KINETICS AS A TOOL FOR POLYHYDROXYALKANOATE PRODUCTION OPTIMIZATION

The increasing commercial importance of polyhydroxyalkanoates calls for the development of new, more efficient production processes. This can only be achieved by considering the kinetics of polyhydroxyalkanoate accumulation in fermenters, but efforts in this area have been few. In a 10-L fed-batch fermenter, Alcaligenes eutrophus G(+3) was used to produce poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) from glucose and gamma-butyrolactone, and a strain of Alcaligenes latus was used to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from glucose and propionate. After 83 h of fermentation, 9.26 g . L(-1) of A. eutrophus contained 77.8% in mass of a copolymer with 7.9 mol% 4HB. The observed maximum specific growth rate (mu(max)) was 0.19 h(-1) for the residual biomass. Alcaligenes latus grew at an observed residual-biomass mu(max) of 0.41 h(-1) and after 33.75 h had produced 6.6 g . L(-1) of dry biomass with 72% of a copolymer with 28 mol% 3-hydroxyvalerate. Yields and specific substrate consumption and product formation rates were calculated. Examination of these results and of data found in the literature led to the proposition that for certain polyhydroxyalkanoate production processes, a multi-stage system consisting of a continuous stirred-tank fermenter in series with a plug-flow tubular reactor would be the most productive solution.