Fig. 1

Impact of Aso limonite on the production of gases (methane and hydrogen sulfide) and ammonia in anaerobic digestion processes using waste sewage sludge (WSS); a methane production in different percentage of Aso limonite, b methane production in the WSS with iron (III) oxide at 5% (w/v), c hydrogen sulfide and d ammonia were measured at day 2, 6, and 10 of incubation in different percentage of Aso limonite. The legend denotes the concentration of Aso limonite as % (w/v). Error bars represent the standard errors (n = 3). Asterisk (*) indicate the significant difference by the addition of Aso limonite