Comparative Laboratory Study of Sewage Treatment by a Capillary Siphon Trench System Versus a Conventional Leaching Trench System

摘要

Laboratory tests were conducted to investigate the performance of the 'Niimi Process' or capillary siphon trench, a soil based wastewater disposal system common in Japan. The system is similar to conventional septic tank leaching field trenches except that the trenches are filled with capillary sand instead of gravel and the lower quarter of the trench is lined with an impermeable membrane. The capillary sand and impermeable membrane are used to induce unsaturated flow of wastewater through the upper soil profile, or zone of aeration, where maximum biological activity occurs. The Niimi Process was evaluated by constructing a laboratory scale Niimi Process trench and a conventional soil absorption trench. Synthetic wastewater characteristic of domestic sewage was then applied to the two trenches in two 14-week experiments. No statistically significant differences were found between the operation of the two systems except for NO3-N and Total-N removal during the second experiment where the Niimi trench was slightly more effective.