Abstract
Effect of biomass on the soil hydraulic conductivity was clarified for andosol soil. The approximate value of the maximum allowable density of biomass was determined as 30mg·cm-3, which corresponds to the minimum hydraulic conductivity of the clogged andosol soil : 2 ×10-5 cm·s-1.
Two-dimensional infiltration experiments were carried out. Infiltration rate decreased as the synthetic sewage percolated into the soil, but finally it achieved the steady state. TOC removal and ATP distribution were measured, and on the basis of these results and the mass balance of the substrate, the mechanisms of the biological clogging was discussed.
In addition, a numerical model was constructed, and the biomass growth and the change of permeability were simulated. Calculated results were compared with the results of two dimensional infiltration flow experiments. By using the model, the conditions to avoid the infiltration failure were determined. The allowable wastewater feed rate of 0.04m3·m-trench-1·d-1 for the BOD concentration of 100mg·l-1 was obtained, which is smaller than the expected value in the empirical criteria.
