Solvent-Selective Complexity Reduction of Effluent Dissolved Organic Matter for ¹H NMR Spectroscopy

Processing of biomass residues for material and energy recovery generate effluents containing complex organic mixtures. Analyses of bulk parameters are conventional for characterization and classification of such effluents, where the limited information offered impedes the development of molecular level management practices. This study assessed the potential of solvent-selective complexity reduction of effluent dissolved organic matter (DOM) from anaerobic bioprocessing of biomass residues for ¹H NMR spectroscopy. The DOM were acquired after filtration and drying of samples from seven full scale anaerobic bioreactor facilities with effluents used as biofertilizer. The ¹H NMR spectra of DOM in indigenous solvent (water) revealed source dependent characteristics primarily due to variable abundance of aliphatic CCH in lipids and peptides, OCCH in carbohydrates, and olefinic and aromatic subunits. Dimethyl sulfoxide solubilized larger proportion of nonfunctionalized aliphatic and aromatic molecules, with ¹H NMR features also varying depending on the DOM source. Methanol, however, reduced the ¹H NMR spectral variability and dissolved sets of aliphatic and aromatic molecules from the dried DOM with similar ¹H NMR features irrespective of their origin. Among the other solvents studied, the reactive dissolution by trifluoroacetic acid decomposed aliphatic units while enriching aromatics (i.e., C_arH:CCH of 0.7 compared to 0.2 in water), also forming small (oligo)saccharides and peptide fragments. Acetone, dichloromethane, and acetonitrile extracted alkyl-rich molecules with varying degrees of functionalization. Acetonitrile separated a fraction enriched in aliphatic carboxylic acids, while dichloromethane mainly dissolved nonfunctionalized aliphatic hydrocarbons. It is proposed that a simple process of filtration, drying, and dissolution of effluent DOM in different solvents substantially reduces the complexity and heterogeneity of the organic mixtures enabling the structural discrimination of diverse molecular classes by ¹H NMR spectroscopy.