Enhanced vacuum UV-based process (VUV/H2O2/PMS) for the effective removal of ammonia from water: Engineering configuration and mechanistic considerations

Highlights: • Co-addition of H₂O₂ and PMS in the VUV photoreactor resulted in synergic ammonia removal. • Ammonia removal rate in the VUV/H₂O₂/PMS was 3.5 times higher of that in the VUV process. • >99 % nitrogen gas selectivity was obtained in the VUV/H₂O₂/PMS process. • Ammonia, TOC & bacteria were efficiently removed in continuous flow VUV/H₂O₂/PMS process. In this work, the VUV, VUV/H₂O₂, VUV/PMS, and VUV/H₂O₂/PMS processes were compared with the corresponding UVC-based AOPs under identical experimental conditions for the ammonia removal. Among the examined AOPs, the VUV/H₂O₂/PMS demonstrated the highest performance in converting ${\text{N}\text{H}}_4^{+}$ to N₂. A 82.7 % removal of 100 mg/L ${\text{N}\text{H}}_4^{+}$, with N₂ selectivity over 99 % was obtained in the VUV/H₂O₂/PMS process within 60 min, operated under near neutral pH. Under these operation conditions, [${\text{N}\text{O}}_3^{-}$] was around 0.5 mg-N/L with [${\text{N}\text{O}}_2^{-}$] remaining below detection. The VUV-mediated generation of $\text{S}{\text{O}}_4^{•-}\text{a}\text{n}\text{d}\text{H}{\text{O}}^{•}$ with ${\text{N}\text{H}}_4^{+}$ had a relative contribution of 37.9 and 62.1 %, respectively. The VUV/H₂O₂/PMS process operated under a flow-through mode achieved efficient removal of 100 mg/L ${\text{N}\text{H}}_4^{+}$ (80.5 %) in a hydraulic retention time (HRT) of 40 min. The continuous-flow VUV/H₂O₂/PMS process efficiently treated a real ammonia-laden groundwater and the concentration of ${\text{N}\text{H}}_4^{+}$ decreased from 30 mg/L to around 1 mg/L within 60 min HRT. In summary, the VUV/H₂O₂/PMS process was effective from the technical and energetical point of view, hence is a viable and promising technique for treating effluent containing high concentrations of ammonia.