As anaerobic digestion (AD) is quickly being harnessed in Italy and in
other European countries, there is a need for a more in-depth description
of the main by-product of the process, the digestate. Little information
on digestate characteristics and composition is available and unclear
legislation causes problems in biogas plant management. In this work,
the organic matter (OM) of this matrix was described through chemical,
biological, spectroscopic, and statistical approaches. It was shown that
AD results in a strong reduction of the easily degradable fraction of the
OM and an accumulation of recalcitrant molecules (possible humus
precursors). This contributes to a relatively high biological stability of
the residual OM content in the digestate and may lead to good amendment
properties. Besides, the observed relative accumulation and the high
mineralisation of nitrogen and phosphorus may point to the digestate
as a readily available liquid fertiliser for agronomic use. Moreover,
xenobiotics and pathogens respected limits for both biosolids and
compost in Italian and European legislation
