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close this bookSourcebook of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean (UNEP-IETC - OAS, 1998, 247 p.)
close this folderPart C. Case studies
View the document5.1 Rainwater harvesting in Honduras
View the document5.2 Fog harvesting in Chile
View the document5.3 Underground dams in Brazil
View the document5.4 Seawater/brackish water desalination by reverse osmosis in the British Virgin Islands
View the document5.5 Recycling of industrial effluent in Jamaica
View the document5.6 Treated wastewater reuse scheme in Barbados
View the document5.7 Clay pot and porous capsule irrigation

5.6 Treated wastewater reuse scheme in Barbados

Sam Lord's Castle Hotel is located on the southeastern coast of Barbados, in the parish of St. Philip. It lies within the coral-covered portion of the island, with a coral cap thickness of about 80 ft. With an average annual rainfall of 45 inches, this is one of the driest areas of the island (the average annual rainfall for the whole island is 60 inches). In this area, except for 4 months of the year (August to November), the average evapotranspiration rate, 4.5 inches/month, exceeds the monthly rainfall figures. The groundwater resources in this area consist of a thin freshwater lens floating on top of saline water.

The hotel was formerly supplied with freshwater from a groundwater well, but because of the high water demand, especially for the irrigation of large expanses of lawns and garden plants, saline groundwater intruded into it to the point where the freshwater supply was virtually exhausted. A decision was made then to abandon the use of the well and the hotel sent an application to the Ministry of Health and Environment seeking permission to use the treated effluent from its extended aeration sewage treatment plant for irrigating lawns and garden plants. Permission for wastewater reuse was granted and treated wastewater was diverted to irrigation use from its former disposal site in four deep suckwells.

This technology is described in Part B, Chapter 3, "Wastewater Treatment Technologies and Reuse."

Technical Description

Effluent consisting of kitchen, laundry, and domestic sewage is conveyed to a collection chamber, from which it is pumped through a comminutor to an aeration chamber. No primary sedimentation is provided. The aerated mixed liquor then flows out of the aeration chamber through a rectangular opening at one end into a clarifier for gravity separation of solids. The effluent from the clarifier chamber is then passed through a 16-foot-deep chlorine disinfection chamber and pumped to an automatic sprinkler irrigation system. The irrigated areas are sub-divided into 16 zones with 12 sprinklers each. Some areas also have a drip irrigation system. This process is illustrated in Figure 46.

Sludge with a high water content is pumped from the sludge chamber to the suckwells for disposal without thickening. Previously this sludge was pumped to the Bridgetown Sewage Treatment Plant for further treatment and additional desludging. This pumping incurred additional transportation costs.

The packaged wastewater treatment plant was designed abroad and constructed using local contractors. The drip and sprinkler irrigation systems were designed and installed in part by a local irrigation system consulting company and in part by the hotel's maintenance personnel. The Environmental Engineering Division (EED) of the Ministry of Health and Environment was responsible for approving, monitoring, and controlling the operation of the packaged plant. Thus, despite the absence of effluent standards enacted into law, some conditions were placed on the system before permission was granted for irrigation reuse. The approval process involved consultations with the Town and Country Planning Offices and the Barbados Water Authority (BWA).

Extent of Use

At present, there are twelve wastewater treatment facilities in use in Barbados, ranging in size from 2 860 gpd to 37 400 gpd for hotel facilities and to 594 000 gpd for the Barbados Water Authority plant. The combined total treatment capacity amounts to 786 280 gpd. Eight of these plants are extended aeration plants, three are rotating biological contactor plants, and one, the Barbados Water Authority plant, is a contact stabilization plant. Two more BWA sewerage systems are planned for the south and west coasts, with the intention of reusing their wastewater effluents.

Reuse of treated wastewater for the irrigation of garden plants and lawn grass is limited at present to Sam Lord's Castle Hotel. Another, the Almond Beach Village Hotel, formerly Heywoods Hotel, in St. Peter on the west coast, is almost ready to start irrigating a 9-hole golf course. Other applications for the reuse of wastewater on golf courses (Westmoreland, Kingsland, and Bushy Park) are pending, and a number of major hotels have indicated their interest in applying for permission to reuse their effluent. In addition, plans are in place to reuse some of the treated effluent from the BWA Bridgetown Sewage Treatment Plant for flushing sewer lines.

Operation and Maintenance

According to the report of a survey on the Operational Aspects of Wastewater Treatment Plants in Barbados undertaken by A. Vlugman of PAHO in 1990, the operational status of the Sam Lord's Castle Hotel plant was considered to be moderate. The plant is about twelve years old and the operator reports few problems; those that have occurred are considered minimal (due to grease). There does not seem to be any problem with obtaining spare parts. However, no design or construction drawings are available to help with the operation and maintenance of the plant, and the basic skills required to operate and maintain the plant, such as some knowledge of microbiology, some electrical/mechanical skills to repair the equipment, and some understanding of the treatment process and the impact of poor performance on the whole scheme, are generally lacking.

Considering the small size of most packaged wastewater treatment plants, it may not be cost-effective for each hotel to employ a qualified operator. However, it might be possible for a number of hotels to employ collectively one qualified operator to look after a number of plants. Alternatively, the Barbados Hotels and Tourism Association (BHTA) could employ an environmental officer or sanitary engineer to oversee or advise the various hotels on wastewater treatment and effluent reuse.

The operation and maintenance required consists of turning the pumps that do not run continuously (such as the sludge pumps) on and off, and checking to ensure that all systems are running smoothly without any blockages. There are no flow meters installed and no laboratory facilities of any kind are provided to document the technical performance of the plant. Any operational monitoring of plant and process by the operator is limited to visual inspections. Plant performance is evaluated by the operator on the basis of the color of the mixed liquor in the aeration chamber; a brownish color is an indicator of good performance. Nevertheless, BOD and TSS analyses are done monthly during inspections by the EED.

Level of Involvement

The only government involvement in this program is licensing, monitoring and administrative control, exercised through the EDD, which is charged with the responsibility of approving and monitoring the performance of packaged wastewater treatment plants. The Sam Lord's Castle Hotel plant is entirely privately owned and operated, except for the monthly inspections and sampling for BOD and TSS conducted by the EED.

Costs

As this plant is privately owned and operated, cost figures are not available.

Effectiveness of the Technology

Based on 1989 and 1990 results, BOD and TSS removal efficiencies of 86%, and of 98% and 83%, respectively, are achievable. Data on the microbiological quality of the effluent are not available; two chlorine tablets are put into the chlorination chamber each week, regardless of effluent quality or quantity. Hence there is need to evaluate in detail the effectiveness of the disinfection before the effluent is used for irrigation. However, from an aesthetic point of view, the irrigation of lawns and plants seems to be very successful, as evidenced by the lush greenery surrounding the hotel. This is a great improvement compared to the period before the effluent reuse program was put into place.


Figure 46. Wastewater Treatment Process for Sam Lord's Castle.

Source: John Bwalya Mwansa, Project Manager, Barbados Water Resources Management & Water Loss Studies, Barbados Water Authority.

Suitability

The applicability of this technology depends on the nature of the land. In Barbados, owing to the karstic nature and topography of the coral rock aquifer system, groundwater contamination by reused wastewater can be avoided only if the wastewater is properly treated. At present, there are very few facilities with a suitable effluent quality. However, the hotels in the belt along the south and west coast, downgradient from the line of public water supply wells, would be obvious candidates for application of this reuse technology, posing the least danger of contamination to the groundwater. The hotel belt also has the advantage of being situated next to the BWA wastewater treatment plants.

Advantages

· The use of the treated effluent results in substantial savings in irrigation water costs and reduces the likelihood of water pollution, assuming that the effluents would otherwise have been disposed of through sea outfalls.

· This technology eliminates the need to use potable water supplied by the BWA public domestic supply system for irrigation and makes it available for other uses.

Disadvantages

· Inadequate operation and maintenance may pose some health risks.

· The WHO criteria on wastewater reuse for recreational purposes with possible human contact may not be fully met in this case. These criteria (effluents should not contain more than 100 coliform organisms/100 ml in 80% of samples, and should not contain chemical contaminants that lead to the irritation of mucous membranes and skin) require primary and secondary treatment and sand filtration, or the equivalent. Provision of such treatment would significantly increase the cost of this technology.

· The potential environmental impacts associated with this technology are contamination of groundwater, human skin irritations caused by bacteria or viruses in inadequately disinfected effluent sprayed on lawns or gardens, and mineral buildup (salination) in the soil, none of which are currently monitored on an adequate and continuous basis. (Because of the proximity of the application area to the coast, there is little risk to the domestic groundwater supply from the Sam Lord's Castle Hotel reuse scheme; however, the flow to the sea could still adversely affect the coastal marine ecosystem. In this case, the irrigation is timed to minimize the health risk to the hotel guests.)

Further Development of the Technology

The technology is well developed; however, local engineers and scientists need to familiarize themselves with it and evaluate its suitability for use elsewhere in Barbados, with any necessary modifications. There is also a need to evaluate the effectiveness of the disinfection process (chlorination by gas or chlorine tablets) in eliminating bacteria and viruses. It is very probable that, in future, more hotels will want to reuse effluent from the packaged treatment plants, especially in the light of proposals to change the domestic water tariff structure. Special training programs, in association with the BWA wastewater treatment facilities, should be developed to improve plant performance and monitoring.

Information Sources

Contacts

B. J. Mwansa, Project Manager, Barbados Water Resources Management and Water Loss Studies, "Invermark," Hastings, Christ Church, Barbados. Tel. (809)430-9372/430-9373. Fax (809)430-9374.

Scofield Alleyne, Maintenance Engineer, Almond Beach Village Hotel, St. Peter, Barbados.

Wilfield Moore, Maintenance Officer, Sam Lord's Castle Hotel, St. Philip, Barbados.

Sylvan Catwell, Senior Environmental Engineering Assistant, Ministry of Health and Environment, EED, Culloden Road, St. Michael, Barbados. Tel. (809)436-4820.

Bibliography

Vlugman, Anthony. 1990. Country Report on Waste-Water Treatment Facilities in Barbados. Washington, D.C,. PAHO.