(_A_) ~Per Million Gallons Pumped To Filter.~
=============+=======+=======+=======+=======+=======+========+========
Month. | Scrap-| Eject-| Wash- |Smooth-|Raking.| Re- | Total.
| ing. | ing. | ing. | ing. | |sanding.|
-------------+-------+-------+-------+-------+-------+--------+--------
1909.
-------------+-------+-------+-------+-------+-------+--------+--------
July | $0.10 | $0.21 | $0.03 | $0.02 | ... | $0.21 | $0.57
August | 0.07 | 0.16 | 0.03 | 0.01 | ... | 0.04 | 0.31
September | 0.05 | 0.13 | 0.02 | 0.01 | $0.01 | 0.27 | 0.49
October | 0.06 | 0.15 | 0.03 | 0.01 | 0.02 | 0.12 | 0.39
November | 0.02 | 0.06 | ... | ... | 0.02 | ... | 0.70
December | 0.02 | 0.04 | 0.01 | ... | 0.01 | 0.01 | 0.09
-------------+-------+-------+-------+-------+-------+--------+--------
1910.
-------------+-------+-------+-------+-------+-------+--------+--------
January | 0.04 | 0.07 | ... | 0.01 | 0.02 | ... | 0.14
February | 0.04 | 0.10 | ... | 0.01 | ... | 0.02 | 0.17
March | 0.04 | 0.06 | ... | 0.01 | 0.01 | 0.05 | 0.17
April | 0.10 | 0.15 | 0.04 | 0.01 | 0.02 | 0.06 | 0.38
May | 0.02 | 0.03 | 0.01 | ... | 0.01 | 0.11 | 0.18
June | 0.02 | 0.04 | ... | ... | 0.02 | 0.01 | 0.09
-------------+-------+-------+-------+-------+-------+--------+--------
Average | 0.05 | 0.10 | 0.01 | 0.01 | 0.01 | 0.08 | 0.26
-------------+-------+-------+-------+-------+-------+--------+--------
Fiscal years:| | | | | | |
-------------+-------+-------+-------+-------+-------+--------+--------
1905-06 | 0.06 | 0.29 | 0.02 | 0.06 | ... | 0.04 | 0.47
1906-07 | 0.07 | 0.20 | 0.05 | 0.02 | ... | 0.24 | 0.58
1907-08 | 0.09 | 0.14 | 0.03 | 0.01 | 0.02 | 0.13 | 0.42
1908-09 | 0.07 | 0.15 | 0.03 | 0.01 | 0.01 | 0.14 | 0.41
-------------+-------+-------+-------+-------+-------+--------+--------
~Table 15~--(_Continued._)
(_B_) ~Per Cubic Yard of Sand.~
=============+=======+=======+=======+=======+=======+=======+=========
Month. | Scrap-| Eject-| Wash- |Smooth-|Raking.| Re- | Total.
| ing. | ing. | ing. | ing. | |sanding.|
-------------+-------+-------+-------+-------+-------+--------+--------
1909.
-------------+-------+-------+-------+-------+-------+--------+--------
July | $0.08 | $0.15 | $0.03 | $0.01 | ... | $0.10 | $0.37
August | 0.07 | 0.15 | 0.03 | 0.01 | ... | 0.11 | 0.37
September | 0.07 | 0.17 | 0.03 | 0.01 | ... | 0.17 | 0.45
October | 0.06 | 0.15 | 0.03 | 0.01 | ... | 0.09 | 0.34
November | 0.10 | 0.23 | 0.02 | 0.02 | ... | ... | 0.37
December | 0.12 | 0.25 | 0.04 | 0.02 | ... | 0.08 | 0.51
-------------+-------+-------+-------+-------+-------+--------+--------
1910.
-------------+-------+-------+-------+-------+-------+--------+--------
January | 0.10 | 0.19 | ... | 0.02 | ... | ... | 0.31
February | 0.07 | 0.15 | ... | 0.01 | ... | 0.09 | 0.32
March | 0.06 | 0.11 | ... | 0.02 | ... | 0.08 | 0.27
April | 0.07 | 0.09 | 0.03 | 0.01 | ... | 0.05 | 0.25
May | 0.06 | 0.09 | 0.03 | 0.01 | ... | 0.06 | 0.25
June | 0.06 | 0.12 | ... | 0.01 | ... | 0.10 | 0.29
-------------+-------+-------+-------+-------+-------+--------+--------
Average | 0.07 | 0.14 | 0.02 | 0.01 | ... | 0.10 | 0.34
-------------+-------+-------+-------+-------+-------+--------+--------
Fiscal years:
-------------+-------+-------+-------+-------+-------+--------+--------
1905-06 | 0.07 | 0.35 | 0.04 | 0.07 | ... | 0.14 | 0.67
1906-07 | 0.06 | 0.19 | 0.03 | 0.02 | ... | 0.17 | 0.47
1907-08 | 0.09 | 0.15 | 0.03 | 0.01 | ... | 0.14 | 0.42
1908-09 | 0.06 | 0.14 | 0.03 | 0.01 | ... | 0.13 | 0.37
=============+=======+=======+=======+=======+=======+=======+=========
For convenience in referring to the different systems, the combined
rapid and slow sand filter 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 preliminary filters consisted of five units containing
gravel of varying sizes through which the water was filtered
successively before it was finally applied to the final slow sand
filter. A general idea of this system may be obtained by referring
to Figure 8.
~Table 16--Turbidity Results with Experimental Filters,
During Period of High Turbidity, January, 1908.~
Columns:
A - Effluent preliminary filter.
B - Effluent sand filter.
C - Effluent preliminary filter.
D - Effluent sand filter.
E - Effluent coagulant basin.
F - Effluent sand filter.
============+======+=============+=============+==============
| Raw |Filter No. 1.|Filter No. 2.|Filter No. 3.
Date. |water.|------+------+------+------+------+-------
| | A | B | C | D | E | F
------------+------+------+------+------+------+------+-------
January 12th| 40 | 10 | 1 | 12 | 1 | 2 | 0
January 13th| 110 | 45 | 2 | 51 | 2 | 2 | 0
January 14th| 210 | 95 | 3 | 113 | 4 | 2 | 0
January 15th| 325 | 190 | 12 | 222 | 15 | 3 | 0
January 16th| 360 | 210 | 37 | 247 | 42 | 5 | 0
January 17th| 242 | 122 | 24 | 147 | 26 | 6 | 0
January 18th| 137 | ... | ... | 73 | 7 | 6 | 0
January 19th| 117 | 40 | 12 |clean-| ... | 5 | 0
| | | | ing | | |
January 20th| 72 | 31 | 6 | sand | ... |clean-| 0
| | | |filter| | ing |
January 21st| 55 | 20 | 4 | 25 | 4 | sand | ...
January 22d | 49 | 17 | 3 | 21 | 4 |filter| ...
January 23d | 40 | 12 | 3 | 15 | 3 | 3 | 0
January 24th| 40 | 11 | 3 | 13 | 3 | 3 | 0
============+======+======+======+======+======+======+=======
It is unfortunate that this system was not in operation in January,
1908, when the water was cold and turbid. The results, however,
indicate that it would be no more successful than either Filter
Plant No. 1 or No. 2.
_Experimental Rate Studies._--In September, 1908, an experimental
plant consisting of six small filters was put in operation. The
object of these experiments was to study the relative efficiencies
and cost for the operation of slow sand filters when operated at
different rates.
The units of the plant consisted of cylindrical galvanized-iron
tanks 4 ft. in diameter and 9 ft. high. The filter sand in these
tanks was taken from the supply for the main filters. It was
supported on gravel layers and supplied with under-drains of
suitable sizes for the proposed rate of flow in each case.
The units of the experimental plant were designated as Nos. 1, 2, 3,
4, 5, and 6, and it was the original intention to operate them at
rates of 1,000,000, 3,000,000, 6,000,000, 10,000,000, 30,000,000,
and 100,000,000 gal. per acre daily, respectively.
This schedule of rates was carried out in a general way with all the
filters, with the exception of Nos. 5 and 6. For these, the rates
were found to be higher than could be maintained for any great
length of time, owing to the deeper penetration of the mud in the
filter sand, which caused high initial losses of head, short runs,
and deep scrapings. A rate of about 30,000,000 gal. was maintained
in the case of Filter No. 5 from the time it was started on
September 9th, 1908, until November 8th, 1909, when it was reduced
to about 17,000,000 gal., which rate was maintained thereafter until
the filter was shut down in February, 1910.
[Illustration: ~Figure 7--Plan of Filter-House and Equipment.~]
In the case of Filter No. 6, it was found impossible to maintain a
rate of 100,000,000 gal. for more than a very few days at a time. It
was started at about this rate, however, at the beginning of each
run, and kept as high as possible for the remainder of the time
during the first seven runs. At the end of the seventh run, on
October 17th, 1908, the filter was given a very deep scraping and
re-sanded.
[Illustration: ~Figure 8--Diagrammatic Sketch Showing Arrangements for
Testing "Puech" System of Water Filtration at Washington D. C.,
U. S. A.~]
The layer of clean sand restored the original capacity, and the
filter was operated as before, but with gradually decreasing rates
until December, 1908, when the rate was reduced to about 40,000,000
gal. Even this lower rate was too high to be maintained without
removing and replacing a large part of the sand. The rates,
therefore, gradually decreased to about 23,000,000 gal. on March
13th, 1909, when the filter was again re-sanded. After this
re-sanding the rate was reduced to about 20,000,000 gal., and the
filter was operated at approximately that rate until it was again
re-sanded on November 13th, 1909, when the rate was again reduced to
about 14,000,000 gal., which was maintained until the filter was put
out of service on February 28th, 1910.
This experimental plant was in service from September, 1908, to the
latter part of February, 1910, or for about 1-1/2 years, and the
leading results are summarized in Table 20.
~Table 17--Record of Experimental Filter Plant No. 1.~
Columns:
A - Rate, millions of gallons per acre daily.
B - Loss of head.
C - Rate, millions of gallons per acre daily.
D - Loss of head.
E - Applied water.
F - Effluent preliminary filter.
G - Effluent final filter.
H - Applied water.
I - Effluent preliminary filter.
J - Effluent final filter.