Water Quality Management in the Yodo River Basin – Case Study

This study investigated an appropriate sewage treatment system to be applied in a river basin where river water is re-used repeatedly. Many sewage effluents are discharged into the river's up-streamside from intake points for drinking water. The Yodo river was selected as a case study. The obtained results are as follows; 1) Investigations of COD, NH₄-N, THMFP are necessary in polluted rivers used as drinkingwater sources. 2) The effect of a sewage treatment system construction for river water conservation should be evaluated with the predicted water quality in the low flow and the average flow condition. 3) Time and place variations of NH₄-N concentration in the Yodo river are predicted by adaptation of a two dimensional unsteady diffusion model. 4) The greater part of TN or NH₄-N load deposited at the Yodo river branches in the dry weather condition are washed away by the wet flow condition. 5) It will be possible to maintain the present water quality level for TN and NH₄-N in the future, despite an increase of population in the Yodo area and the construction of a conventional sewage treatment system. 6) However, an adaptation of an advanced sewage treatment system is recommended for re-use as drinking water of the Yodo river water.