The fulvic acid fraction as it changes in the mature phase of vegetable oil-mill sludge and domestic waste composting.

Sludge resulting from the treatment of effluent from a vegetable oil mill, was composted mixed with domestic waste in a pile for five months. Different proportions of sludge and dry waste were mixed: M1 (1v/2v) and M2 (1v/1v). Monitoring different physical-chemical parameters showed the effect of the substrate on the microbiological activity and on the formation of fulvic acids, affecting the maturity of the final compost. Elemental analysis revealed that the fulvic acids of mixes M1 and M2 presented very low concentrations of carbon, hydrogen, and oxygen and a high level of nitrogen. The FTIR spectroscopy results showed a decrease during composting of the intensity of absorbance of the easily assimilable compounds that are predominant in the initial mixtures i.e. the carbohydrates (1170-1080 cm(-1)) in M1 and long aliphatic chains (2920 cm(-1)) in M2. For mix M1 there was enrichment in compounds bearing oxygen-containing moieties. In M2 it was the nitrogen-containing compounds (in the form of stable amides) which predominated at the end of composting. The first component of PCA analysis, PC1, accounted for 83% of the difference between two distinct groups of parameters governing degradation and restructuration of the fulvic acids during composting. PC2 (17%) explained the variance due to the level of free or less polycondensed compounds in the two mixtures. Oxidised polyphenolic and polysaccharide structures were the least free, or most polycondensed, in the fulvic structures of M1. In M2 fulvic acids however, it was the polyphenols and peptide structures that were involved in the bonding, most likely of the polyphenol-peptide type.

Sequential extraction of heavy metals during composting of sewage sludge.

The major limitation of soil application of sewage sludge compost is the total heavy metal contents and their bioavailability to the soil-plant system. This study was conducted to determine the heavy metal speciation and the influence of changing the physico-chemical properties of the medium in the course of composting on the concentrations, bioavailability or chemical forms of Cu, Zn, Pb and Ni in sewage sludge. Principal physical and chemical properties and FTIR spectroscopical characterization of sludge compost during treatment show the stability and maturity of end product. The total metal contents in the final compost were much lower than the limit values of composts to be used as good soil fertilizer. Furthermore, it was observed by using a sequential extraction procedure in sludge compost at different steps of treatment, that a large proportion of the heavy metals were associated to the residual fraction (70-80%) and more resistant fractions to extraction X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of metals bound to bioavailable fractions X-(KNO3+H2O). Heavy metal distribution and bioavailability show some changes during composting depending on the metal itself and the physico-chemical properties of the medium. Bioavailable fractions of all elements tend to decrease except Ni-H2O. Zn and mainly Cu present more affinity to organic and carbonate fractions. In contrast, Pb is usually preferentially bound to sulfide forms X-HNO3. Nickel shows a significant decrease of organic form. Significant degrees of correlation were found between heavy metal fractions and changes of some selected variables (e.g. pH, ash, organic matter, humic substance) during the course of composting. Mobile fractions of metals are poorly predictable from the total content. The R2 value was significantly increased by the inclusion of other variables such as the amount of organic matter (OM) and pH.

Characterization of fulvic acids by elemental and spectroscopic (FTIR and 13C-NMR) analyses during composting of olive mill wastes plus straw.

Elemental, functional and spectroscopic analyses (FTIR, 13C-NMR) were performed to study fulvic acids of composted olive mill wastes plus cereal straw, in order to follow the maturity of the final product during composting. The extracted fulvic acids were characterized by high nitrogen, acidic functional group and phenolic hydroxyl contents that might have resulted from the high degree of humification and the synthesis of more condensed humic complexes. This was confirmed by a decrease of alcoholic and aliphatic structures and an increase of aromatic structures, as shown by the FTIR and 13C-NMR analyses. The results showed that stability of the final product was reached after 12 months of composting and that fulvic acid levels could constitute an additional tool to assess final product maturity and its agronomic value.