Reuse of Reclaimed Water for Irrigation on Paddy Rice Culture and Its Effect

The effect of reclaimed water irrigation on paddy rice culture was evaluated by pilot study at the experimental field of Konkuk University in Seoul, Korea. The sewage was treated by constructed wetland system, and its effluent was used as irrigation water for four treatments and one control plots with three replications. Irrigation of reclaimed water onto paddy rice cultures did not adversely affect the growth and yield of rice. Instead, experimental rice plots of reclaimed water irrigation displayed about 10 to 50% more yield on average than controls. This implies that reclaimed water irrigation might be beneficial rather than harmful to rice culture as long as the sewage is treated adequately and used properly. The amount of irrigation water had little effect on experimental rice cultures, but its strength was important. The strength of treated sewage was not a limiting factor in this study, and no lodging was observed even with a relatively high nitrogen concentration (up to 160mg/L). In general the paddy soil was not affected by reclaimed water irrigation. However, there was an indication that continuous irrigation with high strength of reclaimed water might cause salt accumulation in the soil. Supplemental use of reclaimed water with existing sources of irrigation water is recommended rather than irrigation with a single source of reclaimed water. Overall, the results demonstrated that reclaimed water could be reused as a supplemental source of irrigation water for paddy rice culture without causing adverse effects as long as it is properly managed. For full-scale application, further investigation should be done on environmental risks, tolerable water quality, and fraction of supplemental irrigation.