Pressurized CO2/zero valent iron system for nitrate removal

A fluidized zero valent iron (ZVI) reactor pressurized by CO2 gas for controlling pH was employed for nitrate reduction. The proposed CO2 pressurized system potentially has advantages of using less CO2 gas and reaching equilibrium pH faster than CO2-bubbled system. However, due to weak acid nature of carbonic acid, system pH gradually increased with increasing oxidation of ZVI and reduction of nitrate. As pH increased with progress of reaction, nitrate removal rate decreased continuously. The results indicate that nitrate removal efficiency increases with increasing initial ZVI dosage but reaches plateau at ZVI doses of higher than 8.25 g l−1, and initial nitrate concentration up to 100 mg l−1 as N has minimal impact on the removal efficiency. Unlike the fluidized system with pH control by strong acid reported in our pervious study, near 100% of nitrogen recovery was observed in the current process, indicating that nitrate reduction by ZVI with different pH controlled mechanisms will have different reaction routes.