Abstract
The purpose of this research was to evaluate the effect of the secondary effluent irrigation by the trench method. Irrigation was continued at a mean rate of 86 1/ (m-trench·d). Soil samples were collected from a test area at each 50-cm-mesh point over the range of 300 cm depth and 500 cm width. Soil permeating water samples were collected with soil-permeating- water sampling devices set at a depth of 120 cm and analyzed together with secondary effluent samples to compare concentrations of chemical components. The average removal of chemical components in soil permeating water based on the secondary effluent was found to be 89.3% in biological oxygen demand (BOD), 92.4% in total phosphorus (T-P), and 22.8% in total nitrogen (T-N). However, accumulation of T-N, T-P, or total carbon (T-C) in soil was rarely observed, and in the lower layer the concentration of these substances was in a negative correlation with the electric conductance of soil extracts (ECex), a measure indicating the amount of secondary effluent loading on soil. Concentrations of nitrate nitrogen (NO-3-N) and chloride ion (Cl-) in soil increased in a positive correlation with ECex anywhere in the secondary effluent permeating area.
