16.4 Factors Affecting Biohydrogen Production in AnMBRs

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16.4.5

Temperature and pH

Temperature is the key factor for biohydrogen generation, which potentially

affects the hydrogenase activity, microbial communities, and their metabolism

and a spectrum of products. It is remarkable that though hydrogen-producing

microorganisms are capable to generate hydrogen at ambient temperature,

hydrogen-manufacturing performance constantly advanced by rising temperature

in the mesophilic system. However, hydrogen generation might be influenced by

further increase in temperature beyond mesophilic range, possibly affected by the

physiological characteristics of microbial culture. Temperature dependence was

also verified by Chang and Lin by studying the hydrogen production efficacy of

a mixed culture with temperature increasing from 15 to 34 ^∘C [26]. In another

study, temperature change strategy was applied and biohydrogen-manufacturing

yield was improved by 62% as the temperature shifted from 37 to 45 ^∘C. Likewise,

metabolic pathway, cell morphology and composition, microbial population shift,

and yield of biohydrogen are also powerfully influenced by the pH as it is measured

as one of the important variables in ecological situation. Earlier studies assured

that increase in pH below 4.5 significantly eliminates the biohydrogen from strong

methanogens. Widespread literature review revealed that optimum pH value

during continuous fermentative hydrogen production is between 5.2 and 6.0 using

pure or mixed microbial cultures. An additional study shown that best possible pH

range may differ depending on the physiological characteristics of the substrate and

composition of the microbial population.

16.4.6

Seed Culture

Biohydrogen can be formed with pure or mixed cultures. Pure culture is preferred

due to high selectivity and hydrogen-manufacturing ability because metabolism of

microorganisms can be simply manipulated by altering growth and working envi-

ronment. However, the majority of studies using pure culture were performed in

batch mode and mandatory aseptic environment, thus increases overall cost. From

the engineering viewpoint, mixed cultures from anaerobic sludge, municipal sewage

sludge, and soil as inoculums are presumably applied in most of the studies for fer-

mentative hydrogen production.

16.4.7

Hydrogen Partial Pressure

The hydrogen partial pressure foundation by the dissolved hydrogen concentration

in the liquid part is one of the blockages in fermentative hydrogen making. Numer-

ous techniques are now being used to conquer negative impact of hydrogen partial

pressure. An enhancement in yield was observed up to 65% by sparging the sys-

tem with nitrogen. A different study showed 1.5 times enhancement of biohydrogen

yield when the nitrogen sparging was carried out in the system. However, the purity

of biohydrogen is influenced because of dilution impact which is a most important

drawback of gas purging strategy. In another study, Lee et al. applied vacuum strategy

to decrease production pressure and enhance biohydrogen production rate [27].