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United Nations Environment Programme
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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 location investigations.

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 some way.

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, Kiribati.

Photo 8.6: Construction of compost toilet in Fiji

 

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