The first introduction of reclaimed wastewater to dry-farming field in Okinawa Island, Japan

Reclaimed wastewater (RWW) will be introduced to the first large-scale irrigation project for dry-farming on Okinawa Island, Japan. The wastewater reclamation for agricultural use sounds attractive to the water resource management. Since there are no specific standards for the RWW irrigation, the monitoring and other demonstrative experiments have been conducted using the experimental reclamation facility, which is based on the criteria “Title22”. The experiments showed that the existing system is sufficient to meet the above criteria of pathogens, protozoa and viruses, and the concentrations of hazardous chemicals are lower than the environmental standards in Japan. In addition, several laboratory soil column experiments were conducted to address the environmental issues. An increase of denitrification due to the continuous irrigation was observed. Salt and nitrate accumulation in the surface soil was observed as well. We can conclude that the RWW of the above facility assures the safety for human health, and further research based on environmental issues is needed in addition to an integrated risk assessment and communication.