Influence of Flow Rate on Nitrate Removal in Flow Process

Abstract

Influence of flow rate on nitrate removal in the flow process was examined in a paddy field plot. Flow rate was changed for three stages. In the first stage flow rate was controlled at 0.040 m d-1, in the second stage at 0.073 m d-1 and in the third stage at 0.136 m d-1. Corresponding to the increase of flow rate, water flows through a plot rapidly. The retention time is 26.3 hours in the first stage, 16.5 hours in the second stage and 9 hours in the third stage. With the increase of flow rate, the nitrate concentrations of outflow water gradually increased. The decrease of nitrate concentration through the flow process also changed. Coefficients of nitrate removal rate (a) changed in a day, but the daily average values (a) in each stage were almost constant.