Semi-continuous anaerobic digestion of different silage crops: VFAs formation, methane yield from fiber and non-fiber components and digestate composition

•Determined removal efficiency of individual fiber and non-fiber components.•Silages with the highest VFAs cumulative effect were the lowest methane production.•Lignin content in silages did not affected methane production.•Digestates of maize and annual crops mixtures were the highest fertilizing value.

This study presents the results of long-term semi-continuous experiments on anaerobic digestion at an HRT of 45 d with ten silages: 2 annual and 4 perennial crops, and 4 mixtures of annual with perennial crops. The composition of substrates and digestates was determined with Van Soest’s fractionation method. Removal of non-fiber materials ranged from 49.4% (Miscanthus sacchariflorus) to 89.3% (Zea mays alone and mixed with M. sacchariflorus), that of fiber materials like lignin ranged from 0.005% (Z. mays alone and mixed with grasses at VS ratio of 90:10%) to 46.5% (Sida hermaphrodita). The lowest stability of anaerobic digestion, as confirmed by normalized data concentrations of volatile fatty acids, was reported for both miscanthuses and sugar sorghum. The methane yield coefficients for non-fiber and fiber materials were 0.3666 and 0.2556 L/g, respectively. All digestate residues had high fertilizing value, especially those from mixtures of crops.