Page 79 - Biodegradable Polyesters

3.7 Industrial Production of Bacterial Polyhydroxyalkanoates: PHAs via Fermentation 57

1. Strain development 2. Shake flask study 3. Lab and pilot fermentor studies 4. Scale up
Centrifugation

Press
filtration

Vacuum
drying
Packaging

Requirements: Requirements on optimizations: Requirements: Requirements:
1. Growth to high density 1. Growth pH, product pH 1. Lab scale process development 1. Robust and rapid growth
2. High PHA content 2. Growth and product temp 2. Lab scale process optimization 2. Rapid product formation
3. Rapid growth 3. Growth and product substrates 3. Optimal downstream processing 3. Low oxygen demand
4. Controllable structures 4. Dissolved oxygen concentration 4. Inducible cell lysis
5. Controllable PHA Mw 5. Downstream processing 5. High substrate to PHA yield
6. Simple substrate 6. Simple substrates
7. Mixed substrates
Figure 3.6 Strain and process development for industrial production of PHAs. (Ref. [60],
reprinted with permission of ACS Publications.)

of growing in low-intensity aeration and producing high-content PHAs within a
reasonable amount of time.
For the bacterial production of PHAs by wild-type strains,the Ralstonia
eutropha (formerly called Alcaligenes eutrophus, Wautersia eutropha,or Cupri-
avidus necator) has been the most commonly used wild-type strain for the
industrial production of PHB, P3HB4HB, and PHBV.
For the bacterial production of PHAs by recombinant strains, recombinant E.
coli has been commonly used for PHA production thanks to its convenience for
genetic manipulation, fast growth, high final-cell density, and ability to utilize
inexpensive carbon sources. Metabolix and Jiang Su Nan Tian Co. Ltd employed
recombinant E. coli for their PHA production.
For the anaerobic PHA production, recombinant E. coli anaerobically accumu-
lated PHB to more than 50% of its cell dry weight during cultivation in either
growth or nongrowth medium. The maximum theoretical carbon yield for anaer-
obic PHB synthesis in E. coli is 0.8, much higher than the aerobic one of 0.48.
Anaerobic PHA production is one of vital ways to reduce PHA production cost.
Unfortunately, the slow growth of bacteria under anaerobic conditions must also
be considered.
PHAs can be produced from waste materials. Waste materials or wastew-
ater may be used to produce PHAs with a reduction in cost. The production
of PHB from the waste-activated sludge generated by a combined dairy and
food processing industry wastewater treatment plant has been evaluated.
Deproteinized jowar grain-based distillery spentwash yielded 42.3 wt% PHB,
followed by filtered rice grain-based distillery spentwash, which yielded
40 wt% PHB.