1090 SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS
Subsequently, this system was replaced by built-in retention
tanks. These retention tanks utilized wash and galley water
for toilet flushing purposes. The system posed several opera-
tional problems, including the fact that the flushing water
taxed the capacity of the retention tanks on longer flights,
and was later replaced by recirculating chemical toilets.
Recirculating chemical toilets currently being used aboard
commercial aircraft have highly improved features to fulfill
the requirements of the modern planes. Reinforced fiber-
glass retention tanks for lightness, teflon coated toilet bowls
for cleanliness, timer assemblies to control the flush cycle,
improved reversible-motor-operated pumps, and a number of
filter and filter-cleaning devices have all been developed to
provide trouble-free operation and an aesthetic facility.
The recirculating chemical toilets provide efficient oper-
ation but, depending on the capacity of the water tank, the
system requires frequent ground servicing. Furthermore, the
amount of space and weight available for waste storage in
aircraft is quite limited. Therefore, a system to concentrate
the wastes during the flight is considered highly desirable.
To achieve this, several waste-volume-reduction techniques
have been investigated for use aboard commercial aircraft.
These include:1) Evaporation of the liquid to yield dry or highly
concentrated solids to reduce the waste-storage
space in the aircraft and eliminate the frequent
ground servicing need.
2) Incineration devices which utilize electrical
and fuel energy for waste incineration. Several
improved incineration systems for aircraft appli-
cation have been built and evaluated. 57 – 59
3) Evapo-combustion system to burn the macerated
waste into a combustion chamber of the jet en-
gine. Vacuum toilets have also been successively
installed on large commercial aircraft. These toi-
lets reduce the waste accumulation. 34, 60 – 64.RAILROAD TRAINSHistorically, wastes from railroad trains have been discharged
into the environment without benefit of any treatment. This
primitive practice poses a threat to the public health. Although
passenger traffic on trains in the US has declined in recent
years, large numbers of persons, including railroad employees
still use toilet facilities on trains. According to Food and Drug
Administration (FDA), about 23 million pounds of human
excrement or 16 million gallons of wastewater are discharged
annually from locomotives and cabooses, and about 9.5 mil-
lion gallons of “untreated human wastes” were discharged in
1968 from intercity and commuter passenger train cars.^56 A
history of some of waste disposal practices of Amtrak was
presented in a hearing before Congress in 1988.^65
Federal laws and regulations now prohibit buses
(42 CFR 72.156) from discharging untreated human
waste. 56,57 As a result, the passenger buses are equipped with
suitable types of chemical or recirculating toilets.Currently, several types of waste treatment and disposal
systems are being marketed which are designed and built for
railroad trains. These include incinerating toilets, retention
tanks, and recirculating toilets.
Incinerating toilets built for railroad cars operate on
natural gas, propane, diesel fuel, or electricity. These toilets
operate without the use of water or chemicals and require no
holding tanks or plumbing fixtures.
Recirculating toilets of various types are also available
for railroad use. One system built for locomotives, cabooses
and crew cars uses a vacuum system. In this system air,
rather than water, is used to carry waste from the toilets to a
centrally located tank. 56,61 This system enables locating the
holding tank elsewhere in the railroad car and two or more
toilets can be connected to this tank.PICKUP CAMPERS, TRAVEL-TRAILERS, TENT
CAMPINGVarious types of portable recirculating toilets are currently
manufactured. These units have suitcase-style handles
molded into their cases for easy carrying; can be used in
tents or in camper.^66 A small family can get a few day’s use
before the facility must be emptied and recharged.
A unique system for reducing the volume of wastes
from recirculating toilets was developed. In this system, the
fecal wastes were liquefied by adding chemicals. The liquid
mixture is pumped to a sanitizer which is a short, stainless
steel tank connected to the exhaust pipe of the vehicle. The
sanitizer operates at about 500°F. At this operating tempera-
ture, the waste is concentrated and the microorganisms are
destroyed.^66 The operating temperature of the sanitizer is
reached at a vehicle speed of about 35 mph.ENVIRONMENTAL CONTROL AND LIFE SUPPORT
SYSTEMS (ECLSS) FOR SPACE STATIONNASA has sponsored programs to develop efficient, compact
equipment to handle the various aspect of environmental life
support for spacecraft and for the planned space station. The
tasks include CO 2 removal, O 2 regeneration, temperature and
humidity control, the purification of water recovered from
the dehumidifier condensate, hygiene uses, and in the future,
from urine. Also the removal of trace contaminants from the
air, the maintenance of the air composition and pressure, and
the storage of solid wastes pending their return to earth are
included. A wide variety of techniques have been evaluated
depending upon their prospects for meeting the desired per-
formance specifications. 67 – 73 Table 1 provides a list of ECLSS
technologies used or evaluated.
The space systems have grown in complexity and compre-
hensiveness as both the duration of the missions and the size
of the crew have increased. With the possibility of long dura-
tion space missions to other planets, and also the establishment
of bases on the moon, NASA is in the early stages of testing
technologies for solid waste treatment and recycling, and theC019_002_r03.indd 1090C019_002_r03.indd 1090 11/18/2005 11:06:46 AM11/18/2005 11:06:46 AM