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The solid matter left behind in the tank consisted mainly of particles of sand, woody fibre,
straw, paper and hair. It was generally of the same character as the matter which had been found
adhering to the coke and which had been choking the bed. The result of this rough settlement was
that by January 12th, 1900, the liquid capacity had increased from 28 per cent. to about 33 per cent.
The purification effected by this bed, as judged by the removal of dissolved organic matter was
practically equal to that obtained by the 4-foot bed.
There is no reason why a deep bed should not give as good results as a shallow bed, provided
that it is as well aerated during the periods when it is empty. Experiments have been already
reported which proved that even the bottom of the 13-foot bed was well supplied with oxygen.
The effluent from this deep coke-bed has been usually slightly turbid; it possessed only a faint
earthy smell, and it was capable of supporting fish life.
During the period under notice, from February 27th, 1899, to December 22nd, 1899, the bed
had been filled 338 times.
Taking the average sewage capacity of the bed as being equal to 6,000 gallons, the quantity of
sewage dealt with per acre per day would be, for one filling, 1,089,000 gallons; for two fillings,
2,178,000 gallons; and for three fillings, 3,267,000 gallons.
Experiments are now in progress which will prove whether this bed is capable of treating
sewage satisfactorily at the rate of four fillings a day, the sewage supplied to it having undergone a
short process of preliminary sedimentation.
2.—EXPERIMENT ON THE BACTERIAL TREATMENT OF RAPIDLY SEDIMENTED
CRUDE SEWAGE.
For three weeks at the end of last year the crude sewage arriving at the Southern Outfall was
not mixed with chemicals, and was allowed to flow through one of the large settling channels at an
average rate of 7.4 feet per minute, the usual rate of flow of chemically-treated sewage being about
1.5 feet per minute. A portion of this sedimented sewage was then treated in a small coke-bed in the
intermittent manner already described, the bed being filled thrice daily. Details of the results
obtained are given on page 38.
An average percentage purification from dissolved oxidisable matter was obtained, amounting
to 53 per cent., calculated on the sedimented sewage ; this purification amounted to 58.7 per cent.,
if calculated on the crudge sewage. The capacity of the bed was not reduced during the period of
treatment.
3.—APPENDED REPORT ON THE 13-FOOT COKE BED. FEEDING WITH SEDIMENTED
SEWAGE, AND INCREASED NUMBER OF FILLINGS PER TWENTY-FOUR HOURS.
JANUARY 15tii TO JULY 28th, 1900.
Continuing the history of this bed from the end of the last statement, the bed was not filled
from December 22nd, 1899, to January 15th, 1900, owing to the experiments with the whole of the
Crossness sewage being carried on at the same time.
From January 15 th to April 5th, 1900, the bed was filled intermittently in the way already described,
the sewage overflowing from a large wooden tank placed on the bed so as to allow the heavier and
coarser suspended solids to settle out. The number of fillings per day is shown in the table which
follows this statement.
On April 5th the bed had been filled with crude sewage three times daily for nearly 7 weeks.
The coke was then seriously clogged upon the surface, and although the degree of purification effected
was fully maintained, the bed had to be stopped in order to give time for the collection of matter in
the upper part to become removed by bacterial action. The bed was allowed to stand in air from
April 5th to May 2nd, 1900.
In the meantime, arrangements had been made to subject the sewage to a short, but more
efficient, process of sedimentation in a brick tank of approximately 8,000 gallons capacity before it
passed into the bed. The settled liquid was drawn off from near the surface of this tank, and as soon
as the coke-bed had been filled the residual liquid remained at rest in the settling tank until it was
again filled up with the crude sewage. Probably most of the liquid which passed into the coke-bed
was therefore settled stale sewage, which was displaced by the incoming sewage. Some anaerobic (septic)
bacterial action undoubtedly took place in this settling tank, and there was a considerable evolution of
inflammable gas, but the extent by which the sludge was reduced in amount by this action could not
be ascertained. The conditions of working would not allow of sufficiently accurate measurements of
the incoming sludge being made, and an intermittent septic process of the above kind could hardly be
suitable for dealing with the sewage of London.
Since May 2nd, the coke-bed has been filled intermittently from the brick settling tank three
and four times daily; no clogging of the upper parts of the coke has been noticed, and the liquid
sinks readily into the coke-bed as soon as it is allowed to pass upon the surface. The liquid capacity
of the coke-bed was taken at long intervals, and has been found to be as follows—
January 12th—6,000 gallons.
June 16th—6,000 gallons.
October 8th—6,290 gallons (calculated from a determination of the capacity of half the bed).
The sludge deposited during eight weeks in the settling tank contained on the average 35 per
cent, of organic matter.