Chemistry Reference
In-Depth Information
d
n
2
r
4
n
g
|
7
Figure 3.1 The morphology of PHA granules in a bacteria cell. The round dot arrow
indicates the cell wall; N
¼
NPCM; G
¼
PHA granule.
solvent and extracted from the NPCM. However, PHA polymers remain in
the form of a solid during the second process while NPCM is digested and/or
dissolved by agents. Finally, the obtained solid and liquid phases are sep-
arated using filtration or centrifugation. A useful classification of different
recovery methods that are available to extract the PHA from the cell is given
in Figure 3.2.
3,4
Some of the most successful laboratory cell disruption techniques have no
possibility of commercialization. Selecting the best recovery method de-
pends on factors such as types of cells and their history, sample volume,
reaction time, possible scale-up potential, effect on downstream purification
processes and economics of disruption. It has been reported that the e-
ciency of a recovery process is dependent on the type of cell. Besides, cell
growth and their storage history can be affected by the destructibility of cells.
The bacteria cells in log phase growth tend to produce thinner cell walls,
which are easier to disrupt. This and other conditions that can influence
microbial cell destructibility are carbon source, micronutrients and media
richness, phase of growth (batch fermentation), retention time (continues
fermentation) and strain of microorganism. Moreover, the operating and
energy requirements, availability and cost of the disruption equipment are
other important parameters.
5
More details about the most common techniques of PHA recovery, which
are classified as chemical, biological, mechanical and physical methods as
independent systems or in combination with other processes, will be pre-
sented in the following sections.
.
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