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A 2.0 L volume of EGSB reactor was operated at 208C for more than 500 days with 0.3-0.4 g COD/L of sucrose base wastewater to investigate the influence of effluent-recirculation on the process performance. At the start up period, the reactor was operated in EGSB mode with 5 m/h upflow velocity by continuous effluent recirculation. The COD loading was set to 7.2-9.6 kg COD/m3 day with HRT of 1 hour. However, in this mode, EGSB reactor exhibited insufficient COD removal efficiency, i.e., 50-60%. Therefore, UASB mode (without recirculation, 0.7 m/h upflow velocity) was used for 30 minutes in every 40 minutes cycle to increase the COD concentration in the sludge bed. As a result, an excellent process performance was shown. The COD removal efficiency increased from 65% to 91% and the reactor could maintain a good physical property of retained sludge (sludge concentration: 33.4 g VSS/L and SVI: 25 mL/g VSS). Furthermore, retained sludge possessed sufficient level of methanogenic activity at 208C. [ABSTRACT FROM AUTHOR]

Whole cell fluorescence in-situ hybridization (FISH) with 16S rRNA targeted oligonucleotides was applied to reveal the microbial ecological structure of UASB-grown granular sludge. The FISH analysis indicated that the members of the domain Archaea accounted for 28 to 53% of the total cells in various granular sludge sources, while Methanosaeta and Methanobacteriaceae cells accounted for 13 to 38%, and 4 to 27%, respectively. Methanosaeta cell density and Methanobacteriaceae cell density were strongly correlated, respectively, with acetate-utilizing methane production activity and with hydrogen-utilizing methane production activity. [ABSTRACT FROM AUTHOR]