Evening star. [volume] (Washington, D.C.) 1854-1972, 1907-03-18
CITY WATER SUPPLY
CAPT. COSBY REPORTS CoNDI-
TONS TO GEN. MACKENZIE.

Capt. Spencer Cosby, the engineer officer in
charge Of the water supply system of the
District, has made a report to Gen. Mac
kenzie, chief of engineers, in regard to the
esta blishment of an experimental filter
plant in connection with the regular f1ltra-
ton plant near the Soldiers Home. The
experimental plant has been completed and
put into service, but has not been operated
long enough, Capt. Cosby says, to give any
important results.
The object in operating this experimental
filter plant" says Capt. Cosby, lis, first to
ascertain whether the Potomac water, after
having received preliminary filtration to
remove part of the tur5idity- producing ma
terials, will at all times give satisfactory
eff1uent from the slow sand filters; second,
to ascertain the most effective system of
preliminary filtration, and, third. to ascer-
tain whether the desired result can be more
cheaply and satisfactorily attained by the
application of a coagulant to the water. The
third question will involve a study of the
amount of coagulant required, the probable
number of days. it would be necessary to
use it, whether by its occasional use the
applied water would be SO much improved
that a relatively high rate Of filtration
would be adopted and the cost Of operating
the filters under these conditions
1.-The plNlt consists of three cylindrical re-
inforced concrete slow sand filters, each
having diameter of ten feet and height
of 95 feet; two preliminary filters Of
similar construction, four feet in diameter
and ten feet in height, and concrete set.
Ting basin ten feet wide, tWenty-nlne 1eet
long and six feet deep.
with the exception Of the settling basin,
the experimental plant Is inclosed by
neat frame building containing stoves, SO
that the temperature can always be Kept
above the freezing point and the plant
operated in winter without danger of the
water being frozen in the pipes.
THE three ten-foot filters contain one
foot of broken stone and three feet OF
filter sand They are equipped with IN
fluent and effiuent pipes and all neces-
sary valves and meters for operating them
as slow sand filters.
THE four-foOt filters are located above
the slow sand filters and 1t is proposed to
operate them as preliminary filters, thus
giving the raw water preliminary treat
ment before it is applied to the slow sand
filters. One of the preliminary filters con-
tains the usual strainers, six inches or
broken stone and three feet of filter sand.
1t is provided with the necessary pipes,
valves and measuring devices for operating
it and washing the sand, when necessary,
by reverse current Of water. In fact,
this filter will be operated at high rate
and in all essential respects as mechani-
cal filter, except that no coagulant Will De
used The eff1uent from this filter Will
afterward be filtered through the slow
sand filter The other preliminary filter Is
Maignen filter and contains twelve
inches of cobble stones ranging from two
to five inches in diameter. four feet OF
coke and about two feet of sponge clip
pings. The water is to be filtered at
rapid rate in an upward direction, hrst
through the cobble stones, then the coke
and finally through the sponge. The eff
fluent of this filter will be again filtered
through the second slow sand filter.
The settling basin is to be used in con-
nection with the third slow sand filter,
and all the water applied to the latter will
first pass through the basin. At times Of
high turbidity the settling coagulant Will
be applied to the water as 1t enters the
settling basin in sufficient quantities to
thoroughly coagulate it. The basin is of
sufficient size so that most of the aluminium
hydrate and mud will be deposited in 1t,
leaving only a small amount to pass on to
the filter