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SUPPLEMENT 2 DRY COMPOSTING TOILETS
Compost toilets are waste-recycling systems used to process
human waste matter into a nutrient-rich fertilizer for use as an
agricultural soil amendment. Risks associated with water-borne
waste disposal include contamination of ground and surface waters
and the spread of disease-causing bacteria and viruses through
possible contact with insects, animals, and human beings. These
risks can be eliminated for all intents and purposes by utilizing
the closed-container type of composting toilet where conditions
are controlled so that proper temperatures, sufficient oxygen,
and adequate carbon/nitrogen ratios can accomplish the necessary
aerobic decomposition of the waste material.
1. History
Early models of composting toilets first appeared in Sweden
in the 1930's and '40's. What prompted research and development
in alternative waste treatment systems were the extremely rocky
soil conditions found in the Swedish countryside. The rocky
soils prevented the installation of the typical water-borne
sewage transport systems to centralized sewage treatment plants.
Likewise, septic tank soil absorption systems proved impractical,
if not impossible, in the rocky terrain. Thus, the need for a
container method of waste collection, storage and processing
emerged.
In early hunter-gatherer cultures and tribal societies,
disposal of human waste material was done in a rather dispersed
fashion. No doubt, careful attention was paid to protection of
drinking water sources, and taboos probably also played a
significant role in preventing water contamination. Low
population densities enabled dispersal of wastes without a need
for waste protection or collection. However, with increasing
concentrations of people, prevention of disease and pollution
became a paramount concern. Use of latrines in rural areas
allowed the separation of wastes, but the threat of ground water
contamination remained. Odor problems and access to wastes by
insects and rodents raise the danger of disease and limit such
use. Furthermore, latrines do not allow access to composted
material for fertilizer.
2. The Composting Process
In dry composting, wastes are not removed by a carrier
medium (water) but remain in the container for a period of time.
Wastes decompose over a bed of carbonaceous materials (peat moss,
wood chips, sawdust, chopped leaves, grass clippings or other
loose organic materials) in a ratio of about five parts organic
material to one feces -- and the helpful bacteria are allowed to
do the rest. The compost toilet generates carbon dioxide and
water vapor that can be easily vented from the decomposition
chamber, and the remaining valuable composted material can be
used as a soil amendment for shrubs, trees, grass, flowers, and
berries. However, because of the very remote possibility of
contamination by long-lived viruses, toilet compost should not be
applied to vegetables.
Early cesspools were distasteful and a messy task to empty.
Ground and surface water contamination accompanied the ultimate
disposal of cesspool wastes which also produced health-related
problems. Use of cesspools has gradually given way to use of
centralized sewage collection and treatment facilities at an
enormous financial cost to communities. Septic tank soil
absorption systems are also problematic in that they can
contribute to ground water pollution, consume vast quantities of
drinking water for toilet flushing, allow minimal access to
resource recovery, and are often found in soils with clay content
that prevents percolation.
The decade of the 1990's opens to the problems of water
shortages, depletion of fresh drinking water resources, and
increasing levels of pollution caused by improper waste
disposal. Widespread adoption and use of compost toilets can
contribute in an important and meaningful way towards a solution
of these problems. The metaphor of composting is apt: Wastes
can be turned into resources, and pollution can be eliminated.
Pure urine is not harmful and can be applied to edible
crops
as well as trees and shrubs. The removed human waste is 5-10%
of the original volume. Only three to ten gallons of humus is
produced per person per year.
3. Some Words on Waste
Of the 2.5 pounds (1.14 kilos) of excreta that humans
produce per day 2 lbs is urine and 1/2 lb is feces. Water makes
up 75% of feces and 94% of urine. The rest is :
Feces
Urine
Carbon - 40-50% Carbon -
11-17%
Nitrogen - 5-7% Nitrogen
- 15-19%
Calcium - 4-5% Calcium
- 4.5-6%
Phosphorus - 3-5% Phosphorus
- 2.5-5%
Potassium - 2.5-5% Potassium -
3-4.5%
4. Varieties of Composters
Compost toilets may be constructed from scratch for
virtually nothing or purchased at costs ranging from $1,500 to
more than $5,000, depending on the type and capacity of the
container. Remember, per capita sewer and treatment costs far
outdistance compost toilet costs. Upgraded public sewer systems
near Mammoth Cave, Kentucky cost over $1,000 per person.
With proper care the compost toilet is long-lasting and
expense-free. Most compost toilets are made of fiber-glass,
masonry, plastic, or other durable material. They could
theoretically last a lifetime. The technology is simple and
there are no delicate mechanisms to malfunction.
Extremely low-cost, low-tech composting toilets can be
made
from recycled 5-gallon buckets (either metal or plastic) that
were used for paint, cooking oil, juices, sheet rock finishing,
or other non-toxic materials. Four to six inches of starter
organic matter beds are placed in the container bottom and after
each use about three or four cups of organic material must be
added to maintain the proper carbon/nitrogen ratio and to keep
odors from developing. The filled bucket must be emptied into a
secondary compost pile that is protected from rain, surface-water
run-off, animals, insects and other human contact. The pile must
be a minimum of one cubic meter in order to retain sufficient
heat to ensure destruction of pathogens, disease-carrying
organisms and long-lived viruses. This pile should be turned
every 3-4 weeks to provide proper aeration. The carbon/nitrogen
ratio should be a minimum of 30:1, but can even be 70:1 or higher
and still ensure adequate decomposition. The finished compost
can be removed and spread after one year.
Compost toilets do require space. The larger ones
have
containers of two or more cubic meters and, when insulated,
require a chamber or extra portion of a room. However, they can
be built as outside facilities, provided they meet the following
conditions: excreta do not come in contact with surface water,
ground water or soil; wastes do not come in contact with insects,
human beings or animals; and the building is properly insulated.
Compost toilets are most easily installed at the time
of
building construction. Ideally, a large insulated containment
room is available directly below the bathroom. Size adds to cost.
Large fragile fiber glass containers require more care in
transport and higher packing costs. However, smaller containers
require more attention.
A comparison of four compost toilets is considered here.
------------------------------------
Diagrams 1-7
Table 1 FOUR VARIETIES OF COMPOST
TOILETS
COST SPACE
EFFECTIVENESS ACCESSIBILITY SERVICE ELECTRIC
Clivus Multrum $4,000- medium excellent purchase from
yearly yes
room
for fan
(Scandinavian) $5,000
agent
Carousel $1,700 small good
agent seasonally yes
room
for fan
(Scandinavian)
Big Batch $500- small fair to good do-
it- yourself seasonally yes
for fan
(American) 1,200
(purchase container)
Solar Composter $300- large good
do- it- yourself seasonally- no
room
annually
(American) 1,200
(contractor) (depends
on
use & size)
(Other small commercial units are available, some of
which
use enormous amounts of electricity in a furnace method, which
are not really composters at all.)
DO-IT-YOURSELF SOLAR COMPOST TOILET, Long Branch Environmental
Education Center, P.O. 369, Leicester, NC 28748
(704)
683-3662
----------------------------------
Another low-cost container is a 55-gallon metal
or plastic
drum the top of which has been cut off to make a collection
chamber. If the unit is to be installed beneath an existing
floor, an approximately 14-inch diameter hole is cut into the
floor. Beneath the floor a recycled rubber tire that has be cut
radially is nailed to form an insect barrier and seal for the top
of the drum. A scissors jack is placed beneath the drum to force
it tightly up against the tire-gasket when the system is in use.
A four-inch diameter PVC pipe (bamboo could also
be used)
is run from the barrel up above the peak of the roof in order to
vent carbon dioxide and moisture from the drum. This vent stack
should be covered with wire screen and a rain cap to avoid the
problems with either unwanted insects or rainwater. Use starter
organic materials including some finished compost or animal
manures in order to inoculate the system with decomposing agents.
Regular use of "dry flush" materials with every use must be
stressed for all users.
5. Public Interest Considerations
Public health approval of compost toilets has been given
in
only seven U.S. states -- Maine, New Hampshire, Vermont,
Kentucky, Nebraska, Oregon, and Iowa. Approval for experimental
use has been given in some states for certain types and brands.
The Passive Solar Composting Toilet has been used in North
Carolina, Georgia, Kentucky, Tennessee, South Carolina,
Massachusetts, Maine, and New York. The first three states
approve that method and the state of New York is currently
reviewing the plans for approval.
If compost toilets are to become popular, they will need
governmental incentives and sponsorship. Extension agencies
could assist by providing technical information. The public
needs to know more about these examples of appropriate
technology, how to build them, and have access to low-cost loans
and grants. Currently, only large waste systems have access to
governmental money. If the same amount were available in the
form of loans or grants to independent builders, the compost
toilet could flourish in this country -- and reduce the need for
extended municipal water and treatment systems.
Some local ordinances require accompanying sewer or septic
tank hook-up for gray water, thus defeating the rationale for
compost toilets. Other agencies permit French drain systems
provided the system does not become overloaded and provided dirty
diaper washing is excluded. See WATER for a discussion of
artificial wetlands, a viable alternative to septic fields that
can be built inexpensively and have general acceptance.
Maintenance of Compost
Toilets
* An inoculating material must be placed in the
bed of the
new and unused composter in order to furnish "friendly" bacteria
for the starting decomposition process;
* Add at least one cup of "dry flush" organic materials
such as sawdust, wood chips, crushed leaves, dry chopped grass,
shredded newsprint, or even dirt after each use. Don't use lime
or ashes which reduce acidity required for proper decomposition.
Straw, rice hulls or hay may be used but are not as absorbent as
the materials already mentioned;
* Keep the container free of foreign objects, meat
scraps,
and materials which do not easily decompose;
* Avoid excess liquids. Never put kitchen
liquids in the
composter (instead, put in graywater system). Harmless human
urine is rich in nitrogen and can be safely recycled in the
garden. Containers of sawdust and urine make excellent lettuce
bedding. Avoid liquid overload of the system. One Swiss
composting idea is to install a manual lever below the composter
seat that shunts urine through a duct to a second sawdust filled
container for direct garden application. Another method is to
run sterile urine directly into a container and to dilute this to
5:1 and the then add to the garden with impunity.
* Use composted materials on flowers, lawn, shrubs,
berries, and fruit trees but not on vegetables due to the very
remote possibility that long-lived pathogens might reside there,
even though 99+% of all harmful bacteria are killed by the heat
of the composter environment.
Advantages
of Composting Toilets
* Easy to build and maintain;
* Environmentally safe and not unsightly. There
is no odor
emitted, especially when a vent fan is installed;
* No high cost sewage treatment is required. Compost
toilets are relatively low-cost compared to complete septic or
municipal waste systems. There is no mess, leach field, sewer or
water bills or hookups, expensive plumbing, septic tanks, spills,
or costly treatment plant breakdowns;
* Do not contaminate soil like water-borne waste
systems,
thus greatly decreasing the possibility of disease;
* Enormous water savings where flushing can account
for up
to half the domestic water use;
* Nutrient-rich fertilizer may be used at the place
of
waste generation, thus eliminating transportation and
distribution costs.
REFERENCES AND RESOURCES
Center for Minimum Cost Housing. Stop the Five Gallon Flush.
Montreal: School of Architecture, McGill University. (3480
University Street, Montreal, H3A 2A7, CANADA)
Compost Toilets: A Guide for Owner-Builders. Butte, MT:
National Center for Appropriate Technology (P.O. Box 3838,
Butte, MT 59701 (406) 494-4572)
We All Live Downstream Eureka Springs, AR: National Water
Center. (P.O. Box 548, Eureka Springs, AR 72632)
Stoner, Carol Hupping, ed. Goodbye to Flush Toilets: Water-
Saving Alternatives to Cesspools, Septic Tanks, and Sewers.
Emmaus, PA: Rodale Press, 1977.
REAL GOODS Trading Company, 966 Mazzoni Street, Ukiah,
CA
95482
National Small Flow Clearing House West Virginia University
Morgantown, WV 26506 (800) 628-8301
The Two-Seater Dry Compost Toilet
ASPI has developed an effective super low-cost dry composting
toilet. This consists of moving the seat rather than the
composting material. Building vaults out of the cheapest
available materials and rotating them from half year to half year
(approximate time to fill depending on amount of use) would allow
adequate decomposition time and still continual use of the
toilet. The cost is a little over $500.
Essentially the construction consisted of three phases:
a) the building of the wooden section in the toilet itself
that included sawdust containers and seats;
b) the building of the vaults of concrete block and the
coating of the sides and floor;
c) the completion of the doors and vent system with chimney
and vent fan (the major expense item of the entire system).
A still simpler model costing one half of that of the
two-
seater is used on our Nature Trail and hermitages. This consists
of a single seating arrangement with similar vault, but the time
for use is regulated to only eight months of the year. The rest
of the time is given to composting activity. By simply cleaning
the toilet each spring (after four months standing unused) for
the next recreation season allows a single seat to be used. This
very low-cost device is adequate for the volume of visitors on
our grounds. The ventilating fan on these isolated structures is
solar powered which operates sufficiently even with relatively
heavy summer tree cover.
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