Comparison of batch, fed-batch and continuous well-mixed reactors for enzymatic hydrolysis of orange peel wastes

An alternative potential feedstock for bioethanol in the automotive sector is citrus peel waste (CPW), which can be processed through enzymatic hydrolysis and fermentation. The present work considers mathematical modeling of orange peel wastes (OPW) hydrolysis with the use of free enzymes and compares the performance of batch, fed-batch and continuous well-mixed reactors after introducing appropriate rate equations in dynamic mass balances. MATLAB® was used for model implementation. Following the Michaelis–Menten approach, the authors used their own kinetic parameters for the pectin hydrolysis rate equation. The parameters were generated in an apposite experimental program for OPW hydrolysis to galacturonic acid with consideration of product inhibition; the corresponding values were obtained after Lineweaver–Burk linearization and are: rmax = 0.28 g/(L min), Km = 19.80 g/L and KIGA = 6.96 g/L, respectively. Vice-versa, the authors adopted the Kadam's group kinetic schemes and parameters for cellulose hydrolysis to cellobiose and glucose. The mathematical model of a well-mixed batch reactor was perfectly validated against the experimental results of OPW hydrolysis to galacturonic acid. In the case of a continuous well-mixed reactor, high dilution rates determine low conversion of OPW. The increased complication of fed-batch operation does not add advantages when compared to batch processing.