Revealing the enhancing role of ubiquitous surfactants on the degradation of emerging contaminants in VUV/UV/micro-nano bubble process

The vacuum-ultraviolet/ultraviolet/air micro-nano bubble (i.e., VUV/UV/MNB) process is a promising solution for wastewater treatment with high-efficiency and chemical-free advantages. However, the influence of surfactants, a common component wide-spread in wastewater on VUV/UV/MNB efficiency remains unknown. This study investigated the overlooked role of surfactants in enhancing the degradation of emerging contaminants in the VUV/UV/MNB process, using carbamazepine (CBZ) as a model contaminant. The addition of surfactants increased the CBZ degradation rate by at least 62 %, compared to 50 % without them. The anionic surfactant, sodium dodecylbenzene sulfate (SDBS), exhibited the highest promoting effect, while the cationic surfactant, dodecyl trimethyl ammonium bromide, exhibited the least. Notably, the enhancement plateaued at an optimal [SDBS] 0 , beyond which competition between HO • and SDBS hindered further degradation. The 75.8 % degradation enhancement with SDBS, compared to 50.8 % for a non-surfactant, was attributed to its amphiphilicity and adsorption capability, which increased CBZ interfacial concentration. Furthermore, SDBS showed enhanced MNBs stabilization, evidenced by a smaller reduction in CBZ degradation (8.6 %) compared to non-surfactant (23.9 %) in the intermittent bubbling mode. Key surfactant properties, including the surface activity, diffusion coefficient, and saturated equilibrium surface excess, were found to govern these reaction mechanisms. Besides, the addition of SDBS increased the relative contribution of interfacial reactions from an average of 55.9 % to 70.1 %, representing a 14.2 % enhancement in interfacial reaction dominance compared with the SDBS-free system. This study demonstrates the potential of VUV/UV/MNB process for effectively treating wastewaters enriched with surfactants.