Comparison of the characteristics of extracellular polymeric substances for two different extraction methods and sludge formation conditions

The characteristics of extracellular polymeric substances (EPSs) were compared for two different extraction methods and dissimilar sludge formation conditions (aerobic versus anaerobic). The measured characteristics included specific ultraviolet absorbance (SUVA) values, fluorescence excitation-emission matrices, molecular weight distributions, Fourier transform infrared (FT-IR) spectra, and the binding affinities for pyrene and Hg(II). The analyses demonstrated that the EPS extracted using cation exchange resin (CER) were composed of more aromatic and more condensed structures with higher molecular weight than those using formaldehyde/NaOH. The FT-IR results further revealed that the EPS using CER contained relatively lower content of protein to carbohydrate and less acidic functional groups (i.e., COOH or OH groups). The observed differences between the two extraction methods were more pronounced for the EPS of anaerobic sludge compared to those of aerobic sludge. The extent of pyrene binding and the apparent stability constants for Hg(II) were very consistent with the implications from the previous EPS physicochemical characteristics. The highest extent of pyrene binding was observed for the EPS of anaerobic sludge using CER while no measurable Hg(II) stability constant was found for the same EPS sample. Our results demonstrated that the EPS characteristics including their binding affinities are likely strongly affected by the sludge formation conditions as well as the extraction methods although the latter produced more differences.