The paper presents results of two year field and laboratory investigations of a denitrifying system below leach lines. More than two days retention time was provided by siphoning of the denitrifying trough located 35 and 60 cm under the leach lines. Due to clogging and capillary suction in medium sand the seepage flow through the denitrifying troughs was limited to less than 10 % of the sewage inflow. Average efficiency of the total nitrogen removal was equal to 55 % after 3-4 days of travel time within the soil. To force wastewater to pass through the anaerobic bed within the trough two lateral vertical impermeable membranes are recommended.
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