Sequential processes of nitrification and denitrification in a single soil column.

Abstract

A step process containing nitrification and denitrification in a column packed soil was studied by using a synthetical wastewater contained NH₄Cl, NaHCO₃, and KH₂PO₄. An influent was infiltrated by down flow to the soil column, nitrification occured in upper layer which the depth was 20 cm from top of the soil column, and denitrification occured in lower layer. The water level in the column was constantly kept at the depth of 20 cm from top of the column.
When the influent contained methanol as organic carbon was infiltrated into the upper layer to be unsaturated (aerobic) zone, a little nitrification occured and the nitrification was suppressed rather than development, and also denitrification did not occure at the lower layer to be saturated (anaerobic) zone. In the case of no methanol in the influent, a complete nitrification occured at the upper layer. When the methanol solution was injected at the boundary between upper and lower layers, the denitrification was promoted and nitrogen removal was 60-80%.
The rates of nitrification and denitrification were determined by finite-difference procedure as an inverse problem for a reactive convectio-dispersive equation using measured concentration profiles of NO₃-N. It was found that the nitrification was carried out at upper layer from 0 to 10 cm depth and the denitrification at lower layer from 15 to 35cm.