Total nitrogen removal by Fe-activated carbon composite coupled with persulfate

Abstract

The conversion of nitrate nitrogen (NO3−-N) or ammonia nitrogen (NH4+-N) to dinitrogen (N2) by chemical process for total nitrogen (TN) removal is meaningful, but still a challenge in wastewater treatment. Herein, zero valent iron (Fe0) loaded active carbon (Fe0@AC) was prepared and used to remove TN from the nitrogen-containing wastewater by an efficient chemical reduction coupled with oxidation process (FeR-PSO). In the step of NO3−-N reduction by Fe0@AC, Fe0@AC with 25 wt% Fe0 could reduce 100 % NO3−-N with the initial concentration of 50 mg N/L after 60 min at the Fe0@AC dosage of 9 g/L and initial pH of 3.0, and over 30 % NO3−-N could be reduced to N2. In the subsequent oxidation step, persulfate (PS) and magnesium oxide (MgO) were introduced into the solution after NO3−-N reduction to selectively oxidize NH4+-N to N2. The removal efficiency of NH4+-N and N2 selectivity after 30 min were 100 % and over 90 %, respectively, at the MgO dosage of 8 g/L and the PS dosage of 20.25 g/L. The developed FeR-PSO process could remove 93.40 % of TN from simulated wastewater, and over 90 % of TN from two actual pickle factory wastewaters. The possible mechanisms of NO3−-N reduction and NH4+-N oxidation by FeR-PSO process were proposed. These findings provide new insights for TN removal from NO3−-N containing wastewater or wastewater containing both NO3−-N and NH4+-N by chemical process.