TM 5-814-3/AFM 88-11, Volume III
b. Incineration toilets. Incineration toilets are available from several manufacturers. They are self-
contained. After each use, when the lid is closed the waste is incinerated, using gas or electricity. Maintenance
costs for new elements and ash removal are high. Such toilets are energy intensive and cannot be
recommended except for isolated sites or for emergency installations. They are, however, safe, easy to install
and, if constructed and maintained properly, are acceptable to personnel.
c. Chemical toilets
. Chemical toilets are usually manufactured
of fiberglass and are inexpensive
and maintain. The chemicals used have a high pH and have been known to cause minor burns. A fragrance
is usually added to mask odors because no biological degradation occurs between cleanings. After cleaning,
pumper trucks usually transport the treated wastes to a sewage treatment plant. Chemical units are less
desirable than humus units because they require not only greater energy costs, but constant maintenance and
hauling to a treatment plant. 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 and do have some
advantage over other chemical toilets. Wastes are pumped to a central holding tank, do undergo considerable
degradation during storage, and are more aesthetically acceptable. Their maintenance requires highly trained
personnel. Ozonation units have been produced by several firms which couple anaerobic and aerobic
treatment and ozone saturation. However, such units installed in California have proven to be expensive.
d. Aerated pit latrines. Military units of small size assigned to the field or to relatively remote outposts
may utilize 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 2x4 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 two feet of the ground
surface. With the structure removed, the remaining pit is buried with topsoil and seeded to grass. Some
modern designs utilize 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
Wagner and Lanoix, 1958.
6-4. Filtration/reuse systems.
In order to meet stricter standards, improved intermittent sand filters have been developed to treat wastes
from Imhoff tanks or septic tanks. The system developed included a recirculation tank and an open sand filter
(fig 6-6). A clock mechanism and pump assure a recirculation rate which 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,
0.0118 to 0.059 inch for the top 2 feet of filter, to allow a dose rate of 5 gallons per day per square foot. The
recirculation tank receives some underdrainings from the filter and mixes this with the septic waste. The
recirculation tank should be between and the size of the Imhoff or septic tank. A simple movable gate
directs flow from the drain either to the recirculation tank, or to chlorination or other further treatment and
ultimate discharge. A tee turned upside-down and a rubber ball suspended in a stainless steel basket under
the open end of the tee will also provide adequate flow control. Recirculation is kept between 3:1 to 5:1.
Pumps are set to dose every 2 to 3 hours and to empty the recirculation tank. The recirculation pumps are
sized so that 4 to 5 times the amount of raw sewage is pumped each day. Duplicate, alternative pumps are
required. Sand and gravel are placed carefully so as not to crush the plastic or tile pipe underdrains. Usually
two separate sand filters are built so that filters can be raked each week and allowed to completely aerate.
Prior to winter operation, the top 2 inches of sand on the filters is replaced. Since these filters are placed on
the surface, they must be surrounded by a fence and landscaped. Effluent will be of good quality, with
biochemical oxygen demand values ranging between 1 to 4 milligrams per liter. In the winter, ammonia may
range 40 to 50 milligrams per liter. Pathogens are practically completely removed. Design concepts are
detailed in Kardos et al., 1974; ASME, 1984; Curds and Hawkes, 1975; and Eikum and Seabloom,1982.