Abstract
ABSTRACTThe effect of pH regulation on biohydrogen production was studied using suspended and immobilized mixed cultures. Four sets of dark fermentation processes were carried out using suspended cells under regulated pH (Sus_R) and non-regulated pH conditions (Sus_N), the nalginate-immobilized cells under pH regulated (Imm_R) and non-pH regulated conditions (Imm_N). Sus_R showed a peak hydrogen fraction of 44% and complete glucose degradation, compared to Sus_N with a peak hydrogen fraction of 36% and a glucose degradation of 37%. Imm_R experiments showed a peak biohydrogen fraction of 35%, while the peak hydrogen fraction observed with Imm_N was 22%.The highest hydrogen fraction was observed using Sus_R conditions. A 100% glucose degradation was observed in both pH regulated and non-regulated processes using immobilized cells. The rate of pH change was slower for immobilized cells compared to suspended cells suggesting a better buffering capacity under non-pH regulated conditions. The study showed that biohydrogen production with suspended cells in a non-regulated pH environment resulted in early termination of the process and lower productivity.
Highlights
IntroductionA large fraction of the global energy needs currently relies on fossil fuels and the constantly increasing human population has led to an upsurge in the global energy demand which may eventually result in the complete depletion of fossil fuel reserves in the near future [1]
Four sets of dark fermentation processes were carried out using suspended cells under regulated pH (Sus_R) and non-regulated pH conditions (Sus_N), the nalginate-immobilized cells under pH regulated (Imm_R) and non-pH regulated conditions (Imm_N)
A large fraction of the global energy needs currently relies on fossil fuels and the constantly increasing human population has led to an upsurge in the global energy demand which may eventually result in the complete depletion of fossil fuel reserves in the near future [1]
Summary
A large fraction of the global energy needs currently relies on fossil fuels and the constantly increasing human population has led to an upsurge in the global energy demand which may eventually result in the complete depletion of fossil fuel reserves in the near future [1]. Fossil fuels are expensive as their combustion results in the release of various pollutants including greenhouse gases, and thereby, raising concerns for global climate change [2,3]. These challenges have fuelled the need to seek for alternative energy sources that are sustainable, renewable and non-polluting. Clostridium species generally produce hydrogen gas during their exponential growth phase until the population reaches stationary phase. At this point, the metabolism shifts from hydrogen and acid production to solvent production. This shift in metabolism known as solventogenesis is induced by a drop in the pH of the fermentation broth below a certain threshold [11]
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