Review Potential and Prospects of Continuous Polyhydroxyalkanoate (PHA) Production (original) (raw)
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Potential and Prospects of Continuous Polyhydroxyalkanoate (PHA) Production
Bioengineering, 2015
Together with other so-called "bio-plastics", Polyhydroxyalkanoates (PHAs) are expected to soon replace established polymers on the plastic market. As a prerequisite, optimized process design is needed to make PHAs attractive in terms of costs and quality. Nowadays, large-scale PHA production relies on discontinuous fed-batch cultivation in huge bioreactors. Such processes presuppose numerous shortcomings such as nonproductive time for reactor revamping, irregular product quality, limited possibility for supply of certain carbon substrates, and, most of all, insufficient productivity. Therefore, single-and multistage continuous PHA biosynthesis is increasingly investigated for production of different types of microbial PHAs; this goes for rather crystalline, thermoplastic PHA homopolyesters as well as for highly flexible PHA copolyesters, and even blocky-structured PHAs consisting of alternating soft and hard segments. Apart from enhanced productivity and constant product quality, chemostat processes can be used to elucidate kinetics of cell growth and PHA formation under constant process conditions. Furthermore, continuous enrichment processes constitute a tool to isolate novel powerful PHA-producing microbial strains adapted to special environmental conditions. The article discusses challenges, potential and case studies for continuous PHA production, and shows up new strategies to further enhance such processes economically by developing unsterile open continuous processes combined with the application of inexpensive carbon feedstocks.
2018
Polyhydroxyalkanoates (PHA) are microbial biopolyesters utilized as “green plastics”. Their production under controlled conditions resorts to bioreactors operated in different modes. Because PHA biosynthesis constitutes a multiphase process, both feeding strategy and bioreactor operation mode need smart adaptation. Traditional PHA production setups based on batch, repeated batch, fed-batch or cyclic fed-batch processes are often limited in productivity, or display insufficient controllability of polyester composition. For highly diluted substrate streams like it is the case for (agro)industrial waste streams, fed-batch enhanced by cell recycling were recently reported as a viable tool to increase volumetric productivity. As emerging trend, continuous fermentation processes in single-, two-, and multi-stage setups are reported, which bring the kinetics of both microbial growth and PHA accumulation into agreement with process engineering, and allow tailoring PHA´s molecular structure....
Chemical and Biochemical Engineering Quarterly, 2014
Poly(hydroxyalkanoates) (PHAs) constitute promising biomaterials for substituting plastics of fossil origin. Until now, all commercial processes for PHA production were based on discontinuous fed-batch cultivation of prokaryotes. Such processes embody several shortcomings: unpredictable product quality, restricted possibility for supply of toxic carbon substrates, and, most of all, low volumetric productivity. Continuous PHA biosynthesis as a remedy was already investigated on laboratory scale for production of highly crystalline PHA homopolyesters as well as for elastomeric and even functional PHA copolyesters. Apart from enhanced productivity, chemostat processes are a feasible method to elucidate kinetics of cell growth and PHA formation under constant environmental conditions. In order to adapt the process engineering to the microbial kinetic characteristics for growth and PHA accumulation, continuous single-and multistage approaches are reported.
Recent developments in bioreactor scale production of bacterial polyhydroxyalkanoates
Bioprocess and Biosystems Engineering, 2019
Polyhydroxyalkanoates (PHAs) are biological plastics that are sustainable alternative to synthetic ones. Numerous microorganisms have been identified as PHAs producers they store PHAs as cellular inclusions to use as an energy source backup. They can be produced in shake flasks and in bioreactors under defined fermentation and physiological culture conditions using suitable nutrients. Their production at bioreactor scale depends on various factors such as carbon source, nutrients supply, temperature, dissolved oxygen level, pH and processes. Once produced, PHAs find diverse applications in multiple fields of science and technology particularly in the medical sector. The present review covers some recent developments in sustainable bioreactor scale production of PHAs and identifies some areas in which future research in this field might be focused.
Production of Polyhydroxyalkanoates from Renewable Sources Using Bacteria
Journal of Polymers and the Environment, 2018
Plastics play a very important role in our daily life. They are used for various purposes. But the disposal of these petrochemical-derived plastics causes a risk to the human and marine population, wildlife and environment. Also, due to the eventual depletion of petrochemical sources, there is a need for the development of alternate sources for the production of plastics. Biodegradable polymers produced by microorganisms can be used as substitutes for conventional plastics derived from petrochemical sources since they have similarity in their properties. Polyhydroxyalkanoate (PHA) is one such biopolymer that will be accumulated inside the cells of microorganisms as granules for energy storage under limiting conditions of nutrients and high concentration of carbon. Research on the microbial production of PHA should focus on the identification of costeffective substrates and also identification of a suitable strain of organism for production. The major focus of this review is the production of PHA from various cost-effective substrates using different bacterial species. The review also covers the biosynthetic pathway of PHA, extraction method, characterization technique, and applications of PHA in various sectors.
Producing microbial polyhydroxyalkanoate (PHA) biopolyesters in a sustainable manner
A B S T R A C T Sustainable production of microbial polyhydroxyalkanoate (PHA) biopolyesters on a larger scale has to consider the " four magic e " : economic, ethical, environmental, and engineering aspects. Moreover, sustainability of PHA production can be quantified by modern tools of Life Cycle Assessment. Economic issues are to a large extent affected by the applied production mode, downstream processing, and, most of all, by the selection of carbon-rich raw materials as feedstocks for PHA production by safe and naturally occurring wild type microorganisms. In order to comply with ethics, such raw materials should be used which do not interfere with human nutrition and animal feed supply chains, and shall be convertible towards accessible carbon feedstocks by simple methods of upstream processing. Examples were identified in carbon-rich waste materials from various industrial braches closely connected to food production. Therefore, the article shines a light on hetero-, mixo-, and autotrophic PHA production based on various industrial residues from different branches. Emphasis is devoted to the integration of PHA-production based on selected raw materials into the holistic patterns of sustainability; this encompasses the choice of new, powerful microbial production strains, non-hazardous, environmentally benign methods for PHA recovery, and reutilization of waste streams from the PHA production process itself.
Recent advances in polyhydroxyalkanoate production by bacterial fermentation: mini-review
International Journal of Biological Macromolecules, 1999
Poly(3-hydroxybutyrate) [P(3HB)] and other polyhydroxyalkanoates (PHAs) have been drawing much attention as biodegradable substitutes for conventional nondegradable plastics. For the economical production of P(3HB), various bacterial strains, either wild-type or recombinant, and new fermentation strategies were developed for the production of P(3HB) with high concentration and productivity. To reduce the cost of carbon substrate, several processes for P(3HB) production from cheap carbon sources were also developed. P(3HB) can now be produced to a content of 80% of cell dry weight with the productivity greater than 4 g/l per h. Fermentation strategy was also developed for the efficient production of medium chain length PHA by high cell density culture. With all these advances, P(3HB) and PHAs can be produced by bacterial fermentation at a cost (ca. $2/kg) similar to that of other biodegradable polymers under development.
Bacterially Produced Polyhydroxyalkanoate (PHA): Converting Renewable Resources into Bioplastics
Dependence on conventional plastics and their boundless usage have resulted in waste accumulation and greenhouse gas emissions. Recent technologies are directed towards the development of bio-green materials that exert negligible sideeffects on the environment. A biologically-synthesized plastic, polyhydroxyalkanoate (PHA), has been attracting major interests due to its similar physical properties to synthetic plastics. Unlike synthetic plastics, PHA is produced from renewable resources and is degraded aerobically by microorganisms to CO 2 and H 2 O upon disposal. The selections of suitable bacterial strains, inexpensive carbon sources, efficient fermentation and recovery processes are important aspects that should be taken into consideration for the commercialization of PHA. This chapter discusses economical strategies to reduce production costs of PHA as well as its applications in various fields.
Process Parameters for Influencing Polyhydroxyalkanoate Producing Bacterial Factories: An Overview
Journal of Petroleum & Environmental Biotechnology, 2013
The ever increasing potentialities of petroleum plastics with respect to lack of degradation, inability to recycle and the toxic effects of incineration, has urged to design biodegradable polymers, often called Green Plastics. These biodegradable plastics are promiscuous due to their analogous properties and environmental friendliness. Bacterial factories and Plants being their natural sources for production made them a promiscuous solution. Fermentation is the procedural technology used with certain fillers that are known to enhance the chemo-mechanical properties. The process at the industrial level is not well accepted due to the certain lacunas. The review mainly focuses to assimilate a few researches that implicate the best known process parameters for Batch, Fed-batch, Continuous and Two stage modes of fermentation without compromising the downstream processing at commercial level.