HUMIC-ACID TRANSFORMATION DURING COMPOSTING OF MUNICIPAL SOLID-WASTE

Composting of municipal solid waste (MSW) was studied in an attempt to characterize concomitant transformations of humic acid (HA). Humic ac id and Core-HA were extracted from MSW at various stages during compos ting using the following methods: (i) The common IHSS method (HA); and (ii) performing organic solvent and sulfuric acid extractions prior t o the alkaline extraction (Core-HA). Mass balance was calculated for e ach compost sample during composting, and cross polarization magic ang le spinning (CPMAS) C-13-NMR and fourier transform infrared (FTIR) spe ctroscopy measurements were employed on the purified HAs and Core-HAs. The absolute level of HA decreased during composting by 50%, whereas the le i el of Core-HA was steady throughout the process. The C-13-NMR and FTIR spectra of the HAs indicated a high rate of change in struct ure during composting. The aromatic and phenolic C-containing groups i ncreased 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'' IIA 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 C-13-NMR spectra resem bled ''young'' (type III) humified materials from soils. The mass-bala nce data, together with the spectroscopic analyses indicate that one o f the major HA transformation processes occurring events during the pr ocess is the degradation of the coating materials, yielding the core H A structure.