Abstract
This work reports a study of the proton-binding capacity of biopolymers obtained from different materials supplied by a municipal biowaste treatment plant located in Northern Italy. One material was the anaerobic fermentation digestate of the urban wastes organic humid fraction. The others were the compost of home and public gardening residues and the compost of the mix of the above residues, digestate and sewage sludge. These materials were hydrolyzed under alkaline conditions to yield the biopolymers by saponification. The biopolymers were characterized by 13C NMR spectroscopy, elemental analysis and potentiometric titration. The titration data were elaborated to attain chemical models for interpretation of the proton-binding capacity of the biopolymers obtaining the acidic sites concentrations and their protonation constants. The results obtained with the models and by NMR spectroscopy were elaborated together in order to better characterize the nature of the macromolecules. The chemical nature of the biopolymers was found dependent upon the nature of the sourcing materials.
Highlights
Municipal biowastes (MBW) are a readily available cost-effective source [1] of soluble biopolymers ( Soluble Bio-Organic Substances (SBOs), Soluble Bio-Organic substances)
The elaboration of potentiometric data has allowed attaining consistent chemical models to assess the number, nature and concentration of acidic functions in SBO biopolymers sourced from the digestate and composts of urban biowastes
Several protogenic sites with different acid strength have been found. This is consistent with the fact that SBOs, as products of biological origin, are mixtures of molecules with different chemical composition, molecular weight, structure and solution behavior
Summary
Municipal biowastes (MBW) are a readily available cost-effective source [1] of soluble biopolymers ( SBOs, Soluble Bio-Organic substances) These products are composed by a mixture of molecules with 67–463 kg·mol−1 molecular weight and 6–53 polydispersity index. The diprotic-like model, proposed by Crea et al [22] assumes that the binding capacity of the carboxylic acid groups is described by two protonation constants, whereas the phenolic group behaves as a second ligand in the alkaline pH range. Both model types assume that the protonation parameters are independent of the dissociation degree. Hereinafter, the concentration values of carboxylic groups obtained with the modeling approach are discussed in relation to previously reported values [23] obtained by NMR and elemental analyses
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