Membrane sparger in bubble column, airlift, and combined membrane-ring sparger bioreactors

The bubble column and the two internal loop airlift reactors (riser/downcom er area ratios of 0.11 and 0.58) characterized in this study were equipped with a rubber membrane sparger, which produced small bubbles, giving high m ass transfer coefficients. The low mixing intensity in the bubble column wa s increased by an order of magnitude in the airlift reactors. We designed a novel aeration and mixing system by adding a ring sparger to the membrane sparger in the bubble column and maintained the advantages of both airlift configuration (good mixing properties) and bubble column configuration (eff icient aeration, without any internal constructions). The combined membrane -ring sparger system has unique features with respect to the efficiency of utilization of substrate gasses and energy. Model experiments showed that t he small bubbles from the membrane sparger do not coalesce with the large b ubbles from the ring sparger. If different gases were added through the two spargers it was possible to transfer a hazardous or expensive gas quantita tively to the liquid through the membrane sparger (dual sparging mode). In the combined membrane-ring sparger system the energy input for mixing and m ass transfer is divided. Therefore, the energy consumption can be minimized if the flow distribution of air through the membrane and ring sparger is c ontrolled by the oxygen demand and the inhomogeneity of the culture, respec tively (split sparging mode). The dual sparging mode was used for mass prod uction of the alga Rhodomonas sp, as the first step in aquatic food chains. Avoiding mechanical parts removes an important risk of malfunction, and a continuous culture could be maintained for more than 8 months. (C) 1999 Joh n Wiley & Sons, Inc.