Additional file 1: Figure S1. Biogas composition vs. time. R1 was the control reactor and maintained at residence time (RT) = 20 days throughout. R2 and R3 had decreasing RTs (20 days, 10 days, 5 days and 3.3 days) with each RT’s period indicated by solid black lines. Contents of CH4 and CO2 were expressed on fractional basis.