Selective reduction of nitrite to nitrogen gas by CO anion radical from the activation of oxalate.

Nitrite (NO) reduction by carbon dioxide anion radical (CO) from the activation of small molecule carboxylic acid was investigated to selectively reduce nitrite to nitrogen gas (N) However, the CO generation efficiency from the activation of small molecule carboxylic acid needs to be enhanced to increase the NO reduction efficiency. In this study, a novel and promising process for selective NO reduction was proposed based on activation of oxalic acid (OA) by UV radiation coupled with Fe. In Fe(III)/OA/UV system, the activation of OA by photo-induced electron transfer process of Fe(III)-oxalate complex and by •OH radical from the photolysis of Fe or NO could promote the generation of CO radical, which enhanced the NO reduction. The 100% removal efficiency of NO, 94.72% of total nitrogen (TN) and 94.72% of selectivity for N were achieved in Fe(III)/OA/UV/NO system, at the Fe dosage of 8 mmol/L, initial pH of 1.70, OA dosage of 16 mmol/L, initial NO concentration of 30 mg N/L, and reaction time of 180 min. CO radical played a significant role in the reduction of NO by Fe(III)/OA/UV system based on the inhibition experiments in which methyl violet was used as a quenching agent of CO radical. Based on the results from batch experiments and FTIR analysis, the activation mechanism of OA and selective reduction mechanism of NO in Fe(III)/OA/UV system was proposed.