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211
It may sfive some idea of the vastness of the operations
in dealing with the sewage of London, to mention that the
Main Drainage Committee in their report for 1890, stated
that the weight of chemicals used in the year was 11,728
tons: the cost of lime used was ,£6,774, that of iron being
,£2,641. The sludge obtained was 421,500 tons of 92 per
cent, moisture, all of which was carried out to sea. In
addition to this outlay for precipitation, £24,560 was also
spent in the summer of 1890 in deodorizing operations at the
outfalls and storm-overflows, the chemicals used being 1,654
tons of manganate of soda and 749 tons of sulphuric acid.
Land and Other Methods of Sewage Purification.
—From what has gone before it will have been inferred that
eminent authorities are in favour of the view that the sewage,
crude or after precipitation, must ultimately be taken to the
land. At Paris it is stated that 5,000 gallons, on an average,
are applied to the acre. At this rate, 30,000 acres would be
required for irrigation purposes, were all the sewage of
London, averaging 150 million gallons daily, disposed of in
this manner. A larger proportion of a partially purified
effluent, presumably, might be used, thus reducing the
amount of land required. The land, however, has yet to be
found, and in any case a large outlay would be required on
main and branch sewers, &c. Projects for conveying the
sewage to the land have been before the public for thirty
years and more, but nothing has been done, and probably it
will be long before anything is done. The questions remain,
therefore, Is the river of necessity to continue to be polluted,
as heretofore, supposing the precipitation works should fail
of their expected effect? Is there no alternative? These
questions were attempted to be answered in my Annual Report
for 1889, (pp. 189—192) wherein I described three schemes
which had then lately been put before the public, viz., the
Amines Process, the International Sewage Purification