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

The conversion of nitrate nitrogen (NO 3 − -N) or ammonia nitrogen (NH 4 + -N) to dinitrogen (N 2 ) by chemical process for total nitrogen (TN) removal is meaningful, but still a challenge in wastewater treatment. Herein, zero valent iron (Fe 0 ) loaded active carbon (Fe 0 @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 NO 3 − -N reduction by Fe 0 @AC, Fe 0 @AC with 25 wt% Fe 0 could reduce 100 % NO 3 − -N with the initial concentration of 50 mg N/L after 60 min at the Fe 0 @AC dosage of 9 g/L and initial pH of 3.0, and over 30 % NO 3 − -N could be reduced to N 2 . In the subsequent oxidation step, persulfate (PS) and magnesium oxide (MgO) were introduced into the solution after NO 3 − -N reduction to selectively oxidize NH 4 + -N to N 2 . The removal efficiency of NH 4 + -N and N 2 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 NO 3 − -N reduction and NH 4 + -N oxidation by FeR-PSO process were proposed. These findings provide new insights for TN removal from NO 3 − -N containing wastewater or wastewater containing both NO 3 − -N and NH 4 + -N by chemical process.