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Characteristics of Granular Sludge in an EGSB Reactor for Treating low Strength Wastewater Yoochatchaval, W.; Ohashi, A; Harada, H.; Yamaguchi, T. & Syutsubo, K. Abstract A lab-scale expanded granular sludge bed (EGSB) reactor was operated at 20°C with low strength wastewater (0.6-0.8 g COD/L) for over 200 days. Reactor was inoculated with mesophilic granular sludge. The up-flow velocity was set to 5 m/h by effluent recirculation. The COD loading was increased up to 12 kg COD/m3/day until the day 76, resulting in hydraulic retention time of 1.5 hours. Physical properties (settleability anddiameter) of retainedsludge tended todeteriorate during the first 2-3 months, however sludge settleability kept sufficiently in the later part of experiment due to the reconstruction of granular sludge. The growth yield (Yg) of retained sludge (0.13 g VSS/g COD) was about two times higher than mesophilic and thermophilic granular sludge processes while the endogenous decay constant (Kd) is very low (0.0001/day) as compared with those processes. The sludge retention time of retained sludge reduced from 100 days to 40 days by the reduction of hydraulic retention time from 4 hours to 1.5 hours. Maintenance of 40 days of sludge retention time caused the stable retainment of biomass and the significant increase of methanogenic activity of the retained sludge. Keywords EGSB reactor, Anaerobic treatment, Granular sludge, Growth yield, Low-strength Wastewater, SRT

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