Kinetics of biomass and polyhydroxyalkanoates synthesis using sugar industry waste as carbon substrate by Alcaligenes sp. NCIM 5085

Abstract

Aim: o optimize the operating parameters and further determine the kinetics of biomass and polyhydroxyalkanoate synthesis using sugar industry waste as a carbon substrate by Alcaligenes sp. NCIM 5085. Methodology: Molasses, clarified and pretreated with sulphuric acid, was taken in a batch reactor for fermentation to generate biomass and further for polyhydroxyalkanoate synthesis where Alcaligenes sp. NCIM 5085 was used as a culture. A number of parameters were observed during fermentation experiments to optimize the biomass and PHA namely: initial substrate concentration, incubation period, C/N ratio, inoculum concentration and pH. Fermented solution was filtered to account the yield of biomass from the solution at each time interval decided for each experiment and polyhydroxyalkanoate was extracted from the biomass by chloroform and methanol extraction. Growth kinetics of biomass was modeled by Monod and Logistic models whereas Luedeking-Piret model was used for polyhydroxyalkanoate production rates. Results: From the fermentation experiments, it was found that for 40 g l-1 of molasses at neutral pH, 4.48 g l-1 of biomass was synthesized when fermentation was observed for 48 hr. One percent of cell dry weight of biomass was extracted as polyhydroxyalkanoate. Logistic model for growth kinetics and Luedeking-Piret model for polyhydroxyalkanoate production rate were found in agreement with the experiments where regression coefficient was maximum with minimum error. Interpretation: The PHA growth kinetics and PHA production kinetics done in this work can be utilized to design a bioreactor for PHA production at industrial scale. Key words: Alcaligenes sp., Biomass, Cane molasses, Growth kinetics, Polyhydroxyalkanoates