Humic‐Acid Transformation during Composting of Municipal Solid Waste

Abstract

AbstractComposting of municipal solid waste (MSW) was studied in an attempt to characterize concomitant transformations of humic acid (HA). Humic acid and Core‐HA were extracted from MSW at various stages during composting using the following methods: (i) The common IHSS method (HA); and (ii) performing organic solvent and sulfuric acid extractions prior to the alkaline extraction (Core‐HA). Mass balance was calculated for each compost sample during composting, and cross polarization magic angle spinning (CPMAS) 13C‐NMR and fourier transform infrared (FTIR) spectroscopy measurements were employed on the purified HAs and Core‐HAs. The absolute level of HA decreased during composting by 50% whereas the level of Core‐HA was steady throughout the process. The 13C‐NMR and FTIR spectra of the HAs indicated a high rate of change in structure during composting. The aromatic and phenolic C‐containing groups increased by 23 and 16%, respectively. In contrast, the Core‐HA spectra were stable, with only minor changes recorded during composting. The “coating” materials (polysaccharides, peptides, and lipids) bonding to the “core” HA structure degraded during composting, resulting in HA structures of higher aromaticity. The FTIR spectra of both HA and Core‐HA exhibited minor peaks in the carboxyl C, and the high rate of aliphatic C‐containing groups recorded from the 13C‐NMR spectra resembled “young” (type III) humified materials from soils. The mass‐balance data, together with the spectroscopic analyses indicate that one of the major HA transformation processes occurring events during the process is the degradation of the coating materials, yielding the core HA structure.