The design, construction and maintenance of sewage disposal works ; being a practical guide to modern methods of sewage purification / by Hugh P. Raikes.

  • Raikes, Hugh Percival.
Date:
1908
Catalogue details

Licence: In copyright

Credit: The design, construction and maintenance of sewage disposal works ; being a practical guide to modern methods of sewage purification / by Hugh P. Raikes. 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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    pie ting his records once a week, but no one day is omitted from the sampling schedule twice in succession, the system adopted being as follows :— The samples are collected at half-hour intervals and placed in 4-oz. bottles, which are completely filled, tightly stop- pered, and placed at once in an ice chest kept at a tempera- ture of 10 deg. C. About 32 hours after the collection of the first sample the contents of the 48 small bottles are mixed in equal proportions in a large bottle and the chemical analysis is then immediately proceeded with, while the samples for bacterial analysis are not stored for more than about an hour. Although the oxygen absorption test is undoubtedly very valuable for the purpose of measuring the organic matter present, it is important to observe that this does not neces- sarily show whether a sample is likely to undergo so-called secondary decomposition or not, as this must largely depend on the amount of nitrate and dissolved oxygen present and whether this is sufficient to oxidise the organic matter, so that, in order to make this test complete, a determination should be made of tlie dissolved oxygen and nitrate* present both before and after the period of incuba- tion, and any change in the appearance of the sample should be carefully noted. When the dissolved oxygen and nitrate are ignored it seems clear that with two samples containing an equal amount of impurity, as shown by the oxygen absorbed test, one may undergo rapid putrefaction owing to the *The determination of nitrate after incubation is not neces- sary except for research purposes, because if a filtered effluent contains at least .4 grain per gallon, or .57 part per 100,000 of nitrate in terms of ammonia before incubation, it is very unlikely to putrefy unless there is a large amount of suspended organic matter present.