In which case are you theoretically likely to get more methane if you use substrates with the following parameters to produce biogas (assuming the same amount of COD goes to biomass production in all cases)?

• COD 20 g/l , sulphate content 2 g/l
• COD 22 g/l, sulphate content 6 g/l
• COD is 17 g/l, substrate is sulphate free