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).