The Providence news. (Providence [R.I.]) 1891-1906, 1896-02-18
Abstract From Report Of
Mr.. Weston.
As Made by Gardner I. SwartS,
M. D.
Efficiency Of Mechanical Filtration
Demonstrated.

atty enigneer's department., upon expert
ments made by natural filtration and In
the use OF the Morrison filter for a period
Of nine months, is now In press to be
published complete with tables and esti-
mates of construction, by the State board
Of health. This report, it will be recalled,
which represented exhaustive research
and experiment that can but be OF value
TO the whole country, and an expense OF
perhaps $4,000, was suppressed, or at
least never printed, by the City Council,
for whose especial information it was
prepared. The excuse a for not print
Ing IL was because OF cost. In reality the
cost Of printing was inconsiderable by
comparison with the value of the report
and the cost involved in its preparation.
The report was suppressed In the inter-
est of the movement for natural filtra-
tion as it was known that the report made
q fayorab bic showing for the mechanical
system.
Last fall, however, the secretary of the
State board of health, Gardiner T.. Swarts,
tion OF the report, drew upon 1t for an
address before the American Public
Health Asso ciation, in session in Denver,
Col. This address Is reprinted in the
December issue OF the Monthly Bulletin
OF the board of health and treats OF the
Psychological Results from Mechanical
Filtration" The address follows in full
with the commission Of tables.
RESULTS OF MECHANICAL IRA
At the last meeting Of this association
Ut Montreal, the statement was made in
the report of the committee on water sup
plies, that no data had been available to
show that filtration by the so-called me-
chanical methods was successful in re-
moving bacteria. The writer at that time
referred to experiments which had been
made in the city of Providence, r. l., in
order to determine this question for the
purpose OF establishing a plant capable of
bltering 16, 900, 600 gallons daily, IL the
experiments were successful.
The figures showing these results were
pot at that time available, and as they
have never been published and as no ex-
periments OF a similar character have
teen made, IL seems desirable to place
these facts before the. association, mas
much as many municipalities are agitat-
cd over the ACCESSIBILITY Of introducing
the so-called natural or sand bed hltra-
tion or mechanical Il filtration.
The mechanical form of filter used in
the experiments was of the type in which
quartz or sand is used as a supporting
bed to a film of precipitated c%oagulant or
fixative of organic matter, produced by
the introduction into the water, before
flter1ng, OF some chemical such as iron
or alum; a filter which is also cieansed
by means of a reversed current of the
W alter passed through the filter assisted
by the use of a rake made to revolve in
the bed OF the quartz while the washing
Is being done.
The filters used in this liue of expert
ments were two OF the natural sand-bed
form initiating the usual filter bed. The
mechanical form was represented by one
OF the New York Filter Company's filters
and one of the so-called Morrison filters.
IT,. tLA ft.a& ere ,A~&L H. ~.~I Al
ters were discontinued, it having been
satisfactorily ascertained that the length
OF run was much less than the mechanical
filter before the bed became clogged and
the rate of flow in the natural bed was
but 80. 600, goo gallons per acre in "a hours,
while the mechanical filter was
run at the rats of 125, 000,-
poo gallons per acre in "a hours.
The efficiency of removal of bacteria was
not as high, and the results variable, eth
er as the result of cracks in the hitter or
from some unknown reason. Although
both of these natural filtration beds were
constructed exactly alike, the results from
the second were much poorer than the
first. When the natural bed was trans
formed or assisted by the addition Of
alum, thus
CONVERTING 1T INTO A MECHANICAL Fill
TER,
the removal OF bacteria was increased to
nearly the same as on the Mori-
son filter, but the length of the run was
co~rrespondingly decreased.
The sand used in the natural beds was
q natural river sand. not over sbo-",
while the sand used I'm the mechan i.
filter was crushed quartz, having sh
edges.
In the beginning OF the experiments
the New York filter gave such varied and
unreliable results that its use was sban-
lApAa YrhfIA 4hA .An.tlAI NlA.g,A. an
was continued in use during the whole
series -of experiments, which lasted for
period of about ten months, the work
Ing of the mechanical parts of the filter
being perfectly satisfactory and the re-
suits obtained being successful.
The filter bed used in this mechanical
filter was two feet ten inches i'm depth,
supported upon a base of iron with circu-
lar perforations of about 4 inches in size,
which were covered with screens. The
crushed quartz used was the defective
size" 0.59 millimeters. The filter was
washed by reverse current which caused
the quartz to boil. The agitation and
friction OF the particles were increased by
means OF a rake with long teeth, which
revolved about a central column in the
filter; the rake penetrating the bed by a
screw motion from top to bottom.
From the various kinds OF coagulant or
precipitant used basic sulphate OF alumina
was selected as being
II MOST SATISFACTORY
aud effective, and was used In all the ex-
periments mentioned. The amount of
alumina used was one half grain to the
gallon OF water filtered, a lesser quantity
failing to satisfactorily remove the organ
isms, while the amount of ~hree-quarters
or one grain per gallon did not Increase
the removal OF the bacteria, willie the
efficiency of the filter was greatly de-
creased by reducing the amount OF flow
through the filter bed.
The alumina was applied In a free flow
st the beginning Of n RON by pouring
into the filter, as the water entered, n
pint OF the cosgulant containing about 81
grains of sulphate OF alumina for an aver
age flow OF lbs, 000, 200 per acre. The soln-
ton was made by adding ore part OF the
slumina TO six parts of water; as a result
OF this addition there forms a white
fiocculent precipitate over the surface of
the grains OF quartz and Is the actual
medium through which the filtration