Fractionation and characterization of dissolved extracellular and intracellular products derived from floccular sludge and aerobic granules

Dissolved extracellular and intracellular polymeric substances (DEPS and DIPS) from floccular sludge and aerobic granules were extracted and fractionated based on compound hydrophobicity. Compared with floccular sludge, aerobic granules contained lower amounts of DEPS and DIPS. Fourier transforms infrared spectra suggested that large amounts of proteins and polysaccharides existed in colloidal form in the extracellular polymeric substances of aerobic granules. Fluorescence excitation-emission matrix spectra revealed that tightly bound DEPS (TB-DEPS) and DIPS were humified after sludge granulation. Meanwhile, the proportions of hydrophilic contents in the TB-DEPS and DIPS fractions decreased from 45.3% to 28.3% and from 40.1% to 18.9%, respectively. These data indicated that TB-DEPS and DIPS from aerobic granules were more hydrophobic than those from floccular sludge. The results of the hierarchical cluster analysis further confirmed that the characteristics of dissolved organic matters between floccular and granular sludge were distinctly different.