## 1 Introduction  
The shortage of water resources in China has become one of the important factors restricting the development of society and economy. The reuse of secondary effluent of municipal wastewater treatment plant is an effective way to improve the comprehensive utilization efficiency of water resources due to its huge amount and relatively good quality [1]. However, there still exist a variety of trace organic pollutants and pathogenic microorganisms that pose potential risk in its direct reuse [2,3]. Endocrine-disrupting chemicals (EDCs) have been widely detected in secondary effluent [4]. They pose a threat to ecological security and human health by interfering with endocrine system even at concentrations as low as ng\(\cdot\)L\({}^{-1}\) level [5]. It has been reported that 0.1 ng\(\cdot\)L\({}^{-1}\) EE2 could induce male rainbow trout to produce vitellogenin, which is only found in female rainbow trout, thus resulting in homozygosity of male and female trout [6]. In addition, EDCs can cause the growth retardation of sea urchin embryos. Early-life exposure to EDCs leads to the development uterine fibroids by impairing DNA repair capacity in myometrial stem cells [7]. In addition, human exposure to EDCs will also suffer adverse health effects as following: obesity, diabetes and metabolic syndrome, decreased secretion and activity of sex hormones, decreased reproductive capability and increasedincidence of cancer [8]. Therefore, it is of great significance to further develop an efficient control technology for EDCs in secondary effluent to ensure the safety of the reuse process. Researchers have explored a number of methods for eliminating EDCs, such as physical removal [9], chemical oxidation [10] and bio-degradation [11]. Among these technologies, ultrafiltration (UF) and ozonation (O\({}_{3}\)) exhibited advantages in practical reclaimed water projects for EDC removal [12]. However, the EDC removal rate with UF is limited because of its (relative to EDCs) large membrane pore size [13]; O\({}_{3}\) can rapidly reduce EDC concentrations but might generate hazardous brominated by-products, which are also harmful to the human body and ecological environment [14]. Moreover, its operating cost is relatively high with high-dose O\({}_{3}\) in large-scale application. The combined process is a promising EDC removal method. UF can retain EDCs to reduce O\({}_{3}\) dosage and cost, and also reject hazardous brominated by-products to ensure the biological safety of reclaimed water. This hybrid process of UF and O\({}_{3}\) also has been studied by many researchers, aiming at pollutant removal and membrane fouling control. In previous work, others have demonstrated that the application of low-dose O\({}_{3}\) within the UF membrane tank is a potentially important approach for fully mitigating membrane fouling [15]. It has also been shown that hybrid ozonation membrane filtration provides a higher removal capacity in turbidity and natural organic matters [16]. Previous studies mostly investigated the removal of EDCs in UF or the ozonation process, or membrane fouling control, or pollutant removal, such as antibiotics in a hybrid process of UF and ozonation. However, there are relatively few reports on the removal of EDCs by the combined O\({}_{3}\) and UF process. The goals of this study were to investigate the removal efficiency of EDCs in secondary effluent by a combined process of O\({}_{3}\) and UF. Five EDCs were chosen because they were typically found in secondary effluent and pose great harm to the natural environment and human body [17]. The reduction of three-dimensional fluorescence spectra at excitation/emission wavelengths of 225-250/325-400 nm and 275-300/325-400 nm, and ultraviolet absorbance at 254 nm, 258 nm, 260 nm and 280 nm are proposed herein as potential surrogates to assess the removal of organic compounds. For example, ultraviolet absorbance at 254 nm can be used to evaluate the removal of aromatic components within organic compounds during ozonation [18].