Characterization of the gas effluent in the treatment of nitrogen containing pollutants in water by Fenton process

Abstract

This work evidences for the first time the production of CO and NOx during the removal of nitrogen containing pollutants in water by Fenton Process, the most popular method for Advanced Oxidation Processes. Four representative nitrogen containing pollutants were selected, viz. aniline, 4-nitrophenol, pyridine and monoethanolamine. The gas effluent accumulated after 3 h of reaction at 90 °C and 3 bar was analysed. In all cases, the carbon and nitrogen mass balance was assessed. Also, an on-line off-gas analysis system was set up to monitor the off-gas variation of CO and CO2 from the beginning of the reaction.

CO2 was the major component of the gas effluent. It was progressively produced upon oxidation. In contrast, CO was detected in fairly lower amounts and it was immediately produced after H2O2 injection, due to the rupture and opening of the aromatic ring. The CO formation was more favorable upon degradation of aromatic than aliphatic compounds, or when the nitrogen was in the aromatic ring, as in the case of pyridine. The nitrogen functional groups were majorly transformed into NH4+ and NO3−, while NOx was detected in low amounts (<1 mg/m3) and favoured in presence of single bondNO2 group.

These results highlight the importance of monitoring the gas phase generated in the treatment of high-loaded wastewater by AOPs in order to guarantee the environmental sustainability of the processes.