| 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 |
TABLE XXVIII
| Cost Per Million Imperial Gallons[A] | ||
| Hypochlorite alone. | Hypochlorite and ammonia. | |
| Mar. 15-31 | $1.12 | $0.46 |
| April | 1.26 | 0.54 |
| [A] Calculated as Bleach at $3.80 per 100 pounds and aqua ammonia (26° Bé.) at51⁄2 cents per pound. | ||
The results were so satisfactory that the author recommended the adoption of the process on the main chlorinating plant but owing to conditions imposed by the Provincial Board of Health the process was not operated until February, 1917.
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 box G from which the mixture is carried by the water injector J through one of duplicate feed pipes and discharged into the suction well through a perforated pipe.
As tank B was previously used as a bleach storage tank, the change from hypochlorite alone to chloramine necessitated very little expense.