PHA Produced in Industrial Scale

The industrial scale fermentative synthesis of PHA uses these pathways to convert the typical nutrients sugar or starch to PHB, but glycerol or palm-oil can also be applied. In addition, copolymers can be produced in this way but special microorganisms, growing condition, and additives are needed. Thus a statistic comonomer distribution starting from 0% (pure PHB) up to 90% co-monomer content can be achieved [35-38]. 

For large-scale recombinant production of bacterial polymers, non-polymer producing bacteria were exposed to biosynthesis pathways. Polymers such as PHA, CGP (cyanophycin granule peptide), HA (hyaluronic acid), and PGA [poly-y-glutamate] were produced by these methods [89, 85-96]. For example, recombinant E.coli [89] was fermented for the lai e-scale production of PHA [89]. In addition the PHB biosynthesis genes of Ralstonia eutropa were harbored in E.coli to produce poljmers such as PHA composed of (R)-S-hydroxybutyrate and (R)-3-hydroxyvalerate and/or (R)-3-hydroxyhexanoate which showed preferable properties for use in industrial applications [97-99, 85-96]. 

It is expected that there will be a shortage of substrate when both PHA and biodiesel are in active production. This is because, at in the current state, pahn oil industry in Malaysia is still not ready to sustain the production of both materials in large scale. The world demand for edible triglycerides is expected to maintain at a minimal growth rate of 3 % per year. At the same time, pahn oil industry in Malaysia is also expected to grow 3 % by year 2009 and subsequently to 10 % in future as more palm oil trees mature. Therefore, some time is needed before Malaysia is able to produce a larger amount of excess pahn oil. Recently, an increase of excess pahn oil was recorded from 1.5 million tons in 2005 to 1.7 million tons in 2007 (Lam et al. 2009). It is expected that the excess supply of... 

Poly[3-hydroxybutyrate] was the first PHA to be produced on an industrial scale, but its brittle nature, its poor mechanical properties and its high production cost limited its application potential. In the early 1990s, Imperial Chemical Industries [ICI] started the production of poly[3-hydroxybutyrate-co-3-hydroxyvalerate] [P3HB3HV] under the trade name Biopol . This material showed lower degrees of crystallinity and superior mechanical properties. Later on, the production of Biopol was continued by Monsanto and subsequently followed up by Metabolix. PHAs were originally intended as bio-based alternatives for polyolefins used in plastic containers, films and bottles. Despite the large interest in PHAs, their application remains, however, limited due to their narrow processing window [84, 85]. 

Since sc/-PHA are stiff and brittle, whereas mc/-PHA are more elastomeric and flexible, incorporation of both scl- and mcl-monomers results in a scl-mcl-copolymer which possesses the properties in between the two states. The resulting polymer has superior properties compared with scl- or wc/-PHA. According to Chen [13], scl-mcl-PHA are ideal to advance the ongoing development in various applications since they exhibit flexible mechanical properties. An attempt to produce this combination of copolymers was started in 1988 by Brandi and co-workers [14] who studied the ability of Rhodospirillum rubrum, a phototrophic bacterium, to produce various kinds of PHA. Among all the sc/-mc/-PHA produced, poly(3HB-co-3HHx) is one of the most successful polymers in this category and has been produced on an industrial scale [13]. 

A different approach is provided by the utilization of carbon sources that have a considerable market value and do not constitute waste materials, but are produced in a process integrating the fabrication of the carbon substrate and PHA. This has been implemented on a pilot scale by the company PHB Industrial in the state of Sao Paulo, Brazil. Starting from sugar cane, the company produces saccharose and ethanol. The waste streams from the sugar production (bagasse) and the bioethanol production (fusel alcohols) are used for running the PHA production and making it economically competitive. 

In 2007, Metabolix and the Archer Daniels Midland Company (ADM) started their joint venture, Telles, and built a 50,000 tonne plant at Clinton, Iowa, USA to produce Metabolix s PHA commercialised under the Mirel trademark [35]. The plant started its production in 2008. However, due to the limited market, ADM announced the end of its commercial alliance with Metabolix on 8 February 2012. As a result of this decision, Telles dissolved and Mirel production on behalf of Telles stopped [36]. At present, the main companies involved in PHA production on a pilot or (semi)industrial scale include Metabolix (USA), Meredian (USA), Kaneka (Japan), Tianan (China), PHB Industrial/Copersucar (Brazil), Biomatera (Canada), Biomar (Germany), Bio-On (Italy), PolyFerm Canada (Canada), Tianjin and DSM (China), and Tianzhu (China). 

This section will review recent reports of attempts to produce PHA. Emphasis will be put on processes using R. eutropha or A. latus, and the survey will be limited to literature on PHA production in bioreactor only. While flask experiments are the necessary first stages in the development of new production strategies (e.g., the use of inexpensive substrates and sources of growth factors, as recently reported in [229] and [230], respectively) and therefore of high interest, the potential of a novel system can be truly assessed only once it has been scaled up to fermentor operation, in which culture conditions at least approach those of industrial fermentations. The other area of research with a possible future impact on large-scale production of PHAs, the use of transgenic plants, will be briefly discussed. 

It has been accounted that, on a production scale of PHB of 100,000 tons per year, the production costs will decrease from US 4.91 to US 3.72 kg , if hydrolysed com starch (US 0.22 kg ) is chosen as the carbon source instead of glucose (US 0.5 kg ) [33]. But this is still far beyond the cost for conventional polymers, which in 1995 was less than US 1 [32]. Lee et al. estimated that PHB and mcI-PHA can be produced at a cost of approximately US 2 kg [36]. The precondition therefore would be attaining high productivity and the use of inexpensive carbon sources. Among such substrates, molasses [37], starch [38], whey from the dairy industry [37-42], surplus glycerol from biodiesel production [39, 43], xylose [44, 45], and plant oils [46] are available. 

---