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Licensed Unlicensed Requires Authentication Published by De Gruyter August 20, 2014

Valorization of Glycerol into Polyhydroxyalkanoates by Sludge Isolated Bacillus sp. RER002: Experimental and Modeling Studies

Mohd Zafar, Shashi Kumar, Surendra Kumar, Jay Agrawal and Amit K. Dhiman


In this study, the feasibility of glycerol valorization into homo- and hetero-polymers of polyhydroxyalkanoates by a sludge isolated Bacillus sp. RER002 in a 3 L bioreactor was investigated. A mathematical model including logistic, Luedeking–Piret, and Luedeking–Piret-like equations that simulated the active residual biomass growth, P(3HB) synthesis, and glycerol consumption, respectively, was developed. In order to describe the dynamics of batch P(3HB) production, the model kinetic parameters viz., µmax, K1, K2, α, β, and KN were optimized using the stochastic search-based genetic algorithm. The synthesis of P(3HB) wasobserved to be highly growth associated and partially non-growth associated as reflected in a significant higher values of K1 (0.2435–0.5477) than K2 (2.2 × 10−6 to 9.1 × 10−3) within the glycerol concentration range of 10–40 g/L. Besides, the maximum 3.2g/L of copolymer [P(3HAscl-co-3HAmcl)] was observed at 30 g/L of glycerol concentration in synthetic crude glycerol medium with a yield coefficient (YP/S) of 0.16 g/g. Furthermore, the analyses of chemical and thermal properties of copolymer P(3HAscl-co-3HAmcl) revealed its enhanced material properties which make it suitable for various applications.


This study is financially supported by Ministry of Human Resources and Development, Govt. of India, New Delhi.



Specific consumption rate of (NH4)2SO4


Growth-associated product constant for Luedeking–Piret model representing P(3HB) concentration (g/g)


Non-growth-associated product constant for Luedeking–Piret model representing P(3HB) concentration (g/h)


Maintenance-energy expenditure coefficient on glycerol (/h)


Number of experiments


P(3HB) concentration (g/L)


Initial P(3HB) concentration at t = 0 during fermentation process (g/L)


Experimental value of P(3HB) concentration (g/L)


Predicted value of P(3HB) concentration (g/L)


Objective function representing the deviation between experimental and simulated data during GA-basedoptimization of kinetic constants


Catalytically active residual biomass concentration (g/L)


Initial active residual biomass concentration at t = 0 (g/L)


Experimental value of active residual biomass concentration (g/L)


Predicted value of active residual biomass concentration (g/L)


Maximum concentration of active residual biomass concentration (g/L)


Residual concentration of glycerol at the end of fermentation process (g/L)


Experimental value of glycerol concentration (g/L)


Predicted value of glycerol concentration (g/L)


Experimental value of (NH4)2SO4 concentration (g/L)


Predicted value of (NH4)2SO4 concentration (g/L)


Glycerol concentration (g/L)


(NH4)2SO4 concentration (g/L)


Initial (NH4)2SO4) concentration (g/L)


Experimental value of active residual biomass concentration, P(3HB) concentration, and glycerol concentration in ith experiment (g/L)


Predicted value of active residual biomass concentration, P(3HB) concentration, and glycerol concentration in ith experiment (g/L)


Mean value of experimental data of active residual biomass concentration, P(3HB) concentration, and glycerol concentration (g/L)


Yield of biomass with respect to simulated crude glycerol consumption (g/g)


Yield of P(HAscl-co-3HAmcl) concentration with respect to simulated crude glycerol (g/g)


Yield of active residual biomass with respect to substrate glycerol (S1) consumption (g/g)


Yield of P(3HB) concentration with respect to substrate glycerol (S1) consumption (g/g)


Maximum specific growth rate for logistic equation (/h)


Specific growth rate for logistic equation (/h)


Constant representing growth-associated substrate consumption for Luedeking–Piret model representing glycerol consumption (g/g)


Constant representing non-growth-associated substrate consumption for Luedeking–Piret model representing glycerol consumption (g/h)


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Published Online: 2014-8-20
Published in Print: 2014-12-1

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