Efficient degradation of antibiotics by photo-Fenton reactive ceramic membrane with high flux by a facile spraying method under visible LED light

Abstract

The traditional treatment of antibiotics confronts high energy consumption but low removal efficiency. In this study, a photo-Fenton ceramic membrane (PF-CM) was prepared by an innovative and facile approach of spray printing method with nano hematite (α-Fe₂O₃) for the removal of tetracycline hydrochloride (TC) as a model antibiotic. The SEM, TEM, XPS, and UV–Vis DRS were used to characterize the PF catalyst of α-Fe₂O₃. The as-prepared α-Fe₂O₃ was loaded to a flat ceramic membrane (CM) by a spray printing and low-temperature sintering method to form a photo-Fenton reactive membrane (α-Fe₂O₃-CM). A new α-Fe₂O₃-CM fixed bed water treatment system with visible LED light was fabricated for the removal of TC by comprehensive consideration of degradation rate and permeates flux. The reusability and stability of the α-Fe₂O₃-CM were also investigated. To reveal the reactive radicals involved in the PF-CM process for a deeper insight into the degradation mechanisms, quenching experiments and EPR analysis were performed. The SEM/EDS images indicated that the α-Fe₂O₃ was loaded tightly onto the α-Fe₂O₃-CM, and pure water permeates flux of the α-Fe₂O₃-CM could reach as high as 55.8 kg/(m²·h·kPa). The α-Fe₂O₃-CM fixed-bed treatment system is suited for TC treatment, and the removal efficiency could reach 82% even when the TC concentration is as low as 20 mg/L. Moreover, α-Fe₂O₃-CM could retain long-term stability and exhibit a self-cleaning function in antibiotic wastewater treatment for five cycles, which was further confirmed by SEM/EDS images and iron dissolution experiments. The quenching experiments and EPR analysis revealed that reactive radicals involved in the PF-CM process were h⁺, ·O₂⁻, and, ·OH responsible for TC degradation. This research also provides a utilization proposal for scale-up α-Fe₂O₃-CM for water and wastewater treatment.

Introduction

As known, antibiotics are one of the most important drugs not only for preventing and treating human bacterial infections but also used as antibacterial and growth-promoting additives for animal infectious diseases (RODRIGUEZ-MOZAZ et al., 2015; CHEN et al., 2020a). Presently, the annual production of pharmaceutical wastewater is up to 250 million tons in China (LI et al., 2020a), which contains a large number of antibiotics and nearly half of them were not well treated (ZHAO et al., 2016). Moreover, the other sources of antibiotics to the environment also include domestic sewage, medical wastewater, animal feed, aquaculture wastewater, etc. (TANG et al., 2015; BIA Ł K-BIELI Ń SKA et al., 2011). Most antibiotics enter the ecosystem through excretion and secretion after use and then migrate among surface water, groundwater, and soil, which is difficult to be effectively eliminated (ZHAO et al., 2016). As a result, antibiotics are emerged and detected in major watersheds of China, such as the Yangtze River (ZHANG et al., 2020), Pearl River (LI et al., 2018), and coastal watersheds (LI et al., 2020b), etc., ranging in concentration from hundreds of ng/L to several mg/L (ZHANG et al., 2020; LEI et al., 2019; LEE et al., 2020). Their residues are subject to re-entry into human bodies in various forms, such as through the transmission of the food chain of drinking water, meat, and vegetables, thus ultimately affecting human health (QIAO et al., 2020). Besides, the widespread low concentration of antibiotics in the ecosystem could cause resistance genes, which may result in the emergence of super-bacteria that will be a potential ecological disaster to human society (ZHANG et al., 2020; HE et al., 2021).

Many studies (TANG et al., 2015; QIAO et al., 2020) also revealed that antibiotics exhibit the characteristics of high-water solubility and resistance to biological degradation. Therefore, the eliminating technology of these micropollutants with high efficiency but low cost is highly desired. At present, various processes are used for the treatment of antibiotics, including biological technology (HE et al., 2021), reverse osmosis (LAN et al., 2019), adsorption (AZHAR et al., 2017), coagulation (LI et al., 2017), and advanced oxidation processes, such as electrochemical oxidation (SORDELLO et al., 2021), Fenton/Fenton-like oxidation (CHENG et al., 2021), TiO₂ photocatalysis (SERNA-GALVIS et al., 2016), etc. However, a single process displays certain deficiencies of costly, time-consuming, low efficiency, excessive chemicals addition, and secondary pollution (AZHAR et al., 2017). So, combined with the two and above single processes of coupling techniques, bring not only synergic effects but also circumvent the disadvantages of single ones, which gradually becomes a new horizon in water and wastewater treatment. Consequently, many novel coupling technologies were proposed for the removal of micropollutants, such as combined membrane separation (YIN et al., 2021), photo-Fenton (LIU et al., 2020), electro-Fenton (LIU et al., 2015), ozone-UV/H₂O₂ (JUSTO et al., 2013), Fenton-SBR (BEN et al., 2009), TiO₂ photocatalysis-ceramic membrane (LI et al., 2019), ozone-nanofiltration (LIU et al., 2014), ozone-ceramic membrane (ASIF et al., 2021), photo-Fenton reactive ceramic membrane (PF-CM) (SUN et al., 2018), etc. Among all these coupled processes, the PF-CM not just retains the superiority of operational simplicity, lower energy consumption, and high efficiency of photo-Fenton oxidation (SEGURA et al., 2021) but also combines the advantages of the CM separation of excellent thermal stability, corrosion resistance, and high flux (YIN et al., 2021; LI et al., 2004). Furthermore, the hydroxyl radical (·OH) generated from the photo-Fenton reaction could oxidize and decompose the pollutants on the surface of the membrane, and result in mitigating membrane fouling (FRONTISTIS et al., 2011). It's worth mentioning that the PF-CM also gives a prospect to use solar energy to cut operating costs as well. In the practice of wastewater treatment, the operation modes of PF-CM mainly include suspended (LI et al., 2020c) and fixed bed (SUN et al., 2018; SUN et al., 2020a) treatment systems. Compared with the former, the latter fixed bed system with a reactive ceramic membrane could effectively solve the loss and reuse problem of the photocatalysts (LI et al., 2020c). Therefore, the crux of this technology is to develop a PF-CM with the economy, facile preparation, visible light response activity, and stable performance (SUN et al., 2020b; XIN et al., 2021). However, to our knowledge, there are limited approaches of the covalent binding method (LIU et al., 2020; SUN et al., 2018; SUN et al., 2020b), sol-gel method (KARNIK et al., 2005), and one-pot method (CHEN et al., 2020b) for the preparation of the PF-CM, which should be further optimized to be more facile, scalable, and eco-friendly.

In this study, low-priced and easily available nano hematite (α-Fe₂O₃) synthesized by a solvothermal method (ZHENG et al., 2020) was used as the photo-Fenton catalyst. Then the as-prepared α-Fe₂O₃ was loaded to a flat ceramic membrane (CM) by a spray printing and low-temperature sintering method to form a photo-Fenton reactive membrane (α-Fe₂O₃-CM). And a new fixed bed reactor with visible LED lights was designed to fabricate a new system for the treatment of a model antibiotic of tetracycline hydrochloride (TC). The effect preparation parameters of printing layers and calcination temperature of α-Fe₂O₃-CM on TC degradation performance and permeate flux were investigated simultaneously. Furtherly, the antifouling performance and reusability of the α-Fe₂O₃-CM were also studied comprehensively. Finally, we performed quenching experiments to study the reactive radicals involved in the photo- Fenton process to achieve deeper insight into the degradation mechanisms of TC in the new reactive CM treatment system. This research could provide an alternative technology for a facile and scalable preparation and application of self-cleaning PF-CM with high flux for micropollutants removal in water or wastewater treatment.