Abstract
Reducing the total cost of poly(3-hydroxybutyrate) (PHB) production as an attractive substitute for conventional petrochemical plastics still remains an unsolved problem. The aim of this research was the screening of PHB-producing microorganisms and selection of the best suitable medium for microbial growth and PHB production from methane. A new isolated methanotroph for PHB production from natural gas was studied in different media. After selection of the suitable medium, the effect of five process variables (content of nitrogen source, disodium hydrogen phosphate, methane to air ratio, seed age, and pH) on PHB production was investigated in a bubble column bioreactor. Also, hydrodynamic and mass transfer factors (flow regime, mixing time, gas hold up, and kLa) were considered. At optimum operating conditions and engineering parameters in a bubble column, PHB content in the dried biomass reached 25 % w/w. The results showed that pH is the most important variable in the selected conditions.
Highlights
Poly(3-hydroxybutyrate) (PHB), as a biodegra dable, biocompatible and thermoprocessible biopo lyester, has attracted the interest of bioresearchers[1,2,3]
Four possible media were compared for rapid growth and PHB production by a new isolated bacterium
After selection of the best medium, an L8 Taguchi design was used to evaluate the impact of some process variables on PHB production
Summary
Poly(3-hydroxybutyrate) (PHB), as a biodegra dable, biocompatible and thermoprocessible biopo lyester, has attracted the interest of bioresearchers[1,2,3]. The main problems, which limit their widespread application, are still high production cost and thermal instability[7]. The costs of PHB production mainly depend on substrate, culture condition, and downstream processing. Recycled gas closed circuit culture system has been reported for the growth of bacteria from gaseous substrate[10]. In this system, the limitation of oxygen causes the formation of intermediates of the Krebs Cycle and even the PHB biosynthesis pathway, harming or even rendering unfeasible the formation of PHB30. Appropriate mass and heat transfer, appropriate gas dispersion, and directed circulation flow, loop bioreactors are applied to develop aerobic fermentation. The circulation creates appropriate mixing in all phases and provides good mass transfer[24,30]
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