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down under the constant flow of effluent gives the best results,
and may be simply piled up in a heap between light retaining walls.
A filter of this kind is found capable of reducing an effluent
containing 1.06 of Alb. Amnion. to .160, or nearly 90 per cent. of
purification. Such filters at Accrington deal with 1,250,000
gallons of sewage on about one-fifth of an acre of filters nine feet
deep, or about three-quarters of an acre three feet deep for
2,000,000. It may therefore be calculated that a partially purified
effluent of that quantity could be treated on about five-eighths "of
an acre. By the adoption of such a system it is clear that there is
a considerable saving in area of filter beds, ami this is due to the
fact that effluent distributed on the surface at intervals of minutes
results in a continuous flow from the bottom of the filter. One
great advantage of this kind of filter is that the simple apparatus
for automatic supply can be so set to work for an average effluent
at one minute flow and three minutes rest, that when storm water
comes down it merely causes the distributions to be more
rapid by shortening the intervals of rest.
The cost of this kind of filter is naturally less than the contact
beds, as the working capacity is reckoned at about
750 gallons per square yard as against 250 gallons.
By laying down five-eighths of an acre of these filters it can be ascertained,
if desired, by actual experiment what the purifying efficiency
will be, not only on the present effluent, but also on septic
tank effluent or even raw sewage. It will also be possible to test
the value of different materials, such as coke, clinker, polarite, etc.,
and also to find out any special action that may be due to peculiar
characteristics of Kingston sewage. There is a difference in the
action of similar filter beds upon the sewage of different towns, and
before proceeding to further alterations it will be advisable to
ascertain such facts by practical working.
The effluent from these sprinkler filters is very rich in nitrates,
it keeps well even when heated, and it has a purifying action on
other effluent water. It would therefore be advisable, when