## 3 Results and Discussion
### Fluorescence EEM and Fluorescence Regional Integration (FRI)  
A fluorescence spectroscopic is a sensitive monitoring tool. The EEMs had similar patterns for each size-fractionated SHS, for both the AD and FD samples. Figure 2d shows 3D EEM plots for AD BHS, HHS, MHS, and LHS samples at 5 mg-C/L DOC of AD samples. The corrected EEMs were analyzed using an FRI technique developed by [PERSON] et al. [22]. The EEM was separated into five excitation-emission regions relating to simple aromatic proteins (Regions I and II, E\({}_{\mathrm{x}}\)/E\({}_{\mathrm{m}}\) = 200-250/280-330 nm for region I, E\({}_{\mathrm{x}}\)/E\({}_{\mathrm{m}}\) = 200-250/330-380 nm for region II), fulvic acid-like materials (Region III, E\({}_{\mathrm{x}}\)/E\({}_{\mathrm{m}}\) = 200-250/380-520 nm), soluble microbial by-product-like materials (Region IV, E\({}_{\mathrm{x}}\)/E\({}_{\mathrm{m}}\) = 250-440/280-380 nm), and humic acid-like compounds (Region V, E\({}_{\mathrm{x}}\)/E\({}_{\mathrm{m}}\) = 250-440/380-520 nm) [22; 27; 31]. The P\({}_{\mathrm{Vn}}\) percentage of the AD HHS samples was significantly higher than the FD HHS samples (Table 3). Figure 2: EEM diagrams of bulk and size-fractionated SHS with the air-dry method and the FRI regions: (a) \(\mathrm{BHS}\), (b) HHS, (c) MHS, and (d) LHS. Table 3 shows the percentages of the five regions for both the AD and FD samples in bulk and three size-fractionated SHS samples. The percentages of P1,n, P1,n, and P1V,n, in the FD samples were higher than in the AD samples (except the P1V,n of MHS), but the percentages of P1I,n, and P1V,n in the FD samples were less than the AD samples for the bulk and individual size-fractionated SHS samples. Fluorophores in the P1,n, P1I,n, and P1V,n regions are attributed to microbial and aquatic sources. The average biochemical fraction (Bio = P1,n + P1I,n + PIV,n) of the AD samples (55.3 \(\pm\) 2.9%) was lower than the FD samples (57.6 \(\pm\) 2.5%) [50,51]. In the PV,n and PIII,n regions, the fluorophores can be attributed to the humic acid- and fulvic acid-like substances. The average geochemical fraction (Geo = PIII,n + PV,n) of AD samples (44.7 \(\pm\) 2.9%) was higher than the FD samples (42.4 \(\pm\) 2.5%). The composition dissimilarity of the AD and FD samples could be due to a continual biochemical reaction in the sediment organic matter of the AD process, which would increase the ratio of long-wavelength pair fluorophores in the AD sample [50,51]. The P1 Vn percentage of HHS in the AD samples was significantly higher than in the FD sample (\(p\) = 0.005), consistent with the considerably higher SUVA254 value of the AD samples in HHS (Figure 1a). Figure 3 shows the percentage of each region for the three size-fractionated SHS samples when the AD and FD samples were combined as a pooled sample. The HHS and MHS had higher P1,n ratios than LHS (\(p\) = 0.003), but HHS had a lower P1I,n ratio than MHS and LHS (\(p\) = 0.003). The P1I region is located at a short emission wavelength having loose, simple aromatic proteins. The P1I,n region is located relative to a long emission wavelength having condensed simple aromatic proteins [52,53]. The HHS had a relatively high, short emission wavelength protein-like substance, but LHS had a relatively high, long emission wavelength protein-like substance. In addition, the HHS had higher ratios of P1V,n than MHS and LHS (\(p\) < 0.001). The HHS Bio percentages (59.3 \(\pm\) 1.5%) were significantly higher than the LHS (53.1 \(\pm\) 2.8%) (\(p\) = 0.002). The LHS had a higher P1I,n ratio than HHS (\(p\) < 0.001), which demonstrated that LHS had a higher fulvic acid-like substance content than HHS and MHS. The HHS had higher ratios of P1V,n than MHS and LHS (\(p\) = 0.013). P1V,n percentage is a fraction of the humic acid-like substance. The percentages of FRI show that HHS had a high humic acid-like substance, but LHS had a high fulvic acid-like substance.