Chemical and Physicochemical Characterization Of Humic Acid-Like Materials From Composts

Abstract

Humic acid (HA)-like materials were extracted from composts prepared from domestic organic wastes (HADu), sawdust (HASc), used coffee (HACf), and farmyard manure (HAFm). The HA-like fractions were characterized for elemental composition, E₄/E₆ ratio, and structural and functional properties by Fourier-transform infrared (FT IR), fluorescence and electron spin resonance (ESR) spectroscopies. Elemental composition and E₄/E₆ ratios were similar to those characteristic of young humic matter. Nitrogen content was related to that in the initial waste being high for HADu and HACf and low for HAFm and HASc. FTIR spectra of HADu and HACf were dominated by absorptions of N-containing groups (1650 and 1540 cm⁻¹), whereas those of HASc and HAFm were dominated by bands of aromatic structures (1595, 1511, 1418 and 1125 cm⁻¹). Data from ESR and fluorescence spectroscopy were similar for all the HA-like fractions analyzed. The low free radical concentrations and type of fluorescence patterns suggested simple structural components, low degree of aromatic polycondensation and low level of conjugated chromophores. In conclusion, HA-like substances obtained from composted materials exhibited an elemental composition related to the nature of the initial wastes and general characteristics close to those of soil fulvic acids rather than soil HAs.