Nitrogen Balance in Soil Columns Intermittently Flooded with Secondary Sewage Effluent

Abstract

Abstract Short, frequent cycles of flooding soil columns (2 days flooded and 5 days dry) with secondary sewage effluent caused no net removal of N but transformed almost all of the N to nitrate. The net N removal during longer cycles (9–23 days flooded and 5 days dry) was 30%, and half of the N remaining in the water was concentrated into a wave of high‐nitrate water, which represented 10% of the total volume of reclaimed water and was collected immediately after the dry period. Water collected from the columns after the wave of high‐nitrate water passed contained 67% less N than the incoming sewage water. Alternate flooding and drying periods were necessary for consistent N removal. The net N removal was probably due to a combination of several reactions dominated by denitrification. Cation exchange was important in holding NH 4 + in the soil until it could be nitrified, thereby concentrating N into smaller volumes of high‐nitrate water. Denitrification is the logical reaction to investigate for higher net N removal because the soil microorganisms nitrified most of the NH 4 + and N can be removed from the system as an inert gas by denitrification.