Clean Technology 2007
B. Olle, L. Bromberg, T.A. Hatton and D.I.C. Wang
Massachusetts Institute of Technology, US
nanoparticle, mass transfer, oxygen, enhancement, magnetic fluids, fermentation, gas absorption
Maintaining an adequate oxygen supply to aerobic cell cultures has been a long-standing problem in fermentation technology. Insufficient oxygen transfer rates limit cell growth and ultimately process productivity. Our approach to reducing the oxygen transport limitation consists in adding functionalized magnetic nanoparticles to the fermentation medium; these materials consist of particles that have a magnetic core and two coatings. The magnetic core facilitates recovery of the fluid after the fermentation by passing it through a magnetic field; the first coating, made of oleic acid, confers high-oxygen storing capacity and the outer coating, made of surfactant, confers colloidal stability in water to the particle. Using magnetic nanoparticles presents several advantages compared to previous approaches, including large interfacial areas and the possibility to readily recover the particles by High-Gradient Magnetic Separation. <br>An increase of 40% in the oxygen uptake rate has been achieved in Escherichia Coli fermentation by using 0.6% w/w particles, which is directly translatable into increased fermenter productivity. Oxygen transfer enhancements of up to 600% have been observed in cell-free media. It has also been shown that (i) both the mass transfer coefficient (kL) and the gas-liquid interfacial area (a) are enhanced in the presence of nanoparticles, (ii) the enhancement in kL levels off at a nanoparticle fraction of approximately 1% w/w, and (iv) the enhancement shows a strong temperature dependence.