Changes in the chemical structure of municipal solid waste during composting as studied by solid-state dipolar dephasing and PSRE C-13 NMR and solid-state N-15 NMR spectroscopy

Solid-state nuclear magnetic resonance (NMR)spectroscopy was used to elucid ate the composition of total organic carbon (TOC) in fresh and composted mu nicipal solid waste (MSW) samples and to estimate the behavior of composted MSW after landfilling. We showed that the cross polarization magic angle s pinning (CPMAS) technique provided C-13 NMR spectra of MSW with representat ive intensity distribution, whereas O-alkyl carbon was underestimated in th e single pulse excitation experiment Fresh MSW was dominated by signals in the O-alkyl C region that are derived most probably from carbohydrates. Sig nals assignable to plastics could also be identified. The presence of plast ics was confirmed by dipolar dephased (DD) and proton spin relaxation editi ng (PSRE) C-13 NMR spectra. During composting, the intensity of O-alkyl C d ecreased, while that of signals from plastics increased. This indicates a d ecrease of the biodegradable fraction and of the landfill emission potentia l. As estimated from a PSRE subspectrum, the content of plastics in the com posted MSW was 37% of TOC, which equals 26% of OM. CPMAS N-15 NMR spectra r evealed that peptide structures play a major role in the organic nitrogen f raction. Some of these peptides appear to resist acid hydrolysis and biodeg radation.