Development of Environmentally Sustainable Methods for Treatment of Domestic Wastewater and Handling of Sewage Sludge on Yap Island

A survey was conducted of the wastewater treatment systems and related sludge handling practices on the island of Yap, in the Federated States of Micronesia, to assist in identifying areas where further work would be merited to improve on effectiveness and sustainability. A detailed inventory was made of communal septic tanks as found at health centers and schools. Though most of these septic tanks appeared to be functional, there were concerns due to some units being positioned within the tidal zone, covered over with vegetation, or out of reach of the pump truck. Furthermore, the centralized wastewater treatment plant on Yap provides only primary treatment consisting of a limited removal of suspended solids. Thus, only partially treated sewage is being discharged to the bay. Excess sludge is drawn from the treatment plant on a quarterly basis, which local farmers regularly make use of as fertilizer for crop application without adequate treatment. As an immediate target for further study and pilot testing, exploring the use of an attached-growth process as an inexpensive retrofit to enhance the effectiveness of the treatment plant is proposed. In addition, the benefits of implementing a composting program for recycle of waste sludge in a safe manner and developing a framework for management of septic tanks are discussed.