INDUSTRIAL AND ENGINEERING CHEMISTRY
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oxide, resulting from removal of sufficient ferric sulfate to dilute the remaining solution to such a degree as to cause precipitation. The amounts of iron fixed by hide powder from solutions at (OH)-/Fef++ = 0.160 are practically twice those from solutions of basicity = 0, 100 grams hide substance combining with 7.0 grams Fer03 from the basic solution and with 3.35 grams from the solution of the normal salt. Taking
gave unreliable results owing to precipitation of hydrous ferric oxide by the added salt and are not included here. With solutions of the normal ferric salt concentrations up to 5 M sodium chloride and 0.75 M sodium sulfate could be employed. With the basic salt, concentrations were limited to 2 M sodium chloride and 0.75 M sodium sulfate. The desired weight of salt was added to 450 cc. of the ferric sulfate solution and agitated until completely dis-
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Figure &Effect of Presence of Neutral Salt AII solutions were clear and free from precipitate.
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Vol. 20, No. 6
for 24 hours, using 400 cc. tanning solution and 2 grams of hide powder, as before. The results are summarized in Figure 4. It is to be noted that in all cases the presence of increasing a m o u n t s of sodium chloride causes, progressively, a decrease in fixation of iron from solution. The results with sodium sulfate are unusual, in that this Salt gives less r e t a r d a t io n t h a n
Availability of Nitrate Oxygen in Filter Effluents' 0.M. Urbain URBAIN& HUNT,COLUMBUS, OHIO
URING the writer's experience in testing filter effluents he has observed some outstanding peculiarities. I n determining the biochemical oxygen demand by a method involving a combination of the dilution and the nitrate methods, the nitrate oxygen is not available until after the dissolved oxygen has been consumed. Furthermore, the rate of consumption of the nitrate oxygen is much slower than that of the dissolved oxygen. These observations have led to the conclusion that nitrate oxygen in filter effluents is available only under anaerobic conditions and that nitrate oxygen does not add to the oxygen balance of waters receiving filter effluents. To substantiate these observations, experiments were made on various filter effluents as well as raw untreated sewage; in each case the results were the same, and in no case was the nitrate oxygen available until after the dissolved oxygen had been consumed.
D
Experimental Methods Used
The standard methods of the American Public Health Association were used in determining the dissolved oxygen, nitrites, and nitrates. The counts for aerobic bacteria were made on plain agar incubated a t 20" C. for 48 hours. The anaerobic counts were made on plain agar in a vacuum. A 1
Received January 31, 1928.
dish of potassium pyrogallate was used on top of the inverted Petri dishes to take up the last traces of oxygen remaining after evacuation. The anaerobic counts were also for 48 hours a t 20" C . I n preparing the dilutions the standard 250-cc. glass-stoppered bottles were used. The exact volume of each bottle was determined and all other factors were carefully controlled. Preparation of Dilution Water
A very pure water that had been specially aerated was used for the dilutions. The quality of this water was important because on its purity depended the accuracy of the final results. This water was prepared about 30 days before use according to the following scheme: To a quantity of distilled water was added c. P. sodium nitrate equivalent to approximately 10 p. p. m. of nitrate nitrogen, which was in turn equivalent to 28.5 p. p. m. of nitrate oxygen. Air was then bubbled through the water for 12 hours to saturate it with dissolved oxygen. This air was passed through concentrated sulfuric acid to remove any ammonia fumes or bacteria it might have contained. A sulfuric acid trap was also attached to the container and the water stored for 30 days. This was thought to correct any supersaturation conditions and the water was assumed to have a normal dissolved oxygen content at the laboratory temperature following this treatment. The
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1928
water thus prepared contained both dissolved and nitrate oxygen. The results of two of the many experiments made are given, one using sewage and the other sprinkling filter effluent. Experiment A-Using
Sewage
Duplicate dilutions containing the following amounts of raw sewage-3, 5, 7, 9, 11, 13, 15, 17.5, and 20 cc.-were prepared, together with blanks. The entire series of samples was then incubated a t 20" C. for 10 days. At the end of this period each set of duplicate samples was tested for dissolved oxygen, nitrate, and nitrite. The analyses are given in Table I. Table I Dxs-
RESIDDEPLESEW-SOLVED NO3 KO; NO? N0z UAL TOTAL TION AGE 0 2 N 0 2 N 0 2 0 2 Oz Oz B.O.D. Cc. P . p . m . P . 0 . m . P . 9 . m . P . 9 . m . P . 9 . m . P . 9 . m . P . 9 . m . P . 9 . m . P . 9 . m . 3.0 5.3 12.0 34.3 0.11 0.19 39.79 43.07 3.28 273 5.0 2.8 12.0 34.3 0.10 0.17 37.27 42.74 5.47 273 7.0 0.3 12.0 34.3 0.10 0.17 34.77 42.43 7.66 273 9.0 0.0 11.5 32.8 0.08 0.13 32.93 42.12 9.16 255 11.0 0.0 11.0 31.6 0.05 0.09 31.69 41.80 10.11 229 13.0 0.0 10.6 30.3 0.03 0.05 30.35 41.48 11.13 214 15.0 0 . 0 10.0 28.6 0.02 0.03 28.63 41.18 12.55 210 17.5 0 . 0 9.6 27.4, 0.02 0.03 27.43 40.77 13.34 191 20.0 0 . 0 9.0 25.7 0.02 0.03 25.73 40.38 14.65 183 Blank 9.2 12.0 34.3 0.025 0.04 43.54 43.54
.. . .. .
The first three dilut i o n s c o n t a i n e d dissolved oxygen a t the end of the 10-day period a n d s h o w e d no decrease in nitrate content during this time. All of the other six dilutions were depleted of dissolved oxygen and there was a gradual decrease in the nitrate, this d e c r e a s e b e i n g greater in proportion to the amount of sewage used. T h e o x y g e n equivalents of the ni6.G. SEWAGE trites and nitrates are Figure 1 given in the table, also the totaloxygen present a t the beginning of each test, the oxygen remaining a t the end (residual), and the oxygen depletion together with the B. 0. D. The B. 0. D. of the first three dilutions is the same because only dissolved oxygen was being used by the bacteria. There was a gradual decrease in the B. 0. D. in the last six dilutions, in which the bacteria used all the dissolved oxygen and began to break down the nitrates. It appears that they are not nearly so ambitious when working on nitrates. The decreasing B. 0. D.'s prove that the bacteria do not use the nitrate oxygen as fast as they do the dissolved oxygen. This phenomenon is believed to be strictly in accordance with nature. The time and energy required to break down the nitrates would necessarily enter into the equation. The preference for the dissolved oxygen is also in accordance with nature, since it is immediately available while the nitrate oxygen is not. The depletion of the nitrate and the dissolved oxygen is shown graphically in Figure 1. It may be noted that the first break in the nitrate curve coincides with the zero point in the dissolved oxygen curve. Experiment B-Sprinkling
Filter Effluent
Analysis of this effluent showing the content of oxygen in various forms was as follows: dissolved oxygen 0.0, nitrate nitrogen 3.0, and nitrite nitrogen 0.075 p. p. m. The diluting
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water tested as follows: dissolved oxygen 8.3, nitrate nitrogen 14.0, and nitrite nitrogen 0.035 p. p. m. Eleven parts per million of c. P. sodium nitrate as nitrate nitrogen were added to the filter effluent before use. This procedure eliminated the necessity of making a correction for each dilution. Twenty cubic centimeters of filter effluent were used in each dilution and the series of samples was incubated at 20" C. Duplicate samples were withdrawn and tested a t the following time periods: 24, 72, 120, 168, and 216 hours. The results of this experiment are given in Table 11. Table I1 DISANAEROBIC AEROBIC TIME SOLVED NOS KO8 BACTERIA BACTERIA Hours P . 9 . m . P . 9 . m . P . 9 . m . No./cc. No./cc. 24 6.8 0.07 14.0 4,300 300,000 72 3.1 0.25 14.0 3,200 32,000 120 1.7 0.20 14.0 2,100 13,000 168 0.0 0.40 13.5 2,600,000 2,300 216 0.0 0.75 13.1 980,000 1,650
Aerobic c o n d i t i o n s 1 w e r e i n effect for a ' ' little more than 5 days and during this period there was no decrease . in the n i t r a t e s . Be- 0" t w e e n t h e fifth and seventh day the condi-
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AEROBIC A NAERQBIC
curve again coincides with the zero point in the dissolved oxygen curve. Conclusions The results of the experiments show that the nitrate oxygen is available only after the dissolved oxygen is depleted, whether the dilutions be made from sewage or filter effluents. Bacteria, the neutralizers and destroyers of sewage, do not break down the nitrates for their oxygen supply except as a last resort. Before the nitrates produced by a filter are of any use as a stabilizing factor or a source of oxygen, it is necessary that anaerobic conditions exist in the waters receiving these effluents; in other words, the bacteria must "destroy" the receiving waters before the nitrate oxygen becomes available to them. Nitrate oxygen does not increase the available oxygen balance of the receiving maters.
Sculptured Portraits on London Chemical Building A feature of the new Imperial Chemical Industries building on the Thames a t Westminster, London, is a series of portraits of eminent chemists and men associated with the chemical industry, These include Alfred Nobel, Sir Alfred Mond, Ludwig Mond, Joseph Priestley, Antoine Laurent Lavoisier, and Justus von Liebig. These portraits are carved on stone and placed over a row of arches on the &1,000,000 building which is approaching completion.
