Study on water quality purification method by aquatic plants at a reservoir for small-scale water supply

The reservoir used for water supply on Haha-jima Island had been experiencing eutrophication. In order to improve water quality an experimental hydrophytic system was set up on-site in 2007. Full-scale operations began from 2009. In this paper, the effectiveness of hydrophytes in improving water quality purification was evaluated. The amount of total nitrogen and total phosphorus that was removed was calculated from the production of plants. Estimated equations of total nitrogen and total phosphorus levels were made by using multiple regression analysis, which were highly statistically significant. Due to the limited water quality data of total nitrogen and total phosphorus concentrations, past data of other recorded measurements for water quality were used and assigned as explaining variables. Furthermore, the concentrations of past total nitrogen and total phosphorus were calculated based on these estimated equations and the state of eutrophication of the reservoir was simulated as longitudinal data. The results of this research are applicable for water quality control and management of other isolated islands, depopulated areas, and developing countries where specialized measuring instruments to determine water quality may be unavailable.