Chlorination does not change the physical appearance of water; it does not reduce or increase the turbidity nor does it decrease the colour in an appreciable degree. The chemical composition is also practically unaltered. When bleach is used there is a proportionate increase in the hardness but the amount is usually trifling and is without significance. During 1916 when the Ottawa supply was entirely treated with bleach at the rate of 2.7 parts per million (0.92 p.p.m. of available chlorine) the average increase in the total hardness as determined by the soap method was 2.5 parts per million. When chlorine is added to prefiltered water, as an adjunct to filtration, an increase in the number of gallons filtered per run has been noted at some plants. This increase is not so great with rapid as with slow sand filters but in some instances it has led to appreciable economies. Clark and De Gage The effect of hypochlorite on the reduction of algÆ growths on slow sand filters was first noticed by Houston during the treatment of the Lincoln supply in 1905. Two open service reservoirs were fed with treated water and were themselves dosed from time to time. “Previous to 1905 they developed seasonally most abundant growths, but during the hypochlorite treatment it was noticed that they remained bright, clear, and remarkably free from growths” (Houston Ellms, In 1916, during the treatment of the London Supply with bleach (dosage 0.5 p.p.m. of available chlorine), Houston made further observations on this point. The Thames water, taken at Staines, had previously been stored for considerable periods in reservoirs, but this necessitated lifting the water by pumps which consumed large quantities of coal that were urgently needed for national purposes. As a war measure,
A portion of this reduction can probably be attributed to the elimination of storage. Chlorination, by decreasing the load on filter beds, has enabled the rate of filtration to be increased in some cases. This increased capacity, which would otherwise have necessitated additional filter units, has been obtained without any further capital outlay. At Pittsburg (Johnson |
Average Typhoid Death Rate Per 100,000 Population | ||||||
City. | Commenced Chlorination. | Before Using. | After Using. | Percentage Reduction. | ||
Period. | Rate. | Period. | Rate. | |||
Baltimore | June 1911 | 1900-10 | 35.2 | 1912-15 | 22.2 | 36 |
Cleveland | Sept. 1911 | 1900-10 | 35.5 | 1912-16 | 8.2 | 77 |
Des Moines | Dec. 1910 | 1905-10 | 22.7 | 1911-13 | 13.4 | 41 |
Erie | Mar. 1911 | 1906-10 | 50.6 | 1912-14 | 15.0 | 70 |
Evanston, Ill. | Dec. 1911 | 1908-11 | 29.0 | 1912-13 | 14.5 | 50 |
Jersey City | Sept. 1908 | 1900-17 | 18.7 | 1909-16 | 8.4 | 55 |
Kansas City, Mo. | Jan. 1911 | 1900-10 | 42.5 | 1911-16 | 14.2 | 66 |
Omaha, Neb. | May 1910 | 1900-09 | 22.5 | 1911-16 | 10.6 | 53 |
Trenton | Dec. 1911 | 1907-11 | 46.0 | 1911-14 | 28.7 | 35 |
Montreal | Feb. 1910 | 1906-10 | 40.0 | 1911-16 | 25.0 | 37 |
Toronto | Apr. 1911 | 1906-10 | 31.2 | 1912-16 | 7.8 | 75 |
Ottawa | Sept. 1912 | 1906-10 | 34.0 | 1913-17 | 17.0 | 50 |
The figures given in this table show the effect of chlorination only; no other form of purification was used during the periods given, except at Toronto where a portion of the supply has been subjected to filtration.
It will be seen that since chlorination was adopted the typhoid death rates have been reduced by approximately 50 per cent and that the averages for the period after treatment are almost invariably less than 20 per 100,000, a figure that a few years ago was regarded as satisfactory. The average death rate for the last available year is 11 per 100,000, a result that is even more satisfactory and exceeds the anticipations of the most optimistic of sanitarians.
A portion of the reduction in the typhoid rates is no doubt due to improvements in general sanitary conditions but the reduction is much greater than can be accounted for in that
DIAGRAM X
TYPHOID IN PHILADELPHIA
During the years 1909-10-11, when practically the whole of the city supply was filtered, the average typhoid death rate was 18, but when the water was also chlorinated, in 1914-15-16, the rate was only 7, a reduction of 61 per cent.
The figures in Table XXXII show that the Torresdale filters, during 1915-16 were unable to adequately purify the water and that chlorination was necessary.
TABLE XXXII.—CHLORINATION OF FILTER EFFLUENTS
(Torresdale) | ||||||||||||
Oxygen Con- sumed. | Colour. | Tur- bidity. | Bacteria Per Cubic Centimeter. | B. coli communis Per Cent Positive Tests. | Added Chlorine Parts Per Million. | |||||||
Untreated. | Treated. | Untreated. | Treated. | |||||||||
Gela- tine. | Agar. | Gela- tine. | Agar. | 10 c.cms. | 1 c.cm. | 10 c.cms. | 1 c.cm. | |||||
1915 | 1.70 | 12 | 0.6 | 141 | 30 | 28 | 14 | 66 | 24 | 5 | 0.3 | 0.18 |
1916 | 1.90 | 12 | Nil. | 88 | 23 | 38 | 11 | 49 | 16 | 7.4 | 1.9 | 0.15 |
In Diagram XI the typhoid death rates of Columbus, Ohio, and New Orleans are shown to exemplify conditions that have not been improved by chlorination. The endemic condition of typhoid in Columbus was brought to an abrupt conclusion by the installation and operation of the softening and filter plant in September, 1908, and no further reduction followed the introduction of chlorination in December, 1909.
DIAGRAM XI
TYPHOID IN COLUMBUS AND NEW ORLEANS
In New Orleans the typhoid rate decreased on the inception of the new water works system in 1909 and again after the installation of the Carrollton filters in 1912. The product of the filtration plants has always been above suspicion but aftergrowths occasionally developed and the bacterial count then exceeded the United States Treasury standard. To overcome this difficulty, hypochlorite was used in 1915, but, as was anticipated, it had no effect on the typhoid rate. The high rate in New Orleans is largely due to outside cases received for hospital treatment and to other circumstances beyond the control of the water and sewerage department.
One of the most conclusive experiments as to the beneficial effect of chlorination is that reported by Young
DIAGRAM XII
AUTUMNAL INCREASE IN TYPHOID, CHICAGO (Young)
These results demonstrate in a most striking manner the beneficial effect of chlorination. The general conditions, with the exception of the raw water supply, were approximately the same in all four districts. Diagram XIII shows that the raw water supply of District No. 1 was slightly worse than any of the others, 21.8 per cent of the samples from District No. 1 containing B. coli in 1 c.cm. as compared with 21.0 per cent in the most polluted supply of the other districts.
DIAGRAM XIII
B. COLI IN CHICAGO RAW WATER (Young)
The results obtained at Ottawa are also conclusive. Following two epidemics of typhoid fever in 1911 and 1912, caused by breaks in the intake pipe, hypochlorite treatment was commenced and has been in continuous operation until February, 1917, when chloramine treatment was substituted. The dosage has been so regulated as to assure a high degree of purity at all times in the water delivered to the mains and as evidence of this it might be mentioned that the average
DIAGRAM XIV
TYPHOID IN OTTAWA
The diagram shows that there has been a constant reduction in the city typhoid rate since the last severe epidemic with the exception of the year 1915. The high rate of that year was caused by a localised epidemic started by polluted well water and spread by flies from an unsewered area. This outbreak was the cause of about seven deaths registered during that year (population 100,000).
The objection might be raised that if the reduction of the typhoid rate were due to the water treatment, the decline should have been abrupt and not a gradual one. It is probable that there has been practically no water-borne typhoid in
It might be further objected that the reduced typhoid rate is due to a general improvement in the sanitary conditions. If the death rate from causes other than typhoid can be regarded as a measure of the general sanitary conditions it is obvious from the data in Table XXXIII that the improvement in the typhoid rate is immeasurably greater than can be ascribed to that cause.
TABLE XXXIII.—DEATH RATES IN OTTAWA BEFORE AND
AFTER CHLORINATION
Cause. | Rate Per 100,000 | Percentage | ||||
1908-12 | 1913-17 | Reduction | Increase | |||
Total | 14 | .90 | 14 | .78 | 1.2 | ... |
Typhoid, total | 34 | [B] | 17 | 50.0 | ... | |
Typhoid, city | 26 | [B] | 8 | 69.2 | ... | |
Pneumonia | 100 | 107 | ... | 7.0 | ||
Tuberculosis | 133 | 138 | ... | 3.7 | ||
Diarrhoea and Enteritis under 2 years | 139 | 128 | 7.9 | ... | ||
One further objection might be made: that the raw water was not infected during 1913-17 or infected to a smaller extent than during the previous period. Attempts to isolate B. typhosus from the raw water have invariably been futile but their presence in 1914 might be inferred from the fact that during the latter part of the summer of that year an epidemic of typhoid fever occurred at Aylmer, a village that discharges its sewage into the Ottawa River about six miles above the Ottawa intake. Hull, situated on the opposite
In 1916 a liquid chlorine plant was installed in Hull, but in 1917, owing to an accident, it was out of commission for a short period and at least 100 cases of fever developed during the following month. During the same period only two cases were reported in Ottawa and of these one was obviously contracted outside the city.
In view of the preceding facts it must be granted that the improvement in the typhoid rate of Ottawa can be definitely attributed to an improvement in the water supply caused by chlorination.
Since the inception of water chlorination in America in 1908, the merit of the method has been very generally recognized
Chlorination is an invaluable adjunct to other forms of water purification and it is not improbable that, in the future, filter plants will be designed to remove Æsthetic objections at the lowest possible cost and that chlorination will be relied upon for bacterial reduction. Chlorination is the simplest, most economical, and efficient process by which the removal of bacteria can be accomplished and there is no valid reason why it should not be used for that purpose.
The popularity of this process has suffered through the efforts of over zealous enthusiasts who have been unable either to recognize its limitations or to appreciate the fact that a domestic water supply should be something more than a palatable liquid that does not contain pathogenic organisms. Every system of water purification has its limited sphere of utility and chlorination is no exception to the rule.