KINETICS AS A TOOL FOR POLYHYDROXYALKANOATE PRODUCTION OPTIMIZATION

The increasing commercial importance of polyhydroxyalkanoates calls fo r the development of new, more efficient production processes. This ca n only be achieved by considering the kinetics of polyhydroxyalkanoate accumulation in fermenters, but efforts in this area have been few. I n a 10-L fed-batch fermenter, Alcaligenes eutrophus G(+3) was used to produce poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) f rom 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) f or the residual biomass. Alcaligenes latus grew at an observed residua l-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-hydroxyva lerate. Yields and specific substrate consumption and product formatio n rates were calculated. Examination of these results and of data foun d in the literature led to the proposition that for certain polyhydrox yalkanoate production processes, a multi-stage system consisting of a continuous stirred-tank fermenter in series with a plug-flow tubular r eactor would be the most productive solution.