Environmental Engineering Reference
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5.5 Sequencing leach bed reactor with upflow anaerobic sludge bed
(UASB) (adapted from Nizami and Murphy, 2011).
5.7
Laboratory analysis and scale up
5.7.1 Single-phase and two-phase systems
This section examines the effect of reactor configuration on the methane
production for a given feedstock (in this case grass silage). High solid
content feedstocks at commercial scale are typically digested in single-phase
systems (all microbiological stages in one vessel). These may be a dry batch
system (Fig. 5.2), a wet continuous system (Fig. 5.3) or a dry continuous
system (Fig. 5.4). Rarely, if ever, are two-phase systems (such as in Fig. 5.5)
employed at commercial scale. Within the scientific literature there are a
number of descriptions of two-phase systems (Cirne et al., 2007; Lehtomaki
and Bjornsson, 2006; Yu et al., 2002), but the authors have yet to encounter
such a system at commercial scale. Potential scale up of two-phase systems
to commercial facilities needs further research and development.
To examine differentiation of single- and two-phase systems, a series of
laboratory experiments was undertaken comparing the same feedstock
(grass silage cut from the same field at the same time) monodigested in
different reactor configurations, as a described by Thamsiriroj and Murphy
(2010), Thamsiriroj and Murphy (2011), Nizami et al. (2011a), Nizami et al.
(2011b) and Nizami and Murphy (2011). The grass silage was analysed (DS
30.66%; 92% of which VS; 19MJ/kg VS; 1 kg of VS produces 1.4 kg COD).
The feedstock was used in a two-step digestion process with recirculation of
liquor (layout similar to Fig. 5.3(b)) and in a two-phase system (Fig. 5.5).
The two-phase system was a sequencing-fed leach bed reactor (SLBR)
complete with upflow anaerobic sludge blanket (UASB). The phases were
separated. Hyrdolysis and acidogensis took place in the leach beds;
methanogensis took place in the UASB reactor (Fig. 5.5).
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