RESUMEN
Two lab-scale expanded granular sludge bed reactors were operated using granular sludge and river sediments as seed sludge respectively, through gradually lowering down the inner pH values, acid-tolerant methanogenic granular sludge with good methanogenic activity were acquired and formed. Two EGSB reactors could be operated steadily under the condition of pH 5.8～6.2, and their volumetric loading rates were about 5.5～7.5 kg COD/(m3/d), the COD removal efficiencies were about 90%. The granular sludges taken from two reactors could maintain relatively higher methanogenic activity under low pH, and the relative activities of the granular could be 51.78% and 55.6% of the value with the condition of pH 7.0 when pH was 5.5. Studies on the diameter distribution, settling velocities, concentrations of different metal elements and microbiological characteristics of these acid-tolerant granular sludges were also conducted.