Utilization of Reclaimed Wastewater for Irrigation and Urban Activities in Okinawa Island, Japan

Reclaimed wastewater (RWW) has been introduced in the Okinawa Island, Japan as an alternative water resource for the existing water scarcity. Currently, RWW is utilized for various urban activities on large-scale. Further, a large-scale project on the RWW irrigation has already been designed in order to be implemented within the next few years. At present, a number of experiments on reclaiming secondary treated wastewater and irrigating on crops are in progress. An experimental reclamation plant has been established in the Naha Wastewater Treatment Plant (NWWTP) to produce RWW. RWW from the above plant is irrigated on crops in several experimental fields. One of the key concerns of these experiments is to investigate the adverse effects on the human health in relation to the consumption of the crops irrigated with RWW.In addition, the effect on the crop quality and the environmental pollution likely to arise due to the various contaminants found in RWW are addressed. Field lysimeters are located in several such experimental fields for the investigations on the adverse environmental effects. The results of the past experiments conducted on these lysimeters indicated to some extent that the nitrogenous compounds of RWW are likely to transfer towards groundwater aquifers under the long-term exposure. However, these conclusions accompany uncertainties since the vast effect of the soil and soil solution on the characteristics of the percolates collected from the lysimeters has masked the proper understanding of the fate of RWW in soil.