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20
SEWAGE WORKS.
The experimental contact filter beds have now got into
working order and are giving an excellent effluent, bright,
clear, without smell, and averaging about one pint per
million of alb. amm. This is by working the beds three
times in the twenty-four hours. It may be possible to work
the beds satisfactorily with four fillings, but that is the
utmost that can be expected. The experimental beds of the
Native Guano Company are worked three times in the
twelve hours, and the results are given in the table.
It must be remembered that these beds are well matured,
having been working now for four or five years. In the
same table the results are shown of distributing the effluent
on to the contact bed by means of a revolving sprinkler.
Sprinklers to serve a filter bed 100ft. sq. would cost about
£175. This is a rough estimate of Mather and Platt
for their open channel revolving sprinkler.
It may be remembered that the experimental filter
with Candy's distributor, became covered on the surface
with sewage fungus. This growth was also found in the
contact bed but was carried away when the penstock was
raised and the filter emptied, and could be seen in the effluent
channel in large pieces.
The experimental sprinkler on the contact bed of the
Native Guano Company shows a considerable excess of
purifying power over the contact beds. The cost of the
revolving sprinkler is not greatly in excess of any other
distributor, and it can be worked with much less cost for
attendance, as the beds could be worked a great part of the
time on the continuous system, it only being necessary to
fill up the beds sufficiently to clear them out—in any case
they could always be allowed to run continuously during
the night time. Eight contact beds with revolving
sprinklers would do the work of ten contact beds with
ordinary distributors.
Considering the difficulties in providing a large
number of filters, it would seem advisable to enquire care-