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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iii- The bed received sediuented sewage between May 3rd and July 28th, 1900,
and it was filled generally four times a day.
The process of sedimentation consisted in allowing the crude sewage to flow through
a tank on its way to the coke-bed. It entered this tank through a broad pipe, which
descended nearly to the bottom, and was drawn off by a pipe, the end of which was
immersed below the surface of the liquid. The passage through the tank occupied about
five hours.
The capacity of the coke-bed on June l6th, 1900, was 6,000 gallons, after resting
from April, 5th to May 2nd, 1900, and on October 8th, 1900, it was 0,290 gallons, after
resting from 28th July, 1900.
In consequence of the bed having been altered before this last measurement was
taken, its capacity was calculated on a measurement of only the lower 6 feet of the bed.
The process of filling this bed occupied from 20 to 25 minutes; it was allowed to remain
full for two hours, and the process of emptying extended over from one hour to one hour and a
half. The number of hours during which the bed rested between the successive emptyings and
fillings varied according to the number of times it was filled during the 24 hours. When the
number of fillings per day did not exceed two, the fillings were made during the daytime, but
when the number of fillings exceeded two, they were distributed evenly over the whole 24 hours.
The following table indicates the average amount of purification which was effected by this
bed during the different periods referred to above. Two purification averages have been calculated
: one from the relative quantities of oxygen absorbed by the crude sewage and by the cokebed
effluent, from potassium permanganate by the total putrescible matter (both suspended and
dissolved), and the other from the oxygen absorbed by the dissolved putrescible matter only—
removal of total
removal of dissolved
I. From February 27th to October 9th, 1899
II. From October 10th, 1899, to April 5th, 1900
III. From May 2nd. 1900, to July 28th, 1900
From February 27th, 1899, to July 28th, 1900
Throughout the period during which the coke-bed was filled four times a day, the effluent
from it was clear and free from odour.

While these experiments were in progress frequent analyses were made of the air in the interstices of the empty coke-bed at depths of 6 feet and 13 feet; the following results were obtained—

Six-foot depth.Thirteen-foot depth.
Number of hours since sewage drained off.Percentage of oxygen in the air from the bed.Percentage of carbonic acid in the air from the bed.Number of hours since sewage drained off.Percentage of oxygen in the air from the bed.Percentage of carbonic acid in the air from the bed.

The results prove that, even in the case of the deep 13-foot bed, the air at the lower part
of the bed was not seriously deficient in oxygen.
On June 20th, 1900, the depth of the sludge in the brick tank from which the 13-foot
coke-bed was filled was between 27/8 inches at the inlet to the tank, to 71/8 inches at the further
end of the tank, and 4f inches at the outlet from the tank to the coke-bed. This outlet was at
about two-thirds of the distance from the inlet to the further end. The depth of the sludge in
this tank at various points is indicated in the accompanying plan.
The average percentage of organic matter in the dried sludge from the tank was 35.8.
No permanent scum was formed on the liquid in the settling tank, and it was found that
the effect produced by the bacteria in the settling tank was independent of the presence or absence
of scum.