Co-treatment of fruit and vegetable waste in sludge digesters: Chemical and spectroscopic investigation by fluorescence and Fourier transform infrared spectroscopy.

In a previous work co-digestion of food waste and sewage sludge was performed in a pilot apparatus reproducing operating conditions of an existing full scale digester and processing waste mixed sludge (WMS) and fruit and vegetable waste (FVW) at different organic loading rates. An analysis of the relationship among bio-methane generation, process stability and digestate phytotoxicity was conducted. In this paper we considered humification parameters and spectroscopic analysis. Humification parameters indicated a higher not humified fraction (NH) and a lower degree of humification (DH) of FVW with respect to WMS (NH=19.22 and 5.10%; DH=36.65 and 61.94% for FVW and WMS, respectively) associated with their different chemical compositions and with the stabilization process previously undergone by sludge. FVW additions seemed to be favourable from an agronomical point of view since a lower percentage of organic carbon was lost. Fourier transform infrared spectra suggested consumption of aliphatics associated with rising in bio-methane generation followed by accumulation of aliphatics and carboxylic acids when the biogas production dropped. The trend of peaks ratios can be used as an indicator of the process efficiency. Fluorescence intensity of peak B associated with tryptophan-like substances and peak D associated with humic-like substances observed on tridimensional Excitation Emission Matrix maps increased up to sample corresponding to the highest rate of biogas production. Overall spectroscopic results provided evidence of different chemical pathways of anaerobic digestion associated with increasing amount of FVW which led to different levels of biogas production.

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.

Study of the biodegradation and transformation of olive-mill residues during composting using FTIR spectroscopy and differential scanning calorimetry.

The aim of this work was to investigate the structural transformations occurring in organic matter and their relationships with organic matter stability during the composting of two different solid olive-mill residues (SOMR). Raw materials were prepared from SOMR (compost C1) and from a mixture of SOMR and olive-mill wastewater for compost C2. Composts evolution was monitored by direct Fourier transform infra-red (FTIR) spectroscopy and differential scanning calorimetry (DSC) and by physicochemical parameters. Results showed that both wastes are suitable for composting and showed a strong thermophilic phase extending over the first 2 months, progressively and slowly reaching maturity after approximately 6 months. By the end of the thermophilic phase the water-soluble phenol content decreased by 93% and the pH and organic matter loss became more stable, oscillating around 8.5 and 41%, respectively. DSC and FTIR results showed that the biodegradation of the heterogeneous raw material is progressive and can be mainly attributed to a loss of aliphatic and peptidic structures and to an increase of the aromatic structures which essentially occurs during the maturity phase. By the end of the maturity phase, the two composts showed DSC and FTIR spectra typical of humic-like substances confirming the high degree of humification of the end products.

Spectroscopic and thermal investigations on compost improved by iron salt addition.

A quality compost obtained from sewage sludge (one part in weight) and yard trimmings and sawdust (two parts) has been investigated as a potential carrier of iron to plants. At the end of the thermophilic phase, the composting materials were added with crystalline FeSO4.7H2O (97%). Chemical properties, respiratory indices, and seed germination tests proved the compost to be suitable as an iron carrier in agriculture. Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy provided evidence of the effective linking of the iron ion to the organic molecule functional groups, thus preventing the loss of iron ion by leaching and precipitation phenomena and allowing the metal ion to be available to plants as both mineral and organic species. The thermogram obtained on compost without iron was similar to that previously obtained for composted materials of different origins, whereas samples with added iron ion exhibited in addition an exotherm in the medium-temperature region. FT-IR spectra carried out on samples heated at different temperatures indicated a loss of iron ion linked to carboxyl groups.

Abstractness and emotionality values for 398 English words.

This study is aimed to replicate Vikis-Freibergs' classic study (1976) on the values of vividness for French words. Vividness resulted from the concreteness and the emotionality values of words, here defined, respectively, as referring to something that can be experienced through senses and that can arouse pleasant or unpleasant emotions. 398 English words were rated on two different scales, Abstractness and Emotionality, by a group of English native speakers and also by a group of Italian subjects who used English as a second language. Results show a low correlation between the concreteness and emotionality ratings in line with Vikis-Freibergs' previous study of French words (1976). A negative correlation between Abstractness and Emotionality was observed for British data but a slightly positive correlation for the Italian data.

Fluorescence behaviour of Zn and Ni complexes of humic acids from different sources.

Conventional fluorescence spectroscopy in the excitation, emission and synchronous scan modes and three-dimensional fluorescence spectroscopy in the form of an excitation-emission matrix (EEM) of fluorescence intensity as a function of excitation and emission wavelengths have been applied to the study of three humic acids (HAs) extracted from soil (SHA), peat (PHA) and compost (CHA) and their interaction products with Zn(II) and Ni(II) ions. Fluorescence spectra of HAs appear to be related to the nature and origin of the sample. A strong reduction of intensity of all peaks is observed in the spectra of HAs-metal complexes as compared to those of untreated HAs. Ni(II) exhibits greater quenching ability than Zn(II). Fluorescence quenching measured for complexes of HAs at increasing Ni(II) concentrations was linearly correlated with metal ion concentration. The different capacity to interact with metal ions showed by various HAs is attributed to their different molecular complexity.