Samples of the liquid fraction of digestate from 6 mesophilic anaerobic co-digestion plants after solid-liquid separation were characterised. The samples represented different types of substrates, different AD process parameters and types of solid-liquid separation devices. Fractionation of the liquid fraction of digestate was performed according to different size in coarse filtration (100 μm, 41 μm, 10 μm) followed by microfiltration (1.2 μm, 0.45 μm, 0.2 μm) and ultrafiltration (100 kDa, 10 KDa and 1 KDa). The fractions were then grouped as suspended particles (> 1.2 μm), coarse colloids (1.2-0.45 μm), fine colloids (0.45μm-1 kDa) and dissolved matter (< 1kDa). The results highlighted that COD was high in liquid fraction of digestates (9-78 g/L) with most of the COD as suspended particles (67.5% to 94.1%) and only 3.2% to 21.5% as dissolved matter. The characterisation of 5 more AD digestates are ongoing and statistical analysis will be performed to assess the correlation between the digestate characterisation and the types of substrates used, process parameters and type of solid-liquid separation used.