In recent years, there has been a growing recognition of the presence of antibiotic-resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in various aquatic environments, including river, lakes, wastewater treatment plants (WWTPs), and estuarine and coastal environments (Amarasiri et al., 2020; World Health, 2022). The dissemination of ARB and ARGs through water streams widely acknowledged to pose significant risks to both human health and the environmental ecosystem. However, conventional water treatment technologies are not specifically designed to effectively eliminate ARGs. Studies have reported that the relative abundance of ARGs can range from 1.3×100–1.9×104 copies /L in tap water and 105–108 copies/L in WWTPs effluent (Hu et al., 2019; Ni et al., 2020). The transmission of ARGs from the raw water source to the drinking water supply and ultimately to humans could impact the efficacy of antibiotic treatments, leading to prolonged illness, increased severity of symptoms, and even mortality (Yu et al., 2022). Consequently, extensive research has been conducted to develop water treatment methods to inactivate ARB and remove ARGs for preventing their dissemination through water streams.
Disinfection is a commonly employed treatment method for bacterial inactivation. Chlorination, ozonation, and UV treatment have demonstrated efficacy in inactivating ARB (Stange et al., 2019). However, these traditional disinfection technologies do not exhibit absolute advantages in the removal of ARGs (Zheng et al., 2017), thus failing to efficiently inhibit the existing ARGs or prevent their horizontal transfer in the effluent. To achieve higher removal efficiencies of ARGs, advanced oxidation processes (AOPs) have been employed in conjunction with disinfection (Li et al., 2021). For example, UV irradiation, when combined with peroxydisulfate or H2O2, can more effectively penetrate the intracellular environment, leading to increased degradation efficiencies of ARGs (Das et al., 2022; Meng et al., 2022). Nevertheless, current research efforts on AOPs-assisted disinfection technology primarily focus on the UV field, which may result in bacterial recovery issues. Therefore, it is crucial to explore alternative AOPs-assisted non-UV disinfection technologies that are efficient in removing ARGs.
Sodium hypochlorite (NaClO) is a commonly used chlorination agent known for its stability and safe operation (Beattie et al., 2020). It easily penetrates bacterial cells, disrupting the enzyme system and ultimately inactivating the bacteria (Yuan et al., 2015). Moreover, the residual chlorine exhibits long-term effectiveness by inhibiting bacterial recovery. However, NaClO's weak oxidation potential does not effectively destroy antibiotic resistant genes (ARGs) during this process (Zhang et al., 2021). It is important to note that the inactivation ability of NaClO can be significantly enhanced when coupled with an electric field (Kunitomo & Obo 2003). Additionally, NaClO can serve as an electrolyte to facilitate the Electro-Fenton process, which can generate H2O2 and •OH in situ (Guo & Liu, 2020). Hence, it is feasible to employ electrochemical oxidation processes to assist NaClO in achieving superior removal efficiencies of ARGs.
Electrified membranes are an innovative class of membrane materials that integrate electrochemical oxidation with filtration processes (S. Yang et al., 2020). The unique feature of these electrified membranes is their significantly enhanced electrochemical reaction rates compared to conventional flow-through electrodes, attributed to the confinement of the electrochemical oxidation process within the pore radius of the membrane (Gayen et al., 2018).
In this study, a novel coupled treatment system was developed by integrating NaClO with an electrified membrane to effectively inactivate ARB and remove ARGs. The removal performances of the system were investigated in various water matrices, including surface water and secondary effluent, to better understand the degradation of ARGs in actual aquatic environment. Furthermore, the generation of H2O2 and •OH in this system was studied to elucidate the mechanisms underlying ARB inactivation and ARG degradation.