Abstract
Soil percolation experiments using aggregated soil of volcanic ash (Akadama) were demonstrated for phosphorus removal from water streams, in which the phosphate removal performance of soil columns and the adsorption capacity of Akadama soil were evaluated through short-term and long-term operations over seven years. The result showed that the removal performance strongly depended on both the empty bed contact time and the thickness of the soil layer. The adsorption capacity test revealed that the cumulative phosphorus adsorption mass was in the range of 0.5-1.5 gP•kg-1, when the phosphate concentration in the effluent began to increase rapidly. A value equivalent to 10% of the phosphate adsorption coefficient was regarded to be the purification capacity of the soil and was suggested to be an effective index for evaluating the lifetime of Akadama soil in facility planning. The regression line obtained from the relationship between effluent phosphorus concentration and cumulative phosphorus adsorption mass may be applicable to the estimation of phosphorus adsorption mass from the observed phosphorus concentration in the effluent. Moreover, cumulative phosphorus adsorption mass could be estimated from water-quality monitoring data, because the cumulative phosphorus removal mass calculated from water-quality monitoring data was in accord with the cumulative phosphorus adsorption mass to some extent.
