Efficacy of Coral Sand for Removal of Escherichia coli and Bacteriophage under Saturated Flow Conditions

Knowledge of how effectively microbes are transported through porous media is useful for water resource/wastewater management. Despite much research having been done to characterize microbial contaminant transport through various sedimentary materials, very little study has been made on coral sand, such as constitutes the primary substrate of many Pacific atolls. We conducted a set of laboratory column experiments as a preliminary examination of how effective coral sand is at attenuating model pathogens Escherichia coli J6-2 and MS2 bacteriophage (phage) under saturated flow conditions mildly representative of field conditions at the Bonriki freshwater lens, South Tarawa, Kiribati. The very poorly sorted gravelly sand coral substrate tested proved very effective at attenuating the bacterial tracer, and spatial removal rates of between 0.02 and 0.07 log 10 cm(-1) were determined for E. coli J6-2. The ability to determine precise removal rates for MS2 phage was compromised by the use of a plastic apparatus, although the evidence weights toward coral sand being less effective at attenuating MS2 phage than it is E. coli. Further research is required to fully assess the ability of coral sand to remove pathogens and to explore how this medium could be engineered into cost-effective water/wastewater treatment solutions on Pacific atolls. The phage data from this work highlight the limitations of using plastic apparatus in experiments targeted at characterizing the fate and transport of viruses.