MIL-HDBK-1005/16
Another chemical treatment method is to use mineral oil
as the transfer liquid. These units are common on cargo vessels,
and at national parks, rest areas, and gas stations. They do have
some advantage over other chemical toilets. Wastes are pumped to
a central holding tank, undergo considerable degradation during
storage, and are more aesthetically acceptable. However, their
maintenance requires highly trained personnel. Ozonation units
that couple anaerobic and aerobic treatment and ozone saturation
have been produced by several firms. However, such units
installed in California have proven to be expensive.
6.5.3
Aerated Pit Latrines. Military units of small size
assigned to the field or to relatively remote outposts may use
aerated pit latrines. These latrines are improved versions of
the "privy." The pit may be excavated, using a backhoe or hand
labor. Usually the pit walls are supported by 2 x 4 lumber and
lagging. The privy structure is best designed to allow easy
transport to a new location. It may be uncoupled from the pit
wall supports and carried to another location when the pit is
filled with waste to within 2 feet (0.6 m) of the ground surface.
Once the structure has been removed, the remaining pit is buried
with topsoil and seeded to grass.
Some modern designs use passive solar panels to produce
a rising current of warm air, which passes out of a screened vent
pipe. Screened openings are provided at the base of the privy
structure to allow cool air to move laterally across the top of
the pit, up, and then out of the vent. Latrines can be operated
as composting toilets if leaves, wood chips, and pine straw are
added to the excreta. If well designed and responsibly
maintained, the aerated pit latrine will not harbor vectors nor
will odors accumulate. For further details, see Excreta Control
for Rural Area, Wagner and Lanoix, 1958.
6.6
Filtration/Reuse Systems. To meet stricter standards,
improved intermittent sand filters have been developed to treat
wastes from Imhoff tanks or septic tanks. The system developed
includes a recirculation tank and an open sand filter
(Figure 21). A clock mechanism and pump ensure a recirculation
rate that results in fresh liquid being dosed onto the surface of
the sand filter. Solids are partially washed onto the sand and
kept odor-free. Float controls provide override of timer clocks
should flows increase to near overflow levels before the clock
sets pumps into action. Dosing is through troughs rather than
through central pipe and splash block. Sand size is coarse
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