Spectroscopic characterization of extracellular polymeric substances (EPS) recovered from anammox granular waste sludge

In this contribution a set of spectrophotometric analysis were used in order to investigate the composition of the extracellular polymeric substances (EPS) of anammox granular sludge originating from a full-scale reactor for autotrophic nitrogen removal from the liquid fraction of municipal digestate. Large amount of EPS (0.21±0.02 g/gVSS) were extracted by dissolution under alkaline conditions and recovered by precipitation under acidic conditions and the relative fractionation was evaluated by gravimetric and spectrophotometric analysis. Characterization using Fourier transform infrared (FTIR) and UV-Vis spectroscopy revealed the dominance of proteinaceous components and a minor fraction of carbohydrates which was corroborated by photometric quantitation measurements (PN/PS=9.8±0.8 g/g). The protein secondary structure was further investigated by the deconvolution of the amide I region of the IR-spectra and by circular dichroism spectroscopy in the far-UV spectral region indicating the prevalence of ordered structures, indicating the proteinaceous fraction as important for the mechanical properties of anammox auto-aggregating biofilm (i.e. granules). The abundance of cross-β structures, probably related to amyloid-like formations, was also confirmed by the red shift of the excitation/emission spectra upon binding with specific dye