Coupling Biogas with PHA Biosynthesis

This chapter critically reviews the potential of biogas, whose main constituent is methane (second most significant greenhouse gas), as a suitable carbon feedstock for the generation of polyhydroxyalkanoates (PHA). The capacity of synthesizing PHA (up to about 60% of their cell dry mass) from this source under nutrient-limiting conditions corresponds to type II methane-oxidizing bacteria, which belong to the α-proteobacteria phylum and assimilate C1 compounds via the serine pathway. The metabolism of methane oxidation and PHA accumulation is systematically described, along with the mechanisms of PHA used as an energy and carbon source by bacteria. In addition, the main operational limitations of this technology, namely, innovative bioreactors for biogas bioconversion and product recovery, are discussed. Finally, the techno-economic analysis of this approach reveals that the production costs of biogas-based PHA are competitive compared with conventional feedstocks used in industrial PHA production. In brief, the use of biogas constitutes an attractive and viable alternative for bioplastics production that might improve the economic sustainability of the anaerobic digestion, with widespread applicability in agro-industrial, livestock, and urban solid waste treatment facilities.