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Reorienting Waste Remediation Towards Harnessing Bioenergy 241

2008a). H 2 production with typical anaerobic consortia is limited due to its
consumption by methanogens. Pretreating biocatalyst plays a vital role in the
selective enrichment of mixed consortia and shifting the metabolic function
to acidogenesis (Goud and Venkata Mohan, 2012a,b; Srikanth et al., 2010a;
Venkata Mohan et al., 2008b; Zhu and Beland, 2006). Physiological differ-
ences between H 2 producing bacteria (AB) and H 2 uptake bacteria (MB)

form the fundamental basis for the methods used in the preparation of H 2
producing inoculums (Goud and Venkata Mohan, 2012a,b; Sarkar et al.,
2013; Venkata Mohan and Goud, 2012; Venkata Mohan et al., 2008b;
Zhu and Beland, 2006). Different pretreatment methods, such as heat-
shock, chemical, acid-shock, alkaline-shock, oxygen-shock, load-shock,
infrared irradiation, microwave irradiation, and freezing and thawing are
reported for the selective enrichment of H 2 producing inoculums (Goud
and Venkata Mohan, 2012a,b; Venkata Mohan and Goud, 2012; Venkata
Mohan et al., 2008b; Wang and Wan, 2008). Efficacy of the pretreatment
method depends on the nature and composition of the parent inoculum,
conditions adopted for pretreatment, and the nature of substrate apart from
other operating conditions (Srikanth et al., 2010a; Venkata Mohan et al.,
2008a,b). Pretreatment facilitates selective enrichment of microbial popula-
tions specific to acidogenic function and therefore leads to relatively less
diversity. It also prevents competitive growth and coexistence of other
H 2 consuming bacteria. Clostridium sp. became the dominant genus after
acid-shock pretreatment (Goud and Venkata Mohan, 2012a; Lee et al.,
2009; Venkata Mohan et al., 2011b). This composition of the microbial
community in the long-term-operated acidogenic reactor with combined
pretreatment (repeated applications) showed the dominance of the Clostridia
followed by Bacteroidetes, Deltaproteobacteria, and Flavobacteria (Venkata
Mohan et al., 2010a) and Aquificales (Goud et al., 2012). On the contrary,
application of pretreatment showed marked reduction in substrate
degradation efficiency due to specific inhibition of MB, which are essential
to metabolize the acid intermediates generated along with the H 2 (Goud and
Venkata Mohan, 2012a).

6.3.1.2 Factors Influencing Biohydrogen Production
Conceptually, the physiological and physicochemical conditions under
which the microorganisms give optimal H 2 yield are important and need
to be established by taking into account other associated aspects. Some of
the operating conditions reported in the literature concerning H 2 produc-
tion are depicted in Table 6.1. Optimization of process parameters is