Maria Rosaria Provenzano

CHARACTERIZATION, DIFFERENTIATION, AND CLASSIFICATION OF HUMIC SUBSTANCES BY FLUORESCENCE SPECTROSCOPY

Fifty samples of humic acids and fulvic acids isolated from various soils and soil-related materials (including paleosols, peat, leonardite, composted and earth-worm-composted organic materials, sewage sludges, and materials synthesized by soil fungi) have been investigated by fluorescence spectroscopy in the emission, excitation, and synchronous-scan excitation modes. Emission spectra are generally characterized by a unique broad band showing a maximum wavelength and relative fluorescence intensity that depend mainly on the nature and origin of the humic material. Excitation and synchronous-scan excitation spectra generally exhibit a number of peaks and shoulders of relative intensity at wavelengths that also vary according to the type and source of the humic material. The observed, distinct fluorescence properties of humic substances provide useful diagnostic criteria for distinguishing between humic and fulvic acids from the same source and between humic or fulvic acids from various sources. As a consequence, a classification of humic substances is proposed on the basis of their fluorescence behavior. Hypotheses on the chemical nature of relevant fluorescing structures in the various humic materials are suggested by comparing experimental data with corresponding fluorescence data available for defined simple molecules. The long wavelengths and low intensities measured for the major fluorescence peaks of paleosol, soil, peat, and leonardite humic acid are mainly ascribed to the presence of linearly-condensed aromatic ring and other unsaturated bond systems, capable of a high degree of conjugation and bearing electron-withdrawing substituents such as carbonyl and carboxyl groups, and to their high molecular weight units. The short wavelengths and high intensities generally measured for main fluorescence peaks of compost and earth-worm-composted humic acid and soil and peak fulvic acid are associated with the presence of simple structural components of low molecular weight, low degree of aromatic polycondensation, low levels of conjugated chromophores, and bearing of electron-donating substituents such as hydroxyls, methoxyls, and amino-groups. In the Conclusions, emphasis is given to the utility of further investigations on fluorescence behavior of humic substances.

Spectroscopic and compositional comparative characterization of I.H.S.S. reference and standard fulvic and humic acids of various origin

Abstract Eleven standard and reference fulvic acids (FA) and humic acids (HA) of aquatic and terrestrial origin from the collection of the International Humic Substances Society have been studied by chemical and spectroscopic methods. Aquatic HA appear richer in O and lower in C than terrestrial HA, while the opposite is generally true for the corresponding FA. The N content of aquatic samples is always much lower, and C/N ratio and E 4 /E 6 ratio much higher than those of terrestrial samples. The infrared spectra of all samples but soil HA are qualitatively similar one to another, but they differ mainly in the relative intensity of carboxyl, aromatic and aliphatic group bands. Fluorescence of terrestrial HA occurs at higher wavelengths than terrestrial FA and aquatic HA and FA in both emission and excitation modes, while synchronous-scan spectra appear more resolved and informative. ESR spectra are featured by resonances consistent with conjugated semiquinone free radicals and Fe(III) ions, the latter resonance being generally more intense for terrestrial than for aquatic samples.

Compost Maturity Assessment Using Calorimetry, Spectroscopy and Chemical Analysis

This work is aimed at characterizing compost maturity and, organic matter transformation during this process, by the use of nondestructive spectroscopic and thermal techniques, together with some chemical analysis. Composting was conducted in a laboratory over a period of one year using the organic fraction of domestic wastes, fresh farmyard manure, spent coffee and sawdust as the raw materials. Samples were retired after different periods of composting and were analyzed by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy as well as by routine chemical parameters including temperature, pH, C/N, ash content and humic-like substances content. Results showed that in case of domestic wastes, spent coffee and farmyard manure, the C/N ratios, ash and humic acid content showed a typical high rate of change during the first 197 days of composting and tended to stabilize thereafter, probably as a result of the maturity of the produced composts. In contrast, sawdust underwent only a very limited transformation even after one year of composting. Thermoanalytical and spectroscopic data confirms these finding and gives useful and complementary information with respect to the structure, the heterogeneity and the relative stability of the compost products. In particular, as the decomposition proceeded, there was an increase in aromatic to aliphatic structure ratio and a decrease in the importance of peptide structures of composts. Besides, both the spectroscopic and the thermal behavior of compost samples, retired beyond 197 days of composting, tended to be regular, less dependent on the raw material and close to that characterizing mature composts, with the exception of sawdust samples. We concluded that the spectroscopic and thermal techniques used are complementary to one another and to chemical tests and could be a powerful and fast approach for the study of compost maturity.

Thermal Properties of Standard and Reference Humic Substances by Differential Scanning Calorimetry

Differential Scanning Calorimetry combined with Fourier transform infrared spectroscopy, was applied to the study of a number of fulvic and humic acids extracted from soils, peat, river and seawater. The thermal patterns obtained were related to the nature and origin of samples. The low-temperature endotherms were attributed to dehydration and loss of peripheral polysaccharide chains. The endotherm at 250°C observed for soil FA was ascribed to partial decarboxylation of more labile surface COOH groups, whereas the high-temperature exotherms at about 500°C were related to the degree of polycondensation of the aromatic network of the humic molecules.

Chemical and spectroscopic characterization of organic matter during the anaerobic digestion and successive composting of pig slurry

In this work, anaerobic digestion of pig slurry and successive composting of the digestate after centrifugation were studied by means of chemical analysis, FTIR and fluorescence spectroscopy as excitation-emission matrix (EEM). Chemical analysis highlighted the organic matter transformation occurring during the processes. A decrease of volatile solids and total organic carbon were observed in the digestate with respect to the fresh pig slurry as a consequence of the consumption of sugars, proteins, amino acids and fatty acids used by microorganisms as a C source. Water Extractable Organic Matter (WEOM) was obtained for all samples and fractionated into a hydrophilic and a hydrophobic fraction. The highest WEOM value was found in the pig slurry indicating a high content of labile organic C. The digestate centrifuged and the digestate composted showed lower hydrophilic and higher hydrophobic contents because of the decrease of labile C. Total phenolic content was lower in the digestate with respect to fresh pig slurry sample (36.7%) as a consequence of phenolic compounds degradation. The strong decrease of total reducing sugars in the digestate (76.6%) as compared to pig slurry confirmed that anaerobic process proceed mainly through consumption of sugars which represent a readily available energy source for microbial activity. FTIR spectra of pig slurry showed bands indicative of proteins and carbohydrates. A drop of aliphatic structures and a decrease of polysaccharides was observed after the anaerobic process along with the increase of the peak in the aromatic region. The composted substrate showed an increase of aromatic and a relative decrease of polysaccharides. EEM spectra provided tryptophan:fulvic-like fluorescence ratios which increased from fresh substrate to digestate because of the OM decompostion. Composted substrate presented the lowest ratio due to the humification process.

Differential Scanning Calorimetric Analysis of Composted Materials From Different Sources

Differential scanning calorimetry (DSC) was applied to the study of material composted from sawdust, used coffee, farmyard manure and the organic fraction of domestic solid waste. Composting trials were carried out in Morocco and samples were collected after different periods of composting. The results obtained provided evidence that sawdust substrate is not a suitable source for composting due to the high content of lignin; samples from used coffee are characterized by a degree of aromaticity that is lower and a functional group heterogeneity that is higher than those of organic wastes from manure and the organic fraction of domestic wastes. The latter organic waste substrates appear to be easily degraded and humified and to give DSC curves that at the end of composting are vary close to those of native soil humic acids.

Chemical characteristics of dissolved organic matter during composting of different organic wastes assessed by 13C CPMAS NMR spectroscopy

This research aimed at assessing the chemical changes occurring in DOM extracted from different composting substrates by means of (13)C CPMAS NMR spectroscopy. During composting a reduction of carbohydrates and an increase of aromatic, phenolic, carboxylic and carbonylic C were observed. The highest increase in alkyl C and the lowest increase in aromatic C were explained by the presence of hardly degradable pine needles in the substrate, whereas the highest reduction in carbohydrates and the highest increase of the alkyl C/O-alkyl C ratio were attributed to the presence of highly degradable materials such as spent yeast from beer production.

Evolution of organic matter during composting of different organic wastes assessed by CPMAS 13C NMR spectroscopy.

In this paper, the evolution of organic matter (OM) during composting of different mixtures of various organic wastes was assessed by means of chemical analyses and CPMAS (13)C NMR spectroscopy measured during composting. The trends of temperatures and C/N ratios supported the correct evolution of the processes. The CPMAS (13)C NMR spectra of all composting substrates indicated a reduction in carbohydrates and an increase in aromatic, phenolic, carboxylic and carbonylic C which suggested a preference by microorganisms for easily degradable C molecules. The presence of hardly degradable pine needles in one of the substrates accounted for the lowest increase in alkyl C and the lowest reduction in carbohydrates and carboxyl C as opposite to another substrate characterized by the presence of a highly degradable material such as spent yeast from beer production, which showed the highest increase of the alkyl C/O-alkyl C ratio. The highest increase of COOH deriving by the oxidative degradation of cellulose was shown by a substrate composed by about 50% of plant residues. The smallest increases in alkyl C/O-alkyl C ratio and in polysaccharides were associated to the degradation of proteins and lipids which are major components of sewage sludge. Results obtained were related to the different composition of fresh organic substrates and provided evidence of different OM evolution patterns as a function of the initial substrate composition.

Characterization of Composts and Humic Acids from Pulp and Paper Mill Biosludges by DSC in Association with FT-IR Spectroscopy

Samples of pulp and paper mill biosludges with different maturation ages (fresh biosludge and composts collected after 3 weeks, 1 year and 2 years of composting) and their corresponding humic acids were analyzed by thermal analysis with DSC in association with FT-IR spectroscopy. The DSC curves obtained exhibited endotherms in the low-temperature region, assigned to dehydration processes, exotherms at around 370°C, attributed to the loss of peptidic structures, and high-temperature exotherms, assigned to the loss of functional groups; the lignins were thermostable, regardless of the maturation age of the compost.The results obtained provided evidence that, during composting, the organic matter evolved in the direction of higher molecular complexity and stability, leading to a more homogeneous product closely resembling humic-like substances.

Maturity degree of composts from municipal solid wastes evaluated by differential scanning calorimetry

Differential scanning calorimetry (DSC) in association with chemical analysis was applied to assess the maturity reached by the organic fraction of Municipal Solid Wastes (MSW) subjected to composting processes with manual and fixed aeration and sampled at different composting times. Thermograms showed that the difference in the treatments, i.e., the manual aeration and the fixed aeration, had no relevant effect on the stabilization and maturation of OM in the substrates. Common thermal effects observed were: a low temperature endotherm assigned to dehydration and/or loss of peripheral polysaccharides chains; a medium temperature exotherm assigned to loss of peptidic structures, and a high temperature exotherm assigned to oxydation and polycondensation of aromatic nuclei of the molecule. Results obtained suggest that in the experimental conditions used, a shorter time of composting (about 30 d) appears adequate, in order to limit the extended mineralization of OM, whereas a prolonged composting time (up to 132 d) would produce a compost of poor quality with high ash content and low OM content.