London's Pulse: Medical Officer of Health reports 1848-1972

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London County Council 1900

[Report of the Medical Officer of Health for London County Council]

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10
to it, and of the effluent obtained from it, up to December, 1899, were published in the Third
Report on the Bacterial Treatment of Crude Sewage, on pp. 13 and 14 and pp. 25 to 34. The
following particulars and the table No. 1 on pp. 28 and 29 bring the publication of the information
respecting the bed up to the end of December, 1901.
Immediately prior to April, 1898, the bed had been increased in depth from 3 feet to
6 feet, by the addition of sifted coke fragments about the size of walnuts, but it was discovered
some time afterwards, that the lower 3 feet of the bed, which consisted of unsifted " fine pan
breeze," had become very much consolidated, and that the effluent drained away from it very
slowly; the effective portion of the bed was, therefore, the upper 3 feet which consisted of sifted
coke.
The average quantity of effluent dealt with by the bed at each filling, during the years
1900-1 was 344,909 gallons, whereas during the period from May 12th, 1898, to December 30th,
1899, the average quantity per filling was 519,367 gallons. This difference is probably due to—
i. The continued consolidation of the lower three feet of the material composing the
bed.
ii. The difference in the average number of hours during which the bed was allowed to
drain throughout the two periods. From May 12th, 1898, to December 30th, 1899,
the average number of fillings per day was 1.05, whereas during the two years
1900-1, the average number of fillings per day was 1.55.
The time for filling the bed was generally so selected that the effluent could be discharged
into the river at low water; this was done in order to avoid the expense of pumping. Under
this arrangement two fillings per 24 hours were usually made. The time-table for the bed was
as follows—
Time occupied in filling 1½ hours
Time occupied in standing full (contact period) 2 „
Time occupied in emptying 2½ „
Time occupied in standing empty (aeration period) 6 „
The high efficiency of the bed has been very well maintained, but it should be borne in
mind that this bed has been dealing only with the effluent from chemically precipitated sewage
and has therefore had a much smaller amount of purification to effect than the beds which
have dealt with crude sewage.
The average purification of the crude sewage which has been effected during the past two
years by the bacterial action of the bed in conjunction with the previous chemical treatment and
sedimentation was 91.2 per cent., as measured by the relative quantities of oxygen absorbed from
permanganate by the total putrescible matter (both suspended and dissolved) in the crude sewage
and in the coke-bed effluent. The average purification effected on the "chemical" effluent by the
coke-bed treatment, when estimated in a similar manner, was 85.6 per cent., whereas it was
only 81.8 per cent. during previous periods when these estimations were made, namely, from
November 8th, 1898, to January 21st, 1899, and from October 18th to December 31st, 1899.
The treatment of effluent from the chemically treated and sedimented sewage is being
continued in this bed.
(b) The Double Bacteria-beds of Kentish Ragstone and of Coke, dealing with Crude
Unsettled Sewage at the Northern Outfall Works. (Series I.)
These experiments were undertaken in order to determine whether a body consisting
largely of carbonate of lime and possessed of neutralising power on acids, was more favourable
to bacterial purification than a neutral substance like coke.
The treatment of crude unsettled sewage in the bacteria-beds of Kentish ragstone and
of coke, was carried out during the period from September 22nd, 1898, to April 15th, 1899. The
full details of the experiments were published in the Third Report on the Bacterial Treatment
of Crude Sewage on pp. 7 to 10 and on pp. 17 to 19.
The material of the beds was contained in galvanised iron tanks four feet square and six
feet deep ; these were filled with the material to a depth of five feet. The coke-beds consisted
of a primary bed composed of coarse fragments of coke, and of a secondary bed composed of fine
fragments of coke; these two were known as the coarse and fine coke-beds respectively. The
ragstone-beds consisted of a primary bed composed of coarse fragments of Kentish ragstone, and of
a secondary bed composed of fine fragments of Kentish ragstone; they were known as the coarse
and fine ragstone-beds respectively. The material of both the coarse beds was of such a size as
would pass a. 4-inch mesh and be rejected by a ½-inch mesh; the material of the fine beds was of
such a size as would pass a ½-inch mesh and be rejected by a l-16th inch mesh.
The method adopted in dealing with these beds, was to fill both of the primary beds as
quickly as possible with crude sewage which had passed through a screen of ½-inch mesh.
The beds were allowed to remain full for two hours, and the effluent from each of the primary
beds was then allowed to flow into the corresponding fine beds. The fine or secondary beds
were allowed to remain full for two hours, and the final effluent was then allowed to flow out.
Each bed received one filling in the 24 hours for about the first four months of the
time during which tbe experiments lasted, and two filling's for about the last three months.
The average percentage purification effected by the beds, as measured by the relative
quantities of oxygen absorbed from permanganate by the crude sewage and by the effluents
from the various beds, is set forth in the following table—