EGSB. An extended granular sludge bed reactor (EGSB) is a variant of the UASB concept (Kato et al. 1994). The differentiating feature is that a higher upward flow velocity is provided for the wastewater passing through the sludge bed.
The increased flow allows partial expansion (fluidization) of the granular sludge bed, improving contact between wastewater and sludge and promoting the segregation of small inactive suspended particles from the sludge bed. The increased flow rate is achieved either through the use of high reactors or through wastewater recirculation (or both).
The EGSB concept is suitable for poorly soluble wastewater (less than 1 to 2 g of soluble COD /l) or for wastewater that contains inert or poorly biodegradable suspended solids that must not be deposited in the sludge bed.
Overview of the performance of the reactors. A recent survey (Frankin, 2001) carefully documented 1215 large-scale, high-speed anaerobic reactors built around the world since the 1970s to treat industrial wastewater. The overwhelming majority (72% of all plants) of existing large-scale plants are based on the UASB or EGSB concept developed by Lettinga in the Netherlands. This statistic highlights that the anaerobic granular sludge bed concept is the most successful for scale-up and implementation. The average design load of the UASB of 682 large-scale systems examined was 10 kg COD/m3.d.
Note: COD stands for chemical oxygen demand and refers to the organic matter in wastewater, expressed as the weight of oxygen required to burn it completely. The average design load of the EGSB of 198 large-scale systems examined was 20 kg COD/m3.d. COD removal efficiency largely depends on the type of wastewater; however, the biodegradable COD removal efficiency is generally over 85 or even 90%.
Biodegradable COD is sometimes expressed by the biological oxygen demand ( BOD ) parameter.
The four main applications for high-load anaerobic reactor systems are:
- Breweries and beverage industry
- Distilleries and fermentation industry
- food industry
- pulp and paper.
These four industries together account for 87% of applications. However, the applications of the technology are rapidly expanding, including the treatment of wastewater from the chemical and petrochemical industries, the textile industry, landfill leachate, as well as applications aimed at sulfur cycle conversion and metal removal (see Other Applications). In addition, the UASB concept is also suitable for the treatment of household wastewater in warm climates.
Sources :
Wang, Xu & Ding, Jie & Ren, Nan-Qi & Liu, Bing-Feng & Guo, Wan-Qian. (2009). CFD simulation of an expanded granular sludge bed (EGSB) reactor for biohydrogen production. International Journal of Hydrogen Energy. 34. 9686-9695. 10.1016/j.ijhydene.2009.10.027. Understanding how a bioreactor functions is a necessary precursor for successful reactor design and operation. This paper describes a two-dimensional computational fluid dynamics simulation of three-phase gas–liquid–solid flow in an expanded granular sludge bed (EGSB) reactor used for biohydrogen production. An Eulerian–Eulerian model was formulated to simulate reaction zone hydrodynamics in an EGSB reactor with various hydraulic retention times (HRT). The three-phase system displays a very heterogeneous flow pattern especially at long HRTs. The core-annulus structure developed may lead to back-mixing and internal circulation behavior, which in turn gives poor velocity distribution. The force balance between the solid and gas phases is a particular illustration of the importance of the interphase rules in determining the efficiency of biohydrogen production. The nature of gas bubble formation influences velocity distribution and hence sludge particle movement. The model demonstrates a qualitative relationship between hydrodynamics and biohydrogen production, implying that controlling hydraulic retention time is a critical factor in biohydrogen-production.
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