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Carbon and Nitrogen Transformation in Fresh Sewage Solids Digestion'.' H. Heukelekian and Willem Rudolfs AGRICULTURAL EXPERIMENT STATION, N E W BRUNSWICK, N. J.
Unlike carbon, nitrogen is utilized by the organisms HE principles of microbiological activities which bring about the transformation of organic matter and the only for synthetic purposes. Microbial cells contain 5 to 15 final stabilization of sewage solids are of paramount per cent nitrogen, which must be supplied either by proimportance for a clear comprehension of the processes in- teins or by their degradation products before growth can take volved in digestion. These transformations of organic place. When carbohydrates are used for energy the organisms matter resulting from microbiological activities itre dependent upon the metabolism and physiology of the organisms. must obtain their nitrogen from another source, either Those transformations which involve carbon and nitrogen, inorganic or organic. Ammonia is left as a waste product the foundation materials of the cell protoplasm, are the most only after the nitrogen required by these organisms for synvital. The physico-chemical character of the org:tnic matter thesis is satisfied. After this brief discussion of carbon and nitrogen transforcontaining these elements largely determines the type and mations, as affected by the degree of decomposition. metabolism of the organT h e microoganisms atisms, it will be understood tack the carbon to obtain The carbon and nitrogen changes in the digestion of that these transformations energy necessary for their limed and unlimed fresh solids have been followed. It are vital to the life and aclife activities and for synhas been found that there is no reduction in the total tivities of the organisms and thesis of their protoplasms. nitrogen content in a given volume of digesting sludge. that fundamental changes A certain amount of energy The percentage nitrogen of the volatile matter, on the are brought about in their is also required for growth other hand, increases as a result of the reduction in activities by such factors as and multiplication of t h e volatile matter. The increase of carbon content of the air and food supply. cells. The proportion of the volatile matter and the reduction of volatile matter, T h i s s t u d y was undertotal energy liberated that in the unlimed material, just balance each other. In taken with the hope that by is utilized for growth is delimed material there is a greater reduction of volatile following the carbon and termined (1) by the enmatter and carbon. The most rapid rate of carbon n i t r o g e n transformations vironmental conditions, (2) reduction takes place after the cellulose-decomposition d u r i n g digestion of fresh by the nature of the organstage, and it is suggested that cellulose decomposition sewage sludge it might be isms, (3) by the source of products, as well as the decomposition of another possible t o d e r i v e some the energy material, and (4) carbonaceous material-namely, the fats-cause this fundamental principles diby the degree of the transrapid reduction of carbon. It is pointed out that a recting the course and naformation. greater proportion of the organic matter decomposed ture of digestion. It was Variation in the air supply is gasified as a result of liming. also hoped that some light is an example of the first of might be thrown on the difthese conditions. U n d e r ferences in the course of diaerobic conditions such as prevail in the activated-sludge process, the amount of the gestion of limed and unlimed material. It has been demontotal energy liberated that is utilized for growth is much strated as a result of studies in this laboratory that judihigher than the amount utilized under anaerobic conditions cious application of lime accelerates the rate of digestion prevailing in separate sludge-digestion or Imhoff tanks. and increases the rate of gas production. Consequently, In other words, more of the material decomposed is resyn- the question presents itself as to the nature of substances thesized in the microbial cells under aerobic conditions that are decomposed as a result of lime addition. That the of the activated-sludge process than is in the anaerobic diges- addition of lime unlocks certain substances the decomposition processes. We would expect to find less reduction of tion of which gives great volumes of gas has not been realized volatile matter in aerobic processes than in anaerobic proc- before. esses. Such was found to be the case in an experiment Method in which two bottles of the same sludge were digested, one under strictly anaerobic conditions and the other occasionally Equal amounts of fresh solids from the Plainfield plant allowed to come in contact with air. The environmental conditions also determine the degree were put into two bottles. To one bottle lime was added of the transformation of the energy material and the amount to maintain a p H of 7.4. The material was incubated a t of energy liberated. Under aerobic conditions the digestion 24' C. Frequent determinations were made of p H value, goes to completion with the liberation of end products such solids, ash, and Kjeldahl nitrogen. Organic carbon was as carbon dioxide, water vapor, and ammonia, which contain determined by the wet combustion method after driving but little energy for microorganisms. Under anaerobic off the dissolved carbon dioxide and the carbonates by bringconditions various intermediate products are formed which ing to a boil in acid solution. contain energy that may be utilized further for synthesis. Mention must be made here of the irregularities in sam1 Presented by Mr. Rudolfs before the Division of Water, Sewage, pling caused by the growth of fungus, especially on the surand Sanitation Chemistry at the 74th Meeting of the American Chemical face of the unlimed material. Some of the apparent inconSociety, Detroit, Mich., September 5 to 10, 1927. sistencies in the curves were caused by uneven distribution 2 Paper No. 5 5 , Department of Sewage Disposal, New Jersey Agriof the fungous mat. cultural Experiment Station, New Brunswick, N. J.
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44
OB
Vol. 20, No. 2
0.16
0.8
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D.Pcxeent c in volatile maIter ‘E. Percent c i n v o \ . maitev corrected fop
50
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va at*lr matter
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30
30
20
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oars 20 40 bb Figure 1-Volatile
80 100 1Zb 140 160 1gO 200 220 240 Matter Carbon a n d Nitrogen in Unlimed Digesting Sewade Solids
Results The results are presented graphically in Figures 1 and 2. UNLIMEDMATERIAL-The digestion of unlimed fresh solids was very slow, as indicated by the curve of volatilematter contenta (Figure 1, curve I). During the 8 months of digestion the volatile matter was reduced only 25 per cent. The amount of carbon present in 100 cc. of this material at different dates showed some fluctuation with a very slow reduction amounting to about 5 per cent (curve 11). But a t the end this reduced amount of carbon was contained in a smaller amount of volatile matter and hence the percentage of carbon in the volatile matter was high (curve IV). With a 25 per cent reduction of volatile matter there was about 30 per cent increase in carbon content of the volatile matter. I n other words, the increase in carbon paralleled the decrease of volatile matter and the original relationship of the organic matter to its carbon content was not altered. When, therefore, the reduction of volatile matter is compared on the basis of the original volatile matter content of the material, the percentage of carbon in the volatile matter is proved to be constant (curve V). The results for curve V are obtained in the following way:
- a,
X b, C
where a = per cent volatile matter at n date b = per cent carbon in volatile matter at c = per cent volatile matter at beginning
t-
” IL .-
volatile rnalter
II.Crams C in IO0 cC. m.Gnams N in 100 ce.
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The nitrogen content of this material showed a slight initial increase followed by slow and gradual decrease (curve 111). LIMED MATERIAkWhen h e was added to the fresh solids to maintain the pH value at 7.4 the digestion of the material was hastened, so that there was about 60 per cent reduction of volatile matter within 3 months (Figure 2: curve I, results corrected for the lime added). The amount of carbon present in this material decreased rapidly after the fird 60 days, until at the end a 30 per cent reduction was evident (curve 11). After the volatile-matter reduction had ceased there was a steady decrease in the carbon content. Volatile matter as given in the test is equivalent to “loss on ignition.”
Pels
in volatllr mane*
20
40
LO
Figure 2-Volatile
Po 100 120 140 /bo /BO 200 220 240 Matter Carbon and Nitrogen i n Limed Digestidg Sewag; Solids
The percentage of carbon in the volatile matter increased steadily from 26 to 50 per cent during the first 100 days of the incubation, after which it became more or less constant (curve IV). The apparent percentage increase is due to the reduction of part of the volatile matter and not to an actual addition of carbon. When compared on the basis of the initial volatile matter, there is obviously a decrease in the percentage carbon content of the volatile matter (curve V). Assuming the original volatile-matter content as 100 with 26 per cent carbon, we find a t the end only 40 parts volatile matter with a carbon content of 50 per cent. The nitrogen content of the limed material showed an initial increase, followed first by a drop and then by a second increase (curve 111). It must be borne in mind that this is the total amount of nitrogen present in 100 cc. of the material. The nitrogen content, on the basis of volatile matter, naturally increased, since with a constant nitrogen content volatile matter was decreasing rapidly. Discussion NITROGEN TRANSFORMATION-TO take up first the changes in the nitrogen content, i t will be seen that if the figures are significant there is an absolute increase in the amount of nitrogen as a result of digestion. It is true that the differences are small and too much emphasis should not be laid on it; yet in view of the fact that the total-nitrogen determination is quite accurate and the results are persistent, an explanation may be offered. The fixation of nitrogen under anaerobic conditions in the presence of abundant and suitable carbon supply is entirely feasible. At any rate, the digestion did not bring about a reduction in the nitrogen content of either the limed or unlimed materials. It is true that a certain amount of nitrogen is lost in the gas, but this does not seem to be appreciable (usually from 3 to 8 per cent). Thus digestion brought about a change in the form rather than in the quantity of nitrogen. On the other hand, on the basis of volatile matter there is an actual increase in the nitrogen content. Thus, if we start with 100 grams of volatile matter in the fresh solids with a 4.0 per cent, nitrogen content, as a result of digestion the volatile
February, 1928
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matter will be reduced to 50 grams but the nitrogen in the remaining volatile matter will be 8.0 per cent. CARBONTRANSFORMATION-The reduction of carbon in the unlimed material parallels the reduction of volatile matter. I n both cases the reduction is lower with unlimed than with the limed material. The addition of lime stimulates the decomposition of organic matter, especially the carbonaceous constituents. The most rapid reduction in the carbon content takes place in the later stages of decomposition. The decomposition of cellulose, which takes place in the early stages of digestion, is not accompanied by a material reduction in the carbon content because. in the first place, cellulose constitutes only 5 to 10 per cent of the dry material of the fresh solids, and second, the decomposition products of cellulose, the organic acids, are broken down in the later stages of digestion. Undoubtedly, the decomposition of some carbonaceous substance besides cellulose is the cause of this rapid decrease in the carbon content. It is suggested that the addition of lime accelerates the decomposition of fats, thus causing a great reduction of carbon and volatile matter. Decomposition of fats takes place only in the later stages of digestion. I n the case of unlimed material a 25 per cent reduction of volatile matter was accompanied by only 5 per cent
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reduction of carbon, while in the limed material a 60 per cent reduction of volatile matter was accompanied by a 30 per cent reduction in the carbon content. It would therefore appear that not only does the addition of lime cause a greater reduction of volatile matter, but also a greater proportion of this volatile matter is gasified, whereas in the unlimed material a greater proportion of the decomposed material is left in intermediate forms-that is, liquefied. Thus, it would seem that the addition of lime not only brings into the range of decomposition a greater proportion of substances, but also causes the decomposition of these substances to give greater volumes of gas. Lime causes a more rapid and also a more complete decomposition of the substances that would either decompose partially or not at all. The increase in the carbon content of the volatile matter is not an actual increase, but only an apparent one due to the reduction of the volatile matter. When this is remembered the percentage content of carbon is seen to be actually decreasing in the limed material. On the other hand, the volatile matter of the sludge obtained a t the end of the decomposition has a higher percentage of carbon. The explanation is obvious since the process of humification is one of enrichment of carbon; the higher the degree of humification the greater the percentage of carbon.
Effect of Addition of Salts on the Germicidal Efficiency of Sodium Hydroxide' Max Levine, J. H. Toulouse, and J. H. Buchanan DEPARTMENTS OF CHEMISTRY AND BACTERIOLOGY, IOWA STATECOLLEGE, AMES,IA. Concentration of Added Salts on Killing Time of N A previous paper2 it was shown that with the same Table I-Effect of0.5 N Sodium Hydroxide at 50° C. sodium hydroxide concentration the addition of sodium KILLING TIME99.9 PER CENT OF EXPOSED BACTERIA NaCl NazCOa ADDEDSALT carbonate increased the efficiency of the germicidal P H cent Minutes Minutes action of the solution. In this paper are given the results 0 41.0 41.0 of adding salts, with particular reference to sodium chloride. 1 33.8 34.4 2 2 9.9 2 9 . 9 The details of preparation of the culture and technic of 3 25.5 25.2 disinfection were identical with that previously de~cribed.~ The time required to effect a reduction of 99.9 per cent of It will be observed from Table I that the addition of sodium the exposed bacteria was employed as a basis for comparison. chloride or sodium carbonate decreased the killing time Preliminary experiments showed the following: of sodium hydroxide and that the decrease was proportional (1) 1.16 per cent NaCl, 1.5 per cent KCl, and 1.07 per cent to the quantities of added salts. Sodium chloride and sodium NazCOa decreased the killing time of 0.5 N NaOH at 50" C. carbonate were equally effective in this respect. The when the salts were added to the alkali. killing time was effectively reduced 16.8, 27.00, and 38.3 (2). .NaCl, KCl, Na~C03,and Na3P04.12H10 were only weakly germicidal for the test organisms, showing reduction of less than per cent by the addition of 1.0, 2.0, and 3.0 per cent of the salts, respectively. There was no significant change in the 30 per cent in 1 hour at 60" C. H-ion concentration due to the addition of these salts. Experimental
I
Concentration of Added Salts on Killing T i m e of EXPERIMENTS AT 50" C.-To 100 cc. of 0.5 N sodium Table 11-Effect of 0.25 N Sodium Hydroxide at 60° C. hydroxide in a three-necked Woulfe bottle was added the R l L L I N G TIME99.9 PER CENT O F EXPOSED BACTERIA ADDEDSALT NaCl NazCOs NasP0~.12HzO desired amount of sodium chloride or carbonate (dry salt). Per cent Minutes Minutes Minutes The mixture was sterilized in the autoclave a t 15 pounds (1 0 42.5 42.5 42.5 atmosphere) for 20 minutes. After cooling, the contents of 1 30.6 29.0 34.9 2 23.4 21.9 28.1 the bottle were brought to the desired temperature in a 3 19.9 20.1 24.7 water bath, inoculated with the test organism, and the surviving bacteria determined as previously described. EXPERIMEKTS a t 60" C.-Owing to the greater sterilThe results are summarized in Table I. izing effect a t 60" C., a sodium hydroxide solution 0.25 N Figures 1 and 2 show curves obtained by plotting logarithms was used in place of the 0.5 N solution employed at 50" C. of the average per cent surviving bacteria against time. Sodium chloride, sodium carbonate, and trisodium phosphate Received September 17, 1927. This study was made possible through were the salts used, in strengths of 1.0, 2.0, and 3.0 per cent, a fellowship maintained by the American Bottlers of Carbonated Beverages respectively. The increased sterilizing efficiency of the at Iowa State College. sodium hydroxide with the addition of these salts is given * I n d . Eng. Chcm., 20, 63 (1928). * Iowa State College J . Science, 1, No. 4, 379 (1927). in Table I1 and in Figures 3, 4, and 5. f
