IDPA - INTERNATIONAL DIATOMITE PRODUCERS ASSOCIATION
6-LOG REDUCTION BY DE FILTRATION...
In a recently completed study by Dr. Jerry Ongerth, Visiting Fellow at the University of New South Wales, testing showed that diatomaceous earth (DE) filtration provides over 6-log reduction in the concentration of Cryptosporidium oocysts. The project was designed to provide definitive information on the log removal capability of DE filtration of river water for use by municipalities and engineering firms. Only limited information had previously been available. The data developed was benefited by advances in analytical techniques and control principles which were developed by the author and have provided increased sensitivity not available in earlier testing.

The testing was conducted using three grades of DE provided by Celite Corporation and Eagle-Picher Minerals, Inc., the two largest producers of DE filter aid products in the world. Cryptosporidium reductions were measured using seeded river water applied to pilot test filters. Tests were conducted for filtration rates of 1 and 2 gpm/ft2. Each run was replicated three times and rigorous quality control was used. Results of the testing indicate that ca. 6-log reduction in the Cryptosporidium oocyst concentration can be expected under routine operating conditions using DE grades commonly available from the above suppliers for water treatment. Log reductions that were observed varied in predictable ways depending on the permeability of the DE grade and on the filtration rate used. Excellent agreement was observed between runs, resulting in the ability to distinguish differences between the conditions examined with consistent statistical significance.

Previous work had shown that DE filtration was capable of controlling protozoan cysts, but the full capabilities had not been clearly defined. Several studies suggested that 3-log reductions were possible, while others suggested even more. This is the first definitive study in which the true capability was measured. The principal investigator in the study, Dr. Ongerth, stated that "[t]he apparent capability of DE filtration to provide 6-log of removal ... offers a dgree of control not demonstrated by any other treatment process in use today." He further states that "[t]he finding is highly attractive and suggests that the size range of communities for which DE filtration has historically been considered economical may be expanded considerably when measured against alternatives for equal levels of Cryptosporidium control."

A manuscript describing in detail the completed work has been submitted for publication to the Journal of the American Water Works Association.

(Editor's Note: "Diatomaceous Earth Filtration for Removal of Cryptosporidium Oocysts", Jerry E. Ongerth et al - Journal AWWA Vol 89 No 12 Pg 39)

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