Development of a new combination of spectroscopic analysis and mathematical model for the enhanced sludge dewaterability: Application to tannic acid effect

The interaction by which sludge proteins bind to conditioners significantly impacts sludge dewatering performance. Nonetheless, a limited understanding of the interaction mechanisms restricts the elucidation of the dewatering process. This study proposes a molecular-level, covariant binding mechanism based on the analysis of the heterogeneity, response sequence, and active site of sludge protein-tannic acid (TA) binding. It utilizes fluorescence spectroscopy and two-dimensional correlation spectroscopy (2DCOS) in combination with fluorescence resonance energy transfer (FRET) theory. The disruption of soluble extracellular polymeric substances (S-EPS) resulted in the exposure of internal EPS, facilitating sludge dewatering. The C-O groups in polysaccharides and proteins within S-EPS were linked to TA before the N-H in amide II. However, the N-H bond in loosely bound EPS preferentially binds to TA. Likewise, higher TA doses (>= 0.3 mM/g TS) shifted the characteristic peak wave number. Protein substrates were transformed and exposed many groups with higher reactivity towards TA, which means TA concentration also affected their binding sites to proteins. In addition, utilizing the Tachiya model with FRET theory corroborated the existence of non-radiative energy transfer. The combination of spectroscopy and mathematical model represents an ideal approach for obtaining molecular-level mechanisms underlying sludge dewatering, thus providing an effective strategy for sludge disposal.