This paper deals with the characteristics of anaerobic microbial granules grown in an UASB reactor treating catechol bearing synthetic wastewater (SWW). The specific methanogenic activity of the sludge showed an increase in trend with an increase in the organic loading rate and the catechol concentration in the SWW. The settling velocity of individual granules in the size range of 0.5-2.5 mm was found to be in the range of 30-75 m h(-1). The ash content in the sludge was 11.7% with a sludge volume index of 18-20 ml g(-1). The inorganic elemental distribution within the granules showed a decrease except that for phosphorous and cobalt, which increased by similar to 12% and 18%, respectively. after the treatment of SWW. Scanning electron microscopy (SEM) coupled with electron disperse X-ray analysis showed an increase in the Sulphur content by similar to 300% after the treatment of SWW. Surface mineral composition of the granules determined by XRD analysis indicated the existence of vuagnatite (CaAlSiO(4)(OH)). SEM observation of the granules showed the predominance of Methanosaeta and Methanobacterium type of species on the surface along with a variety of other species. (C) 2008 Elsevier Ltd. All rights reserved.