SELECTION OF OPERATION POLICIES FOR AN OPTIMAL PRODUCTION OF MICROBIAL POLY (â-HYDROXYBUTYRATE)

JIMMY A. LÓPEZ-JIMÉNEZ; VERÓNICA BUCALÁ; MARCELO A. VILLAR

Palma de Mallorca - España

Congreso; The Third International Meeting on Environmental Biotechnology and Engineering (3IMEBE); 2008

Institut de Recerca i Formació Agrària i Pesquera de les Illes Balears

Currently, both the considerable increases in the environmental pollution and to the reduction of the world petroleum reserves are the two principal problems associated to the use of synthetic polymers. In spite of these factors, almost the totality plastics produced around the world are of petrochemical origin. Also, this kind of industries approximately produced 245 million tones in 2006 which after of its use, 40 % is discarded into landfills. Also, several hundred thousand tonnes of plastics are discarded into marine environments every year and accumulated in oceanic regions. The biopolymers are devised as the solution to this environmental problem. Being the polyhydroxyalkanoates (PHAs) and specially the poly (beta-hydroxybutyrate) (PHB) the most actually studied. PHAs are synthesized as intracellular reserve material by a wide variety of bacteria from at least 75 different genera. These biopolyesters are produced under unbalanced growth conditions, i.e. excess of a carbon source and nitrogen, phosphorous, sulphur or oxygen limitation. PHB is a crystalline thermoplastic with a melting point around 175 °C. Additionally, it is a non xenobiotic plastic. Therefore, it is totally degradable. Actually the production of PHAs at an industrial level is much smaller than the production of plastics of petrochemical origin. It is due to that PHAs are much more expensive to produce in comparison with petrochemical plastics. The two more relevant stages of PHB manufacture are fermentation and extraction process. In the present work, a complete analysis of two different operation policies for producing PHB has been developed. Fed-batch and continuous operation modes have been study and compared in order to obtain the most convenient operation scheme which maximize the PHB productivity. Dynamic optimization techniques were applied to optimization both the feeding profiles in a fed-batch bioreactor and the unstable state operation in a chemostat. The results obtained clearly demonstrate that an adequate configuration of a continuous bioreactor with a flow divisor and a continuous centrifugal is most adequate than a fed-batch bioreactor. The PHB productivities reached for optimal fed-batch and optimal continuous bioreactor were 3.08 and 4.04 gPHB/L-h, respectively.