The Pilot System is Now Working in Tami, Yap
Since fiscal year 2024, TRCT and Ecoplus have been carrying out a toilet wastewater purification project on Yap Island in the Federated States of Micronesia, with support from Japan’s Global Environment Fund. The project addresses the introduction of flush toilets without sewage treatment facilities amid Yap’s ongoing “modernization.” Under the guidance of Nihon University College of Engineering Professor Kazunori Nakano, the project aims to purify wastewater using an “artificial wetland system.”
In fiscal year 2024, a pilot system featuring three layers of sand filtration beds, each 30 to 60 centimeters thick, was constructed. Trial operations connected to actual toilets began in the summer of 2025.
Measurements to date show that wastewater passing through the pilot system exhibits biochemical oxygen demand (BOD) values ranging from 20 to 100 mg/l. Since toilet wastewater typically has a BOD of 260 mg/l upon discharge, Professor Nakano evaluates this as achieving “purification to levels between half and one-tenth or less.”
In Japan, the discharge standard for household septic tanks is 20 mg/l, and the measured values are approaching this standard.
On Yap Island, sewage treatment facilities are only available in the central urban area. However, many households across the island have installed flush toilets.
A survey conducted for this project found that 25% of the 91 households in the Tamil area used traditional toilets with dug pits or bushes and 75% had installed flush toilets. Regarding these flush toilets, however, practices included storing in a tank, percolating underground, or direct discharge. Only about 20% of households knew where the wastewater was actually going.
A key feature of this artificial wetland system is its use of locally sourced materials for the filtration layers. The three-stage filtration system uses small stones, about 2 cm in diameter, for the first layer; stones, slightly under 1cm, for the second layer; and sea sand for the final layer.
Wastewater decomposes and purifies through the action of microorganisms, such as bacteria, that form in each layer.
Although Yap Island retains strong traditional elements, it has experienced a rapid wave of modernization. Support from developed nations has brought infrastructure such as power plants, roads, and internet. However, the so-called “downstream” infrastructure, such as garbage sites and sewage facilities, has been put off. The purification of toilet waste and household drainage remains largely untouched.
Therefore, building an effective wastewater treatment system using locally available materials is crucial for improving sanitation, reducing the impact on ecosystems, and preventing the contamination of groundwater.
TRCT and Ecoplus hope that this pilot system’s operational status will be shared across Yap State and, furthermore, throughout the Federated States of Micronesia and the Pacific Islands, thereby contributing to the solution of these challenges.
