Abstract
The authors had proposed a new method of nitrate nitrogen (NO3-N) removal for drainage from agricultural fields with a layer of waste sludge that was disposed of from rural sewage plants. The present study subsequently investigated nitrate removal ability of the sludge layer. The results indicated that waste sludge (around four months after the removal from a wastewater treatment process) possessed higher nitrate removal potential than upland soil as follows.(1) The sludge contained 106-108 MPN·g-1MLSS of denitrifying bacteria (MPN; most probable number, MLSS; mixed liquor suspended solids).(2) The sludge showed NO3-N removal rate of 0.76 mgN·g-1MLVSS·gd-1 at 20°C and 10 mgN·gl-1 of NO3-N and oxygen consumption rates of 5.9-16.8 mgO·gg-1MLVSS·gd-1 at 20°C (MLVSS; mixed liquor volatile suspended solids). In addition, sludge layers that were formed at around 96 % of the moisture content, showed low hydraulic conductivity of 10-6 cm·s-1, which was comparable to clay. Such low permeability will ensure sufficient retention time for denitrification when water infiltrates through a sludge layer.
