er will be designated as Filter Plant No. 1,
the combined Maignen scrubber and slow sand filter as Filter Plant
No. 2, and the combined coagulating basin and slow sand basin as
Filter Plant No. 3.

The length of run of Filter Plant No. 1 was relatively long at
first. The rapid rate of filtration, however, tended to carry the
clay, which was suspended in the applied water, to a considerable
depth in the filtering material, so that the runs gradually
decreased in length until they were reduced to about three days.
Unfortunately, it was necessary to use unfiltered water for washing,
which, together with the great penetration from the applied water,
finally made it necessary to remove all the filtering materials, and
wash them.

Although this preliminary filter was operated at a high rate, its
efficiency was quite satisfactory. In fact, at times when the
applied water was comparatively good, very little work was left for
the slow sand filter. At times of high turbidity, however, some of
the exceedingly fine mud in the applied water passed through this
filter, as well as the slow sand filter connected with it, and it
proved to be absolutely impossible to produce a clear effluent at
all times with this combination.

Filter Plant No. 2 proved more economical and convenient in
operation, but somewhat less efficient than Filter Plant No. 1.
Neither filter could be depended on to give a clear effluent when
the applied water was turbid.

In the operation of Filter Plant No. 3, sulphate of alumina was used
when the applied water contained too much turbidity to be treated
satisfactorily by slow sand filters.

When the water was comparatively clear, either one of the three
systems, or slow sand filtration alone, was entirely satisfactory.
At times of high turbidity, however, Filter Plant No. 3 was the only
one which could be depended on to produce a clear effluent.

A fair comparison between the results of the three systems when
treating turbid water in January, 1908, is given in Table 16.

Table 16 shows very clearly that neither Filter Plant No. 1 nor No.
2 would prove at all satisfactory when treating turbid water, while
No. 3 could be depended on under all conditions. The results of
operation are shown in detail in Tables 17, 18, and 19. It will be
noticed in Table 17, that on March 10th, 1908, Filter Plant No. 1
was put out of service and a Puech system of preliminary filters was
substituted for it.

The Puech prelim