JANUARY, 1936
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Fermentation by P. citrinum of pure sugar nutrient salt solutions of fructose, sucrose, and glucose gave good yields of gluconic acid from sucrose and glucose solutions, but no gluconic acid was present in the fructose solution. P. citrinum, like P. purpurogenum, did not ferment fructose to gluconic acid, but, unlike the latter, it fermented sucrose to gluconic acid. The presence of copper reducing material which did not reduce alkaline iodine solution indicates that P. citm'num probably hydrolyzes the sucrose to glucose and fructose, and then ferments the glucose to gluconic acid.
Literature Cited (1) Assoc. Official Agr. Chem., Methods of Analysis, 3rd ed., 1930. (2) Amelung, H., Z. physiol. Chem., 166, 209 (1927). (3) Angeletti, A.,Ann. chim. applicata, 22,59 (1932). (4) Angeletti, A., Ann. Schiapparelli, 6, 83 (1932). (5) Angeletti, A,, and Cerruti, C. F., Ann. chim. applicata, 20, 424 (1930). ( 6 ) Bennet-Clark, T. A.. Biochem. J.,28, 45 (1934). (7) Bernhauer, K.,Biochem. Z., 153,517-21 (1924). (8) Ibid., 172,296-312 (1926). (9) Zbid., 197, 136 (1928). (10)Ibid., 197, 287 (1928). (11) Bernhauer, K., French Patent 707,614 (1930). (12) Bernhauer, K., and Schulhof, L., U. S. Patent 1,849,053(1932).
79
(13) Brown, A. J., J . Chem. Soc., 49, 172-87 (1886). (14) Butkevitch. W., Biochern. Z., 154, 177-90 (1924). (15) Ibid., 182, 99-109 (1927). (16) Evans, D.I.. Ann. Botany, 42, 1 (1928). (17) Falck, R.,German Patent 553,238(1924). (18) Falck, R.,and Kapur, S. N.,Ber., 57B, 920-3 (1924). (19) Hermann, T.S.,Austrian Patent 127,373(1931). (20) Herrick, H. T., and May, 0. E. J . B i d . Chem., 77, 185 (1928). (21) Herrick, H. T., and May, 0. E., U. S. Patent 1,726,067(1929). 22, 1172 (22) May, 0.E.,and Herrick, H. T.. IND. ENQ.CHBIM., (1930). (23) May, 0.E.,Herrick, H , T., Meyer, A. J., and Hellback, R., Ibid., 21, 1198 (1929). (24) May, 0. E., Herrick, H. T., Thom, C., and Churoh, M. B., J . BioE. Chem., 75, 417 (1927). (25) Molliard, M.. Compt. rend., 178, 41 (1924). (26) Muller, I. D.,Biochem. Z., 199, 136 (1928). (27) Schreyer, R.,Ibid., 240, 295 (1931). (28) Sumiki, Y.,J . Agr. Chem. SOC.Japan, 6,17 (1930). (29) Ibid., 6,23 (1930). (30) Takahashi, T., and Asai, T., Ibid., 6, 223 (1930). (31) Ibid., 8,703-19 (1932). (32) Wehmer, C., Biochem. Z., 197, 418 (1928). RBUBIVID June 21, 1936. This paper representa one phaae of a, project on the utilization of apple waste. Published a8 Soientifio Paper No, 320, College of Agriculture and Experiment Station, State College of Washing-
ton, Pullman, Waah.
Adsorption by Activated Sludge EMERY J. THERIAULT A N D PAUL D. MCNAMEE U. S. Public H e a l t h Service, Washington, D. C.
HE necessity in sewage treatment for differentiating between clarification, a very rapid process, and the much slower processes of biological or enzymatic oxidation has been emphasized in a previous paper (11). The general conclusion drawn from the review of the various theories of sewage clarification was that in all probability the adsorptive principle or clotting agent in activated sludges was related to the gelatinous matrix itself and not to the bacteria, the protozoa, or the various hypothetical enzymes. I n this sense the gelatinous matrix of the activated sludge flocs should be regarded as an intermediary between the bacteria, etc., and the sewage, thereby avoiding a difficulty in explaining rapid clarification beyond the oxidative powers of the microorganisms. Following this general theory of sewage clarification, it was next shown (10) that the gelatinous envelop of the zooglaal masses or biological slimes of sewage treatment is unmistakably zeolitic in composition if not in actual behavior. Presumptive evidence that the sludge might actually perform as a aeolite was afforded by the colloidal nature of the material, the rapidity of action, and, especially, the absence of replaceable anions. Wagenhals, Theriault, and Hommon ( I S ) , reporting on a survey of sewage treatment plants, noted a striking decrease in alkalinity when sewage was passed through oxidizing devices coated with biological slimes. I n the extreme case the alkalinity of a sewage was reduced from the original value
Further evidence is presented in support of the theory (10)that the clarification of sewage by the so-called activated sludges depends on the presence of an aluminosilicate complex chemically the same as the zeolites of water purification. As in the case of ordinary zeolites the adsorption of ammonia and of organic matters by the sludge complex can be represented with reasonable accuracy by the Freundlich formula. In percentages, the proximate analysis of activated sludge gives: zeolite, 30; bacterial cells, 35; adsorbed matters, 20; water, 5 ; and carbon from humus, 10.
of 99 p. p. m., in terms of calcium carbonate to the highly softened value of 8 p. p. m. in the oxidizing effluent. Since the nitrate content of the effluent was only 5.2 p. p. m., the decrease could not be explained wholly as a result of acid formation during nitrification. In the light of present findings it is pertinent to interpret this decrease in titratable alkalinity in terms of base exchange, particularly as the plant in question (Fitchburg, Mass.) was by no means overloaded a t the time of the survey. Similarly, the rapid decrease in ammonia, which is observed when activated sludge is mixed with sewage, might be interpreted in terms of the well-known procedure of Folin and Bell for the removal of ammonia from urine by zeolites or the corresponding laboratory procedure for producing ammonia-free water. There were good reasons, therefore, for supposing that the gelatinous matrix of the activated sludges, biological slimes,
80
IKDUSTRIAL A N D ENGINEERING CHEMISTRY
or zooglceal aggregates of sewage treatment does behave as a base-exchanging substance chemically identical with the zeolites of water softening. It is the purpose of the present paper to submit further evidence in support of the claim that the clarification of sewage is basically the same as the process of removing impurities from water by the use of the commercial zeolites, remembering always that the correspondence extends only to the clarification of sewage and not t6 the final disposition of adsorbed organic matters through biological oxidation.
Criteria of Zeolite Action Various formulas have been proposed for representing the base-exchanging reactions of zeolites. The conformity of equilibrium data with a suitably selected mathematical expression should therefore constitute an acceptable test of zeolitic action, if certain other conditions are also fulfilled by the system under consideration. I n the case of activated sludge, it has already been shown in a previous paper ( 1 2 ) that equilibrium between the sewage matters and the sludge itself is reached in 30 to 40 minutes or thereabouts, as might be expected in an adsorptive process. Furthermore, it is known that the sludge possesses the jelly-like and waterretaining properties of a partly dried zeolite. Taken in conjunction with the fact that the chemical composition of the sludge, apart from embedded bacteria, is essentially that of zeolite, it appears reasonable to conclude that the necessary supporting data exist from applying the proposed criterion of zeolitic behavior. As to the selection of a mathematical expression for representing equilibrium data in adsorptive systems, it is realized that equations of the rapidly converging type should be used whenever a saturation value is to be approached. For the sludge data a t hand, there is no indication that a welldefined maximum was reached. I n part, this is due to the necessity of using such analytical procedures as the test for permanganate oxygen consumed or the colorimetric determination of ammonia with Nessler’s reagent for the analysis of adsorbed sewage matters. For the reason that the approach to the saturation value of a sludge is very gradual, the usual analytical error of 5 or 10 per cent may exceed the expected difference in amounts of material adsorbed when the adsorption has proceeded to the extent of 70 or 80 per cent of the total capacity. The formula of Gans (7) might profitably be used in representing zeolitic adsorption by activated sludges if certain manipulative difficulties could be overcome. It should be necessary to determine not only the concentration of material adsorbed by the sludge or remaining in the liquid but also the corresponding concentrations of replaceable base. While the implied demonstration of zeolitic action should be far more rigid than that afforded by the first formula of Freundlich, the manipulations could not very well be carried out with such a putrescible material as activated sludge without introducing numerous complications. The relatively simple formula of Freundlich was used by Wiegner (16) and also by Ungerer (1%)and other investigators for representing the adsorption of inorganic substances by zeolites. With the understanding that complete sludge adsorption curves cannot be obtained with any of the available sanitary chemical procedures, use will be made of the F r e u n d l i c h e x p r e s s i o n instead of the more complicated expressions which would be required to describe the final stages of an adsorptive process.
ri
Adsorption by Wet Sludge The term “wet sludge” will be used in referring to activated sludge as normally present in sludge-sewage mixtures, with its water con-
VOL. 28, NO. 1
tent of 99 per cent and over. The data of Parsons and Wilson (9) will serve as a good example of the equilibrium which obtains between the organic matters in sewage and the matters adsorbed by the sludge under these conditions. These observations are given in Table I, together with the values calculated by the Freundlich formula: X/m
aC’I*
where X = amount of organic matter adsorbed as determined by test for permanganate oxygen consumed m = amount of sIudge used C = concn. of organic matter remaining in liquid The constants a and n were &st determined, using the first and fourth observations. The calculation was then extended to the other observations. The general agreement between the observed and calculated values is obviously very satisfactory for this type of data. The importance of this demonstration of a true adsorption equilibrium in sludge-sewage mixtures is not diminished if the hypothetical enzyme postulated by Parsons and Wilson as an adsorptive agent is replaced by the zeolite of the present discussion. It is clear from these results that, for a given amount of sludge, the amount of organic matter adsorbed is not a linear function of the strength of the sewage. The observation by Butler and Coste (2) that “large amounts of sludge do not appear as efficient as smaller ones” is a qualitative expression of the more definite relation represented by the Freundlich adsorption formula.
TABLE I. ADSORPTION OF ORGANICMATTERSBY WET SLUDGE Data of Parsona and Wilson ( 8 )
Organic Matter in Liquid-1.12 1.68 2.14 2 52 Matter in Sludge“Observed 0.39 0.695 0.88 1.00 Celculatedb (0.166) 0.36 0.63 (0.88) 1.10 0 Referred t o 10 per cent of sludge in all casea. 6 The constants in the Freundlich expression are 4 0.3115 and l/n = 1.365.
-
0.60 -Organic 0.155
3
The test for permanganate oxygen consumed was used by Parsons and Wilson as a measure of the removal of organic matters from solution by the sludge. Their results, therefore, can refer only to the adsorption of carbonaceous matters and not to the removal of ammonia. It may also be objected that the adsorption of organic matter could equally well be referred to the “humus” fraction of the sludge complex rather than to the sludge zeolite. These difficulties should be resolved if the “humus” of the sludge is first destroyed by gentle heat, following the general procedure of the agricultural chemists in differentiating between adsorption by the humus complex and the soil zeolites.
Adsorption by Dried Sludge Zeolitic action by dried activated sludge is best demonstrated by placing the coarsely ground or broken material in a short length of glass tubing so as to obtain a column effect. I n some experiments’sludge dried at 100’ C . was placed in a glass tube, approximately 0.5 inch (1.27 em.) in diameter and 10 inches (25.4 cm.) long, suitably protected with a cotton plug at the bottom and held in a vertical position with a clamp. With this arrangement the processes of adsorption, regeneration, and washing can be carried out expeditiously. This cycle of operations can be repeated a number of times with no apparent deterioration in the quality of the sludge zeolite. As a rule it may be assumed that sludge as drawn from a plant is fully saturated with ammonia, etc. The regeneration of the sludge zeolite may be aocomplished by a dilute solution of sodium chloride (2 to 4 per cent). A dilute solution of ammonium chloride is conveniently used as a test substance, and the course of the adsorption with repeated filtrations may be followed with Nessler’s reagent.
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
81
Calcium chloride may also be used as a test substance in demonstrating the zeolitic behavior of TABLE 11. ADSORPTIONOF AMMONIABY DRIEDSLUDGE activated sludge. In one experiment 429 grams Data of Theriault --First Series Second, Series-of sludge, on the dried basis, were centrifuged to a and McNamee Milligrams of ’ N as‘Ammonia i n the Liquid small volume and treated with sodium chloride solution to release adsorbed calcium, ammonia, etc., 7.5 14.7 21.0 30.0 48.0 6.0 12.0 24.0 56.0 88.0 120.0 and again centrifuged after making up to 100 ml. Milligrams of N as Ammonia in the Sludge with distilled water. The supernatant liquid conObserved 2.5 5.3 9.0 10.0 12.0 4.0 8.0 18.0 24.0 32.0 36.0 tained 9.8 mg. of calcium and an undetermined Calculated“ 2.8 5.2 8.8 9.6 14.4 4.7 7.7 12.7 23.4 32.5 40.5 uantity of ammonia and possibly other bases. a For the first series, a = 0.50095 and l / n = 0.86720; for the second series, a = 1.2843 and l/n 0.72135. n shaking with a dilute solution of calcium chloride, the amount of calcium removed in 40 minutes by the sludge was 14.2 mg. The sludge evidently behaved as a zeolite. While it is convenient to use a column of dried sludge for values is very satisfactory, even with a twentyfold range of demonstration purposes, it is difficult to study equilibria under concentration in the solution. these conditions since the liquid, in its passage through the filter, Mention has already been made of the possibility that the is continuously put in contact with increasingly fresh portions adsorption of ammonia and other sewage matters might be of sludge. For quantitative purposes it is necessary to stir the sludge gently in the presence of the test liquid until equilibrium referred to the “humus” of the sludge instead of the sludge zeohas been reached. Regeneration may be accomplished by adding lite. As shown by the carbonization of the sludge and from a suitable amount of salt solution, followed by centrifuging or the known instability of humus a t moderate temperatures, repeated washing to remove the excess of sodium chloride. this objection is certainly not valid when applied to the Starting with regenerated sludge and keeping the amount of sludge constant, a series of adsorption equilibria may be obpartly dried sludge. These experiments, however, do not tained by adding increasing amounts of ammonia, with a suitable preclude the separate possibility that humus may also be delay between the addition of successive portions. partly responsible for adsorption by wet sludge. It should be of interest, therefore, to consider the amount of humus As a rule, a practical degree of equilibrium has been reached which may be concerned in the adsorption process and its with ammonium chloride solutions in 20 to 30 minutes. I n relation to the aluminosilicate complex or sludge zeolite. one experiment observations were made a t intervals of 5, 10, 15, 20, and 40 minutes. The amounts of nitrogen adsorbed H u m u s Content of Activated Sludge were, respectively, 2.0, 3.5, 5.0, 6.0, and 6.0 mg., indicating With the data a t hand, it may be assumed that ordinary that equilibrium was reached in about 20 minutes. I n another activated sludge dried a t 100O C . contains approximately experiment Nessler readings were made a t intervals of 5, 10, 30 per cent of inorganic zeolite (ferro- or aluminosilicates) 15, 20, 30, and 60 minutes. The milligrams of nitrogen adand 35 per cent of dried bacterial and other cells. The figure sorbed were, respectively, 7.5,10,11, 12.5, 14, and 14, indicatfor the inorganic zeolite is based on average results for several ing that equilibrium in this instance was remhed only in 30 sludges. The estimate for the weight of the bacteria, etc., minutes. These periods of adsorption may be compared with is based on the phosphorus content of activated sludge, the the values given by Theriault (11) for the clarification of known percentage of phosphorus i n representative bacterial sewage. Similar considerations may be applied in gaging cells, and the values of Guillemin and Larson (6) for the ash the time which should be allowed for the regeneration of the content of the dried cells of E. coli. The inorganic zeolite sludge with sodium chloride. and the dried bacterial cells ,therefore make up approximately Of the numerous precautions to be observed in adsorption 65 per cent of the total dried sludge. Of the remainder, an experiments with activated sludge, mention should be made allowance of about 20 per cent should be made for adsorbed of the necessity for the thorough removal of the sodium chloor readily oxidizable matters in the sludge, and a further ride or other solutions used for the regeneration of the sludge allowance of 5 per cent seems necessary for the water which zeolite, .particularly in work with very dilute solutions of is retained by the zeolite. The value of 20 per cent for adammonia. Adsorbed ammonia may also be released to dissorbed organic matter is based on the observed decrease in tilled water or, in general, to more dilute solutions of ammonia weight of the suspended matter in an extensive series of than were originally used in saturating the sludge (5). Actiobservations on the oxygen demand of sludge. Since humus vated sludge as drawn from a plant may already be in equilibis known to be highly resistant to bacterial action, this derium with a normal ammonia content of, say, 20 p. p. m. for crease in weight may be taken as a measure of the readily the average American sewage. It should not be expected oxidizable matters adsorbed by the sludge, apart from the that such a sludge will adsorb more ammonia from a solution essential organic constituents of the sludge complex. The unless the concentration of the ammonia exceed the hypothetifigure for the water retained by the sludge is based on the loss cal figure of 20 p. p. m. The same reasoning may be applied on drying between 100’ and 165’ C. and it is probably too to the transfer of other impurities to the sludge besides amlow (8). monia. These and other obvious analytical precautions follow As a first approximation, therefore, it may be assumed that directly from the recognition of the base-exchanging or zeothe percentage composition of dried activated sludge is somelitic properties of the sludge. what as follows, It may be accepted as a readily demonstrated fact that Inorganic zeolite 30 ammonia is certainly removed from solution by activated Bacteria, etc. 35 Readily oxidieable matter8 20 sludge partly dried so as to destroy the “humus” complex. Water of constitution -5 It is also certain that the equilibrium may be displaced by 90 the addition of other bases and that a steady state is reached in a relatively short time. I n answering the further question leaving 10 per cent to be accounted for as carbon present in as to whether the adsorption equilibrium is defined by the the humus previous to its decomposition by drying. The Freundlich expression, reference will be made to the data of carbon content of humus from various sources ranges from 45 Table I1 where the observations in two series of adsorption to 70 per cent. experiments are compared with the values calculated by the Since no allowance is made in this rough calculation for the Freundlich formula using a least-square procedure. As in presence of detritus and also for the various bacterial exudates the case of the experiments by Parsons and Wilson with “wet” such as the gums which the sludge probably contains, it must sludge, the agreement between the observed and the calculated be concluded that the humus content of activated sludge is
8
-
82
INDUSTRIAL A N D ENGINEERING CHEMISTRY
VOL. 28, NO. 1
evidence to the effect that the inorganic zeolites are capable of entering into base-exchanging reactions with organic compounds of carbon and Data of Demolon First Set . -Second Setnitrogen is reasonably definite. Ungerer ( l a ) ,for Grams of Humus per Liter of Liquid and Barbier (3) instance, has shown that the Freundlich formula 0.045 0.108 0.408 0.832 1.57 5.50 0.0105 0 0975 0.68 1.42 holds for the adsorption of guanidine, betaine, Grams of Humus (Per Cent of Adsorbent) aniline, etc., b y a c a l c i u m zeolite. I n most Observed 3 09 5.84 7.83 8.36 8.59 9.9 4.89 9.02 13.2 15.8 Calculateda 4.04 4.89 6.53 7.72 8.76 11.5 5.03 8.53 13.4 16.0 cases an equivalent amount of inorganic base was recovered from the solution, indicating that a For the first set, a = 7.9383 and l/n = 0.21769; for the second set, a = 14.715 and l/n = 0.23537. the adsorption was truly zeolitic. In considering the possible role of “humus” in activated sludge, it is of more consequence that the lignoprotein or organic fraction of the soil zeolites is highly relatively low. Furthermore, as will presently be shown, it resistant to bacterial action (14). Under the conditions of the does not appear possible to consider adsorption by humus biological processes of sewage purification, “there is a residue without introducing the aluminosilicate complex as an of organic matter, etc., which is very resistant to further oxiessential ingredient. dation changes, which either accumulates in the filter or is disRelation of Sludge Humus to Sludge Zeolite charged with the effluent” (1). It is tempting, therefore, to apply these findings of the agricultural chemists to various Waksman and Iyer (14) consider that soil humus is a comproblems of sewage treatment, particularly to the “bulkplex formed by the union of lignins with various nitrogenous ing” of activated sludge as an aging phenomenon. For the compounds, particularly the proteins: “It is quite probable present, however, it must be concluded that, while an inthat the lignoprotein complex in the soil is bound closely organic zeolite of reasonably definite composition and of with other complexes, both organic, especially the hemireadily studied characteristics is undoubtedly present in cellulose, and inorganic, especially the aluminum silicates. sludge, the corresponding body of information regarding the Whether this union is chemical or physical in nature is sludge humus is still to be developed. difficult to determine and is really of little significance . . . . . ” Again, “although the soil humus is usually considered to be Acknowledgment the organic fraction of the soil, there is no doubt that in its The authors are indebted to Lowell J. Reed, consultant, undisturbed condition in the soil it contains various inU. S. Public Health Service, for valuable assistance in the organic elements which are an integral part of the humus statistical treatment of the base data. complex.” I n the case of activated sludge, it is necessary to consider that some of these elements, such as phosphorus, Literature Cited sulfur and possibly potassium, are normal constituents of (1) Ardern, E., Brit. Assoc. Advancement Sci., 2nd Rept. on Colloid the bacterial or other living cells that inhabit the sludge comChem., p. 87 (1921). plex. Other elements, such as calcium and iron, may exist (2) Butler, W., and Coste, J. H., J. SOC.Chem. Ind., 46, 49-59T (1927). partly in the bacterial cells and partly as replaceable items (3) Demolon, A., and Barbier, G., Coonapt. rend., 188, 654-6 (1928). in the sludge zeolite. Finally, the aluminosilicate may be (4) Dienert, F.,Rev. hug., 44, 113-66 (1922). regarded as forming zeolitic adsorption compounds with (5) Genter, A. L.,Sewage Works J., 6,689-720 (1934). various inorganic bases, such as sodium and magnesium, etc., (6) Guillemin, M., and Larson, W. P., J . Infectious Dhsases, 31, 349-55 (1922). or with simple nitrogenous compounds, such as ammonia, or (7) Magistad, 0.C., Ariz. Agr. Expt. Sta., Tech. Bull. 18,446-63 with the more complex proteins to include the humus itself. (1928). This view of the relation of humus to the sludge zeolite (8) Mellor, J. W., “Comprehensive Treatise on Theoretical and Inorganic Chemistry,” Vol. 6, pp. 575 et seq., New York and finds support in the experiments of Demolon and Barbier (3) London, Longmans, Green & Co.,1925. on the adsorption of “humates” by hydrated aluminosilicates (9) Parsons, A. S., and Wilson, H., Surveyor, 72,221-6, 252 (1927); or kaolins (argile) flocculated with potassium or calcium salts. cf. J . Rov. Sunit. Inst., 48,494-509 (1928); Water Works and As shown in Table 111, the Freundlich formula gives a fair Sewerage, 76, 397-9 (1929); Can. Engr., 58, 126 (1930). 27, 683-6 (1935); Bee also (10) Theriault, E. J., IND. ENQ.CHPIM., consistency to the data, considering the extreme range of Pub. Health Repts. concentration covered by the experiments. (11) Theriault, E. J., Sewage Works J., 7, 377-92 (1935); see also ~
TABLE111. ADSORPTION OF HUMUSBY ALUMINO-SILICATE SUSPENSIONS
-
Summary From the viewpoint of the present studies it may therefore be considered that the adsorption of organic matter from sewage is intimately related to the aluminosilicate complex, whether it acts simply as an inorganic zeolite or partly combined with lignoproteins as a humic aluminosilicate. The
Pub. Health Repts. (12) Ungerer, E., KolEoid-Z., 36, 228-35 (1926).
(13) Wagenhals, H. H.,Theriault, E. J., and Hommon, H. B., Pub. Health Bull. 132 (1923). (14) Waksman, 5. A., and Iyer, K. R. N., Soil Sci., 36, 57-67, 69-82 (1933). (15) Wiegner. G., J. Landw., 60, 111-50 (1912). R E C E I V ~July D 26, 1935.
