Performance Analysis of Helical Ribbon Impeller in Production of Red Pigment By Monascus Purpureus Ftc 5391

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.

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