Solid and liquid fractionation of digestate: Mass balance, chemical characterization, and agronomic and environmental value.

Solid-liquid (S/L) separation of digestate (D) represents a simple technology able to produce two fractions having different composition. The aim of this work was to study the effect of S/L separation on dry matter (DM), nitrogen (TKN), phosphorus (P2O5) and heavy metals (HM) repartition into these two fractions and to characterize them. Therefore, thirteen full-scale digestion plants were studied and D, LF and SF were collected during three seasons of the year. Results obtained indicated that unexpectedly, on a mass balance, the liquid fraction still contains the majority of DM, i.e. 67% of the total of D. LF also contained 87% and 71% of TKN and P2O5 respectively. HM contents were in line with typical NP-organic fertilizers. Chemical characterization suggested that the LF can be used as a substitute for mineral N fertilizers because of its high N content, while SF can be proposed as an NP-organic fertilizer.