USE OF COPPER SULPHATE IN DESTROYING WATER ORGANISMS
Fish are Rarely Killed by the Use of This Chemical—Experience of the New fork City Water Department
IN the following short article Dr. Hale gives opinions on two important subjects, the question as to the possibility of destruction of fish in reservoirs by the use of copper sulphate and the methods used in destroying the troublesome growths that infest water supplies:
Fish are rarely killed by poisoning, due to copper sulphate. Also it is very rarely that organisms killed by treatment reduce the oxygen sufficiently to affect the fish life. Several instances have been known in which fish have been killed because of the absence of oxygen, but this has been occasioned usually by sudden over-turning of the water as described in an instance occurring in New Jersey, as has occurred in Kissena Lake, Queens Borough, New York City, and in Silver Lake reservoir. Borough of Richmond, New York City. When organisms are allowed to increase to a large quantity before treatment with copper sulphate, the dead organisms occasionally accumulate upon the gills of the fish and smother them. This we have demonstrated by examination, finding the heart still beating, which would indicate the absence of any poisoning action by the copper sulphate. A brown coating on the gills was very evident.
New York’s Experience with Synura
As regards our experience in New York City during the Synura trouble of the last few years, we have developed the use of chlorine as an aid to control of microscopic organisms. Our experience with Synura has extended to practically all of our water supplies and we have reached the following conclusions with regard to dosage: A dosage of 0.3 ppm., maintaining an excess of 0.1 ppm., will destroy and render odorless and tasteless approximately 50 units of Synura. a dosage of 0.5 ppm. to 0.7 ppm. will handle 100 units, and a dosage oi over 0.7 ppm. is necessary for 200 units. A growth of Uroglena to the number of 2.000 units has been killed and the resulting taste destroyed by a dosage of 0.5 ppm. chlorine, and 6,000 units of Uroglena have been killed by the same dosage, but the taste not destroyed. However, the taste was not noticeable after a flow of some 10 or 15 miles in the aqueduct. A growth of 500 units of Dinobryon have been destroyed and deodorized by 0.5 ppm. chlorine. Previous to the use of the higher dosage of chlorine with maintenance of 0.1 excess on the Croton supply at Dunwoodie, the total number of organisms in Jerome Park reservoir through which this supply passes was greater in the effluent water than in the influent. During the last two years, with a dosage of 0.44 ppm. chlorine in 1922. and 0.50 in 1923, the number of organisms have been reduced in the effluent water of Jerome Park reservoir to about three-quarters the number present in the influent water. This reduction has been apparent throughout the year with the exception of a few weeks when independent growths have occurred in the reservoir. The reduction has occurred with such organisms as Asterionella, Anabaena. Aphanizomenon, Coelosphaerium, Tabellaria, Melosira, etc.
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Trouple with Other Organisms
We have also had trouble with a new organism causing taste and odor for the first time in our experience. Dictyosphaerium has produced a grassy odor with pungent character like Nasturtium, similar in character to that produced by Anabaena and Aphanizomenon. The quantities causing trouble have been about the same as of the latter two organisms, i. e., first noticeable in the laboratory between 500 and 1,000 units, possible complaints between 1,000 and 2.000 units, and general complaint above that figure. Chlorination affected about 700 units so as to produce a characteristic odor, although this disappeared after six hours flow through the aqueduct.
In the control of Synura. which has been almost constantly present in Ashokan reservoir during the last two years, I would call attention to the extent to which we have employed continuous copper sulphate treatment of the water in the aqueduct as it flows front Ashokan to Kensieo reservoir. The chemical, as has been previously reported, has been dryfed to the water in the aqueduct. This treatment has taken place for 154 days, or approximately 5 months, in 1922. and for 184 days, or approximately 6 months, in 1923, and about two-thirds of the copper sulphate used by the department for control of microscopic organism has been fed in this manner. The total amount of copper sulphate used altogether in 1922 was 72 tons, and in 1923 60 tons. This copper sulphate however is all precipitated and sedimented in the reservoirs, tests for copper in the water of the distribution system having been negative, even though 1 1/2 gallons of water have been evaporated to dryness and tested by the most delicate methods known.
Saving Effected by Use of Copper Sulphate
I would also call attention to another experience. During the second winter that Synura was present, 20 tons of copper sulphate were used to entirely eliminate the Synura front Kensieo reservoir. Dosage was one pound per million gallons capacity. This treatment was finished before ice formed. Whereas, the previous winter the absorption of chlorine had been so high that the maximum dosage of chlorine was required in the effluent water, of approximately 0.4 to 0.5 ppm., after the clean up of Kensieo reservoir by copper sulphate in the winter of 1922, the requirements of chlorine were at a minimum, approximately 0.2 ppm. The result was a saving of chlorine for the year 1923, of 0.05 ppm., equivalent to 0.4 lbs. per million gallons, 160 lbs. per day, or approximately 30 tons for the year, with a saving in cost of $3,500. This more than paid for the copper sulphate used by about 50 per cent.
(Excerpt from a discussion at a meeting of the New York Section, American Water Works Association, in New York City.)