Humification process in different kinds of organic residue by composting and vermicomposting: have microbioreactors really accelerated the process?

The organic matter existing in nature presents as a complex system of various substances. The humic fraction refers to the humic substances (HS) and consists of humic acids (HA), fulvic acids (FA), and humins, according to solubility in aqueous solution. The physical and chemical characteristics of HA, FA, and humins depend on many factors, among which is the type of original organic material. Two processes for the stabilization of organic materials are known worldwide: composting and vermicomposting. Cattle manure, rice straw, sugarcane bagasse, and vegetable wastes from leaves were the organic residues chosen for the composting and vermicomposting processes. In this study, the differences between the HS extracted from such composted and vermicomposted residues were evaluated. The so-extracted HS were evaluated by spectroscopy in the regions of infrared and ultraviolet-visible, and pyrolysis coupled with gas chromatography with mass spectrometric detection is applied. Thus, we expect that the results obtained here indicate which of the two processes is more efficient in the biotransformation of organic residues in a short period with respect to the HS content. It was also observed that the basic units of the humic fractions generated (although they presented different degrees of maturation) are the same. Altogether, the data reported here bring to light that the structures of the HS are very similar, differing in quantities. These results can still be extrapolated to several other raw materials, since the most variable organic matrices were used here to allow this data extrapolation. In addition, the process seems to lead to the formation of more aliphatic substances, counterpoising what is found in the literature.