AWWA WQTC55154

Cryptosporidium oocyst and polystyrene microsphere removals were evaluated during the filter ripening period, immediately following filter ripening, and at the end of a 24-hour filter run of pilot scale conventional and biological filters. The main objectives of this study included determining whether or not a high concentration of oocysts pass through the filter during the ripening period or at the end of a continuously seeded filter run. Previous studies have not revealed significantly poorer removals during ripening, but none of those studies seeded oocysts throughout the preceding filter run (allowing oocysts to be present in the backwash remnants which compose a significant portion of the initial filter ripening turbidity spike). The concentration of oocysts and microspheres found in the effluent under the influence of backwash remnants ranged from no higher to 5-times higher than those in water passing through the filter after the ripening period depending on filter type. Conventional and biological filters showed similar oocyst and microsphere removals (roughly 1.5 and 2.0 Log, respectively) during this study, but the biological filters exhibited marginally lower concentrations of oocysts and microspheres present in the effluent samples containing backwash remnants. Microspheres and oocyst removals generally followed the same trends during this study, but there was a tendency for greater removal of the microspheres than oocysts under the conditions encountered in this study. Includes 14 references, tables, figures.