Hints from the Health Department. Leaflet from the archive of the Society of Medical Officers of Health. Credit: Wellcome Collection, London
[Report of the Medical Officer of Health for London County Council]
|During the period when the beds were filled||During the period of the whole experiment.|
|once per day.||twice per day.|
|The combined coarse and fine coke-beds.||64.9||61.5||63.2|
|The combined coarse and fine ragstone-beds||46.8||51.6||49.1|
The effluents from the primary beds killed gold and silver fish in a few hours, but those
from the secondary beds sustained fish life as readily as fresh tap-water does.
The capacity of the coarse beds was measured after they had been in use for about one
week, and again after they had been in use for 24 weeks. The loss in capacity during the 23 weeks
stated as a percentage of the total capacity of each bed, was as follows—•
Coarse coke-bed 6.4 per cent.
Coarse ragstone-bed 5.2 „
The fine beds suffered no loss in capacity throughout the experiments.
The experiments with these beds indicated—
i. That coke produced better results than Kentish ragstone when used in a bacteria-
bed, although the latter produced more nitrates.
ii. That bacteria-beds rapidly decrease in capacity when they are dealing with
iii. That when bacterial-beds have attained their full purifying power, they can deal
as efficiently with two fillings of sewage per day as with one.
iv. That secondary beds effect a considerable additional purification, and dealing as
they do with clear liquid, free from suspended matter, they do not decreme in
(c) The Coarse and Fine Coke-beds, nine feet nine inches in depth, dealing with Crude
Unsettled Sewage at the Northern Outfall Works. (Series II.)
These experiments were undertaken with the object of ascertaining the effect, if any, of
increased depth of bed on the purification effected.
The iron tanks used in the last experiment, were deepened by bolting on four feet of iron
superstructure, the joints being made watertight. The tanks were filled with coke to a depth oi
9 feet 9 inches, and these beds were worked in two series as follows—
Series A consisted of—
(1) A primary coarse bed (A).
(2) A secondary coarse bed (A 1).
Series B consisted of—
(1) A primary coarse bed (B).
(2) A secondary fine bed (B 1).
The average percentage purification effected, as measured by the relative amounts of oxygen absorbed from permanganate by the dissolved putrescible matter in the crude sewage and in the final effluents, is set forth in the following table—
|During the period when the beds received|
|three fillings per week. About two months.||six fillings per week. About three months.||twelve fillings per week. About five months.|
|Primary coarse bed A||43.9||43.6||48.9|
|Primary coarse bed B||43.5||43.9||50.2|
|The combined beds of Series A||62.3||62.8||64.2|
|,, ,, ,, B||79.1||77.0||72.2|
The alteration in the capacities of the various beds during the experiments is indicated by
the following records of the measurements made at the beginning of the experiments and after
the beds had been in use for about eight months, on the 7th February, 1900. A third set of
measurements is added; these were made after the publication of the Third Report.. The
capacities are stated as percentages of the cubical capacity of the total space occupied by the
bed, assuming the coke to be absent.