SLOW SAND AND DIATOMACEOUS-EARTH FILTRATION OF CYSTS AND OTHER PARTICULATES

The performance of slow sand and diatomaceous earth (DE) filtration was compared in removing Giardia muris, Cryptosporidium, coliform bacteria, turbidity, and particles added to a pristine surface water. When operated correctly, both filtration systems removed 99.9% or more of the cysts applied. The removals of coliform and turbidity were not satisfactory in biologically immature slow sand filters, particularly during winter months. When operated correctly, mature filters exhibited satisfactory removal of these contaminants. Coliform removal was not satisfactory with diatomaceous earth filtration except when the finest grade of DE (C512) was used. However, with polymer preconditioning of DE, a significant increase in coliform removal was observed.