Wastewater management in inhabited conservation areas
People have been living on islands for decades. It may be from the busiest, well-developed island to the most isolated one. People are drawn to reside on an island due to its beauty and rich marine biodiversity. As more resorts and tourism spots were developed, there has been a significant spike of inhabited island. Human expansion on an island is often followed by a large number of wastes, which may include solid based litter such as marine debris or wastewater. Wastewater or sewage is the most significant source of marine pollution on an inhabited island. Apart from the foul smell, critical environmental and public health problems resulting from poorly treated wastewater has been identified. These include algae blooms and eutrophication in lagoons, dying reefs, contaminated drinking water wells, and outbreaks of gastro-intestinal disease and cholera. The cause of this pollution is often due to the improper disposal of sewage waste.
One of the commonly used wastewater treatment methods is through septic tanks, installed for the use of each household. For example, at Pulau Siladen, Indonesia, individual small septic pits are situated under each lavatory. This is a primitive ancient Dutch method of sewage disposal, where layers of dirt, coral, and natural fibers filter the effluent by each toilet, collecting the sludge in the membranes. Due to the poor level of treatment and the residual sludge remaining within the ground, this does not classify as an adequate and sustainable practice for providing proper sanitation.
Another case of improper sewage disposal have been reported in Ambergris Caye, Belize. In certain areas, concerned residents point out the daily leakage of raw sewage and blackwater into the western coast of the island and septic tanks along leach beds built near the waterline. Some pipes can be seen protruding from the ground through which the waste allegedly leaks into the environment. The waste is sometimes consumed by marine life while some of it is carried away by the currents. Contaminated groundwater may also occur especially during heavy rainfall due to sewage residue runoffs which originated from infiltration of septic tank effluent. From heavily populated to small islands, more or less, are sharing a common wastewater treatment problem.
The alarming state of the wastewater issue has been made aware to local authorities and are working together with engineers to provide wastewater solutions by implementing an integrated approach and efficient wastewater treatment plan. One of them is by introducing a natural sewage treatment plan. Puerto Villamil on Isabela Island, Ecuador has been using this approach to treat its sewage. It is home to more than 3,500 permanent residents but historically was unable to treat its sewage waste effectively. A major issue threatening both local inhabitants and wildlife was the leaching of bacteria, metals, plastics, pesticides, and sludge into the surrounding ecosystems as there was no treatment system in place. To tackle this, in 2016 WWF contracted an expert to design a low-cost and low-maintenance solution for the municipality of Puerto Villamil, which included updating an existing naval tank with a natural sewage treatment plan using the Reedbed system to reduce environmental contamination.
The Reedbed system is a constructed or artificial wetland system that mimics natural wetland ecosystems. The refurnished naval tank now serves as a septic tank, which separates sewage water from the sludge, as well as other solid components such as plastics, sand, and gravel. The separated sewage water is then passed into five newly created wetlands, providing vital nutrients for several endemic and native species of plants. The new system also has benefits for local residents, as the treated water can be reuse for everyday tasks such as gardening, cleaning cars, and general municipal tasks. Additionally, reusing sewage water reduces the strains placed on freshwater sources on the island by residents. The entire system also low cost as it requires very little maintenance, with the wetlands needing just one hour of maintenance a day, and the treatment system needing checking just once a week. This treatment plant is the biggest of its type in Ecuador and the plan is to implement this sort of design throughout the entire island of Isabela and other islands in Galapagos.
Another method used to curb wastewater problem is by vacuum sewer system. This method was proposed by the German Agency for International Cooperation (GIZ) under the Urban Nexus Project, which provides technical advice for the wastewater treatment system in the coastal settlement of Senggarang Tanjungpinang, Indonesia. The existing infrastructural works for functional water and wastewater management in Senggarang are still limited. Wastewater from the houses at the jetties is directly dumped into the sea. The wastewater from the houses on the ground is led into septic tanks under the floor of the houses. The septic tank overflows flow via open drains directly into the sea.
Conventional drains using gravity flow were tested but failed due to the low height difference between the houses and the discharge point.
Vacuum sewerage systems consist of a vacuum station, where the vacuum is generated, the vacuum pipeline system, collection chambers with collection tanks, and interface valve units. In contrast to conventional gravity sewerage systems with intermediate pumping stations, the permanent pressure within the vacuum system is maintained below atmospheric pressure. Moreover, vacuum technology reduces water consumption considerably, enabling flexible installations regardless of topography and water availability. The vacuum sewer system is the most appropriate collection system as this system can be operated in environments where no gravity slope between the points of discharge and transfer is available. Recent references on vacuum sewer systems implementation are in Maldives, and Danang, Vietnam. In addition, this wastewater management system provides options for water reuse such as treated sludge as fertilizers.
Developing and implementing a truly sustainable wastewater strategy for inhabited islands can be challenging, and this becomes even more difficult for those that are particularly very remote. However, with appropriate levels of realism and pragmatism, it is possible to adopt an approach that provides adequate protection to the local environment. It is important to ensure the continuation of sustainable wastewater management system which largely depends on the availability of operational and maintenance cost, as well as adequate training, knowledge transfer and dissemination for development of a new wastewater treatment project.