A bench-scale bioreactor with a working volume of approximately 10 liter was used to facilitate an animal culture fermentation process. The bioreactor was operated at 400 rpm (in which Rushton turbines with diameter of 70 mm was employed) to give a maximum oxygen transfer rate whilst minimizing the cells disruption due to high shear rate of the impellers. If you were to scale-up the operation to a larger bioreactor system i.e. a bioreactor system with impeller diameter 2 times larger than the one employed in the bench-scale bioreactor at constant impeller tip speed, calculate the impeller speed required in the larger bioreactor system such that similar effects as obtained in the bench-scale setup can be reproduced.