The feasibility of sewage treatment by an upflow anaerobic sludge blanket (UASB) reactor was studied using actual sewage at a fixed hydraulic retention time (HRT) of 4.7 h, and at temperatures in the range of 25-13 degrees C, for six months. The average total COD removals and solid COD removals achieved were 70% and SOS:,, respectively. Total COD removal rate depended on influent strength, especially solid COD concentration, rather than operational temperature. Particulate organic matter in the influent was effectively removed by entrapment in the sludge bed. The hydrolysis rate of the entrapped organics was significantly affected by temperature. that is, 58% of the entrapped particulate organics was liquefied at 25 degrees C, decreasing to 33% at 13 degrees C. The methanogenic activity of the retained sludge decreased eventually to 4-10% of the seed granular sludge which had been formed on carbohydrate wastewater. Microscopic observation of the morphology of the sludge revealed that even though the sludge remained in granular form as a whole, the granules tended to be partly broken in a slate of autolysis.