DIFFERENTIAL SCANNING CALORIMETRY APPLIED TO THE STUDY OF DIGESTATES OBTAINED FROM DIFFERENT ORGANIC SUBSTRATES

Digestates obtained from a 1:1 mixture of the organic fraction of municipal solid waste and sewage sludge under mesophilic and thermophilic conditions evidenced a shift of the high temperature exotherm toward higher temperature with respect to feed-in material indicating stabilization attained by the OM during the process. A further shift of this exotherm toward higher temperature associated to lower enthalpy values were observed for thermophilic digestates with respect to mesophilic digestates. These results were explained by a major degradation of OM attained under stronger operative conditions. Lower enthalpy values were calculated for both mesophilic and thermophilic digestates with respect to feed-in mixtures. DSC applied to digestates obtained by energy crops, poultry manure, stomach residue and others agro-industrial residue sampled in different sections of the digestion plant showed a strong exotherm at lower temperature indicating lower thermal stability of the substrate. Lower enthalpy values of the high-temperature exotherm were calculated for digestates sampled from the storage tank, whereas higher H values were calculated for digestates retrieved from the second digester.