Optimum Design of N Continuous Stirred-Tank Bioreactors in Series for Fermentation Processes Based on Simultaneous Substrate and Product Inhibition

Ibrahim M Abu Reesh

doi:10.3390/pr9081419

Abstract

Optimization of the continuous fermentation process is important for increasing efficiency and decreasing cost, especially for complicated biochemical processes described by substrate and product inhibition. The optimum design (minimum volume) of CSTRs in series assuming substrate and product inhibition was determined in this study. The effect of operating parameters on the optimum design was investigated. The optimum substrate concentration in the feed to the first reactor was determined for N reactors in series. The nonlinear, constrained optimization problem was solved using the MATLAB function “fmincon”. It was found that the optimum design is more beneficial at high substrate conversion and at a medium level of feed substrate concentration. The best number of reactors is two to three for optimum arrangements and two for equal-size arrangements. The presence of biomass in the feed to the first reactor reduces the reactor volume, while the presence of product in the feed slightly increases the required total volume. The percentage reduction in the total volume using the optimum design compared to equal-volume design (R%) was determined as a function of substrate conversion and substrate concentration in the feed to the first reactor. The obtained R% values agree with experimental data available in the literature for ethanol fermentation.

Highlights

In recent years, many studies have used simultaneous substrate and product inhibition kinetics to describe the dependence of microbial specific growth rate on substrate and product concentration
The objective of this work is to compare the performance of the optimum design of CSTRs in series based on substrate and product inhibition kinetics with equal-volume design; i.e., the objective is to determine the operating conditions at which the optimum design is more beneficial compared to equal-volume reactors, which is the current practice in industry
The minimum volume design was determined for continuous stirred-tank reactors in series performing a fermentation process described by simultaneous substrate and product inhibition kinetics

Summary

Introduction

Many studies have used simultaneous substrate and product inhibition kinetics to describe the dependence of microbial specific growth rate on substrate and product concentration. Many fermentation processes, such as ethanol fermentation, have been described by this kinetics. Other mathematical models were developed to describe alcohol production from different substrates such as glucose using yeast [6] and from glycerol [7]; these models describe the inhibition effect on the fermentation process. Modeling of lactic acid production that considers the effect of substrate and product concentration was proposed for glucose [9] and kodo millet bran residue hydrolysate as substrate [10]. The reversible reaction is modeled mathematically with a substrate product inhibition model

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Conclusion