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

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.