Production of size-controlled gellan gum microbeads encapsulating gasoline-degrading bacteria

Controlling the mean diameter of polymeric carriers is crucial to the successful application of encapsulated cells for in situ bioaugmentation of contaminated aquifers. The cell carriers should be small enough to be transported through a granular soil matrix, thus an emulsification-internal gelation technique for production of cell-encapsulating gellan gum microbeads is proposed. Mean diameter and size distribution of microbeads were investigated as a function of the water-in-oil emulsion parameters. The mean diameter of the microbeads ranged from 12 to 135 mum, varying as a descending function of the stirring rate (1000-5500 rpm) and emulsifier concentration (0-0.20% w/w), and as an ascending function of the disperse phase volume fraction (0.08-0.25). A bacterial consortium encapsulated within the microbeads (23 mum mean diameter) showed improved biodegradation activity in the removal of gasoline (400 mg L-1), as compared to free cells. A high degree of repeatability in the microbead formation process and particle size measurements was demonstrated. The results of this study suggest that the emulsification process can potentially be used for the large-scale production of controlled-diameter gellan gum-encapsulated cell microbeads for subsurface bioremediation applications, (C) 2002 Elsevier Science Inc. All rights reserved.