Abstract
Synthetic wastewater containing 209 ppm NH_4-N, 41 ppm organic N, and 554 ppm COD was percolated intermittently at different loading rates through columns packed with 5.6 kg of surface sample of a Humic Andosol at 25℃ for 29 to 71 days. the greater part of NH_4 was nitrified by the percolation through the column and little NH_4 was found in the effluent when 250 ml of wastewater were applied once a day. However, NH_4 was not perfectly nitrified and passed through columns with increased loading rates. Ammonium concentration in the effluents increased linearly with the decrease of mean residence time of wastewater in soil columns. The addition of 1.5% (w/w) calcium carbonate (CC), 10 to 30% (v/v) calcined perlite (PL), 10% (v/v) calcined vermiculite (VM), and 10% (v/v) zeolite (clinoptilolite) (ZL) to the soil accelerated nitrification in soil columns. Ammonium concentration in the effluents decreased in the order of untreated>CC>CC+PL>CC+VM≫CC+ZL, and nitrate concentration increased in the same order. The inoculation of nitrifier enriched soil on soil columns was also effective in accelerating nitrification. Nitrified N ranged from 72 to 93% of total N in wastewater applied to the soil columns mixed with soil amendments at the rate of 500 ml/day during 80 to 107 days. Losses of N through denitrification amounted to 20 to 40% of total N added as wastewater.
