Impact of medium pH regulation on biohydrogen production in dark fermentation process using suspended and immobilized microbial cells

The 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