Page 270 - Industrial Wastewater Treatment, Recycling and Reuse

244 Industrial Wastewater Treatment, Recycling, and Reuse

for the ferridoxin protein, which is a carrier of electrons to the hydroge-
2+
nase. A higher concentration of Fe showed an enhancement in H 2 pro-
duction efficiency due to its role as a component of hydrogenase and Fd
(Karadag and Puhakka, 2010; Lee et al., 2001; Wang and Wan, 2008;
Zhang et al., 2005). Optimum Fe 2+ concentration varied from 25 to
100 mg/L (Srikanth and Venkata Mohan, 2012a).

6.3.1.3 Bioreactor Configuration and Operational Mode
The operation mode of the reactor along with its configuration influences
the reactor microenvironment, hydrodynamic behavior, wastewater-
biocatalyst contact, and survivability of the microbial population. Diverse
reactor configurations, such as suspended growth, biofilm/packed-bed/
fixed bed, fluidized bed, expanded bed, upflow anaerobic sludge blanket,
granular sludge, membrane-based systems, and immobilized systems, were
reported for biohydrogen production. Biofilm systems are resistant to
shock-loads, and facilitate an improved reaction potential, leading to stable
and robust systems that are also more resilient to changes in the process
parameters. More importantly, biofilm systems are well suited for treating
highly variable wastewater (Lalit Babu et al., 2009; Venkata Mohan et al.,
2007a,b).
Batch, fed-batch, semi-batch/continuous, periodic discontinuous batch
(sequencing batch operation), and continuous modes of reactor operation
have all been evaluated for H 2 production. Batch mode operation coupled
with biofilm configuration helps to maintain stable and robust cultures suit-
able for treating highly variable wastewater due to the dual operational
advantages of both the systems (Lalit Babu et al., 2009; Luo et al., 2010;
Venkata Mohan et al., 2007a–d, 2008a–c; Yokoi et al., 1997). Fed-batch
mode operation reduces poor biomass retention/cell washout (Yokoi
et al., 1997) and accumulation of soluble metabolic intermediates due to
fill-draw mode operation (Venkata Mohan et al., 2007a,b, 2011a).
6.3.2 Renewable Wastewater as Feedstock

The last decade witnessed significant progress in the dark-fermentation pro-
cess, owing to its feasibility of utilizing a broad range of wastewaters as a sub-
strate with mixed cultures as biocatalysts. In conjunction with wastewater
treatment, this process is capable of solving two issues: reduction of pollut-
ants in waste and the generation of a clean alternative fuel. The simplicity of
the process, its efficiency, and its smaller footprint are some of the striking
features of the dark-fermentation process that make it particularly more