  Ca(OCl)2 + (NH4)2C2O4 = CaC2O4 + 2NH4OCl. The velocity of the germicidal action of the solution was found to be about ten times greater than the germicidal velocities of other hypochlorites of equal concentrations, (Race[3]), and from a consideration of the chemical formula of ammonium hypochlorite it appeared probable that it would be very unstable and decompose into chloramine, which Rideal had previously shown to have an abnormal germicidal action, and water. NH4OCl = NH2CL + H2O. After these results have been confirmed, the effect of adding ammonia to bleach solution was tried and it was found that 0.20 p.p.m. of available chlorine and 0.10 p.p.m. of ammonia produced equally good results as 0.60 p.p.m. of chlorine only. Similar results were obtained on the addition of ammonia to electrolytic hypochlorite. Experiments made with a view to determining the most efficient ratios of ammonia gave very surprising results: chlorine to ammonia ratios (by weight) between 8:1 and 1:2 gave approximately the same germicidal velocity.[3] The action of the ammonia on the oxidising power of bleach, as measured by the indigo test, was also found to be disproportionate to the amount added. The oxidising action of various mixtures of bleach and ammonia as measured by the rate of absorption of the available by the organic matter in the Ottawa River water is shown in Table XXV.
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| Percentage of Original Found After | |||||||||||
| 10 Mins. | 4 Hours. | 20 Hours. | ||||||||||
| Infinity (ammonia absent) | 66.8 | 40.0 | 25.1 | |||||||||
| 8:1 | 83.2 | 77.8 | 67.3 | |||||||||
| 4:1 | 97.2 | 94.7 | 88.5 | |||||||||
| 2.7:1 | 98.3 | 96.5 | 92.8 | |||||||||
| 2:1 | 99.8 | 98.2 | 96.2 | |||||||||
The 8:1 ratio caused a marked reduction in the rate of absorption of the chlorine whilst a 4:1 ratio was almost as active as the ratios containing more ammonia.
At the time when the abnormal results were obtained with ammonium hypochlorite and mixtures of bleach and ammonia, the phenomenon appeared to be of scientific interest only and especially so as Rideal had attributed the obnoxious tastes and odours, sometimes produced by chlorination, to the formation of chloramines. During the winter of 1915-1916 the price of bleach, however, advanced to extraordinary heights and the author then determined to try out the process on a practical scale for the purification of water. A subsidiary plant pumping about 200,000 Imperial gallons per day (240,000 U. S. A. gallons) was found to be available for this purpose and the chloramine process was substituted for the bleach method previously in operation. The process was commenced by the addition of pure ammonia fort, in the amount required to give a chlorine to ammonia ratio of 2:1, to the bleach solutions in the barrels. The results were not in accordance with those obtained in the laboratory and it was found that the samples of bleach solutions received for analysis were far below the strength calculated from the amount of dry bleach used. This experience was repeated on subsequent days and the deficiency was found to increase on increasing the ammonia dosage. Solutions of similar
From a consideration of the work of Raschig and Rideal, it appeared that the most efficient proportions of available chlorine and ammonia would be two parts by weight of the former to one part of the latter and this ratio was maintained during the run on the experimental plant. Lower ratios of chlorine to ammonia were contra-indicated by the laboratory experiments, which showed that the efficiency was not increased thereby whilst higher ratios were left for future consideration.
The cost data were calculated on the current New York prices of bleach and ammonia.
| Bacteriological Results | ||||||||||||
| 1916 | Raw Water. | Treated with Hypochorite Alone. | Treated with Hypochlorite and Ammonia. | |||||||||
| Bacteria per cubic centimeter. | B. coli Index per 100 cc. | Bacteria per cubic centimeter. | B. coli Index per 100 cc. | Available chlorine parts per million. | Bacteria per cubic centimeter. | B. coli Index per 100 cc. | Available chlorine parts per million. | Ammonia, parts per million. | ||||
| Agar 1 day at 37° C. | Agar 3 days at 20° C. | Agar 1 day at 37° C. | Agar 3 days at 20° C. | Agar 1 day at 37° C. | Agar 3 days at 20° C. | |||||||
| Mar. 15-31 | 44 | 238 | 35.7 | 4 | 12 | <0.14 | 0.90 | 4 | 12 | 0.14 | 0.22 | 0.11 |
| April 1-19 | 3,099 | 14,408 | 195.5 | 32 | 56 | 0.50 | 1.10 | 33 | 246 | 0.74 | 0.25 | 0.13 |
| Percentage Reduction | ||||||||
| Hypochlorite Alone. | Hypochlorite and Ammonia. | |||||||
| Bacteria per cubic centimeter. | B. coli Index per 100 cubic centi- meters. | Available Chlorine Parts per Million. | Bacteria per cubic centimeter. | B. coli Index per 100 cubic centi- meters. | Available Chlorine Parts per Million. | |||
| Agar 1 day at 37° C. | Agar 3 days at 20° C. | Agar 1 day at 37° C. | Agar 3 days at 20° C. | |||||
| Mar. 15-31 | 90.9 | 95.8 | 99.9+ | 0.90 | 90.0 | 95.0 | 99.7 | 0.22 |
| April 1-19 | 98.9 | 99.6 | 99.7 | 1.10 | 98.3 | 98.9 | 99.6 | 0.25 |
| Cost Per Million Imperial Gallons | ||
| Hypochlorite alone. | Hypochlorite and ammonia. | |
| Mar. 15-31 | $1.12 | $0.46 |
| April | 1.26 | 0.54 |
and aqua ammonia (26° BÉ.) at 51/2 cents per pound. | ||
In place of ammonia fort, aqua ammonia (26° BÉ.), containing approximately 29 per cent of anhydrous ammonia, was used. The material was first examined by the presence of such noxious substance as cyanides and found to be very satisfactory.
Fig. 12.—Sketch of Ottawa Chloramine Plant.
The general design of the plant is shown in Fig. 12. The bleach is mixed in tank A as a solution containing 0.3 to 0.6 per cent of available chlorine and delivered to tanks B and D, each of which has a twenty-four-hour storage capacity. The ammonia solution is mixed and stored in tank B and contains 0.3-0.5 per cent of anhydrous ammonia. The two solutions are run off into boxes E and F which maintain a constant head on valves V and V' controlling the head on the orifices. Both orifices discharge into a common feed
As tank B was previously used as a bleach storage tank, the change from hypochlorite alone to chloramine necessitated very little expense.
The treatment was commenced by gradually increasing the quantity of ammonia, until a dosage of 0.12 p.p.m. was reached, and constantly increasing the dosage of bleach, which was formerly 0.93 p.p.m. of available chlorine. Owing to the restrictions imposed by the Provincial authorities it has not been possible to maintain a dosage as low as that indicated as sufficient by the experimental plants results, but some interesting data have been obtained. Table XXIX shows the results obtained from February to October, 1917, from the chloramine treatment at Ottawa and also those obtained with liquid chlorine at Hull where the same raw water is treated with 0.7-0.8 p.p.m. of chlorine.
| 1917 | B. coli Per 100 c.cms. | Tur- bidity. | Colour. | Dosage p.p.m. | Hull B. coli Per 100 c.cms. | ||
| Raw Water. | Tap Water. | Chlo- rine. | Ammo- nia. | ||||
| Feb. | 268 | 0.88 | 3 | 40 | 0.57 | 0.05 | .... |
| Mar. 1-18 | 250 | 0.96 | 4 | 40 | 0.32 | 0.11 | .... |
| Mar. 1-31 | 643 | 0.43 | 4 | 40 | 0.47 | 0.14 | .... |
| April | 5228 | 0.34 | 31 | 32 | 0.56 | 0.10 | .... |
| May | 162 | <0.08 | 3 | 39 | 0.52 | 0.08 | .... |
| June | 114 | <0.08 | 3 | 41 | 0.51 | 0.08 | .... |
| July | 237 | 0.08 | 5 | 41 | 0.51 | 0.08 | 44.4 |
| Aug. | 165 | 0.08 | 4 | 42 | 0.51 | 0.10 | 28.0 |
| Sept. | 55 | <0.08 | 6 | 42 | 0.50 | 0.09 | 15.2 |
| Oct. | 31 | 0.15 | 5 | 42 | 0.42 | 0.08 | 1.1 |
| Average | 211 | 0.22 | 7 | 40 | 0.51 | 0.09 | |
During the period of nine months covered by the results in Table XXIX, only five cases of typhoid fever were reported in which the evidence did not clearly indicate that the infection had occurred outside the city. The reduction in the bleach consumed during the same period effected a saving of $3,200.
During one period of operation the hypochlorite dosage was gradually reduced to ascertain what factor of safety was maintained with a dosage of 0.5 p.p.m. of available chlorine and 0.06-0.08 p.p.m. of ammonia. The results are shown in Diagram VIII. The percentage of samples of treated water showing B. coli in 50 c.cms. was calculated from the results of the examination of 4-7 samples daily.
The results showed that it was possible to reduce the chlorine dosage to 0.25 p.p.m. with 0.06 p.p.m. of ammonia without adversely affecting the bacteriological purity of the tap supply and fully confirmed the experimental results previously obtained.
Ca(OCl)2 + 2NH3 = 2NH2Cl + Ca(OH)2
| 2CaOCl2 | = CaCl2 + Ca(OCl)2 | andCa(OCl)2 + | 2NH3 | = 2NH2Cl + Ca(OH)2. |
| Cl = 142 | 34 | |||
The chlorine to ammonia ratio is very important because of its influence on the economics of the process (vide p. 124).
DIAGRAM VIII
CHLORAMINE TREATMENT, OTTAWA
All the laboratory and works results that have been obtained in Ottawa indicate the importance of an adequate contact period. The superiority of chloramine over other processes is due to the non-absorption of the germicidal agent and to obtain the same degree of efficiency the contact period must be increased as the concentration is decreased. For this reason the best results will be obtained by chlorinating at the entrance to reservoirs or under other conditions that will ensure several hours contact. At Ottawa the capacity
The general results obtained during the use of chloramine at Ottawa in 1917 have shown that the aftergrowths noted during the use of hypochlorite (see p. 56) have been entirely eliminated and that the B. coli content of the tap samples from outlying districts has been invariably less than that of samples taken from taps near to the point of application of the chloramine. At Denver, Col., where the chloramine process has also been used, similar results were obtained
During the latter part of 1917 the relative cost of bleach and ammonia changed (see Diagram IX).
When calculated on the New York prices for January, 1918, the cost of chloramine treatment in the United States would be greater than hypochlorite alone unless a large reduction in the dosage could be secured by very long contact periods. This condition is only temporary, however, and
DIAGRAM IX
BLEACH AND AMMONIA PRICES
In Canada, the market conditions are still (1918) favourable to the chloramine process: bleach is 25 per cent higher than the U.S.A. product and ammonia can be obtained for one-half the New York prices.
The most important advantage of the process is the elimination of the aftergrowth problem. At Denver, where the aftergrowth trouble is possibly more acute than at any other city on the continent, it was effectively banished by the use of chloramine. At Ottawa, the sanitary significance of B. coli aftergrowths is no longer of practical interest because such aftergrowths have ceased to occur. Whatever may be their opinion as to the sanitary significance of aftergrowths, all water sanitarians will agree that the better policy is to prevent their occurrence.
AND AMMONIA
| Hypochlorite containing 4.35 per cent available chlorine. Ammonia contained 2.2 per cent NH3 | |||
| Ratio Chlorine to Ammonia by Weight. | Loss of Available Chlorine After | ||
| Few Minutes. | 1 Hour. | 24 Hours. | |
| Per cent | Per cent | Per cent | |
| 6:1 | 19 | 19 | 19 |
| 4:1 | 24 | 25 | 25 |
| 2:1 | 45 | 47 | 47 |
| 1:1 | 91 | 91 | 92 |
| 1:2 | 20 | 28 | 65 |
The stability of chloramine is a function of the concentration and the temperature and in practice it will be found advisable to determine in the laboratory the maximum concentrations that can be used at the maximum temperature attained by the water to be treated (cf. Muspratt and Smith
| (1) | NH2Cl + NH3 = N2H4HCl hydrazine hydrochloride | |
| and | (2) | 3NH2Cl + 2NH3 = N2 + 3NH4Cl. |
When the excess of ammonia is large, as on the addition of ammonia fort, the second reaction predominates and the yield of nitrogen gas is almost quantitatively proportional to the quantity of available chlorine present. As ammonium chloride has no germicidal action, and hydrazine a carbolic coefficient of only 0.24 (Rideal), the formation of these compounds should be avoided.
The dosage of chloramine can be checked by titration of the available chlorine (see p. 82) immediately after treatment or by the estimation of the increment in the total ammonia (free and albuminoid). Routine determinations of the latter made in Ottawa show that practically the whole (90-95 per cent) of the added ammonia can be recovered by distillation with alkaline permanganate and that 85-90 per cent is in the “free” condition.
Ca(OCl)2 + 2NH3 = 2NH2Cl + Ca(OH)2.
The marked activity of chloramine as a chlorinating agent could be predicated from its heat of formation, which is 8,230 calories. The other possible chloramines should be even more active as the heat of formation of these compounds are:
| Dichloramine | NHCl2 | — | 36,780 calories. |
| Nitrogen trichloride | NCl3 | — | 65,330 calories. |
The “available” chlorine content of the chloramines is double the actual chlorine content as each atom of chlorine will liberate two atoms of iodine from hydriodic acid.
| NH2Cl + 2HI | = | I2 + NH4Cl. |
| NCl3 + 6HI | = | 3I2 + NH4Cl + 2HCl. |
Halazone
For the sterilisation of small individual quantities of water such as are required by cavalry and other mobile troops bleach and acid sulphate tablets have been usually employed.
The subject was investigated by Dakin and Dunham,
Toluene sulphodichloramines were next tried. Excellent bacteriological results were obtained but the manufacture of tablets again presented difficulties. When the necessary quantity of dichloramine was mixed with what were assumed to be inert salts—sodium chloride for example—the normal slow rate of decomposition was accelerated. The dichloramine, in tablet form, was also found to be too insoluble to effect prompt sterilisation.
The starting point in the preparation of halazone is p-toluenesulphonic chloride, a cheap waste product in the manufacture of saccharine. By the action of ammonia, p-toluene sulphonamide is produced and is subsequently oxidised by bichromate and sulphuric acid to p-sulphonamidobenzoic acid. This acid, on chlorination at low temperatures, yields p-sulphondichloraminobenzoic acid (halazone). The reactions may be expressed as follows:
Halazone is a white crystalline solid, sparingly soluble in water and chloroform, and insoluble in petroleum. It readily dissolves in glacial acetic acid from which it crystallizes in prisms (M.P. 213° C.).
The purity of the compound can be ascertained by dissolving in glacial acetic acid, adding potassium iodide, and titrating with thiosulphate; 0.1 gram should require 14.8 to 14.9 c.cms. of N/10 sodium thiosulphate. Each chlorine atom in halazone is equivalent to 1 molecule of hypochlorous acid and the “available” chlorine content is consequently 52.5 per cent or double the actual chlorine content.
>SO2·NCl2 + 4HI=>SO2·NH2 + 2HCl + 2I2.
From the bacteriological results given by Dakin and Dunham it would appear that 3 parts per million of halazone (1.5 p.p.m. available chlorine) are sufficient to sterilise heavily polluted waters in thirty minutes and that this concentration can be relied upon to remove pathogenic organisms.
The formula recommended for the preparation of tablets is halazone 4 per cent, sodium carbonate, 4 per cent (or dried borax 8 per cent), and sodium chloride (pure) 92 per cent.
Halazone and halazone tablets, when tested in the author’s laboratory on the coloured Ottawa River water seeded with B. coli, have given rather inferior results. With 1 tablet per quart, over six hours were required to reduce a B. coli content of 100 per 10 c.cms. to less than 1 per 10 c.cms. Clear well waters gave excellent results and large numbers of B. coli were reduced to less than 1 per 10 c.cms. in less than thirty minutes. McCrady
