EFFECT OF ALKYL BENZENE SULFONATE ON HYDROUS ALUMINA FLOC N
C
. R.
.D,
S E D L A N D E R , I'niversity of Toledo, Toledo, Ohio G A T ES
,
Y.
Cornell University, Ithaca,
Distilled, synthetic, and natural surface waters containing alkyl benzene sulfonate were coagulated with alum. Photographs of water containing 1 to 7 mg. per liter of alkyl benzene sulfonate revealed marked changes in floc characteristics of coagulated water. Changing pH produced greater differences in floc characteristics. At pH levels between 4.5 and 4.8 removal was greatest. Filtration of water containing alkyl benzene sulfonate through a sand filter produced higher head losses than losses in control samples. Greatest head loss differentials occurred at lower pH levels. The presence of bentonite improved sedimentation, which resulted in reduced head losses in the filter.
study \cas made to determine how a n alkyl benzene \vould affect the characteristics of alum floc formed in \cater, and the nature of any physical and chemical reactions betbveen the surfactant and alum. T h e surfactant used throughout the study was a standard formulation, 39% alkyl benzene sulfonate, 41% Na2S04 and NaCI, and the remainder moisture. Aluminum sulfate [.412(S0J3, 1 8 H 2 0 ) ] was used as the coagulant. Concentrations of aluminum sulfate and alkyl benzene sulfonate \cere varied, so that the nature and the effects of the reaction benveen the surfactant and the aluminum ion could be measured by both chemical and physical means. Sanford (79) found that the addition of 5 mg. of polypropylene benzene sulfonate per liter to the coagulated and settled influent of a clean sand filter caused head losses to increase more rapidly than in a control filter. Below this concentration there \vas no apparent effect. H e assumed that a change in alum floc characteristics was responsible. \?arious investigators ( 4 , 22, 23) have reported that certain difficulties in the production of potable water appear to be due to the presence of surfactants in ra\v \cater. Other investigators ( 6 , 7) have estimated that the quantity of surfactant that will cause trouble in conventional water treatment may vary over a considerable range. T h e use of synthetic detergents has increased greatly since LVorld \Var 11. Since anionic surfactants of the alkyl benzene sulfonate type make u p about 60% of the detergents on the market, more informat:ion is needed about the reactions into kvhich the alkyl benzene sulfonates enter ( 7 7 ) . They are difficult to remove from sewage and as a result their concentration in many natural \cater:, is increasing. Sawyer and Ryckman (20)report that sulfonated amides and esters can be biologically degraded, but that the alkyl benzene sulfonates derived from polypropylene are much more resistant to biological oxidation. HIS
Tsulfonate
hlcBain ( 9 ) : Philippoff (73),and \\'insor (2,5) believe that some form of micellar association can exist a t concentrations of the surfactant below the critical micelle concentration. Prins ( 7 0 ' ) and others have shown that the addition of cations such as S a - and Car2 act as counter ions and lorver the critical micelle concentration. Studying the effect of loicering the critical micelle concentration by addition of cations, Po\vney and Addison (75) found that Fet3 and 'ivere not as effective as C a L 2because the valence effect \vas obscured by hydrolysis. Aluminum. .Aqueous solutions of aluminum salts contain a variety of ionic species. including polynuclear complexes. the distribution being governed primarily by H ion concentration. A t p H values less than 4, hydrated aluminum ions, [Al(HOH),If3>predominate. At p H greater than 4, various anions may displace one or more of these "aquo" groups. Because hydroxy ions have a strong coordinating tendency, they are very likely to be present, acting as bridges bet\ceen aluminum or ferric ions ( 7 4 . .4ccordingly, in the p H range 4 to 7.5, the aluminum sol probably exists as a n equilibrium mixture of aluminum and hydrates, \vith mono- and divalent charges, [A1(HOH)5(OH)+z, [.411HOH)4(OH)]'. Such forms probably polymerize ivith the formation of polynuclear species like [.416(OH)lj]t3 ( 3 ) . Aluminum ions are oriented a t the center of a n octahedral configuratioii and OH ions act as bridging agents between the octahedra. Because of the octahedral configuration? the bonds of metal atoms occur in pairs, each of Lchich lies in a plane perpendicular to the planes of the other pairs. Therefore: cross-linkage can occur, creating a three-dimensional complex ion. T h e follo\ving diagram illustrates an aluminum hl-drate or hydroxide floc structure: HO
\
HOH----
,
Theoretical
Surfactants. T h e alkyl benzene sulfonates (ABS) in concentrations belo\\ the ci-itical micelle concentration (that concentration a t which the anions aggregate to form micelles), are generally considered to exist in \vater as large anions. T h e hydrocarbon chain is hydrophobic, \\.hereas the polar end is hydrophilic. According to Harkins (8).the attraction of one \cater molecule for another, because of its dipole moment, is greater than that of icater for hl-drocarbon. \Vhen the hydrocarbon chain escapes from the Lvater phase, the free energy is greatly decreased becaiise of the great attraction of one water molecule for another.
/ OH
.
/%,
O H, ,
_ '
-_
,OH
-\
AI
A8 /,
ou' \ OH
' OH
OH
,
'
>,
,
__
O ,H
/ OH -\
AI
1
\OH,?
> O H /
,
OH OH
OH
1
OH
, '
,
/ OH
'
-
HOH
,, OH
~
Structures of aluminum soaps in accord with the theories discussed above have been proposed ( 7 , IO? 77). Apparent confirmation of the theory is found in the fact that the manufacture of these soaps is more successful in nonaqueous solutions than in \cater. T h e introduction of any water causes a marked gelling and an increase in viscosity even a t low concentrations VOL. 4
NO. 1
JANUARY
1965
55
Table I. Synthetic Water Hardness, Alkalinity, Turbidity, Mg. 'Liter as CaCOo Mg.:'Liter as CaCOa Turbidity Units 100 100 0 20 80 20 20 0 20 80
1 1 1 INFLUENT (21 A I R
SUPPLY
SUPPLY
(31 DRIVE MOTOR (41 CONSTANT HD S I P H O N 15) AIR I N L E T
( 6 ) STIRRER ( 7 ) NOZZLE
LEVEL ADdUSTER-
181 W E I R ( S I NOZZLE L E V E L A D J U S T E R - 2 110) A U T O M A T I C
1111 F I L T E R 1121 F I L T E R 11%
SIPHON
SAND SAND
(141 I N F L U E N T
SUPPORT
HpO
BACKWA8H
SUPPLY
OVERFLOW
U5) M A N O M E T E R U61 BACKWASH O V E R F L O W 1171 F L O W M E T E R (181 N E E D L E
1191 F I N A L
VALVE
EFFLUENT
120) D R A I N
Figure 1 . complex
Structure of monoaluminum-hydroxy-fatty
acid Figure
3.
Schematic diagram of filtration apparatus
,-MOTOR
JARS -FAN
/
LIGHT S O U R C E
Figure 2.
Laboratory stirring apparatus
of soap. Because of the extreme difficulty of maintaining an anhydrous solution. McGee (70) believes that trisoaps d o not exist, but that disoaps may. H e found that monosoaps contain from 0.8 to 1.2 molecules of fatty acid per atom of aluminum (Figure l ) , Robinson and Peak (77) have suggested that an aluminum soap may consist of large molecules, loosely held together by OH bonds and by van der TZ'aals attraction bet\veen long hydrocarbon chains. Experimental Methods
A preliminary series of coagulation experiments \vas run using X1,(S04)3,1 8 H L 0 and alkb-l benzene sulfonate in distilled. synthetic. and natural creek water. T h e synthetic raw Ivater \\-as prepared by adding calcium chloride, magnesium chloride, and sodium bicarbonate to obtain the desired hardness and alkalinity. TVyoming bentonite \vas added to produce turbidity, Hardness. alkalinity, and turbidity (measured with a Jackson turbidimeter) values for the synthetic \caters used are given in Table I. Sodium h>-droxideand hydrochloric acid (0,1.\-) \\.err used to adjust pH. .As repeated chemical analyses \cere consistent1)- similar, turbidities of synthetic waters are described as 20 or 80. The coagulation experiments were run using the t>-pesof \vater described belo\v.. A six-gang stirring machine (Figure 2) large enough to hold six 3-liter battery jars. \\-as used for rapid and slo\v mixing. I n a typical coagulation experiment, three jars contained ABS 56
l&EC P R O C E S S DESIGN AND DEVELOPMENT
while the other three served as controls. Rapid mixing took place for 15 seconds and slo\v mixing for 30 minutes a t 20 r.p.m. A series of filtration experiments \cas run. using coagulated and settled ABS-dosed \vater as filter influent. After sedimentation. 2 liters of the supernatant coagulated water \cere carefully siphoned from each jar and then applied to the filtration apparatus as shown in Figure 3 , T h e rate of filtration \vas 2 gallons per square foot per minute. This procedure made it possible to maintain a continuous flo\\ through the filters for 1.5- to 2-hour periods. The sand in the filter tubes \cas vibrdted to a predetermined depth before each run. so that all initial head losses \\ere identical. Data on head losses through the filters \cere recorded a t regular intervals during the runs. Composite samples of the ra\\- \rater. filter influent. and filter effluent \vere collectrd and ABS concentrations \cere measured according to the procedure developed by XLloore and Kolbeson (72). Hardness. alkalinity. and p H \rere measured according to standard procedures (2). T h e sand column diameter \vas 1; '16 inches; the sand depth was 2 feet. and the effective size of the sand kcas 0.58 m m . The uniformity coefficient was 1.58. Discussion
After a number of coagulation experiments had been run. it became apparent that the floc characteristics of the samples containing ABS \vere different from those of the controls. Photographs were taken of the various types of floc formed a t different pH levels. Electron micrographs \vere made to try to determine the structure of the floc particles obtained. Figure 4 shows that the reaction benveen ABS and aluminum sulfate is strongly pH-dependent for all the types of \cater tried. T h e reactions and subsequent removals \cere maximum in the p H range 4.5 to 4 . 8 . For an initial ABS concentration of mg. per liter. the maximum reaction and removal occurred with aluminum sulfate doses of 200 mg. per liter (Figure 5). The reason whb- greater doses resulted in lesser removals is not readily evident I n stud>-ingthe use of alum to remove ABS from laundromat waste \\.ater: Rosenthal and others reported that maximum
PH
Figure 4.
Effect of pH on reaction of ABS with alum MOLES
ALUM D O S E
4-5
s-t
x
\
\
"
3
40
I,
4
60
IC
5
100
6
150
II
7
200
IS
8
300
9
400
"
It
I O Y1N.DET.I
01
\
ITHACA RAW
7 MG/L-ABS
)
Mo/L.
20
SYNTHETIC t CLAY(3o uin D E T I
D
0
13.33
2
'F?
DISTILLED
Q SYNTHETIC A
I
4.2
Figure 5 .
(IMlTIALl
I
I
4.4
4.6
A-I
4.0 PH
5.0
5.2
1
5.4
Effect of pH on maximum ABS reactions
reaction and renioval occurred in the p H range 4 . 3 to 4.6. A n initial concentration of 65 mg. per liter of ABS: and an alum dose of 800 mg. pcr liter, resulted in approximzt-lv 807, removal of ABS ( I N ) , Eckenfelder and Barnhart (5) investigated the effectiveness of active carbon adsorpion and subsequent alum coagulation for the removal of ABS from laundromat waste water; they found the optimum pH for the coagulation to be 5.8 to 6.2. This range is not comparable \vith the 4.5 to 4.8 range reported in this study, or the 4 . 3 to 4.6 range reported by Rosenthal. because the Eckenfelder values were optimum for coagulation and settling of the turbidity of the ivaste; in contrast, the 4.5 to 4.8 values \ v e x optimum for the complexing reaction betxveen thc .ABS a n d the alum.
Figure 6.
A B S X IO-'
Molar ratios of AI-3 to ABS reacted
-4fter the fact had been established that p H a n d alum dosage play an important part in the reaction and removal of ABS! another series of experiments \vas carried out? in Lvhich increasing amounts of ABS Ivere added to fixed doses of alum. This procedure was repeated four times and in each series the alum concentrations were 30, 40, 60, and 100 mg. per liter. T h e results (Figure 6) reveal that there was approximately a 1 to 1 ratio of moles of aluminum ion to moles of ABS u p to 60 mg. of alum per liter. T h e reason for the erratic nature of the curve for 100 mg. per liter is not known. Generally, increasing the alum dosage increased the amount of ABS reacting with aluminum ion. T h e results may be interpreted in terms of existing theory. Belo\\ p H 4 to 5 hydrated aluminum ions predominate. Relatively insoluble hydrous aluminum oxide or hydroxide compounds prevail in the p H range 5 to 8. I n this range ions are preferentially adsorbed but foreign ions other than OH enter these complexes, displacing aquo or even OH ions. depending on their coordinating tendency with aluminum or with iron. Moderately strong coordinators with aluminum, like sulfate. are displaced by OH except a t high pH. Strong coordinators, like citrate and oxalate, displace O H . T h e reaction of interest here is one between a polymeric aluminum-hydroxyhydrate, probably a positively charged sol and amphlpathic anions. These anions could enter the complex, displacing aquo groups. and coordinating the aluminum. '4s the p H falls below 5, the ABS anions compete more a n d more successfully for the coordination sites. Stumm has proposed the existence of aluminum-hydroxosalicylate and aluminum-hydroxo-oxalate complexes ( 2 7 ) . No specific experiments were carried out below p H 4.0: but it is assumed that before particle formation begins ,ABS acts in the same manner as other anions that promote alum floc formation. IYayman. Robertson? and Page ( 2 I ) have postulated the adsorption of the ABS anion on these positive sites to form a complex such as (.A~I;OH~B) -3-.ABS. Filterability
From the resiilts of the preceding experiments it appeared that there \vould be some effect on the filterability of the coagulated and settled water. A series of filtration experiments \vas run using the type of water previously mentioned. Selrcted filtration runs have been graphed in Figures 7 through 10. Figure 7 sho\vs that increasing ABS dosage caused increased head losses. T h e pH of the Lvater being tested \vas adjusted VOL. 4
NO. 1
JANUARY
1965
57
:"-
ITHACA RAW
-
,o 2
0
Y?
v) 4 0
rot
I
2
3
4
5
6
7
8
9
1
r
-
0
VOL LITERS
Figure 7.
/ O
Effect of ABS dosage on filterability of water
VOL LITERS Figure 10. Effect on filterability containing ABS
of lthaca raw water
+-
50t
A
I 4
Figure 8. Effect of turbidity on filterability of water containing ABS
0 5
Figure 1 1 . with alum
6or 50t IABSI t
l
111
COAG
I
FILTER
I
34 4
I I
41 8
1
5
6
7
8
9
SYNTHETIC
1
I - 4
1
66 66
1
I
10
PH Effect of variation of pH on reaction of ABS
2 0 0
1333 1333 26 66
66 66 66 66
ID'
;
; ; a
;
6
; b
b
VOL LITERS
Figure 9. Effect on filterability of lthaca raw water containing ABS
Figure 1 2 . Relation between head loss in test filter and control filter at various pH
hvith 0,l.Y HCI to the level tvhere maximum reaction and removal took place. During the filtration a lvhire gelatinous film formed on the water surface. At intervals this film disintegrated and sank to the top of the sand column. and from that point on the head losses in the .ABS filter tended to increase a t a higher rate than in the control filter. TVhen the pH \vas raised to 7 : the gelatinous film disappeared and ABS residuals in the filter effluent increased markedly. 'I'he addition of artificial turbidity reversed this relationship. producing lo\ver head loss rates in the ,ABS filters than in the control filters a t pH levels from 4 . 5 to 4.8. 'Ihis experiment was repeated several times to confirm the original results. Three of the runs are showm (Figure 8) Because of the possibility that a synthetic water might show different results than a natural Lvater. a series of filtration runs \vas carried out using raw water obtained from the Ithaca. S.Y..lvater treatment plant. T h e data show that filtration
of Ithaca raiv Xvater produced the same results a t the loiver pH range, and that raising the pH caused greater head losses in the ;IBS filters, as \vas the case for the synthetic water (Figure 9). A s a check, Ithaca r a \ i ~water was treated Ivith alum a t a concentration of 200 mg. per liter a t tivo pH levels (Figure 10). Increasing the hydrogen ion concentration increased the ABS removals but also increased head losses. The second filtration run \vas made using alum a t 200 mg. per liter at a higher pH, with a corresponding reduction in the percentage of ABS removed and with a considerably reduced divergence in head loss rates. The data obtained tend to agree with the findings shown in Figure 6 . There apparently is a limiting alum dose beyond Xvhich the amount of ABS reacting and being removed does not increase. T h e percentage of ABS removed increases Lvith increasing
58
I & E C PROCESS D E S I G N A N D DEVELOPMENT
Figure 13.
Electron micrograph of alum in distilled water
Figure 15. Electron micrograph of ABS ond alum in distilled water
Figure 14.
Electron micrograph of ABS in distilled water
alum dosage, hut only u p to a limiting value. I n most cases some ABS was removed as it passed through the filter. To facilitate an over-all graphic picture, the data shown in Figure 11 portray the percentage of ABS which has reacted with alum prior to filtration. ABS does not react with alum and is not removed in significant amounts a t p H 5 and above, whereas there are significant reaction and removal in the p H range 4.5 to 4.8. T h e relationship between p H and percentage of ABS reacting resembles the curve describing the effect of p H a n the solubility ofalumfloc. Secondly, comparison of the ratios of head loss in the ABS test filter to head loss in the control filter (Figure 12) depicts graphically the effect of ABS on the filterability of coagulated and settled water. Analysis of this graph indicates that ABS does not affect filtration to any great extent a t p H 5 and above. As the hydrogen ion concentration was increased, head losses increared a t an increasing rate except where turbidity was present and an optimum dose of alum was applied to the water. I t was possible to observe the differences in floc characteristics a t different p H levels and time intervals, hut with the same alum dosage. At p H 4.78 no floc appeared in the control heaker, and a milky nonsettling floc formed in the beaker containing ABS. Floc variations a t p H 5.2 were observed prior to sedimentation. Observations were made a t 15-minute intervals a t this hydrogen ion concentration. I n every case
Figure 16. Electron micrograph of alum in distilled water
ABS and
floc particles were larger and did not settle as well as those in the control beakers. Electron micrographs were taken to determine the possible structure of floc particles containing ABS. Figures 13 through 16 depict micrographs of alum alone, ABS alone, and the combination of alum and ABS. T h e micrographs were made a t p H s below 5 on the assumption that more coordination sites were available for incorporation of ABS into the complex. I t would he difficult to reach any conclusions from Figures 13 and 14, hut the configurations of the particles in the two are different. Floc particles are very much in evidence. Figure 16 shows one of the particles magnified 12,000 times; although there is no means of determining the exact structure, one can see the ABS as dark spheres embedded in the amorphous VOL. 4
NO, 1
JANUARY 1965
59
-
AI-
Figure 17.
-
AI
Proposed structure of aluminum hydroxy-alkylbenzene sulfonate complex
alum floc. Micrographs of other organic polymers have shown a tendency to “ball up” into spherical shapes. Although there is still much to be done to determine the structure of the complex, it is assumed that many aluminumhydroxy-.ilBS complex formations take place when both are present in solution. Figure 17 is a proposed ideal model of such a structure, but there may be many variations of this configuration. Conclusions
At p H 5 and above with alum doses in the range from 15 to 50 mg. per liter, 15%: of the ABS present in solution will react and be removed. Lowering the hydrogen ion concentration to betlveen 4.5 and 4.8 increases ABS reaction and removal from solution to a range from 50 to 607, of the initial dose. Hydrogen ion concentrations less than 4.5 decrease .4BS removal. ,4t pH’s from 4.5 to 4.8 and alum dosages from 15 to 50 mg. per liter sedimentation is improved by the presence of turbidity. Increasing alum concentration up to 200 mg. per liter increases ABS removal, while a t 200 mg. per liter removals are not as great. I n the absence of initial turbidity, the presence of ABS in solution a t p H 4.5 to 4.8 causes head losses to increase a t a faster rate than in the control filter. At the same p H and no initial turbidity, increasing concentrations of ABS cause increased head losses. At p H levels of 7.0 and above (no turbidity) the divergences in head losses are not very- great; most of the 4 B S present passes through the filter. Head losses can be decreased if the pH is adjusted to a range between 4.5 and 4.8! there is turbidity present, and the alum dose is approximately 15 to 50 mg. per liter. Floc particles containing .4BS are larger than floc particles in the control at all pH levels used in this study. I n the absence of ABS there is no visible floc formation a t pH’s below 4.8. I n the presence of 4 B S a milky-type floc occurs a t pH’s below 5, Electron micrographs indicate the formation of an aluminum-hydroxy-ABS complex ion.
60
A I-
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
Literature Cited
(1) Alexander, A. E., Gray, V., Proc. Roy’. Sac. London. Ser. A , 200, 162 (1950). (2) .4m. Public Health Assoc., Kew York, “Standard Methods for the Examination of LVater. Sewage, and Industrial LVastes,” 11th ed., 1960. (3) Brosset. C., Biedermann, G.. Sillen, L. G., Acta Chem. Scand. 8, 1917 (1954). (4) Culp. R. L., Stoltenberg, H . A.: J . A m . Jlhter Llbrks Assoc. 45, 1187 (1953). (5) Eckenfelder, 14.. \V.> Barnhart. E., Jlbter Seuage Morks 108, 347 11961) (6) G h a g h e r , \V. O., J . A m . N’ater Tlhrks Assoc. 42, 22 (1950). ( 7 ) Gross, J . T., Zbid.,42, 17 (1950). (8) , , Harkins. LV. D., “Phvsical Chemistrv of Surface Films.” Reinhold,’New York, 1952. (9) McBain, J. LV., ”Colloid Science,” D. C. Heath and Co.; Boston. 1950. (10) McGee, C., J . A m . Chem. Soc. 71, 278 (1949). (11) McKinney, R. E.. Sezeage Znd. Tlhstes 29, 654 (1957). (12) Moore, \c. A.. Kolbeson. R., Anal. Chem. ‘28, 161 (1956). (13) Philippoff, LV.. Discussions Faraday Soc. 11, 96 (1951). (14) Pokras, L., J . Chem. Educ. 33, 152 (1956). (15) Powney. J.; Addison, C. C.. Trans. Faraday Soc. 33, 1243 (1937). (16) Prins, LV., “Studies on Some Long-chain Sodium-Alkyl-1 Sulfates,” doctoral thesis. Leyden, Holland, 1955. (17) Robinson, C.. Peak. D. A . ! Phys. Chem. 39, 1125 (1935). (18) rosenthal. B. L.. O’Brien. J. E., Joly. G. T.. Lawrence Experiment Station. Mass. Dept. of Public Health. March 1963. [ l 9 ) Sanford, 1,. H., Gates. C. D.. J . .4m. Ll-ater T l o r k s Assoc. 48, 45 (1956). (20) Sawyer, C. K.>Ryckman. D.. Ibid..49, 480 (1957). (21) Stumm, LY,! Morgan, J. J.. Ibid.. 54, 9’1 (1962). (22) Todd, A . R.. Jlhter TLorXsEzg. 107, 50 (1954). (23) Vaughn. .J. C.; Falkenthal. R. F., Schmidt, R. LY,>J . A m . Tl’aler Tlhr-XsAssoc. 48, 30 (1956). (24) LVayman, C. H.. Robertson. J . B., Page, G. G., U. S. Geol. Survey, Prof. Paper 475-B, 205-16 (1963). (25) LVinsor, P. A , . “Solvent Properties of Amphiphilic Compounds,” Butterworths, London, 1954. RECEIVED for revie\v December 5. 1962 ACCEPTEDOctober 6. 1964 Division of bl-ater and LVaste Chemistry, 142nd Meeting .4CS. Atlantic City, N. J..September 1962. Investigation supported in part by Public Health Seri-ice Research Grant RG 4798 from the Division of General Medical Sciences.
