View report page

24
Sanitary Circumstances.
raised some 3 or 4 feet; the material used was the surplus
excavated materials taken from the sewer trenches while they
were being constructed.
The sewers enter the Purification Works 40 feet below the
level of the ground, and pumping machinery is installed to lift the
sewage from the bottom of the well, into which all the sewers
discharge, sufficiently high to allow it to gravitate to the various
tanks and filters.
Various buildings of a substantial and decorative character
are provided for carrying out pumping operations, treating the
sewage by chemical precipitation, and operating on the sludge
taken from the precipitation tanks.
When operations were started, it was decided that the sewage
should be treated on what was called the chemical precipitation
process; that is, adding certain chemicals (generally lime and
sulphate of alumina), and allowing the treated sewage to flow into
tanks, and settle for one or two hours. The grosser matters are
deposited, and a comparatively clear effluent can be drawn off and
discharged.
Further to purify the effluent, filters are provided which
oxidise and aerate it, so that it may be discharged into the river
without injurious effects.
This method of working has now been in operation for above
twenty-one years, and has satisfactorily fulfilled all requirements.
In 1904, the Board installed the bacterial process, in an
extension of the works. In this system the sewage is allowed to
pass through large tanks, where, by natural means, a large amount
of the solid matter is dissolved, and the effluent discharged is
passed through filters, which aerate and oxidise out a considerable
amount of the polluting matter.
This process has also worked very well on the amount for
which it was designed, which was about one-sixth of the daily flow.