Fig. 2

Performance of the bioreactors M1–M4: a pH of the effluents, b total biogas production per day (left axis) and percentage of methane in biogas (right axis), c substrate utilization measured as COD reduction, d methane production per g of COD reduction for each medium variant presented in Table 1. Methane production was calculated per g of COD reduction according to the equation: daily biogas production × % of methane in biogas / (COD of the medium —COD of the effluent). The periods of Experiments 1 and 2 are framed in all parts of Fig. 2.