Transport of gellan gum microbeads through sand: an experimental evaluation for encapsulated cell bioaugmentation

Transport of 10-40 microm gellan gum microbeads was studied in horizontal sand columns to evaluate the feasibility of using gel-encapsulated bacteria for bioaugmentation of contaminated aquifers. Three 5.2 x 110 cm columns were packed with sand (column A: 0.5-2 mm, column B: 0.25-2 mm, and column C: 0.125-2 mm). Microbeads in artificial groundwater were injected at 0.5 l h(-1) during intermittent 12-h periods. Breakthrough of microbeads increased with injection time, varying as a descending function of travel distance. After 72 h of injection, about 75% of injected microbeads were dispersed across a 5-110 cm distance from the inlet in column A, compared to 78% across a 5-50 cm in column B, and 76% across a 5-20 cm in column C. The wider dispersion of microbeads across the length of column A, compared to those observed in columns B and C, suggests a higher potential for the formation of a uniform bioactive zone of encapsulated cells across a sandy aquifer with such grain size distribution and hydrodynamic properties.