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with the exception of Sundays when it rested entirely, and of Saturdays when it received one filling
only.
On June 23rd it was decided to give the coke-bed complete rest for a fortnight, since both the bed
and the effluent were becoming foul. There is little doubt that this foulness arose from the fact that
undue work was thrown upon the bed before it had become "matured." The impurities, therefore,
gradually collected in the coke, since they could not be dealt with by the bacteria, which were not
established in the bed at that period in sufficient number. Ultimately the impurities accumulated in
the bed in such quantity as to render the purification insufficient. There is no doubt that this
state is unlikely to arise in a coke-bed which is not overworked in its immature state.
After the fortnight's rest, the bed was filled only once a day, and effected satisfactory
purification of the crude sewage continuously until November 7th, 1898.
During this period the coke-bed was stopped on certain public holidays and for the repair of the
sewage pump, these stoppages amounting in all to 12 days.
On November 8th, 1898, a commencement was made with two fillings a day, and this was maintained
until February 18th, 1899. The results obtained by two fillings have been perfectly satisfactory.
Up to the present date (February 18th) this coke-bed has been charged with raw sewage 339 times,
and the one layer of coke has dealt with about 847,500 gallons of the raw sewage. The coke-bed has,
therefore, removed from the sewage an amount of solid matter which in the dry condition would weigh
32.4 cwt. This solid matter would represent 20.25 tons of sludge, containing 92 per cent. of moisture;
or taking one ton of sludge as occupying 33 cubic feet, the sludge removed by the coke-bed would fill
the empty coke-bed tank to a depth of 2 feet 9 inches.
The Primary Coke-had for the first stage of Double Treatment.
This coke-bed was charged with coke somewhat slowly owing to the difficulty of procuring coke at
the time when the bed was being constructed. From July 12th to September 1st, the period over
which the introduction of coke extended, the coke-bed was, however, frequently charged with crude
sewage, in order to carry on the ''maturing" process during the lengthened process of construction.
The bed started its regular work in the treatment of crude sewage on September 1st, and from
that date until February 18th it has been tilled 213 times.
This coke-bed, which is six feet in depth, is now producing an effluent in which the purification is
practically the same as that effected by the single coke-bed, which is four feet in depth. It may therefore
be inferred that the purification effected by the bed will not be diminished when its depth
is still further augmented.
The Secondary Coke-bed for the second stage of Double Treatment.
The Secondary Coke-bed was "matured" by treatment with sewage during its construction. It
received its first charge of raw sewage on June 21st, and was worked until August 31st as a single
crude sewage coke-bed. During that period it received 60 fillings of raw sewage, and 244,200
gallons of sewage in all were passed through it. It removed during this period an amount of solid
matter from the sewage, which in the dry condition would weigh 935 cwt. This solid matter would
be equivalent to 5.85 tons of sludge containing 92 per cent, of moisture.
Since September 1st this coke-bed has been used as a secondary bed, and has received
the effluent from the primary coke-bed and subjected it to. a second process of treatment. Since the
primary effluent is usually clear, this secondary bed has been spared the process of removal
of solid suspended matter and has exerted all its purifying action upon the dissolved oxidisable
matter. Since the secondary coke-bed has been in operation the use of the small laboratory vessel
has been stopped.
4.—Experimental proof of the aeration of the coke-beds.
In order to ascertain whether the surface of the fragments of coke became fully aerated
throughout the bed between the successive chargings with raw sewage, two vertical pipes were
inserted into the bed reaching to the depths of 6 feet and 13 feet respectively. After the sewage had
flowed away from the bed samples of air were drawn off from the interspaces between the coke
fragments at stated intervals, and the percentage proportions of oxygen and carbonic acid were
estimated in this air. The results, which in the case of the 13-foot depth were only of a preliminary
character, indicated that even after the air had been in contact with the lower strata of the coke for
seventy hours, the air still contained an average of about 75 per cent, of its original oxygen, and the
average amount of carbonic acid did not exceed 3 per cent., as is indicated by the tabulated results
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