DISSOLVED ORGANIC-CARBON FRACTIONS FORMED DURING COMPOSTING OF MUNICIPAL SOLID-WASTE - PROPERTIES AND SIGNIFICANCE

The properties and transformation of dissolved organic matter (DOM) ex tracted (10 L water per kilogram compost) from municipal solid waste ( MSW) compost at five stages (days 47, 77, 105, 126, and 187) of compos ting were investigated. The DOM was fractionated into hydrophobic or h ydrophilic neutrals, acids, and bases. The unfractionated DOM, the hyd rophobic acids and neutrals (HoA and HoN, respectively), and the hydro philic neutrals (HiN) fractions were studied using solid-state C-13-NM R, FTIR, and DRIFT spectroscopy. The HoA fraction was found to be the dominant (percentage of total DOM) hydrophobic fraction, exhibiting a moderate increase during composting. The HoN fraction increased sharpl y from less than 1 % to 18 % of the total DOM during 187 days of compo sting, while the hydrophobic bases (HoB) exhibited the opposite trend. The HIN represented the major fraction of the hydrophiles up to 120 d ays of composting, decreasing thereafter by 38 %. The relative concent ration of the hydrophilic acids and bases (HiA and HiB, respectively) exhibited no consistent trend during composting. DRIFT spectra of the unfractionated DOM taken from the composting MSW revealed a decreasing level of polysaccharide structures with time. The C-13-NMR and FTIR s pectra of the HoA fraction exhibited a polyphenol-humic structure, whe reas the HoN spectra exhibited strong aliphatic features. The spectra of the HiN fraction confirmed its polysaccharide nature. During the fi nal stage of composting, the DOM concentration was steady, while a rel ative decrease of HiN concomitant with an increase of HoA and HoN frac tions was observed. These indicate that the DOM contained a low concen tration of biodegradable organic matter and a higher content of macrom olecules related to humic substances. The biological significance and heavy metal binding of these fractions are being studied based on earl ier observations showing enhanced plant growth in the presence of DOM extracted from mature as opposed to immature compost.