Efficient TN removal and simultaneous TOC conversion for highly toxic organic amines based on a photoelectrochemical-chlorine radicals process

Abstract

Abstract Organic amines, including amine groups and carbon groups, are highly toxic chemicals with regard to both human health and ecosystems. However, the treatment of organic amines in wastewater remains a challenge using existing methods because of poisonousness of amines to microorganisms and simultaneous poor denitrification. In this work, we used a photoelectrochemical-chlorine radicals process to selectively and efficiently degrade organic amines into N2 and CO2. The proposed process was based on the reaction of organic amines with chlorine radicals (Cl ) and hydroxyl radicals (HO ) and a fast reduction reaction of nitrate-N on a porous Pd-Cu/porous nickel cathode (Pd-Cu/PN). For dimethylamine (DMA), this system achieved removal rates of 99.20% and 51.34% for total nitrogen (TN) and total organic carbon (TOC) within 2.5 h, respectively. Four main intermediate products, including methylamine (MA), ammonia (NH4+), nitrate (NO3−) and nitrite (NO2−), were observed, and no chlorohydrocarbon was detected. The analysis of electron-spin resonance (ESR) and a free-radical capture experiment confirmed that free radicals, especially Cl , played an important role in the denitrification of DMA. Trimethylamine (TMA), ethylamine (EA) and diethylamine (DEA) were also degraded to demonstrate the general applicability of this system, and the corresponding TN removal rates were 96.23%, 93.85% and 92.37%, respectively. This work provides a new, efficient, highly selective and environmentally friendly treatment method for removing organic amines from wastewater.