Report on the deodorisation of metropolitan sewage at the outfalls. With appendix and diagrams. July-October, 1887. / by Henry E. Roscoe.

  • Metropolitan Board of Works.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: Report on the deodorisation of metropolitan sewage at the outfalls. With appendix and diagrams. July-October, 1887. / by Henry E. Roscoe. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    They consisted in the observation, extending over a considerable number of days, of samples of Sewage to which known quantities of the two deodorants had been added. The microscopic examination had for its aim, the determination of the quantity and quality of the growths, as existing in the liquid from time to time. The result of these experiments, most of which were made with Results of carefully sterilised vessels, is (1) that a quantity of bleaching powder, mentswith equal to 9 grains per gallon of Sewage, completely and permanently stops J^der8 the growth of all organisms visible under a high power; (2) that smaller P ™ ^ doses, amounting to, say, 3 grains per gallon, appear for a considerable time to exert an equally powerful effect; (3) that the addition of one grain, though interfering with the growth of certain organisms, seems scarcely to affect the growth of others. Further experiments were made, with the view of ascertaining the action of bleaching powder on the life of higher organisms, such as minnows. It was found that water containing 1 grain per gallon killed such fish in two hours, that containing 3 grains in 1 hour and 4 grains in half an hour. Smaller quantities, down to ^ grain per gallon, also exerted a similar effect, but in a longer time. I am not able to report on the action of still smaller quantities than the above. It is important here to notice that the action of bleaching powder on Peculiar Sewage differs from that of manganate, inasmuch as whilst the latter is bleaching immediately destroyed, the former disappears but slowly, it being possible P0*'^^ to detect it some days after its addition, even when originally present in small quantities only. For detail of experiments on this point, see Appendix B, on page 15. Hence the action of the bleaching powder on the organisms is one lasting over a considerable period of time, and its effect upon the River is greater than it would have been if its action had been instantaneous. With regard to the effect produced upon life by the addition of man- Action of ganate of soda to the Sewage, experiment showed—(1) That neutral per- ™aonSanate mangate of soda added to Sewage in quantities amounting to 9 grains per ^ ^ gallon, whilst it does not prevent, appears to retard the growth of organisms ; (2) That smaller doses from 1 to 3 grains produce no visible effect, and therefore do not act as poisons. In corroboration of this, it was found that minnows will live for some days in fresh water to which 1 grain of permanganate has been added, and smaller doses do not seem to affect the fish in any way, whilst a dose of 2 grains per gallon does not prove fatal until after the lapse of twelve hours. It is to be remembered that 1 grain of permanganate per gallon in fresh water gives a pink solution, showing the presence of the undecomposed salt, whereas if Sewage had been used, the permanganate would have been instantly destroyed, even if added in very much larger quantity. Hence the conclusion is to be drawn, that apart from the consideration Conclusion of cost, manganate is to be preferred as a deodorant to bleaching powder. as to ™ * & r manganate.