HOW NEW YORK PREVENTS TASTES DUE TO SYNURA
Method Adopted by the Department of Water Supply in Treating the Catskill System to Remove Disagreable Tastes Due to Presence of Pest
THE follwing short article by Mr. Brush, giving an account of the experience of the New York department of water supply, gas and electricity with synura, is particularly timely as supplementing the paper in last week’s issue by Mr. Garratt on the experiments of the Hartford, Conn., water department along the same lines. In transmitting the article to FIRE AND WATER ENGINEERING Mr. Brush says: “I have set forth the story in a good deal of detail, as it seemed to me that it has much more than local interest, confirming the correctness of the excess chlorine treatment as a preventive of taste in chlorinated waters, where such taste was due to small quantities of microscopic organisms.
About a year ago the Catskill supply was rendered objectionable in taste to the consumer due to_ the presence of a small quantity of synura, generally from 50 to 100 units per c. c., the characteristic cucumber taste being imparted to the wate following the chlorination of the supply at the Kensico reservoir The experiments carried on at that time showed that the synura could be destroyed and the taste removed by either a combination of copper sulphate treatment by chlorination or by a material increase in the dose of chlorine, in general increasing the residual free chlorine to approximately 0.2 p. p. m. by weight. The number of synura that caused the disagreeable cucumber taste was so small there was a possibility of their presence not being detected in the samples examined microscopically, and theretore a part ot the regular procedure in connection with the test of the water supply has been the tasting by the laboratory force of the Kensico water, using a sample taken immediately after chlorination, and also having one of the attendants twice daily taste the water coming through the Hillview reservoir uptake from Kensico reservoir, to determine whether there was any unusual flavor in the water.
All the Catskill supply passes through the aqueduct running from Kensico reservoir to Hillview reservoir, the point of chlorination being immediately adjacent to the Hillview reservoir and the water requiring about six hours to travel the some twelve miles front Kensico reservoir to Hillview reservoir At Hillview reservoir the water may be bypassed through the aqueduct from the intake chamber to the outlet chamber, or may be delivered into the reservoir and taken directly from the reservoir into the outlet chamber. The capacity of the reservoir of 900 m. g. is slightly over twice the daily draft on the Catskill system of about 400 m. g. d The synura have been present for the past year in small numbers in the water in Ashokan reservoir, at times being present in both basins, and at other times being found only in one of the two basins. Their presence in the Kensico reservoir has been noted in very small quantities during the summer At one time during the summer there was a slight cucumber taste. typical of synura, noted by the laboratory from the Kensico chlorinated sample, but no taste was noticeable in the water when it entered Hillview reservoir.
At the time this taste occurred in the summer the dosage at Kensico was about 0.3 p. p. m. with 0.1 p p. m residual free chlorine, this amount of residual free chlorine being the usual amount regularly maintained in both the Croton and the Catskill supplies after treatment. The determination of the excess chlorine is made within about thirty minutes after the sample is taken. The laboratory at Mt Kisco where the Kensico samples are tested reported on Monday. November 13 a strong fishy taste in the Catskill treated sample. On Tuesday the attendant at the Hillview reservoir noticed a slight cucumber taste in the water coming from Kensico reporting it. On Wednesday the taste was greatly intensified, and a cucumber odor was noticeable in the gate chamber at Hillview reservoir. At this time the reservoir was being bypassed and immediately bypassing the reservoir was stopped and the dose of chlorine increased from 0.3 p. p. m. which cave 01 residual free chlorine to about 0.6 p. p. m., with a residual free chlorine of about 0.2 p. p. m. As the water entering Hillview reservoir that had received the higher dose of chlorine still gave a slight taste of cucumber the does of chlorine was increased to 0.7 p. p. m. This dose had been shown to be successful in removing the taste of the synura last winter. Even with the 0.7 part of chlorine there was a very slight cucumber taste to the water entering the reservoir, and a noticeable chlorine taste. Both of those had disappeared by the time the water reached the effluent chamber, which represented the effect of the one to two days storage in the Hillview reservoir. Those consumers of Catskill water who received a supply direct from the Catskill tunnel in the borough of the Bronx, which is the area lying nearest to the Hillview reservoir, noticed the cucumber taste in the water on Wednesday and Thursday, but by Friday it had disappeared. The department received no complaint, however, and it was only known through employes of the department reporting the taste. The Catskill supply as delivered to Brooklyn was free from such taste, as far as could be determined by those who receive this supply, after a relatively short travel through the distribution mains of that borough.
The microscopic examination of the water did not disclose the presence of synura until Friday, November 17, nearly a week after it was first tasted, 100 units then being found to be present. On Friday and Saturday. November 17 and 18. respectively, Kensico reservoir was treated with copper sulphate to destroy the synura and other microscopic organisms in the reservoir, Uroglena being one of those present, from which a taste might be imparted to the supply. The copper sulphate is applied so that the water from the reservoir that is treated will not reach the intake for probably two or three days after the copper is applied. It is expected, as a result of this copper treatment that the application of an increased dose of chlorine to the water supply can lie stopped. The recent experience with synura is given in detail for three reasons:
- It has again been shown that disagreeable tastes may follow the chlorination of water containing such small amounts of synura that their presence is not shown by microscopic examination.
- That the excess chlorine treatment developed in connection with the Catskill supply a year ago has effectively prevented the disagreeable synura taste being present in the Catskill water as delivered to the consumer.
- The additional dosage of chlorine, while giving a taste of chlorine after the water travelled for six hours through the aqueduct was entirely dissipated by the relatively short storage of the water in the distribution reservoir.
While it is not noted in the experience previously given, tests nevertheless showed that it is possible that the residual free chlorine may have reached as high as 0.4 p. p. m. and still this amount of chlorine did not impart any taste to the water after passing through the reservoir.
This method of excess chlorine treatment has also been demonstrated to be effective in the Croton water during last spring, when synura and uroglena were present in small quantities.