The difference in the fluorescence

The difference in the fluorescence properties of the EPSs extracted from the activated sludge of the oxic reactors of the A2O-B and A2O-C processes is provided in Table 4. The EPSs of the A2O-B process showed two pairs of fluorescence peaks at Ex = 230 nm and Em = 305 nm (A2O-B I, maximum intensity = 6150 mV), and Ex = 280 nm and Em = 350 nm (A2O-B II, maximum intensity = 6150 mV), which are closely related to protein-like fluorophores produced by bacterial activity (Chon et al., 2013). In case of the EPSs of the A2O-C process, two distinct protein-like fluorophores were detected at Ex = 230 nm and Em = 310 nm (A2O-C I, maximum intensity = 4491 mV), and Ex = 285 nm and Em = 350 nm (A2O-C II, maximum intensity = 10,000 mV). In contrast, a relatively weak humic-like fluoophore occurred at Ex = 355 nm and Em = 445 nm (A2O-C III, maximum intensity = 1625 mV). The relatively weak intensities of proteinlike fluorophores in the EPSs of the A2O-B process with indistinct humic-like fluorophores, compared to those of the A2O-C process, implied that the inoculation of eneficial microorganisms into the sludge digestion tank can elevate the sludge compressibility through disintegration of sludge flocs due to increased decomposition of EPSs (Zhou et al., 2017).