Keywords: 
• anaerobic /
• granules sludge /
• low temperature /
• low strength /
• oxygen-limited /
• characteristic

Abstract: The characteristics of the settled velocity, size, activity and morphology at the conditions of low strength(100～500 mg/L), low temperature(8～15 ℃), oxygenlimited(with the oxidation-reduction potential of 380～400 mV) for the granules in the EGSB reactor seeded with municipal digestion sludge were investigated in this paper. The results showed that the settled velocity of the granules was higher at medium temperature than that at low temperature or under the micro-aerobic conditions, but not lower than the velocity of 15 m/h, thus the sludge was not washed out from the reactor. The weight percent of the large granules was increased gradually at low temperature. The size of the granules was more uniformity under the oxygen-limited conditions. The methanogenic activity of the granules decreased distinctly at 15 ℃ low temperature and the decreased percentage was 55.5%. But supplement of limited oxygen was not harmful to the methanogens and on the contrary stimulated the methanogenic activity of the granules, the increased percentage was 10%. In stable operation at medium temperature, the granules were regular and dense. And more methanosarcina were existed in the granules. At low temperature, The microbes distributed loosenly in district on the surface and in the interior of the granular sludge. At low temperature and medium, high concentration, it was appeared not the methanosarcina but the predominance of the mathanothrix. In the oxygen-limited EGSB reactor the granules had more microbe species. The microbes distributed in district on the surface and in the interior of the granular sludge,there was no distinct predominance of methanosarcina at medium and high concentration.