Agitation in stirred tank bioreactors require a great deal of attention as damage to
microorganisms limit the extent of impeller speed or power input, which in effect
will disturb the actual mass transfer capability and productivity of a bioreactor. A
new variant of low shear impeller under helical ribbon class (Paravisc) was
investigated for its potential to replace the Rushton turbine which was found to exert
excessive shearing in mixing processes and proved less efficient in handling non-
Newtonian fluids. Performance analysis on Paravisc impeller covered the aspect of
physical mixing as well as the integration model fungal system. Under nonbiological
environment, the impeller torque measurement gave Newtonian powerflow
relationship with a power constant (Kp) of 424.7 for mixing under laminar
condition. Reynolds number (Re) at 60 marked the critical point, Recrit, where flow
shifted to transitional regime. In case of non-Newtonian fluids, impeller power draw
decreases as shear thinning behavior increases. The vessel shear rate was calculated
from the superposition of both Newtonian and non-Newtonian power data. The
vessel shear rate constant (Ks) was then derived as a function of Kp(n) of the given power law fluids. The mixing time analysis produced a mixing time constant (Km) of
53.8 throughout laminar regime but decreases when approaching Recrit before
stabilized again at 11.8 in turbulent flow regime. The volumetric oxygen transfer
coefficient (kLa) was more affected by the agitation of Paravisc than it had with
superficial gas velocity for non-viscous fluids when mixing was above a certain
critical impeller speed (NC). However, gassing rate became more influential on
oxygen transfer for tests using 0.2 % to 0.8 % w/v carboxymethylcellulose sodium
(CMCNa) solutions. Predictive kLa correlations in the form power law equations
derived via multiple linear regressions resulted in separate correlations for water,
electrolytes and viscous simulant fluids. Application of Paravisc in red pigment
production by Monascus purpureus FTC5391 was based on the theoretical kLa
attainable in media using calculations from the developed model. The highest yield
and productivity by Paravisc mixing was achieved at 250 rpm and 1.5 VVM with
YP/S and P equaled to 0.47 UA500/g.glucose and 0.15 UA500/h, respectively. These
were 58% and 14% more than what was obtained by Rushton impeller. Operationwise,
mixing with a single Paravisc was more efficient since it require 42% less
energy than a typical double Rushtons operation. Consequently, this led to two-fold
red pigment yield per energy consumed (YP/E) for helical ribbon impeller, of which
152.1 UA500/kW.h was measured from stirred tank bioreactor retrofitted with the
novel agitator compared to 69.2 UA500/kW.h produced by Rushtons at 600 rpm
