The granular sludge used in this experiment was from a UASB reactor described by Jing et al. (2013). Based on an assay of microbial community, methane was mainly produced by Methanosaetaconcilii GP6; sulfate was mainly reduced by Desulfovibrio fructosovorans and Desulfovibrio sp. (Jing et al., 2013). In order to compare the difference in tolerance between intact and physically disrupted granules, half of the sludge was blended with a homogenizer at 10000 rpm for 2 min (AS ONE LM-Plus). The experimental methods followed previous research (Jing et al., 2013), and every experiment was repeated at least 3 times over 5 d.