Avaliação de transferência de calor e massa em biorreator Airlift de bancada para a produção de ácido clavulânico.
Resumo
The importance of the airlift bioreactor has grown in the biotechnology
field by aspects as high oxygen transfer, with power input low.
In this work were study the conditions heat and mass transfer, as well
as the condenser efficiency in the water retention, of an airlift bench bioreactor of
internal circulation of useful capacity 6 L. Such bioreactor is endowed with hollow
draft tube working as a heat charger for temperature control and of aspersor type
crosspiece for aspersion of air.
Values of the heat transfer global coefficient (U) were certain in different
operation conditions starting from applied energy balance in the system after the
same to reach the steady state. Values of U varied in the range from 300 to 700
W.m-2.°C-1, showing that the device of thermal change proposed was efficient to
heat removal. The results were correlated with the water flow inside the draft tube
and with the feeding air flow in the bioreactor.
After this stage, it was evaluated water drags of the bioreactor system
plus condenser in different conditions of air flow and temperatures in the
bioreactor and in the condenser. The condenser was shown efficient in the water
retention, obtaining efficiency superior values to 80%, but it didn't solve the
problem of water loss by water drag for the high air flows in that the airlift
bioreactor is operated. The variable air flow was the variable that influenced more
significantly water drags.
The transfer oxygen was evaluated through the oxygen transfer
volumetric coefficient (kLa). For comparison, kLa values were obtained in the airlift
bioreactor operated in a range of specific feeding air flow from 1 to 5 vvm and in
conventional bioreactor of 4 L, in different agitation conditions (600, 800 and
1000 rpm) and aeration (0,5 and 1,0 vvm). Two methods for kLa determination
were employees, the sulfite method and the dynamic method considering the
delay of the electrode answer. This last one that generated results between 2 and
6 times inferior, depending of bioreactor type, because it evaluates the kLa in
coalescent media, similar to most of the media fermentation.
Finally, to validate the use of the system as bioreactor, cultivations with
Streptomyces clavuligerus seeking to the production of clavulanic acid, a potent
inhibitor of β-lactamase, enzyme producted by patogenics microorganism that
broke β-lactamic rings of antibiotics. Four cultivations were accomplished, two in
airlift bioreactor and two in bioreactor conventional (Bioflo III) in two different
conditions of oxygen transfer (kLa) and the results were compared in terms of
clavulanic acid production.
The maximum clavulanic acid concentrations obtained in the cultivations
in airlift bioreactor were superior those obtained in conventional bioreactor, with
minors consistence index (K), showing larger shear rate in the airlift bioreactors in
the same conditions of transfer oxygen.
In global terms, the obtained results suggest that bioreactor as the most
appropriate for this cultivation type, justified for the appropriate heat and mass
transfers formed an alliance with the smallest energy consumption.