¹⁵Nトレーサー法を用いたヨシフィルターの窒素除去性能に関する研究

抄録

The mechanisms of nutrient removal in sand-filled reed filter bed system (RFB system) are explained by filtration, sedimentation, plant uptake and microbial degradation occurring in soil-water interface and in the plant rhizosphere, which includes nitrification-denitrification process. There is, however, little information on it, especially information on denitrificaton rate in RFB system has not been obtained. The objective of this study is to measure denitrification rates using ¹⁵N tracer method and investigate seasonal changes of them throughout a year. The results of bench-scale RFB system using ¹⁵N tracer method showed that the denitrification rates of the RFB and the sand tank without reeds ranged from 0.0∼5.5 (average 2.28) and 0.0∼3.4 (average 1.48) g-N · m^-2 · d^-1, respectively. These values mean that about 60% in the RFB and about 80% in the sand tank for inflow nitrogen loading were removed by denitrification. A part of remaining nitrogen loss in nitrogen balance of the RFB tank might be caused by plant uptake. High denitrification rate in the RFB suggested that microbial activity in the reed rhizosphere played an important role in nitrogen removal efficiency during the stationary phase of reed's growth curve.