View report page

17
2.—SUMMARY OF THE DETAILS, PREVIOUSLY REPORTED, OF THE EXPERIMENTAL
BACTERIAL OR NATURAL TREATMENT OF SEWAGE AT THE
SOUTHERN OUTFALL WORKS (CROSSNESS), WITH SUCH ADDITIONS AS
ARE NECESSARY TO COMPLETE THE INFORMATION RESPECTING
THE EXPERIMENTS.
(a) Treatment of Crude Sewage in a Single Coke-bed and in Primary and Secondary
Coke-beds in Series (Series I.).
I.—The Single Coke-led.
This bed was composed of coke fragments about the size of walnuts, and was made in tank
B by filling it with the coke to a depth of 4 feet. The bed was underdrained by a series of
parallel loose-jointed stoneware drain pipes. Its capacity was 3,000 gallons.
The bed was first charged with crude unsedimented sewage on April 22nd, 1898, and it
continued to receive two fillings per day until June 23rd, 1898, except on Saturdays, when it
received only one filling, and on Sundays, when it rested entirely. After a fortnight's rest,
which was necessitated through overwork in its imperfectly "matured" condition, the bed
received only one filling per day until November 7th, 1898, and from November 8th, 1898, to
February 22nd, 1899, when this series of experiments was concluded, it received two fillings per
day. During the whole period this bed was filled 345 times.
The average amount of purification effected on the crude sewage by this bed, as measured
by the relative quantities of oxygen absorbed from permanganate by the dissolved putrescible
matter in the crude sewage and in the coke-bed effluent, was 51'3 per cent.
II.—The Primary and Secondary Coke-beds worked in series.
The filling in of the primary bed of this series with coke occupied from July 12th to
September 1st, 1898, but during that period it was frequently charged with sewage in order to
avoid any delay in "maturing" it.
The secondary bed was also "matured" by treatment with sewage during its construction,
but after it had been completed on June 21st, 1898, it had to be worked as a single coke-bed until
September 1st, on which date the primary bed was completed. From that date these beds were
worked in series until February 22nd, 1899.
From September 1st, 1898, to February 22nd, 1899, the beds were filled 219 times.
The average amount of purification effected on the crude sewage was 69.2 per cent. when
measured, as in the foregoing case, by the removal of dissolved putrescible matter.
Full information respecting these beds was published in the Second Report on the "Bacterial
Treatment of Crude Sewage."
(b) Treatment or Crude Sewage in a Coke-bed 13 feet deep. (Series II.)
This series of experiments was carried out in order to ascertain whether any variation
in the purifying action was caused by increasing the depth of the coke-bed. With this object
in view, the 6-foot secondary bed of the previous experiment was deepened to 13 feet and waa
then worked as a single bed. The coke fragments of which the bed was composed were of such
a size as would pass a 2-inch mesh and be rejected by a 1-inch mesh.
On February 28th, 1899, the first addition was made to the bed, and its depth was increased
to 7 feet 5 inches, but the full depth of 13 feet was not attained until April 11th, 1899. The
bed was, however, worked while it was being deepened, so as to "mature" the new coke as
rapidly as possible.
The history of the bed may be divided into three periods—
i. The bed received crude, unsettled sewage between February 27th, 1899, and
October 9th, 1899. It was filled once a day from February 27th to March 25th, 1899,
and generally twice a day from March 27th to October 9th, 1899, except on Saturdays,
when it received only one filling, and on Sundays, when it rested entirely.
Its capacity diminished rapidly, as is shown by the following figures—
March 9th, 1899, capacity 7,900 gallons or 41 per cent. of the empty tank
capacity;
June 8th, 1899, capacity 6,670 gallons or 35 per cent. of the empty tank
capacity;
October 10th, 1899, capacity 5,530 gallons or 29 per cent. of the empty tank
capacity.
ii. The bed received very roughly sedimented sewage between October 13th, 1899,
and April 5th, 1900, and was filled twice a day until December 22nd, 1899, and then
three times a day until April 5th, 1900.
In consequence of the loss of capacity suffered by the bed when it was fed with
crude sewage (Period I.), it was decided to allow the crude sewage to settle before it
reached the bed. This was effected by pumping it into a large wooden tank placed on
the top of the bed ; the overflow from this tank passed on tf the bed.
The capacity of the bed on January 12th, 1900, was 6,000 gallons or 32 per cent.
of the empty tank capacity. The bed had been resting from December 22nd, 1899.
[3]