Since the foregoing remarks were written, I have been somewhat struck
with the views expressed at one or two meetings by some of those who
ought to have the full facts of the case at their fingers’ ends. There
seems to be a considerable vagueness as to the sanitary results to be
obtained by either the natural or one of the artificial methods of
sewage treatment, and with a view to making this point quite clear I
have prepared the following comparative statement (see next page),
which, I trust, will show at a glance what one may expect from either
system.
This statement has not been prepared from experimental installations,
where, as a rule, better results are obtained than in actual every-day
work; but it refers to fairly large works dealing from day to day with
the whole town’s sewage. It has further been assumed, that the plant
both for the natural as well as for the artificial treatment is
suitable, and managed carefully and on intelligent lines.
As in all sewage treatments the sanitary results have first to be
considered, I have only dealt with them in the statement, but even if
I had extended it to economic considerations the result would have
been practically the same.
From a careful examination of the facts recorded in the statement it
follows that with natural treatment we get five distinct advantageous
results, against which we have to place only two on the side of the
artificial treatments; but this means, that if we wish to bring up the
results of these treatments to those obtained by the natural
treatment, we have to supplement them by three further treatments for
the extraction of pathogenic germs, and of the manurial elements, and
for the reduction of the liquid.
It is these facts which ought to be carefully considered by all those
who wish to study the comparative advantages of these two systems, or
who have to decide on a definite method to be employed in a particular
case, and no step ought to be taken before every one of these five
points has been very carefully weighed. Generally speaking, that
system will be preferred which confers the greatest number of
advantages.