Abstract
Oxygen supply by the photosynthesis of phytoplankton in oxidation ponds was investigated by using outdoor ponds (4m (1) ×8m (w) ×.92m (d)) fed with synthetic wastewater. Hydraulic residence time were 4.4, 8.9, 13.4 and 18.0 days. The numerical model assuming steady state was developed and the following results were obtained by this model.
1) The rate of oxygen supply by phytoplankton per unit area was not so affected by mean residence time nor pond depth, and dependent on the rate of nutrient supply per unit area.
2) The maximum rate of the oxygen supply per unit area ranged from 10 to 15 [g/ (m2day)].
3) The oxidation pond with the depth of im and the appropriate mean residence time of 10 days seemed to be effective for the treatment of gray water.
