Environmental Engineering Reference
In-Depth Information
3.9 Laboratory digesters for solid substrate utilisation, showing two
reactors with electric heat jackets, temperature control unit and stirring
devices.
in substrate composition or the presence of inhibitors). Real representative
conditions appear only after three volume changes (three retention times).
In a CSTR (continuously stirred tank reactor), this means at least four
months of operation (including start-up).
Standard VDI 4630 describe a simplified strategy for the fermentation
start-up. The start-up should initiate at an organic loading rate (OLR) of
0.5 kg VS/(m 3 *d). If the gas production is constant for 4 days, the OLR can
be increased by 0.5 kg VS/(m 3 *d). After that, the OLR can be increased by
steps of 0.5 kg VS/(m 3 *d) every 14 days until gas production declines (Fig.
3.10).
Start-up can also be carried out by adapting the feed of the reactors to the
performance of the microbes. However, this requires experience and
knowledge of the fermentation process, as well as a well-equipped
laboratory. The reactor is started at an OLR of 0.5 kg VS/(m 3 *d) and the
following parameters are monitored: gas production (online), gas composi-
tion (two or three times per week) and volatile fatty acid (VFA) composition
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