3D-EEM fluorescence spectra of sludge EPS
Fig. 5 showed the 3D-EEM fluorescence spectra of sludge EPS
after 15 days of co-digestion. Two main peaks, marked as Peaks A
and B, respectively, were identified from the EEM fluorescence
spectra of soluble organic matters. Peaks A and B occurred at
excitation/emission wavelengths (Ex/Em) of 285e290/
340e366 nm and 221e231/315e349 nm, respectively, which
have been reported to be tryptophan-like and tyrosine-like substances (Henderson et al., 2009). The intensities of Peaks A and B
were related to soluble microbial substrates in EPS, and could
confirm the biological activity of sludge in the AD process. In this
study, the fluorescent intensities of Peaks A and B gradually
increased with FW/AS increasing from 10% to 30%, and a shift wasobserved when FW/AS continued to increase to 50%. The results
indicated that the activity of anaerobic bacteria was highest at
FW/AS of 30%, which might be responsible for the high biogas
yield.