Size fractionation as a tool for separating charcoal of different fuel source and recalcitrance in the wildfire ash layer.

Charcoal is a heterogeneous material exhibiting a diverse range of properties. This variability represents a serious challenge in studies that use the properties of natural charcoal for reconstructing wildfires history in terrestrial ecosystems. In this study, we tested the hypothesis that particle size is a sufficiently robust indicator for separating forest wildfire combustion products into fractions with distinct properties. For this purpose, we examined two different forest environments affected by contrasting wildfires in terms of severity: an eucalypt forest in Australia, which experienced an extremely severe wildfire, and a Mediterranean pine forest in Italy, which burned to moderate severity. We fractionated the ash/charcoal layers collected on the ground into four size fractions (>2, 2-1, 1-0.5, <0.5mm) and analysed them for mineral ash content, elemental composition, chemical structure (by IR spectroscopy), fuel source and charcoal reflectance (by reflected-light microscopy), and chemical/thermal recalcitrance (by chemical and thermal oxidation). At both sites, the finest fraction (<0.5mm) had, by far, the greatest mass. The C concentration and C/N ratio decreased with decreasing size fraction, while pH and the mineral ash content followed the opposite trend. The coarser fractions showed higher contribution of amorphous carbon and stronger recalcitrance. We also observed that certain fuel types were preferentially represented by particular size fractions. We conclude that the differences between ash/charcoal size fractions were most likely primarily imposed by fuel source and secondarily by burning conditions. Size fractionation can therefore serve as a valuable tool to characterise the forest wildfire combustion products, as each fraction displays a narrower range of properties than the whole sample. We propose the mineral ash content of the fractions as criterion for selecting the appropriate number of fractions to analyse.

Chemical characterization of municipal wastewater sludges produced by two-phase anaerobic digestion for biogas production.

In the present study, the chemical features of municipal wastewater sludges treated in two-phase separate digesters (one for acetogenesis and the other one for methanogenesis), were characterized by using chemical analysis, stable carbon isotope ratios (delta(13)C), HS-SPME-GC-MS, TG-DTA analysis and DRIFT spectroscopy. The results obtained showed that sludges from acetogenesis and methanogenesis differed from each other, as well as from influent raw sludges. Both processes exhibited a diverse chemical pattern in term of VFA and VOC. Additional variations were observed for delta(13)C values that changed from acetogenesis to methanogenesis, as a consequence of fermentation processes that led to a greater fractionation of (12)C with respect to the (13)C isotope. Similarly, the thermal profiles of acetogenesis and methanogenesis sludges greatly differed in terms of heat combustion produced. These changes were also supported by higher lipid content (probably fatty acids) in acetogenesis than in methanogenesis, as also shown by DRIFT spectroscopy.

TG-DTA, DRIFT and NMR characterisation of humic-like fractions from olive wastes and amended soil.

The purpose of the present study is to investigate, by means of thermogravimetric analysis (TG) and differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform (DRIFT) and 2D nuclear magnetic resonance (NMR) spectroscopies, the structural features of the humic-like fraction (HLF) from olive pulp (OP), its effluents originated from the fermentation processes for hydrogen (EH2) and methane production (ECH4) and humic acid (HA) from soil amended with each of these materials. A considerable structural modification emerged between the HLF, in particular from the ECH4 effluent, which was characterised by a high content of polyphenolic and polypeptidic substances. The short-term amendment trial with OP and EH2 indicated that no chemical or structural changes in soil HA appeared. In contrast, the amendment with ECH4 substantially influenced the chemical and structural composition of soil HA. The structural interpretation performed by 2D NMR indicated the presence of aliphatic and aromatic protons while the sugar-like content and O-CH3 groups decreased with respect to the soil control HA. It emerges from this study that olive wastes contain stabilised humic-like material that may be recycled as an amendment in areas where olive trees are cultivated.

Characterisation of Ca- and Al-pectate gels by thermal analysis and FT-IR spectroscopy.

Thermal analysis (TG-DTA) and FT-IR spectroscopy have been performed on calcium-pectate membranes to investigate their structure and the consequent variation caused by aluminium sorption. Calcium-polygalacturonate (Ca-PG) membranes, model systems of the soil-root interface, were exposed to aluminium solutions at different concentrations (25-800 microM). Three different pHs (3.50, 4.00 and 4.50) were chosen to study the influence of different aluminium species, such as [Al(H2O)6]3+, [Al(OH)(H2O)5]2+ and [Al(OH)2(H2O)(4)]+, on the structure of the Ca-PG membrane. The DTA profiles and FT-IR spectra showed how aluminium sorption induces structural modifications leading to a reorganisation of the chain aggregates and a weakening of the structure. Higher pH, that is, 4.00 and 4.50, and thus hydrolytic aluminium species and related higher calcium content maintain a more regular structure than at pH 3.50. At pH 3.50, both the effect of [Al(H2O)6]3+ and a major calcium release had a greater impact and thus induced a greater weakening of the structure.