Fig. 1

Biohythane production (a) and biohythane composition (b) in MECs during a steady operation cycle. The circle lines represent biohythane production (on the left), the last point with standard deviation were calculated based on three cycles of two duplicate reactors. The columns represent biohythane production rate (on the right). RS-OCMEC: raw sludge fed open-circuit MEC; AS-OCMEC: alkali-pretreated sludge fed open-circuit MEC; RS-MEC: raw sludge MEC with an applied voltage of 0.6 V; AS-MEC: alkali-pretreated sludge fed MEC with an applied voltage of 0.6 V