Effect of Fe3O4 nanoparticles on composition and spectroscopic characteristics of extracellular polymeric substances from activated sludge

The composition and spectroscopic characteristics of extracellular polymeric substances (EPS) from activated sludge were analyzed in a sequencing batch reactor under Fe3O4 nanoparticles (Fe3O4 NPs) stress. Fe3O4 NPs promoted the activated sludge to secrete more total EPS, loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) under long-term exposure. The protein and polysaccharide contents in the LB-EPS and TB-EPS displayed an increasing trend with the increase of Fe3O4 NPs concentration from 0 to 60 mg/L. The protein-like substances belonged to dominant fluorescence components in the EPS, whereas their peak location and intensity in the excitation-emission matrix fluorescence spectra had some evident changes under different Fe3O4 NPs concentrations. The groups of −OH and –NH2 branches of hydroxyl and amine groups in the LB-EPS and TB-EPs were sensitive to Fe3O4 NPs. The O/C ratio in the LB-EPS and TB-EPS was more than the N/C ratio at each Fe3O4 NPs concentration, suggesting that the mass fraction of element was in the order of C > O > N.