Fig. 3

Impact of Aso limonite to the hydrolysis and the acidogenesis stages of anaerobic digestion; a protease activity at day 2, 6, and 10 to evaluate the hydrolytic activity of WSS and b organic acids at day 6 to evaluate the acidogenesis process. Aso limonite was mixed with WSS to be the following concentrations (0%, 0.5%, 1%, 5%, and 10% w/v). Error bars indicate standard errors (n = 3). Asterisk (*) indicate the significant difference by the addition of Aso limonite