An expanded granular sludge bed (EGSB) reactor is a variant of the up flow anaerobic sludge blanket digestion (UASB) concept for anaerobic wastewater treatment. The distinguishing feature is that a faster rate of upward-flow velocity is designed for the wastewater passing through the sludge bed. The increased flux permits partial expansion (fluidisation) of the granular sludge bed, improving wastewater-sludge contact as well as enhancing segregation of small inactive suspended particle from the sludge bed. The increased flow velocity is either accomplished by utilizing tall reactors, or by incorporating an effluent recycle (or both).

The EGSB reactor is the family of UASB reactor. With a high recycle ratio, the up flow of this reactor is typically maintained higher than 6 m/hr; meanwhile the general range of the UASB reactor is 0.5 to 1.0 m/hr. The height to width of EGSB is 4 ~ 5 so that it enables the EGSB reactor to contact granules with wastewater enough. Additionally, due to the high velocity, granules are expended and the hydraulic mixing is intensified as to also give granules more chances to contact with wastewater. Thus, this reactor is able to treat high-strength organic wastewater (up to loading rate about 30 kg/m3∙d). The definitive feature of EGSB reactor is the rapid up flow velocity. It enables this reactor to separate dispersed sludge from mature granules in the reactor. It makes a lot of contacts between granules and wastewater and withdraws suspended sludge out of the reactor. Influent concentration of COD is often less than 1000 ~ 2000 mg /L so that this reactor is also used to treat low-strength wastewater, especially low to mid temperature.

Compared with UASB reactor, EGSB reactor has a much higher flow rate (3~7 m/h). Accordingly, its height/diameter ratio is also bigger than that of UASB, in a range of 3~8. To answer question, the minimum height/diameter ratio could be 3.

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Mr. Wendong Wang, Do you have any article where where the information that indicates me is cited or referenced? thanks for your support