I am trying to remove a high concentration of nitrate (~7500 mg/L) from wastewater using iron powder, mixing it at an elevated temperature (65°C) and low pH=2. Unfortunately, no reduction of NO₃⁻ to NO₂⁻ or N₂ is occurring. The total organic carbon (TOC) content in raw wastewater is 725 mg/L and after the process it dropped to 425 mg/L. Does anybody know what to do to remove nitrate?