August', 1929
IhTDUSTRIAL A.1-D EiYGIATEERING CHEXISTRY
showers (commonly called safety showers) should be provided in ample number to enable a man splashed with acid to reach one conveniently from any position adjacent to the apparatus. They should be placed not more than 50 feet from any operating position in which a man might be splashed or sprayed with acid, and the man should not have to make more than one right-angle turn in his effort to reach one. The showers should be equipped with quick-opening valves and the sizes of the heads and riser pipes should be sufficient to deluge one with water. Work inside tanks and apparatus requires the utmost precaution for safety. 'The tanks or apparatus should be thoroughly freed of all acid and fumes by thorough and repeated washing and steaming, winding up by filling with a weak soda solution and allowing i t to stand long enough to neutralize all acid. All mud should be removed, became when stirred up i t liberates fumes. It pays to have the men who enter protect themselves with gas masks and safety belts. The belts are used with life lines attached so that quick rescue can be made from outside the tanks or apparatus if anything goes wrong. Attendants should always be stationed a t the tank manholes while men are inside. Each acid pipe line leading to the tank should have a section removed and the
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end blanked off so there can be no possibility of acid entering while the men are a t work. Ample provision should be made for the handling of heavy parts in time of repairs. Much can be done to facilitate this in the original design of the buildings by providing anchorage of sufficient strength for hoists and by including large doorways and floor openings. The latter should be protected with railings and toe-boards. I n general, it is well to make all parts of the apparatus easily accessible by the provision of good permanent walkways and stairways. Stairways should be provided in preference to ladders in so far as possible. It is always good from a safety standpoint to place acid pipe-line valves not more than 18 inches above floor levels, so that the operator can keep his face well away from them. However, all important passagemys should be kept clear of pipes which would form stumbling hazards. Floors should be of acid-resisting material and sloped to drain well to sewers or pumps. Ample water hose and outlets should be available for washing away spills of acid. Adequate ventilation is always important in buildings housing acid processes and is usually obtained by roof monitors supplemented with wall openings a t the ground level to provide the necessary circulation of air.
Effect of Nitrate Oxygen upon Tannery Effluent' Edwin R. Theis and John A. Lutz WILLIAM H CHAXDLERC H ~ M I C ALABORATORIES, L LEHIGHUNIVERSITY, BETHLEHEM, P A
NE of the most imporThe reduction of nitrate in the presence of oxidizable presence of n i t r a t e s . Butant processes in the organic material has been studied and the following chanan and Fulmer further manufacture of leather facts have been noted: (a)the amount and composition point out that the oxygen is the proper soaking of the of the gas produced during the reduction; ( b ) the secured through reduction of hides or skins, and for this amount of reduction taking place under various condinitrates and nitrites is availreason l a r g e a m o u n t s of tions; ( c ) the gas pressure attained during the reducable to the organism quite as tannery soak water are passed tion of the nitrate. readily as atmospheric oxyIt is shown that large amounts of nitrogen are libergen. The reduction of nito rivers and streams. Hides and skins are generally soaked ated through the reduction of nitrate by bacterial actrate with subsequent oxidafrom 24 to 48 hours, and it is tion and it is pointed out that this nitrogen may be tion of sulfur liberates energy usually found upon examinaderived from several sources. During the early stages f o r b a c t e r i a l u s e . Extion that the resulting soak of the reduction considerable carbon dioxide is properiments have shown that miter contains no dissolved duced, indicating that the carbonaceous material is tannery soak water is very oxygen-in bacteriological acted upon most readily. At a later period it appears s t r o n g l y reducing in charparlance, the water is strictly that the sulfur compounds are oxidized by the nitrate. acter and acts upon sodium anaerobic. The effluent from nitrate with great avidity, a 48-hour soak may contain upward of 300 million bacteria giving a variety of products. When nitrate is added t o per milliliter of soak water, and for this reason the oxygen these lvaters, the folloming reactions may be visualized: requirement of the wvster is extremely high. RIany workers have studied the effect of nitrate oxygen upon sewage in (N01)2H' 2 e ---f (NOz) Hz0 NOz 2 H + Z E +NO HzO general, but apparently little has been done with regard to 250 4 H C 46 +J S z 2H20 tannery effluent. IS0 f 6 H + 5, +NH3 + H2O Urbain (4)has pointed out that it is necessary for anaerobic NH3 HNOz +XHaNOz +NO 2H2O conditions to exist before nitrate oxygen can be utilized by bacteria. The present writers have found this contention I n determining the biochemical oxygen demand by the nito be in accordance with their experimental work. However, trate method it is usual to estimate the residual nitrate and in utilizing tannery soak water, the effluent is practically free nitrite in the incubated solution. The writers believe that from dissolved oxygen and is consequently anaerobic. Many this leads to erroneous interpretation, because it appears that bacteria have been foiind which are capable of rtbducing nitrates to nitrites. Buchanan and Fulmer ( I ) point out more of the nitrogen cycle should be estimated. Theis and that most of these barteria are strictly aerobes except when AIchIillen (5) showed that on treating tannery soak water able to reduce nitrates and nitrites. These bacteria are pro- with standard solutions of sodium nitrate large amounts of the teolytic and unable to act upon carbohydrates except in the nitrate were consumed. Table I gives a summary of the data. This table shows that comparatively large amounts of nitrate 1 Received April 6, 1929 Presented before t h e Division of Water, are consumed but only small amounts accounted for in the Sewage, and Sanitation Chemistry a t t h e 77th Meeting of t h e Amerlcan Chemical Society, Columbus, Ohio, April 29 t o M a y 3, 1929. usual analysis. Buswell (8)points out the conflicting evi-
0
+
+ +
+
+ + ++
+ +
+
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IlVDUSTRIAL A1l-D ElYGIXEERING CHEMISTRY
764
Vol. 21, No. 8
/&7/ZO?/Q-N,
,/'
k -
5
/
c
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4m o
'p 2 +o
y
,qhw/cc-N,
01 0
=
-4trate
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20;
-4
/ 0 , 2 , 9 , ' , #
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1
4
c
a /o /a i%Y*
H
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Figure 9 shows the type of apparatus used and Figures 10 and 11 show the analytical data obtained.
Figure 1-Reduction of Nitrate, When 230 p. p. m. Are Added
dence existing with regard to the evolution of nitrogen gas through the reduction of nitrate by sewage. The experiences of the writers have indicated that large amounts of gas are formed through this reduction and for this reason the following experimental work was undertaken. Table I-Nitrate
Reduction by Soak Waters PERIOD OF SOAK------24 Hours 48 Hours 96 Hours 120 Hours
S i t r a t e nitrogen reduced Nitrite nitrogen formed Ammonia nitrogen formed
P.p.m. 1550.0 1.4 42.0
P.p.m.
P.p.n.
P.p.m
1670.0 200.0 32,6
3150.0 280.0 22.0
8800.0 2100.0 67.5
Experimental Procedure
SERIES1-The soak water was prepared by soaking heavy steer hides in water for 96 hours a t 25" C. Fifteen hundred milliliters of this prepared water were placed in a 2000-ml. bottle and this solution in turn was treated with standard nitrate solution. The space above the solution was flushed completely with nitrogen gas in order t o keep the solutions Figure 4-Reduction When 5oo anaerobic. The bottles were _u. D._ m. of Nitrate Are Added s h a k e n o n c e d a i l v and samples withdrawn for estimation of nitrate, nitrite, and ammonia. These samples were withdrawn in an atmosphere of nitrogen and only nitrogen gas came in contact with the solutions in question. Figures 1 to 5 show the experimental data obtained under these conditions. SERIES2-In another series of experiments 100 ml. of the same soak Twter were placed in 200-ml. bottles together with varying amounts of standard nitrate solution. These bottles in turn Jvere fitted with mercury manometers and placed in a thermostat maintained at 37.5" C. Pressures Tvere recorded several times daily. Runs were also made similarly a t 25" C. Figures G t o 8 give in graphics1 form the experimental results of this work. SERIES3-In this series of experiments 1500 ml. of solution as made in Series 1 were connected directly t o a gas analysis apparatus and each 100 ml. of gas evolved was analyzed for carbon dioxide, oxygen, and nitrogen. A complete analysis of the evolved gas showed only these three gases to be present and in all subsequent work only these were determined.
Discussion
From Figures 1 t o 5 it is readily seen that when using 110 p. p. m. of nitrate nitrogen most of the nitrate is reduced within 24 hours; the nitrite nitrogen reaches a maximum the third day and then decreases sharply to practically zero; the ammonia increases abruptly, rising t o 400 per cent in 7 days. When using 500 p. p. m. of nitrate nitrogen, it requires nearly 7 days to bring the nitrate reduction t o a practical equilibrium. The ammonia again shows a sharp rise. When 2500 p. p. m. of nitrate are used, an entirely different picture results. For 7 days no reduction of nitrate occurs, but after this latent period a rapid reduction takes place which does not attain equilibrium in 30 days. When small amounts of nitrate are used as illustrated by Figures 1 and 2, equilibrium is attained a t a very early period. In the early stages of reduction much gas is formed, sufficient in most cases to expel the stoppers from the bottles. This generation of gas continues until about the time that the
k'7
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/bo
-
Arnrnonla
-N
--/-
00 2
Nitrite-N ------6 8 I O /2 I4 D a/6 y s I8
4
20 22 24 26 28
L
Figure 5-Reduction When Large Amounts of Nitrate Are Added
nitrite formation ceases. It is also during this period that ammonia formation begins. It is quite possible that a part of the gas formed during the earIy stages is due to the interaction of nitrite and ammonia to form ammonium nitrite, which by autoxidation yields molecular nitrogen.
I.1-DCSTR1A.L A-YD EiVGIA1%ERI.VG CHEXIXTRY
August, 1929 NH4NOz
+N P + 2Hz0
This suggestion is further strengthened by the fact that if the Bottles are shaken violently for a few minutes the gas pressure increases very greatly. When large amounts of nitrate are used, as illustrated in Figure 5, other factors enter into the reaction. For a certain period of time there is apparently no reaction, the nitrate is not reduced, practically no nitrite is formed, arid no gas is
I n reduction of nitrate t o nitrite, energy to the amount of 10,000 gram-calories would have to be added for cach grammolecule of nitrate consumed. The nitrites are more readily utilizable than the nitrates, which may explain to some degree why they do not show up strongly on analysis. The nature of the gases found, through the simultaneous interaction of the nitrate and sewage, opened up a very interesting field of investigation. Table I1 and Figures 10 and 11 show the data taken. Table 11-Amount
20 24 26 43 49
evolved. After this lag period (in Figure 5 abcut 7 days) there is a rapid reduction of the nitrate and a copious evolution of gas, but there is no apparent equilibrium a t the end of about 30 days. It appears that in the initial stages the large amount of nitrate present acts as ai1 antiseptic aiid thus hinders the reaction. This antiseptic action is finally broken down and the bacteria become acclimated to this environment, and it is at this stage that rapid reduction takes place. The solutions t o which nere added small amounts of nitrate, though having attained an equilibrium and still generating some gas, shon-ed that the oxygen demand had not been satisfied. These solutions had a putrid odor of volatile sulfides. The solutions to which 1000 p. p. m. of nitrate had been added showed that thrir oxygen demand had been practically satisfied.
86.3 170.6 256.7 939.3 1141.0
Developed during Incubation i n an Atmosphere of Air
69.0 140.0 216.0 895.0 1137.0
COz
.4N 4LYsIs---0,
n
5
S? r-
9,65 8.75 8.00 2.00
10.5 6.9 3.2 0 5 0.0
79 85 84.40 88.60 97.,50 98.21
1.79
From Table I1 it is readily seen that the available free oxygen is rapidly consumed whereas the carbon dioxide iiicreases to a maximum and then decreases rapidly. On the other hand, the nitrogen percentage increases constantly. Figure 10 shows the volume of gas produced when tsnnery effluent is treated with varying amounts of nitrate oxygen. Using 1000 to 5000 p. p. m., the volume of the gas increaqes to a niaximuin within 96 hours and then rapidly decreabe5. Using a small concentration of nitrate 1200 p. p. ni.), the volume of gas reaches a peak value within 48 hours and then also decreases. Analysis of the gas produced a t different intervals shoTTed that carbon dioxide is produced in the early stages but decreases in the later stages of the reaction. The nitrogen continually increases similarly to data given in Table I1 and Figure 11. The above data show coiiclusively that much nitrogen gas is formed during this reduction.
Figure 8-Pressures
Figure 7-Pressures
----
and Composition of Evolved Gases
P E R I O D O F GAS NITROGEN I ~ C U B X T IEVOLVED ON EIOLVED Hours 111. -111
Figure 6-Pressure Developed during Incubation a t 25' C. i n a n Atmosphere of Nitrogen Gas
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Developed at 36'C. i n a n Atmosphere of Nitrogen Gas
Figures 6, 7 , aiid 8 show pressures attained when tannery soak water is treated with nitrate oxygen. As will be seen, regardless of the concentration of the nitrate used, the pressure curves increase gradually and after a certain period of iiicubation attain either a maximum or a point of inflection. In the high concentrations, showing a point of inflection, the pressure cur\-e then continues t o rise but with no apparent equilibrium. I n the lower concentrations the pressure curve always exhibits a maximum point, decreases, and then usually riies to a new maximum and may even repeat. Figure 6 shows the pressure curve for incubation a t 25" C. The first sharp break in the curve occurs a t about 48 hours. Incubation at 36" C., as shown in Figure 7 , shows the first distinct dis-
IhTDUSTRIAL AND ENGIXEERIiY’G CHEMISTRY
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Vol. 21, KO. 83
continuity a t about 25 hours. This difference would be expected in view of the temperature conditions. An atmosphere of air was used for the data in Figure 7, while in Figure 8 an atmosphere of nitrogen was used. A high concentration of nitrate always gave a “sweet” water and no sulfide odor, hut a nitrate concentration of 1000 p. p. m. or less gave invariably a putrid water with a very strong sulfide odor, showing that the oxygen demand of the water had not been satisfied.
Figure 11-Composition
A- Reoct/’on Bottle COS co//ecCion gottk
a-
fur is supposed to liberate energy for bacterial utilization, Another possible reaction appears to be: 8KNOs 5H2S +4KzSO4 HzSOd 4Hz0 4Nz This reaction would also liberate energy for bacterial use. It is well known that sulfur compounds are present in tannery soak water and are derived from the decomposition of t h e amino acid, cystine. Cystine may then break down, giying the simpler substance, hydrogen sulfide. The above reactions may account, a t least to some extent, for the liberation of molecular nitrogen. Analysis of the gas has also shown high percentages of carbon dioxide, and this undoubtedly is derived from the oxidation of carbonaceous matter by the nitrate, as illustrated:
+
c- orsot Appurutus Figure 9-Apparatus for Continuous Analysis of Gases Developed
I n view of the compIexity of the dissolved substances in tannery effluent, it is not easy to account for the extreme variations in gas composition and gas pressure. The nitrate added must necessarily (in the presence of bacteria) oxidize the carbonaceous material, thus producing carbon dioxide. It may also act upon the organic sulfur and hydrogen sulfide present, producing possibly sulfates and nitrogen.
of Gas Formed a t Different Stages of Incubation
5C~H1206f 24HN03 +3ocoz c
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It is also possible that during oxidation various oxides of’ nitrogen may appear. As shown earlier in this paper, t h e nitrate is reduced to nitrite and this nitrite in turn m a y react R-ith various amino acids that are present in the effluent.
A- mm parts p r mt/kun Nttrrrle N2
a-,000
+
+
-I
CHz(NH2)COOH
+ HNOz +CHz(0H)COOH + Nz + Hz0
The variations in the gas pressure produced are undoubtedly due to the solubilities of the gases under the pressures produced and to the various strains of bacteria present in the effluent. It is also possible that the action of various strains is retarded or accelerated by the pressures attained during the incubation. Literature Cited (1) Buchanan and Fulmer, “Physiology and Biochemistry of Bacteria,” Vol. I, p. 434, Williams & Wilkins Co., 1928. ( 2 ) Buswell, “Chemistry of Water and Sewage Treatment,” p . 271, Chemical Catalog Co., 1928. ( 3 ) Theis and McMillen, J . A m . Leather Cizem. A s s o c n . , 23, 377 (1928). (4) Urbain, IND. ENG.CHEM., 20, 635 (1928). 21
4s
72
96
Hours o f hrubdmn
Figure 10-Amount and Composition of Evolved Gases, Using Varying Amounts of Nitrate
It is well known that through bacterial action in the presence of nitrates and sulfur compounds an oxidation of the sulfur occurs with corresponding reduction of the nitrate. This may be illustrated by the following equation: 6KN03
+ 5s + 2H20
--f
3K2SO.i
+ 2HzS04 + 3x2
The reduction of nitrate with accompanying oxidation of sul-
Potash Land Withdrawn from Entry On the basis of new prospecting developments, nearly 2,000,000 acres of land in New Mexico were included in potash withdrawal, according to ct public announcement by Secretary of the Interior, Ray Lyman Wilbur. More than 90,000 acres in Arizona, previously included in petroleum withdrawal, were restored to entry. More than 5000 acres of land in Montana and Wyoming, classified as valuable coal land, were included in coal reserve for the use of the United States.
