Environmental Engineering Reference
In-Depth Information
Operating bioreactors at low H
2
partial pressure by stripping H
2
from the solu-
tion is as it is generated [57, 102], accomplishes both efforts simultaneously [11].
Conceptually, efforts are to be made in optimizing operational conditions to prevent
consumption of H
2
by propionic acid-producing bacteria, ethanol-producing bacte-
ria and homoacetogens and those that channel more reducing equivalents towards
reduction of H
+
by hydrogenases to maximize H
2
production [11]. The physiolog-
ical and physicochemical conditions under which the microorganisms give optimal
H
2
yields is important and needs to be established. Optimization of process param-
eters is one of the vital steps as to enhance H
2
yield as well as to enhance substrate
degradation efficiency and assumes significance prior to up-scaling the process.
7 Strategies to Enhance Process Efficiency
7.1 Process Integration Approach
Utilization of remaining carbon present in wastewater from acidogenic H
2
produc-
tion (an organic acid rich effluent) for additional biogas (H
2
or CH
4
) generation
is one way to sustain the process. Integration of an acidogenic process with a
terminal photo-fermentative process (for additional H
2
production) [6, 7, 110] or
acidogenic process (for additional H
2
production) [86] or methanogenic process
(for methane production) [23] were reported along with enhanced substrate degra-
dation (Fig. 5). Soluble metabolites formed during methanogenic or from acidogenic
processes could be utilized by photosynthetic bacteria [6, 7] or acidogenic cultures
20
4.25
Methane
Hydrogen
SDR
4.00
16
3.75
12
3.50
8
3.25
4
3.00
0
2.75
30
35
40
45
50
55
60
65
70
75
80
85
90
Time (day)
Fig. 5
Biogas generation and substrate degradation pattern during integration of acidogenic H
2
production (acidophilic) process with methaogenic (neutral) process [23]
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