f. Activated-sludge process.
The
be such that there is a possibility of
activated-sludge
process
works
by
contaminating a water supply with raw
diffusing air into a tank of primary
sewage, provisions should be provided
effluent.
Large numbers of aerobic
for chlorinating at a rate of 200
bacteria can live in the effluent and
pounds per million gallons at the 4-
decompose the organic matter, creating
hour peak rate of sewage flow.
(The
large amounts of sludge which settle
4-hour peak rate is considered to be
to the bottom.
Because of the large
175 percent of the average daily rate
amount of aerobic bacteria present, it
of flow.)
In other cases where
is called activated sludge.
Some of
chlorination is required, provisions
this activated sludge is introduced
should be made for chlorination at a
into the incoming primary effluent to
rate of 125 pounds per million gallons
keep the process self-sustaining. The
at the 4-hour peak rate of sewage
activated-sludge
process
has
not
flow.
Chlorine can be applied by
proved to be as efficient in treating
mechanical
chlorinators
or
by
an
sewage at Army plants as in municipal
improvised drum chlorinator.
plants
where
the
contributing
8.
COMPLETE TREATMENT
population is less subject to sudden
and wide fluctuation.
However, where
local
conditions
are
such
that
Most
of
the
treatment
processes
trickling
filters
would
not
be
mentioned above require a considerable
practical, consideration may be given
amount
of
engineer
effort
to
to the use of this process.
Because
construct. A simply designed, easy to
of
the
considerable
amount
of
construct facility for complete (both
construction
effort,
specialized
primary and secondary) treatment of
equipment, and constant supervision
sewage is available. This facility is
which is necessary, this process will
a lagoon and is very much like an
not be covered further in this course.
oxidation pond.
The lagoon system is
the
recommended
means
under
most
g. Chemical
treatment.
circumstances for providing adequate
Disinfectants, such as liquid chlorine
sewage disposal by military engineers
or calcium hypochlorite, may be added
under
theater
of
operations
to sewage in emergencies to safeguard
conditions.
health
and
prevent
odor
and
fly
nuisances.
They are sometimes used
a. Lagoons.
In its simplest form,
during periods of low stream flow when
the lagoon is a relatively large,
there is not enough stream water for
shallow
pond,
either
natural
or
proper dilution.
They also may be
artificial, into which raw sewage is
used when a part of a plant is
discharged for natural stabilization
bypassed
during
cleaning
or
a
under the influence of sunlight and
breakdown.
Since
chlorine
kills
air.
The size of the lagoon depends
bacteria it will greatly decrease the
on the amount of BOD which can be
decomposition
rate
of
the
sewage
handled per acre of lagoon.
This
therefore
delaying
the
BOD.
It
value has been quoted from 15 pounds
sometimes is used to delay the demand
per acre to 80 pounds per acre.
It
for oxygen until the sewage reaches a
has become generally accepted that a
body of water large enough to provide
figure of 40 pounds per acre is
the oxygen required.
It is effective
sufficiently
accurate.
Military
also
in
killing
disease-producing
sources assume a BOD loading of 0.2
organisms if the contact period and
pounds per capita per day.
Based on
the
chlorine
concentration
are
this figure and the requirement of 1
sufficient and if all particles are
acre per 40 pounds of BOD, a figure of
finely
enough
divided
to
permit
1 acre for every 200 persons should be
chlorine contact.
Should conditions
used in the design of lagoons.
4-13
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