17beta-estradiol (E2) is classified as an endocrine disruptor and it poses a significant threat to the environment. Despite our previous work on the preparation of green-reduced graphene immobilized Ochrobactrum sp. FJ1(FJ1@rGO) to achieve high efficiency in removing E2, the functions of strain FJ1 and rGO, as well as their removal mechanism of E2, remain not well understood. In this study, FJ1@rGO was used to remove E2 to comprehend the removal mechanism where efficiency was found to be 93.74% after 10 days of removal compared to only rGO (43.82%). This indicated that E2 degradation was based on the integration of adsorption using rGO and biodegradation through strain FJ1, as evidenced by HPLC-UV. Additionally, results confirmed that the E2 removal process by FJ1@rGO conforms to first-order degradation kinetics and pseudo-second-order kinetics, further demonstrating the synergistic effect of physical adsorption and biodegradation. LC-Q/TOF-MS analysis identified the primary degradation products as estrone (E1), 4-OH-E1, and catechol. Combining characterization analysis, rGO facilitates the transfer of electrons between cells and E2, improving the strain's tolerance of environmental changes. Finally, the assessment of various wastewaters showed that the removal efficiency was 99.76%, 96.89%, and 78.09%, respectively. Overall, the mechanism by FJ1@rGO to remove E2 was proposed here, providing new insights into green and sustainable technology for treating E2 in wastewater.
Biodegradation using free cells is limited to low cell density, biological activity, and subsequent cell collection and regeneration are difficult. Meanwhile the limitations of using graphene-based nanomaterials for the removing emerging contaminants are adsorption and required further regeneration. To address these problems, reduced graphene oxide (rGO) synthesized by green tea extract as the carrier served to immobilize Ochrobactrum sp. FJ1 to form a functional bionanomaterial (FJ1@rGO). Its function was to degrade 17beta-estradiol (E2). To obtain a highly functional bionanomaterial, response surface methodology (RSM) with central composite design (CCD) was deployed to evaluate the synthesis conditions, which guided the ability of FJ1@rGO to remove pollutants. Results show that inoculation amount and immobilization time greatly affect removal efficiency, and the efficiency in removing E2 utilizing the optimized FJ1@rGO reached 93.7 % within 10 days. This proved to be significantly higher than prior to optimization. To provide evidence for functional FJ1@rGO, a series of advanced characterization results confirmed that FJ1 was successfully immobilized on rGO. It appears that FJ1@rGO has: firstly, excellent removal effect on E1, BPA, and triclosan; and secondly, excellent recycling properties.
The widespread presence of 17β-estradiol (E2) in the environment is an emerging problem because it poses a potential threat to human health and aquatic organisms. In this study, a strain of E2 degrading bacteria was isolated from activated sludge . 16s rRNA analysis combined with physiological and biochemical detection confirmed that the bacterium was Ochrobactrum sp. strain FJ1. At an initial E2 concentration of 15 mg L −1 , strain FJ1 degraded 98 ± 1% of E2 after 10 days. Furthermore, when methanol was added as an additional carbon source, the biomass of strain FJ1 increased by 35 ± 1%, and E2 degradation efficiency was slightly inhibited. Compared with E2 alone when glucose, sodium acetate, and methanol were added as additional carbon sources, biomass decreased by 20 ± 1, 13 ± 1 and 35 ± 1%, respectively. Analysis of the degradation products of E2 by LC/Q-TOF-MS confirmed that the major degradation products of E2 were estrone (E1) and 4,16-OH-E1, which was further degraded by strain FJ1 to several other unknown compounds. Based on SEM and FTIR analysis, the morphology of the bacteria became thicker and the thickness of the cell walls decreased under initial E2 stress, and thereafter E2 was transported into the bacteria primarily via several proteins on the cell surface. Considering the ability and efficiency of Ochrobactrum sp. strain FJ1 to degrade high E2 content, the strain could provide a new bioremediation technology for the effective biodegradation of E2. Finally, a potential bioremediation pathway of E2 by Ochrobactrum sp. strain FJ1 was proposed.
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