It is nowadays widely recognized that successful implementation of industrial PHA production will only be achieved through satisfaction of sustainability aspects coupled with production of biodegradable poly­mers with desirable properties. Sustainability aspects include cost-competitiveness, environmental benign­ness and production of biodegradable polymers that serve certain market and societal needs. Additional ad­vantages will be provided through the ability to produce PHAs with adjustable properties that could be used in different end-uses by simple modification of fermenta­tion conditions. For instance, the production of different types of PHAs that could be used for both commodity

(e. g. food packaging) and specialty (e. g. scaffolds for tis­sue engineering applications) end-uses by simple modi­fication of fermentation parameters could provide process flexibility.

An important innovation on future PHA-based pro­cesses will be the creation of cascade processing schemes in order to increase resource efficiency (Anonymous, 2012b). Cascade processing is based on the reutilization of packaging material after its use (also called postcon­sumer plastics) for other commercial purposes. For instance, hydrolysis into monomers could create value — added platform molecules for the chemical industry. In addition, bioplastics could be used as replacements for coal and heating fuel due to their high calorific value (Anonymous, 2012b). Reutilization of PHA-based pack­aging materials is strongly dependent on the develop­ment of suitable recycling technologies.

Despite their significant advantages, industrial pro­duction of PHAs is hindered by high production cost.

Previous attempts to produce PHAs in large scale had to rely on conventional fermentation technologies that cannot compete with low-cost petroleum-derived plas­tics. As mentioned earlier, raw material supply is one of the most important factors that should be optimized in order to reduce processing costs. For this reason, recent research focuses on the utilization of low-cost feedstock for PHA production (e. g. molasses, crude glycerol, whey, animal fats, and waste cooking oils among others) aiming to substitute for conventional and expensive carbon sources. Table 24.2 presents the re­sults regarding PHA production from various waste and by-product streams. However, even if waste or by­product streams are used as fermentation feedstocks, aerobic cultivation for PHA production in industrial scale operations is still an expensive unit operation. For this reason, integration of PHA production into existing industrial plants or the development of new in­dustrial plants for PHA production should be combined

with the production of value-added co-products. This can be achieved through fractionation of agricultural re­sources or by-product and waste streams from existing industrial processes.

PHA production cost increases further due to down­stream separation and purification of PHAs from resid­ual microbial mass. Several methods have been reported for the recovery of PHAs based on the utilization of organic solvents such as acetone, chloroform or dichlo — roethane. However, these methods are unfavorable for large-scale production since solvents increase opera­tional cost and additional equipment for solvent recov­ery is often needed. Alternative extraction methods have been also proposed including enzymatic lysis of re­sidual microbial mass (Kapritchkoff et al., 2006; Verlin — den et al., 2007), supercritical fluid extraction (Hejazi et al., 2003), mechanical disruption of bacterial cells coupled with chemical treatment, autolysis of bacterial cells, and chemical treatment under acidic or alkaline conditions (Yu and Chen, 2006; Verlinden et al., 2007).

Several studies have also focused on the estimation of PHA production costs from different feedstocks (Choi and Lee, 1997; van Wegen et al., 1998; Posada et al.,

2011) . However, there are limited studies on the evalua­tion of integrated biorefineries focusing on the fraction­ation of the initial raw material combining the production of PHAs with the extraction or production of value-added co-products. In addition, future costing studies should also focus on the evaluation of the poten­tial to integrate PHA production in existing industries.

In recent years, several studies focused on the pro­duction of PHAs from low-cost renewable resources (Akaraonye et al., 2010; Koller et al., 2010; Du et al.,

2012) . This study focuses on the presentation of repre­sentative biorefinery concepts targeting the production of PHAs and other value-added products. In particular, PHA production could be combined with biofuel and bioenergy production.