Fig. 5

Anaerobic digestion by a contactless system of WSS with or without Aso limonite. a A contactless system was constructed as illustrated. Two vials were prepared: (left) Aso limonite cannot be used for the anaerobic digestion and (right) Aso limonite cannot be mixed with WSS by separately placing it on a sponge. b Methane production and c hydrogen sulfide production from control WSS and with contactless limonite. The concentration of Aso limonite used in this experiment was 5% (w/v). Error bars represent the standard errors (n = 3)