INDVSTRIAL A.\-D
December, 1929
ENGIAVEERISGCHEIWISTRY
Table VI-Chemical Composition of a n 8-12-20 Mixed Fertilizer a8 Delivered a t Intervals from a Fertilizer Distributor SAMPLE
NH3
PzO~
KzO
Per cent
Per cent
P e r cent
8.32 8.27 8.71 8.85 9.31 10.13 9.97
9.14 9.23 9.76 10.06
18.06 19.80 16.70 16.06 14.37 11 39 11 97
10.s1 11.37 12.63
1223
facture by making a slurry of the components to be mixed and graining or spraying them all together. This process probably would not be practical with most present mixtures, but it is feasible with mixtures composed entirely of chemicals. Acknowledgment
In the field this segregation undoubtedly would proceed further than it did in the laboratory, because a machine passing over a tilled field mould shake up its contents more than a distributor running smoothly in the laboratory. This difficulty may be entirely eliminated in the process of manu-
Credit is due W. H. Ross, senior chemist in charge of concentrated fertilizer investigations, and R. B. Gray, 11.A. R. Kelley, and G. A. Cumings, agricultural engineers of the Bureau of Public Roads, for valuable assist,ance in this study. Literature Cited (1) Adams and Merz, I N D . EKG.CHEX.,21, 305 (1929) ( 2 ) Deming and Mehring, I b i d . , 21, 661 (1929). (3) Ross, Mehring, and hierz, I b i d . . 19, 211 (1927).
Biological Purification of Creamery Wastes' Max Levine IOWA EKGIKEERING
EXPERIYEKT STATION
H E rapid growth of the dairy industry and the tendency of creameries to locate in towns rather than on the outskirts of communities has accentuated the problem of waste disposal. At one time agricultural authorities recommended large septic tanks, of about 6 clays' storage capacity, and many such installations may be found, but there is no instance, t o the author's knodedge, where such a device has proved satisfactory. On the contrary, an inspection of several such installations in Iowa disclosed accumulations of precipitated undigested casein and very malodorous effluents. The inadequacy and inefficacy of septic tanks for treatment of creamery wastes as compared with domestic sewage may be readily understood from a consideration of their chemical compositions.
T
Effect of Acidity on Efficiency of Septic Tanks
Domestic sewages rarely show oxygen-consumed values over 90 p. p. m., while the organic and ammonia nitrogen is generally less than 30 p. p. m. Creamery wastes, on the other hand, gave oxygen-consumed values of 600 to 1600 p. p. m. with corresponding nitrogen contents of 40 to 150 p. p. m. S o t only are creamery wastes more concentrated but, what is of considerably greater significance, they are qualitatively different from domestic sewage. The ratio of oxygen consumed to nitrogen is 2 or 3 to 1 for municipal sewage, as compared with over 10 to 1 in the case of creamerv wastes. This high ratio for the industrial waste is due to the presence of lactose, which is practically, if not entirely. absent from domestic sewage. The decomposition of this milk sugar under anaerobic conditions, such as exist in septic or Imhoff tanks, results in the development of high acidities which seriously interfere with septic action. If acid-coagulable substances such as casein are present. these are precipitated. and the septic tank becomes merely a sedimentation or acid-precipitation tank, which rapidly fills, discharging casein and other solids which may soon clog filters. In a paper previously reported ( 2 ) it was shown that digestion of casein and gelatin by proteolytic bacteria from creamery wastes is markedly inhibited by acidify and that it may be completely stopped if the reaction tieconies pH 5.0 to 5.5. Thus a mixture of Flanobacteriunz sitctveolens and Bacterium conzmunior growing aerobically in gdatin for 6 1
Received October 12, 1929.
A N D IOXIrA S T A T E C O L L E G E , A Y E S , I O W A
days produced 855 nig. of ammonia and amino nitrogen and showed a reaction of p H 7.7. In the presence of 0.1 per cent lactose only 329 mg. of ammonia and amino nitrogen were produced, the reaction becoming pH 7.0. Increasing the lactose to 0.2 per cent resulted in a reaction of p H 4.8, with no increase in ammonia or amino nitrogen. As the acidity increased owing to the decomposition of lactose by Bacterium communior, proteolysis by Flavobacterium sztaLieolens was prevented until at p H 4.8 the proteolytic organism in this case was killed. Septic tanks are teeming with lactose-fermenting organisms, so that, if milk wastes enter, the resulting acidities must inevitably interfere with septic action, which is essentially proteolytic. A concentration of about 0.05 per cent milk sugar is sufficient under strictly anaerobic conditions to develop inhibiting acidities. A number of samples of creamery wastes were collected from representative Iowa creameries. The samples were, in each instance, composites of an entire day's run, collected at 30-minute intervals. Of sixteen such samples eight developed germicidal acidities (pH 4.5) and three others markedly inhibitory reaction (pH 5.5 to 5.0) when stored for 2 days at 20" C. The problem of purification of creamery wastes I esoh-eh itself, therefore, into that of devising a mean5 for destroying inilk sugar without the development of detrimental aciditieq. If a creamery located in a city could so treat its waste as to eliminate the acid-producing constituents. the resulting product could safely be added to the municipal sewage. The biological oxidation of sugar under aerobic conditions appeared feasible for such preliminary or partial treatment, and in 1923 (I) it was reported that this could be acconiplished experimentally by the activated sludge process. It way felt, however, that for the small creamery with its fluctuating quantity and variable character of waste, and its limited personnel, the activated sludge process would be impractical but that trickling filters might be feasible and economical. Experimental
Obserrations have been made on the efficiency of trickling filters for the purification of creamery wastes when employing different kinds of filling materials, such as lath, rock, gravel, broken tile, cinders, spiral ring packing, and corncobs. This brief report is restricted to a portion of the ob-
rcrvatioii on the elimination of acid-producing constituents by an experimental lath filter. This filter consist.ed of six tiers of laths 2 feet square and 1 foot dcep vith about 4inch spaces between the tiers for convenience in sampling. Ahout 6 inelies above the uppermost tier of laths was a perforated nietal tray, 2 feet square, rvliich served as a rlistributing device, upoil which the waste was spilled by means of a double-grooved tipping trough, which served as an automatic dosing mechanism. (Figure 1) The wastes employed consistcd of 0.5 to 7 per cent skim milk powtlcr solution and 1 per cent skim m i l k t o which various concentrations of milk sugar (approximately 0.1 to 0.3 per cent) had been added. Treatment was at the rate of 800,000 g. p. a. p. d. for a period of 10 to 14 liours daily, samples heing taken daily of the efKuents f r o m the endire area of each foot of the filter, after5 to 6 hours of operation. Estimations o f t h e removal of acid-fonning s u b s t a n c e s were Pigure I - - E ~ Lath ~ F~ U~ ~~ made ~~ ~in ~ two ~ N ~ ~ Y~S : (1) I b y d e t e r m i n i n g the quantit.ies of milk sugar in the effluents from different depths and (2) by observing whether these effluentswould develop appreciable acidities on anaerobic incubation for 2 days at 20" C . Table I-Destruction of Lactose and Development of Acidity in Emvents frwn Lath Filter ReceivinQ Varlouv Milk Wastes
(Z " A Y S AT 20" C.)
4.3
5.3 6.6 7.1 7.4 7.5
7.6
4.2 4.6 58
4 2 4.5
7.0
8.6 6.9 7.2
70
7.5
7.3
7.3
4.2 4.3 5.0 6.0
7.3
4.1
5.5 8.5
Results
The results for four of the runs ernploying wastes containing from 1700 to 3460 p. p. m. of reducing sugars calculated as lactose are summarized in Table I, and Figure 2 shows the rates of destruction of lactose when various quantities were added to 1 per cent skim milk solution as a hais.
The rate of destruction of lactose is apparently very rapid in the upper part of the filter. Thus, therc were effected reductions of over 90 per cent on the 4 and 7 per cent milk wastes which contained 1700 and 3250 p. p. m. of milk sugar,
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