The Sunday herald and weekly national intelligencer., 1891-08-02
the crude, pneumatic, filtration, irrigation,
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method is recommended, with notifications
of the present method. The pneumatic sys-
tenn, as the name implies, consists in forcing
sewage, by the action Of the air, by plenum
or vacuum, to receivers. This system is used
in countries thickly populated, where there is
demand for the solid matter for fertilizers,
as in France, or where the country is below
the level of the sea, as in Holland. The
great objection to the pneumatic system is
the enormous cost of construction and main
tenance, double set of pipes being required
and the machinery being expensive.
AS to applying the sewage to irrigation pur-
poses, 1t is considered undesirable on account
of the large tract of land required, with the
expense of pumping and superintendent.
The method of purifying the sewage by filtra-
tion consists in allowing it to flow intermit-
tantly over porous soil, whether used for ag-
ricultural purposes or not. The objections to
the irrigation system apply also to the method
by filtration.
The method of filtration or separation of the
solid matter from the liquid by chemicals,
mechanical methods or by electricity is resort
ed to where it is specially desirable that the
sewage should bc purified
The new system proposed is, in short, pro-
vision for concentration, by means of inter
cepting Sewers of all sewage and part of the
surface water at pumping station to be loca-
ted at the intersection of First and N streets
in South Washington, thence to be pumped
through an inverted siphon Of cast iron pipes
laid in dredged channel across the Anacostia
River, thence up the steep hillside to the out
fall sewer, whence the sewage passes by gray
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the Potomac, on the Maryland side of the
river, below Alexandria. This reservoir re-
tains the sewage that flows on the flood tide
and part of the ebb tide, and discharges only
on the first part of the ebb tide, SO that the
cities Of Washington and Alexandria would
be wholly rid of this refuse matter.
One prominent feature of this system is the
application of an artificial drainage in lieu of
the natural one which was faulty in the low
area in not allowing sufficient fall for prop
erly shaped large sewers. This defect is over
come by diking out high water by two dikes at
narrow necks where it is necessary, and by
providing a greater slope by reconstructing
Tiber Creek and street sewers so that at the
receiving well and the pumping station the
invert of the sewer is Is feet below low water
level.
The pumping of sewage and an equal amount
OF suface water to the outfall sewer is accom-
plished by means of strong high-service pumps,
capable of overcoming the pressure due to a
lift Of CO.'S feet, and the head due to friction
of pipes and entrance
The low area comprises something less than
500 acres from which the surface water and
sewage will be pumped. When the rain is ex-
fha ctn
area, will be pumped by means of centrifugal
pumps directly into the river. The storm
water from high area is collected by means of
high level interceptors, and, before reaching
the low area, an excessive amount of it is car
red to the river by means of weirs or over
flows, which are provided at advantageous
points.
The E-street sewer to the north and
west, and the Tiber Creek and New Jersey
avenue sewer to the north and east of low area
are high level interceptors.
With drainage area within city limits to
the south of Boundary street of about 6,55O
acres, or an equivalent discharge for 9 inch
rainfall of 3,275 cubic feet per second, 900
being provided for by both kinds of pumps),
to carry shis amount of water away by pumps
would lead to an expenditure several times
that actually required, and the discharge
of diluted sewage on the borders of the city at
such times would not be very Objectionable,
on account of the greater amount of water
flowing in the river at such times
AT the pump the sewage from the intercept
tors leads to a receiving well, after passing
through cage work, the bars of which stop
any matter likely to interfere with the proper
action OF the pumping valves. The matter
thus collected is lifted by means of suitable
machinery, and is carried away.
An outfall between Washington and
Alexandria, would subject both cities to the
bad effects OF sewage, that is without
reservoir. With q reservoir, Alexandria
would be a sufferer With the point of dis
charge, midway between the two cities with a
reservoir, the sewage would be carried by the
flood tide back to the city in about two hours
and half.
The outfall sewer is located south of the
Anacostia River, connecting the iron siphon
pipes and extending to the reservoir. 1t has
a uniform diameter of feet and fall of three
feet in one mile.
The kind of high-service pump recon-
mended is of the class known as direct-acting
duplex pump, compound or triple expansion,
and worked at high pressure, with condensing
low-pressure cylinders, the water for CON
densers being drawn direct from the river
The centrifugal pump for the low service
Concluded on si1teeRth page.