Feasibility studies for encapsulated cell bioaugmentation of contaminated aquifers

Encapsulated cell bioaugmentation is a novel approach to in situ bioremediation of contaminated aquifers. This study was carried out to develop encapsulated cell microbeads of appropriate size suitable for in situ bioaugmentation, and to evaluate the feasibility of such a remediation strategy based on the performance of entrapped cells in the biodegradation of a common groundwater contaminant and the transport of cell carriers through porous soil media.A two-phase dispersion technique, termed emulsification-internal gelation, was developed to encapsulate a gasoline-degrading bacterial consortium in gellan gum microbeads. The influence of emulsion parameters including stirring rate, disperse phase volume fraction, emulsifier concentration, emulsification time, and cell mass loading on size distribution of microbeads was studied.A suspension of microbeads in artificial groundwater (AGW) was pulsed into a column for 6 h, followed by injection of bead-free AGW for 42 h. In general, the total amount of microbeads traveling across a given section of the column decreased with the decrease of mean grain size. The results of this study demonstrated the feasibility of transport of gellan gum microbeads through a wide range of soil grains, i.e. medium sand to medium gravel (0.25--16 mm), across distances up to 110 cm.An enriched bacterial consortium, isolated from a gasoline-polluted site was encapsulated in gellan gum microbeads. The capacity of encapsulated cells to degrade gasoline under aerobic conditions was evaluated in comparison with free (non-encapsulated) cells. Encapsulated cells (2.6 mgcells g-1 bead) degraded over 90% gasoline hydrocarbons (initial gasoline concentration 50--600 mg L-1) within 5--10 days at 10°C. Equivalent levels of free cells removed comparable amounts of gasoline (initial concentration 50--400 mg L-1) within the same period, but required up to 30 days to degrade the highest level of gasoline tested (600 mg L-1). (Abstract shortened by UMI.