Using Three-Dimensional Fluorescence Excitation-Emission Matrix Spectroscopy with Regional Integration Analysis to Determine Properties of Extracellular Polymeric Substances in Nitrifying Sludge at Different C/N Ratios

The influences of the carbon/nitrogen ratio (C/N) on extracellular polymeric substances (EPS) of activated sludge were investigated in four laboratory-scale sequencing batch reactors using threedimensional excitation–emission matrix (3D-EEM) with fluorescence regional integration (FRI). When the C/N ratio increased from 0 to 15, the polysaccharide (PS), protein (PN), and nuclei acid (NA) contents of tightly bound EPS (TB-EPS) increased, the PS, PN, and NA contents in LB-EPS at the C/N ratio of 0 obviously higher than the C/N ratio of 5, 10, and 15. According to FRI, the C/N ratio had a significant impact on Regions III, IV, and V of EPS, Region V (34%~63%) was the dominant fraction in both types of EPS fractions and TB-EPS and LB-EPS contained similar functional groups, furthermore, the percent fluorescence response (Pi,n) of humic acid in TB-EPS was dramatically lower than LB-EPS. Meanwhile, a significant decrease of soluble microbial by-product of EPS after nitrification was obtained.