Effect of the impeller-sparger configuration over Trichoderma harzianum growth in four-phases cultures under constant dissolved oxygen
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Three impeller-sparger configurations were used to evaluate the effect of different hydrodynamic conditions over fungal growth in rheologically complex cultures of Trichoderma harzianum using castor oil as sole carbon source. Three spargers (ring, sintered and 5-orifice) in combination with a turbine impeller system “TIS” (two Rushton turbines) or a hybrid impeller system “HIS” (Rushton turbine and a marine propeller as lower and upper impellers) were used. Their performance was assessed in terms of the response towards disturbance (PID oxygen control settings) and oxygen mass transfer (k L a). To avoid oxygen limitations, all cultures were controlled at 10% DOT by gas blending. Top to bottom mixing, and hence bulk blending, was improved when the – axial flow – HIS was used, ensuring phase interaction and substrate (oil) circulation. The 5-orifice sparger in combination with the TIS configuration yielded the longest lag phase and lowest k L a due to poor bulk blending and to the low gas–liquid interfacial area developed. The highest k L a was achieved with the sintered sparger-HIS probably due to considerable interfacial bubble area enhancement. However, growth limitation occurred as consequence of poor substrate availability as a stable air–oil emulsion was formed at the top of the tank. The best compromise between bulk blending (phase interaction), oxygen transfer (k L a) and fungal growth (growth rate) was achieved with the ring sparger-HIS configuration.
KeywordsFungal Growth Trichoderma Harzianum Phase Interaction Oxygen Mass Transfer Complex Culture
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