Application of a set of complementary techniques to understand how varying the proportion of two wastes affects humic acids produced by vermicomposting

8 págs., 3 figuras y 4 tablasA better understanding of how varying the proportion of different organic wastes affects humic acid (HA)formation during vermicomposting would be useful in producing vermicomposts enriched in HAs. With the aim of improving the knowledge about this issue, a variety of analytical techniques [UV–visible spectroscopic, Fourier transform infrared, fluorescence spectra, solid-state cross-polarization magic-angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectra, and thermal analysis] was used in the present study to characterize HAs isolated from two mixtures at two different ratios (2:1 and 1:1)of tomato-plant debris (TD) and paper-mill sludge (PS) before and after vermicomposting. The results suggest that vermicomposting increased the HA content in the TD/PS 2:1 and 1:1 mixtures (15.9% and 16.2%, respectively), but the vermicompost produced from the mixture with a higher amount of TD had a greater proportion (24%) of HAs. Both vermicomposting processes caused equal modifications in the humic precursors contained in the different mixtures of TD and PS, and consequently, the HAs in the vermicomposts produced from different waste mixtures exhibited analogous characteristics. Only the set of analytical techniques used in this research was able to detect differences between the HAs isolated from each type of vermicompost. In conclusion, varying the proportion of different wastes may have a stronger influence on the amount of HAs in vermicomposts than on the properties of HAs.This study was financed by ‘‘Junta de Andalucía’’ Project P05-AGR-00408. M.J. Fernández-Gómez thanks the Science and Innovation Ministry for their FPU doctoral Grant (AP2006-03452). J.M. Fernández is the recipient of a fellowship from the JAE-Doc subprogram financed by the CSIC and the European Social Fund. The authors also thank the professional proof corrector D. Nesbitt for assisting in the writing of the manuscript.Peer reviewe