Fig. 4
a Cumulative methane production (NmL) in grey, the concentrations of lignin intermediates (mM) in green (triangle), phenyl acids (mM) in blue (diamond), and acetate (mM) in red (circle) of thermophilic samples fed with gallic (upper row), syringic (middle row), and vanillic acid (lower row) under low (left column), medium (middle column), and high (right column) overload conditions from day 0 to 28. Marker points and boxes show median and percentiles (25–75%), respectively. b Cumulative methane production (NmL in grey), the concentrations of lignin intermediates (mM) in green (triangle), phenyl acids (mM) in blue (diamond), and acetate (mM) in red (circle) of thermophilic samples fed with ferulic (upper row) and coumaric acid (lower row) under low (left column), medium (middle column), and high (right column) overload conditions from day 0 to 28. Marker points and boxes show median and percentiles (25–75%), respectively