| 2CaOCl2 | = CaCl2 + Ca(OCl)2 | and Ca(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 of the pipes connecting the pumping station (point of chlorination) and the distribution mains provides a contact period of one and a quarter hours but even better results would be obtained if the contact period were increased.
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[5]: four days after the initiation of the chloramine treatment the aftergrowth count on gelatine of the Capitol Hill reservoir dropped from 15,000 to 10 per c.cm. The hypochlorite dosage was cut from 0.26-0.13 p.p.m. of available chlorine and 0.065 p.p.m. of ammonia added.
Economics of the Chloramine Process. The chloramine process was introduced at Ottawa for the purpose of obtaining relief from the effect of the high price of bleach caused by the cessation of imports from Europe in 1915. The results obtained with the experimental plant indicated that, calculated on the prices current at the beginning of 1917, appreciable economies could be made. Although the reduction in the chlorine dosage has not been as great as was anticipated, due to the restrictions previously mentioned, the cost of sterilising chemicals in 1917 was $3,200 less than the cost of straight hypochlorite treatment.
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 the price of ammonia will probably gradually decline as the plants for fixation of atmospheric nitrogen commence operations and reduce the demand for the ammonia produced from ammoniacal gas liquor.