Nuclear magnetic resonance, infra-red and pyrolysis: Application of spectroscopic methodologies to maturity determination of composts

Compost maturity or stability reflects the degree of decomposition of the organic matter (OM). Since stability of natural OM is a relative term, defining it is not a trivial challenge. In addition, it requires a series of chemical, physico-chemical and spectroscopic determinations. Among the methods applied, ¹³C-NMR and FTIR (or DRIFT) and pyrolysis have been shown to be of significance and therefore this review will be dedicated to studies focusing on the application of these methods to composting research. In fact, solid-state ¹³C-NMR spectroscopy has become the most important tool for examining the chemical structure of natural OM (NOM) and the chemical changes associated with OM decomposition. Changes can be measured on the bulk OM either fresh or composted, on humic substances (HS) extracted from the compost or on dissolved organic matter (DOM). Recently, 2D ¹H NMR has been employed to study properties of HS extracted from MSW compost. In general, changes measured on decomposing OM are more distinct in the following order of tested materials: DOM > Bulk OM > HS > Core HS. In conclusion, compost HS which are “young” relative to soil HS were shown to differ from the latter mostly in their high levels of aliphatic and polysaccharide components, which tend to decompose during composting. ¹³C-NMR is the most effective instrument applied to date to structural studies of NOM.