3.3 Three-dimensional excitation-emission matrix fluorescence spectra
C1 was identified as tryptophan-like substances [27]. Two apparent peaks were observed in C1 (Fig. 3. A & B), i.e., a strong peak at 225/325 nm (Ex/Em) and a weak peak at 225/290 nm. Under Mt200 and Mt500, the relative intensity of C1 declined to 31.6% and 30.2%. The addition of Pal200 and Pal500, also led to a decrease of C1 to 39% and 36.5%, respectively (Fig. 3B). The major peaks of C2 had represented tyrosine-like substance [28], which was located at 280/340 nm (Ex/Em). The treatments of Mt200and Mt500 increased the intensity of C2 to 34.5% and 31.8%, but the Pal addition did not significantly alter the level of C2. The major peaks of C3 and C4, which were located at wavelengths of 280/475 nm and 290/460 nm (Ex/Em) respectively, indicating that the EPS contained humic-like substances [29]. The intensities of these two components were lower than C1 and C2, although they also varied upon Mt and Pal additions (Fig. 3B).