Environ. Sci. Technol. 2000, 34, 4034-4038
Changes in the Chemical Structure of Municipal Solid Waste during Composting as Studied by Solid-State Dipolar Dephasing and PSRE 13C NMR and Solid-State 15N NMR Spectroscopy MARTIN PICHLER, HEIKE KNICKER,* AND INGRID KO ¨ GEL-KNABNER Lehrstuhl fu ¨ r Bodenkunde (Chair of Soil Science), Technische Universita¨t Mu ¨ nchen, 85350 Freising-Weihenstephan, Germany
Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to elucidate the composition of total organic carbon (TOC) in fresh and composted municipal solid waste (MSW) samples and to estimate the behavior of composted MSW after landfilling. We showed that the cross polarization magic angle spinning (CPMAS) technique provided 13C NMR spectra of MSW with representative intensity distribution, whereas O-alkyl carbon was underestimated in the single pulse excitation experiment. Fresh MSW was dominated by signals in the O-alkyl C region that are derived most probably from carbohydrates. Signals assignable to plastics could also be identified. The presence of plastics was confirmed by dipolar dephased (DD) and proton spin relaxation editing (PSRE) 13C NMR spectra. During composting, the intensity of O-alkyl C decreased, while that of signals from plastics increased. This indicates a decrease of the biodegradable fraction and of the landfill emission potential. As estimated from a PSRE subspectrum, the content of plastics in the composted MSW was 37% of TOC, which equals 26% of OM. CPMAS 15N NMR spectra revealed that peptide structures play a major role in the organic nitrogen fraction. Some of these peptides appear to resist acid hydrolysis and biodegradation.
Introduction In the year 2005, Germany will dispose approximately 22 million Mg of municipal solid waste (1). To avoid the adverse ecological impacts of landfilling untreated municipal solidwaste (MSW), e.g. methane and leachate emissions (2), the German legislation demands a pretreatment prior to landfilling, starting from 2005. Aerobic composting or anaerobic digestion of MSW are pretreatments that focus on preventing landfill emissions by humification of waste organic matter (OM). To predict possible degradation reactions and the emission potential of pretreated humified MSW after landfilling, it is essential to know the composition of waste OM. In a previous investigation (3) we applied a suite of chemolytic methods to characterize the major organic compound classes * Corresponding author phone: +49-8161-714423; fax: +49-8161714466; e-mail:
[email protected]. 4034
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 18, 2000
TABLE 1: Elemental Composition of Municipal Solid Waste Samples Obtained during 9 Weeks of Aerobic Windrow Composting with Subsequent 46 Weeks of Nonaerated Windrow Composting treatment time (weeks)
total organic carbon (TOC) (mg/g dry matter)
total nitrogen (Nt) (mg/g dry matter)
TOC/Nt (w/w)
0 9 16 24 37 55
300 205 191 183 164 155
11.0 9.5 1.07 10.4 11.1 11.0
27.3 21.7 17.9 17.7 14.8 14.1
(carbohydrates, proteins, lipids, lignin) in MSW. However, these analyses allowed the identification of
