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Characteristics of Granular Sludge in an EGSB Reactor for Treating low Strength Wastewater

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A lab-scale expanded granular sludge bed (EGSB) reactor was operated at 20°C with low strength wastewater (0.6-Q.8 g CODIL) 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/mJ/dayuntil the day 76, resulting in hydraulic retention time of 1.5 hours . Physical properties (settleabilityand diameter) of retained sludge tended to deteriorate 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 (Y) 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 (K) is very low (0.000 l/day) as compared with those processes. The sludge retention time ofretained sludge reduced from 100 days to 40 days by the reduction of hydraulic retention time from 4 hours to 1.5 hours. Maintenance of40 days ofsludge retention time caused the stable retainment of biomass and the significant increase ofmethanogenic activity ofthe retained sludge.

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