Hiroyuki Iwaki

Characteristics of Domestic Sewage Treatment by an EGSB reactor

Akiyoshi Ohashi, Hiroyuki Imachi, Hideki Harada


To maintain and form the granular sludge is one of the important factors for successful anaerobic treatment. Domestic wastewater is mainly low concentration (less than 1 gCOD/L) and also low temperature (less than 20��). Generally it is difficult to maintain the granular sludge since low substrate containing in domestic wastewater. EGSB (Expanded Granular Sludge Bed) reactor is an advanced anaerobic wastewater system to solve these problems.

In this study, EGSB reactor was applied for sewage treatment. Process performance of EGSB and characteristics of retained sludge were observed.

Continuous flow experiment was performed by 70.5 L of pilot-scale EGSB reactor and mesophilic granular sludge was inoculated. Gritted raw sewage was used as a feed and temperature range was 9-26��. HRT was 2 hour and up-flow velocity was 6 m/h.
EGSB reactor was operated for over 350 days with a domestic sewage. When high concentration of SS was fed to reactor, process performance was drastically decreased and it is difficult to observed the characteristics of process performance. After 218 days, clarifier was installed before the reactor, and then process was stabilized.�@Removal efficiency of total COD and SS were 42% and 48%, respectively. Methane gas and dissolve methane production were 0.19 and 0.61 kgCOD/m3/day respectively. Most of methane production in EGSB system was flowed as dissolve methane.

The concentration of retained sludge (MLVSS) after 297 days, was 20-30 g/L until 3.0m height of the reactor. The settleability of retained sludge (SVI) was 20~30 ml/gSS. The methanogenic activities with respect to acetate, hydrogen and propionate were decreased. But it has no effect to the decrease of process performance.

Compare to the process performance of UASB reactor with raw sewage. Unlike UASB reactor, process performance of EGSB reactor was not decreased drastically.