Dissolved oxygen budget in a small oxidation pond for the gray water treatment is investigated by using a numerical model. The numerical model incorporates the relation between light intensity and the photosynthesis rate, extinction of incident light by photoplankton, sedimentation of photoplankton, vertical diffusion, atmospheric reaeration and benthic oxygen demand. Diurnal change of vertical distribution of dissolved oxygen concentration in a small pond is used for the verification of the presented model. By using parametric sensitivity analysis, the oxidation pond with the depth of about 1m seemed to be effective for the oxygen supply into the oxidation pond.

View full abstract

An experiment of wastewater treatment was conducted using G, C and E type trench set in three lysimeters in which volcanic ash soil was packed. The main object of this research was to evaluate the behavior of wastewater permeation and the removal efficiency of wastewater in soil, and the following results were obtained.
1) The declining velocity of water level in G, C and E type trench was 11, 4.0 and 1.7 mm·min^-1, respectively.
2) The discharging ratio of soil water from the lysimeter against the volume loaded to the one was 96.6, 84.2 and 73.8% in G, C and E type trench, respectively.
3) The amount of evapotranspiration in G, C and E type trench was 5.1, 6.4 and 11.7 mm·d^-1, respectively.
4) The removal efficiency of BOD, COD, NH₄-N and TP in wastewater was more than 90% in G, C and E type trench.
5) The removal efficiency of TN in wastewater was 27.442.5%, and the value was highest in E type trench.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract