n d W a t e r T r e a t m e n t Problems Involving Detergents Introductory Remarks. Leslie C o r p . , Wyandotte, Mich.
R.
Bacon,
Wyandotte
Chemicals
Structural Characteristics a n d Behavior o f M o d e r n Surfactants. Anthony M . Schwartz, Harris Research Laboratories, Washington, D. C . Synthetic D e t e r g e n t s a n d Associated M a t e r i a l s in Domestic a n d Industrial S e r v i c e . A. Lloyd Taylor, Leslie R. Bacon, and H. R. Suter, Wyandotte Chemicals Corp., Wyandotte, Mich. D e t e r g e n t Properties a n d Their Effects in S e w a g e a n d Treatment. William Stericker and A. B. Middlefon, delphia Quartz C o . , Philadelphia, Pa. jL· ROM the t i m e of t h e spectacular eruption of the Mt. P e n n s e w a g e treatment plant i n 1 9 4 7 on the day following doorto-door distribution o f samples of a new household-purpose detergent, there have been scattered b u t increasing reports indicating that detergents affect sewage and water treatment operations. To collect and evaluate these reports, a n d t o determine just w h a t part of t h e responsibility for greater s e w a g e plant operational difficulties can justly b e placed on the rapidly increasing u s e of detergents, the Division of Water, S e w a g e and Sanitation Chemistry held a symposium devoted, to t h e subject at the AIMJSRICAN C H E M I C A L SOCIETY'S
119th m e e t i n g in Cleveland. The symposium was planned t o bring together information o n detergents to show t h e purposes, amounts, and l a n d s of detergents used. It would provide a source to w h i c h those concerned with sewa g e and water treatment problems could refer for possible explanations of operati n g difficulties. Included on the program were papers b y detergent specialists describing t h e development o f syntlietic detergents, their major applications, appearance, properties, and increased "utilization. T w o papers showed, difficulties VOLUME
3 1,
NO.
11
Review o f the L i t e r a t u r e on D e t e r g e n t s in S e w a g e . D e t e r g e n t s on S e w a g e Plant O p e r a t i o n . R. W . Gilbert Associates, Inc., Reading, Pa.
Water Phila-
Effect o f Simpson,
United Kingdom E x p e r i e n c e o f Synthetic D e t e r g e n t s in S e w a g e Processing. M. Elton, J. Hurley, and A. L. Waddams, Shell Chemicals, Ltd., London, England S e w a g e T r e a t m e n t ProbSems in Relation to D e t e r g e n t s . Willem Rudolfs and Raymond M. ManganeHi, New Jersey Agricultural Experiment Station, New Brunswick, N. J. Effect o f D e t e r g e n t s o n Slime Rudolfs and E. S. Crosby, New Station, New Brunswick, N. J.
G r o w t h in S e w e r s . Willem Jersey Agricultural Experiment
Syndets in Relation t o Biological Problems in Lakes. Clair N . Sawyer, Massachusetts Institute o f Technology, Cambridge, Mass. C o r r e c t i o n o f Tastes a n d O d o r s f r o m D e t e r g e n t s . John W . Hassler, J. G. Filicky, and C. W . Aman, West Virginia Pulp and Paper C o . , Tyrone, Pa.
/MARCH
16,
1953
1073
pietely enveloped most of the treatment plant. Analyses of raw sewage and plant effluent failed to show any variation in the sewage over past records, but consulting engineers learned of the sampling the day before the trouble began and quickly knew where to place t h e blame. It is interesting to consider that nonionic detergents are nonfoamers; in this case, some anionic material was evidently present. T h e foaming continued every d a y for 80 days but began to decrease after two weeks as the quantity of detergent decreased. T h e trouble was partially caused by the clogging of catch basins with grease which was removed from the sewer pipes. Control measures included dispersal with a stream of water and spraying the surface with antifoaming agent. The use of antifoaming agents for general use is. considered too costly. Trie release of quantities of sewer slimes may clog sewers and create treatment problems. Copious foaming occi i at the Hyr perion Treatment Plant o s Angeles, Calif., w h e n the activate 'udge portion of the plant was places opération about 18 months ago. The fo. or froth was undoubtedly caused b y the presence in the sewage of considerable quantities of synthetic detergents and was considered by the operators as not only a nuisance but was also believed to have been detrimental to biochemical oxidation as practiced in an activated sludge plant. The foam was greasy and c a u s e d deposits upon the hand rails and walkways of the plant. On windy days, frequent in the seaside location of the plant, large quantities of the foam were blown away to adjacent residential districts. For a number of months, more o r less unsuccessful attempts were made to control the foam by hosing down at a considerable cost for labor. Subsequently, a system of water sprays, located along the tank walls at the point where the foam collects, was installed and has been quite successful. On occasions w h e n the foam builds u p to troublesome quantities, t h e injection of relatively small amounts of antifoam chemicals into the spray -water promptly brings the foam under control; however, t h e operators have not found this to b e necessary very often. I n some cases, foam has b e e n a factor in producing a poor effluent, and, if it gets into the trickling filters, it will cause short runs. Mountains of foam developed when the Northeast sewage plant in Philadelphia was put into operation a little over two years ago. Bushels of such froths, tossed into the air by gusty winds, have shown scant respect for persons or places. A t Batavia, 111., a problem o f foaming also occurred in an activated sludge plant. This plant is similar to the o n e a t Mt. Perm and utilizes mechanical aeration for secondary treatment. In August 1949, a thick foam developed on t h e aeration units of one of two sewage plants. This foam, sticky and smelling similar t o sour milk, carried a high concentration of
1074
grease, which was deposited all over t h e plant. In early 1950, the foam w a s still evident and the plant effluent and settling qualities of the aeration liquid deteriorated as a result. The formation of calcium and magnesium soap curds through the neutralization of fatty acids and fats by alkalies aids sedimentation in some primary s e w a g e treatment plants. When syndets are used, these nuclei are eliminated and overloading of a biological sewage plant can b e a n expected result. In Great Britain, which has been plagued with sewage plant problems said to be due to synthetic detergents, alarm has developed over the problems resulting from wool-scouring detergent waste. Bradford, England, a textile city, is a n example where such a problem has been experienced. Wool greases are removed b y a sewage disposal filter and the sale of these greases in the past has provided funds for operation of the plant. As a result of the increased usage of syndets
in waste effluents, the sulfuric acid method for recovery of the grease is no longer satisfactory, inasmuch as the wool grease remains dispersed or dissolved and cannot be separated or recovered efficiently. The reduced efficiency of sewage processing attributed to the presence of synthetic detergents and wetting agents implies enlarged plant design and greater processing costs. Large Tonnage Detergents The problem of surfactants in waste and sewage streams and in treatment plants is considerably simplified because a relative handful of molecular types account for a high percentage of the total surfactant production. Of these, fewer still are likely to find their way into sewage streams in troublesome quantities. The major types, shown in T a b l e I include: alkyl aryl sulfonates, fatty alkyl sulfates, nonionic esters, nonionic ethers, sulfonated and sulfated fatty amides, nonionic fatty amides, and cationics.
Introduction of "Syndets" and Detergent Types The surface active agents include soaps, detergents, emulsifiers, wetting agents, and penetrants, and all owe their surface activity to a modification of the properties of the surface layer between t w o phiases i n contact with one another. The term surfactant, coined as a contraction of surface active agent, technically includes the soaps, but is more generally limited in ordinary usage to synthetic products used for their detergent, w e t t i n g , foaming, and emulsifying properties. Of these, the synthetic detergents or syndets are economically most important and are used in greatest tonnages. The development of surfactants came about as a. result of the one great disadvantage of soaps—namely their chemical sensitivity to the ions of hydrogen and heavy metals, particularly calcium. These ions convert soaps to waterinsoluble products. A need for less sensitive surfactants first occurred in the textile finishing industry over 70 years ago. At t h i s time sulfated oils were developed. Lower alkylated naphthalene sulfonates, t h e first surfactants based o n nonfatty raw materials, appeared i n Germany during the fat shortage period of World War I, and, while poor soap substitutes, t h e y are still used as wetting agents in some textile processing operations. Most of our modern surfactants were developed i n the years between 1928 and 1943. Though the number of individual surfactant molecules now runs into thousands, only about 3 0 0 are listed as commercial products by the U. S. Tariff Commission Census and but a fraction of these n a v e achieved pronounced economic success and importance. Current studies a n d industrial research deal largely with formulation, synergistic mixtures, applications, and improved processes for manufacture.
Detergent Types Most organic detergents, including -soaps, are essentially dipolar elongated molecules equivalent in effect t o a straight aliphatic chain of 12 to 18 carbon atoms. One end consists of a hydrophobic or water repelling group, and the other of a hydrophiliic or water solubilizing group. The surfactants can be classified chemically according to the structural nature of these two end groups and of the intermediate group ( w h e n it is present), 'which serves as a linkage. The hydrophiliic group may be anionic, cationic, o r nonionic in nature. The major anionic solubilizing groups are the sulfonic acid and sulfuric ester groups. T h e sulfonates and sulfates bearing these groups account for over 85ψο of the total production of synthetic surfactants. Other hydrophiliic groups include the anionic carboxyl group; the cationic group, built around basic nitrogen, which may be primary, secondary, tertiary, or quaternary amines; and polyethylene ether and polyhydroxy radicals, the only important nonionic solubilizing groups. The hydrophobic groups include several classes o f hydrophobes. More im portant are t h e naturally occurring straight fatty cHains of 10 to 2 0 carbon atoms, characteristic of t h e fats and soaps, and the hydrophobes of rosin acids; and synthetic hydrophobic radicals, most of which a r e derived from petroleum or natural gas. Important linkage groups include esters and amides. From a very general viewpoint, important surfactants can b e classified on the basis of the solubilizing groups a s anionic (sulfates and sulfonates) or non ionic. The cationics are essentially specialty products. O n the basis of the hydrophobe, surfactants are fat-based, petroleum-based, or rosin-based.
CHEMICAL
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ENGINEERING
NEWS
Table L General Properties of Major Types of Surfactants
:_-_Ι;„^
*
GENERIC NAME
- ;
~ TYPICAL STRUCTURE
Λ
FHOBK
\ , *" BASE
EMULSIFI-
FOAM-
STA-
STA-
WATKB
CATION , WETTINC TSG BIUTX ; BUTT JELOUDNKSS'
1 on- Ci^—GA—SOsNa v?AIkyl aryl sulf _^ *.;,*t ;~Petroleum Good , Excel-lent Excellent fîS'i'ateg·*·-**:' **•"-·-"-"--."• • > · - Fat "*- . ^-Excellent \ ·.good- ..Good „***„„.-^Good, * „ .Excel· ο lent. ^good ^Fatty. aBcyl sulfCHjiCHjJwCH^OSOsNa Very Good Poor to Fair to Very J ''j$(xmte*^?-.yt~^, ί%^ ^*~ ~~ -Y "'^-v^.'V^-' -^^''MuLiibN-- % or /;MIXJLIONV; detergents ' :.— Laundering, dishwashing,. u N- Nonionics such as polyoxyethylene ethers, alkyl aryl sodium p>;4irù * : ,- ^c"^:? '"--'•"{ *"'.r :''" ^scouring, special;xises,; and sulfonates, and sulfated alcohols ψ-ψ^ί^ ^'j \: ^ v i : ^ ândl_; j Proprietary preparations of wide composition range ^Ôâirjr^"industry>ί : iff "-*. Bolde; swashingt/' ^^'^Si'liy-'^1 .^omordcs^or^ combination of agents with little or no foaming Mi*, ^^H^-^f ^ - $*'4*ψ>iH^-r>- '"'^ bz^ï^^hcCZ ^:^: T^^-v^SSf;*tendency - ' - -v _V: • * 'v ~ v4 . \ . ËlcFoodi industry-"Τ: -"^V^ ^*x .Beniôval ^^Tàriô^^typ€»*/bf K* ""Pr6prietary,:detergënts ranging from highly alkaline to strongly Ι||Ι£Τ*:;ΐ^^ rvCâùstic''with\JalkyI-aryL'Sulfonates * ^ - . :/ f\%~X!~ '>A>^^^^ anundmum,compounds, ,-
|S^;^3£^M
. "" \ -* *
{à&glïfe^^^
. ·
"
•
: .- ,'
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