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practical value of improved understanding of odor will apply equally to what we call odor, and to that complex of odor and taste that we call flavor. Literature Cited (1) Bogert, Am. Perfumer, 24, 15, 235, 357 (1929). (2) Bogert, J. IND.ENO.CHEM.,14, 359 (1922). (3) Crooker and Henderson, Am. Perfumer, 22, 325 (1927). (4) Ibid., 27, 156 (1932). (5) Davis, Handbook of General Experimental Psychology, p. 962, Clark University, 1934.
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(6) Fair, Haward Eng. School, P u b . 108 (1934); Am. P e - f i m z e r , 28, 573 (1934). (7) Henning, “Der Geruch,” Leipzig, 1924. (8) Parker, “Smell, Taste, and Allied Senses in the Vertebratee.” p. 23, Philadelphia, J. B. Lippincott Co., 1922. (9) Ranson, Science, 78, 395 (1933). (10) Renshaw, Ibid., 80 (Suppl.), 8 (1934). (11) Zwaardemaker, “Die Physiologie des Geruchs,” Leipzig, 1S95.
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RECEIVEDM a y 6, 1935. Presemed before the Division of .igricultural and Food Chemistry at the 89th .Meeting of the American Chemical Society, S e w York, N.Y., April 22 to 26, 1935.
Cation Exchange Capacity of Activated Sludge .L. R. SETTER, G. RI. RIDEXOUR,
Activated sludge produced under normal operating conditions was used to study the cation exchange capacity as a measure of the colloidal property of the floc. It was found, that under conditions of sufficient oxygen tension and good purification, (1) activated sludge exhibits the colloidal property of having exchangeable cations, (2) the magnitude of exchangeable cations is similar to clays of high silica sesquioxide ratio such as bentonite, and (3) the settling character of the sludge improves with an increase in the cation exchange capacity and with a decrease in the total fat and fatty acid content.
HE activated sludge process can be coiiveniently subdivided into two separate and distinct parts; each part possesses definite functions: 1. The adsorption of sewage colloids and organic electrolytes by an “active” sewage floc or a returned, aerobically “humified” floc. 2. The stabilization of the freshly adsorbed material caused by partial, aerobic microbiological decomposition, resulting in the regeneration of the floc.
The first function occurs almost immediately whereas the second requires a longer time. The mechanism of the first function, that of adsorption or coagulation, has been described by various authors as being physical, chemical, and electrical in nature, with only vague explanat’ions as to what is meant. The purpose of this paper is to present a more clearly defined picture of the mechanism whereby sewage colloids are
AND
C. 3. HENDERSON
New Jersey Agricultural Station, New Bruiiswick, N. J
removed by activated sludge floc, and to show that variations in the colloidal properties of the active floc as determined by the cation exchange capacity are reflected in the composition and settling character of the floc. In several papers Mattson and his collaborators (1, 2 , 3, 8) have shown that soil clays, soil organic complexes, and laboratory-prepared colloids are amphoteric in nature; that they possess colloidal properties by virtue of the dissociation of ions; and that these ions may be displaced by exchange reaction with less dissociated ions of like charge. Recently Smith (9) found that various alkaloids could be removed by neutral bentonite. The soluble or dissociated cations of the bentonite were replaced by the alkaloid cation through the amine linkage. Similar evidence by numerou? investigators leads us to the assumption that the activated h d g e matrix also has both acidoid and basoid propertie. by virtue of dissociated ions which will be displaced by lesq di-qociated sewage colloidal ions. To substantiate this assumption, samples were collected every two weeks for one year from a New Jersey activated Yludge plant operating under normal conditions of purification. Daily operating and chemical control records were available over the entire period of study. The determination of cation exchange capacity and total fats and fatty acid4 on these samples, along with the purification and settling indices, were used to determine the effect of fats, fatty acids, and cation exchange capacity of the activated sludge floc on It. settling and compacting characteristics. These same determinations mere also correlated with the sexage purification resultq. JIethods Wherever possible official methods were used; new and modified methods were briefly as follows :
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BASE-EXCHANGE CAPACITY.Cation exchange capacity was determined on 50- to 100-ml. samples of activated sludge mixtures hy the barium acetate-ammonium chloride method for soils. dfter decanting the bulk of the moisture by centrifuging for 5 to 10 minutes at 2600 r. p. m., the leaching process was accomplished by successive washings with normal barium acetate to a pH of 7.0. The excess barium was removed prior to displacing the exchange harium with normal ammonium chloride. AU1leachates were decanted after centrifuging. Exchangeable harium was determined by the gravimetric method. TOTALFATSAND FATTYACIDS. A 0.2- to 0.5-gram sample of dry solids was acidified (hydrochloric acid) to a pH of 4. Th: wet samples, mixed with asbestos, were dripd in an oven at 65 C. for 3 days. The dry solids-asbestos mixture was extracted with anhydrous ethyl ether for 6 hours. The extract was titrated with sodium hydroxide to a pH of 8.0 in ether-alcohol solution, clried at 103' C., and weighed. FATSOR NEUTRAL ETHEREXTRACT.The method used was *imilar to the above determination except that the solids were not xcidified prior t,o drying and extraction. SETTLING CHARACTERISTICS. One lite1 of sample in a graduated cylinder was allowed to settle quiescently for 30 minutes. From the volume of settled sludge obtained, the concentration of the settled sludge solids was calculated from the suspended *olids of the original mixture. The various indices used to show t h e settling characteristics iwre calculated as follow :
I,et A = grams supended solids per liter of aeration tank mixture B = grams suspended solids per liter of settled sludpc. f hen RIA = index 1 B - A = index2 E = index 3 lndex 3 is identical with 'I'heriault's sludge index ( I C ) and inversely proportional to Mohlman's sludge index (5). DISSOLVED OXYGEN.The Stewart-Rideal modification of the Winkler method was used on a 250-ml. sample of the supernatant after a 30-minute quiescent settling of an &quart (7.6-liter) -;ample of sludge mixtures. BIOCHEMICAL OXYGENDEhlaND. After 30-minute quiescent .;ettling of an &quart sample of sludge mixture, dilutions of the supernatant liquor (0 to 75 per cent dilution water) \Tere made .md incubated at 20" C. for 5 days. The initial dissolved oxygen content of the dilutions wcre calculated from the dissolved oxygen of the sample and the dilution water.
o
I
1
SETTLING
z /ND€X
3
2
FIGURE 1. REL4TION OF FATS, FATTYACIDS,A N D C41ION EXCHANGETO SEWAGEPURIFICATION AND SLUDGE-SETTIJNG INDICES
the indices is commonly known as the Theriault, ratio. The other two were originated for this paper. The purpose of comparison on the basis of the two additional indices, coincidentally with Theriault's ratio, was (1) to represent more exactly the true settling and Compacting value of the sludge under the different conditions and (2) to obtain a more true correlation of the data on the basis of Yettling and compacting ability. An inspection of the three indices in a comparative manner shows the necessity of the Indices for Comparison of Results two additional indices. By Theriault's index (index 3 of this The results obtained over the year of operation have been paper) the concentration of dry suspended solids in the settled rmrrelated on the hasiq of three individual indice.. . One of Judge indicated doubtful correlation over fairly wide index ranges. Upon close inspection it was found that a considerable variation in the index occurred 'I' LBLE I. CORRELATION OF SETTLING CHARACTERISTICS, CATIOSEXCHASGE, with only slight variations in the amount of ETHEREXTUCTS,AND PURIFIC.4TION INDICES O F - k T I V . i T E D SLUDGE +upernatant liquor above the sludge blanket. SamTotal F a t s l'or example, two mixtures of 1000 and4000p. p.m. ?le -Settling Characteristic--. Cation and F a t t y Dis10. Index 1 Index 2 Indel- 3 Exchange .ii-pended solids, which settled to the same Fats Acid solved 0 B. 0. D. .MiiZiequimv Jlume, would have a fourfold difference in sludge lents/g. P. p . m. P. p . m M 3 ./ 3 . .~fQ./Q index. However, by either index 1 or 2 a more 18 .02 0.03 1.83 0.731 41.0 144 1.8 20.0 19 .05 1.57 0.07 rational index is obtained which evaluates more 0.632 32.0 141 1.3 9.0 0.08 13 .05 1.93 0,818 19.0 46 2.6 .... truly and distinctly the change in the dry solids 0.08 0 802 12 ,04 2.13 11.0 66 ,... 2.6 0.09 0,770 .06 1.57 S 58.0 136 2.0 .. . c mcentration of a mixture because of settling. 0.10 .06 1.82 i 0 810 50.0 110 2.0 ... 0.10 .05 2.08 6 44.5 148 0.851 Iiidex 1 @ / A ) is the quotient of the dry solids 1.7 5.4 ,06 2.05 5 0.11 35.0 0.795 116 1.7 5.4 (.,incentration per unit volume of the settled sludge 14 .07 0.10 1.60 0.713 45.0 105 1.9 3.0 15 .13 0.15 1.42 0.720 56.0 118 0.8 3.0 a i d the dry solids concentration per unit volume IO 1.73 ,ll .... 0.15 0.778 184 0.7 28.0 1 2.18 ,10 0.21 0.652 7.5 121 of the original mixture, whereas index 2 ( B - A ) is 4.5 0.6 1 2.18 .10 0.21 0.664 20.0 93 4.5 1.2 the difference in the dry solids concentration per 9 .15 0.24 1.85 0.765 . . . . 1.2 194 19.0 I 1.80 0.731 .3 0.41 0 101 4.5 0.7 tinit volume before and after settling. 1.67 0.62 1.54 0.724 79 204 2.0 2.0 Arrangement of the results (Table I) according 1.58 0.83 2.26 0.776 65 205 2.1 2.7 to increasing magnitude of either index 1 or index 1.66 0.91 2.27 0.814 60 193 S.5 2.3 4 1.91 1.05 2.20 0.704 0 124 3.2 4 5 2 showed that fifteen of the twenty-seven analyses "1 1.86 1.71 3.69 0.840 10 10 0.9 2.0 26 1.96 2.16 4.40 0 865 11 22 ... .... differed only slightly in settling characteristics, "7 2.05 2.41 4.70 0 922 13 22 0.8 13.0 and that more or less distinct groupings were apparent. Consequently the analyqes were subdirided into groups where a maximum change !.U ... ..., appeared and the averages of each group were i.1 30 0.7 2.0 qecured.
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The average results of the three groups thus chosen as representing distinct changes in settling characteristics and cation exchange capacity are shown in Table I1and are graphically represented in Figure 1.
becomes more isoelectric or isoionic (6). Consequently t h e volume occupied by unit weight of the acidoid should decrease. However, if that newly associated cation is in itself more voluminous or hydrated than the displaced cation, the resulting complex will be more voluminous per unit weight than the original. With respect to TABLE11. MEANRESULTS OF GROUPING ANALYSES OF SLUDGE MIXTURES the settling characteristic of the floc, the sewage WITH SIMILAR SETTLING CHdRACTERISTICS colloids in which we are mainly interested are DeterNo. of Fats and Disaggregate salts of fatty acids which may or may mlna- -Settling CharacteristicBase Fatty solved Group tions Index 1 Index 2 Index 3 Exchange F a t s Acid 0 B. 0. D. not contain reactive nitrogen Or groups* I n any event the specific gravity of this group is Jlilliequivalenl/g. M u . , 8 . + M ~ L LP. p . VL P. p . m. low, and considerable adsorption of this material 1 15 1.09 0.014 1.85 0.740 32.2 121 2.25 8.67 would have a positive buoyancy which would 2 7 1.80 1.38 3.01 0.808 34.0 113 1.88 5.45 3 5 2.53 3.19 5.28 0.964 9.22 2 1 . 2 1.13 2.00 result in poor settling. Given the proper time and conditions, microbiological actiirity will regenerate the active sludge Within the range of sludge settling characteristics covered, matrix by decomposing or stabilizing a large part of the an increase in the settling character corresponds to an increase newly adsorbed organic constituents, and the matrix will rein the cation exchange capacity. Conversely with increased vert back to its original character. settling, the neutral ether-extract solids and the total fats and However, if the time period of regeneration is not suffifatty acids decreased. The purification indices, dissolved cient, there will be an accumulation of sewage colloids oxygen, and B. 0. D. likewise decreased. of low specific gravity-i. e., high fatty acid content and low While not shown with the results given in this paper, the cation exchange-which will first impair the settling characash content of the activated sludge floc varied between 20 and terist’ics and eventually impair the purification. The re25 per cent and showed no apparent relation with the cation results presented indicate this trend. However too much exchange capacity. emphasis cannot be placed on the apparent increase in B. 0. D. The cation exchange capacity of the activated sludge varied since individual analyses varied widely. More positive inbetween 0.6 and 1.1 milliequivalents per gram of dry solids dication of t’his trend was previously reported by one of the as compared to 1.1 per gram of clay for bentonite, and 0.67 m-iters ( 7 ) . per gram of Marshall loam soil colloid (1). If, on the other hand, the loading of fresh colloids per unit weight of matrix is decreased by maintaining higher concent,rations of activated sludge in the aerators, the settling char. Discussion of Results acter is improved and the cation exchange capacity ie higher The adsorption of selvage colloids by an “active” sludge per gram of dry solids and considerably higher per liter of floc is undoubtedly accomplished by the exchange of a mobile mixture. However, a proportionately greater demand of ion of the sludge matrix with a like immobile or more strongly oxygen must be supplied to maintain aerobic conditions. In associated colloidal sewage ion. this study it was shown that a gradual decrease in dissolved Electrophoretically both the sewage colloids and the “acoxygen occurred. If solids were allowed to accumulate in tive” sludge floc were found to be negatively charged, which the aeration tank, the oxygen demand per unit volume of mixindicates that the product of the quantity and intensity of ture \muld increase, and it is suspected that the dissolved cation dissociation is in excess of the product of the quantity oxygen would be reduced to the point where localized anaeroand intensity of anion dissociation. It is obvious therefore bic conditions in the matrix would cause dispersion of the that a given portion of sludge matrix may be distinctly negafloc. Such a condition is being inrestigated at the present time. tive in character because of t,he dissociation of cations, and would favor cation exchange with sewage colloidal cations to I n this particular study stress has been placed on the cation form a more stable or a less dissociated complex. This reexchange capacity of the active floc. Studies are being made action @) can be more clearly explained by representing in of the anion exchange capacity which may be of equal importhis case the acidoid and basoid nature of the active sludge tance because of considerable overlapping when we are dealing by the formula HA.BOH where d represents the acidoid with with the coagulation or exchange reaction of one ampholyte its dissociated hydrogen or other cations, and B the basoid by another. with its dissociated hydroxyl or other anions. The resulting Literature Cited exchange reaction of an amine R.XH3Cl might be as follows: R.NHI.Cl
+ HA.BOH +R.KHI.A.BOH + HCI
Calcium, magnesium, iron, or aluminum fatty acids can be shown to exhibit anion dissociation and react similar to the above example. Since there was no turbidity in the barium acetate leachate, it can be assumed that the resulting bonding of the above type of reaction was quite stable. Sssuming the cation exchange capacity of the recently added cation to be low, both the increased weight of the RKH8 cation and the displacement of a dissociated cation for a nonexchangeable cation would tend to decrease the cation exchange capacity per gram of dry solids of the resulting sludge floc. Theoretically the displacement of a dissociated cation by a less dissociated one decreases t,he hydration. and the complex
Mattson, Soil Sci., 28, 179 (1929); 31, s i , 311 (1931); 32, 343 (1931). Ihzd., 33, 301 (1932). Mattson and Csiky, Soil Sci., 39, 161 (19353. Mattson and Hester, Ibid., 39,75 (19353. Mohlman, Sewage Works J . , 6,119 (1934). Pugh, Soil Sci., 38,315 (1934). Ridenour, G.hl., Sewage W o r k s J.,5,74 (19331. Setter and Mattson, IND.ENG.CHEM.,27, 94 (1935). Smith, J . Am. Chem. Soc., 56, 1561 (1934). Theriault, U. S. Pub. Health Service, Bdl.’132, 24 (19201.
RECEIVED April 27, 1935. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t t h e 89th Meeting of t h e American Chemical Society, N e a York, N. Y . , April 22 t o 2 6 , 1935. This is a Journal Series paper of t h e Department of Water and Benage Research, N e r Jersey .\gricultural Esperiment Station.
