(620ab) Simulation and Comparison Between the Real and Supplied Oxygen Demand of a Fermentation Process

Simulation and
Comparison between the real and supplied oxygen demand of a fermentation
process

Serna
Sebastián¹, Sánchez Julio C.¹, García Carlos A.¹,
Cardona Carlos A.^A1

¹ Instituto de Biotecnología y
Agroindustria, Departamento de Ingeniería Química. Universidad Nacional de
Colombia Sede Manizales. Cra. 27 No. 64-60,
Manizales, Colombia

Acetic acid bacteria (AAB) derive
their energy from the oxidation of ethanol to acetic acid during fermentation.
Acetic acid bacteria are airborne and are ubiquitous in nature. They are
actively present in environments where ethanol is being formed as a result of
fermentation of sugars. They can be isolated from the nectar of flowers and
from damaged fruit. Other good sources are fresh apple, cider and unpasteurized
beer that have not been filter sterilized. In these liquids, they grow as a
surface film due to their aerobic nature and active motility [1].

This work analyzes by simulation the
physic-chemical conditions of fermentation that affect both viscosity and
oxygen solubility of acetic acid fermentation using Acetobacter pasteurianus. Concentration profiles of
biomass, substrate (ethanol) and product (acetic acid) through the fermentation
were tested [2]. A. pasteurianus
was chosen due to available data (kinetic parameters and microorganism
characteristics). 

The aim of this analysis is to
demonstrate the relation between concentrations of biomass, substrate and
product with the viscosity of the fermentation media, in order to show the
dependence of those with the oxygen supply. The real proficiency of
fermentation was analyzed in terms of oxygen supply respect to oxygen demand of
the microorganisms, and required agitation for full oxygen supply.

The viscosity of the fermentation is
function of substrate, product and biomass concentrations, previously
calculated by separate. Biomass viscosity was calculated using Vand's equation [3]. For the calculation of the viscosity
of the ethanol and the acetic acid on an aqueous solution it was used the
method of Teja and Rice [4], [5]. Mass transfer
coefficient was calculated with the equation proposed for stirred fermenters
containing non-coalescing non-viscous media [6]. The power dissipated and the amount of oxygen in
the liquid was
calculated with the model proposed by [7], and dissolved oxygen supply was
calculated from [8].

It was concluded that viscosity of
the fermentation solution and oxygen solubility are important variables to
analyze. Both variables were directly related with the conditions that allow
the proper functionality of the microorganism and therefore they are directly
related with performance of the fermentation for acetic acid production. This
analysis can be extended to any fermentation process. Results also reveal that
agitation is an important variable on fermentation and affect directly the
amount of available oxygen in fermentation media and therefore satisfy the
microorganism oxygen demand.  Two cases
were found, one in which the agitation and the oxygen supply exceeds the real
requirements and another one doing the exact opposite, supplying less than the
real requirements. In the first case we talk about over-costs and in the second
one we talk about lower productivity. Therefore, the real equilibrium point
between costs and productivity must be found within these two cases, with the
aim of proposing an optimized performance of the fermentor.

Finally, this approach to the fluid
dynamics of fermentation and its relation with the energetic demands opens a
new perspective in which it is necessary to deepen the functioning of the
associated processes of fermentation.

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