A gravel filter designed to simulate subsurface horizontal-flow constructed wetland.

Sodium thiosulfate applied as an electron donor for autotrophic denitrification.

96% of added nitrate nitrogen (${\text{NO}}_3^{-}$–N) was converted to nitrogen gas.

98.86% of thiosulfate was gradually converted to sulfate throughout the system.

Utilization of Na₂S₂O₃ could reduce operating cost and prevent secondary pollution.