Since 1998, the island of Bora Bora regularly has to face water shortages, due primarily to decreasing rainfall and frequent droughts combined with hotel development and population growth. As a result, severe water shortage has been observed with periodic interruptions of water supply. In 2000, to ensure a reliable water supply 24/24 h, the island was equipped with alternative resources such as desalination and water reuse.

Consequently, a municipal policy of sustainable development was implemented in Bora Bora, known as the "Pearl of the Pacific" and globally renowned for the beauty of its lagoon. This policy found support in an intense willingness of the elected representatives for a meticulous respect of the environment, preservation of the island's charm and water resources, as well as building design adapted to landscape and local tradition. The concept of sustainable development of the municipality of Bora Bora is a model of economic development and aims at a conciliation of the following elements (Figure 1):

A very important element in this policy is the management of water resources. The freshwater resources of the island are not sufficient to provide for the resident population (8,000 inhabitants) and 200,000 tourists a year. Following a growth in water demand and increasingly more severe dry seasons, the production capacity of drinking water was due to be increased several times, with the introduction of alternative resources such as desalination of seawater and water reuse (Figure 2).

The major steps in improving the island’s water supply were:

It is important to emphasize that in the context of sustainable development, water resource management should include not only reliable water supply, but also adequate sanitation services of collection and treatment of wastewater. In the case of Bora Bora, the construction of hotels and housing rapidly upset the island’s way of life: uncontrolled sewage discharge led to the eutrophication of the lagoon and the beautiful white-sand beaches started to be covered by green algae. It was under the leadership of its elected officials that the Island was then attached to adopt all possible means to achieve efficient sanitation services.

All raw sewage of the island is collected and transported in a pressurized network by means of 70 pumping stations. It is then treated in two wastewater treatment plants (one on the north side and the other on the south side of the island). The first water reuse scheme was build on the basis of a natural tertiary treatment in a maturation pond. However, the quality of this recycled water was not approved by the local health authorities for spray irrigation. Moreover, recurrent odor problems and bacteria regrowth (in particular sulfur-reducing bacteria) in the distribution network associated to the relatively high cost of recycled water led the consumers, in particular the luxury hotels, to limit their recycled water demand.

In 2005, the water reuse project was upgraded to the production of high quality recycled water for unrestricted non-potable urban uses. Over the years, this project has expanded, including diversification of water reuse applications and design of a new project for indirect potable reuse. The recycled water distribution network has been extended to completely cover the demand of non-potable water of all luxury hotels. The quality of recycled water is rigorously monitored by the Territorial Public Health and Hygiene Department. The good quality of basic wastewater treatment and the reduced wastewater discharge have had a pronounced effect on the natural habitat, the algae development was stopped, the white-sand beaches have been restored to the original beauty so treasured by tourists and photographers around the world.

Therefore, the strong willingness of the local decision makers for the protection and restoration of environment was the first driver for implementing sanitation, which in turn has made possible water reuse and the resulting additional environmental enhancement. In addition to the protection of environment and water reuse, the other measures adopted by the municipality in the frame of their program on sustainable development is the use of geothermal energy for cooling, use of solar energy, preservation of local tradition and employment, as well as social and economic development taking advantage of revenues generated by tourist activity. Thus, Bora Bora was the only municipality of French Polynesia, which has been awarded the “Blue Flag of Europe” and has been able to preserve this award for ten consecutive years. This categorization is highly prized by foreign visitors, mostly from northern Europe, who tend to select their vacation spot based on environmental criteria.

In summary, the most important driving forces for the implementation of water reuse in Bora Bora were water stress (impacts of climate change and frequent droughts) and the increasing water demand of tourist activities. The strong community engagement with close cooperation between stakeholders was the major factor for the recognition of the benefits of water reuse and its important role in integrated water resource management of this isolated tourist island.

The new recycling scheme, implemented in 2005 in the wastewater treatment plant of Povai, included an advanced membrane treatment by ultrafiltration, using the hollow fiber submerged membranes Zenon manufactured by GE Water (Figure 3). The existing maturation pond was upgraded for storage of storm water. Recycled water is stored in covered reservoir and pumped into the industrial (non-potable) water distribution network after chlorination in order to maintain 0.5 mg/L chlorine residual. The choice of ultrafiltration as tertiary treatment was driven by the willingness to produce recycled water of high quality that is completely disinfected. The ultrafiltration membranes have small pore size of 0.035 µm, which represents an effective physical barrier for all microorganisms and pathogens, including protozoa, cysts, bacteria and viruses.

The excess sludge is treated and recycled by rhizocomposting in reed beds. The compost obtained (>1200 m³/year) is reused to fertilize the poor coral based soils of hotel’s landscapes, public areas and private gardens.

Table 1 illustrates the routine monitoring of wastewater quality (raw sewage, secondary effluent and recycled water) for one year. Despite the high variations of raw sewage characteristics, tertiary ultrafiltration consistently produced an effluent with a very good quality, almost free of suspended solids and with a very low content of organic carbon. The produced recycled water was almost totally disinfected. The detailed microbiological monitoring during the first 6-months of operation demonstrated the good removal of all monitored indicators (E.coli, enterococci, total coliforms, Clostridium spores) and pathogens (Salmonella spp.). Salmonella spp. were not detected in any sample of recycled water. As a rule, microbial indicators were always below detection limits in all samples from the inlets of membranes and the storage reservoir.

During the 5-year operation of the submerged UF membranes, only two samples at the inlet of the ultrafiltration were contaminated with fecal coliforms (E.coli repectively 64 and 100 MPN/100mL) and Clostridium spores (respectively 20 and 60 UFC/20 mL). The additional chlorination was able to inactivate the residual E.coli to concentration below 10/100 mL, but 7 to 10 UFC/20 mL of Clostridium spores still remained in the recycled water.

The poor microbiological quality was due to operational failures of valve leakage and overflow of unfiltered secondary effluent. To improve the reliability of operation of the ultrafiltration, the treatment plant was upgraded to not allow any by-pass of unfiltered water or external contamination of the permeate. An on-line turbidity measurement was recommended as an efficient measure to control any valve leakages or breaks of membrane fibbers.

The analysis of agronomic parameters, shown in Table 2, indicates slight to moderate restriction on the use of this recycled water for irrigation [10]. Sodium is the dominant cation with a concentration of 176 mg/L resulting on a relatively high sodicity with a sodium adsorption ratio, SAR of 4.9.

As the conductivity is also relatively high, about 1400 µS/cm, no specific restrictions on the use for irrigation could be required. In fact, as demonstrated by years of research, the ratio of salinity to sodicity (SAR) determines the effects of salts and sodium on soils. Salinity promotes soil flocculation and sodicity promotes soil dispersion. As the values of both salinity and sodicity are moderate, no effect on infiltration rate can be expected from the irrigation with this recycled water. Other factors such as climate, soil type, crop and plant species and management practices also need to be accounted for when determining the acceptable levels of salinity and sodicity of irrigation water. In the case of Bora Bora, the soil has a high permeability, as constituted predominantly of calcareous sand.

The dominant toxic ion is chloride with a concentration of 271 mg/L, which can cause foliar damage to sensitive plants. Bicarbonate content is also relatively high, 223 mg/L, with a risk of carbonate precipitation during sprinkling. The monitored trace elements are below the recommended maximum concentration limits in irrigation water.

Compared to some decorative plants, the turf grass used in the island is characterized by high salinity tolerance. During the 5-year period of use of recycled water for sprinkler irrigation, no negative impacts on vegetation and turf grass were reported.

The most important requirement of the end users was the reliability of supply of recycled water 24/24 h. Consequently, specific operating and maintenance procedures have been implemented to achieve 100% reliability of the operation of the recycling facility.

Figure 4 illustrates the evolution of the permeability of submerged ultrafiltration membranes in Bora Bora for the investigated period. Applying the recommended maintenance and cleaning procedures, a good recovery of membrane permeability was observed, 202 to 247 L/ h·m² bar at 20 °C compared to the initial value of 250 L/h·m² bar. It is important to underline that despite some minor operational failures and a major damage of the wastewater treatment plant in September 2005, due to a tsunami with seawater intrusion and loss of activated sludge from the clarifier, an excellent membrane flux was consistently maintained at 24 ± 2 L/h·m² at 20 °C.

Preventive measures against membrane fouling are the crucial factor to avoid excessive loss of membrane permeability (on-line cleaning using scouring air, backpulses, membrane relax, automated maintenance cleaning). The frequency of chemical recovery cleaning varied from 2 to 6 months depending on the wastewater quality. By safety, the recovery cleaning was carried out before reaching the lower limit value of the permeability, which was fixed at 100 L/h·m² bar.

The adequate choice of the treatment technology and the ability to provide high-quality recycled water without any interruption were the two key factors that ensured the fast growth in recycled water demand (Figure 5). A twofold increase in the recycled water consumption was observed shortly after the start-up of the new recycling facility, with an average annual volume of about 70,000 m³/yr. The number of end users in early 2006 tripled compared to that in 2004.

Large consumers are primarily the luxury hotels with landscape irrigation as the major use of recycled water (Figure 6). For 8 of these located on “motu” (small coral islands), the connections were achieved by means of underwater drains (0.5 to 2 km, maximum depth 40 m).

The growth in recycled water demand was associated with the development of other urban uses than the traditional landscape irrigation:

Currently, new satellites recycling facilities are under development for golf course irrigation and aquifer recharge.

Capital costs were covered by governmental subsidies, loans and a public-private partnership. The operating and maintenance costs are about 38% of the life costs. The main component of operating costs is labor, accounting for 46% of total operation costs, followed by repair and maintenance, 21%. The cost of spare parts and scouring equipment is relatively high because the remoteness of this island, and thus, the high transportation costs. Chemical costs for membrane cleaning and final chlorination contribute to another 12% of operating costs. Despite the very high price of electricity (0.18 €/kWh) in this isolated tourist island, the contribution of energy costs is only 14%, a relatively low percentage.

The average energy consumption at nominal flow is estimated at 0.36 kWh/m³ with a twofold increase to 0.62 kWh/m³ when hydraulic load drops to 50% (Figure 7). During operation with flow rates below 30%, the energy consumption raises to 1.0–1.6 kWh/m3 due to the high fixed energy needs of membrane treatment.

Large users, i.e., the luxury hotels, were the first to recognize the economic benefits of water reuse as the cost of high-quality recycled water was, in fact, 2.5 to 3 times less expensive than potable water. Consequently, recycled water demand increased, encouraged further by an appealing pricing policy.

In the case of Bora Bora, pricing decision was a crucial factor for the success and economic viability of the water reuse project. As underlined in previous studies [11], recycled water price must reflect the end-users’ willingness to pay and the reliability of recycled water supply. The municipality of Bora Bora selected a declining block rate, considered as the most appropriate pricing instrument to achieve economies in delivery costs and attract large water-consumers while providing lower charges for small private users (Table 3).

According to this new recycled water pricing established in November 2005, recycled water charges vary from 30 to 100% of the potable water rate, depending on the user category in terms of water demand. In addition to these consumption-based rates, a fixed annual charge of 187 € is required for each connection. In comparison, the previous recycled water charge for polished secondary effluent (not allowed for spray irrigation and other urban uses) was fixed at 0.67 €/m³ regardless of water consumption.

The adequate pricing of recycled water ensured the economic viability of water reuse. This enabled to cover the operating and maintenance costs of tertiary treatment, pumping and distribution network.

In addition to economic benefits to large end-users, another important benefit was the avoided revenue losses of private building and tourist companies during drought periods. In fact, because of severe drought at the end of 2005, the use of drinking water for non-potable purposes was proscribed and four important building sites were to be interrupted because of the lack of water for concrete preparation and tests, as well as for landscaping. The economic damage that has been caused by the delay of construction was estimated at 2 to 3 million €. This does not take into account the potential loss of revenue during the peak tourist season that would have been over 50 million €.

The economic and social benefits of the new recycling scheme were also recognized by the local public authorities. The start-up of the membrane facility enabled not only to postpone the construction of an additional desalination plant, but also to limit frequent and unavoidable water supply interruptions for the local residents during drought periods.

Finally, the principal environmental benefit of the reuse of well-treated wastewater was the protection of local natural freshwater resources with an estimated saving of 10% of drinking water for domestic potable uses. Another important environmental benefit is the reduction of wastewater discharge, contributing to the safeguard of the lagoon and its biodiversity.

An important factor for the appreciation and recognition of economic viability and water reuse benefits is strong community involvement, political support and active collaboration between stakeholders (decision-makers, legislative officers, operators, end-users, local residents).

Public education program was an essential part of the water reuse project. Periodic forums have been organized with the municipality, legislative officers, consultants, operators, local entities, end users and public representatives to present the membrane technology, water quality and health aspects, as well as to assess economic and environmental benefits of water reuse (Figure 8).

Currently, several new water reuse projects with an extension of the existing recycling facility are under consideration: