Kinetics as a tool for polyhydroxyalkanoate production optimization

Abstract

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 fermentors, but efforts in this area have been few. In a 10-L fed-batch fermentor, Alcaligenes eutrophus G+3was used to produce poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) from glucose and γ-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−1of A. eutrophus contained 77.8% in mass of a copolymer with 7.9 mol% 4HB. The observed maximum specific growth rate (μmax) was 0.19 h−1for the residual biomass. Alcaligenes latus grew at an observed residual-biomass μmaxof 0.41 h−1and after 33.75 h had produced 6.6 g∙L−1of 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 fermentor in series with a plug-flow tubular reactor would be the most productive solution.Key words: polyhydroxyalkanoate, Alcaligenes latus, Alcaligenes eutrophus, kinetics, optimization.