vvEPA
United States
Environmental Protection
Agency
Off ice of Water
Washington, D.C.
EPA 832-F-00-048
September 2000
Water Efficiency
Technology Fact Sheet
Oil Recirculating Toilets
DESCRIPTION
Oil recirculating toilets are "non-water carriage"
toilets, meaning that they do not require water to
operate. Instead, human wastes are deposited into
mineral oil, or another similarly non-aqueous
medium. The water-based urine and the solid waste
products are separated from the oil medium, which
is then filtered and reused in the toilet. The waste is
separated and contained in a holding tank until it can
be disposed of at an approved facility.
APPLICABILITY
Oil recirculating toilets are not widely used in the
United States. Nevertheless, they are an option for
numerous situations, including:
• Rural areas where no municipal sewage
system exists, especially where installation of
septic systems is impractical or prohibitively
expensive due to shallow soils, deep slopes,
high groundwater levels or extremely cold
weather conditions.
Remotely located roadside rest areas, where
connection to a piped sanitary system is
impractical and the cost prohibitive.
Large marine vessels, which are faced with a
prohibition against discharging untreated
waste into bodies of water and must either
hold accumulated wastes in tanks or must
treat before discharge.
Areas where water is scarce, either due to
drought or to other environmental conditions,
and the need to conserve water motivates
consideration of alternative, water-free toilet
systems.
• Where community, environmental, and health
organizations have concerns regarding
existing sewage disposal practices, especially
seepage of contaminants into local water
supplies from improperly functioning septic or
other treatment systems, or exposure of
residents to improperly dumped waste
products from rudimentary collection pails, or
"honey buckets."
ADVANTAGES AND DISADVANTAGES
Advantages
Requires no water.
Coast Guard-approved for marine use.
Disadvantages
• Emul si on format on b erween oil and urine can
cause an incomplete separation.
• Recycled flushing media can become
discolored and unpleasant smelling with use.
Flushing media eventually deteriorate and
must be replaced.
• System requires a relatively large space for
the holding tank and equipment for
separation/purification.
• Disposal of separated waste products may be
problematic due to oil content.
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DESIGN CRITERIA
An oil recirculating toilet consists of a commode-
type receptacle, a storage tank typically 53 cubic
feet in size, and a recycling system (see Bishton et.
al. for the following discussion). The flushing bowl
is coated with Teflon or a similar coating product to
minimize adherence of the waste products to the
bowl. A closet reservoir with a float-controlled
refilling mechanism is often attached to the toilet
bowl for flushing, akin to conventional water-
flushing systems. The simplest separation device
simply relies on waste products settling to the
bottom of the holding tank while the oil-based
flushing medium floats to the top. The flushing
medium can then be drawn from the top of the
mixture for reuse, and waste products can be
removed from the bottom periodically. In this way,
waste products are stored in the same tank used for
separation.
When the flushing medium is drawn from the
reservoir for reuse, it is first directed to a coalescer,
which is designed to remove suspended particulate
matter and water droplets. Water and particulate
matter thus removed are drained to the holding tank
via a return line. The pump used to transfer liquid
from the holding tank to the coalescer should be a
reciprocating piston pump or other pump that will
minimize break-up of aqueous droplets in the non-
aqueous medium. From the coalescer, the flushing
medium then passes through a filtering medium
(such as Fuller's earth) to remove any residual water
not caught by the coalescer. The fluid then passes
through a disinfecting chemical bath, typically a
hypochlorite solution, to treat odorous and
pathogenic contaminants present. Following
disinfection, the fluid is finally directed through
another adsorbent medium (usually activated
carbon) to remove non-water-borne dissolved
contaminants.
To prolong the life of the adsorbent and filtering
medium, it is desirable for the fluid drawn from the
holding tank to be as water- and particle-free as
possible before recycling begins. For this reason,
commode-and-tank design should be configured so
as to prevent mixing of the holding tank contents to
the greatest extent possible. Ramping systems are
often used to reduce the velocity of waste products
entering the tank from the commode and to create
an oblique angle of entry. Moreover, waste
products from the commode should be deposited on
the opposite side of the tank from the intake for
fluid recycling and the intake point should be
situated at the top-most liquid layer of the tank.
Finally, the size of the holding tank relative to that
of the commode, closet reservoir, and filtration
system should be designed so that at least eight
minutes of settling time is allowed in the holding
tank between uses. For a five gallon toilet/closet
reservoir capacity, and a filtration unit capacity of
five gallons, the holding tank should have a capacity
of twenty gallons. Figure 1 illustrates the primary
components of a typical mineral oil recirculating
toilet system.
To Toilet Reservoir
t
Flushing
Chemic
Bath
^^ 1
al\ — >|
J
1
f ^^^-~^^ ^~~'
- - » Oil Layer
Pump
1 Aqueous/Sludge Laye
["'
Activated Carbon
i 1
! Fuller's Earth
1
^~~~~Coalescer
~~~— ^\
Moisture
Return
r I
J
Waste Receiving Tank
Source: Parsons Engineering Science, 1999.
FIGURE 1 PRIMARY COMPONENTS OF A
TYPICAL MINERAL OIL RECIRCULATING
TOILET SYSTEM
PERFORMANCE
The Commonwealth of Virginia Department of
Transporation (VDOT) installed oil recirculating
toilets at four rest areas on the interstate highway
1-64 in the late 1970s, all of which have been
operative to date. According to VDOT's Director
of Special Operations, complaints of odors and of
discolored flushing medium have been common. A
representative of the property management company
responsible for maintaining the toilet systems, DTH
Contract Services, stated that the oil recirculating
systems require constant maintenance. Transport of
the oil, which has a higher viscosity than water,
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causes pipe vibration with each flush leading to
development of leaks on a regular basis. Moreover,
the multi-component assembly of filters and
cleansing solutions requires frequent checking and
changing. During the high-traffic season, from April
through October, a full-time operator needs to be on
hand to repair leaks and tend to maintenance, taking
approximately 5 hours per day. Pump-out of the
holding tank must be performed approximately two
to three times a week. In the off season,
maintenance consumes approximately 2.5 hours per
day. According to both the Commonwealth's
Director of Special Operations and the property
manager, plans are underway to remove the oil
recirculating toilet systems and replace them with
traditional, water-flushed toilets.
OPERATION AND MAINTENANCE
Removal of waste products from the tank bottom
must be performed on a routine basis. For proper
system functioning, the filtration and adsorbent
media and chemical disinfection solution must be
replaced when exhausted. Mineral oil flushing
media lost through waste disposal must be
replenished and the total volume of oil used must be
replaced periodically because of breakdown.
COSTS
The cost of purchase and installation varies widely
depending on the capacity of the system and
application (shipboard versus land). Maintenance
costs will include replacement of filters and
sanitizing solutions, replacement of flushing medium
lost through tank pump-out, and routine holding
tank pump-out. Operation cost will include
electricity to run the pumping system. The State of
Virginia experienced additional maintenance costs
associated with fixing leaks and other malfunctions.
Most or possibly all of the U.S. companies that
once made recirculating toilets have since
discontinued production of these systems. As a
result, cost estimates for package systems are
currently not available.
REFERENCES
Other Related Fact Sheets
Incinerating Toilets
EPA 832-F-99-072
September 1999
Composting Toilets
EPA 832-F-99-066
September 1999
High-Efficiency Toilets
EPA 832-F-00-047
September 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. Bishton, N.I, Jr.; Rod, R.L.; Wagenhals, B;
Woltanski, T.M.; and Blink, J.S., III, 1974.
Recirculating Toilet and Human Waste
Storage System. U.S. Patent No.
4,070,714.
2. Director of Special Operations,
Commonwealth of Virginia, Department of
Transportation, Richmond, Virginia.
Personal communication with Donna
Messner, Parsons Engineering Science, Inc.,
1999.
3. Kollmar, Ray. DTK Contract Services,
Dunn, North Carolina. Personal
Communication with Donna Messner,
Parsons Engineering Science, Inc., 1999.
4. Ward, Cindy. Commonwealth of Virginia,
Department of Transportation, Richmond,
Virginia. Personal Communication with
Keith Kornegay, 1998.
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ADDITIONAL INFORMATION
Director of Special Operations
Commonwealth of Virginia
Department of Transportation
1401 East Broad Street
Richmond, Virginia 23219
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U.S. Environmental Protection
Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, NW
Washington, D.C. 20460
IMTB
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