3.2 Two stage fermentation
pH in the hydrogen fermentation (first stage) slightly decreased and stabilized at 5.4 until the end of
fermentation, while that in the methane fermentation (second stage) was stabilized at the narrow range of 7.11 –
7.22 (Fig. 5). Those stabilized pH ranges are optimum for hydrogen- and methane-producing bacteria. Since no
buffer was added into the reactor, the results suggested that the stabilized pH in both stages was due to the buffer
capacity from the banana peel.
4