Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for
in Small Island Developing States>
PART B - ALTERNATIVE TECHNOLOGIES
1. TECHNOLOGIES GENERALLY APPLICABLE TO ISLAND STATES
1.3 Wastewater Treatment Technologies and Reuse
1.3.1 Alternative (Dry) Sanitation
There are a number of different types of sanitation that are generally
used on small islands, including simple pit latrines; ventilated improved
pit (VIP) latrines, in which a ventilation stack is introduced to reduce
nuisance from flies and odours; the pour flush toilet where a water seal
is installed to completely eliminate odours, fly nuisances and mosquito
breeding in the pit; septic tanks and effluent disposal pipes; and
composting toilets. Detailed information on these technologies is readily
available in the general literature, and the emphasis here is on their
application in SIDS.
Contamination of water supplies by human and animal excrement is a
recognised means of transmission of diseases. In addition, the high
nutrient loading from such contamination can also negatively affect human
health and cause ecological damage. For these reasons it is advisable to
take all measures possible to prevent human and animal excrement from
reaching freshwater sources. Faecal contamination of groundwater from
human sources can also occur due to the percolation of the effluents from
septic tanks or pit latrines into the groundwater, or through infiltration
of faecal material into the groundwater from the land surface. One way to
avoid faecal contamination of groundwater is to use a composting toilet
which is a sanitation technique that is capable of converting excrement
and organic material into a soil-like substance that has a pleasant earthy
odour, and which can be safely disposed of in the environment after an
adequate composting period. This section focuses on the dry sanitation
technology used in composting toilets as this technology both conserves
water and protects the groundwater. The protection of the groundwater is
of particular importance to the very small islands, where the groundwater
lens is very limited and close to the land surface.
The features of a composting toilet include on-site dry biological
treatment; one or more containers under the toilet pedestal to receive
human excrement (faeces and urine) and other bodily discharges; use of a
bulking agent containing accessible carbon that is added to the containers
regularly to keep the pile aerated; ventilation either passively or by
electric fans; storage of the solids in the containers while they are
being broken down by composting; disposal of excess liquid in an
appropriately designed evapotranspiration trench adjacent to the toilet
building (or, in the case of some commercial units, disposal by
evaporation using an electric heater or a solar array); and reduction of
pathogens. The material in the containers undergoes primarily aerobic
decomposition through the process of mesophyllic composting; (i.e.,
mesophyllic microorganisms that thrive in a temperature range of 19oC to
40oC contribute to the decomposition of organic matter in the system).
Composting toilets can be purchased as prefabricated units or constructed
as owner-built units from a number of designs that have been developed
over the last 50 years.
There are three main types of composting toilets; namely, (1) the
continuous system with a single container in which excrement is deposited
by the user from the top of the system and from which compost is removed
from the base after an extended period of time, (2) the batch system with
two or more containers that are alternated so that an active container is
in use in the system while a fallow container has time to compost without
the addition of further excrement, and (3) a separation system which
separates liquids from the solids which are collected in a moveable
container. This latter type is still being developed.
The Clivus Multrum (Figure 12), which originated in Scandinavia, is a
continuous system. The material which is deposited in the toilet slides
down the inclined bin over time and is emptied from the end-product
chamber in a composted form. In practice, blockages or compacting of waste
can occur if the material does not slide down the incline. To rectify
this, the pile should be raked or stirred to move the material further
down into the bin. Another commercial continuous system is the Dowmus
which uses worms to assist with the decomposition process.
The alternating batch system (Figure 13), available commercially as the
Rota-Loo, the Nature-loo and the Wheelibatch toilet, is based on the
original "two holer" used in rural areas of Viet Nam, and has
two or more containers which are alternated. The advantage of the
alternating batch system is that it allows a period of time when no new
material is being deposited in the toilet, thus preventing
re-contamination of the composting pile. There is usually no requirement
for raking the pile or having any contact with the material during the
composting period, but the bins do have to be changed with both the mobile
system and fixed pedestal units when they become full. Some designs use
turning devices to aerate the pile, but these should not be necessary and
often cause difficulties.
Figure 12. Schematic of a composting toilet (of Clivus
Extent of Use
Composting toilets are currently being used experimentally on Christmas
Island, Kiribati (see Part C, Case Studies), as well as in the Federated
States of Micronesia. In Australia, the United States, Canada, and Europe,
composting toilets are used by managers of public recreational areas such
as national parks, state reserves, water-supply catchment areas, and
forestry reserves, and are particularly favoured in areas of
high-conservation value and at remote sites.
Figure 13. Wheelibatch toilet.
Operation and Maintenance
Composting toilets require a certain amount of attention and involvement
by the householders or maintenance staff. A small quantity of bulking
agent has to be added to the toilet regularly. Operators must collect the
bulking agent from the bulk store and provide small quantities in a
container beside the toilet for users to add after using the system. When
the bin that is in use is full, it must be changed by the operator so that
the pile can lie fallow to compost the excreta while the alternate bin is
in use. This should happen approximately every four months, depending on
household size. In a tropical climate, the excreta is fully composted, and
all pathogens have been eliminated, in a four month period. If the system
is a mobile system like the Nature-loo or the Wheelibatch toilet (see Part
C, Case Studies), the bins must be manually changed. If the system is a
static system like the Cage Batch toilet, the pedestal must be shifted
from the full bin to the empty bin. When the pile in the fallow bin is
composted, the compost must be extracted and dug into the garden. Placing
the compost around a fruit tree is a common use for the treated product.
Level of Involvement
As each household and/or group of houses is encouraged to participate in
the construction of the unit, and, as each is responsible for the
operation and maintenance of the toilets, there is a high level of
involvement by the user.
The Australian products range in price from $1 500 to $3 500 for the
unit, to which must be added the cost of an outhouse, or the cost of
retro-fitting a bathroom or pre-existing building. Some companies offer a
range of sizes to meet differing intensities of usage, and prices vary
accordingly. Those constructed in 1995 on Christmas Island, Kiribati, cost
approximately $2 200 (Table 3). The very high cost of these units is due
to the fact that most of the construction materials are imported, and the
costs reflect the high transportation costs incurred.
Effectiveness of the Technology
There is a considerable amount of water to be saved by using a
composting toilet. Composting toilets in a typical home can reduce
residential water consumption by up to 28% from that of a home served by
flush toilets (Chapman, 1993). On low-lying atolls and in those parts of
larger islands where even properly functioning septic systems can pollute
the groundwater, composting toilets offer a potential means to reduce the
risk of groundwater contamination (although, as the use of composting
toilets is not yet widespread, no conclusive results have been
Composting toilets are particularly suited for use on small, low-lying
islands where there is a shortage of water, and where the groundwater is
very sensitive to contamination.
TABLE 3. Construction Costs of a Composting Toilet.
|Trenches and fittings
Composting toilets are an onsite sewage management technology that can
offer significant protection for water quality and quantity since the
toilets provide dry, biological treatment of human excrement and do not
generate quantities of contaminated water that must be discharged into the
environment. The excrement in a composting toilet is contained in bins
that are installed at ground level so the waste is not in contact with the
groundwater. The liquid that drains through the pile is of a sufficiently
small quantity that it can be adequately isolated and treated in a sealed
trench adjacent to the toilet. This technology also avoids the use of
scarce groundwater or rainwater supplies for flushing toilets. Also, use
of manufactured toilet paper in composting toilets is not required,
resulting in a cost savings within the household. Any organic material
that can be decomposed is suitable for personal cleansing (e.g., leaves,
coconut fibre, writing paper, cardboard, and rags). The systems can also
accommodate washwater to the extent that the quantity of water introduced
into the bins does not saturate the pile. Composting toilet design can be
adapted to local social and physical circumstances as long as the basic
conditions for composting are maintained and the protection of public
health and the environment is assured. About 4 months is required for
effective composting and treatment of disease-causing organisms, at the
end of which period, the excrement has changed its appearance and odour to
that of compost which can be used as a fertiliser and dug in around fruit
trees. Because composting toilets rely mainly on aerobic decomposition,
the material in the bins does not have a faecal or unpleasant odour while
it is breaking down. Consequently, it is not necessary to remove the
material from the site while it is being treated, saving money, time, and
resources and avoiding the risk of contact during transportation.
Composting toilets are designed be easily maintained by the householder,
and there are no chemicals involved or moving parts that can break down.
As the composting toilet is a dry method of treatment, and the material is
contained immediately below the pedestal, it is very difficult for the
system to become blocked or obstructed even if a large object is dropped
into the toilet. Therefore, repair rarely required and seldom require
contact with fresh sewage. The only pipe on the system is a short 50 mm
fitting from the liquid drainage area at the base of the bin to the
trench, which should be easily accessible should there be reason to clear
it. The composting toilet involves a simple, self-sufficient, recycling of
waste material that can have added benefit through the practical
demonstration of these principles on a daily basis as well as significant
long term educational value, particularly for children.
Because the bins of the composting toilets are generally installed at
ground level, the toilet enclosure is elevated, and stairs or a ramp are
required for access. This could be a problem for the elderly or disabled.
Also, this requirement often means that the toilet building is taller than
the surrounding buildings and can be quite obvious. However, these
difficulties can be alleviated by building the toilet room close to a one
storey, pre-existing house, by growing trees around the enclosure, or by
designing a house that has an elevated verandah area under which the bins
can be installed. Likewise, while composting toilets are capable of
providing protection of the public health and environment by preventing
contamination and waste of precious water resources, they can become a
health hazard if not designed appropriately or maintained properly. For
example, liquid from the drainage trench may surcharge and come in contact
with people or waterbodies. Similarly, if the compost is removed from the
fallow bin before it has had time and/or the right conditions to fully
compost, disease organisms may be transmitted to those who handle the
material, especially if they are careless. Simple precautions and
guidelines for using and maintaining the systems can overcome these
limitations, but must be taught to users as part of the information
programme that must accompany the introduction of composting toilets (or
any other sanitation strategy, for that matter).
Insects are attracted to human excrement and decomposing organic matter.
Although certain insects or invertebrates play an important role in
breaking down the material into a more accessible for the microbial
digesters, some insects can act as vectors of disease. It is important
that these insects, especially common houseflies, do not enter the bin and
breed. This requires that the lid of the toilet be kept closed, a courtesy
that people often forget. Spring loading the seat so that it closes
automatically after each use has been tried, but, in practice, suffers
from a number of drawbacks. Use of the bulking agent after each use should
use a sufficient quantity of the material to cover the fresh excreta and
minimize its attractiveness to insects.
Finally, when compared to the standard pit latrines which are widely
used on small islands, composting toilets are too expensive for most
island people to afford. Locally manufactured designs may be one way to
make composting toilets more affordable. Also, being a new technology, it
may be difficult to persuade people to use dry techniques instead of the
more traditional water-borne methods of sewage treatment. People may be
sceptical, and technology transfer of composting toilets should be
undertaken cautiously and with maximum community participation. Use of the
composting toilet also requires that separate treatment be provided for
water used for washing, laundry and other household or personal needs.
Every culture has taboos relating to human excrement. Most of these
taboos are based upon an understanding that ill-health can be caused by
contact with faeces, especially faeces from a diseased person or stranger.
For some, there are issues of sorcery involved or religious restrictions.
These taboos may initially cause people to be concerned about using a
composting toilet since the excrement is contained and treated on-site,
and the compost can be recycled as a soil improver. This is in contrast to
septic tank and sewerage systems which remove the excrement from the
immediate surrounds and requires little or no further user involvement.
For this reason, conduct of a demonstration project using a
well-functioning composting toilet system in which the transformation of
excrement to an acceptable compost can be observed may be necessary before
a final opinion can be formed in the user community. If the prospect of
using the end-product, however transformed it may be, remains a cultural
obstruction to the use of the composting toilet, then some other,
acceptable method of disposal of the compost must be found if composting
toilets are to be an effective sewage treatment option.
Another concern is that, because the waste material is contained and
treated in bins under the toilet, some people may feel that the use of a
composting toilet is like using a pit latrine and, therefore, a backward
step in sanitation practice. This caution and scepticism can only be
allayed by direct experience with a well-functioning composting toilet. As
with any technological introduction, informational programmes will be
necessary to explain the risks and benefits. Health and environmental
problems caused by a variety of sanitation practices are universal.
However, it can be demonstrated that the composting toilet is sometimes
preferred by people in countries where water-borne sewerage systems are
readily available. This can help people understand that
appropriately-designed, composting toilets are one of the latest
developments in sanitation practice, and in certain situations they may be
the only sensible choice
Further Development of the Technology
There is a need to develop this technology further to comply with the
conditions of the islands where composting toilets are installed.
Developments are especially needed to reduce the cost of the units,
perhaps through the use of local materials for construction. Also, design
improvements are needed to better conform the units to their surroundings
and minimise the aesthetic and societal impacts of the toilets.
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