Avaliação da velocidade de cisalhamento média em biorreator convencional tipo tanque agitado e aerado
Abstract
In biochemical processes, shear rate ( γ&) in the system is an important variable on design
and operation of bioreactors. Shear can result in damage to the cells and the microorganisms,
taking to the viability loss and even to the cellular breaking and the microbial death. In the
present work was proposed a methodology to quantify average shear rate ( av γ & ) in stirred
bioreactor with a 4 L working volume, through volumetric oxygen transfer coefficient (kLa),
varying the operating conditions, as the impeller rotational speed (N: 600, 700, 800, 900 and
1000 rpm) and the specific air flow rate (Φar: 0.50 and 1.00 vvm). Five different glycerol
solutions and distilled water were utilized as Newtonian fluids and six different xantham gum
solutions were utilized as non-Newtonian fluids. Dynamic viscosity (µ) of the glycerol solutions
and rheological parameters (K, n) for the xantham gum solutions, were determined at 28ºC from
rheograms using a digital concentric-cylinders rheometer. Based on the obtained results, a
correlation for average shear rate ( av γ & ) as function of the impeller rotational speed (N),
rheological parameters (K, n) and volumetric oxygen transfer coefficient (kLa) was proposed. The
correlation obtained for the average shear rate ( av γ & ) showed appropriate to estimate av γ & , because
the estimated values approximated of others values described in literature for another
correlations. In a second stage, four cultivations of Streptomyces clavuligerus ATCC 27064 was
realized in a stirred bioreactor, aerated 0.50 vvm and agitated in 700, 800, 900 and 1000 rpm.
Process variable values, as consistency index (K), flow index (n), cellular concentration (Cx),
glicerol concentration (CGlic) and
2 CO n& produced ag of the cultivations were evaluated. It was
observed that the consistency index (K), flow index (n) and cellular concentration (Cx) varied
due to shear conditions imposed to the cultivations. Finally, based on experimental literature
results, average shear rate ( av γ & ) was determined in function of the time for cultivation of S.
clavuligerus in stirred bioreactor for 600, 800 and 1000 rpm and specific air flow rate (Φar) of
0.50 vvm, using the proposed methodology, the obtained values were more consistent, because
the experimental values of kLa were obtained by gaseous balance.