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II.—EXPERIMENTAL BACTERIAL TREATMENT OF CRUDE SEWAGE AT
THE NORTHERN OUTFALL WORKS (BARKING).
I.—PRIMARY AND SECONDARY TREATMENT IN BEDS OF KENTISH RAGSTONE
AND COKE, 5 FEET IN DEPTH.
For the purpose of these experiments four galvanised iron tanks, 4 feet square by 6 feet
in depth were erected on some waste land at the liming station and were filled with material to a
depth of 5 feet, and were so arranged that the effluent from the two primary tanks should drain completely
into the two corresponding secondary tanks. The crude sewage supplied to the beds was
obtained from a large pipe conveying sewage to the overhead lime tank, and was raised by means of a
portable auxiliary pump. This pump was stopped for a few days periodically for cleaning, and on
these occasions the bacteria beds could not be filled.
On the 21st of July, 1898, it was suggested that in series I. the first tank should contain
a coarse bed of large coke and should discharge its effluent into a fine bed of small coke. Series
II. should consist of a coarse bed of large pieces of Kentish ragstone, and should discharge its
effluent into a fine bed of the same material. It seemed desirable to experiment with the Kentish
ragstone, on account of its great durability and its acid-neutralising power.
It seemed probable that the calcium carbonate in the ragstone would furnish a base for
the neutralisation of the nitric acid formed by the bacterial action.
The material employed in the two coarse primary beds of coke and ragstone was of such a
size that the pieces would pass a 4-inch mesh and be rejected by a ½-inch mesh. The material in
the two fine beds was of such a size that it would pass a ½-inch mesh and be rejected by a 1/16th-inch
mesh.
The procedure was as follows—
The two coarse beds were filled with crude sewage simultaneously and as quickly as
possible to a level with the top of the solid material; the beds were allowed to remain full for
two hours, and were then drained into the fine beds. These remained full for two hours, and
were then drained off. During the outflow of the effluent from each bed it was sampled
every few minutes. These samples were mixed, and the average liquid thus obtained was subjected
to analysis. The crude sewage with which the primary beds were filled was sampled and
examined in a similar manner.
The beds were first filled with crude sewage on the 22nd of September, 1898, and their
capacity was ascertained a week later by the careful measurement of the effluent while they were
being emptied. On the 29th September the capacity of the coarse beds was as follows—
Description of bed.
Capacity of each
bed in gallons.
Percentage of whole
volume of bed.
Corresponding capacity per
acre of bed.
Ragstone 200 40.0 544,500
Coke 250 50.0 680,625
The beds received one filling daily until January 11th, 1899, and then two fillings daily
until the experiments were stopped. Before starting the two daily fillings the capacity of the
beds was ascertained to be as follows—
Description of bed.
Capacity of each
bed in gallons.
Percentage of whole
volume of bed.
Corresponding capacity per
acre of bed.
Ragstone 183 36.6 498,217
Coke 195 39.0 530,887
Two daily fillings would represent a million gallons per acre per day.

Complete saturation with oxygen was taken as 100.
The effluent obtained from the primary beds did not show as high a purification as had
been expected; it is probable that the large size of the material had the effect of presenting
an insufficient surface of contact with the sewage; the putrescible matter in the sewage was not
therefore thoroughly dealt with by the bacteria.