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45
volume of sewage received at the works in wet or stormy weather is
greatly increased, over 45,000,000 gallons being recorded for the
month of December, 1914, or an average of about 1,500,000 gallons
per day, and each year the difficulty of proper disposal is intensified,
also a very large amount of ground water enters the sewers.
Owing to the rapid growth of the population it has been found
necessary to considerably increase the means of sewage disposal.
In the Annual Report for 1913 a new scheme for extensions and
additions to the purification plant was briefly touched upon. This
scheme has been completed and brought into use. The method of
treatment is as follows:—
The sewage after reception in the sump is lifted by means of a
12in. Tangye centrifugal pump, and 8in. centrifugal pump and two
three-throw plunger pumps, of 12m. and 10in. diameters respectively,
into the delivery chamber situated immediately on the north
side of the Engine House, from whence it flows to two Detritus
tanks each about 15ft. square by 15ft. deep. The sludge
accumulating in these tanks is lifted by the head of sewage in the
tanks to such a level as will permit it to flow by gravitation to the
sludge beds. The sewage passes over a weir from the Detritus
tanks into three concrete sedimentation tanks, two 108ft. by 31ft. by
8ft. deep, and the third 93ft. by 31ft. by 8ft. deep. The
sedimentation tanks are so arranged that they may be used either in
series or in parallel, on the intermittent principle. They may be
sludged by means of channels which empty into a gin. drain leading
to an ejector chamber which will be described hereafter. At the
outlet end of the tanks is placed a chamber, constructed so as to
pass the tank effluent up to three times the dry weather flow on to
the filters, the excess over this amount passing to the storm-water
area and storm filters.
Percolating Filters.
These are six in number, each 80ft. in diameter, fitted with
revolving distributors, five being new, the one constructed in 1911
still giving excellent results. The filtering material is of clinker
suitably graded, the average depth being about 4ft. 9in. The
surrounding walls of the filters are of large lump clinker. Each
filter rests on a concrete base and has also a false floor composed of
stoneware tiles of special design for drainage and aeration. The