methods of disposing of the effluent
treatment by lagoons is accomplished
naturally if three conditions can be
met: (1) depths in lagoons must be
kept from 2 to 5 feet for optimum
Dilution is the
results; (2) normal sunlight and winds
process of adding liquid waste to a
must be kept available on the pond
body of water.
At the present time,
surface by keeping heavy timber or
it is the most common method of
brush removed to a distance of 300
feet from the water's edge; and (3)
influent and effluent piping must be
located to minimize short circuiting
within the lagoon.
used, large surface areas of sewage
are exposed to the air.
effluent is 99.8 percent water, it
The process is
lagoons is based on two phenomena. If
limited to arid climates since climate
ample dissolved oxygen is available,
variations (rain, cold, and so on) do
bacteria will aerobically attack the
not permit the process to take place.
organic matter in the sewage and
rapidly convert it to more stable
takes place to a limited extent in a
lagoon or oxidation pond, although
this is not the primary disposal
Secondly, algae and other multicell
method in these systems.
plants grow very rapidly in shallow
(3) Irrigation. The third method
of disposing of the effluent is by
sunlight, are available.
irrigation, that is, the spreading of
with aid of light by a photosynthesis
the polluted water onto or through
process, utilize the carbon dioxide
As in the dilution method,
and liberate oxygen thus maintaining
irrigation allows some purification
aerobic conditions for the bacteria.
although this is not its primary
Under normal operating conditions the
The irrigation may be
sewage lagoon combines the above two
either surface or subsurface.
principles to the degree that the
SEWAGE COLLECTION SYSTEMS
biochemical oxygen demand reduction
a. Grease traps.
The presence of
with the most efficient conventional
grease in sewage is the cause of one
sewage treatment system.
The use of
of the most serious difficulties in
Where sewage is
seeking an efficient and economical
treatment, grease film on the surface
means of sewage treatment has grown
of the water retards reoxygenation.
considerably in recent years. Lagoons
Therefore, it is necessary to remove
are not recommended for military units
as much of the grease as feasible. In
order to prevent the deposit of grease
because if the surface of the pond is
on the walls of the sewer, and also to
frozen too long it prevents efficient
preserve the salvage value of the
grease, removal at the source is
At installations this is
b. Effluent disposal.
usually done by grease traps (fig 10).
treatment process has been carried out
to the degree necessary, the effluent
must be disposed.
The three basic