Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
8.5 Disposal (Topic e)
Table 8.3 notes the
Regional SIDS that discharge wastewater through ocean and river outfall
systems. (See Photo 8.4 a typical ocean outfall in Honiara)
Over water latrines also uses the ocean and
rivers to dispose of waste. All
countries in the Region use land based disposal systems of various types.
With SIDS populations concentrated on
coastal areas, much of the land based wastewater discharges would eventually
enter the ocean through groundwater and surface water flows. Many coastal areas
are being polluted by wastewater disposal resulting in large algae blooms,
dying corals (reefs) and the decline in marine life.
This all impacts on traditional food resources, public health and
the tourism industry. With most SIDS
relaying on tourism for economic growth, pristine marine environments are
essential to attract tourists and getting them to come back.
Thus the promotion of suitable wastewater disposal
facilities should be encourage by governments.
Photo 8.4: Typical ocean outfall in Honiara, Solomon Islands
8.5.1 Ocean and river outfalls
Detrimental effects to the
environment from areas that are sewered, with various degrees of treatment, can
be minimised by using good effluent disposal practices.
Locations of ocean outfalls ideally should
be beyond the reef, in high circulation areas and below the thermocline. No
outfall disposal system in the Region meets all these criteria while a few systems
do meet some of the criteria. All too often the outfall locations are chosen by
treatment plant or pump station siting opposed to the best outfall locations.
These basic design criteria should be investigated for the construction of any
new system or the upgrading of an existing system to avoid problems currently
experienced by many SIDS. The regional
organisation, SOPAC, has both the expertise and equipment to implement outfall
The use of wetlands for
wastewater is not used much in the Region with only PNG indicating its
use. Overseas, wetlands have proved to
be an acceptable alterative to discharge of treated wastewater.
Wetlands may be either natural or
artificial. There is potential in the Region to develop wetlands for the
disposal of treated effluent.
8.5.2 Land based
In the Region the Cook
Islands, Niue, Samoa, Tonga, Tokelau, Tuvalu and Vanuatu exclusively used
land-based disposal of wastewater. Note
that groundwater is the main water source for Niue and Tonga hence protection
from wastewater pollution is most important.
All other countries use this method as well especially in rural areas
and on remote islands.
In the urban areas septic tanks are normally use to treat wastewater. If properly
designed, constructed and maintained, septic tank systems can treat wastewater
adequately. However it is the authorís observation that too much effort
goes into the sizing and construction of the septic tank itself and very little
effort goes into the design and installation of disposal systems for the septic
tank effluent. (See Photo 8.5 where septic tank effluent is discharge into unsuitable
soils in Suva) In most low island cases the effluent from the septic tanks is
discharged into a "soakage" pit giving more or less direct access
to the groundwater instead of using the soil as a filter to further improve
effluent quality. Infiltration drains may over come this problem but generally
are not implemented for digging a soakage pit is less of a task and cheaper
then laying a drain. Often when located in urban communities there is insufficient
area available to construct adequate effluent disposal systems. In this case
the groundwater should not be used for domestic use unless it is treated in
Pollution of groundwater is
common in the Region especially on crowded atolls due to ineffective land based
disposal methods. On Funafuti, Tuvalu, the groundwater is not used for domestic
use due to land based pollution from wastewater disposal. Groundwater reserve
areas have been created in Tarawa, Kiribati to protect groundwater lens
resources, used for suppling populated areas with water, from pollution.
Both Tonga and Niue use the unpopulated
areas of the islands to supply freshwater from groundwater lenes.
Increasing population growth in the Region
is creating pressure on reserve areas to be used for settlement and this may
adversely affect the groundwater quality.
With populated areas
located on coastal margins, poor land based disposal methods still have impacts
on reef and lagoon areas with pollutants being conveyed by groundwater and
surface water flows. Hence any
improvement to land based treatment and disposal methods would benefit the
Regions residents in many ways.
Photo 8.5: Septic tank discharge problem into unsuitable soil conditions
The use of composting toilets, currently being trialed in the Region, has much
potential to reduce groundwater pollution, eliminate the need for "flushing"
water, and the compost material generated can be use to improve soil conditions.
(See case study two) Photo 8.6 shows the construction of a composting toilet
in Fiji while Figure 8.4 shown the type of composting toilet used in Kiritimati,
Photo 8.6: Construction of compost toilet in Fiji