When HRT is at 6 days, the TN removal efficiencies of steel slag, limestone, maifanite
and bamboo charcoal systems are 74.4%, 50.1%, 79.2%, and 69.2% respectively.
The average TN concentration indices in the final effluents are 6.92 mg/L, 13.71 mg/L, 8.87 mg/L and 11.4 mg/L respectively.