Yu et al. studied the effects of powdered activated carbon (PAC) and GAC on sludge granulation during start-up of UASB reactors. The results showed that the addition of PAC or GAC clearly enhanced the sludge granulation process and accelerated the start-up process. Sludge granulation, defined as the time by which 10% of the granules are larger than 2.0 mm, took approximately 95 days to be achieved in the reactor with no addition of inert materials and was reduced by 25 and 35 days in the PAC and GAC-added reactors, respectively. Besides, the addition of GAC and PAC provoked higher biomass concentrations throughout the experiment, earlier ob-servation of visible granules and improved the volu-metric COD removal capacity. Moreover, the addition of GAC showed slightly more beneficial effects for the

start-up of UASB reactors than PAC. The enhanced granulation by the addition of PAC or GAC was attributed to a better attachment of the filamentous bacteria on the activated carbon. However, in this study, the characteristics of PAC and GAC were not examined in detail. The different characteristics are likely respon-sible for the minor difference between the PAC and GAC-added reactors.