B. 0. D. Removal from Waste Sulfite Liquor-Sewage Mixtures by Activated Sludge Factors Governing the Rate of Removal U
C. N. SAWYER' University of Wisconsin, Madison, Wis. tration in the mixture, and the N A PREVIOUS publicaThe rate of B. 0. D. removal from waste s most suitable amount of each tion (6) it was reported liquor-sewage mixtures containing in excess was determined by gradually that neutralized waste sulper cent waste liquor by activated sludge increasin the amount fed until stricted because of an insufficient supply of availfite liquor when mixed with a residua7 of from 3 to 8 p. p. m. remained in the effluents at the domestic sewage is susceptible able nitrogen. The restriction becomes especially of the aeration period. A end to treatment by the activated significant when the ratio of 5-day B. 0. D. to amrecord-of the growth rates of the sludge process. Studies on the monia nitrogen exceeds 30 to 1. activated sludges on the various rate of B. 0. D. removal from With sewage mixtures containing 10 per cent of diets was made over a 7-day interval. Portions of the sludges sewage mixtures containing 2 waste sulfite liquor, the addition of ammonjum fed on the sewage mixtures conto 20 per cent of sulfite liquor chloride or urea in slight excess of actual needs taining 10 per cent of waste sulshowed, in the mixtures conresults in reducing the time necessary for satisfite liquor were analyzed for taining more than 8 per cent of factory treatment by about 50 per cent. With the their volatile solids, nitrogen, and hosphorus contents at the the waste, the effect of some concentrations of waste liquor investigated (0-10 concksion of each ex rimentd limiting factor which gradually per cent), the addition of phosphorus does not feeding. Routine anacses were slowed the rate at which the shorten the time required for treatment. performed as described (6) exB. 0. D. was removed. Since Studies on the relation of nitrogen and phoscept as follows: In determining the nitrogen content of the actithe primary function of mixing phorus utilized to B. 0. D. removed show that apvated sludges, copper selenite the waste sulfite liquor with proximately 3 parts of nitrogen and 1 part of was used as a catalyst as recomsewage prior to treatment was phosphorus are used in the removal of 45 parts of mended by Schwoegler, Babler, to have the sewage furnish the $day B. 0. D. from the feed mixtures when excess and Hurd (8). The inorganic phosphorus content of the varinecessary mineral substrate nitrogen and phosphorus are available. ous effluents was determined (nitrogen, phosphorus, etc.) Rate-of-growth studies made on the activated colorimetrically with the aid of for normal biological mesludges fed sulfite liquor in their diets indicate that an Evelyn photoelectric colortabolism and growth, it was approximately 0.25 ton of activated sludge can be imeter. The total phos horus content of the activated Sudges considered possible that the produced from the sulfite liquor wasted in the was determined by a method capacity of the sewage to manufacture of each ton of sulfite pulp, provided it outlined by the A. 0. A. C . (1) supply these necessary mineral can be diluted with a t least 9 volumes of domestic exce t that a wet combustion elements had been overstepped sewage prior to treatment. metgod recently described by Brenner and Harris (8) was used in the mixtures with the highest to free the organic phosphorus. concentrations of the waste Ail B. 0.D. determinations were made with a sup lemented and that the insufficientSupply Of such substances Was limiting dilution water&8 recommendedby L~~and Nichoh (ef the rate of stabilization. The purpose of the investigations reported in the present paper was to gain information-on the Significance of Nitrogen and Phosphorus nature of the limiting factors and obtain, if possible, some Since the retardation in the rate of B. 0. D. removal from quantitative measurements of what would be required to waste sulfite liquor-sewage mixtures by activated sludge a p satisfy deficiencies in the diets. peared to be related to an insufficient supply of mineral elements, it was decided to make a study of the relative sipnifiSources of Materials and Methods canee of nitrogen and phosphorus on this factor and to gain, Sewage and waste sulfite liquor for the studies were obtained if possible, some conception of the quantities of each which as previously described (6). The feeding experiments were conwould be utilized in the stabilization Of a given B.0. D. load. ducted essentially as before (6)exce t that in some cases the It was considered that the latter information would be 6sactivated sludges were fed waste sul&e liquor-sewage mixtures supplemented with nitro en or phosphorus and sometimes with pecially important in situations where the sewage available both nitrogen and phospgorus. The quantities of these mineral was insuffiaient to satisfy the requirements for mineral eleelements added were in ~ r o ~ o f i i oton the sulfite liquor concenments, and it would be necessaw to suDDlement the wastes with mineral-salts td facilitate bihogicaf stabilization 1 Present address,New York University, New York, N. Y. of the pollutional load.
I
411
INDUSTRIAL AND ENGINEERING CHEMISTRY
412
PER
CENT OF W.S.L.
IN SEWAGE MIXTURE
PER CEN'
OF
W.S.L.
Vol. 33, No. 3
IN SEWAGE MIXTURE
FIGTJRE 1. IXFLUENCE OF NITROGEX A N D PHOSPHORUS o x B. 0. D. REMOVAL FROM WASTESULSer/es F:
Jyy&vefl/ed w//h N//royen B.O.D. KQ
-
3
HOURS
AERATION
__
k.IG
REMOVAL
BY DILUTION WITH A C T I V A T E D 0
/&e4
SLUDGE
FITE LIQUOR-SEWAGE MIXTURES BY ACTIVATED
SLUDGE CONCENTRATIONS O F 2000 P. P. M.
.2 ,2 t $ 4 5 Preliminary investigations on the nitrogen and phosphorus requirements of activated sludge when treating waste sulfite liquor-sewage mixtures showed that, when the feed mixture contained as little as 4 per cent of the waste by volume, all the available ammonia nitrogen (average, 23 p. p. m.) and inorganic phosphorus (average, 4.0 p. p. m.) supplied by the sewage was utilized by the sludge. Early studies made with the diets supplemented with enough nitrogen and phosphorus, so as to leave slight residuals at the end of the aeration period, indicated that approximately 1 p. p. m. of phosphorus and 3 p. p. m. of ammonia nitrogen were utilized in the removal of 40 p. p. m. of 5-day B 0. D. from such mixtures. On the basis of this information, six series ( A , B , C, D , E, F ) of feeding experiments were undertaken. Unfortunately all six series could not be run simultaneously; therefore, series A and B were run concurrently, C and D next, and then E and F. Activated sludges used in the preliminary experiments for treating waste sulfite liquor-sewage mixtures were mixed together and distributed among ten bottles for the start of the experiment with series A and B. Each series consisted of five separate portions of sludge which were fed daily on sulfite liquor-sewage mixtures containing 2, 4, 6, 8, and 10 per cent of waste.
IX
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March, 1941
Sludges in series A were fed mixtures of waste sulfite liquor and sewage only, those in series B were fed mixtures of the same waste and sewage supplemented with ammonium chloride as a source of nitrogen. On the second day of feeding, it was found that the quantity of ammonium chloride had to be increased in order to have residual ammonia nitrogen present in the effluents at the end of the aeration period. Determinations were made daily of the B. 0. D., ammonia nitrogen, and inorganic phosphorus contents of the original feed mixtures and of the effluents produced a t the end of the aeration period. After the experiment had been under way for 5 days and conditions of equilibrium had become somewhat established, a study of the rate of B. 0. D. removal from the supplemented and unsupplemented mixtures of waste sulfite liquor and sewage was performed in a manner similar to the method already described (6) except that samples were taken a t 3hour intervals during the first 9 hours of the run. The results are given in Figure 1and show that the addition of ammonia nitrogen in the form of ammonium chloride hastened the rate a t which B. 0. D. was removed. For instance, in the case of the mixture containing 10 per cent of sulfite liquor, the 5-day B. 0. D. removed during 6-hour aeration with added nitrogen corresponded to an amount removed during approximately 15-hour aeration from the unsupplemented mixture. This shows the importance of nitrogen in determining the rate of biological stabilization of wastes. Quantitative studies on the utilization of ammonia nitrogen and B. 0. D. removals were made on the third, fourth, fifth, and sixth days of the feeding experiment. Values for the ratio of 5-day B. 0. D. removed to nitrogen utilized were computed from the data and are given in Table I. Disregarding the values obtained with the 2 per cent mixtures, because in those cases some of the ammonia nitrogen was converted to nitrites and nitrates, the values obtained with the other mixtures indicate that about 1 part of ammonia nitrogen was utilized for every 11 parts of B. 0. D. removed or stabilized. At the end of 7 days of feeding, the sludges used in series A had their diets of waste sulfite liquor and sewage supplemented with phosphorus (NaH2P04.H20)and became series C. The sludges from series B had their diets augmented with both phosphorus and nitrogen and became series D.
TABLEI. NITROGEN REQUIREMENTS OF THI ACTIVATED SLUDGE PROCESS AS RELATED TO B. 0. D. REMOVAL FROM WASTE SULFITE LIQUOR-SEWAGE MIXTURES % w. s.L.
in Sewage Mixture
Ratio, B. 0. D. Removed/Ammonia N Used 3rd day 4th day 5th day 6th day Series B , Mixtures Supplemented with N (NH4CI)
Series D , Mixtures Supplemented with N (NH4C1) 2-
4
6 8 10
11.0 11.8 13.0 13.0 12.2
12.0 14.2 15.2 13.8 13.2
12.5 14.2 14.6 14.8 14.2
,
Series E , Mixtures Supplemented with N (Urea) 24 4
6 8
10
9.3 13.0 13.6 14.2 14.0
9.5 14.0 19.0 14.8 14.7
+P 12.5 20.0 15.6 13.8 17.4
+P
9.2 13.1 13.7 13.5 14.4
Series F , Mixtures Supplemented with N (Urea) 2s
4
6
8
10
n
9.3 11.5 12.3 13.4 13.8
9.5 12.4 13.3 14.8 15.2
'Values influenced by nitrifioation.
9.2 12.1 13.4 14.4 15.4
.... .... .... .... ....
.. .. .. ..
....
.... ....
413
TABLE11. PHOSPHORUS REQUIREMENTS OF ACTIVATEDSLUDGE PROCESS AS RELATED TO B. 0. D. REMOVAL FROM WASTESWLFITE LIQUOR-SEWAGE MIXTURES 70 w. s. L. Ratio of B. 0. D. Removed to P Used in Sewage
Mixture
3rd day
4th day
5th day
6th d a y
Series C,Mixtures Supplemented with P (NaHzPOcH20) 2 4 6 S 10
32.6 33.8 38.0 39.2 43.5
.
28.0 33.4 38.2 38.0 40.0
24.0 31.2 36.6 38.6 39.2
Series D , Mixtures Supplemented with N (NHaCl) 2 4 6 8 10
64 64 60.5 58.5 54
54.5 59 61 69 64
27.0 32.2 38.6 41.2 40.4
+P 50 59 71 88 100
47.5 5b 57.5 62.5 60
Series E , Mixtures Supplemented with N (Urea)
+P
On the fifth day after series C and D had been fed their respective diets, a study of the rate of B. 0. D. removal by activated sludge was made. The results are given in Figure 1 and show that phosphorus alone as a supplement appeared to have very little effect. This is concluded by comparing the results of series C with the results of series A which had no supplement (Figure 1). The combination of added nitrogen and phosphorus in series D appeared to give somewhat more rapid B. 0. D. removal than nitrogen alone (series B ) . However, since the runs covering these two variables were not made concurrently, a direct comparison should be made with caution. Studies of nitrogen and phosphorus utilization as well as B. 0. D. removal were made on the third, fourth, fifth, and sixth days of the experiment. Ratios of B. 0. D. removed to nitrogen used for series D are given in Table I, which shows that the amount of 5-day B. 0. D. removed per unit of nitrogen used is in the neighborhood of 14 units. This value is somewhat higher than was obtained in series B, in which no phosphorus was added. Ratios of B. 0. D. removed to phosphorus used for both series C and D are shown in Table 11, and indicate that in the absence of nitrogen considerably more phosphorus is used in removing the B. 0. D. load imposed on the sludge. During the course of these experiments it was found that the continued feeding of ammonium chloride in concentrations sufficient to leave a slight residual of ammonia nitrogen led to the lowering of the pH to values below 7 in the case of the sludges fed 8 and 10 per cent waste sulfite liquor mixtures. This did not appear to have any detrimental effect during the course of the experiment but might have had if the experiment had been continued for a longer period. This difficulty was overcome by the use of urea as a source of ammonia nitrogen in the succeeding experiments. At the end of 7 days of feeding, the sludges used in series C had their diets supplemented with urea as a source of ammonia nitrogen as well as with phosphorus and became series E; the sludges of series D had their diets supplemented with urea nitrogen only and became series F. Again, the sludges of both series were fed their respective diets for about 5 days to allow a condition of approximate equilibrium to become established, and then a study of the rate of B. 0. D. removal was.made. The results are given in Figure 1 (series E and F ) and show that the rate of B. 0. D. removal was practically as rapid with nitrogen as the only supplement as with both phosphorus and nitrogen present. Ratios of B. 0. D. removed to nitrogen and phosphorus utilized for series E and F are shown in Tables I and 11. Table I shows that the ratios of &day B. 0. D. to nitrogen (urea) are approximately the same for both series E and F
INDUSTRIAL A N D ENGINEERING CHEMISTRY
414
and average about 13.5. These values are probably somewhat more representative of the true requirements than those obtained with ammonium chloride as a source of nitrogen since the pH remained above 7 a t all times when urea was used. In Table I1 we fmd that the ratio of 5-day B. 0. D. removed to phosphorus used is somewhat higher for series E than for series C. This again seems to indicate that the phosphorus requirements in the presence of limited supplies of nitrogen will be greater than when sufficient nitrogen is available. A record of the quantity of activated sludge wasted, to maintain activated sludge concentrations in all the aeration mixtures near 2000 p. p. m., was kept for each of the series of feeding experiments over the 7-day period during which each was fed. The results obtained for the various waste sulfite liquor-sewage mixtures with and without supplements are given in Figure 2. The data show that the rate of growth of the sludges increased in proportion to the amount of waste in the diet. This correlates with the B. 0. D. removal data which showed that more than 92 per cent was removed from all of the mixtures, up to and including 10 per cent of sulfite liquor.
Vol. 33, No. 3
that a deficiency of phosphorus and nitrogen existed in the 10 per cent waste sulfite liquor-sewage diet, since the nitrogen and phosphorus content of the sludge produced on this unsupplemented diet was less than in the sludge fed on sewage alone, and also because the content of each in the sludge was increased when the diet was supplemented with these mineral elements. TABLE111. VOLATILE SOLIDS,NITROGEN, AND PHOSPHORUS CONTENTS OF ACTIVATED SLUDGES PRODUCED ON DIETSCONTAININQ 10 PER CENTWASTESULFITE LIQUOR AND 90 PERCENT SEWAGE %.
Week Series Diet Supplement Starting sludge * 1 A 2 C P(NaHzPOa.Hz0) 3 E N(Urea1 P(NaHaP04.HzO) 21 iV{X& aC1) l) P(NaHzPOd.Hz0)
....... . . .. . . . .
g
3
F Control
+ +
N(Urea) Sewage only
%
%
Volatile Solids
Nitrogen
Phosphorus
88.2 88.1 83.4 85.5 90 2 . 25
6.26 4.37 3.82 6.97 8.10 7.55
1.20 0.70 2.58 2.49 01.79 .93
92.0 71.5
7.10 6.13
0.88 1.51
Discussion
PER CEi\T
OF K.S.L.
IN SEWAGE MIXTURE.
FIGURE2. GROWTHRATESOF ACTIVATED SLUDGEON DAILYFE~EDINGS 01 WASTE SULFITELIQUOR-SEWAGE 2000 MIXTURES(ACTIVATED SLUDGECONCENTRATION, P. P. M.)
At the end of each feeding experiment a portion of the sludge fed on the 10 per cent waste sulfite liquor mixtures was filtered, dried a t 1 0 5 O C.,and prepared for analysis. The sludges were analyzed for their volatile solids, nitrogen, and phosphorus contents. The results given in Table I11 show that all the sludges produced on diets containing sullite liquor had a much higher volatile solids content than the sludge fed on sewage alone. The heavy nature of the sludges fed on waste sulfite liquor-sewage mixtures cannot, therefore, be a result of high ash content. The addition of phosphorus to the diet tended to decrease the volatile solids content, and the addition of nitrogen in each case caused an increase in the volatile solids content. The higher nitrogen and phosphorus contents of the sludges fed on diets supplemented with those two substances show that the added nitrogen and phosphorus were fixed in the sludge. The lower phosphorus content of the dudge produced in series D as compared to the sludges of series C or E is probably due to the lower pH values obtained in the former case, The data in Table I11 show definitely
The decision to study the influence of ammonia nitrogen and inorganic phosphorus on the rate of B. 0. D. removal from waste sulfite liquor-sewage mixtures by activated sludge was based on several factors. The selection of nitrogen was made chiefly on the argument that, since normal activated sludges contain about 6 per cent of organically combined nitrogen, its presence must be necessary if protein synthesis is to progress normally. The choice of phosphorus was based on the knowledge that oxidation of carbohydrates in animal tissue involves the formation of intermediate oxidation products containing phosphorus. I n case corresponding reactions were involved in the oxidation of carbohydrates by activated sludge, it was felt that a limitation of phosphorus would seriously hamper the rate of oxidation of the carbohydrates in waste sulfite liquor. That nitrogen and phosphorus were limiting factors was further substantiated when it was found that the effluents from the activated sludge treatment of waste sulfite liquor-sewage mixtures, containing in excess of 2 per cent of the waste were always devoid of both ammonia nitrogen and inorganic phosphorus. On the basis of the information obtained from the 5-day B. 0. D. values of waste sulfite liquor-sewage mixtures, using standard bicarbonate and supplemented dilution waters (6), it was not surprising to find that the addition of nitrogen and phosphorus to corresponding mixtures, before treatment with activated sludge, resulted in increased rates of B. 0. D. removal. The rapid rates of B. 0. D. removal obtained by supplement of nitrogen alone were unexpected and indicate the importance this element has in the synthesis of new sludge and stabilization of B. 0. D. The apparent inability of added phosphorus to influence the rate of B. 0. D. removal was equally surprising, but the small amount of phosphorus present in the sewage and that available in the sludge may have been sufficient to satisfy the normal requirements. It is known that only a small portion of the phosphorus utilized by activated sludge is converted to organic forms and that the majority is present in the sludge in a form which is readily extractable with mineral or organic acids (4). The determination of ratios of B. 0. D. to nitrogen was hampered by the inability to determine directly the extent of the conversion of ammonia nitrogen to nitrite and nitrate in the highly colored solutions. Some nitrification did occur in the mixtures containing only 2 per cent of waste sulfite liquor; the effect is shown by the lower results obtained with such
March, 1941
x
INDUSTRIAL A N D ENGINEERING CHEMISTRY
mixtures as those given in Table I. In the case of the 4 per cent mixtures it is questionable that any nitrification occurred. No nitrification occurred with the 6, 8, and 10 per cent mixtures, and since the ratios of B. 0. D. to nitrogen in these three cases agreed well with those obtained with the 4 per cent mixtures, it may be assumed that practically all the ammonia nitrogen which disappeared in the latter case was used in the production of new organisms. The ratios of B. 0. D. to phosphorus are undoubtedly influenced by the fact that the phosphorus was utilized to produce inorganic as well as organic growth. The inhibition of inorganic growth should result in higher ratios of B. 0. D. to phosphorus than would be obtained if the deposition of inorganic phosphates was unhindered. That such was the case is shown by the series D sludges which were fed both phosphorus and ammonia nitrogen (ammonium chloride). The lowered pH caused by the residual hydrochloric acid after utilization of the ammonia apparently prevented the deposition of inorganic phosphorus, as shown by the lower phosphorus content of series D sludges in Table 111. This prevention of phosphate precipitation is reflected in greater amounts of B. 0. D. being removed for each unit of phosphorus utilized for series D in Table 11. The amount of ammonium chloride added to the waste sulfite liquor ranged between 0.95 and 3.80 grams per liter, depending upon whether the waste was fed as a 2,4, 6,8, or 10 per cent mixture with sewage. The amounts of urea and NaHSP04.HtO ranged from 0.55 to 2.15 grams and 0.75 to 1.8 grams per liter of waste, respectively. If it can be assumed that approximately 4000 gallons of this rather dilute waste sulfite liquor was produced in the manufacture of each ton of pulp, the 5-day B. 0. D. would amount to 430 pounds, since the waste had a 5-day B. 0. D. of 12,800 p. p. m. Addition of enough nitrogen and phosphorus to give a ratio of B. 0. D. to nitrogen to phosphorus of 45 to 3 to 1 would require 29 pounds of nitrogen and 9.5 pounds of phosphorus. At current market prices for nitrogen (6 cents) and phosphorus (9.5 cents) the necessary amounts of each would cost $1.75 and $0.90, respectively. Such charges per ton of pulp produced are untenable in such a highly competitive business, unless they can be offset in some manner. The sludge produced would have a deilnite value as fertilizer or as a source of methane. Under proper control all of the nitrogen fed can be fixed in the sludge, and such nitrogen has a market value of about 10 cents per pound when sold as fertilizer. If the sludge were used to produce methane, considerable quantities of nitrogen would undoubtedly be available from the compounds released in the digester supernatant liquor. This factor, in conjunction with the value of the methane produced, should overcome or at least markedly reduce the outlay for chemicals. The data in Figure 1 (series A and B) show that the addition of nitrogen had little effect in speeding B. 0. D. removal until the waste sulfite liquor concentration had reached more than 6 per cent. The 2,4, 6,8, and 10 per cent feed mixtures
415
in series A had ratios of 5-day B. 0. D. to ammonia nitrogen of approximately 10 to 1,20 to 1,30 to 1,40 to 1, and 50 to 1. This indicates that the rate of B. 0. D. removal is not restricted a t ratios of 20 to 1, but above 30 to 1 is definitely restricted. Thus, rapid removal of B. 0. D. can be obtained with smaller quantities of nitrogen than indicated above. This difference may be due to the functioning of other groups of organisms which have lower nitrogen requirements. The curves in Figure 2 showing the rate of growth of the activated sludges fed on the different diets indicate from their straight-line relations that the amount of growth obtained on supplemented or unsupplemented diets does not differ much, provided sufficient time is allowed to give equal B. 0. D. removals. On the basis of the growth curves in Figure 2, it has been estimated that, if the waste sulfite liquor from a mill with a daily capacity of 100 tons of pulp could be diluted with enough sewage to give a 10 per cent mixture and then treated with activated sludge, about 24 tons of activated sludge would be produced each day. This quantity of sludge would contain approximately 21 tons of volatile solids and should have considerable value as a source of methane for the production of power and heat. The value of such sludge as a fertilizer would be rather low unless the original feed mixture was supplemented with nitrogen before treatment, as the data in Table I11 show. Part of the cost of supplying nitrogen would be saved in the smaller capital investment and lower operating costs involved, because of the shorter period of treatment necessary to remove the B. 0. D. load in the presence of sufficient nitrogen to allow the sludge t o act unrestricted. Although the results reported here were obtained with only one waste sulfite liquor, which was somewhat more dilute than is obtained in actual practice (6.15 per cent total solids), i t is believed that the information will be of considerable value in further studies on the problem. Investigations on the influence of the kind of wood used for pulping and the method of cooking are now under way in this laboratory to determine whether the waste sulfite liquor produced under the various conditions is always susceptible to activated sludge treatment when the proper mineral substrate is provided.
Acknowledgment This research project was supported by a grant-in-aid from funds given the University of Wisconsin by the Wisconsin Alumni Research Foundation.
Literature Cited (1) Assoc. Official Agr. Chem., Official Methods of Analysis (1925). (2) Brenner and Harris, J. T. Baker Chemical Co., Phillipsburg, N. J., Chemist Analyst, 28. 55 (1939). (3) Lea and Nichols, rseUraue Works J., 8,436 (1936). (4) Rehling and Truog, IND.ENG.CHEM.,Anal. Ed.. 11, 281 (1939). (5) Sawyer, c. N.,IND. ENO.CHew., 32, 1469 (1940). (6) Schwoegler, Babler, and Hurd, J . Biol. Chem., 113, 749 (1936). PR~SBINTED (as part of the previous paper, 6 ) before the Division of Water, Sewage, and Sanitation Chemistry a t the 99th Meeting of the American Chemical Society, Cinoinnati, Ohio.