## 3 Results and Discussion
### Effects of UF, O\({}_{3}\), and Their Combination on Reduction of Ultraviolet Absorbance (UVA)  
UVA spectrum can reflect the content of organic compounds. It has been well accepted the UVA at 254 nm (UVA254) can be considered as a parameter representing organics [23]. This is because organic compounds with multiple conjugated double bonds are strongly absorbed at 254 nm. The UVA at 258 nm (UVA258) can mainly represent aromatic unsaturated organics. The maximum absorption peak of nucleic acid is at 260 nm (UVA260), and the UVA at 280 nm (UVA280) is shown to have a relationship with aromatic substances [24]. Therefore, effects of O\({}_{3}\), UF, and their combination on UVA254, UVA258, UVA260 and UVA280 of secondary effluent were further investigated and the results are presented in Figure 4. UVA254, UVA258, UVA260 and UVA280 of secondary effluent before treatment were 0.102, 0.098, 0.095 and 0.082, respectively. The four UVA spectra had a certain degree of decline, indicating that all these substances could be partly rejected by UF membrane and also be oxidized by O\({}_{3}\). UF or O\({}_{3}\) treatment alone resulted in 8%-10% or 18%-25% UVA reduction, respectively. When secondary effluent was treated by the combination of O\({}_{3}\) and UF, about 34%-36% reduction in UVA reduction was achieved, which was 11%-18% higher than O\({}_{3}\) treatment alone and 24%-26% higher than the UF treatment alone. Overall, the removal efficiency of organic compounds was significantly enhanced by the combination of UF and O\({}_{3}\), which is consistent with the result of fluorescence adsorption reduction. This may be because pre-ozonation reduced the membrane fouling potential of the organic matters; therefore, the following UF membrane has more absorptive sites to retain more organic matters, thus leading to a higher removal efficiency. In addition, the membrane permeable flux during UF and O\({}_{3}\) + UF process was measured to authenticate the conclusion. The average membrane flux in the UF and O\({}_{3}\) + UF process was 23 L/(m\({}^{2}\cdot\)h) and 32.3 L/(m\({}^{2}\cdot\)h), respectively. The increased membrane  
Figure 3: EEM fluorescence spectra of secondary effluent in different processes.  
flux indicated that pre-ozonation of secondary effluent could delay the fouling of UF membrane. Similar results were reported by [PERSON] et al. [25], who found that O\({}_{3}\) oxidation caused a significant alleviation of membrane fouling for all investigated nanofiltration and UF membranes.  
The photographs of used membranes after UF and O\({}_{3}\) + UF treatment also verified the result. As shown in Figure 5, the thickness and density of the fouling layers on the membrane surface after O\({}_{3}\) + UF treatment were obviously lower than those in the UF treatment.  
Moreover, protein, carbohydrate and humic compounds are the three most important dissolved effluent organic matters (EFOM), and they account for 75% of the dissolved organic matter (DOC) according to previous studies and our survey [26]. Therefore, the contaminant removal was represented by DOC data. The relationships of DOC between UVA data and excitation emission data are shown in Figures 6 and 7. It could be observed that DOC and UVA data or excitation-emission data exhibited an excellent linear relationship, indicating that UVA data and excitation emission data could reflect the content of organic compounds efficiently.  
Figure 4: Effects of ultrafiltration (UF), O\({}_{3}\), and their combination on ultraviolet absorbance (UVA) reduction.  
Figure 5: Photographs of used membranes after UF and O\({}_{3}\) + UF treatment.