Evening star. [volume] (Washington, D.C.) 1854-1972, 1903-03-20
DELAY FOR ONE YEAR
Preliminary Treatment of
Potomac Water.
MILLER RECOMMENDS
ENGINEER OFFICER SUBMITS Elk
HAUSTIVE REPORT
In Connection With Proposed Slow
Sand Filtration Plant-Copy
Sent to Senate.
MILLER RECOMMENDS

Sent to Senate.
Col. Miller the engineer officer In charge
of the District water supply system. has
made an exhaustive report on the subject
OF the preliminary treatment Of Potomac
water in connection with the proposed slow
sand filtration plant.
During the session of Congress just closed
Senator Dillingham; proposed an amend
ment to the District appropriation bill to
provide for such preliminary treatment OF
the water above the distributing reservoir
before filtration by the slow sand process.
In his report Col. Miller calls attention
to a previous report made in March. 1910.
In regard to the f1ltering Of the District
water supply. That report gave the results
OF experiments carried on for continuous
period OF nine months. Two methods OF
filtration were investigated-the slow sano
or English method and the rapid sand,
aided by coagulation, or American method
As a result of these experiments. It was
recommended by Col. Miller that the rapid
method of filtration with the use of
coagulant, sulphate of alumina, be adopted
for the Washington filtration plant
Why Conclusion Was Reached.
This conclusion" says Col. Miller. was
arrived at from the fact that the expert
ments clearly demonstrated that during the
periods in which the Potomac river water
was at its greatest turbidity the English,
or slow sand method, would not afford an
effiuent acceptable as to turbidity. Further
experiments conducted after the date or
the above report confirmed this conclusion.
I'm my opinion. 1t Is clearly demonstrate
ed that II an effluent satisfactory as to
turbidlty is required. 1t cannot be obtained
at all times by the slow sand process from
~ tnr OF tYyoa
bidity. From the above 1t Is evident that
IL a perfectly satisfactory result OF fltra-
ton Is to be obtained some method OF pre-
iiminary treatment or preparation or the
raw Potomac water Is absolutely necessary
with a system of slow sand filtration.
There are two methods of preliminary
treatment of water to be filtered by the slow
sand method: First. preliminary treatment
by coagulation; second, preliminary treat
ment by rapid filtration through coarse
material without coagulation.
Neither Of these two methods has yet
been applied to filtration plants of large
capacity in practice. but the results Of ex-
perlmentation with both are available. The
preliminary treatment by coagulation con-
sists of applying in proper proportion and
with the necessary care and mechanical APP
planes, a coagulant to the fnfluent at
time and place sufficiently remote from the
filter infuent to allow a thorough coagula-
ton and sedimentation.
1T Is essential In this method that, after
the coaguant be applied, the treated inf1u-
ent be allowed by sedimentation to drop
the coagulant and coagulated sediment. For
this purpose 1t Is necessary that settling
basins be provided. Mr.. Allen HaZen, the
consulting engineer for the Washington fl
tration plant. recommends this method.
= Mr.. Hazen's estimate of the cost Of in
stallihg this plant is Ss5.400.
THE operating expenses he estimates at
$14.750. In my opinion this estimate Is too
low. Mr.. Hazen's estimate for the cost of
coagulant Is based on the supposition that
the use OF coagulant will only be necessary
, for thirty-six days in year. Coagulant
will probably be necessary for a much long
er period in my estimation"
Slow Sand Experiments.
table is given to show the results of ex-
perments on the filtration of Potomac
water under the English slow sand system
for nine months. from June. 1899. to April.
1900 This table shows that there were
ninety days when the effiuent was not
UP to the standard as to turbidity
IF 1t Is assumed" Colonel Miller says
that for nineteen Of these days. which Is a
fair estimate. the turbidity was so near the
standard that 1t might be unobjectionable to
the consumer. there would still remain sew
enty-two days on which an unsatisfactory
effiuent was obtained.
The observed turbidity Of the Potomac
water for the last twentyfour years shows
that the year of observation was not above
the average. . Mr.. Hazen in his
estimate assumes that coagulation would be
necessary for thirty-six days. whereas.
from the tables given. 1t would appear that
| 1t would be required for seventy-two days.
or double the time estimated for. This
would double the amount Of coagulant re-
quired.
1T would also double the amount of
storage room and thus add to the cost of
, installation. or Increase the estimate as
follows: Total cost Of installation, $sS, 400;
total operating expenses SO 800 This would
m fhn So
atlng the filtration plant at a rate Of 49,
100000 gallons day. The preliminary
method OF treatment by coagulation Is open
to the same objection that is involved in
any treatment Of potable water by means
OF chemical substances
AT the hearing before the committees of
both the Senate and House Of Representa-
tives on the subject of the adoption NJ a
plan for the filtration of the Washington
water supply strong and very decided OBJ
lection Yves raised by those representing the
citizens OF the District Of Columbia against
the use Of a coagulant, especially the sui
phate or alumlna. In the treatment of the
water Intended for domestic purposes and
In consequence of this objection the law
making appropriation for the construction
OF a filtration plant was drawn with the In
tention OF designating slow sand filtration
plant In contradistinction to any method
employing coagulant. This objection on
the part OF the citizens appears as strong
as ever.
Would Mean Exclusion.
1T would. therefore, appear that a proper
Interpretation OF the law and a regard for
the wishes of those most interested In the
subject would exclude the method of pre-
liminary treatment by means of coagulation
with sulphate of alumina
"A preliminary process following the
method of treatment by a rapid filtration
through coarse material without coagula-
ton has been experimental with at Phila-
delphia and has been adopted there for the
preliminary treatment of the raw water
when II Is so turbid to prevent slow
sand filtration from producing a satisfac-
torily clear effluent
The process there experimental with con-
sfsts In upward filtration through thirtv
eight inches of Stag. varying In size from
three inches to ne-half-inch particles. and
finally at the last through twelve inches of
sponge. The filtrate thus obtained ia then
passed to the regular slow sand filter.
THE rate of filtration in this preliminary
treatment is e00O0.OO0 gallons per acre per
diem. or about twenty times the rate ADOPT
ed for final or slow sand filtration. This
system Is known as the Maignen system
and is sometimes called 'scrubber'
I..r l..NAa 49,, = Il