The Ocala evening star. [volume] (Ocala, Fla.) 1895-1943, 1914-01-29
IMHOFF TANKS
tBy Alex H. rwombiy, Civil Eng,

i The disposal of sewage presents
two problems-the disposal Of liquids
and the disposal of solids. The aver
age sewage contains more than 999
j per cent. water, and less than lilo
of one per cent solid matter.
1 The Imhoff tank accomplishes two
important things. It separates the
/ liquids form the solids and 1t reduc-
es the solids to form in which they
can be handled safely.
| The Imhoff tank Is divided into
two compartments. typical section, .
and upper compartment thru which
the fresh sewage flows slowly so that
the solid matter contained in it
which is capable of being settled
falls by gravity to the bottom of the
upper compartment, and thence by
an outlet in its hopper bottom into
the lower compartment. The fresh
sewage passes thru the upper COM
partment in from one hour and a
half to two hours, which time is SO
short that no septic action takes
place and the eff1uent running away
| from the tank has not fermented.
In settling tank without two
compartments. the fermentation of
| the solid matter which is settled to
| the bottom causes gases to arise
| which, passing thru the sewage pre-
| vent complete settling of the solid
| matter. In the Imhoff tank the solid
matter settles to the lower compart
ment and the gases arising from
fermentation pass outside of the up
per compartment to the atmosphere,
thus causing no interference with
| the settling action in the upper
compartment. Result prove that in
stead of settling the usual so or 60
per cent. of such solid matter as can
be settled, that in the Imhoff tank
i the settling reaches So to SO per
cent.
The gases which come away from
an Imhoff tank are mainly carbonic
acid gases and march gas, both of
which are odorless. In contrast to
this the gases which come off from
single shallow tanks are apt to con-
tain large quantities of hydrogen sui
phide, which is very offensive
The Imhoff tank is so constructed
that the solids which have been re-
moved from the sewage remain in
the lower compartment for three
months longer, at the end of which
time the destruction of non-resistant
organic matter and germs has been
accomplished to such a degree that
an odorless sludge can be discharged
thru the outlet pipe directly from
the tank without further purifica-
ton. At the end of about three
months, part of the sludge is re-
moved from the bottom of the tank
at frequent intervals, so that the OPP
Grafton of the tank becomes practi-
cally continuous, new sludge form
ing on top of the older sludge and
gradually taking the place of the
older sludge at the bottom as it is
removed.
The disposal of sludge has been
the most difficult problem with
which to contend, as the sludge has
La strong odor and is very Shiny, caus-
ing a nuisance.
The methods of disposing of
sludge in general use have been to
carry it to sea in barges where pos
sible, to transport 1t in tram cars to
uninhabited sections and to dump it.
after removing as much water as is
possible by the sand liberation on.
drying beds or by the filter presses.
These methods are more or less
productive of odors and nuisance.
The sludge from the Imhoff tank
when drawn tru the sludge outlet,
has only a faint odor similar to tar,
which disappears in a short time,
leaving the sludge with an odor SIM
liar to garden soil. The sludge is
run on to drying beds consisting of
ABOUT 4 luCuSS Vi SIdsSi
drained, where the sludge rapidly
dries. Ordinarily the sludge form
other systems requires from six to
seven months to dry, but the sludge
from the Imhoff tank on account of
slime and it's peculiar consistency
dries in from three to ten days, when |
it can be shoveled into carts or tram |
cars and dumped upon any waste or
fill land without annoyance from |
odors or danger from fermentation. |
The amount of sludge is only about |
one-fifth of that ordinarily obtained, |
as its destruction has been more |
complete, and the amount Of water |
contained in the sludge averages
about rs per cent. against an ordl- |
nary average of o. ner cent in other |