Environmental Engineering Reference
In-Depth Information
3.6 Correct storage of inoculum for BMP tests (in a temperature-
controlled environment).
Inoculum
In standard BMP tests, anaerobically stabilised sewage sludge is used as
inoculum (standards EN 11734 and DIN 38 414 (S8) apply). However, for
special substrates such as crops, sludge from a crop digester could perform
better due to adaptation to this substrate. It is important not to use sludge
from instable biogas reactors as these are likely to contain inhibitors and
microorganisms with reduced activity. If the sludge contains bigger
particles, it should be sieved before utilisation. Apart from that, depending
on the sludge type, the buffer capacity can be very limited. Consequently,
sludges with a high buffer capacity are preferable, or buffer media can be
added to the sludge. For a high-throughput laboratory it could be also
attractive to operate a seed digester with an operational inoculum
(EN 11734). In order to improve the set-up, EN 11734 recommends
washing the inoculum material, centrifuging it and re-suspending it in a
buffered medium. Trace element solutions may also be added to the sludge
to counteract possible reduced activity due to trace element limitation.
Short-term storage of
inoculum can be done at
the appropriate
temperature (mesophilic inoculum at 35-38
C) in a plastic canister that
maintains anaerobic conditions but allows gas to escape (Fig. 3.6). Active
inoculum can be stored for about a week before utilisation. If the inoculum
has to be stored for a longer period, small amounts of degradable material
can be added regularly to sustain the activity of the inoculum. However,
long storage times are not preferable.
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