United States
                       Environmental Protection
                       Off ice of Water
                       Washington, D.C.
EPA 832-F-00-048
September 2000
Water  Efficiency
Technology  Fact  Sheet
Oil  Recirculating  Toilets

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.


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

                         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."



                          Requires no water.

                          Coast Guard-approved for marine use.


                         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

                         Disposal of separated waste products may be
                          problematic due to oil content.


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

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

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
^^ 1 	

al\  >|


f ^^^-~^^ ^~~'
 - -  Oil Layer
1 Aqueous/Sludge Laye

Activated Carbon
i 	 1
! Fuller's Earth
~~~ ^\
r I
Waste Receiving Tank
Source: Parsons Engineering Science, 1999.

              TOILET SYSTEM


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,

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.


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.


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.

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:

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.

2.     Director   of   Special   Operations,
      Commonwealth of Virginia, Department of
      Transportation,  Richmond,   Virginia.
      Personal  communication  with   Donna
      Messner, Parsons Engineering Science, Inc.,

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.


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
                                                       For more information contact:

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                                                       U.S. EPA
                                                       Mail Code 4204
                                                       1200 Pennsylvania Avenue, NW
                                                       Washington, D.C. 20460

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