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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Small Island Developing States>


PART B - ALTERNATIVE TECHNOLOGIES

4. TECHNOLOGIES APPLICABLE TO SMALL ISLANDS WITH SPECIFIC PROBLEMS OR CIRCUMSTANCES

4.3 Wastewater Treatment Technologies and Reuse

4.3.1 Wastewater Reuse

Technical Description

The technology for water reuse is a combination of existing wastewater treatment technologies and water supply treatment technologies. Processes under the general heading of wastewater reuse range from the most sophisticated and complex engineering processes to some of the simplest, natural systems. Detailed descriptions of these technologies can be found in general literature on wastewater treatment, but, for purposes of wastewater reuse, the type of wastewater treatment technology chosen depends on factors such as the type of wastewater; the potential use of the reused water (for potable uses or non-potable uses); capital and operating costs; and, existing local facilities and skills for the maintenance and operation of the selected facility.

Extent of Use

For health and aesthetic reasons, reuse of treated sewage effluent is presently limited largely to non-potable applications such as irrigation and industrial cooling (UNESCO, 1991). Examples of such uses on small islands include irrigation on the Cape Verde islands; sanitation (toilet flushing) and garden watering in the US Virgin Islands and Fiji; irrigation of tomato plantations, golf courses, and municipal gardens in the Canary Islands; irrigation of a golf course on Bermuda; and, irrigation of a golf course and use as a water source for an ornamental pond in a bird sanctuary on Aruba. There are no known schemes in SIDS which utilise treated wastewater from sewage systems for potable purposes.

Operation and Maintenance

Wastewater treatment facilities require a high level of operation and maintenance, and close monitoring of discharge effluent quality to minimise health and environmental risks associated with wastewater reuse.

Level of Involvement

This technology requires engineers and highly skilled plant operators for both construction and operation of reuse facilities.

Costs

The costs of wastewater treatment are inevitably high, but will vary widely according to location, type of wastewater being treated, and public requirements governing the degree of treatment needed before reuse is acceptable. Costs for small island applications are not readily available. However, the main component of the cost would be the cost of the wastewater treatment plant.

Effectiveness of the Technology

This technology can produce large quantities of low quality water which can be used to service high water consumptive uses such as irrigation. This use conserves the available freshwater resources for more essential purposes including domestic use.

Suitability

The potential for wastewater reuse on small islands may be limited for a number of reasons. On very small islands, there may be insufficient land for agriculture or industry. This limits the amount of potential wastewater as well as the potential for its reuse; some small islands may not have a suitable source of wastewater. If seawater flushing is already used in sewage systems as a means of conserving freshwater, the resultant wastewater cannot be used. Notwithstanding, opportunities do exist for the use of wastewater on a small scale. For instance, tourist resorts can make use of treated wastewater from package treatment plants to irrigate gardens and lawns (UNESCO, 1991).

Advantages

Wastewater reuse conserves freshwater resources, by making use of the potentially large volumes of low quality water for irrigation and similar uses.

Disadvantages

Wastewater reuse carries a potential public health risk when directly reused for potable use or indirectly reused to irrigate crops that are commonly eaten without cooking (e.g., vegetable crops such as tomatoes and most fruit crops). Consumers may also be unwilling to use treated wastewater for agricultural and domestic uses. Variations in wastewater flows and composition may lead to variable quality of the treated water for irrigation use. Close monitoring of the treatment processes by skilled staff is required.

Cultural Acceptability

Some cultures may have a problem with using wastewater to irrigate food crops.

Further Development of the Technology

As wastewater discharge standards for urban areas, hotels, and industries become stricter, more cost effective methods to treat wastewater that could be reused or recycled are likely to be developed, especially in the case of industry.

Information Sources

AGDRE [Australian Government Department of Resources and Energy] 1983. Water Technology, Reuse and Efficiency, Water 2000. Australian Government Department of Resources and Energy Report No. 10, Canberra.

Malhew, K. and G. Ho (Ed.) 1994. Workshop Papers on Localised Treatments and Recycling of Domestic Wastewater. Murdoch University, Perth.

Shuval, H.I., B. Fattal, and P. Yekutiel 1986. State of the Art Review: an Epidemiological Approach to Health Effects of Wastewater Reuse. Water Science and Technology, 18(9):147-161.

UNDTCD [United Nations Department of Technical Cooperation and Development] 1985. The Use of Non-conventional Water Resources in Developing Countries. United Nations Natural Resources/Water Series No. 14.

United Nations 1987. Non-Conventional Water Resources Use in Developing Countries. Proceedings of the Interregional Seminar. United Nations Natural Resources/Water Series No. 22.

UNDESD [United Nations Department of Economic and Social Development] 1992. Water Resources Management Techniques for Small Islands. United Nations Report No. INT-88-R41, United Nations, New York.

UNESCO [United Nations Education Scientific and Cultural Organization] 1991. Hydrology and Water Resources of Small Islands, A Practical Guide. Studies and Reports on Hydrology No. 49, UNESCO, Paris.

Vlugman, A. 1990. Country Report on Waste-Water Treatment Facilities in Barbados. Pan-American Health Organisation (PAHO/CEPIS), Washington.

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